CN113013386A - Composite negative electrode material and preparation method thereof - Google Patents

Composite negative electrode material and preparation method thereof Download PDF

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CN113013386A
CN113013386A CN201911320566.1A CN201911320566A CN113013386A CN 113013386 A CN113013386 A CN 113013386A CN 201911320566 A CN201911320566 A CN 201911320566A CN 113013386 A CN113013386 A CN 113013386A
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silicon
negative electrode
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刘忆恩
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Shanxi Wote Haimer New Materials Technology Co ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M4/362—Composites
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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
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    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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Abstract

The invention discloses a composite negative electrode material and a preparation method thereof. The composite negative electrode material comprises a graphite negative electrode material and a silicon-carbon material, wherein the content of the silicon-carbon material is not higher than 10 wt% of the total amount of the composite negative electrode material; the silicon-carbon material comprises the following raw materials: silicon alloy powder, graphene, a silicon-containing inorganic adhesive and more than one organic carbon source; the graphene accounts for 3-5 wt% of the weight of the silicon alloy powder, the silicon-containing inorganic adhesive accounts for 1-3 wt% of the weight of the silicon alloy powder, and the organic carbon source accounts for 3-6 wt% of the weight of the silicon alloy powder. According to the invention, a brand-new composite cathode material is formed by doping a silicon-carbon material in a graphite cathode material, and the first efficiency of the composite cathode material is more than 91 percent and is similar to that of the graphite cathode material; the stable cycle specific capacity is improved by more than 20 percent compared with the graphite cathode material; the capacity retention rate of the graphite anode material is better than 80 percent of that of the graphite anode material after 3000 times of circulation. The composite negative electrode material has long service life and can be used as a negative electrode material of a power lithium ion battery.

Description

Composite negative electrode material and preparation method thereof
Technical Field
The invention relates to the field of lithium ion battery materials, in particular to a composite negative electrode material and a preparation method thereof.
Background
The lithium ion battery is a common battery type at present, and from the aspect of performance evaluation indexes of the lithium ion battery, specific capacity, first efficiency and cycling stability are important index parameters. The cathode material is one of the factors influencing the indexes, and common cathode materials comprise a graphite cathode and a silicon cathode; the graphite cathode has the characteristics of high initial efficiency and high cycling stability, can reduce the capacity attenuation of the battery and ensure the service life of the battery; the silicon negative electrode has better specific capacity, and the first efficiency and the cycling stability are poorer.
How to complement the advantages of the two to form the composite electrode material is the key to improve the performance of the battery. For the composite electrode material, at present, two common composite methods are included, specifically as follows:
direct composite preparation, for example, a method for preparing a graphene-coated silicon-carbon composite negative electrode material disclosed in chinese patent document CN108807868A, the method has strict requirements on the amounts of graphite and silicon, the addition ratio of graphite and silicon must be controlled to be greater than 1:1, the graphite and silicon are added into an ethanol solution to be directly mixed, and the graphite/silicon composite electrode material is obtained through post-treatment and drying.
The preparation method comprises two processing steps of carbon coating of Si particles and mixing, for example, Chinese patent document CN106784743A discloses a low-expansion-rate porous silicon/graphite composite negative electrode material, which comprises the steps of firstly carrying out dealloying treatment on porous silicon spheres, then carrying out carbon coating on the silicon spheres by using a carbon source, and then uniformly mixing the carbon-coated porous silicon spheres and graphite in proportion. According to the technology, the carbon source forms carbon coating on the silicon surface through coating treatment, so that the first efficiency and the cycling stability of the battery are improved to a certain extent. However, the first efficiency and the cycling stability are still not significantly superior to those of the graphite cathode material, and particularly, the first efficiency is significantly lower than that of the graphite cathode material, and the cycling stability is significantly attenuated after 100 cycles.
When the composite electrode material is prepared, because the performance requirement of the battery is higher and the electrode sensitivity is stronger, the auxiliary components except the necessary raw materials are not added as much as possible in the preparation process so as not to influence the electrode material and further influence the battery performance. In the coating mixing technique, when Si particles are carbon-coated, the carbon source conventionally used is white sugar, starch, resin, graphene, or the like. White sugar, starch, resin and the like have good dispersion and adhesion performance, so that the surfaces of the Si particles can be easily coated with the white sugar, the starch, the resin and the like; and graphite alkene is neotype carbon material, when using graphite alkene to carry out the carbon cladding to the Si granule, the not good problem of mixed effect often appears, consequently, in order to make graphite alkene homodisperse under the condition of not adding the auxiliary agent as far as possible, adopt the technique that the sanding stirring was mixed among the prior art usually, because the sanding stirring requirement must be the wet process environment, so need add to account for more than 50% water, the requirement of sanding has been satisfied on the one hand in the addition of water, the most important is still improved the dispersibility of graphite alkene through the addition of water, the not good problem of ubiquitous graphite alkene and Si granule mixed effect among the prior art has been solved.
However, even though the formula and preparation process of the composite negative electrode material are strictly considered in the prior art, the composite negative electrode material prepared by the carbon coating technology in the industry still has the problem that the first efficiency and the cycle stability are poorer than those of the graphite electrode.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the problem that the first efficiency and the cycling stability cannot be effectively improved while the specific capacity is improved by the graphite and silicon composite negative electrode material in the prior art is solved; a composite anode material solving the above problems and a preparation method of the composite anode material are provided.
A composite negative electrode material comprises a graphite negative electrode material and a silicon-carbon material, wherein the content of the silicon-carbon material is not higher than 10 wt% of the total amount of the composite negative electrode material;
the silicon-carbon material comprises the following raw materials: silicon-containing particles, graphene, a silicon-containing inorganic binder and an organic carbon source; the graphene accounts for 3-5 wt% of the weight of the silicon alloy powder, the silicon-containing inorganic adhesive accounts for 1-3 wt% of the weight of the silicon alloy powder, and the organic carbon source accounts for 3-6 wt% of the weight of the silicon alloy powder.
The silicon-containing particles are silicon alloy powder, the silicon alloy powder is in a porous structure, and the particle size of the silicon alloy powder is less than 75 micrometers. Specifically, the silicon alloy powder in the invention is alloy powder with a porous structure on the surface, which is obtained by using silicon as a raw material through process control. The preparation process of the silicon alloy powder preferably adopts a water atomization process. The silicon alloy powder can be made by mixing silicon and other metals in different proportions, and can be any silicon alloy powder which can be applied to electrodes, such as: silicon-aluminum alloy powder, silicon-aluminum-copper alloy powder, silicon-tin-boron alloy powder, silicon-zinc-tin alloy powder and the like.
The organic carbon source is selected from sugars and PVDF. Wherein, the sugar accounts for 1-3 wt% of the weight of the silicon alloy powder, and the PVDF accounts for 1-4 wt% of the weight of the silicon alloy powder. The sugar can be monosaccharide or polysaccharide, such as glucose and sucrose; or complex saccharide such as white sugar.
The silicon-carbon material also comprises NMP, and the NMP is 0.1-1 wt% of the silicon alloy powder.
The inorganic adhesive containing silicon is pressure swing adsorption silica gel.
The content of the silicon-carbon material is 5-10 wt% of the total amount of the negative electrode material.
The raw materials of the graphite negative electrode material comprise graphite, a carbon black conductive agent and a bonding agent; the carbon black conductive agent accounts for 5-10 wt% of the composite negative electrode material, and the adhesive accounts for 5-10 wt% of the composite negative electrode material.
The carbon black conductive agent is conductive carbon black SP.
The preparation process of the composite anode material comprises the following steps:
preparing a silicon-carbon material: adding a solvent into the raw materials of the silicon-carbon material according to the proportion to prepare slurry, and performing heat treatment at 400-750 ℃ after sanding; and (3) uniformly stirring the silicon-carbon material prepared in the step and the graphite cathode material.
In the above process, the solvent is water. The sanding rotating speed is 1500-5000 r/min, and the grinding time is 2-4 h. The heat treatment time is more than 2 h.
Specifically, the heat treatment process comprises the following steps: in a vacuum state, heating to 400-450 ℃, preserving heat for 2-4 h, then heating to 650-750 ℃ at a heating rate of 25-35 ℃/min, preserving heat for 1-3 h, and then cooling along with the furnace. Or the heat treatment process comprises the following steps: in a vacuum state, heating to 470-530 ℃ at a heating rate of 25-35 ℃/min, preserving heat for 2-4 h, then heating to 570-630 ℃ at a heating rate of 25-35 ℃, preserving heat for 5-8 h, and then cooling along with a furnace.
The particle size D50 of the prepared silicon-carbon material is less than 5 mu m, the particle size D90 of the prepared silicon-carbon material is less than 10 mu m, and the tap density of the prepared silicon-carbon material is 1-1.35 g/cm3The specific surface area is 1.5-3 cm2/g。
The specific process for preparing the negative pole piece by using the silicon-carbon material and the graphite negative pole material comprises the following steps:
and (2) carrying out sand grinding on silicon alloy powder, graphene, pressure swing adsorption silica gel, glucose, NMP, PVDF and water to form slurry, wherein the rotation speed of the sand grinding is 1500-5000 r/min, and the grinding time is 2-4 h. And (3) carrying out heat treatment after sanding, wherein the heat treatment temperature is 400-750 ℃, and the treatment time is more than 2 h. And stirring the silicon-carbon material, the graphite, the carbon black conductive agent and the adhesive in a planetary stirrer for 4-8 hours to form the composite negative electrode material. And preparing the composite negative electrode material into a structure with a required shape to form the composite coated silicon-carbon negative electrode piece.
The technical scheme of the invention has the following advantages:
1. the invention adopts the silicon-carbon material with optimized composition and proportion in the composite cathode material, introduces an auxiliary agent 'silicon-containing inorganic binder' which is not an essential raw material into the silicon-carbon material for the first time as a coating auxiliary material, and researches show that the addition of the auxiliary material effectively coats the organic carbon source and the graphene together on the surface of the silicon alloy powder to form carbon coating layers with various molecular structures, so that silicon atoms are restricted in the coating films with different molecular structures, the strength and toughness of the graphene material are combined, and the proportion of the graphene, the inorganic binder and the organic carbon source is optimized, thereby avoiding the cracking of the coating layer caused in the expansion process of silicon particles, enabling the silicon atoms after lithium removal to be more easily recovered to the structure before lithium insertion, basically eliminating the problem of pulverization of silicon phases in the lithium insertion and lithium removal circulation processes, and leading the composite cathode material to have very good cycle life, thereby effectively improving the cycling stability of the battery.
2. The invention further optimizes the composition of silicon-containing particles in the silicon-carbon material, preferably silicon alloy powder with a porous structure, and particularly silicon alloy powder with a honeycomb structure. The honeycomb structure on the silicon alloy powder is the basis of the nucleation growth of the silicon-rich phase, the nano thin layer of the silicon-rich phase grows on the honeycomb alloy phase, a large number of shrinkage holes, namely shrinkage porosity, exist in the center of the honeycomb structure, the shrinkage porosity leaves a space for the shrinkage and expansion of the negative electrode material, the alloy phase of the honeycomb structure is combined with carbon coating layers of various molecular structures, the moving space of silicon atoms is limited together, the silicon atoms are easier to recover to the original structure after the lithium removal, the pulverization phenomenon of the silicon phase is greatly reduced, and the composite negative electrode material has a very good cycle life. The verification is carried out to obtain the result; after the silicon-carbon material with optimized proportion and composition is added into the graphite cathode material to form the composite cathode material, under the condition that the addition amount of the silicon-carbon material is less than 10 wt%, the first efficiency is similar to that of the graphite cathode material, the cycling stability is obviously superior to that of the graphite cathode material, and meanwhile, the stable cycling ratio capacity is gradually improved along with the increase of the addition amount of the silicon-carbon material. In addition, the silicon alloy powder of the invention can achieve obvious specific capacity, first efficiency and cycling stability without removing alloy elements, and the optimization of the silicon-carbon material not only reduces the workload, but also avoids the pollution of acid corrosion process to the environment caused by removing the alloy elements, and also reduces the material cost.
3. The organic carbon source adopts more than one organic carbon source, so that carbon coating layers with more molecular structures can be formed, and the coating effect is improved. The organic carbon source adopts a mode of mixing sugar and PVDF together, wherein PVDF is a carbon source used for coating, and can make the surface of the silicon alloy powder etched rougher when the PVDF is heated and decomposed, so that the adhesive force between the silicon alloy powder and the coating layer can be increased, and the cycle performance of the composite negative electrode material is further improved. According to the invention, NMP is further added, and experimental research shows that the addition of NMP can greatly reduce the dosage of graphene, so that the graphene can still obtain a good coating effect under an extremely low condition (the maximum is 5 wt% of the total amount of silicon alloy powder). And certain bonding force exists between the silicon alloy particles after the sugar, the NMP and the PVDF are decomposed at high temperature, and the graphene is assisted to coat the silicon alloy particles.
4. The addition amount of the silicon-carbon material is further optimized, when the addition amount of the silicon-carbon material is too small, the specific capacity is low, and the expectation of people cannot be met, but when the addition amount of the silicon-carbon material is too large, the cycling stability can be reduced, and in order to obtain higher specific capacity and cycling stability, the addition amount of the silicon-carbon material is selected to be 5-10 wt%, and under the addition amount, not only can the first efficiency be kept to be close to that of the graphite negative electrode material, but also the specific capacity of the graphite negative electrode material can be remarkably improved, and the cycling stability of the graphite negative electrode material can be remarkably improved. The verification is carried out to obtain the result; the stable cycling specific capacity of the invention is improved by more than 10 percent compared with that of the graphite cathode material, and the capacity retention rate is better than that of the graphite cathode material when the cycle is 3000 times; namely, compared with the graphite negative electrode material, the composite negative electrode material provided by the invention has the advantages that the first efficiency is effectively maintained and the cycling stability is obviously improved under the condition of improving the specific capacity. Therefore, the composite negative electrode material has long service life and can be used as a negative electrode material of a power lithium ion battery.
5. The invention provides a preparation method of a composite cathode material, which is very simple, and particularly, the preparation process of the silicon-carbon material is very simple and convenient to operate. According to the invention, by optimizing the composition of the silicon-carbon material, various organic carbon sources and graphene are adhered to the surface of the silicon alloy powder through the silicon-containing inorganic adhesive, and after the silicon-carbon material is uniformly mixed, the silicon-carbon material with excellent coating effect can be prepared by combining a heat treatment process, so that the problem that the graphene and the silicon alloy powder are not easy to combine during coating is solved, and the processing work of removing an auxiliary agent is not required after coating, so that the coating operation is simpler.
Drawings
In order to show the structure of the present invention more clearly, the present invention also provides the following drawings.
Fig. 1 is a microscopic SEM image of the silicon carbon alloy prepared in example 1.
Fig. 2 is a graph of the cycling ratio capacity and efficiency of the composite anode material prepared in example 1.
Fig. 3 is a graph of the cycling ratio capacity and efficiency of the composite anode material prepared in example 2.
Fig. 4 is a graph of the cycling ratio capacity and efficiency of the composite anode material prepared in example 3.
Fig. 5 is a graph of the cycling ratio capacity and efficiency of the composite anode material prepared in example 4.
Fig. 6 is a graph of the cycling ratio capacity and efficiency of the composite anode material prepared in example 5.
Fig. 7 is a plot of the cycling ratio capacity and efficiency of the composite anode material prepared in example 6.
Fig. 8 is a plot of the cycling ratio capacity and efficiency of the composite anode material prepared in example 7.
Fig. 9 is a plot of the cycling ratio capacity and efficiency of the composite anode material prepared in example 8.
Fig. 10 is a plot of the cycling ratio capacity and efficiency of the composite anode material prepared in example 9.
Fig. 11 is a graph of the cycling specific capacity and efficiency of the composite anode material prepared in comparative example 1.
Fig. 12 is a graph of the cycling specific capacity and efficiency of the composite anode material prepared in comparative example 2.
Fig. 13 is a graph of the cycling ratio capacity and efficiency of the silicon carbon anode material prepared in comparative example 3.
Fig. 14 is a plot of the cycling ratio capacity and efficiency of the pure graphite anode material.
Detailed Description
The following examples are provided to further understand the present invention, not to limit the scope of the present invention, but to provide the best mode, not to limit the content and the protection scope of the present invention, and any product similar or similar to the present invention, which is obtained by combining the present invention with other prior art features, falls within the protection scope of the present invention.
The examples do not show the specific experimental steps or conditions, and can be performed according to the conventional experimental steps described in the literature in the field. The reagents and other instruments used are not indicated by manufacturers, and are all conventional reagent products which can be obtained commercially.
Example 1
The composite negative electrode material comprises a graphite negative electrode material and a silicon-carbon material, wherein the content of the silicon-carbon material is 5 wt% of the total amount of the composite negative electrode material. Wherein the silicon carbon material comprises: silicon alloy powder, graphene, pressure swing adsorption silica gel, PVDF, glucose and NMP. Graphene accounts for 4 wt% of the weight of the silicon alloy powder, pressure swing adsorption silica gel accounts for 2 wt% of the weight of the silicon alloy powder, PVDF accounts for 4 wt% of the weight of the silicon alloy powder, glucose accounts for 1 wt% of the weight of the silicon alloy powder, and NMP accounts for 0.5 wt% of the weight of the silicon alloy powder. The silicon alloy powder in the embodiment is 42 wt% Si-8 wt% Al-50 wt% Cu alloy which is prepared by a water mist method and has the grain diameter of less than 75 mu m. The graphite negative electrode material comprises graphite, conductive carbon black and a binder, wherein the binder is SBR and CMC.
The preparation method of the composite negative electrode material comprises the following steps:
firstly, preparing a silicon-carbon material, which specifically comprises the following steps: firstly, mixing and stirring raw materials of a silicon-carbon material and water according to the proportion to form slurry; secondly, grinding the slurry in a sand mill at the rotation speed of 5000r/min for 2 h; thirdly, placing the ground slurry into a vacuum heat treatment furnace for heat treatment, wherein the heat treatment process comprises the following steps: heating to 400 ℃ at a heating rate of 30 ℃/min, preserving heat for 3h, then heating to 750 ℃ at a heating rate of 30 ℃, preserving heat for 1h, and cooling along with the furnace. The prepared silicon carbon material is shown in figure 1, and the diameter of the silicon alloy particle is about 5 mu m; a carbon coating layer with the thickness of about 100nm exists on the surface of the silicon alloy particles; the alloy phase is positioned in the middle area of the silicon-rich phase, and the color is darker; the thickness of the silicon-rich phase with lighter color is about 100 nm; there is a large amount of shrinkage porosity inside the silicon alloy particles.
Secondly, adding the prepared silicon-carbon material into the graphite cathode material, and stirring for 4-8 hours in a planetary stirrer to form a composite cathode material, wherein the compounding ratio is as follows: 75% of graphite, 5% of silicon carbon material, 10% of conductive carbon black, 5% of SBR and 5% of CMC. The composite silicon-carbon-coated negative plate is prepared by adopting the existing graphite negative electrode preparation process, and then is prepared into a button cell which is tested by using a blue test system. As shown in fig. 2, only one line is shown in fig. 2 because the charge/discharge specific capacities substantially overlap in fig. 2. When the composite negative electrode material is charged and discharged at 0.2C, the first-cycle lithium insertion capacity can reach more than 417.0mAh/g, the stable cycle specific capacity can reach 375.0mAh/g, and the capacity is improved by more than 12.0% compared with that of a graphite negative electrode material. Moreover, the first efficiency of the composite negative electrode material is more than 91.50%; the capacity retention rate can reach more than 99.0% when the battery is charged and discharged at 0.2C after 1000 cycles, and can reach more than 95.0% when the battery is charged and discharged at 0.2C after 3000 cycles.
Example 2
The composite negative electrode material comprises a graphite negative electrode material and a silicon-carbon material, wherein the content of the silicon-carbon material is 6 wt% of the total amount of the composite negative electrode material. Wherein the silicon carbon material comprises: silicon alloy powder, graphene, pressure swing adsorption silica gel, PVDF, glucose and NMP. 3 wt% of graphene, 1 wt% of pressure swing adsorption silica gel, 4 wt% of PVDF, 1 wt% of glucose and 0.6 wt% of NMP. The silicon alloy powder in the embodiment is 45 wt% Si-6 wt% Al-49 wt% Cu alloy which is prepared by a water mist method and has the grain diameter of less than 75 mu m. The graphite negative electrode material comprises graphite, conductive carbon black and a binder, wherein the binder is SBR and CMC.
The preparation method of the composite negative electrode material comprises the following steps:
firstly, preparing a silicon-carbon material, which specifically comprises the following steps: firstly, mixing and stirring raw materials of a silicon-carbon material and water to form slurry; secondly, grinding the slurry in a sand mill at the rotation speed of 5000r/min for 2 h; thirdly, placing the ground slurry into a vacuum heat treatment furnace for heat treatment, wherein the heat treatment process comprises the following steps: heating to 520 ℃ at a heating rate of 25 ℃/min, preserving heat for 2h, then heating to 580 ℃ at a heating rate of 25 ℃, preserving heat for 7h, and cooling along with the furnace.
Secondly, adding the prepared silicon-carbon material into the graphite cathode material, and stirring for 4-8 hours in a planetary stirrer to form a composite cathode material, wherein the compounding ratio is as follows: 74% of graphite, 6% of silicon carbon material, 10% of conductive carbon black, 5% of SBR and 5% of CMC. The composite silicon-carbon-coated negative plate is prepared by adopting the existing graphite negative electrode preparation process, and then is prepared into a button cell which is tested by using a blue test system. The test result is shown in fig. 3, and the first efficiency of the composite anode material is 91.52%; when the lithium battery is charged and discharged at 0.2C, the first-week lithium intercalation capacity can reach more than 464.5mAh/g, the stable cycle specific capacity can reach 425.0mAh/g, and the lithium intercalation capacity is improved by more than 22.0 percent compared with a graphite negative electrode material; the capacity retention rate can reach 100.0% when the lithium ion battery is charged and discharged at 0.2C and is cycled for 200 times.
Example 3
The composite negative electrode material comprises a graphite negative electrode material and a silicon-carbon material, wherein the content of the silicon-carbon material is 7 wt% of the total amount of the composite negative electrode material. Wherein the silicon carbon material comprises: silicon alloy powder, graphene, pressure swing adsorption silica gel, PVDF, glucose and NMP. 5 wt% of graphene, 3 wt% of pressure swing adsorption silica gel, 3 wt% of PVDF, 1 wt% of glucose and 0.6 wt% of NMP. The silicon alloy powder in the embodiment is 42 wt% Si-8 wt% Al-50 wt% Cu alloy which is prepared by a water mist method and has the grain diameter of less than 75 mu m. The graphite negative electrode material comprises graphite, conductive carbon black and a binder, wherein the binder is SBR and CMC.
The preparation method of the composite negative electrode material comprises the following steps:
firstly, preparing a silicon-carbon material, which specifically comprises the following steps: firstly, mixing and stirring raw materials of a silicon-carbon material and water to form slurry; secondly, grinding the slurry in a sand mill at the rotation speed of 5000r/min for 2 h; thirdly, placing the ground slurry into a vacuum heat treatment furnace for heat treatment, wherein the heat treatment process comprises the following steps: heating to 480 ℃ at a heating rate of 35 ℃/min, preserving heat for 4h, then heating to 620 ℃ at a heating rate of 25 ℃, preserving heat for 6h, and then cooling along with the furnace.
Secondly, adding the prepared silicon-carbon material into the graphite cathode material, and stirring for 4-8 hours in a planetary stirrer to form a composite cathode material, wherein the compounding ratio is as follows: 73% of graphite, 7% of silicon carbon material, 10% of conductive carbon black, 5% of SBR and 5% of CMC. The composite silicon-carbon-coated negative plate is prepared by adopting the existing graphite negative electrode preparation process, and then is prepared into a button cell which is tested by using a blue test system. The test result is shown in fig. 4, the first efficiency of the composite cathode material is more than 90.00%; when the lithium battery is charged and discharged at 0.2C, the first-cycle lithium insertion capacity is 484.0mAh/g, the stable cycle specific capacity can reach 440.0mAh/g, and the capacity is improved by more than 25.0% compared with that of a graphite negative electrode material; when the lithium ion battery is charged and discharged at 0.2C, the capacity retention rate can reach 100.0% after 100 cycles.
Example 4
The composite negative electrode material comprises a graphite negative electrode material and a silicon-carbon material, wherein the content of the silicon-carbon material is 8 wt% of the total amount of the composite negative electrode material. Wherein the silicon carbon material comprises: silicon alloy powder, graphene, pressure swing adsorption silica gel, PVDF, white sugar and NMP. Graphene accounts for 4 wt% of the weight of the silicon alloy powder, pressure swing adsorption silica gel accounts for 2 wt% of the weight of the silicon alloy powder, PVDF accounts for 1 wt% of the weight of the silicon alloy powder, white sugar accounts for 2 wt% of the weight of the silicon alloy powder, and NMP accounts for 0.5 wt% of the weight of the silicon alloy powder. The silicon alloy powder in the embodiment is 42 wt% Si-8 wt% Al-50 wt% Cu alloy which is prepared by a water mist method and has the grain diameter of less than 75 mu m. The graphite negative electrode material comprises graphite, conductive carbon black and a binder, wherein the binder is SBR and CMC.
The preparation method of the composite negative electrode material comprises the following steps:
firstly, preparing a silicon-carbon material, which specifically comprises the following steps: firstly, mixing and stirring raw materials of a silicon-carbon material and water to form slurry; secondly, grinding the slurry in a sand mill at the rotation speed of 5000r/min for 2 h; thirdly, placing the ground slurry into a vacuum heat treatment furnace for heat treatment, wherein the heat treatment process comprises the following steps: heating to 500 ℃ at a heating rate of 30 ℃/min, preserving heat for 3h, then heating to 700 ℃ at a heating rate of 30 ℃, preserving heat for 7h, and then cooling along with the furnace.
Secondly, adding the prepared silicon-carbon material into the graphite cathode material, and stirring for 4-8 hours in a planetary stirrer to form a composite cathode material, wherein the compounding ratio is as follows: 72% of graphite, 8% of silicon carbon material, 10% of conductive carbon black, 5% of SBR and 5% of CMC. The composite silicon-carbon-coated negative plate is prepared by adopting the existing graphite negative electrode preparation process, and then is prepared into a button cell which is tested by using a blue test system. The test result is shown in fig. 5, the first efficiency of the composite cathode material is more than 90.00%; when the lithium battery is charged and discharged at 0.2C, the first-week lithium intercalation capacity is close to more than 500.0mAh/g, the stable cycle specific capacity can reach 450.0mAh/g, and is improved by more than 25.0 percent compared with a graphite negative electrode material; when the lithium ion battery is charged and discharged at 0.2C, the capacity retention rate can reach 100.0% after 100 cycles.
Example 5
The composite negative electrode material comprises a graphite negative electrode material and a silicon-carbon material, wherein the content of the silicon-carbon material is 9 wt% of the total amount of the composite negative electrode material. Wherein the silicon carbon material comprises: silicon alloy powder, graphene, pressure swing adsorption silica gel, PVDF, white sugar and NMP. 3 wt% of graphene, 2 wt% of pressure swing adsorption silica gel, 1 wt% of PVDF, 3 wt% of white sugar and 0.5 wt% of NMP. The silicon alloy powder in the embodiment is 42 wt% Si-8 wt% Al-50 wt% Cu alloy which is prepared by a water mist method and has the grain diameter of less than 75 mu m. The graphite negative electrode material comprises graphite, conductive carbon black and a binder, wherein the binder is SBR and CMC.
The preparation method of the composite negative electrode material comprises the following steps:
firstly, preparing a silicon-carbon material, which specifically comprises the following steps: firstly, mixing and stirring raw materials of a silicon-carbon material and water to form slurry; secondly, grinding the slurry in a sand mill at the rotation speed of 5000r/min for 2 h; thirdly, placing the ground slurry into a vacuum heat treatment furnace for heat treatment, wherein the heat treatment process comprises the following steps: heating to 480 ℃ at a heating rate of 30 ℃/min, preserving heat for 4h, then heating to 580 ℃ at a heating rate of 25-35 ℃, preserving heat for 7h, and cooling along with the furnace.
Secondly, adding the prepared silicon-carbon material into the graphite cathode material, and stirring for 4-8 hours in a planetary stirrer to form a composite cathode material, wherein the compounding ratio is as follows: 71% of graphite, 9% of silicon carbon material, 10% of conductive carbon black, 5% of SBR and 5% of CMC. The composite silicon-carbon-coated negative plate is prepared by adopting the existing graphite negative electrode preparation process, and then is prepared into a button cell which is tested by using a blue test system. The test result is shown in fig. 6, and the first efficiency of the composite negative electrode material is close to 90.00%; when the lithium battery is charged and discharged at 0.2C, the first week lithium embedding capacity can reach more than 500.0mAh/g, the stable cycle specific capacity can reach 450.0mAh/g, and the lithium battery is improved by more than 25.0% compared with a graphite negative electrode material; the capacity retention rate can reach more than 99.0 percent when the battery is charged and discharged at 0.2C and is cycled for 100 times.
Example 6
The composite negative electrode material comprises a graphite negative electrode material and a silicon-carbon material, wherein the content of the silicon-carbon material is 10 wt% of the total amount of the composite negative electrode material. Wherein the silicon carbon material comprises: silicon alloy powder, graphene, pressure swing adsorption silica gel, PVDF, white sugar and NMP. 3 wt% of graphene, 2 wt% of pressure swing adsorption silica gel, 2 wt% of PVDF, 2 wt% of white sugar and 0.5 wt% of NMP. The silicon alloy powder in the embodiment is 42 wt% Si-8 wt% Al-50 wt% Cu alloy which is prepared by a water mist method and has the grain diameter of less than 75 mu m. The graphite negative electrode material comprises graphite, conductive carbon black and a binder, wherein the binder is SBR and CMC.
The preparation method of the composite negative electrode material comprises the following steps:
firstly, preparing a silicon-carbon material, which specifically comprises the following steps: firstly, mixing and stirring raw materials of a silicon-carbon material and water to form slurry; secondly, grinding the slurry in a sand mill at the rotation speed of 5000r/min for 2 h; thirdly, placing the ground slurry into a vacuum heat treatment furnace for heat treatment, wherein the heat treatment process comprises the following steps: heating to 500 ℃ at a heating rate of 30 ℃/min, preserving heat for 2 hours, then heating to 620 ℃ at a heating rate of 25-35 ℃, preserving heat for 5 hours, and then cooling along with the furnace.
Secondly, adding the prepared silicon-carbon material into the graphite cathode material, and stirring for 4-8 hours in a planetary stirrer to form a composite cathode material, wherein the compounding ratio is as follows: 70% of graphite, 10% of silicon carbon material, 10% of conductive carbon black, 5% of SBR and 5% of CMC. The composite silicon-carbon-coated negative plate is prepared by adopting the existing graphite negative electrode preparation process, and then is prepared into a button cell which is tested by using a blue test system. The test result is shown in fig. 7, the first efficiency of the composite negative electrode material is more than 89.00%; when the lithium battery is charged and discharged at 0.2C, the first week lithium embedding capacity can reach more than 520.0mAh/g, the stable cycle specific capacity can reach 460.0mAh/g, and the capacity is improved by more than 25.0 percent compared with a graphite negative electrode material; when the lithium ion battery is charged and discharged at 0.2C, the capacity retention rate can reach over 90.0 percent after 3000 times of circulation.
Example 7
The difference between this embodiment and embodiment 6 is that the composition ratio of the graphite anode material in this embodiment is different, and in this embodiment, the blending ratio is: 75% of graphite, 10% of silicon carbon material, 5% of conductive carbon black, SBR 5% and CMC 5%
Through tests, the first efficiency of the composite anode material is about 87.00%; when the lithium battery is charged and discharged at 0.2C, the first-cycle lithium intercalation capacity is only 410.0mAh/g, the stable cycle specific capacity is only 380.0mAh/g, and the lithium intercalation capacity is improved by more than 10.0 percent compared with a graphite negative electrode material; during charging and discharging at 0.2C, the conductive carbon black is less, the early-stage circulation efficiency is improved slowly, the stable state can be entered after 20 times of circulation, and compared with the 20 th time, the capacity circulation retention rate can reach 99.8%, as shown in figure 8.
Example 8
The difference between this embodiment and embodiment 6 is that the composition ratio of the silicon-carbon material in this embodiment is different, and in this embodiment, the composition of the silicon-carbon material is: silicon alloy powder, graphene accounting for 3 wt% of the weight of the silicon alloy powder, pressure swing adsorption silica gel accounting for 2 wt% of the weight of the silicon alloy powder, and PVDF accounting for 4.5 wt% of the weight of the silicon alloy powder.
Through tests, the first efficiency of the composite negative electrode material is more than 90.00%; during charging and discharging at 0.2C, the first week lithium intercalation capacity is only 380.0mAh/g, the stable cycle specific capacity can reach more than 410.0mAh/g, and is improved by more than 20.0 percent compared with the graphite cathode material; in the 0.2C charging and discharging process, the PVDF is too much, NMP is not used, the electrolyte needs a long time to wet the carbon-coated layer, the early-stage circulation capacity is not ideal, the carbon-coated layer can enter a stable state after being circulated for 30 times, and the retention rate during stable circulation can reach more than 100.0%, as shown in fig. 9.
Example 9
The difference between this embodiment and embodiment 6 is that the composition ratio of the graphite anode material in this embodiment is different, and the blending ratio in this embodiment is: 75% of graphite, 10% of silicon carbon material, 10% of conductive carbon black, 2% of SBR and 3% of CMC.
Through tests, the first efficiency of the composite negative electrode material is more than 91.00%; when the lithium battery is charged and discharged at 0.2C, the first week lithium embedding capacity can reach over 502.0mAh/g, the stable cycle specific capacity can reach over 450.0mAh/g, and is improved by over 38.0 percent compared with a graphite negative electrode material; however, the number of stable cycles was only about 60 times at 0.2C charge and discharge. SBR is used in a small amount, and the adhesion between the active material and the copper current collector is insufficient, so that a water-jump type decay occurs during the circulation process, as shown in fig. 10.
Comparative example 1
The composite negative electrode material comprises a graphite negative electrode material and a silicon-carbon material, wherein the content of the silicon-carbon material is 9 wt% of the total amount of the composite negative electrode material. Wherein the silicon carbon material comprises: silicon alloy powder, graphene, PVDF, white sugar and NMP. 3 wt% of graphene, 1 wt% of PVDF, 3 wt% of white sugar and 0.5 wt% of NMP. The silicon alloy powder in the embodiment is 42 wt% Si-8 wt% Al-50 wt% Cu alloy which is prepared by a water mist method and has the grain diameter of less than 75 mu m. The graphite negative electrode material comprises graphite, conductive carbon black and a binder, wherein the binder is SBR and CMC.
The preparation method of the composite negative electrode material comprises the following steps:
firstly, preparing a silicon-carbon material, which specifically comprises the following steps: firstly, mixing and stirring raw materials of a silicon-carbon material and water to form slurry; secondly, grinding the slurry in a sand mill at the rotation speed of 5000r/min for 2 h; thirdly, placing the ground slurry into a vacuum heat treatment furnace for heat treatment, wherein the heat treatment process comprises the following steps: heating to 480 ℃ at a heating rate of 30 ℃/min, preserving heat for 4h, then heating to 580 ℃ at a heating rate of 25-35 ℃, preserving heat for 7h, and cooling along with the furnace.
Secondly, adding the prepared silicon-carbon material into the graphite cathode material, and stirring for 4-8 hours in a planetary stirrer to form a composite cathode material, wherein the compounding ratio is as follows: 71% of graphite, 9% of silicon carbon material, 10% of conductive carbon black, 5% of SBR and 5% of CMC. The composite silicon-carbon-coated negative plate is prepared by adopting the existing graphite negative electrode preparation process, and then is prepared into a button cell which is tested by using a blue test system. The test result is shown in fig. 11, the first efficiency of the composite cathode material using the inorganic binder not containing silicon is 88%; the first cycle lithium insertion capacity can reach more than 630mAh/g when charging and discharging at 0.2C, the cycle stability is poor, and the cycle life is only 30 times when charging and discharging at 0.2C.
Comparative example 2
The composite negative electrode material comprises a graphite negative electrode material and a silicon-carbon material, wherein the content of the silicon-carbon material is 15 wt% of the total amount of the composite negative electrode material. Wherein the silicon carbon material comprises: the composite material comprises silicon alloy powder, graphene, silica gel, PVDF, glucose and NMP, wherein the graphene accounts for 2 wt% of the silicon alloy powder, the silica gel accounts for 4 wt% of the silicon alloy powder, the PVDF accounts for 6 wt% of the silicon alloy powder, the glucose accounts for 4 wt% of the silicon alloy powder, and the NMP accounts for 1 wt% of the silicon alloy powder. The silicon alloy powder in the embodiment is 42 wt% Si-8 wt% Al-50 wt% Cu alloy which is prepared by a water mist method and has the grain diameter of less than 75 mu m.
The preparation method of the composite negative electrode material comprises the following steps:
firstly, preparing a silicon-carbon material, which specifically comprises the following steps: firstly, mixing and stirring raw materials of a silicon-carbon material and water to form slurry; secondly, grinding the slurry in a sand mill at the rotation speed of 5000r/min for 2 h; thirdly, placing the ground slurry into a vacuum heat treatment furnace for heat treatment, wherein the heat treatment process comprises the following steps: heating to 500 ℃ at a heating rate of 30 ℃/min, preserving heat for 3h, then heating to 600 ℃ at a heating rate of 30 ℃, preserving heat for 6h, and then cooling along with the furnace.
Secondly, adding the prepared silicon-carbon material into the graphite cathode material, and stirring for 4-8 hours in a planetary stirrer to form a composite cathode material, wherein the compounding ratio is as follows: 65% of graphite, 15% of silicon carbon material, 10% of conductive carbon black, 5% of SBR and 5% of CMC. The composite silicon-carbon-coated negative plate is prepared by adopting the existing graphite negative electrode preparation process, and then is prepared into a button cell which is tested by using a blue test system. The test result is shown in fig. 12, and the first efficiency of the composite anode material is 87%; when the lithium is charged and discharged at 0.2C, the lithium intercalation capacity of the first week can reach more than 560 mAh/g; the capacity retention rate can reach more than 70% when the battery is charged and discharged at 0.2C and is cycled for 3000 times.
Comparative example 3
The embodiment provides a silicon-carbon negative electrode material, which comprises 7 wt% of carbon-coated silicon particles, 10 wt% of conductive carbon black SP, 5 wt% of SBR, 5 wt% of CMC and the balance of graphite; the carbon-coated silicon particles adopt silicon powder with the particle size of less than 70 mu m, and the raw material of the outer coating layer of the silicon powder is only white sugar. In the embodiment, white sugar is used as a carbon source to prepare carbon-coated silicon particles, and the carbon-coated silicon particles are combined with conductive carbon black SP, SBR and CMC to prepare a negative plate, and then the negative plate is prepared into a button cell to be tested by a blue test system. The test result is shown in fig. 13, the first efficiency of the commercial silicon-carbon negative electrode material is 90%, the first cycle lithium insertion capacity can reach 460Ah/g, the specific capacity can reach 400mAh/g after 50 cycles, and then the specific capacity is attenuated more rapidly when the commercial silicon-carbon negative electrode material is charged and discharged at 0.2C.
Comparative example 4
This embodiment provides a pure graphite as graphite negative electrode, and this graphite negative electrode's raw materials include: 10 wt% of conductive carbon black SP, 5 wt% of SBR, 5 wt% of CMC, and the balance of graphite; the cathode sheet is prepared by adopting the existing preparation process of the graphite cathode, and then the button cell is prepared and tested by using a blue test system. The test result is shown in fig. 14, the first efficiency of the graphite cathode material is more than 91%; when the lithium battery is charged and discharged at 0.2C, the first cycle lithium embedding capacity is 354mAh/g, and the stable cycle specific capacity is more than 300 mAh/g; the capacity retention rate is 86.7% when the lithium ion battery is charged and discharged at 0.2C and is cycled 3000 times.
As can be seen from the comparison of the results of the above tests of examples 1 to 8 with comparative example 4: the cycling specific capacity of the cathode material can reach more than 410mAh/g, which is improved by more than 10.0 percent compared with the graphite cathode material in the comparative example 4. The first efficiency of the composite negative electrode material can reach more than 87 percent, and is equivalent to the first efficiency of the graphite negative electrode in the comparative example 4. The capacity retention rate of the composite cathode material can reach more than 99.99 percent when the composite cathode material is cycled for 100 times, can reach more than 99 percent when the composite cathode material is cycled for 1000 times, and can reach more than 90 percent when the composite cathode material is cycled for 3000 times, the cycling stability of the composite cathode material is obviously higher than that of the graphite cathode material in the comparative example 4, and the composite cathode material is also obviously superior to the conventional carbon-coated silicon-carbon cathode material disclosed in the comparative example 3. In conclusion, the invention can achieve the purposes of keeping the first efficiency and improving the cycling stability while improving the specific capacity, and has very obvious effect.
In example 5, compared with comparative example 1, under the same conditions, only the auxiliary agent "silicon-containing inorganic binder" identified as an unnecessary raw material was reduced, and the comparison of the results of the two tests shows that: without the aid "siliceous inorganic binder", the first efficiency and cycle stability are significantly reduced. By comparison of examples 6 to 7 with example 9, it can be seen that: when the binder in the graphite negative electrode material is SBR and CMC and the SBR content is not lower than 5 percent, the circulation stability of the prepared composite negative electrode material is effectively maintained. It can be seen from the comparison between example 6 and example 8 that, when PVDF is too much and NMP is not used, the electrolyte takes a long time to wet the carbon-coated layer, and the early-stage cycling capacity is not satisfactory, but after 30 cycles or more, the cycling stability is still very significant, and the purpose of the present invention can be achieved. As can be seen from comparison of examples 1-8 with comparative example 2, the present invention can effectively make the cycling stability better than that of the graphite negative electrode material in the preferred range, and the effect is very significant.
It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.

Claims (10)

1. The composite negative electrode material is characterized in that raw materials comprise a graphite negative electrode material and a silicon-carbon material, wherein the content of the silicon-carbon material is not higher than 10 wt% of the total amount of the composite negative electrode material;
the silicon-carbon material comprises the following raw materials: silicon-containing particles, graphene, a silicon-containing inorganic binder and an organic carbon source; the graphene accounts for 3-5 wt% of the weight of the silicon alloy powder, the silicon-containing inorganic adhesive accounts for 1-3 wt% of the weight of the silicon alloy powder, and the organic carbon source accounts for 2-6 wt% of the weight of the silicon alloy powder.
2. The composite anode material according to claim 1, wherein the silicon-containing particles are silicon alloy powder, the silicon alloy powder has a porous structure, and the particle size is less than 75 μm.
3. The composite anode material according to claim 1 or 2, wherein the organic carbon source is selected from sugars and PVDF; the sugar accounts for 1-3 wt% of the weight of the silicon alloy powder, and the PVDF accounts for 1-4 wt% of the weight of the silicon alloy powder.
4. The composite anode material according to any one of claims 1 to 3, wherein the silicon carbon material further comprises NMP; NMP accounts for 0.1-1 wt% of the weight of the silicon alloy powder.
5. The composite anode material according to any one of claims 1 to 4, wherein the silicon-containing inorganic binder is pressure swing adsorption silica gel.
6. The composite anode material according to any one of claims 1 to 5, wherein the content of the silicon-carbon material is 5 to 10 wt% of the total amount of the anode material.
7. The composite negative electrode material according to any one of claims 1 to 6, wherein the raw material of the graphite negative electrode material comprises graphite, a carbon black conductive agent and a binder; the carbon black conductive agent accounts for 5-10 wt% of the composite negative electrode material, and the adhesive accounts for 5-10 wt% of the composite negative electrode material.
8. The preparation process of the composite anode material according to any one of claims 1 to 7, comprising:
preparing a silicon-carbon material: adding a solvent into the raw materials of the silicon-carbon material according to the proportion to prepare slurry, and performing heat treatment at 400-750 ℃ after sanding;
and (3) uniformly stirring the silicon-carbon material prepared in the step and the graphite cathode material.
9. The process according to claim 7 or 8, wherein the heat treatment comprises: in a vacuum state, firstly heating to 400-450 ℃, preserving heat for 2-4 h, then heating to 650-750 ℃ at a heating rate of 25-35 ℃/min, preserving heat for 1-3 h, and then cooling along with a furnace;
or, the heat treatment process is as follows: in a vacuum state, heating to 470-530 ℃ at a heating rate of 25-35 ℃/min, preserving heat for 2-4 h, then heating to 570-630 ℃ at a heating rate of 25-35 ℃, preserving heat for 5-8 h, and then cooling along with a furnace.
10. The preparation process of claim 8 or 9, wherein the prepared silicon carbon material has a particle size D50 of less than 5 μm, a particle size D90 of less than 10 μm, and a tap density of 1-1.35 g/cm3The specific surface area is 1.5-3 cm2/g。
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