SILICON-OXYGEN PARTICLE FOR ELECTRODE MATERIAL, PREPARATION METHOD THEREFOR AND USE THEREOF

Abstract

A silicon oxide particle for an electrode material, including: silicon suboxide particles with a general formula of SiOx; and a carbon layer, where a plurality of silicon suboxide particles are bonded by the carbon layer, and the plurality of silicon suboxide particles are bonded and meanwhile coated by the carbon layer. The silicon oxide particle is dense, with narrow particle size distribution and small specific surface area, and has advantages such as high capacity, high Coulombic efficiency, low swelling rate and high capacity retention.

Claims

1-26. (canceled)

27. A silicon oxide particle for an electrode material, comprising: silicon suboxide particles with a general formula of SiOx; and a carbon layer, wherein a plurality of said silicon suboxide particles are bonded by the carbon layer, and the plurality of silicon suboxide particles bonded by the carbon layer are coated with the carbon layer.

28. The silicon oxide particle according to claim 27, wherein the carbon layer is obtained by carbonizing one or a combination of more precursor materials selected from a group consisting of: glucose, sucrose, chitosan, starch, critic acid, gelatin, alginic acid, carboxymethyl cellulose, coal pitch, petroleum pitch, phenolic resin, tar, naphthalene oil, anthracene oil, polyacrylic acid, polyacrylic ester, polystyrene, polyvinylpyrrolidone, polyoxyethylene, polyvinyl alcohol, epoxy resin, polyacrylonitrile, and polymethyl methacrylate.

29. The silicon oxide particle according to claim 27, wherein the x in general formula of SiOx ranges from 0.5 to 1.5.

30. The silicon oxide particle according to claim 27, wherein a median particle size D50 of the silicon suboxide particles is between 0.05 μm and 20 μm.

31. The silicon oxide particle according to claim 27, wherein a mass ratio of the silicon suboxide particles to the silicon oxide particle is in the range of 80 wt % to 99.9 wt %.

32. The silicon oxide particle according to claim 27, further comprising a conductive agent uniformly dispersed inside and on an outer surface of the silicon oxide particle, wherein the conductive agent is one or a combination of more selected from a group consisting: of Super P, Ketjen black, vapor grown carbon fibers, acetylene black, electroconductive graphite, carbon nanotubes and graphene.

33. The silicon oxide particle according to claim 32, wherein a mass ratio of the conductive agent to the silicon oxide particle is in an amount from 0.01 wt % to 10 wt %.

34. The silicon oxide particle according to claim 27, further comprising one or more additional carbon layers coating on an outer surface of the silicon oxide particle.

35. The silicon oxide particle according to claim 34, wherein the additional carbon layer is obtained by carbonizing one or a combination of more precursor materials selected from a group consisting of coal pitch, petroleum pitch, polyvinyl alcohol, epoxy resin, polyacrylonitrile and polymethyl methacrylate, or is obtained by performing chemical vapor deposition on any one or a combination of more selected from a group consisting of methane, ethane, ethylene, acetylene, propane, propylene, butane, butene, butadiene, benzene, toluene, xylene, styrene and phenol.

36. The silicon oxide particle according to claim 34, wherein a mass ratio of the additional carbon layer to the silicon oxide particle is in the range of 0.1 wt % to 10 wt %.

37. The silicon oxide particle according to claim 27, wherein the silicon oxide particle has D50 between 1 μm and 40 μm.

38. The silicon oxide particle according to claim 37, wherein the particle size of the silicon oxide particle meets: (D90−D10)/D50≤1.4.

39. The silicon oxide particle according to claim 37, wherein the specific surface area of the silicon oxide particle is in the range of 0.1 m.sup.2/g to 10 m.sup.2/g.

40. The silicon oxide particle according to claim 39, wherein a tap density of the silicon oxide particle is ≥0.6 g/cm.sup.3.

41. A negative electrode material, comprising the silicon oxide particle according to claim 27.

42. A method for preparing the silicon oxide particle according to claim 27, comprising: mixing and granulating silicon suboxide particles with a carbon-layer precursor material, carbonizing composite particles in a non-oxidizing atmosphere, and pulverizing and sieving the carbonization product, and removing magnetic impurities.

43. The method according to claim 42, wherein said mixing and granulating the silicon suboxide particles with the carbon-layer precursor material comprises a step of adding a conductive agent.

44. The method according to claim 42, further comprising a step of coating the silicon oxide particle with one or more additional carbon layers.

45. The method according to claim 42, wherein the granulating process is performed by using a granulating device comprising a VC mixer, a mechanical fusion machine, a coating machine or a reactor; and wherein a linear velocity at a maximum diameter of a stirring component in the granulating device is in the range of 1 m/s to 30 m/s during the granulating process performed at a temperature between 100° C. and 1050° C. for 0.5 hours to 10 hours under protection of an inert atmosphere.

46. The method according to claim 42, wherein the granulating process is performed by using a granulating device comprising a spraying dryer; the carbonization is performed by using a carbonization device comprising a tube furnace, an atmosphere chamber furnace, a pusher kiln, a roller kiln or a rotary furnace; wherein a carbonization reaction occurs at a temperature between 600° C. and 1200° C. for 0.5 hours to 24 hours; and wherein the non-oxidizing atmosphere is provided by at least one gas selected from nitrogen, argon, hydrogen and helium.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] FIG. 1 is a high magnification scanning electron microscope (SEM) image of a secondary particle prepared according to Example 1.

[0045] FIG. 2 is a schematic illustration of the secondary particle prepared according to Example 1.

[0046] FIG. 3 is a schematic illustration of the secondary particle prepared according to Example 2.

[0047] FIG. 4 is a schematic illustration of the secondary particle prepared according to Example 4.

[0048] FIG. 5 is a diagram showing particle size distribution curves of a starting material of silicon suboxide used in Comparative Example 2 and Example 6, and secondary particles prepared in Comparative Examples 1 and 2 and Example 6.

[0049] FIG. 6 is a low magnification SEM image of secondary particles prepared according to Example 6.

[0050] FIG. 7 is a high magnification SEM image of secondary particles prepared according to Example 6.

[0051] FIG. 8 is an SEM image showing a cross section of a negative electrode after the formation of a battery containing the secondary particles prepared according to Example 6.

[0052] FIG. 9 is a high magnification SEM image of secondary particles prepared according to Example 14.

[0053] FIG. 10 is a SEM image of particles prepared according to Comparative Example 1.

[0054] FIG. 11 is a SEM image of particles prepared according to Comparative Example 2.

DETAILED DESCRIPTION OF EMBODIMENTS

[0055] Specific embodiments of the present invention will be illustrated below in more detail in combination with examples for a better understanding of the solutions of the present invention as well as the advantages thereof in various aspect. Nevertheless, the specific embodiments and examples described below are merely for illustrative purposes, and are not intended to limit the present invention.

Example 1

[0056] 1. Preparation Method

[0057] 1.1 Preparation of secondary particles

[0058] 100 kg of silicon suboxide powder (i.e., primary particles, with D10=0.60 μm, D50=1.78 μm, D90=3.59 μm, SPAN=1.68 and a specific surface area of 8.9 m.sup.2/g, and with x=1 in the general formula SiOx) together with 12 kg of coal pitch powder were added to a VC mixer, and mixed for 30 min at a linear velocity of 16 m/s at the maximum diameter of a stirring component, to uniformly mix the two starting materials. Subsequently, the rotation speed was reduced so that the foregoing linear velocity was reduced to 8 m/s, meanwhile, nitrogen was introduced as an inert protective gas; then the temperature was initially raised to 300° C. at a rate of 3° C./min, held for 4 h, and then reduced to room temperature through free cooling. Hence, the granulating process of the silicon suboxide and pitch was completed. In this process, the pitch was gradually softened with the increase of the temperature inside the VC mixer, and then uniformly coated on the surface of each of the silicon suboxide primary particle under continuous high-speed stirring; meanwhile, the silicon-suboxide primary particles coated with pitch were bonded and aggregated with one another to form silicon-suboxide/coal pitch composite secondary particles of a certain size. The secondary particles above became denser and denser under long-time shearing, extruding and colliding in the VC mixer, meanwhile, the pitch was deprived of small-molecule volatiles and partially cross-linked and carbonized to shape the secondary particles at the temperature of 300° C.

[0059] A resulting intermediate product was loaded into a graphite saggar which was then put in a roller kiln, nitrogen protective gas was introduced, and the temperature was raised to 900° C. at a rate of 3° C./min, held for 4 h, and then reduced to room temperature through free cooling. Hence, the carbonization was completed. In this step, the pitch was carbonized at high temperature in an oxygen-free atmosphere. A resulting carbonized product was jet-milled, where by adjusting the pressure of the jet, composite material lumps obtained after carbonization were pulverized into fine powder of the secondary particles without destroying the secondary particle structure. Finally, a resultant was sieved and magnetic separation was carried out to obtain a final product applicable to the negative electrode material.

[0060] FIG. 1 is a high magnification SEM image of the secondary particle prepared in Example 1, and FIG. 2 is a schematic illustration of said secondary particle. The particles prepared in Example 1 are dense secondary particles that are formed by combining the silicon-suboxide primary particles A with the carbon layer B connecting and coating the same.

[0061] 1.2 Preparation of Electrode

[0062] 9 parts of the foregoing secondary particles, 43.5 parts of artificial graphite, 43.5 parts of natural graphite, 1 part of conductive agent Super P, 0.5 parts of multi-wall carbon nanotubes, 1 part of sodium carboxymethylcellulose (CMC) and 1.5 parts of modified polyacrylic ester as binders were taken and subjected to homogenizing, coating, drying and calendering to obtain a negative electrode containing the silicon oxide secondary particles.

[0063] 2. Product Testing

[0064] The particle size of the secondary particles were as follows: D10=1.89 μm, D50=4.02 μm, D90=7.16 μm, with SPAN=1.31, the specific surface area of 2.7 m.sup.2/g, the tap density of 0.88 g/cm.sup.3 and the carbon content of 4.9 wt %. The silicon suboxide material may go through a disproportionation reaction (2SiO.fwdarw.Si+SiO.sub.2) after thermal treatment at above 800° C. to form silicon nano crystals/nanoclusters uniformly dispersing inside SiOx matrix. Based on the X-ray diffraction spectra and Scherrer equation, a grain size corresponding to a Si(111) crystal facet in the material obtained in Example 1 was calculated to be 2.9 nm.

[0065] Instruments and devices used in the testing items above were:

[0066] Hitachi SU8010 field-emission scanning electron microscope was used to observe the morphology and the like of a sample.

[0067] Dandong Bettersize 2000LD laser particle size analyzer was used to test the particle size and particle size distribution of the material.

[0068] Quantachrome Nova4200e specific surface area tester was used to test the specific surface area of the material.

[0069] Dandong Bettersize BT-301 tap volumeter was used to test the tap density of the material.

[0070] Elementar vario EL cube element analyzer was used to determine the carbon content in the material.

[0071] Rigaku MiniFlex600 X-ray diffraction instrument was used to test the crystal structure of the material.

[0072] 3. Performance Testing

[0073] Half cell evaluation: the negative electrode containing the silicon oxide secondary particles as prepared above, a separator, a lithium foil and a stainless-steel gasket were sequentially stacked, added 200 μL of electrolyte dropwise and then sealed to get a 2016 lithium-ion coin cell. The capacity and discharge Coulombic efficiency of the half cell was tested by using a battery testing system from Wuhan LANHE Electronics Co., Ltd. It was tested that the half cell with the above negative electrode had an initial reversible lithium deintercalation capacity of 1593.3 mAh/g, and an initial Coulombic efficiency of 78.6%.

[0074] Full cell evaluation: the negative electrode containing the silicon oxide secondary particles as prepared above was cut, vacuum-baked, and then wound and packed with a positive electrode (a ternary material of Ni—Co—Mn, LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2) and a separator into an aluminium-plastic bag of a corresponding size; then a certain amount of electrolyte was added and sealed for formation, thereby obtaining a complete lithium-ion full cell with a negative electrode containing the silicon oxide secondary particles. The capacity and average discharge voltage at 0.2 C discharge rate, and a capacity retention at 1 C charge/discharge rate after 500 cycles of the full cell were tested by using a battery tester from Shenzhen Neware Electronics Co., Ltd., with a voltage range of 4.2-2.75 V. Weighed the battery, combined with the above electrochemical data, the gravimetric energy density of the full cell was calculated to be 301 Wh/kg. The first Coulombic efficiency is 84.1% and the capacity retention rate is 85.3% after 500 charge/discharge cycles. After 500 cycles, the battery was fully charged and then measured in thickness, and compared with an initial thickness of the battery, a battery swelling rate was calculated to be 9.0%. Then the battery was disassembled in an inert atmosphere and measured the thickness of the negative electrode which was fully intercalated with lithium, and compared with the initial thickness of the negative electrode before the battery is assembled. The swelling rate of the fully charged negative electrode was 29.4%. The results of the above tests were summarized in Table 1.

Example 2

[0075] The process in Example 2 is similar to that in Example 1, with a difference lying in that a conductive agent powder containing 0.3 kg of Ketjen black and 0.2 kg of multi-wall carbon nanotubes was added additionally. Therefore, the final product was silicon-suboxide/amorphous-carbon composite secondary particles containing the conductive agent, with a structure as shown in FIG. 3. These secondary particles were formed by combining the silicon-suboxide primary particles A, the conductive agent C and a carbon layer B for connecting and coating the two, with the conductive agent C uniformly dispersed inside and on the outer surfaces of the secondary particles. The final product had D10=1.78 μm, D50=3.89 μm, D90=7.01 μm, SPAN=1.34, the specific surface area of 3.0 m.sup.2/g, the tap density of 0.84 g/cm.sup.3 and the carbon content of 5.3 wt %, with a grain size of 2.9 nm corresponding to a Si(111) crystal facet.

[0076] The methods for evaluating the half cell and the full cell were the same as in Example 1, and the results were summarized in Table 1. It can be seen that the performances of the batteries are somewhat improved after the addition of the conductive agent.

Example 3

[0077] 100 kg of the secondary particles prepared in Example 1 and 1 kg of petroleum pitch powder were added to the VC mixer, and mechanically mixed for 10 minutes at a linear velocity of 3 m/s, which was then reduced to 2 m/s; and introduce a nitrogen protection atmosphere, the temperature of the device was raised to 300° C. under stirring and held for 1 h, which was subsequently cooled to room temperature freely. A resulting material coated with the pitch was placed in an inert atmosphere of argon at 400° C., which was held for 2 h, then increased to 900° C. for carbonization for 4 h and then cooled to room temperature freely; and a resultant was pulverized, sieved and magnetic separation was carried out to obtain silicon-suboxide/amorphous-carbon composite particles having a second amorphous-carbon coating layer. The final product had D10=2.13 μm, D50=4.65 μm, D90=7.87 μm, SPAN=1.23, the specific surface area of 2.4 m.sup.2/g, the tap density of 0.95 g/cm.sup.3 and the carbon content of 5.8 wt %, with a grain size of 2.9 nm corresponding to a Si(111) crystal facet.

[0078] The methods for evaluating the half cell and the full cell were the same as in Example 1, and the results were summarized in Table 1.

Example 4

[0079] 100 kg of the secondary particles prepared in Example 2 were processed with the second coating process in Example 3 to obtain silicon-suboxide/multi-wall carbon nanotubes/Ketjen black/amorphous-carbon composite particles having a second amorphous-carbon coating layer. FIG. 4 is a schematic of the secondary particles prepared in this example. As shown in FIG. 4, these secondary particles were formed by combining the silicon-suboxide primary particles A, the conductive agent C and a carbon layer B for connecting and coating the two, where the conductive agent C was uniformly dispersed inside and on the outer surfaces of the secondary particles, and the outer surfaces of the secondary particles were provided with the second continuous carbon coating layer D. The final product had D10=2.01 μm, D50=4.45 μm, D90=7.76 μm, SPAN=1.29, the specific surface area of 2.7 m.sup.2/g, the tap density of 0.89 g/cm.sup.3 and the carbon content of 6.2 wt %, with a grain size of 2.9 nm corresponding to a Si(111) crystal facet.

[0080] The methods for evaluating the half cell and the full cell were the same as in Example 1, and the results were summarized in Table 1. It can be seen that like Example 3, the product performance can be significantly improved by additional coatings.

Example 5

[0081] 0.2 kg of sucrose was dissolved in 8 kg of deionized water to prepare a sucrose solution; then, a carbon nanotube slurry containing 0.6 g of single-wall carbon nanotubes was added to the sucrose solution and dispersed; 2 kg of silicon suboxide powder (the same as in Example 1) was added under stirring; and subsequently, ultrasonic dispersion was performed for 1 h under stirring to prepare a sucrose/single-wall carbon nanotubes/silicon suboxide particle composite slurry. Said composite slurry was spray dried with an inlet-air at 150° C. under a nozzle atomizing pressure of 0.2 Mpa. The dry powder of sucrose/single-wall carbon nanotubes/silicon suboxide composite secondary particles was obtained. Said powder was loaded into a graphite saggar which was then put in an atmosphere chamber furnace; nitrogen as an inert protective gas was introduced; and the temperature was raised to 900° C. at 3° C./min, held for 6 h, and then cooled to room temperature freely. Hence, the carbonization was completed. A resulting carbonized product was pulverized by a fluted-disk mill, with a maximum linear velocity of 3 m/s at an outer edge of a rotor of the fluted-disk mill. 1 kg of said secondary particles and 0.04 kg of petroleum pitch powder were simply mixed and then added to the mechanical fusion machine for treatment for 0.5 h, where the linear velocity at an outer edge of a rotor was controlled at 15 m/s; a processed product was placed in an inert atmosphere of nitrogen at 400° C., which was held for 2 h, then increased to 900° C. for carbonization for 4 h and then cooled to room temperature freely; and a resultant was pulverized, sieved and magnetic separation was carried out to obtain silicon-suboxide/single-wall carbon nanotubes/amorphous-carbon composite particles having a second amorphous-carbon coating layer. The final product had D10=1.90 μm, D50=4.87 μm, D90=8.62 μm, SPAN=1.38, the specific surface area of 3.7 m.sup.2/g, the tap density of 0.82 g/cm.sup.3 and the carbon content of about 4.8 wt %, with a grain size of 2.9 nm corresponding to a Si(111) crystal facet.

[0082] The methods for evaluating the half cell and the full cell were the same as in Example 1, and the results were summarized in Table 1. Taken together, the performance of the battery prepared through spray-drying was improved compared with the prior art, but was not outstanding in some performances compared with other examples in the present invention.

Example 6

[0083] 100 kg of silicon suboxide powder (with D10=1.07 μm, D50=4.68 μm, D90=8.84 μm, SPAN=1.66 and a specific surface area of 2.9 m.sup.2/g, and with x=1 in the general formula SiOx) together with 5 kg of petroleum pitch powder were added to a vertical coating machine, and mixed for 1 h at a linear velocity of 7 m/s at a maximum diameter of a stirring component, to uniformly mix the two starting materials. Subsequently, the linear velocity was reduced to 3 m/s, meanwhile, nitrogen was introduced as an inert protective gas; and then the temperature was raised to 500° C. at a rate of 3° C./min, held for 3 h, and then cooled to room temperature freely. A resulting intermediate product was loaded into a graphite saggar which was then put in a roller kiln, a nitrogen protective gas was introduced, and the temperature was raised to 1020° C. at a rate of 3° C./min, held for 2 h, and then cooled to room temperature freely. A resulting carbonized product was pulverized for 1 h by a plow blender, with a linear velocity of the plow blade as 3 m/s. Finally, sieving and magnetic separation magnetic separation were performed to obtain a final product, which had D10=4.32 μm, D50=7.06 μm, D90=10.90 μm, SPAN=0.93, the specific surface area of 1.1 m.sup.2/g, the tap density of 1.09 g/cm.sup.3 and the carbon content of 3.2 wt %, with a grain size of 4.1 nm corresponding to a Si(111) crystal facet.

[0084] FIG. 5 illustrates the particle size distribution curves of the starting material of silicon suboxide powder and the silicon suboxide composite material (i.e., the secondary particles). In addition, FIG. 6 and FIG. 7 show the SEM images of the secondary particles prepared in this embodiment. FIG. 8 is an SEM image showing a cross section of a negative electrode of a lithium-ion battery containing the secondary particles prepared in this example. From FIG. 6, it can be seen that the particles prepared in this example are secondary particles with uniform size, without small individual primary particles. Referring to both FIG. 7 and FIG. 8, it can be seen that the particles prepared in this example are dense secondary particles.

[0085] The methods for evaluating the half cell and the full cell were the same as in Example 1, and the results were summarized in Table 1.

Example 7

[0086] 100 kg of silicon suboxide powder (the same as in Example 6) together with 9 kg of polyvinyl alcohol powder were added to the vertical coating machine, and mixed for 2 h at a linear velocity of 5 m/s at the maximum diameter of a stirring component, to uniformly mix the two starting materials. Subsequently, the linear velocity was reduced to 3 m/s, meanwhile, nitrogen was introduced as an inert protective gas; then the temperature was raised to 300° C. at a rate of 2° C./min, held for 6 h, and then cooled to room temperature freely. A resulting intermediate product was loaded into a graphite saggar which was then put in a roller kiln, nitrogen protective gas was introduced, and the temperature was raised to 1020° C. at a rate of 3° C./min, held for 2 h, and then cooled to room temperature free. A resulting carbonized product was pulverized for 1 h by a plow blender, with a linear velocity of the plow blade as 3 m/s. Finally, sieving and magnetic separation were performed to obtain a final product, which had D10=3.97 μm, D50=6.91 μm, D90=10.40 μm, SPAN=0.93, the specific surface area of 1.2 m.sup.2/g, the tap density of 1.05 g/cm.sup.3 and the carbon content of 3.0 wt %, with a grain size of 4.1 nm corresponding to a Si(111) crystal facet.

[0087] The methods for evaluating the half cell and the full cell were the same as in Example 1, and the results were summarized in Table 1.

Example 8

[0088] 100 kg of silicon suboxide powder (with D10=0.87 μm, D50=3.88 μm, D90=7.73 μm, SPAN=1.77 and a specific surface area of 3.8 m.sup.2/g, and with x=1 in the general formula SiOx) together with 7 kg of petroleum pitch powder were added to the VC mixer, and mixed for 1 h at a linear velocity of 8 m/s at the maximum diameter of a stirring component, to uniformly mix the two starting materials. Subsequently, the linear velocity was reduced to 4 m/s, meanwhile, nitrogen was introduced as an inert protective gas; then the temperature was raised to 900° C. at a rate of 3° C./min, held for 1 h, and then cooled to room temperature freely. A resulting intermediate product was loaded into a graphite saggar which was then put in a pusher kiln, nitrogen protective gas was introduced, and the temperature was raised to 1000° C. at a rate of 3° C./min, held for 3 h, and then cooled to room temperature freely. A resulting carbonized product was pulverized for 1 h by a plow blender, with a linear velocity of the plow blade as 3 m/s. Finally, sieving and magnetic separation were performed to obtain a final product, which had D10=4.51 μm, D50=7.15 μm, D90=11.07 μm, SPAN=0.92, the specific surface area of 1.0 m.sup.2/g, the tap density of 1.12 g/cm.sup.3 and the carbon content of 4.0 wt %, with a grain size of 3.9 nm corresponding to a Si(111) crystal facet.

[0089] The methods for evaluating the half cell and the full cell were the same as in Example 1, and the results were summarized in Table 1. The full cell had the gravimetric energy density up to 311 Wh/kg, the capacity retention up to 90.7%, and the cell swelling rate of 7.6%. Taken together, the battery prepared in this example had an excellent performance.

Example 9

[0090] The process steps of Example 9 were similar to those of Example 8, with an only difference lying in that in the granulating step, the temperature in the VC mixer was held at 400° C. for 3 h. The final product had D10=4.26 μm, D50=7.46 μm, D90=11.98 μm, SPAN=1.03, the specific surface area of 1.2 m.sup.2/g, the tap density of 1.07 g/cm.sup.3 and the carbon content of 3.9 wt %, with a grain size of 3.9 nm corresponding to a Si(111) crystal facet.

[0091] The methods for evaluating the half cell and the full cell were the same as in Example 1, and the results were summarized in Table 1.

Example 10

[0092] The process steps of Example 10 were similar to those of Example 8, with an only difference lying in that in the granulating step, the temperature in the VC mixer was held at 150° C. for 6 h. The final product had D10=4.00 μm, D50=8.47 μm, D90=14.10 μm, SPAN=1.19, the specific surface area of 1.4 m.sup.2/g, the tap density of 1.02 g/cm.sup.3 and the carbon content of 3.9 wt %, with a grain size of 3.9 nm corresponding to a Si(111) crystal facet.

[0093] The methods for evaluating the half cell and the full cell were the same as in Example 1, and the results were summarized in Table 1.

Example 11

[0094] The process steps of Example 11 were similar to those of Example 9, with an only difference lying in that the amount of the added petroleum pitch is 9 kg. The final product had D10=4.78 μm, D50=8.90 μm, D90=14.90 μm, SPAN=1.14, the specific surface area of 1.6 m.sup.2/g, the tap density of 1.01 g/cm.sup.3 and the carbon content of 6.1 wt %, with a grain size of 3.9 nm corresponding to a Si(111) crystal facet.

[0095] The methods for evaluating the half cell and the full cell were the same as in Example 1, and the results were summarized in Table 1.

Example 12

[0096] The process steps of Example 12 were similar to those of Example 9, with an only difference lying in that the amount of the added petroleum pitch is 3 kg. The final product had D10=3.78 μm, D50=6.98 μm, D90=10.76 μm, SPAN=1.00, the specific surface area of 1.1 m.sup.2/g, the tap density of 1.11 g/cm.sup.3 and the carbon content of 2.7 wt %, with a grain size of 3.9 nm corresponding to a Si(111) crystal facet.

[0097] The methods for evaluating the half cell and the full cell were the same as in Example 1, and the results were summarized in Table 1.

Example 13

[0098] 2 kg of silicon suboxide powder (with D10=3.62 μm, D50=7.90 μm, D90=13.40 μm, SPAN=1.24 and a specific surface area of 1.8 m.sup.2/g, and with x=1 in the general formula SiOx) together with 0.08 kg of coal pitch powder and 0.01 kg of vapor growth carbon fiber powder were added into the mechanical fusion machine, and mixed for 10 minutes at a linear velocity of 20 m/s at an outer edge of a rotor, to uniformly mix the three starting materials. Subsequently, the linear velocity was kept at 20 m/s, and the temperature was raised to 180° C., held for 0.5 h, and then cooled to room temperature freely. A resulting intermediate product was loaded into a graphite saggar which was then put in a tube furnace, nitrogen protective gas was introduced, and the temperature was raised to 930° C. at a rate of 3° C./min, held for 8 h, and then cooled to room temperature freely. A resulting carbonized product was pulverized by a fluted-disk mill, with the maximum linear velocity of 3 m/s at an outer edge of a rotor of the fluted-disk mill. Finally, sieving and magnetic separation were performed to obtain a final product, which had D10=5.91 μm, D50=10.21 μm, D90=17.60 μm, SPAN=1.14, the specific surface area of 1.1 m.sup.2/g, the tap density of 1.10 g/cm.sup.3 and the carbon content of 3.2 wt %, with a grain size of 3.1 nm corresponding to a Si(111) crystal facet.

[0099] The methods for evaluating the half cell and the full cell were the same as in Example 1, and the results were summarized in Table 1.

Example 14

[0100] 100 kg of silicon suboxide powder (with D10=2.44 μm, D50=4.55 μm, D90=6.99 μm, SPAN=1.00 and a specific surface area of 1.7 m.sup.2/g, and with x=1 in the general formula SiOx) together with 6 kg of coal pitch powder were added to the vertical coating machine, and mixed for 1 h at a linear velocity of 6 m/s at the maximum diameter of a stirring component, to uniformly mix the two starting materials. Subsequently, the linear velocity was reduced to 2 m/s, meanwhile, nitrogen was introduced as an inert protective gas; then the temperature was raised to 300° C. at a rate of 3° C./min, held for 6 h, and then cooled to room temperature freely. A resulting intermediate product was loaded into a graphite saggar which was then put in a pusher kiln, nitrogen protective gas was introduced, and the temperature was raised to 950° C. at a rate of 3° C./min, held for 5 h, and then cooled to room temperature freely. A resulting carbonized product was pulverized by a fluted-disk mill, with the maximum linear velocity of 3 m/s at an outer edge of a rotor of the fluted-disk mill. Finally, sieving and magnetic separation were performed to obtain a final product, which had D10=4.92 μm, D50=8.32 μm, D90=14.70 μm, SPAN=1.18, the specific surface area of 1.2 m.sup.2/g, the tap density of 1.07 g/cm.sup.3 and the carbon content of 3.2 wt %, with a grain size of 3.7 nm corresponding to a Si(111) crystal facet. FIG. 9 is a high magnification SEM image of a secondary particle prepared according to Example 14.

[0101] The methods for evaluating the half cell and the full cell were the same as in Example 1, and the results were summarized in Table 1.

Example 15

[0102] 100 kg of silicon suboxide powder (the same as in Example 14) together with 6 kg of coal pitch powder and 0.5 kg of Super P were added to the vertical coating machine, and mixed for 1 h at a linear velocity of 6 m/s at the maximum diameter of a stirring component, to uniformly mix the three starting materials. Subsequently, the linear velocity was reduced to 2 m/s, meanwhile, nitrogen was introduced as an inert protective gas; then the temperature was raised to 300° C. at a rate of 3° C./min, held for 6 h, and then cooled to room temperature freely. A resulting intermediate product was loaded into a graphite saggar which was then put in a pusher kiln, nitrogen protective gas was introduced, and the temperature was raised to 950° C. at a rate of 3° C./min, held for 5 h, and then cooled to room temperature freely. A resulting carbonized product was pulverized by a fluted-disk mill, with the maximum linear velocity of 3 m/s at an outer edge of a rotor of the fluted-disk mill. 2 kg of the pulverized material was loaded into the rotary furnace; the temperature was raised to 950° C. at 3° C./min; acetylene and nitrogen were introduced at a flow rate of 0.2 L/min and 0.3 L/min, respectively; a reaction was allowed to proceed for 5 h, then a resultant was cooled to room temperature and taken out. Finally, sieving and magnetic separation were performed to obtain a final product, which had D10=5.38 μm, D50=8.80 μm, D90=15.60 μm, SPAN=1.16, the specific surface area of 1.8 m.sup.2/g, the tap density of 0.99 g/cm.sup.3 and the carbon content of 5.2 wt %, with a grain size of 3.7 nm corresponding to a Si(111) crystal facet.

[0103] The methods for evaluating the half cell and the full cell were the same as in Example 1, and the results were summarized in Table 1.

Comparative Example 1

[0104] Silicon suboxide chunks (with an average size of about 2 cm) were placed in the box furnace, which was then introduced with an argon protective atmosphere; the temperature was raised to 1000° C. at 3° C./min for thermal treatment for 2 h; and disproportionated silicon suboxide chunks were hence obtained. The disproportionated silicon suboxide chunks were pulverized to obtain a powder with D10=1.04 μm, D50=4.61 μm, D90=9.01 μm and SPAN=1.73. 2000 g of the obtained silicon suboxide powder was loaded into the rotary furnace, which was then heated to 900° C. at 3° C./min and introduced with an acetylene at a flow rate of 0.2 L/min, and with the nitrogen at a flow rate of 0.1 L/min, and the reaction lasted for 10 h to prepare a precursor; and the precursor was placed into the mechanical fusion machine for treatment for 10 min by controlling the linear velocity at the outer edge of the rotor to be 15 m/s, and subsequently mixed, sieved, magnetic separation was carried out, dried and packed to prepare a silicon suboxide composite material with D10=2.05 μm, D50=5.25 μm, D90=9.54 μm, SPAN=1.43, the specific surface area of 5.2 m.sup.2/g, the tap density of 0.93 g/cm.sup.3, and the carbon content of about 5.2 wt %, and with a grain size of 4.0 nm corresponding to a Si(111) crystal facet.

[0105] FIG. 10 is an SEM image of the silicon suboxide composite material prepared in Comparative Example 1. It can be seen that the composite material includes many fine particles which are mostly individual primary particles having sharp edges and corners. From the diagram of particle size distribution curve of the silicon suboxide composite material of Comparative Example 1 in FIG. 5, it can be seen that the product in Comparative Example 1 has a wider particle size distribution and higher proportion of small particles than those in Example 6. The particle size distribution curves in FIG. 5 are mass/volume size distribution curves. If the mass/volume size distribution curves are high in small particles region, the count size distribution curves are even orders of magnitude higher in this small-particle region, indicating high specific surface area of this material. Therefore, from FIG. 5, it can be seen that compared with Example 6, the proportion of the count of small particles in Comparative Example 1 is greatly higher, and the specific surface area also increases greatly.

[0106] The performances of batteries prepared with the particles from this comparative example were evaluated by referring to the method for evaluating the half cell and the full cell in Example 1, and the results were summarized in Table 1.

Comparative Example 2

[0107] 100 kg of silicon suboxide powder (the same as in Example 6) and 10 kg of petroleum pitch powder were loaded into the VC mixer, and mixed for 0.5 h after the linear velocity was adjusted to 10 m/s, thereby preparing a precursor 1. The precursor 1 was added to a vacuum kneading machine, and mixed and kneaded for 6 h until the precursor 1 was sticky, where the temperature of the precursor 1 was controlled to be above 250° C. by heating via circulating heat transfer oil; then, the precursor 1 was cooled and then quickly transferred to a sheet mill for sheet rolling, where the thickness of a rolled sheet was controlled to be 2.0-5.0 mm; the rolled sheet was cooled and then mechanically pulverized, where a median particle size was controlled to be 2.0-15.0 μm; next, a resulting pulverized material was subjected to hot isostatic pressure treatment, where the pressure was controlled to be 20 MPa and the temperature was controlled to be 250° C.; and pressurization was performed for 0.1 h to obtain a precursor 2. The precursor 2 was placed into the roller kiln, nitrogen protective gas was introduced, and the temperature was raised to 1000° C. at a rate of 3° C./min, held for 7 h, and then cooled to room temperature freely. Then, the precursor 2 was crushed for 1 h by plow blender at the maximum linear velocity of 3 m/s, and subsequently sieving magnetic separation and drying were carried out to prepare silicon suboxide particles. A resulting material had D10=3.22 μm, D50=6.77 μm, D90=13.36 μm, SPAN=1.50, the specific surface area of 2.2 m.sup.2/g, the tap density of 0.99 g/cm.sup.3 and the carbon content of 6.3 wt %, with a grain size of 4.0 nm corresponding to a Si(111) crystal facet.

[0108] FIG. 11 is a SEM image of the silicon suboxide particles in Comparative Example 2. It can be seen that the composite material includes many fine particles, many individual primary particles, as well as some loose secondary particles which are formed by combining big and small primary particles and have large specific surface area. From the diagram of particle size distribution curve of the silicon suboxide particles of Comparative Example 2 in FIG. 5, it can be seen that the product in Comparative Example 2 has a particle size distribution wider than that in Example 1, and the proportions of small and big particles are both high.

[0109] The performances of batteries prepared with the particles from this comparative example were evaluated by referring to the method for evaluating the half cell and the full cell in Example 1, and the results were summarized in Table 1.

Comparative Example 3

[0110] The process steps of Example 3 were similar to those in Examples 8-10, with an only difference lying in that after the mixture was completed by using the VC mixer at room temperature, a product was directly taken out without granulating process at elevated temperature, and then the product was subsequently carbonized, pulverized, sieved and magnetic separation was carried out. The final product had D10=1.93 μm, D50=8.68 μm, D90=16.22 μm, SPAN=1.65, the specific surface area of 2.2 m.sup.2/g, the tap density of 1.02 g/cm.sup.3 and the carbon content of 3.9 wt %, with a grain size of 3.9 nm corresponding to a Si(111) crystal facet.

[0111] The methods for evaluating the half cell and the full cell were the same as in Example 1, and the results were summarized in Table 1.

TABLE-US-00001 TABLE 1 Summary of performance testing data Half cell Full cell Lithium Lithium Initial Gravimetric Initial Electrode 500-cycle deintercalation intercalation Coulombic energy Coulombic swelling capacity Battery capacity capacity efficiency density efficiency rate at full retention swelling (mAh/g) (mAh/g) (%) (Wh/kg ) (%) charge (%) rate (%) rate (%) Example 1 1593.3 2027.1 78.6 301.0 84.1 29.4 85.3 9.0 Example 2 1588.5 2021.0 78.6 302.0 84.0 29.0 87.1 8.4 Example 3 1585.9 2010.0 78.9 301.0 84.7 28.5 87.3 7.9 Example 4 1584.3 2013.1 78.7 303.0 84.8 28.2 88.2 7.8 Example 5 1579.9 2012.6 78.5 300.0 84.0 31.4 85.2 9.4 Example 6 1618.8 2018.4 80.2 310.0 85.7 28.5 89.5 7.9 Example 7 1610.3 2012.9 80.0 309.0 85.6 28.0 88.4 8.1 Example 8 1610.2 2020.3 79.7 311.0 85.5 27.6 90.7 7.6 Example 9 1598.1 2015.3 79.3 307.0 84.9 28.3 89.2 7.9 Example 10 1593.4 2014.4 79.1 304.0 84.7 29.7 87.7 8.6 Example 11 1587.7 2009.7 79.0 302.0 84.6 30.0 88.5 8.3 Example 12 1619.5 2050.0 79.0 306.0 84.6 28.5 86.4 8.4 Example 13 1598.5 2028.6 78.8 302.0 84.2 29.6 89.9 9.2 Example 14 1609.8 2032.6 79.2 307.0 84.8 28.4 89.5 8.1 Example 15 1594.3 2018.1 79.0 302.0 84.5 27.9 90.3 7.9 Comparative 1592.2 2036.1 78.2 295.8 83.9 33.4 84.9 10.8 Example 1 Comparative 1587.7 2056.6 77.2 291.0 82.7 38.5 77.1 12.4 Example 2 Comparative 1597.6 1976.9 77.8 289.0 83.3 40.1 73.4 13.5 Example 3

[0112] The preparation process of the prior art is complicated, and it is difficult to realize mass production by the processes such as mixing and kneading, sheet rolling and hot isostatic pressure treatment. Moreover, the carbon precursor after carbonization tends to adhere and aggregate to adjacent silicon suboxide particles, and the subsequent breaking, pulverization and other processes may damage the carbon coating layer. The material prepared with the prior art has wide particle size distribution and high proportions of both small and big particles, and the battery prepared therefrom is undesirable in Coulombic efficiency, swelling rate and capacity retention and has nonuniform distribution of micro-area swelling in electrode. The secondary particles for the negative electrode material as prepared according to the present invention are dense, narrow in particle size distribution and low in specific surface area, and have been tested to have advantages such as high capacity, high Coulombic efficiency, uniform distribution of areal capacity, low swelling and high capacity retention. Described above are merely preferred embodiments of the present invention, and are not intended to limit the present invention in any forms. Without departing from the scope of the technical solutions of the present invention, any simple modification, equivalent substitution, improvement and the like made by any person skilled in the art to the embodiments above based on the technical essence of the present invention are still construed to fall within the protection scope of the technical solutions of the present invention.