Lithium ion battery and electrolyte thereof

Abstract

The present invention provides a lithium ion battery and an electrolyte thereof. The electrolyte for the lithium ion battery includes a non-aqueous organic solvent, a lithium salt and additives, wherein the additives include additive A cyclophosphazene compound, additive B lithium fluorophosphate compound, and additive C selected from at least one of silane phosphate compound, silane phosphite compound and silane borate compound. Compared with conventional technologies, the nickel-rich positive electrode lithium ion battery using the electrolyte of the present invention has a desirable cyclic capacity retention rate, a desirable storage capacity retention rate and a low gas production at high temperature, and has a low DC internal resistance at low temperature, which can remarkably improve the thermal stability of lithium ion battery.

Claims

1. A lithium ion battery, comprising: a positive electrode plate, a negative electrode plate, a separator interposed between the positive electrode plate and the negative electrode plate, and an electrolyte, the positive electrode plate comprising a positive electrode current collector and a positive electrode active material formed thereon, the negative electrode plate comprising a negative electrode current collector and a negative electrode active material formed thereon, wherein the electrolyte comprises a non-aqueous organic solvent, a lithium salt, and additives, the additives comprise additive A cyclophosphazene compound, additive B lithium fluorophosphate compound, and additive C selected from at least one of silane phosphate compound, silane phosphite compound and silane borate compound, wherein the positive electrode active material is LiNi.sub.1-x-yCo.sub.xM.sub.yO.sub.2, M is Mn or Al, 0≤x≤0.5, 0≤y≤0.5, 0≤x+y≤0.5, and a weight content of the additive A in the electrolyte is no less than a weight content of the additive B in the electrolyte, and no less than a weight content of the additive C in the electrolyte, and wherein the additive A is selected from at least one of the compounds represented by formula I; ##STR00008## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6 are each independently selected from F, Cl, Br, I, an alkyl group having 1 to 20 carbon atoms, a halogenated alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, a halogenated alkenyl group having 2 to 20 carbon atoms, an aryl group having 6 to 26 carbon atoms, a halogenated aryl group having 6 to 26 carbon atoms, a halogenated alkoxy group having 1 to 20 carbon atoms, an aryloxy group having 6 to 26 carbon atoms, a halogenated aryloxy group having 6 to 26 carbon atoms, at least one of R.sub.1, R.sub.3 and R.sub.5 represents an alkyl group having 1 to 20 carbon atoms, a halogenated alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, a halogenated alkenyl group having 2 to 20 carbon atoms, an aryl group having 6 to 26 carbon atoms, a halogenated aryl group having 6 to 26 carbon atoms, a halogenated alkoxy group having 1 to 20 carbon atoms, an aryloxy group having 6 to 26 carbon atoms, a halogenated aryloxy group having 6 to 26 carbon atoms, at least two of R.sub.2, R.sub.4, R.sub.6 are selected from F, Cl, Br, I.

2. The lithium ion battery according to claim 1, wherein the weight content of the additive A in the electrolyte is 0.1 wt % to 10 wt %.

3. The lithium ion battery according to claim 1, wherein the weight content of the additive B in the electrolyte is 0.1 wt % to 3 wt %.

4. The lithium ion battery according to claim 1, wherein the additive C is selected from at least one of the compounds represented by formulas II, III and IV; ##STR00009## wherein R.sub.7, R.sub.8, R.sub.9, R.sub.10, R.sub.11, R.sub.12, R.sub.13, R.sub.14, R.sub.15 are each independently selected from an alkyl group or a halogenated alkyl having 1 to 6 carbon atoms.

5. The lithium ion battery according to claim 4, wherein the weight content of the additive C in the electrolyte is 0.1 wt % to 2 wt %.

6. The lithium ion battery according to claim 1, wherein the organic solvent is selected from at least two of the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, 1,4-butyrolactone, γ-butyrolactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, and ethyl butyrate.

7. The lithium ion battery according to claim 1, wherein the lithium salt is selected from at least one of LiPF.sub.6, LiClO.sub.4, LiAsF.sub.6, LiTFSI, LiFSI, LiDFOB, LiDFOP, LiBOB, and a mole concentration of the lithium salt is 0.5M to 1.5M.

8. The lithium ion battery according to claim 1, wherein the electrolyte further comprises at least one of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), succinonitrile (SN), adiponitrile (ADN), ethylene sulfate (DTD), 1,3-propane sultone (1,3-PS), 1,3-propene sultone (PST).

9. The lithium ion battery according to claim 1, wherein the lithium salt is selected from at least one of LiPF.sub.6, LiClO.sub.4, LiAsF.sub.6, LiTFSI, LiFSI, LiDFOB, LiDFOP, LiBOB, and a mole concentration of the lithium salt is 0.8M to 1.2M.

Description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(1) Example embodiments of the present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like reference numerals refer to like elements throughout.

(2) Without specific instructions, the reagents, materials and apparatus used in the Examples and Comparative Examples are commercially available and the reagents used in the present invention may also be prepared by conventional methods.

Example 1

(3) (1) Preparation of Positive Electrode Plate

(4) Uniformly stirring and mixing positive electrode active material of LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2, conductive agent of conductive carbon black Super P and binder of PVDF in solvent of NMP at a weight ratio of 97:1.4:1.6 to obtain positive electrode slurry, wherein the solid content of the positive electrode slurry is 77 wt %. Coating the positive electrode slurry on an Al foil evenly, drying the Al foil coated with positive electrode slurry at 85° C., and obtaining the positive electrode plate after cold-pressing, cutting and dividing, and drying under vacuum at 85° C. for 4 h.

(5) (2) Preparation of Negative Electrode Plate

(6) Uniformly stirring and mixing negative electrode active material of graphite, conductive agent of conductive carbon black Super P, thicker of carboxymethylcellulose sodium (CMC) and binder of styrene-butadiene rubber emulsion (SBR) in a solvent system of de-ionized water at a weight ratio of 96.4:1.5:0.5:1.6 to obtain negative electrode slurry, wherein the solid content of the negative electrode slurry is 54 wt %. Coating the negative electrode slurry on a Cu foil evenly, drying the Cu foil coated with the negative electrode slurry at 85° C. and obtaining the negative electrode plate after cold-pressing, cutting and dividing, and drying under vacuum at 120° C.

(7) (3) Preparation of Electrolyte

(8) Mixing ethylene carbonate (EC) and methyl ethyl carbonate (EMC) at a weight ratio of 30:70 in an argon atmosphere glove box having a water content of less than 10 ppm to obtain the organic solvent, dissolving the lithium salt LiPF.sub.6 into the organic solvent, and adding additive A (compound 1), additive B (compound 11) and additive C (compound 12) to obtain the electrolyte, wherein the concentration of LiPF.sub.6 is 1 mol/L.

(9) (4) Preparation of Separator

(10) A polyethylene film (PE) having a thickness of 16 μm is used as the separator.

(11) (5) Preparation of Lithium Ion Battery

(12) The positive electrode plate, the separator and the negative electrode plate are folded in sequence to obtain a battery cell in which the separator is located between the positive electrode plate and the negative electrode plate, and the battery cell is wound to obtain a square naked battery having a thickness of 4.0 mm, a width of 60 mm, a length of 140 mm. The pole tab is welded. The battery cell is put in an aluminum foil package. After baking and removing water at 80° C., the prepared electrolyte is injected and the foil package is packed. After standing, cold pressing, charging at constant current of 0.02 C to 3.3 V and at constant current of 0.1 C to 3.6 V, shaping and capacity test, a lithium ion battery is obtained.

(13) The tests of Examples 2 to 23 and Comparative examples 1 to 8 are substantially the same as Example 1. The battery systems, the related substances and the content of the Examples and Comparative examples, and the test results are shown in Tables 1 to 2.

(14) Testing Process of the Lithium Ion Battery

(15) (1) Cycle Performance Test of the Lithium Ion Battery

(16) The battery is charged at a constant current of 1 C to 4.2 V at 45° C., and charged at a constant voltage of 4.2 V to reach 0.05 C, and further discharged to 2.8 V at a constant current of 1 C. Take it as a charge-discharge cycle process and the resulting discharge capacity is the discharge capacity of the lithium ion battery after the first cycle. The lithium ion batteries are subjected to 500 cycles of charge/discharge test according to the method above.
The capacity retention rate (%) of the lithium ion battery after 500 cycles=the discharge capacity after 500 cycles/the discharge capacity after the first cycle*100%.
(2) High Temperature Storage Test of the Lithium Ion Battery

(17) The lithium ion battery is allowed to stand at 25° C. for 30 minutes, charged to 4.2 V at a constant current of 1 C, and further charged to 0.05 C at a constant voltage of 4.2 V. The volume of the lithium ion battery is tested and marked the volume as V0. The fully-charged battery is put into a baking oven at 80° C. for 10 days, after the storage procedure, the volume is tested by drainage method and marked the volume as V1.

(18) The volume expansion rate of the lithium ion battery after being stored at 80° C. for 10 days is the volume expansion rate (%)=(V1−V0)/V0*100%.

(19) (3) Low Temperature Direct Current Resistance (DCR) Test of the Lithium Ion Battery

(20) The state of charge (SOC) is adjusted to 20% of the battery capacity at room temperature, and then the lithium ion battery is put into a −25° C. low temperature box for 2 hours, until the battery temperature reaches −25° C. The lithium ion battery is discharged at 0.3 C for 10 s. The voltage before being discharged is marked as U1, the voltage after being discharged is marked as U2, the discharge DCR=(U1−U2)/I.

(21) (4) High Temperature Thermal Stability Test of the Lithium Ion Battery

(22) The lithium ion battery which had been subjected to 500 cycles is charged to 4.2V at a constant current of 0.5 C under 25° C., further charged to 0.05 C at a constant voltage of 4.2 V, and then is put into a baking oven at 150° C. for 1 h, to observe the state of lithium ion battery.

(23) TABLE-US-00001 TABLE 1 The battery system, related substances and content of Examples 1 to 23 and comparative Examples 1 to 8 Other Lithium salt additive Concen- Additive A Additive B Additive C and Battery system Species tration Species Content Species Content Species Content content Example1 LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiPF.sub.6 1M Compound 1 5% Compound 11 0.1%   Compound 12 1.0% / graphite Example 2 LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiPF.sub.6 1M Compound 1 5% Compound 11 0.5%   Compound 12 1.0% / graphite Example 3 LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiPF.sub.6 1M Compound 1 5% Compound 11 1% Compound 12 1.0% / graphite Example 4 LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiPF.sub.6 1M Compound 1 5% Compound 11 2% Compound 12 1.0% / graphite Example 5 LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiPF.sub.6 1M Compound 1 5% Compound 11 3% Compound 12 1.0% / graphite Example 6 LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiPF.sub.6 1M Compound 1 5% Compound 10 1% Compound 12 1.0% / graphite Example 7 LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiPF.sub.6 1M Compound 1 0.1%   Compound 11 1% Compound 12 1.0% / graphite Example 8 LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiPF.sub.6 1M Compound 1 1% Compound 11 1% Compound 12 1.0% / graphite Example 9 LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiPF.sub.6 1M Compound 1 3% Compound 11 1% Compound 12 1.0% / graphite Example 10 LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiPF.sub.6 1M Compound 1 10%  Compound 11 1% Compound 12 1.0% / graphite Example 11 LiNi.sub.0.8Co.sub.0.15Al.sub.0.05O.sub.2/ LiPF.sub.6 1M Compound 3 5% Compound 11 1% Compound 13 0.5% / graphite Example 12 LiNi.sub.0.6Co.sub.0.2Mn.sub.0.2O.sub.2/ LiPF.sub.6 1M Compound 4 5% Compound 11 1% Compound 14 1.5% / graphite Example 13 LiNi.sub.0.5Co.sub.0.2Mn.sub.0.3O.sub.2/ LiPF.sub.6 1M Compound 5 5% Compound 11 1% Compound 12 0.1% / graphite Example 14 LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiPF.sub.6 0.5M   Compound 6 5% Compound 11 1% Compound 12 0.3% / graphite Example 15 LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiPF.sub.6 0.8M   Compound 7 5% Compound 11 1% Compound 12 0.5% / graphite Example 16 LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiPF.sub.6 1.2M   Compound 8 5% Compound 11 1% Compound 12 2.0% / graphite Example 17 LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiPF.sub.6 1.5M   Compound 9 5% Compound 11 1% Compound 13 1.0% / graphite Example 18 LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiFSI 1M Compound 1 5% Compound 11 1% Compound 14 1.0% / graphite Example 19 LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiPF.sub.6 1M Compound 2 5% Compound 11 1% Compound 12 0.5% 0.5% FEC, 95% graphite + 1% PST 5% SiO Example 20 LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiDFOB 1M Compound 2 5% Compound 11 1% Compound 12 0.5% 0.3% VEC, 90% graphite + 2% 1,3-PS 10% SiO Example 21 LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiPF.sub.6 1M Compound 2 5% Compound 11 1% Compound 12 0.5% 0.5% VC, 85% graphite + 1% DTD, 15% SiO 0.5% SN Example 22 LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiTFSI 1M Compound 2 5% Compound 11 0.5%   Compound 12 0.5% 0.5% VC, 75% graphite + 1% ADN, 25% SiO 2% DTD Example 23 LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiTFS 1M Compound 2 5% Compound 11 0.5%   Compound 12 0.5% 0.5% VC, 75% graphite + 0.3% SN 25% silicon-carbon composite Comparative LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiPF.sub.6 1M / / / / / / / example 1 graphite Comparative LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiPF.sub.6 1M Compound 1 5% / / / / / example 2 graphite Comparative LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiPF.sub.6 1M / / Compound 11 1% / / / example 3 graphite Comparative LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiPF.sub.6 1M / / / / Compound 12 1.0% / example 4 graphite Comparative LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiPF.sub.6 1M Compound 1 5% Compound 11 1% / / / example 5 graphite Comparative LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiPF.sub.6 1M Compound 1 5% / / Compound 12 1.0% / example 6 graphite Comparative LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiPF.sub.6 1M Compound 1 15%  Compound 11 1% Compound 12 1.0% / example 7 graphite Comparative LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2/ LiPF.sub.6 1M Compound 3 5% Compound 11 4% Compound 12 1.0% / example 8 graphite

(24) TABLE-US-00002 TABLE 2 Performance Test Results of Examples 1 to 23 and Comparative Examples 1 to 8 The capacity Volume expansion rate retention rate after after being stored at 80° C. −25° C. 500 cycles at 45° C. for 10 days DCR/mohm Hot box test at 150° C. Example 1 83.1% 16.7% 240.5 5 batteries are in good condition Example 2 89.5% 15.4% 248.9 5 batteries are in good condition Example 3 92.1% 14.7% 256.1 5 batteries are in good condition Example 4 86.5% 13.2% 254.3 5 batteries are in good condition Example 5 78.9% 10.9% 260.4 5 batteries are in good condition Example 6 91.2% 15.9% 265.3 5 batteries are in good condition Example 7 76.7% 13.2% 265.4 5 batteries are in good condition Example 8 84.6% 12.5% 245.6 5 batteries are in good condition Example 9 90.7% 11.4% 240.5 5 batteries are in good condition Example 10 79.4% 9.8% 270.8 5 batteries are in good condition Example 11 91.4% 10.7% 258.4 5 batteries are in good condition Example 12 92.5% 11.5% 260.3 5 batteries are in good condition Example 13 90.7% 12.4% 300.7 5 batteries are in good condition Example 14 89.6% 10.0% 281.6 5 batteries are in good condition Example 15 91.2% 9.8% 260.3 5 batteries are in good condition Example 16 84..3% 9.5% 240.5 5 batteries are in good condition Example 17 89.1% 13.4% 253.4 5 batteries are in good condition Example 18 91.0% 12.1% 264.8 5 batteries are in good condition Example 19 92.1% 14.3% 286.7 5 batteries are in good condition Example 20 93.5% 8.7% 290.4 5 batteries are in good condition Example 21 90.7% 9.0% 285.3 5 batteries are in good condition Example 22 92.8% 10.5% 290.2 5 batteries are in good condition Example 23 93.4% 12.4% 278.9 5 batteries are in good condition Comparative 69.1% 42.1% 290.3 5 batteries are on example 1 fire Comparative 72.2% 28.9% 280.6 2 batteries are on example 2 fire 3 batteries are in good condition Comparative 62.4% 13.6% 347.8 4 batteries are on example 3 fire 1 battery is in good condition Comparative 74.3% 35.8% 234.6 5 batteries are on example 4 fire Comparative 87.5% 12.4% 340.7 5 batteries are in example 5 good condition Comparative 73.9% 30.4% 237.1 5 batteries are on example 6 fire Comparative 58.4% 9.3% 356.4 5 batteries are in example 7 good condition Comparative 60.5% 10.7% 324.5 2 batteries are on example 8 fire 3 batteries are in good condition
Result Analysis

(25) (1) Comparison Between Comparative Example 1 and Comparative Example 2

(26) It can be seen from Comparative Example 1 and Comparative Example 2, when only additive A (Compound 1) is added to the non-aqueous electrolyte of the lithium ion batteries of Comparative Example 2, the storage volume expansion rate of the lithium ion batteries at 80° C. is remarkably reduced, from 42.1% to 28.9%, reduced by 13.2%. The storage life after 500 cycles at 45° C. and the low temperature DC resistance at −25° C. are also slightly improved.

(27) (2) Comparison Between Comparative Example 1 and Comparative Example 3

(28) It can be seen from Comparative Example 1 and Comparative Example 3, when only additive B (Compound 11) is added to the non-aqueous electrolyte of the lithium ion batteries of Comparative Example 3, the storage volume expansion rate of the lithium ion batteries at 80° C. is remarkably reduced, from 42.1% to 13.6%, reduced by 28.8%; However, the storage performance of the batteries after 500 cycles at 45° C. is obviously deteriorated. After being stored under 150° C., there are four lithium ion batteries on fire, and the low temperature DC resistance is also obviously increased.

(29) (3) Comparison Between Comparative Example 1 and Comparative Example 4

(30) It can be seen from Comparative Example 1 and Comparative Example 4, when only additive C (Compound 12) is added to the non-aqueous electrolyte of the lithium ion batteries of Comparative Example 4, the storage volume expansion rate of lithium ion batteries at 80° C., the cycle storage performance at 45° C. and the low temperature DC resistance at −25° C. are slightly improved. However, the high temperature storage performance at 150° C. is poor, the five batteries tested are on fire.

(31) (4) Comparison Between Comparative Example 5 and Comparative Examples 2 to 3

(32) It can be seen from Comparative Example 5 and Comparative Examples 2 to 3, when additive A (Compound 1) and additive B (Compound 11) are added to Comparative Example 5, under the synergistic effect of compound 1 and compound 11, the cycle performance of lithium ion batteries at 45° C. is improved remarkably, the capacity retention rate after 500 cycles is 87.5%, but the low temperature DC resistance value is still large, i.e. is about 340.7 mohm.

(33) (5) Comparison Between Examples 1 to 18 and Comparative Examples 1 to 8

(34) It can be seen from Examples 1 to 18 and Comparative Examples 1 to 8, when additive A, additive B and additive C are added to the non-aqueous electrolyte of the lithium ion batteries at the same time, due to the synergistic effect of additives A, B and C, the lithium ion batteries have a high cyclic capacity retention rate and a storage capacity retention rate and a low gas production rate at high temperature, have a low direct current resistance at low temperature. The thermal stability of the batteries can be significantly improved, the five batteries after being stored under 150° C. are in good condition.

(35) (6) Comparison Between Examples 19 to 23 and Comparative Examples 1 to 8

(36) It can be seen from Examples 19 to 23 and Comparative Examples 1 to 8, when additive A, additive B, additive C and other additives are added to the non-aqueous electrolyte of the lithium ion batteries, due to the synergistic effect of additives A, B and C together with other additives, the performance of lithium ion batteries have been significantly improved. The lithium ion batteries have a high cyclic capacity retention rate and a storage capacity retention rate and a low gas production rate at high temperature, and have a low direct current resistance at low temperature. The thermal stability of the batteries can be significantly improved. Five batteries after being stored under 150° C. are in good condition.

(37) (7) Comparison Between Examples 1 to 23 and Comparative Example 5

(38) Since additives A, B and C are added at the same time in Examples 1 to 23, the performances of the lithium ion batteries are good under the synergistic effect of additives A, B and C. However, in Comparative Example 5, only additive A and additive B are added. Although the capacity retention rate after 500 cycles of the batteries and the storage volume expansion rate at 80° C. are similar to those of Examples 1 to 23, the DCR value at −25° C. is up to 340.7 mohm and the DCR values in Examples 1 to 23 is only 240.5 mohm to 300.7 mohm. The DCR value directly reflects the power performance of the battery. The lower the value is, the better the power performance of the battery is, especially the low-temperature performance of lithium ion battery. The comparison example shows that for the addition of additive C in Examples 1 to 23, the DCR value of the lithium ion batteries can be significantly reduced, which explains that additive C could cooperate with additives A and B in the electrolyte to improve the performance of lithium ion batteries.

(39) (8) Comparison Between Examples 1 to 23 and Comparative Example 6

(40) Because additives A, B and C are added in Examples 1 to 23 at the same time, the performances of the lithium ion batteries are good under the synergistic effect of additives A, B and C. However, in Comparative Example 6, only additive A and additive C are added. Although the DCR value of the battery at −25° C. is equivalent to that of the embodiment or even much smaller than the DCR value of some embodiments, the capacity retention rate after 500 cycles and the storage volume expansion rate at 80° C. are much worse than those of Examples 1 to 23. As a result, the five tested batteries are all on fire after being stored at 150° C.

(41) It can be seen from the comparison that only when additive A, additive B and additive C are added to the electrolyte at the same time, additives A, B, C can work together so as to keep the good performance of the battery. In absence of any one of the additives, the test results will be affected, and could not meet the actual demand.

(42) (9) Comparison Between Examples 3, 10 and Comparative Example 7

(43) It can be seen from Examples 3 and 10 and Comparative Example 7, when the weight content of additive A in the electrolyte of Comparative Example 7 is 15%, due to the content of additive A is too high, the viscosity of the electrolyte will be significantly increased, and the conductivity of the electrolyte will be reduced, which will reduce the migration rate of lithium ion and deteriorate the cycle performance of lithium ion battery.

(44) Compared with the conventional technologies, the lithium ion battery and the electrolyte thereof according to the present invention at least have the following technical advantages.

(45) (1) The lithium ion battery electrolyte of the present invention has a cyclic phosphazene compound, a lithium fluorophosphate compound and at least one compound selected from a group consisting of a silane phosphate compound, a silane phosphite compound and a silane borate compound as additive, which can significantly improve the high temperature storage performance and stability of the battery and can inhibit the gas production phenomenon of the lithium ion battery at high temperature;

(46) (2) The lithium ion battery of the invention has excellent high temperature cycle storage performance; and

(47) (3) The lithium ion battery of the present invention has low low-temperature resistance.

(48) Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Moreover, although the foregoing descriptions describe example embodiments, it should be appreciated that alternative embodiments without departing from the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.