A negative electrode material for lithium-ion button battery and preparation method thereof

Abstract

The present invention discloses a negative electrode material for lithium-ion button batteries and a preparation method thereof, belonging to the technical field of battery materials. This lithium battery negative electrode material, prepared by compounding a Mn-Ce-modified biochar material and chitosan-phytic acid-modified nano-silicon powder in a specific ratio, effectively alleviates the volume expansion problem of silicon materials during charging and discharging, while also increasing ion migration channels and enhancing electron conduction pathways. The material exhibits excellent electrochemical properties, improves the capacity retention and cycle stability of lithium-ion batteries, and has promising market application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and in particular relates to a negative electrode material for a lithium-ion button battery and a preparation method thereof. Background Art

[0002] With the rapid development of science and technology, applications such as portable electronic devices and electric vehicles have increasingly higher requirements for energy storage devices. Lithium-ion batteries (LIBs) have become the preferred energy storage devices in these fields due to their outstanding advantages such as high voltage, high energy density, good cycle performance and low self-discharge. However, the performance of lithium-ion batteries depends to a large extent on the selection and performance of their negative electrode materials. Traditional lithium-ion battery negative electrode materials mainly include carbon materials such as graphite, hard carbon and soft carbon. Among them, graphite, as a traditional negative electrode material, has relatively stable electrochemical properties and low cost, but its theoretical specific capacity is only 372mAh / g, which limits the further improvement of the energy density of lithium-ion batteries. Silicon-based materials (such as SiO x , Sn, SnO2, etc.) have attracted much attention due to their relatively high specific capacity characteristics. However, silicon-based materials have problems such as poor conductivity and large volume changes (up to 200% or more) during the process of inserting and extracting lithium ions. These characteristics cause battery capacity decay and cycle performance deterioration in two aspects when used as negative electrode materials. On the one hand, the destruction of the material structure and mechanical pulverization lead to the separation of the negative electrode material and the current collector, which physically reduces the battery capacity and cycle performance. On the other hand, the expansion and contraction of the volume causes the continuous rupture and reconstruction of the SEI film, which continuously consumes active materials, causing adverse effects such as battery capacity decay and cycle performance deterioration. These problems have seriously limited the practical application of silicon-based materials in lithium-ion batteries.

[0003] In order to solve the above problems, researchers have conducted a lot of research and exploration. The performance of negative electrode materials can usually be improved through structural design. For example, by constructing a three-dimensional structure, introducing a porous skeleton or using composite materials, the lithium ion storage capacity, lithium ion transmission rate and cycle stability of the negative electrode material can be effectively improved. In addition, surface doping modification or coating modification of the negative electrode material can also improve its electrochemical performance and conductivity. The most common modification is the modification of carbon-silicon composite materials. However, the existing preparation methods of silicon-carbon composite materials still have certain shortcomings. For example, the range of carbon source selection is limited, the cost is high and the effect is poor, and the cycle performance improvement is not obvious. Summary of the Invention

[0004] The present invention aims to provide a high-performance negative electrode material for lithium-ion button batteries to meet the demand for high-performance energy storage devices in fields such as portable electronic devices and electric vehicles.

[0005] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0006] A method for preparing a negative electrode material for a lithium-ion button battery comprises the following steps:

[0007] (1) Dissolve chitosan in 5 wt% citric acid solution, heat in a 55°C water bath and stir for 30 min to obtain solution A;

[0008] (2) Add nano-silicon powder to 10 wt% phytic acid solution according to the material-liquid ratio and stir evenly to obtain suspension B;

[0009] (3) Solution A and suspension B were mixed according to the mass ratio, and then ultrasonically treated for 30 min and then magnetically stirred in a water bath at 60°C for 30 min. After the reaction, the mixture was filtered and washed with deionized water until neutral, and then dried in a vacuum drying oven to obtain modified nano-silicon powder.

[0010] (4) The walnut shells were washed, dried, and crushed, and passed through a 100-mesh sieve to obtain walnut shell powder. 5 g of walnut shell powder was dispersed in 200 ml of deionized water, and 0.02 mol of MnCl2 and 0.04 mol of Ce(NO3)3 were added thereto respectively. The mixture was stirred evenly and ultrasonically dispersed for 2 h. After solid-liquid separation, the solid product was placed in an oven for drying, and then transferred to a tubular furnace, nitrogen was introduced for protection, and calcined at high temperature for 2 h. After cooling to room temperature, the product was washed with deionized water for 3-5 times, then dried and crushed, and passed through a 100-mesh sieve to obtain Mn-Ce modified biochar material.

[0011] (5) The modified nano-silicon powder and the Mn-Ce modified biochar material were mixed in a mass ratio and placed in a ball mill at a ball-to-liquid ratio of 5:1. Anhydrous ethanol was then added as a ball milling medium at a material-liquid ratio of 1:4. The speed was set to 400 rpm and the ball milling treatment was carried out for 10-12 hours. The mixture was transferred to a tubular furnace, and argon was introduced as a protective gas. The mixture was calcined at a high temperature, cooled naturally, and ground to obtain the negative electrode material for lithium-ion button batteries.

[0012] Preferably, in step (1), the material-liquid ratio of chitosan to citric acid solution is 1 g:50 ml.

[0013] Preferably, in step (2), the material-liquid ratio of nano-silicon powder to phytic acid solution is 1 g:20 ml.

[0014] Preferably, in step (3), the mass ratio of solution A to suspension B is 1:2.

[0015] Preferably, the specific calcination method in step (4) is: heating to 600°C at a rate of 10°C / min and then keeping the temperature for 2h.

[0016] Preferably, in step (5), the mass ratio of the modified nano-silicon powder to the Mn-Ce modified biochar material is 1:2-5.

[0017] Preferably, the specific method of high-temperature calcination in step (5) is: heating to 800°C at a rate of 5°C / min and then keeping the temperature for 2h.

[0018] The present invention also provides a negative electrode material for lithium-ion button batteries prepared by the above-mentioned method for preparing negative electrode materials for lithium-ion button batteries, which can effectively alleviate the volume expansion problem of silicon materials during the charging and discharging process, and at the same time can increase more ion migration channels and enhance the electron conduction path. It has excellent electrochemical properties, improves the capacity retention rate and cycle stability of lithium-ion batteries, and has good market application prospects.

[0019] The negative electrode material for lithium-ion button batteries prepared by the above method is used as follows: the negative electrode material prepared by the present invention is thoroughly ground and then ground with conductive black and a binder in a mass ratio of 8:1:1, stirring until a uniformly dispersed slurry is formed. The slurry is then coated onto copper foil using an I-shaped scraper to a thickness of 75 μm. The slurry is then dried in a vacuum drying oven at 60°C for 12 hours, cut into 10 mm diameter discs on a microtome, and pressed at a pressure of 6 MPa to obtain the negative electrode sheet.

[0020] The nano silicon powder used in the present invention is a commercially available product with a particle size of 100 nm. The other raw materials and reagents used can be purchased from the market unless otherwise specified.

[0021] The beneficial effects of the present invention are:

[0022] (1) Chitosan and phytic acid are both natural biomolecular active substances containing functional groups such as amino, hydroxyl and phosphoric acid. These functional groups are simultaneously adsorbed on the surface of nano-silicon through chemical bonds, which enhances the interaction between nano-silicon materials and biological small molecules, thereby being more conducive to reducing the surface activity of silicon, promoting the formation of a more complete and stable SEI film, and being able to better resist the volume expansion of silicon materials and reduce the occurrence of side reactions between active substances and electrolytes.

[0023] (2) Walnut shell biochar itself is a renewable resource, and its preparation process helps reduce environmental pollution and greenhouse gas emissions. Biochar prepared from walnut shells has a large specific surface area and a rich porous structure. The use of Mn-Ce modified biochar material further optimizes its pore structure and surface chemical properties by introducing Mn and Ce elements, improving the adsorption and desorption capacity of lithium ions, thereby increasing the energy density of the battery. At the same time, Mn-Ce modified biochar also enhances the structural stability of the biochar material, reduces structural damage during the charge and discharge process, and thus extends the cycle life of the battery.

[0024] (3) The nano-silicon powder modified with chitosan-phytic acid is coated with chitosan and phytic acid, which enhances the stability and dispersibility of nano-silicon, and at the same time improves its conductivity and cycle stability. When used in combination with Mn-Ce modified biochar, the two work synergistically to further enhance the conductivity and cycle stability of the negative electrode material, improve the specific capacity, and have good market application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 These are the surface morphologies of the negative electrode material prepared in Example 3 of the present invention at different resolutions, where a is a low-resolution SEM image and b is a high-resolution SEM image;

[0026] Figure 2 This is a graph showing the electrochemical cycle performance test results of negative electrode materials A1, A2, A3 and A4 for lithium-ion button batteries prepared by mixing raw materials in different proportions according to the present invention. DETAILED DESCRIPTION

[0027] The technical solution of the present invention will be further described below with reference to specific embodiments, but is not limited thereto.

[0028] Example 1

[0029] A method for preparing a negative electrode material for a lithium-ion button battery comprises the following steps:

[0030] (1) Dissolve 2 g of chitosan in 100 ml of 5 wt% citric acid solution, heat in a 55°C water bath and stir for 30 min to obtain solution A;

[0031] (2) Add 5 g of nano-silicon powder to 100 ml of 10 wt% phytic acid solution and stir evenly to obtain suspension B;

[0032] (3) Solution A and suspension B were mixed in a mass ratio of 1:2, and then ultrasonically treated for 30 min and then magnetically stirred in a water bath at 60°C for 30 min. After the reaction, the mixture was filtered and washed with deionized water until neutral, and then dried in a vacuum drying oven to obtain modified nano-silicon powder.

[0033] (4) The walnut shells were washed, dried, and crushed, and passed through a 100-mesh sieve to obtain walnut shell powder. 5 g of walnut shell powder was dispersed in 200 ml of deionized water, and 0.02 mol of MnCl2 and 0.04 mol of Ce(NO3)3 were added thereto respectively. The mixture was stirred evenly and ultrasonically dispersed for 2 h. After solid-liquid separation, the solid product was placed in an oven for drying, and then transferred to a tubular furnace, nitrogen was introduced for protection, and the temperature was increased to 600 °C at a rate of 10 °C / min and kept at this temperature for 2 h. After cooling to room temperature, the product was washed with deionized water for 3-5 times, dried and crushed, and passed through a 100-mesh sieve to obtain Mn-Ce modified biochar material.

[0034] (5) The modified nano-silicon powder and the Mn-Ce modified biochar material were mixed in a mass ratio of 1:2 and placed in a ball mill at a ball-to-liquid ratio of 5:1. Anhydrous ethanol was then added as a ball milling medium at a material-liquid ratio of 1:4. The speed was set to 400 rpm and the ball milling treatment was carried out for 10 h. The mixture was transferred to a tubular furnace, and argon was introduced as a protective gas. The temperature was raised to 800 °C at a rate of 5 °C / min and then kept at this temperature for 2 h. The negative electrode material for lithium-ion button batteries was obtained by natural cooling and grinding.

[0035] Example 2

[0036] A method for preparing a negative electrode material for a lithium-ion button battery comprises the following steps:

[0037] (1) Dissolve 2 g of chitosan in 100 ml of 5 wt% citric acid solution, heat in a 55°C water bath and stir for 30 min to obtain solution A;

[0038] (2) Add 5 g of nano-silicon powder to 100 ml of 10 wt% phytic acid solution and stir evenly to obtain suspension B;

[0039] (3) Solution A and suspension B were mixed in a mass ratio of 1:2, and then ultrasonically treated for 30 min and then magnetically stirred in a water bath at 60°C for 30 min. After the reaction, the mixture was filtered and washed with deionized water until neutral, and then dried in a vacuum drying oven to obtain modified nano-silicon powder.

[0040] (4) The walnut shells were washed, dried, and crushed, and passed through a 100-mesh sieve to obtain walnut shell powder. 5 g of walnut shell powder was dispersed in 200 ml of deionized water, and 0.02 mol of MnCl2 and 0.04 mol of Ce(NO3)3 were added thereto respectively. The mixture was stirred evenly and ultrasonically dispersed for 2 h. After solid-liquid separation, the solid product was placed in an oven for drying, and then transferred to a tubular furnace, nitrogen was introduced for protection, and the temperature was increased to 600 °C at a rate of 10 °C / min and kept at this temperature for 2 h. After cooling to room temperature, the product was washed with deionized water for 3-5 times, dried and crushed, and passed through a 100-mesh sieve to obtain Mn-Ce modified biochar material.

[0041] (5) The modified nano-silicon powder and the Mn-Ce modified biochar material were mixed in a mass ratio of 1:3 and placed in a ball mill at a ball-to-liquid ratio of 5:1. Anhydrous ethanol was then added as a ball milling medium at a material-liquid ratio of 1:4. The speed was set to 400 rpm and the ball milling treatment was carried out for 11 hours. The mixture was transferred to a tubular furnace, and argon was introduced as a protective gas. The temperature was raised to 800°C at a rate of 5°C / min and then kept at this temperature for 2 hours. The mixture was naturally cooled and ground to obtain the negative electrode material for lithium-ion button batteries.

[0042] Example 3

[0043] A method for preparing a negative electrode material for a lithium-ion button battery comprises the following steps:

[0044] (1) Dissolve 2 g of chitosan in 100 ml of 5 wt% citric acid solution, heat in a 55°C water bath and stir for 30 min to obtain solution A;

[0045] (2) Add 5 g of nano-silicon powder to 100 ml of 10 wt% phytic acid solution and stir evenly to obtain suspension B;

[0046] (3) Solution A and suspension B were mixed in a mass ratio of 1:2, and then ultrasonically treated for 30 min and then magnetically stirred in a water bath at 60°C for 30 min. After the reaction, the mixture was filtered and washed with deionized water until neutral, and then dried in a vacuum drying oven to obtain modified nano-silicon powder.

[0047] (4) The walnut shells were washed, dried, and crushed, and passed through a 100-mesh sieve to obtain walnut shell powder. 5 g of walnut shell powder was dispersed in 200 ml of deionized water, and 0.02 mol of MnCl2 and 0.04 mol of Ce(NO3)3 were added thereto respectively. The mixture was stirred evenly and ultrasonically dispersed for 2 h. After solid-liquid separation, the solid product was placed in an oven for drying, and then transferred to a tubular furnace, nitrogen was introduced for protection, and the temperature was increased to 600 °C at a rate of 10 °C / min and kept at this temperature for 2 h. After cooling to room temperature, the product was washed with deionized water for 3-5 times, dried and crushed, and passed through a 100-mesh sieve to obtain Mn-Ce modified biochar material.

[0048] (5) The modified nano-silicon powder and the Mn-Ce modified biochar material were mixed in a mass ratio of 1:5, and placed in a ball mill at a ball-to-liquid ratio of 5:1. Anhydrous ethanol was then added as a ball milling medium at a material-liquid ratio of 1:4. The speed was set to 400 rpm and the ball milling treatment was carried out for 12 h. The mixture was transferred to a tubular furnace, and argon was introduced as a protective gas. The temperature was raised to 800 °C at a rate of 5 °C / min and then kept at this temperature for 2 h. The negative electrode material for lithium-ion button batteries was obtained by natural cooling and grinding.

[0049] Comparative Example 1

[0050] A method for preparing a negative electrode material for a lithium-ion button battery comprises the following steps:

[0051] (1) The walnut shells were washed, dried, and crushed, and passed through a 100-mesh sieve to obtain walnut shell powder. The walnut shell powder was then transferred into a tubular furnace, nitrogen was introduced, and the temperature was raised to 600°C at a rate of 10°C / min and kept at that temperature for 2 h. After cooling to room temperature, the powder was crushed and passed through a 100-mesh sieve to obtain biochar material.

[0052] (2) Nano-silicon powder and biochar material were mixed in a mass ratio of 1:5, and placed in a ball mill at a ball-to-liquid ratio of 5:1. Anhydrous ethanol was then added as a ball milling medium at a material-liquid ratio of 1:4. The speed was set to 400 rpm and the ball milling treatment was carried out for 12 h. The mixture was transferred to a tubular furnace, and argon was introduced as a protective gas. The temperature was raised to 800 °C at a rate of 5 °C / min and kept at this temperature for 2 h. The mixture was naturally cooled and ground to obtain the negative electrode material for lithium-ion button batteries.

[0053] Comparative Example 2

[0054] A method for preparing a negative electrode material for a lithium-ion button battery comprises the following steps:

[0055] (1) Dissolve 2 g of chitosan in 100 ml of 5 wt% citric acid solution, heat in a 55°C water bath and stir for 30 min to obtain solution A;

[0056] (2) Add 5 g of nano-silicon powder to 100 ml of 10 wt% phytic acid solution and stir evenly to obtain suspension B;

[0057] (3) Solution A and suspension B were mixed in a mass ratio of 1:2, and then ultrasonically treated for 30 min and then magnetically stirred in a water bath at 60°C for 30 min. After the reaction, the mixture was filtered and washed with deionized water until neutral, and then dried in a vacuum drying oven to obtain modified nano-silicon powder.

[0058] (4) The walnut shells were washed, dried, and crushed, and passed through a 100-mesh sieve to obtain walnut shell powder, which was then transferred to a tubular furnace and protected by nitrogen. The temperature was raised to 600°C at a rate of 10°C / min and kept at that temperature for 2 h. After cooling to room temperature, the walnut shells were crushed and passed through a 100-mesh sieve to obtain biochar material.

[0059] (5) The modified nano-silicon powder and biochar material were mixed in a mass ratio of 1:5, and placed in a ball mill at a ball-to-liquid ratio of 5:1. Anhydrous ethanol was then added as a ball milling medium at a material-liquid ratio of 1:4. The speed was set to 400 rpm and the ball milling treatment was carried out for 12 h. The mixture was transferred to a tubular furnace, and argon was introduced as a protective gas. The mixture was calcined at high temperature, cooled naturally, and ground to obtain the negative electrode material for lithium-ion button batteries.

[0060] This comparative example is basically the same as Example 3, except that the biochar used is unmodified biochar material.

[0061] Comparative Example 3

[0062] A method for preparing a negative electrode material for a lithium-ion button battery comprises the following steps:

[0063] (1) The walnut shells were washed, dried, and crushed, and passed through a 100-mesh sieve to obtain walnut shell powder. 5 g of walnut shell powder was dispersed in 200 ml of deionized water, and 0.02 mol of MnCl2 and 0.04 mol of Ce(NO3)3 were added thereto respectively. The mixture was stirred evenly and ultrasonically dispersed for 2 h. After solid-liquid separation, the solid product was placed in an oven for drying, and then transferred to a tubular furnace, nitrogen was introduced for protection, and the temperature was increased to 600 °C at a rate of 10 °C / min and kept at this temperature for 2 h. After cooling to room temperature, the product was washed with deionized water for 3-5 times, dried and crushed, and passed through a 100-mesh sieve to obtain Mn-Ce modified biochar material.

[0064] (2) Nano-silicon powder and Mn-Ce modified biochar material were mixed in a mass ratio of 1:5, placed in a ball mill at a ball-to-liquid ratio of 5:1, and then anhydrous ethanol was added as a ball milling medium at a material-liquid ratio of 1:4. The speed was set to 400 rpm and the ball milling treatment was carried out for 12 hours. The mixture was transferred to a tubular furnace, argon was introduced as a protective gas, and the mixture was calcined at high temperature. After natural cooling and grinding, the negative electrode material for lithium-ion button batteries was obtained.

[0065] This comparative example is basically the same as Example 3, except that the nano-silicon powder is not modified.

[0066] Comparative Example 4

[0067] A method for preparing a negative electrode material for a lithium-ion button battery comprises the following steps:

[0068] (1) Dissolve 2 g of chitosan in 100 ml of 5 wt% citric acid solution, heat in a 55°C water bath and stir for 30 min to obtain solution A;

[0069] (2) Add 5 g of nano-silicon powder to 100 ml of 10 wt% phytic acid solution and stir evenly to obtain suspension B;

[0070] (3) Solution A and suspension B were mixed in a mass ratio of 1:2, and then ultrasonically treated for 30 min and then magnetically stirred in a water bath at 60°C for 30 min. After the reaction, the mixture was filtered and washed with deionized water until neutral, and then dried in a vacuum drying oven to obtain modified nano-silicon powder.

[0071] (4) The walnut shells were washed, dried, and crushed, and passed through a 100-mesh sieve to obtain walnut shell powder. 5 g of walnut shell powder was dispersed in 200 ml of deionized water, and 0.02 mol of MnCl2 was added thereto. The mixture was stirred evenly and ultrasonically dispersed for 2 h. After solid-liquid separation, the solid product was dried in an oven, then transferred to a tubular furnace, nitrogen was introduced, and the temperature was raised to 600 °C at a rate of 10 °C / min and kept at this temperature for 2 h. After cooling to room temperature, the product was washed with deionized water for 3-5 times, then dried and crushed, and passed through a 100-mesh sieve to obtain Mn-modified biochar material.

[0072] (5) The modified nano-silicon powder and the Mn-modified biochar material were mixed in a mass ratio of 1:5, and placed in a ball mill at a ball-to-liquid ratio of 5:1. Anhydrous ethanol was then added as a ball milling medium at a material-liquid ratio of 1:4. The speed was set to 400 rpm and the ball milling treatment was carried out for 12 h. The mixture was transferred to a tubular furnace, and argon was introduced as a protective gas. The temperature was raised to 800 °C at a rate of 5 °C / min and then kept at this temperature for 2 h. The negative electrode material for lithium-ion button batteries was obtained by natural cooling and grinding.

[0073] This comparative example is basically the same as Example 3, with the only difference being that the modified biochar is modified using only MnCl2.

[0074] Comparative Example 5

[0075] A method for preparing a negative electrode material for a lithium-ion button battery comprises the following steps:

[0076] (1) Dissolve 2 g of chitosan in 100 ml of 5 wt% citric acid solution, heat in a 55°C water bath and stir for 30 min to obtain solution A;

[0077] (2) Add 5 g of nano-silicon powder to 100 ml of 10 wt% phytic acid solution and stir evenly to obtain suspension B;

[0078] (3) Solution A and suspension B were mixed in a mass ratio of 1:2, and then ultrasonically treated for 30 min and then magnetically stirred in a water bath at 60°C for 30 min. After the reaction, the mixture was filtered and washed with deionized water until neutral, and then dried in a vacuum drying oven to obtain modified nano-silicon powder.

[0079] (4) The walnut shells were washed, dried, and crushed, and passed through a 100-mesh sieve to obtain walnut shell powder. 5 g of walnut shell powder was dispersed in 200 ml of deionized water, and 0.04 mol of Ce(NO3)3 was added thereto. The mixture was stirred evenly and ultrasonically dispersed for 2 h. After solid-liquid separation, the solid product was dried in an oven, then transferred to a tubular furnace, nitrogen was introduced, and the temperature was raised to 600 °C at a rate of 10 °C / min and kept at this temperature for 2 h. After cooling to room temperature, the product was washed with deionized water for 3-5 times, dried, crushed, and passed through a 100-mesh sieve to obtain Ce-modified biochar material.

[0080] (5) The modified nano-silicon powder and Ce-modified biochar material were mixed in a mass ratio of 1:5, placed in a ball mill at a ball-to-liquid ratio of 5:1, and then anhydrous ethanol was added as a ball milling medium at a material-liquid ratio of 1:4. The speed was set to 400 rpm and the ball milling treatment was carried out for 12 h. The mixture was transferred to a tubular furnace, and argon was introduced as a protective gas. The temperature was raised to 800 °C at a rate of 5 °C / min and then kept at this temperature for 2 h. The negative electrode material for lithium-ion button batteries was obtained by natural cooling and grinding.

[0081] This comparative example is basically the same as Example 3, with the only difference being that the modified biochar is modified using only Ce(NO3)3.

[0082] Comparative Example 6

[0083] A method for preparing a negative electrode material for a lithium-ion button battery comprises the following steps:

[0084] (1) Dissolve 2 g of chitosan in 100 ml of 5 wt% citric acid solution, heat in a 55°C water bath and stir for 30 min to obtain solution A;

[0085] (2) Add 5 g of nano-silicon powder to solution A, ultrasonicate for 30 min, and then magnetically stir in a water bath at 60°C for 30 min. After the reaction, filter and wash with deionized water until neutral, then dry in a vacuum drying oven to obtain modified nano-silicon powder.

[0086] (3) The walnut shells were washed, dried, and crushed, and passed through a 100-mesh sieve to obtain walnut shell powder. 5 g of walnut shell powder was dispersed in 200 ml of deionized water, and 0.02 mol of MnCl2 and 0.04 mol of Ce(NO3)3 were added thereto respectively. The mixture was stirred evenly and ultrasonically dispersed for 2 h. After solid-liquid separation, the solid product was placed in an oven for drying, and then transferred to a tubular furnace, nitrogen was introduced for protection, and the temperature was increased to 600 °C at a rate of 10 °C / min and kept at this temperature for 2 h. After cooling to room temperature, the product was washed with deionized water for 3-5 times, dried and crushed, and passed through a 100-mesh sieve to obtain Mn-Ce modified biochar material.

[0087] (4) The modified nano-silicon powder and the Mn-Ce modified biochar material were mixed in a mass ratio of 1:5, and placed in a ball mill at a ball-to-liquid ratio of 5:1. Anhydrous ethanol was then added as a ball milling medium at a material-liquid ratio of 1:4. The speed was set to 400 rpm and the ball milling treatment was carried out for 12 h. The mixture was transferred to a tubular furnace, and argon was introduced as a protective gas. The temperature was raised to 800 °C at a rate of 5 °C / min and then kept at this temperature for 2 h. The negative electrode material for lithium-ion button batteries was obtained by natural cooling and grinding.

[0088] This comparative example is basically the same as Example 3, with the only difference being that the modified nano-silicon powder is only modified with chitosan.

[0089] Comparative Example 7

[0090] A method for preparing a negative electrode material for a lithium-ion button battery comprises the following steps:

[0091] (1) Add 5 g of nano-silicon powder to 100 ml of 10 wt% phytic acid solution and stir evenly to obtain suspension B;

[0092] (2) The suspension B was first ultrasonically treated for 30 min and then magnetically stirred in a water bath at 60°C for 30 min. After the reaction, it was filtered and washed with deionized water until neutral, and then dried in a vacuum drying oven to obtain modified nano-silicon powder.

[0093] (3) The walnut shells were washed, dried, and crushed, and passed through a 100-mesh sieve to obtain walnut shell powder. 5 g of walnut shell powder was dispersed in 200 ml of deionized water, and 0.02 mol of MnCl2 and 0.04 mol of Ce(NO3)3 were added thereto respectively. The mixture was stirred evenly and ultrasonically dispersed for 2 h. After solid-liquid separation, the solid product was placed in an oven for drying, and then transferred to a tubular furnace, nitrogen was introduced for protection, and the temperature was increased to 600 °C at a rate of 10 °C / min and kept at this temperature for 2 h. After cooling to room temperature, the product was washed with deionized water for 3-5 times, dried and crushed, and passed through a 100-mesh sieve to obtain Mn-Ce modified biochar material.

[0094] (4) The modified nano-silicon powder and the Mn-Ce modified biochar material were mixed in a mass ratio of 1:5, and placed in a ball mill at a ball-to-liquid ratio of 5:1. Anhydrous ethanol was then added as a ball milling medium at a material-liquid ratio of 1:4. The speed was set to 400 rpm and the ball milling treatment was carried out for 12 h. The mixture was transferred to a tubular furnace, and argon was introduced as a protective gas. The temperature was raised to 800 °C at a rate of 5 °C / min and then kept at this temperature for 2 h. The negative electrode material for lithium-ion button batteries was obtained by natural cooling and grinding.

[0095] This comparative example is basically the same as Example 3, with the only difference being that the modified nano-silicon powder is only modified with phytic acid.

[0096] Performance Testing

[0097] The electrochemical performance of the negative electrode materials for lithium-ion button batteries prepared in Examples 1-3 and Comparative Examples 1-7 was tested in the following steps:

[0098] Preparation of the negative electrode sheet: The negative electrode material prepared in this invention was thoroughly ground and then ground with acetylene black and a binder, PVDF (polyvinylidene fluoride), in a mass ratio of 8:1:1. An appropriate amount of NMP (N-methylpyrrolidone) was then added and stirred until a paste formed. The paste was then coated onto copper foil using an I-shaped scraper to a thickness of 75 μm. The mixture was dried in a vacuum oven at 60°C for 12 hours, cut into 12 mm diameter discs on a microtome, and pressed at a pressure of 6 MPa to obtain the lithium battery negative electrode sheet.

[0099] Battery assembly: Using the aforementioned electrode sheet as the negative electrode and the metallic lithium sheet as the positive electrode, CR-2032 button cells were assembled in an argon atmosphere glove box. The separator model was Celgard 2400, and the electrolyte was 1 mol / L LiPF6 conductive salt and a solvent with DMC:DEC:EC (wt%) = 1:1:1. After the assembly was allowed to stand for 12 h, various electrochemical performance tests were performed.

[0100] Cyclic charge-discharge testing was performed using a battery charge-discharge test system at a set current density within a voltage range of 0.01–2.00 V. The battery was first activated for three cycles at a current density of 50 mA / g, followed by a long-term cycle test at a current density of 100 mA / g. The test results are shown in Table 1.

[0101] Table 1 Performance test results

[0102]

[0103] As can be seen from the data in the table above, the lithium battery negative electrode materials prepared in the examples of the present invention have an initial discharge specific capacity of 3741 mAh / g and an initial coulombic efficiency of over 92%. After 400 cycles, the capacity retention rate is over 87%. This demonstrates that the negative electrode materials prepared in the present invention have excellent electrochemical performance. The synergistic effect of the modified biochar and nano-silicon powder can promote the formation of a more complete and stable SEI film, which can better resist the volume expansion of the silicon material and reduce the occurrence of side reactions between the active material and the electrolyte, thereby improving the specific capacity and cycle stability of the battery material. In contrast, the negative electrode materials prepared by changing any of the raw material compositions in Comparative Examples 1-7 showed a decrease in battery performance. This is due to the disappearance of the interaction between the modified nano-silicon powder and the Mn-Ce modified biochar material.

[0104] The surface morphology of the negative electrode material for lithium ion button battery prepared in Example 3 of the present invention was tested by SEM. The results are as follows: Figure 1 As shown in the figure, the material is irregularly lumpy or granular, with a large number of micro- and nano-sized particles appearing on the surface. This is due to the successful loading of modified Mn-Ce metal particles and nano-silicon particles onto the biochar particles. The Mn-Ce-modified biochar further optimizes its pore structure and surface chemistry, improving its adsorption and desorption capacity for lithium ions, thereby increasing the battery's energy density. The chitosan-phytic acid-modified nano-silicon powder, through the coating of chitosan and phytic acid, enhances the stability and dispersibility of the nano-silicon. The two are uniformly and stably adsorbed together, simultaneously improving its conductivity and cycling stability.

[0105] The present invention also studies the lithium ion button battery negative electrode materials A1, A2 and A3 prepared by mixing modified nano silicon powder and Mn-Ce modified biochar material in a mass ratio of 1:1, 1:6 and 1:7 respectively. The negative electrode materials A1, A2 and A3 for lithium ion button battery prepared by the lithium ion button battery negative electrode material (denoted as A4) obtained in Example 3 were tested for electrochemical performance using the same test method as above. The cycle performance test results are as follows: Figure 2 shown.

[0106] From the above Figure 2 It can be seen from the contents that the electrochemical performance of the negative electrode material deteriorates significantly when the raw material ratio of the present invention is changed, and the raw material composition ratio of the present invention is the optimal ratio.

[0107] It should be noted that the above embodiments are only some of the preferred embodiments of the present invention, and not all of them. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a negative electrode material for a lithium-ion button battery, characterized in that: It includes the following steps: (1) Dissolve chitosan in 5 wt% citric acid solution, heat in a 55°C water bath and stir for 30 min to obtain solution A; (2) Add nano-silicon powder to 10 wt% phytic acid solution according to the material-liquid ratio and stir evenly to obtain suspension B; (3) Solution A and suspension B were mixed according to the mass ratio, and then ultrasonically treated for 30 min and then magnetically stirred in a water bath at 60°C for 30 min. After the reaction, the mixture was filtered and washed with deionized water until neutral, and then dried in a vacuum drying oven to obtain modified nano-silicon powder; (4) The walnut shells were washed, dried, and crushed, and passed through a 100-mesh sieve to obtain walnut shell powder. 5 g of walnut shell powder was dispersed in 200 ml of deionized water, and 0.02 mol of MnCl2 and 0.04 mol of Ce(NO3)3 were added thereto respectively. The mixture was stirred evenly and ultrasonically dispersed for 2 h. After solid-liquid separation, the solid product was placed in an oven for drying, and then transferred to a tubular furnace, nitrogen was introduced for protection, and the temperature was increased to 600 °C at a rate of 10 °C / min and kept at this temperature for 2 h. After cooling to room temperature, the product was washed with deionized water for 3-5 times, dried and crushed, and passed through a 100-mesh sieve to obtain Mn-Ce modified biochar material. (5) The modified nano-silicon powder and the Mn-Ce modified biochar material were mixed in a mass ratio and placed in a ball mill at a ball-to-liquid ratio of 5:

1. Anhydrous ethanol was then added as a ball milling medium at a material-to-liquid ratio of 1:

4. The speed was set to 400 rpm and the ball milling treatment was carried out for 10-12 hours. The mixture was transferred to a tubular furnace, and argon was introduced as a protective gas. The temperature was raised to 800°C at a rate of 5°C / min and then kept at this temperature for 2 hours. The mixture was naturally cooled and ground to obtain the negative electrode material for lithium-ion button batteries.

2. The method for preparing a negative electrode material for a lithium-ion button battery according to claim 1, wherein: In step (1), the material-liquid ratio of chitosan to citric acid solution is 1 g:50 ml.

3. The method for preparing a negative electrode material for a lithium-ion button battery according to claim 1, wherein: In step (2), the material-liquid ratio of nano-silicon powder to phytic acid solution is 1 g:20 ml.

4. The method for preparing a negative electrode material for a lithium-ion button battery according to claim 1, wherein: The mass ratio of solution A to suspension B in step (3) is 1:

2.

5. The method for preparing a negative electrode material for a lithium-ion button battery according to claim 1, wherein: In the step (5), the mass ratio of the modified nano-silicon powder to the Mn-Ce modified biochar material is 1:2-5.

6. A negative electrode material for a lithium-ion button battery, characterized in that: The method according to any one of claims 1 to 5 is used to prepare the present invention.

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