CN113488637A - Composite negative electrode material, negative plate and lithium ion battery - Google Patents
Composite negative electrode material, negative plate and lithium ion battery Download PDFInfo
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- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
- H01M4/386—Silicon or alloys based on silicon
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- H—ELECTRICITY
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
- H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
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- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
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- H—ELECTRICITY
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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Abstract
The invention provides a composite negative electrode material, a negative electrode plate and a lithium ion battery, which comprise a silicon-based material and graphite; the ratio of the particle size D50 of the graphite to the particle size D50 of the silicon-based material is 1-6; the ratio of the particle size D10 of the graphite to the particle size D10 of the silicon-based material is 2-4. Compared with the prior art, the composite cathode material provided by the invention has the advantages that the silicon-based material and the graphite are subjected to adaptability limitation, and the ratios of D50 and D10 are respectively limited, so that the problems that the silicon-based material is separated from the graphite due to poor adaptability of the silicon-based material and graphite particles or the graphite cannot leave a buffer space for expansion of the silicon-based material during lithium intercalation and lithium deintercalation can be avoided.
Description
Technical Field
The invention relates to the field of lithium batteries, in particular to a composite negative electrode material, a negative plate and a lithium ion battery.
Background
The negative electrode material is a very important component of the lithium ion battery, and directly influences the energy density and the electrochemical performance of the lithium ion battery. The excellent negative electrode material can improve the reversible capacity, the cycle performance and the rate performance of the lithium ion battery; otherwise, the performance of lithium ions is degraded and even the lithium ions cannot work.
The conventional negative electrode material is generally graphite, but the capacity is limited, and the capacity of the silicon oxide material is 1000-. However, if the silicon oxide is used as the negative active material, the volume expansion of the silicon oxide can reach 180% when the battery is fully charged, and the volume expansion of the graphite is only 20-40% when the battery is fully charged, so that the negative effect of the silicon oxide caused by the volume effect can be reduced by adopting a mode of mixing the graphite and the silicon oxide in the industry, and the expansion of the negative material after the mixing of the graphite and the silicon oxide is 40-70% when the battery is fully charged.
The current mixing conditions of graphite and silicon oxide are as follows: the silicon oxide/graphite negative electrode material is formed by mixing 0-60% of silicon oxide into graphite, wherein the particle size D50 of the silicon oxide is 2-8um, and the particle size D50 of the graphite is 6-20um, but the range is generally selected arbitrarily and is not limited by other suitability, so the following problems can be caused: 1) when the particle size of the silicon monoxide is small and the particle size of the composite graphite is large, when lithium intercalation is carried out on the prepared electrode plate, the gap between the graphite particles is large, so that the contact between the silicon monoxide particles and the graphite is poor, and the adverse effect on the conductivity network and ion migration is further caused, thereby being not beneficial to the large-rate capacity exertion and the cycling stability of the battery during charging and discharging; 2) when the particle size of the silicon monoxide is larger and the particle size of the graphite composite is smaller, the graphite loses the function of limiting the expansion of the silicon monoxide, so that the silicon monoxide is pulverized and fails due to the volume effect in the lithium desorption and insertion process, and the cycle life is shortened.
In view of the above, it is necessary to provide a technical solution to the above problems.
Disclosure of Invention
One of the objects of the present invention is: the composite negative electrode material provided by the invention effectively reduces the negative influence of the volume effect of the silicon oxide, so that the battery has better rate performance and cycle performance.
In order to achieve the purpose, the invention adopts the following technical scheme:
a composite negative electrode material comprises a silicon-based material and graphite;
the ratio of the particle size D50 of the graphite to the particle size D50 of the silicon-based material is 1-6;
the ratio of the particle size D10 of the graphite to the particle size D10 of the silicon-based material is 2-4.
Preferably, the ratio of the particle size D50 of the graphite to the particle size D50 of the silicon-based material is 2-4.
Preferably, the ratio of the particle size D10 of the graphite to the particle size D10 of the silicon-based material is 2.2-3.6.
Preferably, the silicon-based material has a particle size concentration N of 0 to 2, wherein the particle size concentration N of the silicon-based material is (difference between the particle size D90 of the silicon-based material and the particle size D10 of the silicon-based material)/(the particle size D50 of the silicon-based material.
Preferably, the particle size concentration ratio N of the silicon-based material is 0.5-1.5.
Preferably, the particle size D50 of the graphite is 8-35 μm; the particle size D50 of the silicon-based material is 2-8 mu m.
Preferably, the particle size D10 of the graphite is 4-12 μm; the particle size D10 of the silicon-based material is 1-4 mu m.
Preferably, the specific surface area of the graphite is 0.8-2.5 m2(ii)/g; the specific surface area of the silicon-based material is 1-4 m2/g。
Preferably, the mass of the silicon-based material is 0.01-80% of that of the composite negative electrode material.
Preferably, the silicon-based material is SiOxCarbon-containing SiOxSiO containing lithiumxAnd SiO containing magnesiumxAt least one of (1), 0<x<2; wherein the lithium-containing SiOxThe mass ratio of the medium lithium is 0-15%; the SiO containing magnesiumxThe mass percentage of the medium magnesium is 0-15%.
Preferably, the graphite is one or more of artificial graphite, natural graphite, modified graphite, soft carbon and hard carbon.
Preferably, the composite negative electrode material further comprises a carbon coating agent, and the carbon coating agent is coated on the surface of the material consisting of the silicon-based material and the graphite.
Another object of the present invention is to provide a negative electrode sheet comprising the composite negative electrode material described above.
The invention also provides a lithium ion battery, which comprises a positive plate, a negative plate and a diaphragm which is arranged between the positive plate and the negative plate, wherein the negative plate is the negative plate.
Compared with the prior art, the invention has the beneficial effects that:
1) according to the composite cathode material provided by the invention, the silicon-based material and the graphite are subjected to adaptability limitation, and the ratios of D50 and D10 are respectively limited, so that the problem that the silicon-based material is separated from the graphite or the graphite cannot leave a buffer space for the expansion of the silicon-based material due to poor adaptability of the silicon-based material and graphite particles can be avoided during lithium intercalation and lithium deintercalation.
2) The content ratio of the particle sizes D50 and D10 is regulated, so that the problem of capacity attenuation caused by the fact that a large number of small-particle-size silicon-based materials are easy to separate from graphite can be solved, and the problem that sufficient expansion space cannot be reserved for the silicon-based materials due to the existence of a large number of small-particle-size graphite can be solved.
3) In addition, the concentration ratio N of the particle size of the silicon-based material is further regulated and controlled, so that the particle size can be more concentrated, and the influence caused by side reaction caused by contact of excessive fine powder and electrolyte is avoided, thereby improving the long-term cycle life and the rate capability of the battery.
Drawings
FIG. 1 is a schematic view showing a calculated ratio of particle sizes of a silicon-based material and graphite according to the present invention.
Detailed Description
As used herein, the particle diameter D10 of the graphite means that graphite particles smaller than this particle diameter account for 10% of the composite anode material particles; the particle diameter D50 of the graphite means that the graphite particles smaller than this particle diameter account for 50% of the composite anode material particles.
As used herein, the particle size D10 of the silicon-based material means that silicon-based material particles smaller than this particle size account for 10% of the composite anode material particles; the particle size D50 of the silicon-based material means that the silicon-based material particles smaller than this particle size account for 50% of the composite anode material particles; the particle diameter D90 of the silicon-based material means that the silicon-based material particles smaller than this particle diameter account for 90% of the composite anode material particles.
Among them, D10 and D50 of graphite and silicon-based materials and D90 of silicon-based materials can be measured by a method known in the art, for example, by a laser particle size analyzer.
The invention provides a composite cathode material in a first aspect, which comprises a silicon-based material and graphite; the ratio of the particle size D50 of the graphite to the particle size D50 of the silicon-based material is 1-6; the ratio of the particle size D10 of the graphite to the particle size D10 of the silicon-based material is 2-4. As shown in fig. 1.
Specifically, the ratio of the particle size D50 of the graphite to the particle size D50 of the silicon-based material can be 1-2, 2-3, 3-4, 4-5 and 5-6; more preferably, the ratio of the particle size D50 of the graphite to the particle size D50 of the silicon-based material is 2-3 and 3-4. The median particle diameters of the graphite and the silicon-based material are preferentially limited, so that the situation that the particle diameters of the graphite and the silicon-based material are too large and too small in quantity is avoided to a certain extent, and the adaptability between the graphite and the silicon-based material particles is improved.
Specifically, the ratio of the particle size D10 of the graphite to the particle size D10 of the silicon-based material can be 2-2.2, 2.2-2.5, 2.5-2.8, 2.8-3, 3-3.2, 3.2-3.6 and 3.6-4; further preferably, the ratio of the particle size D10 of the graphite to the particle size D10 of the silicon-based material is 2.2-2.5, 2.5-2.8, 2.8-3, 3-3.2 and 3.2-3.6. Silicon-based materials with small particle sizes are more susceptible to pulverization and pulverization during the expansion of the silicon-based materials, and materials with too small particle sizes are also susceptible to electrical contact loss, thereby causing capacity loss. The invention simultaneously regulates and controls the small grain diameter D10 on the basis of the regulation and control of D50, the grain diameter D10 of the graphite is set to be at least two times larger than that of the silicon-based material, and the small grain diameter contents of the graphite and the silicon-based material correspond to each other, so that the situation that a large amount of graphite is separated from contact due to the excessive content of the silicon-based material with smaller grain diameter can be avoided, and meanwhile, the grain diameter D10 of the graphite is set to be 4 times smaller than that of the silicon-based material, so that sufficient expansion space can be reserved for the volume expansion of the silicon-based material.
Further, the silicon-based material has a particle size concentration N of 0 to 2, wherein the particle size concentration N of the silicon-based material is (difference between the particle size D90 of the silicon-based material and the particle size D10 of the silicon-based material)/(the particle size D50 of the silicon-based material.
Specifically, the particle size concentration ratio N of the silicon-based material can be 0-0.2, 0.2-0.5, 0.5-0.8, 0.8-1, 1-1.2, 1.2-1.5, 1.5-1.8, or 1.8-2. More preferably, the particle size concentration ratio N of the silicon-based material is 0.5-0.8, 0.8-1, 1-1.2 and 1.2-1.5. More preferably, the silicon-based material has a particle size concentration ratio N of 0.98-1.2. Setting the particle size concentration ratio of the silicon-based material within the above range makes it possible to further concentrate the particle size and further reduce the influence of the fine powder on the battery, on the basis of the D10 definition.
Further, the particle size D50 of the graphite can be 8-12 μm, 12-15 μm, 15-18 μm, 18-20 μm, 20-25 μm, 25-28 μm, 28-30 μm, 30-32 μm, 32-35 μm; the particle size D50 of the silicon-based material can be 2-3 μm, 3-4 μm, 4-5 μm, 5-6 μm, 6-7 μm and 7-8 μm. More preferably, the particle size D50 of the graphite can be 12-15 μm, 15-18 μm, 18-20 μm and 20-25 μm; the silicon-based material has a particle size D50 of 3-4 μm, 4-5 μm, 5-6 μm, 6-7 μm. Compared with the conventional graphite and silicon-based material, although the particle size range set by the invention is similar to that of the conventional graphite and silicon-based material, the adaptability of the two particles is greatly improved by regulating the ratio of D50 to D10, and on one hand, the problem that the conductivity network and lithium ion migration are influenced due to poor contact between the silicon-based material and the graphite when the silicon-based material is small and the graphite particles are large is avoided; on the other hand, the problem that the graphite particles cannot play a role in limiting the expansion of the silicon-based material when the silicon-based material particles are large and the graphite particles are small is avoided, so that the silicon-based material is pulverized and loses efficacy due to the volume expansion effect, and the cycle life of the battery is greatly shortened.
Further, the particle size D10 of the graphite can be 4-5 μm, 5-6 μm, 6-7 μm, 7-8 μm, 8-9 μm, 9-10 μm, 10-11 μm, or 11-12 μm; the particle size D10 of the silicon-based material can be 1-1.5 μm, 1.5-2 μm, 2-2.5 μm, 2.5-3 μm, 3-3.5 μm, 3.5-4 μm. More preferably, the particle size D10 of the graphite can be 6-7 μm, 7-8 μm, 8-9 μm, 9-10 μm, 10-11 μm, or 11-12 μm; the silicon-based material has a particle size D10 of 2.5-3 μm, 3-3.5 μm, 3.5-4 μm. The content of the graphite and the silicon-based material D10 is limited by the cooperation of the graphite and the D50, so that the situation that due to the fact that the content of the D10 is too much, silicon-based material fine powder is separated from the graphite in the initial charging and discharging process, a large amount of silicon-based material fine powder and electrolyte are subjected to side reaction, the capacity is rapidly attenuated, and the rate performance and the cycle performance of the battery are affected is avoided.
The silicon-based material has a particle diameter D90 of 5 to 20 μm calculated from the above definition. Specifically, the particle size may be 5 to 8 μm, 8 to 12 μm, 12 to 15 μm, 15 to 18 μm, or 18 to 20 μm. The graphite D90 is not limited to a large amount, and the particle size concentration of the graphite is not limited to a large amount, so that the graphite D10 and D50 are within the above-mentioned ranges.
Further, the specific surface area of the graphite can be 0.8-1 m2/g、1～1.2m2/g、1.2～1.5m2/g、1.5～1.8m2/g、1.8～2m2/g、2～2.5m2(ii)/g; the specific surface area of the silicon-based material can be 1-1.5 m2/g、1.5～1.8m2/g、1.8～2m2/g、2～2.2m2/g、2.2～2.5m2/g、2.5～2.8m2/g、2.8～3m2/g、3～3.2m2/g、3.2～3.5m2/g、3.5～4m2(ii) in terms of/g. More preferably, the specific surface area of the graphite is 0.8 to 1m2/g、1～1.2m2/g、1.2～1.5m2/g、1.5～1.8m2(ii)/g; the specific surface area of the silicon-based material can be 1.8-2 m2/g、2～2.2m2/g、2.2～2.5m2/g、2.5～2.8m2/g、2.8～3m2/g、3～3.2m2(ii) in terms of/g. Setting the specific surface area of the graphite and the silica material within the above range, which is adapted to the D10 and D50 of the particles, may better allow the graphite to have a better contact surface with the silicon-based material to limit the volume expansion of the silicon-based material. Preferably, the specific surface area of the silicon-based material is set to be larger than that of the graphite, correspondingly, the particle size of the silicon-based material is smaller than that of the graphite, and the graphite can provide more expansion space for the volume expansion of the silicon-based material, so that the negative influence of the silicon-based material due to the volume effect is further reduced.
Further, the mass of the silicon-based material is 0.01-80% of that of the composite negative electrode material. More preferably, the mass of the silicon-based material is 2-5%, 5-10%, 10-15%, 15-20%, 20-25%, 25-30%, 30-35%, 35-40%, 40-50% of the mass of the composite negative electrode material.
Further, the silicon-based material is SiOxCarbon-containing SiOxSiO containing lithiumxAnd SiO containing magnesiumxAt least one of；0<x<2. The arrangement of additionally adding lithium in the silicon-based material can play a role of supplementing lithium in advance, further make up for lithium ions lost due to volume expansion of the silicon-based material in the first charge-discharge process, and improve the first cycle efficiency of the battery. Wherein the lithium-containing SiOxThe mass ratio of the medium lithium is 0-15%; the SiO containing magnesiumxThe mass percentage of the medium magnesium is 0-15%.
Further, the graphite is one or more of artificial graphite, natural graphite, modified graphite, soft carbon and hard carbon.
Further, the composite negative electrode material also comprises a carbon coating agent, and the carbon coating agent is coated on the surface of the material consisting of the silicon-based material and the graphite. The purpose of further inhibiting the silicon-based volume expansion can be achieved by further coating the mixed material consisting of the silicon-based material and the graphite. In addition, the composite negative electrode material of the present invention may be processed in other manners, which should be considered as falling within the scope of the present invention, and is not limited herein. Of course, the mixed material composed of the silicon-based material and graphite obtained by the present invention can also be directly used as a negative electrode active material.
The invention provides a negative electrode sheet, which comprises the composite negative electrode material. The negative plate comprises a negative current collector and a negative active substance layer coated on at least one surface of the negative current collector, wherein the negative active substance layer is formed by coating the composite negative material prepared into slurry. The silicon-based material and the graphite in the slurry can be prepared by mixing in a ball-milling stirring mode, a mechanical stirring mode and the like.
The third aspect of the invention provides a lithium ion battery, which comprises a positive plate, a negative plate and a diaphragm spaced between the positive plate and the negative plate, wherein the negative plate is the negative plate.
The positive plate comprises a positive current collector and a positive active material layer coated on at least one surface of the positive current collector. The positive active material layer may be of a chemical formula including, but not limited to, LiaNixCoyMzO2-bNb(wherein a is more than or equal to 0.95 and less than or equal to 1.2,x>0, y is more than or equal to 0, z is more than or equal to 0, and x + y + z is 1,0 is more than or equal to b and less than or equal to 1, M is selected from one or more of Mn and Al, N is selected from one or more of F, P and S), and the positive electrode active material can also be selected from one or more of LiCoO (lithium LiCoO), but not limited to2、LiNiO2、LiVO2、LiCrO2、LiMn2O4、LiCoMnO4、Li2NiMn3O8、LiNi0.5Mn1.5O4、LiCoPO4、LiMnPO4、LiFePO4、LiNiPO4、LiCoFSO4、CuS2、FeS2、MoS2、NiS、TiS2And the like. The positive electrode active material may be further modified, and the method of modifying the positive electrode active material is known to those skilled in the art, for example, the positive electrode active material may be modified by coating, doping, and the like, and the material used in the modification may be one or a combination of more of Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, W, and the like. The positive electrode current collector adopted by the positive electrode plate is generally a structure or a part for collecting current, and the positive electrode current collector can be various materials suitable for serving as a positive electrode current collector of a lithium ion battery in the field, for example, the positive electrode current collector can include but is not limited to metal foil and the like, and more specifically, can include but is not limited to aluminum foil and the like.
And the separator may be various materials suitable for a lithium ion battery separator in the art, for example, may be one or a combination of more of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, natural fiber, and the like, which include but are not limited thereto.
The lithium ion battery also comprises electrolyte, and the electrolyte comprises an organic solvent, electrolyte lithium salt and an additive. Wherein the electrolyte lithium salt may be LiPF used in a high-temperature electrolyte6And/or LiBOB; or LiBF used in low-temperature electrolyte4、LiBOB、LiPF6At leastOne kind of the material is selected; or LiBF used in anti-overcharge electrolyte4、LiBOB、LiPF6At least one of, LiTFSI; may also be LiClO4、LiAsF6、LiCF3SO3、LiN(CF3SO2)2At least one of (1). And the organic solvent may be a cyclic carbonate including PC, EC, FEC; or chain carbonates, including DEC, DMC, or EMC; and also carboxylic acid esters including MF, MA, EA, MP, etc. And additives include, but are not limited to, film forming additives, conductive additives, flame retardant additives, overcharge prevention additives, control of H in the electrolyte2At least one of additives of O and HF content, additives for improving low temperature performance, and multifunctional additives.
In order to make the technical solutions and advantages of the present invention clearer, the present invention and its advantages will be described in further detail below with reference to the following detailed description and the accompanying drawings, but the embodiments of the present invention are not limited thereto.
Example 1
A composite anode material comprising 0.5kg of silica and 4.5kg of graphite; the ratio of the particle size D50 of the graphite to the particle size D50 of the silicon-based material is 2.55; the ratio of the particle size D10 of the graphite to the particle size D10 of the silicon-based material is 3.125; the particle size concentration ratio N of the silicon-based material is 1. Wherein the particle size D50 of the silicon monoxide is 5.5um, D10 is 3.2um, and the silicon monoxide accounts for 10 percent of the composite cathode material by mass; the particle size of the graphite is 14um D50, 10um D10, and the graphite accounts for 90% of the composite negative electrode material by mass.
The preparation method of the composite negative electrode material comprises the following steps: mechanically stirring and mixing the silicon monoxide and the graphite for 2 hours; wherein the stirring revolution speed is 30r/min, and the rotation speed is 300r/min, so as to prepare the composite cathode material.
The utility model provides a negative pole piece, includes the negative pole mass flow body and coat in the negative pole active substance layer of the at least surface of negative pole mass flow body, the coating forms after the thick liquids is made by above-mentioned composite negative electrode material in the negative pole active substance layer.
The preparation method of the negative plate comprises the following steps: mixing the composite negative electrode material, the conductive carbon Super-P, the conductive carbon tube CNT, the binder carboxymethyl cellulose sodium CMC and the binder styrene butadiene rubber SBR according to the mass ratio of 95:1.5:1.4:0.1:2, adding deionized water, stirring in vacuum to obtain uniform slurry, uniformly coating the slurry on a copper foil, and drying to obtain the negative electrode sheet.
A lithium ion battery comprises a positive plate, a negative plate and a diaphragm which is arranged between the positive plate and the negative plate, wherein the negative plate is the negative plate.
The preparation method of the lithium ion battery comprises the following steps:
1) the preparation method of the positive plate comprises the following steps: mixing a positive electrode active material NCM811, conductive carbon Super-P and a binder polyvinylidene fluoride PVDF (polyvinylidene fluoride) according to a mass ratio of 97:2:1, adding a solvent N-methylpyrrolidone NMP, stirring in vacuum to obtain uniform slurry, uniformly coating the slurry on an aluminum foil, and drying to obtain the positive electrode plate.
2) Assembling according to the corresponding relation of the positive plate/the diaphragm/the negative plate, putting into a shell, drying, adding electrolyte, standing in vacuum, forming and grading to obtain the lithium ion battery.
Examples 2 to 19
Referring to the preparation method of example 1, examples 2 to 19 were carried out, and the arrangement of the composite anode material was different from that of example 1, as shown in table 1 below.
TABLE 1
The lithium ion batteries prepared in the above examples 1 to 19 were subjected to cycle performance detection, and the capacity retention rate after 500 cycles of 1C/1C normal temperature cycle was detected. The results are shown in Table 2.
TABLE 2
From the results, the content ratio of the particle sizes D50 and D10 of the graphite and the silicon monoxide is regulated and controlled simultaneously, so that the capacity retention rate of the battery is effectively improved.
However, as can be seen from the comparison among examples 1 to 6, examples 7 to 9, and examples 10 to 12, even if the D50 of graphite is set to 8 to 35 μm and the D50 of silica is set to 2 to 8 μm, if the small particles D10 of graphite and silica are not synchronously controlled and the graphite D50/silica D50, graphite D10/silica D10 are controlled within the scope of the present invention, the capacity retention ratio of the battery cannot be effectively improved, as in examples 2 to 3, examples 8 to 9, and the like. The main reason is that when the content ratio of the particle diameters D50 and D10 of graphite and silicon oxide is regulated and controlled simultaneously, the adaptability between graphite and silicon oxide particles can be better ensured, and the problem that too many small-particle silicon-based materials are separated from graphite or a large amount of small-particle graphite cannot leave buffer space for the expansion of the silicon-based materials is avoided.
Further, the present inventors verified through a large number of experiments that when the graphite D10 is more than 2.415 times that of the silica D10 in a non-charged state, the problem that the particle size of the silica is too small to be detached from the graphite can be prevented; meanwhile, when the graphite D10 is less than 3.6 times of the volume of the silicon oxide D10, the graphite can reserve enough buffer space for the volume expansion of the silicon oxide.
In addition, it can be found from the above test results that the difference in the concentration ratio N of the silicon monoxide also affects the performance of the battery. The results show that the capacity retention rate of the battery can be further improved by a certain range of concentration ratio of the silicon monoxide. This is mainly because in this concentration range, the particle size can be made more concentrated, thereby further reducing the influence of the fine powder particles. The inventor verifies through a large number of experiments that when the concentration ratio N is 0.98-1.2, the adaptability of the silicon monoxide and the graphite is better.
The results show that the composite negative electrode material provided by the invention solves the problem of poor adaptability of the existing silicon-based material and graphite, thereby effectively reducing the negative influence of the volume effect of the silicon monoxide, and enabling the battery to have better rate performance and cycle performance.
Variations and modifications to the above-described embodiments may also occur to those skilled in the art, which fall within the scope of the invention as disclosed and taught herein. Therefore, the present invention is not limited to the above-mentioned embodiments, and any obvious improvement, replacement or modification made by those skilled in the art based on the present invention is within the protection scope of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
Claims (14)
1. The composite negative electrode material is characterized by comprising a silicon-based material and graphite;
the ratio of the particle size D50 of the graphite to the particle size D50 of the silicon-based material is 1-6;
the ratio of the particle size D10 of the graphite to the particle size D10 of the silicon-based material is 2-4.
2. The composite anode material of claim 1, wherein a ratio of a particle size D50 of the graphite to a particle size D50 of the silicon-based material is 2-4.
3. The composite anode material of claim 1, wherein a ratio of a particle size D10 of the graphite to a particle size D10 of the silicon-based material is 2.2-3.6.
4. The composite negative electrode material according to any one of claims 1 to 3, wherein the silicon-based material has a particle size concentration ratio N of 0 to 2, wherein N is (the difference between the particle size D90 of the silicon-based material and the particle size D10 of the silicon-based material)/(the particle size D50 of the silicon-based material.
5. The composite anode material according to claim 4, wherein the silicon-based material has a particle size concentration ratio N of 0.5 to 1.5.
6. The composite anode material according to claim 1 or 2, wherein the particle size D50 of the graphite is 8 to 35 μm; the particle size D50 of the silicon-based material is 2-8 mu m.
7. The composite anode material according to claim 1 or 3, wherein the particle size D10 of the graphite is 4-12 μm; the particle size D10 of the silicon-based material is 1-4 mu m.
8. The composite anode material according to claim 1, wherein the specific surface area of the graphite is 0.8 to 2.5m2(ii)/g; the specific surface area of the silicon-based material is 1-4 m2/g。
9. The composite negative electrode material of claim 1, wherein the mass of the silicon-based material is 0.01-80% of the mass of the composite negative electrode material.
10. The composite anode material of claim 1, wherein the silicon-based material is SiOxCarbon-containing SiOxSiO containing lithiumxAnd SiO containing magnesiumxAt least one of (1), 0<x<2; wherein the lithium-containing SiOxThe mass ratio of the medium lithium is 0-15%; the SiO containing magnesiumxThe mass percentage of the medium magnesium is 0-15%.
11. The composite negative electrode material of claim 1, wherein the graphite is one or more of artificial graphite, natural graphite, modified graphite, soft carbon and hard carbon.
12. The composite anode material of claim 1, further comprising a carbon coating agent, wherein the carbon coating agent coats the surface of the material consisting of the silicon-based material and graphite.
13. A negative electrode sheet comprising the composite negative electrode material according to any one of claims 1 to 12.
14. A lithium ion battery comprising a positive plate, a negative plate and a separator spaced between the positive plate and the negative plate, wherein the negative plate is the negative plate of claim 13.
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