Process and system for producing LiPF[.SUB.6.], and mixture crystal, composition, electrolyte solution, and lithium battery containing LiPF[.SUB.6.]

Abstract

Disclosed are a process and continuous system for producing LiPF.sub.6, and a prepared mixture crystal, composition, electrolyte solution and lithium ion battery containing LiPF.sub.6. During preparation, a first feed stream containing PF5 and a second feed stream containing LiF and HF are introduced into a first microchannel reactor, a gas part of a product in the first microchannel reactor is introduced into a second microchannel reactor to react with a third feed stream containing LiPF.sub.6, LiF and HF, and a liquid part of the product in the first microchannel reactor is subjected to crystallization and drying to obtain LiPF.sub.6. The LiPF.sub.6 has the advantages of a high purity, a uniform particle size, a high product quality stability, etc., and is suitable for use as a component of an electrolyte solution of a lithium ion battery.

Claims

1. A fluorine-containing electrolyte solution, comprising LiPF.sub.6, the LiPF.sub.6 used in the preparation of the fluorine-containing electrolyte solution is LiPF.sub.6 with 68% (wt) or more of the particle size greater than or equal to 0.2 mm and less than or equal to 0.3 mm, the water content of the LiPF.sub.6 is lower than 6 ppm, the purity of LiPF.sub.6 is above 99.99%, and the mass percentage of LiPF.sub.6 in the fluorine-containing electrolyte solution is 5-20 wt %.

2. The fluorine-containing electrolyte solution according to claim 1, wherein the particle size of the LiPF.sub.6 crystal used in the preparation of the fluorine-containing electrolyte solution is uniformly distributed, and 30-50% of the crystal particle size is greater than or equal to 0.2 mm and less than 0.25 mm, and 30-50% of the crystal particle size is greater than or equal to 0.25 mm and less than or equal to 0.3 mm.

3. The fluorine-containing electrolyte solution according to claim 2, wherein the particle size of the LiPF.sub.6 crystal used in the preparation of the fluorine-containing electrolyte solution is uniformly distributed, and 40-50% of the crystal particle size is greater than or equal to 0.2 mm and less than 0.25 mm, and 40-50% of the crystal particle size is greater than or equal to 0.25 mm and less than or equal to 0.3 mm.

4. The fluorine-containing electrolyte solution according to claim 1, wherein the fluorine-containing electrolyte solution further comprises at least one of LiPO.sub.2F.sub.2, LiBF.sub.2C.sub.2O.sub.4, LiBF.sub.4, LiPF.sub.6, LiFSI, LiTFSI, LiAsF.sub.6, LiClO.sub.4, LiSO3CF.sub.3, LiC.sub.204BC.sub.2O.sub.4, LiF.sub.2BC.sub.2O.sub.4, LiPO.sub.2F.sub.2, LiPF.sub.2, LiPF.sub.4C.sub.2O.sub.4 and LiPF.sub.2C.sub.4O.sub.8, and the mass percentage thereof in the electrolyte solution is 0.1-5 wt %.

5. The fluorine-containing electrolyte solution according to claim 4, wherein the fluorine-containing electrolyte solution comprises LiPO.sub.2F.sub.2 and LiBF.sub.2C.sub.2O.sub.4.

6. The fluorine-containing electrolyte solution according to claim 4, wherein the fluorine-containing electrolyte solution further comprises 1,2-Bis(trifluoromethyl)benzene, and the mass percentage of 1,2-Bis(trifluoromethyl)benzene in the fluorine-containing electrolyte solution is 0.1-3 wt %.

7. The fluorine-containing electrolyte solution according to claim 1, wherein the fluorine-containing electrolyte solution comprises ethylene carbonate, ethyl methyl carbonate and diethyl carbonate, and the total mass percentage of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate in the fluorine-containing electrolyte solution is 70-90 wt %, and the mass ratio of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate is (2.5-3.5):(4.5-5.5):(1.5-2.5).

8. The fluorine-containing electrolyte solution according to claim 1, wherein LiPF.sub.6 is LiPF.sub.6 prepared by using two microchannel reactors.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flow chart of a process for producing LiPF.sub.6 of the present invention.

(2) FIG. 2 is a process flow diagram of a continuous system for producing LiPF.sub.6 in Example 2.1.

(3) FIG. 3 is a process flow diagram of a continuous system for producing LiPF.sub.6 in Example 2.2.

(4) FIG. 4 is a SEM image of a mixture crystal containing LiPF.sub.6 prepared in Example 3.1 and Example 5.1;

(5) FIG. 5 is a SEM image of a mixture crystal containing LiPF.sub.6 prepared in Comparative Example 3.1;

(6) FIG. 6 is a XRD pattern of a mixture crystal containing LiPF.sub.6 prepared in Example 3.1.

(7) Reference numerals: 1solid conveyor; 2PF5 generator; 3first microchannel reactor; 4first gas-liquid separator; 5synthetic liquid tank; 6second microchannel reactor; 7second gas-liquid separator; 8separation system; 9crystallization tank; 10drying system; 11mother liquor tank; 12LiF dissolution tank.

DETAILED DESCRIPTION

(8) The production process of the present invention will be described in detail through the following embodiments, but the present invention is not limited to these embodiments.

Example 1.1

(9) PCl5 was transported to a PF5 generator 2 with a cooling jacket that stored HF through a solid conveyor 1 with a metering device, and the temperature was controlled to be about 0 C. PCl5 reacted with HF to produce PF5 and HCl. The mixed gas PF5, HCl and entrained HF gas were introduced into a first microchannel reactor 3 to form a first feed stream. In the dissolution tank with cooling jacket and stirrer, HF was added, and LiF was added into the dissolution tank with a solid feeding device while cooling, and the dissolution temperature was controlled at about 0 C., and the mass fraction of LiF to be 2 wt %. The HF solution with dissolved LiF was pumped into the first microchannel reactor 3 to form a second feed stream. The reaction temperature of the first microchannel reactor 3 was 3 C., and the residence time was 5 seconds. The gas-liquid mixture material from the first microchannel reactor 3 entered the first gas-liquid separator 4, and the liquid in the first gas-liquid separator 4 was transported to the synthetic liquid tank 5 for storage, and the gases separated by the first gas-liquid separator included unreacted PF5, HCl and entrained HF. The mixed gas was transported to the second microchannel reactor 6 to react with the third feed stream containing LiPF.sub.6, LiF and HF. The reaction temperature of the second microchannel reactor 6 was 3 C., and the residence time was 5 seconds. The gas-liquid mixture in the second microchannel reactor entered the second gas-liquid separator 7, and the gas separated by the second gas-liquid separator 7 contained HCl and entrained HF, and the mixed gas entered a HF and HCl separation system 8 through a pressurized device. The liquid separated by the second gas-liquid separator 7 contained LiPF.sub.6 in the original mother liquor, LiPF.sub.6 produced by the new reaction and LiF that was not reacted completely. The mixed liquid was transported to the first microchannel reactor 3 as a fourth feed stream. The synthetic liquid in the synthetic liquid tank 5 was transported to a crystallization tank 9 for crystallization of LiPF.sub.6, and LiPF.sub.6 was crystallized in a cooling state. In the crystallization tank 9, the cooling rate of the synthetic liquid was 2 C./h, the stirring rate of the stirrer was 50 rpm, the synthetic liquid was cooled from 20 C. to 45 C., and kept for 6 hours after cooled to 45 C. Then drying and acid removal was carried out in the drying system 10 after solid crystallization and filtration, to obtain a LiPF.sub.6 crystal. The filtered mother liquor was stored in the mother liquor tank 11. After the content of LiPF.sub.6 in mother liquor in mother liquor tank 11 was determined quantitatively, the mother liquor was conveyed to the LiF dissolution tank 12 for the preparation of quantitative LiF solution. The HF solution containing LiPF.sub.6 dissolved a certain amount of LiF and was transported to the second microchannel reactor 6 for reaction to form the third feed stream. The molar ratio of PF5 to LiF in the first microchannel reactor was 2:1, and the molar ratio of PF5 to LiF in the second microchannel reactor was 1:1.

(10) After testing, the purity of the generated LiPF.sub.6 crystal was 99.99%, the yield was 99.6%, the particle size of more than 82% (wt) of the crystal particles was 0.2-0.3 mm, and the particle size of more than 91% (wt) of the crystal particles was 0.18-0.35 mm.

Example 1.2

(11) The process of this example was basically the same as that of Example 1.1, except the difference that the reaction temperature of the first microchannel reactor was 5 C., the residence time was 10 seconds, the reaction temperature of the second microchannel reactor was 8 C., and the residence time was 10 seconds.

(12) After testing, the purity of the generated LiPF.sub.6 crystal was 99.994%, the yield was 99.8%, the particle size of more than 85% (wt) of the crystal particles was 0.2-0.3 mm, and the particle size of more than 93% (wt) of the crystal particles was 0.18-0.35 mm.

Example 1.3

(13) The process of this example was basically the same as that of Example 1.2, except the difference that the molar ratio of PF5 to LiF in the first microchannel reactor was 2.5:1, and the molar ratio of PF5 to LiF in the second microchannel reactor was 1:1.1.

(14) After testing, the purity of the generated LiPF.sub.6 crystal was 99.995%, the yield was 99.8%, the particle size of more than 85% (wt) of the crystal particles was 0.2-0.3 mm, and the particle size of more than 94% (wt) of the crystal particles was 0.18-0.35 mm.

Example 1.4

(15) The process of this example was basically the same as that of Example 1.1, except the difference that the reaction temperature of the first microchannel reactor was 4 C., the residence time was 10 seconds, the reaction temperature of the second microchannel reactor was 6 C., and the residence time was 12 seconds.

(16) After testing, the purity of the resulting LiPF.sub.6 crystal was 99.995%, the yield was 99.85%, the particle size of more than 85% (wt) of the crystal particles was 0.2-0.3 mm, and the particle size of more than 94% (wt) of the crystal particles was 0.18-0.35 mm.

Example 1.5

(17) The process of this example was basically the same as that of Example 1.1, except the difference that in the crystallization tank, the cooling rate of the synthetic liquid was 35 C./h, the stirring speed of the stirrer was 800 rpm, the synthetic liquid was cooled from 25 C. to 10 C., and kept for 1 hour after cooling to 10 C.

(18) After testing, the purity of the generated LiPF.sub.6 crystal was 99.994%, the yield was 99.83%, the particle size of more than 86% (wt) of crystal particles was 0.2-0.3 mm, and the particle size of more than 92% (wt) of crystal particles was 0.18-0.35 mm.

Comparative Example 1.1

(19) This comparative example was basically the same as that of Example 1.1, except the difference that the first feed stream that was introduced into the first microchannel reactor was purified PF5 gas.

(20) After testing, the purity of the generated LiPF.sub.6 crystal was 99.91%, the yield was 99.3%, the particle size of more than 70% (wt) of crystal particles was 0.2-0.3 mm, and the particle size of more than 75% (wt) of crystal particles was 0.18-0.35 mm.

Comparative Example 1.2

(21) This comparative example was basically the same as that of Example 1.1, except the difference that the first feed stream that was introduced into the first microchannel reactor was purified PF5 gas. No second microchannel reactor was set. The molar ratio of PF5 to LiF in the first microchannel reactor was 1.5:1.

(22) After testing, the purity of the generated LiPF.sub.6 crystal was 99.85%, the yield was 98.3%, the particle size of more than 62% (wt) of crystal particles was 0.2-0.3 mm, and the particle size of more than 67% (wt) of crystal particles was 0.18-0.35 mm.

Comparative Example 1.3

(23) This comparative example was basically the same as that of Example 1.1, except the difference that the first and second microchannel reactors were replaced by the first and second reactors, respectively. After being replaced with reactors, for batch production, the reaction time of the first and second reactors increased to 5 hours.

(24) After testing, the purity of the resulting LiPF.sub.6 crystal was 99.7%, the yield was 95.6%, the particle size of more than 55% (wt) of crystal particles was 0.2-0.3 mm, and the particle size of more than 60% (wt) of crystal particles was 0.18-0.35 mm.

Comparative Example 1.4

(25) This comparative example was basically the same as that of Example 1.2, except the difference that in the crystallization tank, the cooling rate of the synthetic liquid was 10 C./h, the stirring speed of the stirrer was 100 rpm, the synthetic liquid was cooled from 25 C. to 45 C., and kept for 6 hours after cooling to 45 C.

(26) After testing, the purity of the generated LiPF.sub.6 crystal was 99.96%, the yield was 99.5%, the particle size of more than 72% (wt) of crystal particles was 0.2-0.3 mm, and the particle size of more than 80% (wt) of crystal particles was 0.18-0.35 mm.

Instructions for Examples 2.1 to 2.3

(27) Examples 2.1 to 2.3 provided a continuous system for producing LiPF.sub.6 based on a microchannel reactor. The continuous system included a PF5 generator (2), a first microchannel reactor (3), a gas-liquid separator A (4), a second microchannel reactor (6), and a gas-liquid separator B (7). The reverse cycle reaction was carried out by using the gas containing PF5 and HF solution with dissolved LiF as raw materials. Wherein, the first microchannel reactor (3) and the second microchannel reactor (6) were reactors with the same structure, which were enhanced hybrid channel structures; the cross-sectional shape of the channel was a heart-shaped structure, the equivalent diameter of the channel was 2 mm, and the liquid holding volume was 50 ml. The hard material of the channel walls was silicon carbide.

(28) Preferably, the continuous system transported PCl.sub.5 to a PF5 generator (2) that stored HF through a solid conveyor (1) with a metering device, and PCl.sub.5 reacted with HF to generate PF5 and by-product HCl, as shown in the chemical formula (1). Further, the solid conveyor (1) was preferably a solid conveyor (1) with a metering device; the PF5 generator (2) that stored HF was preferably a PF5 generator (2) with a cooling jacket that stored HF, further preferably a PF5 generator with a stirring device.
5HF+PCl.sub.5.fwdarw.5HCl+PF5(1)

(29) The mixed gas PF5, HCl and entrained HF gas generated in the PF5 generator (2) were introduced into the microchannel reactor A (3), and the HF solution with dissolved LiF was transported simultaneously with a pump in the first microchannel reactor (3). LiF in PF5 and HF solution reacted rapidly and released the reaction heat, as shown in the chemical formula (2).
LiF(liquid)+PF5(gas).fwdarw.LiPF.sub.6(2)

(30) The gas-liquid mixture material from the first microchannel reactor (3) mainly contained the target product LiPF.sub.6, unreacted PF5, and HCl and HF that were not involved in the reaction.

(31) The gas-liquid mixture material from the first microchannel reactor (3) entered the gas-liquid separator A (4) for gas-liquid separation, and the liquid therein, namely the LiPF.sub.6-containing component, was transported to the synthetic liquid tank (5) to store. The separated gas that contained unreacted PF5 and entrained HF and HC components was transported to the second microchannel reactor (6), and reacted with the HF solution in which LiF and LiPF.sub.6 were dissolved.

(32) LiF in PF5 and HF solution reacted rapidly and released the reaction heat, as shown in the chemical formula (3).
LiF+PF5(gas).fwdarw.LiPF.sub.6(3)

(33) The gas-liquid mixture material coming out of the second microchannel reactor (6) mainly contained the target product LiPF.sub.6, HCl and HF.

(34) The gas-liquid mixture coming out of the second microchannel reactor (6) entered the gas-liquid separator B (7), the gas separated in the gas-liquid separator B (7) contained HCl and HF, and the separated liquid contained LiPF.sub.6 and unreacted LiF.

(35) Preferably, the gas separated in the gas-liquid separator B (7) was transported to the HF and HCl separation system (8) through a pressurized device. The HCl at the top of the separation system (8) was absorbed by water to form industrial hydrochloric acid, and the HF at the bottom could be recycled as the reaction raw material. The HF and HCl separation system (8) was preferably a separating tower.

(36) The liquid separated in gas-liquid separator B (7), namely, the mixed liquid containing LiPF.sub.6 and unreacted LiF, was transported to the first microchannel reactor (3) to continue to react with the PF5 therein, so that the LiF in the mixed liquid could react completely.

(37) The synthetic liquid in the synthetic liquid tank (5) was transported to the crystallization tank (9) for crystallization of LiPF.sub.6. LiPF.sub.6 was crystallized in the cooling state. After the crystallization and filtration, drying and acid removal was carried out in a drying system (10), to obtain the LiPF.sub.6 product.

(38) Further preferably, the filtered mother liquor was stored in the mother liquor tank (11), and after the LiPF.sub.6 content in the mother liquor in the mother liquor tank (11) was quantitatively determined, the mother liquor was delivered to the LiF dissolution tank (12) for the preparation of quantitative LiF solution. The HF solution containing LiPF.sub.6 dissolved a quantitative amount of LiF and was transported to the second microchannel reactor (6) for the reaction. So far, the reaction system could run continuously.

(39) A LiPF.sub.6 product prepared by the above continuous system for producing LiPF.sub.6 could achieve high purity, and there was no need of further purification. The purity could reach more than 99.98%, preferably more than 99.99%. The types and contents of impurities included were as follows: water20 ppm, preferably 15 ppm; free acid (calculated as HF)90 ppm, preferably 80 ppm, more preferably 50 ppm; insoluble substance200 ppm, preferably 160 ppm, more preferably 110 ppm; sulfate (calculated as SO.sub.4)5 ppm, preferably 4 ppm; chloride (calculated as Cl)2 ppm; other various metal ions1 ppm.

Example 2.1

(40) Example 2.1 was further described in detail below with reference to FIG. 2. HF was transported by a pump in a dissolution tank with a cooling jacket and a stirrer, and LiF was added through a solid feeding device while cooling. The speed of adding LiF should be appropriate to control the HF temperature at 0 C. The concentration of LiF was 5 wt %. At the same time, PCl.sub.5 was transported to the PF5 generator (2) containing HF through the solid conveyor (1) with a metering device to generate PF5 gas. Under pressurization, the HF solution with dissolved LiF and PF5 gas were transported to the first microchannel reactor (3) by a pump. The molar ratio of the reactant PF5 to LiF in the first microchannel reactor (3) was 2:1, the residence time of the reactants was 30 seconds, and the reaction temperature was 15 C. The reactants entered the first microchannel reactor (3) in a continuous state, and the output materials were output in a continuous state and then entered the gas-liquid separator A (4) for gas-liquid separation. The liquid phase product obtained by separation, namely the component containing LiPF.sub.6, was transported to the synthetic liquid tank (5) for standby. The separated gas phase product, namely, the component containing unreacted PF5 and entrained HF and HCl, was transported to the second microchannel reactor (6), and reacted with the HF solution with dissolved LiF (containing LiPF.sub.6). The molar ratio of the reactant PF5 to LiF in the second microchannel reactor (6) was 1:1.67, the residence time of the reactants was 30 seconds, and the reaction temperature was 15 C.

(41) The mixed material coming out of the second microchannel reactor (6) entered the gas-liquid separator B (7), the gas separated in the gas-liquid separator B (7) contained HCl and HF, the separated liquid contained LiPF.sub.6 and unreacted LiF. The gas separated in the gas-liquid separator B (7) was pressurized by entering a compressor, and then transported to the HF and HCl separation system (8), namely, the separating tower. The HCl at the top of the tower was absorbed by water to form industrial hydrochloric acid, and the HF at the bottom of the tower could be recycled.

(42) The liquid separated in the gas-liquid separator B (7), namely, the mixed liquid containing LiPF.sub.6 and unreacted LiF, was transported to the synthetic liquid tank (5), and the synthetic liquid in the synthetic liquid tank (5) was transported to the crystallization tank (9) by a pump for crystallization of LiPF.sub.6. LiPF.sub.6 was crystallized in a cooling state. After the crystallization and filtration, heating and nitrogen purging and drying, and acid removal were carried out in the drying system (10), to obtain the LiPF.sub.6 product.

Example 2.2

(43) Example 2.2 was further described in detail below with reference to FIG. 3. HF was transported by a pump in a dissolution tank with a cooling jacket and a stirrer, and LiF was added through a solid feeding device while cooling. The speed of adding LiF should be appropriate to control the HF temperature at 0 C. The concentration of LiF was 4 wt %. At the same time, PCl.sub.5 was transported to the PF5 generator (2) containing HF through the solid conveyor (1) with a metering device to generate PF5 gas. Under pressurization, the HF solution with dissolved LiF and PF5 gas were transported to the first microchannel reactor (3) by a pump. The molar ratio of the reactant PF5 to LiF in the first microchannel reactor (3) was 2:1, the residence time of the reactants was 30 seconds, and the reaction temperature was 15 C. The reactants entered the first microchannel reactor (3) in a continuous state, and the output materials were output in a continuous state and then entered the gas-liquid separator A (4) for gas-liquid separation. The liquid phase product obtained by separation, namely the component containing LiPF.sub.6, was transported to the synthetic liquid tank (5) for standby. The separated gas phase product, namely, the component containing unreacted PF5 and entrained HF and HCl, was transported to the second microchannel reactor (6), and reacted with the HF solution with dissolved LiF (containing LiPF.sub.6). The molar ratio of the reactant PF5 to LiF in the microchannel reactor B (6) was 1:1.67, the residence time of the reactants was 30 seconds, and the reaction temperature was 15 C. The mixed material coming out of the second microchannel reactor (6) entered the gas-liquid separator B (7), the gas separated in the gas-liquid separator B (7) contained HCl and HF, the separated liquid contained LiPF.sub.6 and unreacted LiF. The gas separated in the gas-liquid separator B (7) was pressurized by entering a compressor, and then transported to the HF and HCl separation system (8), namely, the separating tower. The HCl at the top of the tower was absorbed by water to form industrial hydrochloric acid, and the HF at the bottom of the tower could be recycled.

(44) The liquid separated in the gas-liquid separator B (7), namely, the mixed liquid containing LiPF.sub.6 and unreacted LiF, was transported to the first microchannel reactor (3) by a pump, to continue to react with PF5 therein, so that the LiF in the mixed liquid reacted completely. Namely, the continuous reverse cycle LiPF.sub.6 synthesis reaction consisting of two microchannel reactors was completed. The synthetic liquid in the synthetic liquid tank (5) was transported to the crystallization tank (9) by a pump for crystallization of LiPF.sub.6. LiPF.sub.6 was crystallized in a cooling state. After the crystallization and filtration, heating and nitrogen purging and drying, and acid removal were carried out in the drying system (10), to obtain the LiPF.sub.6 product.

Example 2.3

(45) Example 2.3 was further described in detail below with reference to FIG. 1. HF was transported by a pump in a dissolution tank with a cooling jacket and a stirrer, and LiF was added through a solid feeding device while cooling. The speed of adding LiF should be appropriate to control the HF temperature at 0 C. The concentration of LiF was 4 wt %. At the same time, PCl.sub.5 was transported to the PF5 generator (2) containing HF through the solid conveyor (1) with a metering device to generate PF5 gas. Under pressurization, the HF solution with dissolved LiF and PF5 gas were transported to the first microchannel reactor (3) by a pump. The molar ratio of the reactant PF5 to LiF in the first microchannel reactor (3) was 2:1, the residence time of the reactants was 30 seconds, and the reaction temperature was 15 C. The reactants entered the microchannel reactor A (3) in a continuous state, and the output materials were output in a continuous state and then entered the gas-liquid separator A (4) for gas-liquid separation. The liquid phase product obtained by separation, namely the component containing LiPF.sub.6, was transported to the synthetic liquid tank (5) for standby. The separated gas phase product, namely, the component containing unreacted PF5 and entrained HF and HCl, was transported to the second microchannel reactor (6), and reacted with the HF solution with dissolved LiF (containing LiPF.sub.6). The molar ratio of the reactant PF5 to LiF in the second microchannel reactor (6) was 1:1.67, the residence time of the reactants was 30 seconds, and the reaction temperature was 15 C.

(46) The mixed material coming out of the second microchannel reactor (6) entered the gas-liquid separator B (7), the gas separated in the gas-liquid separator B (7) contained HCl and HF, the separated liquid contained LiPF.sub.6 and unreacted LiF. The gas separated in the gas-liquid separator B (7) was pressurized by entering a compressor, and then transported to the HF and HCl separation system (8), namely, the separating tower. The HCl at the top of the tower was absorbed by water to form industrial hydrochloric acid, and the HF at the bottom of the tower could be recycled.

(47) The liquid separated in the gas-liquid separator B (7), namely, the mixed liquid containing LiPF.sub.6 and unreacted LiF, was transported to the first microchannel reactor (3) by a pump, to continue to react with PF5 therein, so that the LiF in the mixed liquid reacted completely. Namely, the continuous reverse cycle LiPF.sub.6 synthesis reaction consisting of two microchannel reactors was completed. The synthetic liquid in the synthetic liquid tank (5) was transported to the crystallization tank (9) by a pump for crystallization of LiPF.sub.6. LiPF.sub.6 was crystallized in a cooling state. After the crystallization and filtration, heating and nitrogen purging and drying, and acid removal were carried out in the drying system (10), to obtain the LiPF.sub.6 product.

(48) The filtered mother liquor was further stored in the mother liquor tank (11), and after the LiPF.sub.6 content in the mother liquor in the mother liquor tank (11) was quantitatively determined, the mother liquor was delivered to the LiF dissolution tank (12) for the preparation of quantitative LiF solution. The HF solution containing LiPF.sub.6 dissolved a certain amount of LiF and was transported to the second microchannel reactor 6 for reaction.

Comparative Example 2.1

(49) HF was transported by a pump in a dissolution tank with a cooling jacket and a stirrer, and LiF was added through a solid feeding device while cooling. The speed of adding LiF should be appropriate to control the HF temperature at 0 C. The concentration of LiF was 4 wt %. At the same time, PCl.sub.5 was transported to the PF5 generator (2) containing HF through the solid conveyor (1) with a metering device to generate PF5 gas. Under pressurization, the HF solution with dissolved LiF and PF5 gas were transported to the first microchannel reactor (3) by a pump. The molar ratio of the reactant PF5 to LiF in the first microchannel reactor A (3) was 2:1, the residence time of the reactants was 30 seconds, and the reaction temperature was 15 C. The reactants entered the first microchannel reactor A (3) in a continuous state, and the output materials were output in a continuous state and then entered the gas-liquid separator A (4) for gas-liquid separation. The liquid phase product obtained by separation, namely the component containing LiPF.sub.6, was transported to the synthetic liquid tank (5). The synthetic liquid in the synthetic liquid tank (5) was transported to the crystallization tank (9) by a pump for crystallization of LiPF.sub.6. LiPF.sub.6 was crystallized in a cooling state. After the crystallization and filtration, heating and nitrogen purging and drying, and acid removal were carried out in the drying system (10), to obtain the LiPF.sub.6 product.

Comparative Example 2.2

(50) HF was transported by a pump in a dissolution tank with a cooling jacket and a stirrer, and LiF was added through a solid feeding device while cooling. The speed of adding LiF should be appropriate to control the HF temperature at 0 C. The concentration of LiF was 4 wt %. At the same time, PCl.sub.5 was transported to the PF5 generator (2) containing HF through the solid conveyor (1) with a metering device to generate PF5 gas. Under pressurization, the HF solution with dissolved LiF and PF5 gas were transported to the first microchannel reactor (3) by a pump. The molar ratio of the reactant PF5 to LiF in the microchannel reactor A (3) was 2:1, the residence time of the reactants was 30 seconds, and the reaction temperature was 15 C. The reactants entered the first microchannel reactor (3) in a continuous state, and the output materials were output in a continuous state and then entered the second microchannel reactor (6), the residence time of the reactants was 30 seconds, and the reaction temperature was 15 C. The mixed material coming out of the second microchannel reactor (6) entered the gas-liquid separator A (4) for gas-liquid separation. The liquid phase product obtained by separation, namely the component containing LiPF.sub.6, was transported to the synthetic liquid tank (5). The synthetic liquid in the synthetic liquid tank (5) was transported to the crystallization tank (9) by a pump for crystallization of LiPF.sub.6. LiPF.sub.6 was crystallized in a cooling state. After the crystallization and filtration, heating and nitrogen purging and drying, and acid removal were carried out in the drying system (10), to obtain the LiPF.sub.6 product.

(51) TABLE-US-00001 TABLE 1 Example Example Example Comparative Comparative Test Item 2.1 2.2 2.3 Example 2.1 Example 2.2 Purity (%) 99.98 99.98 99.98 99.83 99.79 (wt) Insoluble 150 160 145 240 220 substances (ppm) Water (ppm) 14 12 15 28 25 Free acid 73 76 79 160 180 (calculated as HF) (ppm) Sulfate 4 4 4 11 17 (calculated as SO4 .sub.) (ppm) chloride 4 4 4 25 25 (calculated as Cl ) (ppm) Other metal 0.8 0.8 0.8 3 3 ions (ppm) HF 86 88 90 72 75 conversion rate (%) PCl.sub.5 88 90 91 71 73 conversion rate (%) LiF 85 89 89 69 70 conversion rate (%)

(52) As shown in Table 1, Example 2.1-2.3 adopted two groups of microchannel reactors. After the reverse cycle reaction, the purity of the product was significantly higher than that of Comparative Example 2.1 using a single microchannel reactor and that of Comparative Example 2.2 directly connecting two groups of microchannel reactors in series; the content of impurities was lower, and the conversion rate of the product was higher.

Example 3.1

(53) PCl5 was transported to a PF5 generator with a cooling jacket that stored HF through a solid conveyor with a metering device, and the temperature was controlled to be about 0 C. PCl5 reacted with HF to produce PF5 and HCL. The mixed gas PF5, HCl and entrained HF gas were introduced into a first microchannel reactor to form a first feed stream. In the dissolution tank with cooling jacket and stirrer, HF was added, and LiF was added into the dissolution tank with a solid feeding device while cooling, and the dissolution temperature was controlled at about 0 C., and the mass fraction of LiF to be 2 wt %. The HF solution with dissolved LiF was pumped into the first microchannel reactor to form a second feed stream. The reaction temperature of the first microchannel reactor was 3 C., and the residence time was 5 seconds. The gas-liquid mixture material from the first microchannel reactor entered the first gas-liquid separator, and the liquid in the first gas-liquid separator was transported to the synthetic liquid tank for storage, and the gases separated by the first gas-liquid separator included unreacted PF5, HCl and entrained HF.

(54) The mixed gas was transported to the second microchannel reactor to react with the third feed stream containing LiPF.sub.6, LiF and HF. The reaction temperature of the second microchannel reactor was 3 C., and the residence time was 5 seconds. The gas-liquid mixture in the second microchannel reactor entered the second gas-liquid separator, and the gas separated by the second gas-liquid separator contained HCl and entrained HF, and the mixed gas entered a HF and HCl separation system through a pressurized device. The liquid separated by the second gas-liquid separator contained LiPF.sub.6 in the original mother liquor, LiPF.sub.6 produced by the new reaction and LiF that was not reacted completely. The mixed liquid was transported to the first microchannel reactor as a fourth feed stream. The synthetic liquid in the synthetic liquid tank was transported to a crystallization tank for crystallization of LiPF.sub.6, and LiPF.sub.6 was crystallized in a cooling state. In the crystallization tank, the cooling rate of the synthetic liquid was 2 C./h, the stirring rate of the stirrer was 50 rpm, the synthetic liquid was cooled from 20 C. to 45 C., and kept for 6 hours after cooled to 45 C. Then drying and acid removal was carried out in the drying system after solid crystallization and filtration, to obtain a LiPF.sub.6 crystal. The filtered mother liquor was stored in the mother liquor tank. After the content of LiPF.sub.6 in mother liquor in mother liquor tank was determined quantitatively, the mother liquor was conveyed to the LiF dissolution tank for the preparation of quantitative LiF solution. The HF solution containing LiPF.sub.6 dissolved a certain amount of LiF and was transported to the second microchannel reactor for reaction to form the third feed stream. The molar ratio of PF5 to LiF in the first microchannel reactor was 2:1, and the molar ratio of PF5 to LiF in the second microchannel reactor was 1:1.

(55) The specific performance parameters of the prepared crystal were shown in Table 2, the SEM image of the crystal was shown in FIG. 4, and the XRD pattern of the crystal was shown in FIG. 6.

Example 3.2

(56) The mixture crystal containing LiPF.sub.6 was prepared according to the steps and conditions of Example 3.1, except that the molar ratio of PF5 to LiF in the first microchannel reactor was 2.5:1, and the molar ratio of PF5 to LiF in the second microchannel reactor was 1:1.1.

(57) The specific performance parameters of the prepared crystals were shown in Table 2.

Example 3.3

(58) The mixture crystal containing LiPF.sub.6 was prepared according to the steps and conditions of Example 3.1, except that the reaction temperature of the first microchannel reactor was 4 C., the residence time was 10 seconds, the reaction temperature of the second microchannel reactor was 6 C., and the residence time was 12 seconds.

(59) The specific performance parameters of the prepared crystals were shown in Table 2.

Comparative Example 3.1

(60) The LiPF.sub.6 crystal was prepared according to the steps and conditions of Example 3.1, with the difference that no second microchannel reactor was set, and the reaction was only carried out in the first microchannel reactor. The specific performance parameters of the prepared crystal were shown in Table 2, and the SEM image of the crystal was shown in FIG. 5.

(61) TABLE-US-00002 TABLE 2 Compar- ative Example Example Example Example 3.1 3.2 3.3 3.1 Aspect ratio 1-1.5 1-1.3 1-1.4 1-1.6 Average particle size(mm) 0.2 0.25 0.3 0.4 Proportion of crystals with a 82% 85% 85% 48% particle size of 0.2-0.3 mm (wt) Proportion of crystals with a 91% 94% 94% 60% particle size of 0.18-0.35 mm (wt) Proportion of family of crystal 91% 95% 93% 75% planes {110} and family of crystal planes{111} accounting for 20- 80% of the crystals (wt) respectively Proportion of family of crystal 80% 88% 85% 67% planes {110} and family of crystal planes{111} accounting for 40- 60% of the crystals (wt) respectively Angle of repose 38 20 25 45 Bulk density (g/mL) 1.35 1.8 1.7 1.2 Mass percentage of LiPF.sub.6 99.99% 99.995% 99.995% 99.89% Yield 99.6% 99.8% 99.85% 98% Insoluble substances (ppm) 70 18 20 200 Free acid (calculated as HF) (ppm) 20 5 5 100 Capacity retention rate for 500 89.32% 90.12% 90.02% 88.16 cycles Capacity retention rate under 6 C 92.51% 93.91% 93.61% 89.56 high-rate charge-discharge conditions

Example 4.1

(62) Referring to FIG. 1, the water content in anhydrous HF was reduced to 8 ppm using the F2 foaming method. The foaming time was 2 hours, the temperature was 20 C., and the F2 flow was 20 g/hr. PCl5 was transported to a PF5 generator 2 with a cooling jacket that stored anhydrous HF through a solid conveyor 1 with a metering device, and the temperature was controlled to be about 0 C. PCl5 reacted with anhydrous HF to produce PF5 and HCL. The mixed gas PF5, HCl and entrained HF gas were introduced into a first microchannel reactor 3 to form a first feed stream. In the dissolution tank with cooling jacket and stirrer, HF was added, and LiF was added into the dissolution tank with a solid feeding device while cooling, and the dissolution temperature was controlled at about 0 C., and the mass fraction of LiF to be 3 wt %. The HF solution with dissolved LiF was pumped into the first microchannel reactor 3 to form a second feed stream. The reaction temperature of the first microchannel reactor 3 was 5 C., and the residence time was 10 seconds. The gas-liquid mixture material from the first microchannel reactor 3 entered the first gas-liquid separator 4, and the liquid in the first gas-liquid separator 4 was transported to the synthetic liquid tank 5 for storage, and the gases separated by the first gas-liquid separator included unreacted PF5, HCl and entrained HF. The mixed gas was transported to the second microchannel reactor 6 to react with the third feed stream containing LiPF.sub.6, LiF and HF. The reaction temperature of the second microchannel reactor 6 was 5 C., and the residence time was 10 seconds. The gas-liquid mixture in the second microchannel reactor entered the second gas-liquid separator 7, and the gas separated by the second gas-liquid separator 7 contained HCl and entrained HF, and the mixed gas entered a HF and HCl separation system 8 through a pressurized device. The liquid separated by the second gas-liquid separator 7 contained LiPF.sub.6 in the original mother liquor, LiPF.sub.6 produced by the new reaction and LiF that was not reacted completely. The mixed liquid was transported to the first microchannel reactor 3 as a fourth feed stream. The synthetic liquid in the synthetic liquid tank 5 was transported to a crystallization tank 9 for crystallization of LiPF.sub.6, and LiPF.sub.6 was crystallized in a cooling state. In the crystallization tank 9, the cooling rate of the synthetic liquid was 2 C./h, the stirring rate of the stirrer was 50 rpm, the synthetic liquid was cooled from 25 C. to 45 C., and kept for 6 hours after cooled to 45 C. Then drying and acid removal was carried out in the drying system 10 after solid crystallization and filtration, to obtain a LiPF.sub.6 crystal. The filtered mother liquor was stored in the mother liquor tank 11. After the content of LiPF.sub.6 in mother liquor in mother liquor tank 11 was determined quantitatively, the mother liquor was conveyed to the LiF dissolution tank 12 for the preparation of quantitative LiF solution. The HF solution containing LiPF.sub.6 dissolved a certain amount of LiF and was transported to the second microchannel reactor 6 for reaction to form the third feed stream. The molar ratio of PF5 to LiF in the first microchannel reactor was 2:1, and the molar ratio of PF5 to LiF in the second microchannel reactor was 1:1.

(63) After testing, in the resulting composition, the content of LiPF.sub.6 crystal was 99.995%, the yield was 99.8%, the particle size of 41% crystals was greater than or equal to 0.2 mm and less than 0.25 mm, and the particle size of 42% crystals was greater than or equal to 0.25 mm and less than or equal to 0.3 mm, the water content was 3 ppm. The water content was determined by the method specified in GB/T 19282-2014.

Example 4.2

(64) The production process of this example different from Example 4.1 was as follows: Heat treatment was performed after drying and acid removal in the drying system, and the dried product was supplied to a heating furnace. The interior of the heating furnace was vacuumized and sealed with PF5 gas, the heating time was 2 hours, the temperature was 98 C., the pressure was atmospheric pressure, after cooled to room temperature, the interior of the container was vacuumized to obtain the composition. After testing, in the generated composition, the content of the LiPF.sub.6 crystal was 99.9952%, the water content was 2 ppm, the particle size of 45% crystals was greater than or equal to 0.2 mm and less than 0.25 mm, and the particle size of 45% crystals was greater than or equal to 0.25 mm and less than or equal to 0.3 mm.

Comparative Example 4.1

(65) The production process of this comparative example different from Example 4.1 was as follows: the first feed stream introducing into the first microchannel reactor was purified PF5 gas. No second microchannel reactor was set. The molar ratio of PF5 to LiF in the first microchannel reactor was 1.5:1. After testing, in the resulting composition, the content of the LiPF.sub.6 crystal was 99.88%, the yield was 98.5%, the particle size of 34% crystals was greater than or equal to 0.2 mm and less than 0.25 mm, and the particle size of 29% crystals was greater than or equal to 0.25 mm and less than or equal to 0.3 mm. The water content was 9 ppm.

Comparative Example 4.2

(66) The production process of this comparative example different from Example 4.1 was as follows: the first and second microchannel reactors were replaced by the first and second reactors, respectively. After being replaced with reactors, for batch production, the reaction time of the first and second reactors increased to 8 hours.

(67) After testing, in the resulting composition, the content of the LiPF.sub.6 crystal was 99.75%, the yield was 96.1%, the particle size of 31% crystals was greater than or equal to 0.2 mm and less than 0.25 mm, and the particle size of 23% crystals was greater than or equal to 0.25 mm and less than or equal to 0.3 mm. The water content was 10 ppm.

Instructions for Examples 5.1 to 5.14

(68) The preparation method of LiPF.sub.6 mixture crystal used in Examples 5.1 to 5.14:

(69) PCl5 was transported to a PF5 generator with a cooling jacket that stored HF through a solid conveyor with a metering device, and the temperature was controlled to be about 0 C. PCl5 reacted with HF to produce PF5 and HCl. The mixed gas PF5, HCl and entrained HF gas were introduced into a first microchannel reactor to form a first feed stream. In the dissolution tank with cooling jacket and stirrer, HF was added, and LiF was added into the dissolution tank with a solid feeding device while cooling, and the dissolution temperature was controlled at about 0 C., and the mass fraction of LiF to be 2 wt %. The HF solution with dissolved LiF was pumped into the first microchannel reactor to form a second feed stream. The reaction temperature of the first microchannel reactor was 3 C., and the residence time was 5 seconds. The gas-liquid mixture material from the first microchannel reactor entered the first gas-liquid separator, and the liquid in the first gas-liquid separator was transported to the synthetic liquid tank for storage, and the gases separated by the first gas-liquid separator included unreacted PF5, HCl and entrained HF. The mixed gas was transported to the second microchannel reactor to react with the third feed stream containing LiPF.sub.6, LiF and HF. The reaction temperature of the second microchannel reactor was 3 C., and the residence time was 5 seconds. The gas-liquid mixture in the second microchannel reactor entered the second gas-liquid separator, and the gas separated by the second gas-liquid separator contained HCl and entrained HF, and the mixed gas entered a HF and HCl separation system through a pressurized device. The liquid separated by the second gas-liquid separator contained LiPF.sub.6 in the original mother liquor, LiPF.sub.6 produced by the new reaction and LiF that was not reacted completely. The mixed liquid was transported to the first microchannel reactor as a fourth feed stream. The synthetic liquid in the synthetic liquid tank was transported to a crystallization tank for crystallization of LiPF.sub.6, and LiPF.sub.6 was crystallized in a cooling state. In the crystallization tank, the cooling rate of the synthetic liquid was 2 C./h, the stirring rate of the stirrer was 50 rpm, the synthetic liquid was cooled from 20 C. to 45 C., and kept for 6 hours after cooled to 45 C. Then drying and acid removal was carried out in the drying system after solid crystallization and filtration, to obtain a LiPF.sub.6 crystal. The filtered mother liquor was stored in the mother liquor tank. After the content of LiPF.sub.6 in mother liquor in mother liquor tank was determined quantitatively, the mother liquor was conveyed to the LiF dissolution tank for the preparation of quantitative LiF solution. The HF solution containing LiPF.sub.6 dissolved a certain amount of LiF and was transported to the second microchannel reactor for reaction to form the third feed stream. The molar ratio of PF5 to LiF in the first microchannel reactor was 2:1, and the molar ratio of PF5 to LiF in the second microchannel reactor was 1:1.

Example 5.1

(70) The LiPF.sub.6 mixture crystal was added to the organic solvent of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate in a volume ratio of 2:4:4; in the prepared non-aqueous electrolyte solution, the concentration of LiPF.sub.6 was 1.2 mol/L, after mixed and dissolved, the aspect ratio of the LiPF.sub.6 mixture crystal was 1-1.5, the average particle size was 0.2 mm, and among the 80% (wt) of the crystal particles, the family of crystal planes{110} accounted for 40-60%, and the family of crystal planes{111} accounted for 40-60%; among 91% (wt) of the crystal particles, the family of crystal planes{110} accounted for 20-80%, the family of crystal planes{111} accounted for 20-80%, and the average particle size of 82% (wt) of the mixture crystal was 0.2-0.3 mm, the average particle size of 91% (wt) of the mixture crystal was 0.18-0.35 mm; the angle of repose of the mixture crystal was 38, the bulk density was 1.35 g/mL, the mass percentage of LiPF.sub.6 in the mixture crystal was 99.99%; relative to 100% (wt) of the electrolyte solution, the additive was added in an amount of 2% (wt). The additives were lithium difluorophosphate, lithium bis(trifluoromethanesulphonyl) imide and fluorocarbonate, and the weight ratio thereof was 1:1:3, wherein fluorocarbonate was a mixture of fluoroethylene carbonate and trifluoropropylene carbonate in a weight ratio of 1:2, which was used to prepare a non-aqueous electrolyte solution for secondary batteries.

Example 5.2

(71) The non-aqueous electrolyte solution was prepared according to the steps and conditions of Example 5.1, except that the organic solvent was ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1:4.

Example 5.3

(72) The non-aqueous electrolyte solution was prepared according to the steps and conditions of Example 5.1, except that no additive was used.

Example 5.4

(73) The non-aqueous electrolyte solution was prepared according to the steps and conditions of Example 5.1, except that the amount of the additive was 5%.

Example 5.5

(74) The non-aqueous electrolyte solution was prepared according to the steps and conditions of Example 5.1, except that the additive was lithium difluorophosphate.

Example 5.6

(75) The non-aqueous electrolyte solution was prepared according to the steps and conditions of Example 5.1, except that the additives were lithium difluorophosphate and lithium bis(trifluoromethanesulphonyl)imide in a weight ratio of 1:1.

Example 5.7

(76) The non-aqueous electrolyte solution was prepared according to the steps and conditions of Example 5.1, except that the additives were lithium difluorophosphate, lithium bis(trifluoromethanesulphonyl)imide, fluorocarbonate and bis(4-fluorophenyl) sulfone in a weight ratio of 1:1:3:0.5.

Example 5.8

(77) The non-aqueous electrolyte solution was prepared according to the steps and conditions of Example 5.1, except that the additives were lithium difluorophosphate, lithium bis(trifluoromethanesulphonyl)imide, fluorocarbonate and LiF in a weight ratio of 1:1:3:0.5.

Example 5.9

(78) The non-aqueous electrolyte solution was prepared according to the steps and conditions of Example 5.1, except that the additives were lithium difluorophosphate, lithium bis(trifluoromethanesulphonyl)imide, fluorocarbonate, bis(4-fluorophenyl) sulfone and LiF in a weight ratio of 1:1:3:0.5:0.5.

Example 5.10

(79) The non-aqueous electrolyte solution was prepared according to the steps and conditions of Example 5.1, except that the fluorocarbonate was fluoroethylene carbonate.

Example 5.11

(80) The non-aqueous electrolyte solution was prepared according to the steps and conditions of Example 5.1, except that the organic solvents were propylene carbonate, vinylene carbonate, methyl propyl carbonate, dipropyl carbonate in a volume ratio of 1:2:1.1:2.5, and the concentration of LiPF.sub.6 was 0.9 mol/L.

Example 5.12

(81) The non-aqueous electrolyte solution was prepared according to the steps and conditions of Example 5.1, except that the volume ratio of ethylene carbonate, vinylene carbonate, ethyl methyl carbonate and diethyl carbonate was 1:1:6:6.

Example 5.13

(82) The non-aqueous electrolyte solution was prepared according to the steps and conditions of Example 5.1, except that the concentration of LiPF.sub.6 was 1.4 mol/L.

Example 5.14

(83) The non-aqueous electrolyte solution was prepared according to the steps and conditions of Example 5.1, except that the concentration of LiPF.sub.6 was 1.6 mol/L.

Comparative Example 5.1

(84) The non-aqueous electrolyte solution was prepared according to the steps and conditions of Example 5.1, except that the amount of the additive was 6%.

Comparative Example 5.2

(85) The non-aqueous electrolyte solution was prepared according to the steps and conditions of Example 5.1. The difference was that the aspect ratio of the LiPF.sub.6 mixture crystal was 0.7-1.3, the average particle size was 0.2 mm, and among 70% (wt) of the crystal particles, the family of crystal planes {110} accounted for 40-60%, the family of crystal planes{111} accounted for 40-60%; among 80% (wt) of the crystal particles, the family of crystal planes{110} accounted for 20-80%, the family of crystal planes{111} accounted for 20-80%, and the average particle size of 45% (wt) of the mixture crystal was 0.2-0.3 mm, the average particle size of 62% (wt) of the mixture crystal was 0.18-0.35 mm, and the angle of repose of the mixture crystal was 18, the bulk density was 1.3 g/mL.

Comparative Example 5.3

(86) The non-aqueous electrolyte solution was prepared according to the steps and conditions of Example 5.1. The difference was that the aspect ratio of the LiPF.sub.6 mixture crystal was 0.6-0.9, the average particle size was 0.11 mm, and among 55% (wt) of the crystal particles, the family of crystal planes {110} accounted for 40-60%, the family of crystal planes{111} accounted for 40-60%; among 70% (wt) of the crystal particles, the family of crystal planes{110} accounted for 20-80%, the family of crystal planes{111} accounted for 20-80%, and the average particle size of 35% (wt) of the mixture crystal was 0.2-0.3 mm, the average particle size of 50% (wt) of the mixture crystal was 0.18-0.35 mm, and the angle of repose of the mixture crystal was 15, the bulk density was 1.2 g/mL.

(87) The secondary lithium batteries in Examples 5.1 to 5.14 and Comparative Examples 5.1 to 5.3 were prepared as follows.

(88) (1) Preparation of Positive Electrode Sheet

(89) The lithium nickel-cobalt-manganese ternary material LiNi0.5Co0.2Mn0.3O2, the binder polyvinylidene fluoride and the conductive agent acetylene black were mixed in a mass ratio of 97:1.5:2, and N-methylpyrrolidone (NMP) was added to mix and stir evenly, to obtain positive electrode slurry; the positive electrode slurry was uniformly coated on the aluminum foil, positive electrode current collector, with a thickness of 14 m; the aluminum foil was dried at room temperature and baked to dryness, and then cold-pressed and cut to obtain a positive electrode sheet.

(90) (2) Preparation of Negative Electrode Sheet

(91) The negative electrode active materials (artificial graphite, carbon black, and the binder polyvinylidene fluoride) were mixed in a mass ratio of 98:1:1, and N-methylpyrrolidone (NMP) was added to mix and stir evenly, to obtain negative electrode slurry. The slurry was uniformly coated on the copper foil, negative electrode current collector, with a thickness of 8 m; the copper foil is dried at room temperature and baked to dryness, and then cold-pressed and cut to obtain a negative electrode sheet.

(92) (3) Preparation of Separator

(93) Polyethylene with a thickness of 12 m was used as a separator.

(94) (4) Preparation of Secondary Lithium Battery

(95) The positive electrode sheet, separator, and negative electrode sheet were stacked in sequence, and then rolled into a square bare battery cell, put into aluminum plastic film, then dried, injected with corresponding electrolyte solution and sealed, after the processes of standing, hot and cold pressing, pre-forming, clamping and divided capacity, etc., the secondary lithium battery was obtained.

Test Example

(96) In the following test examples, the performance of batteries prepared in Example 5.1 to 5.14 and Comparative Example 5.1 to 5.3 was tested. Results were shown in Table 3.

(97) (1) High Temperature Storage Performance Test of Secondary Lithium Battery

(98) At room temperature of 25 C., the secondary lithium battery was charged with a constant current of 1C to a voltage of 4.2V, further charged with a constant voltage of 4.2V to a current of 0.05C, allowed to standing for 10 minutes, then discharged with a constant current of 1C to a voltage of 2.75V to measure the initial discharge capacity. After that, the secondary battery was charged to a voltage of 4.2V at a room temperature of 25 C. with a constant current of 1C, further charged with a constant voltage of 4.2V until a current of 0.05C, and then stored at 60 C. for 4 weeks. Subsequently, it was charged with a constant current of 1C to a voltage of 4.2V, further charged with a constant voltage of 4.2V to a current of 0.05C, allowed to standing for 10 minutes, then discharged with a constant current of 1C to a voltage of 2.75V, to measure the discharge capacity after storage, and calculate the capacity retention rate.
Capacity retention rate (%)=[Discharge capacity after 4 weeks of storage/initial discharge capacity]100.
(2) High Temperature Cycle Performance Test of Secondary Lithium Battery

(99) At 60 C., the secondary lithium battery was charged with a constant current of 1C to a voltage of 4.2V, further charged with a constant voltage of 4.2V to a current of 0.05C, allowed to standing for 10 minutes, then discharged with a constant current of 1C to 2.75V; this was a charge-discharge cycle process. The discharge capacity this time was the initial discharge capacity of the secondary lithium battery. The secondary lithium battery was subjected to 500-cycle charging/discharging test according to the above method, to obtain the capacity retention rate after 500 cycles at 60 C.
Capacity retention rate (%)=(Discharge capacity after 500 cycles/Initial discharge capacity)100%.
(3) High-Rate Charging Performance Test of Secondary Lithium Battery

(100) At room temperature of 25 C., the secondary lithium battery was charged with a constant current rate of 1C to a voltage of 2.75V, after standing for 10 minutes, charged to 4.2V with a constant current rate of 0.5C, after standing for 10 minutes, discharged to 2.75V with a constant current rate of 1C, to obtain the charging capacity under 0.5C rate charging.

(101) At 25 C., the secondary lithium battery was charged with a constant current rate of 1C to a voltage of 2.75V, after standing for 10 minutes, charged to 4.2V with a constant current rate of 5C, after standing for 10 minutes, discharged to 2.75V with a constant current rate of 1C, to obtain the charging capacity under 5C rate charging.
The charging capacity ratio (%) of the secondary lithium battery under 5C rate charging=Charging capacity under 5C rate charging/Charging capacity under 0.5C rate charging100%.
(4) Low-Temperature Discharge Performance Test of Secondary Lithium Battery

(102) At 25 C., the secondary lithium battery was charged with a constant current of 1C to a voltage of 4.2V, further charged with a constant voltage of 4.2V to a current of 0.05C, allowed to standing for 10 minutes, after standing for 4 h under different temperatures (25 C., 0 C., 10 C.), discharged with a constant current of 1C to 2.75V; after the end of discharging, allowed to standing for 5 minutes, and the discharge capacity of the secondary lithium battery was recorded at this time.
Discharge capacity ratio (%) of the secondary lithium battery at different temperatures=(Discharge capacity at 0 C.,10 C.)/(Discharge capacity at 25 C.)100.

(103) Table 3 showed the performance test results of Example 5.1 to 5.14 and Comparative Example 5.1 to 5.3.

(104) TABLE-US-00003 TABLE 3 Capacity Capacity Charge retention retention capacity Discharge rate/% after rate ratio capacity ratio 4 weeks of after 500 under at different storage at cycles at 5 C rate temperatures 60 C. 60 C./% charging/% 0 C. 10 C. Example 5.1 97.33% 91.67% 90.67% 94.12% 82.32% Example 5.2 91.21% 87.45% 87.59% 89.67% 77.54% Example 5.3 90.15% 85.79% 84.24% 86.54% 76.66% Example 5.4 95.35% 90.64% 89.36% 92.67% 80.95% Example 5.5 91.57% 87.96% 85.95% 87.36% 77.82% Example 5.6 94.54% 89.01% 88.01% 91.37% 81.21% Example 5.7 98.42% 92.62% 91.43% 95.14% 83.54% Example 5.8 98.22% 92.72% 91.55% 95.47% 83.68% Example 5.9 98.97% 93.01% 92.11% 96.34% 84.78% Example 5.10 95.42% 90.21% 88.56% 92.01% 80.95% Example 5.11 96.84% 91.54% 90.63% 93.67% 82.24% Example 5.12 94.36% 89.64 86.56% 89.12% 80.32% Example 5.13 96.89% 92.01% 89.67% 92.86% 81.88% Example 5.14 93.11% 89.21% 86.76% 90.36% 79.42% Comparative 78.67% 79.23% 75.33% 80.45% 70.21% Example 5.1 Comparative 80.15% 78.35% 79.43% 77.64% 71.06% Example 5.2 Comparative 70.31% 68.54% 69.65% 70.52% 60.85% Example 5.3

(105) As shown in the above Table 3, the lithium battery prepared by using the LiPF.sub.6 mixture crystal of the present invention as a non-aqueous electrolyte solution of lithium salt had excellent high-temperature cycle performance, high-temperature storage performance, low-temperature discharge performance, and high-rate charging performance. By adding the specific additive and organic solvent of the present invention, the above performance of the secondary lithium battery was obviously improved.

Instructions of Examples 6.1 to 6.3

(106) The LiPF.sub.6 used in Examples 6.1 to 6.3 of the present invention was prepared in Example 4.1.

Example 6.1

(107) A fluorine-containing electrolyte solution comprised LiPF.sub.6, LiPO.sub.2F.sub.2, LiBF.sub.2C.sub.2O.sub.4, ethylene carbonate, ethyl methyl carbonate and diethyl carbonate. The purity of LiPF.sub.6 used in the preparation of the electrolyte solution was 99.995 wt %, the water content was 3 ppm, 41% of the crystal particle size was greater than or equal to 0.2 mm and less than 0.25 mm, and 42% of the crystal particle size was greater than or equal to 0.25 mm and less than or equal to 0.3 mm. The water content was determined by the method in GB/T 19282-2014. In the fluorine-containing electrolyte solution, the mass fraction of LiPF.sub.6 was 18 wt %, the mass fraction of LiPO.sub.2F.sub.2 was 1 wt %, the mass fraction of LiBF.sub.2C.sub.2O.sub.4 was 1 wt %, the mass fraction of ethylene carbonate was 24 wt %, the mass fraction of ethyl methyl carbonate was 41 wt %, and the mass fraction of diethyl carbonate was 15 wt %.

(108) After testing, the conductivity of fluorine-containing electrolyte solution was 10.07 mS/cm at 25 C. The capacity retention rate of the assembled LiCoO2/graphite full battery after 500 cycles under 0.5C rate at a cut-off voltage of 3.0-4.4 V was tested at 25 C., and the result was 90.5%.

Example 6.2

(109) A fluorine-containing electrolyte solution comprised LiPF.sub.6, LiPO.sub.2F.sub.2, LiBF.sub.2C.sub.2O.sub.4, 1,2-Bis(trifluoromethyl)benzene, ethylene carbonate, ethyl methyl carbonate R diethyl carbonate. The purity of LiPF.sub.6 used in the preparation of the electrolyte solution was 99.995 wt %, the water content was 3 ppm, 41% of the crystal particle size was greater than or equal to 0.2 mm and less than 0.25 mm, and 42% of the crystal particle size was greater than or equal to 0.25 mm and less than or equal to 0.3 mm. The water content was determined by the method in GB/T 19282-2014. In the fluorine-containing electrolyte solution, the mass fraction of LiPF.sub.6 was 18 wt %, the mass fraction of LiPO.sub.2F.sub.2 was 1 wt %, the mass fraction of LiBF.sub.2C.sub.2O.sub.4 was 1 wt %, the mass fraction of 1,2-Bis(trifluoromethyl)benzene was 3 wt %, the mass fraction of ethylene carbonate was 24 wt %, the mass fraction of ethyl methyl carbonate was 38 wt %, and the mass fraction of diethyl carbonate was 15 wt %.

(110) After testing, the conductivity of fluorine-containing electrolyte solution was 10.42 mS/cm at 25 C. The capacity retention rate of the assembled LiCoO2/graphite full battery after 500 cycles under 0.5C rate at a cut-off voltage of 3.0-4.4 V was tested at 25 C., and the result was 91.6%.

Example 6.3

(111) A fluorine-containing electrolyte solution comprised LiPF.sub.6, LiPO.sub.2F.sub.2, LiBF.sub.2C.sub.2O.sub.4, 1,2-Bis(trifluoromethyl)benzene, ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, diethyl ether, trifluoromethyl ethyl sulfone. The purity of LiPF.sub.6 used in the preparation of the electrolyte solution was 99.995 wt %, the water content was 3 ppm, 41% of the crystal particle size was greater than or equal to 0.2 mm and less than 0.25 mm, and 42% of the crystal particle size was greater than or equal to 0.25 mm and less than or equal to 0.3 mm. The water content was determined by the method in GB/T 19282-2014. In the fluorine-containing electrolyte solution, the mass fraction of LiPF.sub.6 was 12 wt %, the mass fraction of LiPO.sub.2F.sub.2 was 3 wt %, the mass fraction of LiBF.sub.2C.sub.2O.sub.4 was 2 wt %, the mass fraction of 1,2-Bis(trifluoromethyl)benzene was 2 wt %, the mass fraction of ethylene carbonate was 20 wt %, the mass fraction of ethyl methyl carbonate was 38 wt %, and the mass fraction of diethyl carbonate was 13 wt %, the mass fraction of diethyl ether was 5 wt %, the mass fraction of trifluoromethyl ethyl sulfone was 5 wt %.

(112) After testing, the conductivity of fluorine-containing electrolyte solution was 10.85 mS/cm at 25 C. The capacity retention rate of the assembled LiCoO2/graphite full battery after 500 cycles under 0.5C rate at a cut-off voltage of 3.0-4.4 V was tested at 25 C., and the result was 92.8%.

Comparative Example 6.1

(113) The differences between this comparative example and Example 6.1 were as follows: the purity of LiPF.sub.6 used in the preparation of the electrolyte solution was 99.89 wt %, the water content was 20 ppm, 28% of the crystal particle size was greater than or equal to 0.2 mm and less than 0.25 mm, 23% of the crystal particle size was greater than or equal to 0.25 mm and less than or equal to 0.3 mm. The water content was determined by the method in GB/T 19282-2014.

(114) After testing, the conductivity of fluorine-containing electrolyte solution was 8.77 mS/cm at 25 C. The capacity retention rate of the assembled LiCoO2/graphite full battery after 500 cycles under 0.5C rate at a cut-off voltage of 3.0-4.4 V was tested at 25 C., and the result was 86.5%.

Comparative Example 6.2

(115) The difference between this comparative example and Example 6.1 was as follows: 1,2-Bis(trifluoromethyl)benzene was replaced by benzotrifluoride. After testing, the conductivity of fluorine-containing electrolyte solution was 9.56 mS/cm at 25 C. The capacity retention rate of the assembled LiCoO2/graphite full battery after 500 cycles under 0.5C rate at a cut-off voltage of 3.0-4.4 V was tested at 25 C., and the result was 88.6%.