A negative electrode additive, a preparation method and application thereof

Abstract

The application relates to the technical field of batteries, in particular to a negative electrode additive as well as a preparation method and application thereof. The preparation method of the negative electrode additive comprises the following steps: mixing polyvinyl alcohol, a template agent, a phosphate buffer and a soluble calcium source to obtain a first system; adjusting the pH of the first system by using lye, and then performing solid-liquid separation to collect solid substances to obtain the negative electrode additive. According to the preparation method of the negative electrode additive, the polyvinyl alcohol can be used to cross-link the template agent to form nanoscale micelles, so that the particle size of final hydroxyapatite nanoparticles is reduced; through cooperation of various raw materials and steps, the obtained negative electrode additive has a hollow spherical structure, the particle size and wall thickness are suitable, the liquid absorption performance is good, the liquid absorption speed of the negative electrode can be improved, and the infiltration performance of the negative electrode sheet can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a negative electrode additive and a preparation method and application thereof. BACKGROUND

[0002] Batteries have the characteristics of high capacity and long service life, and are widely used in electronic devices such as mobile phones, notebook computers, electric vehicles, electric vehicles, electric vehicles, electric toys, electric toy cars, electric toy ships, etc. With the step-by-step improvement of the energy density of the battery, the compaction of the positive and negative electrodes is further required. Among them, the negative electrode itself has good conductivity as graphite, which makes it possible to apply the liquid retaining agent with relatively high resistivity to the negative electrode. However, with the improvement of the compaction of the negative electrode, the porosity of the negative electrode sheet is greatly reduced, resulting in poor wettability, which may cause abnormal problems such as lithium precipitation in the center of the electrode sheet.

[0003] Therefore, the present application is proposed. SUMMARY

[0004] One object of the present application is to provide a preparation method of a negative electrode additive, which can improve the wettability of the negative electrode sheet by cooperating the raw materials and steps to obtain a negative electrode additive with good liquid absorption performance.

[0005] Another object of the present application is to provide a negative electrode additive with a hollow structure, suitable particle size and wall thickness, and good physical and chemical properties, which can improve the wettability of the negative electrode.

[0006] Another object of the present application is to provide a negative electrode material layer.

[0007] Another object of the present application is to provide a negative electrode sheet.

[0008] Another object of the present application is to provide a battery.

[0009] In order to achieve the above objects of the present application, the following technical solutions are adopted:

[0010] A preparation method of a negative electrode additive, comprising the following steps:

[0011] Mixing polyvinyl alcohol, a template agent, a phosphate buffer and a soluble calcium source to obtain a first system; adjusting the pH of the first system with lye, and then performing solid-liquid separation to collect the solid to obtain a negative electrode additive.

[0012] In some embodiments, the weight average molecular weight of the polyvinyl alcohol is 10000-55000.

[0013] In some embodiments, the template agent includes phytic acid and / or sodium phytate.

[0014] In some embodiments, the polyvinyl alcohol has a concentration of 4-20 g / L in the phosphate buffer.

[0015] In some embodiments, the template agent has a concentration of 6.6-66 g / L in the first system.

[0016] In some embodiments, the molar ratio of the soluble calcium source to the phosphate buffer is 1:1 in terms of calcium element and phosphate.

[0017] In some embodiments, the phosphate buffer comprises sodium chloride, potassium chloride, disodium hydrogen phosphate, potassium dihydrogen phosphate, and water; and the sodium chloride, potassium chloride, disodium hydrogen phosphate, potassium dihydrogen phosphate, and water are used in a ratio of 80 g:2 g:14.4 g:2.4 g:1000 mL.

[0018] In some embodiments, the rotation speed of the mixing treatment is 200-400 rpm, and the mixing treatment time is 40-70 min.

[0019] In some embodiments, the pH of the first system is adjusted to 7-10 using a lye.

[0020] A negative electrode additive is prepared by the preparation method of the negative electrode additive.

[0021] In some embodiments, the negative electrode additive has a hollow structure; the particle size of the negative electrode additive is 200-400 nm, and the wall thickness is 10-30 nm.

[0022] A negative electrode material layer comprises a negative electrode active material, a conductive agent, a binder, and a negative electrode additive, wherein the negative electrode additive is prepared by the preparation method of the negative electrode additive.

[0023] In some embodiments, the mass ratio of the conductive agent to the negative electrode additive is (1-2):(1-2).

[0024] In some embodiments, in the negative electrode material layer, the mass content of the negative electrode active material is 94%-97%, the mass content of the conductive agent is 0.25%-0.5%, the mass content of the binder is 2.5%-5%, and the mass content of the negative electrode additive is 0.25%-0.5%.

[0025] In some embodiments, the negative electrode active material comprises graphite.

[0026] In some embodiments, the conductive agent comprises conductive carbon black.

[0027] In some embodiments, the binder comprises sodium carboxymethyl cellulose and styrene-butadiene rubber, and the mass ratio of the sodium carboxymethyl cellulose to the styrene-butadiene rubber is (1-1.5):2.

[0028] In some embodiments, the negative electrode material layer is prepared by drying a negative electrode slurry, and the preparation method of the negative electrode slurry specifically comprises: performing first mixing treatment on sodium carboxymethyl cellulose glue solution, the conductive agent, and the negative electrode additive, then performing second mixing treatment on the negative electrode active material and a first solvent, and then performing third mixing treatment on the butadiene-styrene rubber, and adding a second solvent to obtain the negative electrode slurry.

[0029] In some embodiments, the total mass of the sodium carboxymethyl cellulose, the butadiene-styrene rubber, the negative electrode active material, the conductive agent, and the negative electrode additive is R, the mass of the conductive agent accounts for 0.25% to 0.5% of the total mass R, the total mass of the sodium carboxymethyl cellulose and the butadiene-styrene rubber accounts for 1.5% to 4.5% of the total mass R, the mass ratio of the sodium carboxymethyl cellulose to the butadiene-styrene rubber is (1 to 1.5):2, the mass of the negative electrode additive accounts for 0.25% to 0.5% of the total mass R, and the mass of the negative electrode active material accounts for 94% to 97% of the total mass R.

[0030] In some embodiments, the viscosity of the negative electrode slurry is 3000 to 4000 cps.

[0031] In some embodiments, the rotation speed of the first mixing treatment is 3000 to 4000 rpm in rotation and 20 to 100 rpm in revolution, and the time of the first mixing treatment is 1 to 2 hours.

[0032] In some embodiments, the rotation speed of the second mixing treatment is 3000 to 4000 rpm in rotation and 20 to 100 rpm in revolution, and the time of the second mixing treatment is 3 to 4 hours.

[0033] In some embodiments, the rotation speed of the third mixing treatment is 500 to 700 rpm in rotation and 20 to 50 rpm in revolution, and the time of the third mixing treatment is 20 to 35 minutes.

[0034] A negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer arranged on at least one side surface of the negative electrode current collector, and the negative electrode material layer is the negative electrode material layer.

[0035] A battery comprises the negative electrode sheet.

[0036] Compared with the prior art, the present application has the following beneficial effects:

[0037] (1) The preparation method of the negative electrode additive of the present application, the addition of polyethylene can cross-link the template agent to form nanoscale micelles, which reduces the particle size of the final hydroxyapatite nanoparticles. Through the cooperation of each raw material and step, the obtained negative electrode additive has a hollow spherical structure, the particle size is 200-400 nm, the wall thickness is 10-30 nm, the liquid absorption performance is good, and the liquid absorption speed of the negative electrode can be improved, and the wettability of the negative electrode sheet is improved.

[0038] (2) The negative electrode material layer of the present application adds the above-mentioned negative electrode additive, which can replace part of the conductive agent, can be filled between the negative electrode active materials, and can reduce the ratio of being crushed, so as to improve the wettability of the negative electrode material layer.

[0039] (3) The negative electrode sheet of the present application has excellent wettability and good comprehensive electrochemical performance.

[0040] (4) The battery of the present application has improved cycle capacity under the cycle standard of 4C fast charging and does not cause other performance degradation. BRIEF DESCRIPTION OF DRAWINGS

[0041] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings needed in the specific embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings without creative labor on the basis of these drawings.

[0042] Figure 1 The transmission electron microscope image of the negative electrode additive in Example 1 of the present application. DETAILED DESCRIPTION

[0043] The embodiments of the present application will be described in detail below with reference to the examples, but those skilled in the art will understand that the following examples are only used to illustrate the present application, and should not be regarded as limiting the scope of the present application. The specific conditions are not specified in the examples, and are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be obtained by purchase.

[0044] According to one aspect of the present application, the present application relates to a preparation method of a negative electrode additive, comprising the following steps:

[0045] Polyvinyl alcohol (PVA), a template agent, a phosphate buffer and a soluble calcium source are mixed and treated to obtain a first system; the pH of the first system is adjusted by using lye, and then solid-liquid separation is carried out, and the solid is collected to obtain a negative electrode additive.

[0046] The preparation method of the negative electrode additive of the present application, the addition of polyethylene alcohol can cross-link the template agent to form nanoscale micelles, reduce the particle size of the final hydroxyapatite nanoparticles, and through the cooperation of each raw material and step, the obtained negative electrode additive has a hollow spherical structure and good liquid absorption performance, which can improve the liquid absorption speed of the negative electrode and improve the infiltration performance of the negative electrode sheet.

[0047] In some embodiments, the weight average molecular weight of the polyvinyl alcohol is 10000-55000, such as 10000, 12000, 15000, 20000, 25000, 30000, 35000, 40000, 45000, 50000 or 55000, or any range between any two of them. The present application uses polyvinyl alcohol with a suitable weight average molecular weight, which is more conducive to synergistic cooperation with the template agent to ensure the structural characteristics and physical and chemical properties of the final negative electrode additive.

[0048] In some embodiments, the template agent includes phytic acid and / or sodium phytate. The concentration of the template agent in the first system is 6.6-66 g / L, such as 6.6 g / L, 10 g / L, 15 g / L, 20 g / L, 25 g / L, 30 g / L, 50 g / L, 66 g / L, etc.

[0049] In some embodiments, the concentration of the polyvinyl alcohol in the phosphate buffer is 4-20 g / L, such as 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 10 g / L, 12 g / L, 15 g / L, 18 g / L, 20 g / L, etc.

[0050] In some embodiments, the molar ratio of the soluble calcium source to the phosphate buffer, calculated based on calcium element and phosphate, is (1-2):(1-2).

[0051] In some embodiments, the phosphate buffer includes sodium chloride, potassium chloride, disodium hydrogen phosphate, potassium dihydrogen phosphate and water; the amount ratio of the sodium chloride, potassium chloride, disodium hydrogen phosphate, potassium dihydrogen phosphate and water is 80 g:2 g:14.4 g:2.4 g:1000 mL. The preparation method of the phosphate buffer of the present application: 80 g of sodium chloride, 2 g of potassium chloride, 14.4 g of disodium hydrogen phosphate and 2.4 g of potassium dihydrogen phosphate are dissolved in 800 mL of water, oscillated until completely dissolved, and then diluted to 1000 mL to obtain the required phosphate buffer.

[0052] In some embodiments, the rotation speed of the mixing treatment is 200-400 rpm, such as 200 rpm, 250 rpm, 280 rpm, 300 rpm, 330 rpm, 350 rpm, 400 rpm, etc., and the mixing treatment time is 40-70 min, such as 40 min, 50 min, 60 min, 70 min, etc.

[0053] In some embodiments, the pH of the first system is adjusted to 7-10 using a base solution. The base solution includes a sodium hydroxide solution.

[0054] According to another aspect of the present application, the present application also relates to a negative electrode additive prepared by the above-mentioned method for preparing a negative electrode additive. The negative electrode additive of the present application has excellent physicochemical properties and can improve the wettability of the negative electrode sheet. The negative electrode additive has a hollow structure; the particle size of the negative electrode additive is 200-400 nm, such as 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, etc., and the wall thickness is 10-30 nm, such as 10 nm, 12 nm, 15 nm, 20 nm, 22 nm, 25 nm or 30 nm, etc.

[0055] In some embodiments, the particle size of the negative electrode additive is tested by a laser particle size analyzer, and the D50 value is observed. The wall thickness is tested by a transmission electron microscope, and the wall thickness of more than ten particles is measured by taking pictures, and the average value is calculated.

[0056] If a simple phytic acid template agent (without adding polyvinyl alcohol) is used, hydroxyapatite hollow spheres with a diameter of 3-5 are formed, and the wall thickness is 50-100 nm. The hollow particles with large particle size are prone to be damaged in the subsequent rolling process of preparing the negative electrode sheet, thereby affecting the electrochemical performance of the negative electrode sheet.

[0057] According to another aspect of the present application, the present application also relates to a negative electrode material layer comprising a negative electrode active material, a conductive agent, a binder and a negative electrode additive prepared by the above-mentioned method for preparing a negative electrode additive.

[0058] The negative electrode material layer of the present application adds the above-mentioned negative electrode additive, which can replace part of the conductive agent, can be filled between the negative electrode active materials, and can reduce the rate of being crushed, so as to improve the wettability of the negative electrode sheet and ensure the comprehensive electrochemical performance of the negative electrode sheet.

[0059] In some embodiments, the mass ratio of the conductive agent to the negative electrode additive is 1:1. The conductive agent and the negative electrode additive of the present application adopt a suitable mass ratio, which can ensure coordinated action to improve the liquid absorption rate of the negative electrode sheet without causing other performance degradation of the battery.

[0060] In some embodiments, in the negative electrode material layer, the mass content of the negative electrode active material is 94% to 97%, for example, 94%, 95%, 96%, or 97%, etc.; the mass content of the conductive agent is 0.25% to 0.5%, for example, 0.25%, 0.3%, 0.4%, 0.45%, or 0.5%, etc.; the mass content of the binder is 2.5% to 5%, for example, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, etc.; and the mass content of the negative electrode additive is 0.25% to 0.5%, for example, 0.25%, 0.3%, 0.4%, 0.45%, or 0.5%, etc. In the negative electrode material layer of the present application, the negative electrode additive and other components are combined in a suitable ratio, which is more conducive to improving the wettability of the negative electrode sheet and ensuring its comprehensive performance.

[0061] In some embodiments, the negative electrode active material comprises graphite. The graphite comprises 4C graphite and / or 1C graphite.

[0062] In some embodiments, the conductive agent comprises conductive carbon black.

[0063] In some embodiments, the binder comprises sodium carboxymethyl cellulose and styrene-butadiene rubber, and the mass ratio of the sodium carboxymethyl cellulose to the styrene-butadiene rubber is (1 to 1.5):2, for example, 1:2, 1.1:2, 1:1.3, 1:1.4, or 1:1.5, etc.

[0064] In some embodiments, the negative electrode material layer is prepared by drying a negative electrode slurry. The preparation method of the negative electrode slurry specifically comprises: performing first mixing treatment on sodium carboxymethyl cellulose glue, the conductive agent, and the negative electrode additive, then performing second mixing treatment on the negative electrode active material and a first solvent, then performing third mixing treatment on styrene-butadiene rubber, and adding a second solvent to obtain the negative electrode slurry. The preparation method of the negative electrode material layer of the present application is more conducive to ensuring the performance of the negative electrode slurry and improving the coating effect of the negative electrode sheet and the comprehensive performance of the film layer through the cooperation of each step.

[0065] In some embodiments, the total mass of the sodium carboxymethyl cellulose, the styrene-butadiene rubber, the negative electrode active material, the conductive agent, and the negative electrode additive is R, the mass of the conductive agent accounts for 0.25% to 0.5% of the total mass R, the total mass of the sodium carboxymethyl cellulose and the styrene-butadiene rubber accounts for 1.5% to 4.5% of the total mass R, the mass ratio of the sodium carboxymethyl cellulose to the styrene-butadiene rubber is (1 to 1.5):2, the mass of the negative electrode additive accounts for 0.25% to 0.5% of the total mass R, and the mass of the negative electrode active material accounts for 94% to 97% of the total mass R.

[0066] In some embodiments, the concentration of the sodium carboxymethyl cellulose glue solution is 1.1% to 1.3%. In some embodiments, the concentration of the sodium carboxymethyl cellulose glue solution is 1.2%.

[0067] In some embodiments, the first solvent comprises water. The first solvent comprises 15% to 25% of the total mass of the slurry, for example 20%.

[0068] In some embodiments, the second solvent comprises water. The second solvent is added to adjust the viscosity of the negative electrode slurry to a desired viscosity.

[0069] In some embodiments, the viscosity of the negative electrode slurry is 3000 to 4000 cps, for example 3000 cps, 3200 cps, 3500 cps, 3700 cps, 3800 cps, 3900 cps, 4000 cps, etc.

[0070] In some embodiments, the rotation speed of the first mixing process is 3000 to 4000 rpm (for example 3000 rpm, 3400 rpm, 3500 rpm, 3800 rpm, etc.) in the self-rotation direction and 20 to 100 rpm (for example 20 rpm, 30 rpm, 50 rpm, 80 rpm, or 100 rpm) in the revolution direction, and the time of the first mixing process is 1 to 2 hours (for example 1 hour, 1.5 hours, or 2 hours, etc.).

[0071] In some embodiments, the rotation speed of the second mixing process is 3000 to 4000 rpm (for example 3000 rpm, 3500 rpm, 4000 rpm, etc.) in the self-rotation direction and 20 to 100 rpm (for example 20 rpm, 50 rpm, 100 rpm, etc.) in the revolution direction, and the time of the second mixing process is 3 to 4 hours (for example 3 hours, 3.5 hours, or 4 hours, etc.).

[0072] In some embodiments, the rotation speed of the third mixing process is 500 to 700 rpm (for example 500 rpm, 550 rpm, 600 rpm, etc.) in the self-rotation direction and 20 to 50 rpm (for example 20 rpm, 30 rpm, 50 rpm, etc.) in the revolution direction, and the time of the third mixing process is 20 to 35 minutes (for example 20 minutes, 25 minutes, 30 minutes, or 35 minutes, etc.).

[0073] The present application adopts appropriate first mixing conditions, second mixing conditions, and third mixing conditions to ensure the sufficient mixing of the materials and the performance of the slurry.

[0074] According to another aspect of the present application, the present application also relates to a negative electrode sheet, comprising a negative electrode current collector and a negative electrode material layer arranged on at least one side surface of the negative electrode current collector, wherein the negative electrode material layer is the negative electrode material layer according to the present application.

[0075] The negative electrode sheet of the present application has excellent wettability and good comprehensive electrochemical performance.

[0076] According to another aspect of the present application, the present application also relates to a battery comprising the above negative electrode sheet.

[0077] The battery of the present application has improved cycle capacity and does not cause other performance degradation under the cycle standard of 4C fast charging. In some embodiments, the battery comprises the above negative electrode sheet, positive electrode sheet, separator and electrolyte.

[0078] The following further explains and describes with specific examples and comparative examples.

[0079] Example 1

[0080] A preparation method of a negative electrode additive, comprising the following steps:

[0081] (1) Dissolve 8 g / L of PVA with MW = 10000 in a phosphate buffer, stir at 300 rpm for 0.5 h, add sodium phytate to make the concentration of sodium phytate in the solution 66 g / L, stir at 300 rpm for 0.5 h, and add calcium chloride with equal molar amount of phosphate in the phosphate buffer to obtain a first system.

[0082] (2) Neutralize the first system using 0.5% mol / L NaOH to adjust to pH = 7.

[0083] (3) Filter and separate the precipitate, wash with water for three times to obtain the negative electrode additive.

[0084] The transmission electron microscope image of the negative electrode additive in this example is shown in Figure 1 .

[0085] A preparation method of a negative electrode sheet, comprising the following steps:

[0086] The sodium carboxymethyl cellulose glue solution, the conductive agent and the negative electrode additive are subjected to first mixing treatment, the rotating speed of the first mixing treatment is 3800 rpm, the time of the first mixing treatment is 1.5 h; then the negative electrode active layer material and the first solvent are added to perform second mixing treatment, the rotating speed of the second mixing treatment is 3200 rpm, the time of the second mixing treatment is 3.5 h; then the butadiene styrene rubber is added to perform third mixing treatment, the rotating speed of the third mixing treatment is 600 rpm, the time of the third mixing treatment is 30 min; the second solvent is added to adjust the viscosity of the slurry to 3500 cps, and the negative electrode slurry is obtained. The mass of the negative electrode active material accounts for 96% of the total mass R of the binder (sodium carboxymethyl cellulose and butadiene styrene rubber), the negative electrode active material, the conductive agent and the negative electrode additive, the mass of the conductive agent accounts for 0.35% of the total mass R, the mass content of the negative electrode additive is 0.35%, the mass of the sodium carboxymethyl cellulose accounts for 1.3% of the total mass R, and the mass of the butadiene styrene rubber accounts for 2% of the total mass R; the negative electrode active material is 4C graphite, the conductive agent is conductive carbon black, and the first solvent and the second solvent are deionized water.

[0087] The negative electrode slurry is coated on both sides of the copper foil, dried at 65 DEG C for 2 min, and a negative electrode sheet is obtained.

[0088] Example 2

[0089] A preparation method of a negative electrode additive, which is different from that of example 1.

[0090] The molecular weight of PVA is 50000.

[0091] A preparation method of a negative electrode sheet, which is different from that of example 1, except that the negative electrode additive in the embodiment is used.

[0092] Example 3

[0093] A preparation method of a negative electrode sheet, which is different from that of example 1.

[0094] The molecular weight of PVA is 30000.

[0095] A preparation method of a negative electrode sheet, which is different from that of example 1, except that the negative electrode additive in the embodiment is used.

[0096] Example 4

[0097] A preparation method of a negative electrode sheet, which is different from that of example 2.

[0098] The negative electrode active material is 1C graphite.

[0099] Example 5

[0100] A preparation method of a negative electrode additive, comprising the following steps:

[0101] (1) Dissolve 8 g / L of PVA with MW = 20000 in a phosphate buffer, stir at 250 rpm for 35 min, and add sodium phytate to make the concentration of sodium phytate in the solution 66 g / mol / L; stir at 250 rpm for 35 min, and add calcium chloride with the same molar amount of phosphate in the phosphate buffer to obtain the first system.

[0102] (2) Neutralize the first system using 0.5% mol / L NaOH to adjust to pH = 7.

[0103] (3) Filter and separate the precipitate, and wash with water three times to obtain the negative electrode additive.

[0104] The preparation method of the negative electrode sheet comprises the following steps:

[0105] The sodium carboxymethyl cellulose glue solution, the conductive agent, and the negative electrode additive are subjected to first mixing treatment, the rotating speed of the first mixing treatment is 4000 rpm, and the time of the first mixing treatment is 2 h; then the negative electrode active layer material and the first solvent are added for second mixing treatment, the rotating speed of the second mixing treatment is 3500 rpm, and the time of the second mixing treatment is 3 h; then butadiene styrene rubber is added for third mixing treatment, the rotating speed of the third mixing treatment is 500 rpm, and the time of the third mixing treatment is 20 min; the second solvent is added to adjust the viscosity of the slurry to 3800 cps to obtain negative electrode slurry. The mass of the negative electrode active material accounts for 96% of the total mass R of the binder (sodium carboxymethyl cellulose and butadiene styrene rubber), the negative electrode active material, the conductive agent, and the negative electrode additive, the mass of the conductive agent accounts for 0.5% of the total mass R, the mass content of the negative electrode additive is 0.5%, the mass of the sodium carboxymethyl cellulose accounts for 1% of the total mass R, and the mass of the butadiene styrene rubber accounts for 2% of the total mass R; the negative electrode active material is 4C graphite, the conductive agent is conductive carbon black, and the first solvent and the second solvent are deionized water.

[0106] The negative electrode slurry is coated on both sides of the copper foil, dried at 50°C for 2 min to obtain the negative electrode sheet.

[0107] Example 6

[0108] A preparation method of a negative electrode additive comprises the following steps:

[0109] (1) Dissolve 16 g / L of PVA with MW = 20000 in a phosphate buffer, stir at 350 rpm for 20 min, and add sodium phytate to make the concentration of sodium phytate in the solution 33 g / L, stir at 350 rpm for 20 min, and add calcium chloride with the same molar amount of phosphate in the phosphate buffer to obtain the first system.

[0110] (2) Neutralize the first system using 0.5% mol / L NaOH to adjust to pH = 7.

[0111] (3) The precipitate is separated by filtration and washed with water three times to obtain the negative electrode additive.

[0112] The preparation method of the negative electrode sheet comprises the following steps:

[0113] The sodium carboxymethyl cellulose glue solution, the conductive agent and the negative electrode additive are subjected to first mixing treatment, the rotating speed of the first mixing treatment is 3600 rpm, and the time of the first mixing treatment is 3 h; then the negative electrode active layer material and the first solvent are added to perform second mixing treatment, the rotating speed of the second mixing treatment is 3000 rpm, and the time of the second mixing treatment is 4 h; then butadiene styrene rubber is added to perform third mixing treatment, the rotating speed of the third mixing treatment is 700 rpm, and the time of the third mixing treatment is 35 min; the second solvent is added to adjust the viscosity of the slurry to 3200 cps, and the negative electrode slurry is obtained. The mass of the negative electrode active material accounts for 95.5% of the total mass R of the binder (sodium carboxymethyl cellulose and butadiene styrene rubber), the negative electrode active material, the conductive agent and the negative electrode additive, the mass of the conductive agent accounts for 0.5% of the total mass R, the mass content of the negative electrode additive is 0.5%, the mass of the sodium carboxymethyl cellulose accounts for 1.5% of the total mass R, and the mass of the butadiene styrene rubber accounts for 2% of the total mass R; the negative electrode active material is 4C graphite, the conductive agent is conductive carbon black, and the first solvent and the second solvent are deionized water.

[0114] The negative electrode slurry is coated on both sides of the copper foil, dried at 80℃ for 2 min, and the negative electrode sheet is obtained.

[0115] Comparative Example 1

[0116] The preparation method of the negative electrode sheet is different from that of Example 1 in that:

[0117] No negative electrode additive is added in the preparation process, and the mass of the conductive agent accounts for 0.7% of the total mass R.

[0118] Experimental Example

[0119] The negative electrode sheets in the examples and the comparative example are respectively prepared into batteries, and the specific method comprises:

[0120] Preparation of the positive electrode sheet: PVDF and NMP are added to a double-planetary stirrer, and the glue is beaten at medium speed for 3 h to obtain a PVDF glue solution. The PVDF glue solution and SP are added to the double-planetary stirrer, and dispersed at medium speed for 1-2 h. NCM811 is added in two times, and NMP is added each time. The high-speed dispersion is performed for 2 h each time. After the end, an appropriate amount of NMP is added to adjust the viscosity of the slurry to 3500 cps. The slurry is coated on both sides of the aluminum foil by transfer coating, and the positive electrode sheet is obtained by baking in an oven at a temperature of 100℃ for 2 min. The above-mentioned positive electrode sheet, negative electrode sheet, separator and electrolyte are assembled to obtain a battery.

[0121] The negative electrode sheets of each embodiment and comparative example are subjected to wettability test, and the test conditions include: dropping electrolyte on the negative electrode sheet at 25 DEG C, and recording the time required for the electrolyte to be completely absorbed.

[0122] The negative electrode sheets of each embodiment and comparative example are subjected to resistivity test. The resistivity test method is to form a series circuit by using Kelvin four-wire plus controllable upper and lower plane double probes for test, and the electrode sheet wafer is placed on the sample support jig of the electrode sheet resistivity meter, and the test is conducted after the cabin door is closed.

[0123] The batteries of each embodiment and comparative example are subjected to electrochemical performance test.

[0124] The test results are shown in Table 1.

[0125] Table 1 test results

[0126]

[0127] As shown in Table 1, the negative electrode additive obtained by the method has excellent liquid absorption performance, and the negative electrode sheet prepared by replacing part of the conductive agent with the negative electrode additive has excellent wettability.

[0128] In Examples 1-2, after the negative electrode additive replaces the carbon black in equal amount, the resistivity of the negative electrode sheet slightly increases, and the electrical performance does not deteriorate, and the 4C normal temperature cycle 600cls is improved by 0.4%-0.7%, and the 4C, 45 DEG C cycle 600cls is improved by 0.8%-1.2%.

[0129] In Example 3, different molecular weight PVA is used to obtain the negative electrode additive product, and the short-term performance is basically the same as that of Examples 1-2, wherein the Example 3 is slightly improved by 0.3% at 25 DEG C, 4C rate cycle 600cls, and improved by 0.4% at 45 DEG C, 4C rate cycle 600cls.

[0130] Examples 5-6 use different PVA and phytic acid ratios compared with Example 2, and the short-term performance and 4C rate cycle of the negative electrode additive product are basically the same as those of Example 2.

[0131] In Example 4, after the negative electrode additive replaces the carbon black in equal amount, the resistivity of the negative electrode sheet slightly increases, and the electrical performance does not deteriorate. The cycle performance at normal temperature and 45 DEG C is slightly improved by 0.2%-0.4%.

[0132] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions recorded in the above embodiments can still be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a battery negative electrode additive, characterized in that: The following steps are involved: polyvinyl alcohol, a template, a phosphate buffer, and a soluble calcium source are mixed to obtain a first system; an alkali solution is used to adjust the pH of the first system, and then solid-liquid separation is performed to collect solids to obtain a battery negative electrode additive; The template comprises phytic acid and / or sodium phytate; The battery negative electrode additive has a hollow structure; the particle size of the battery negative electrode additive is 200-400 nm, and the wall thickness is 10-30 nm; The concentration of the template in the first system is 6.6-66 g / L; The molar ratio of the soluble calcium source to the phosphate buffer, calculated as calcium element and phosphate radical, is 1:1; The battery negative electrode additive is hydroxyapatite.

2. The method for preparing a negative electrode additive for a battery according to claim 1, wherein: Contains at least one of the following features (1) to (5): (1) The weight average molecular weight of the polyvinyl alcohol is 10,000 to 55,000; (2) The concentration of the polyvinyl alcohol in the phosphate buffer is 4-20 g / L; (3) The phosphate buffer solution comprises sodium chloride, potassium chloride, disodium hydrogen phosphate, potassium dihydrogen phosphate and water; the dosage ratio of the sodium chloride, potassium chloride, disodium hydrogen phosphate, potassium dihydrogen phosphate and water is 80g:2g:14.4g:2.4g:1000mL; (4) The mixing process is performed at a rotation speed of 200 to 400 rpm and for a time of 40 to 70 min; (5) Using alkaline solution to adjust the pH of the first system to 7-10.

3. A battery negative electrode additive, characterized in that: The negative electrode additive is prepared by the preparation method of the battery negative electrode additive according to claim 1 or 2.

4. A negative electrode material layer, characterized in that: The invention comprises a negative electrode active material, a conductive agent, a binder and a battery negative electrode additive, wherein the battery negative electrode additive is prepared by the preparation method of the battery negative electrode additive according to claim 1 or 2.

5. The negative electrode material layer according to claim 4, characterized in that Contains at least one of the following features (1) to (5): (1) The mass ratio of the conductive agent to the battery negative electrode additive is (1-2): (1-2); (2) In the negative electrode material layer, the mass content of the negative electrode active material is 94% to 97%, the mass content of the conductive agent is 0.25% to 0.5%, the mass content of the binder is 2.5% to 5%, and the mass content of the battery negative electrode additive is 0.25% to 0.5%; (3) The negative electrode active material includes graphite; (4) The conductive agent includes conductive carbon black; (5) The binder comprises sodium carboxymethyl cellulose and styrene-butadiene rubber, and the mass ratio of the sodium carboxymethyl cellulose to the styrene-butadiene rubber is (1-1.5):

2.

6. The negative electrode material layer according to claim 4, characterized in that The negative electrode material layer is prepared by drying the negative electrode slurry. The preparation method of the negative electrode slurry specifically includes: performing a first mixing treatment on sodium carboxymethyl cellulose glue, the conductive agent, and the battery negative electrode additive, then adding the negative electrode active material and a first solvent for a second mixing treatment, then adding styrene-butadiene rubber for a third mixing treatment, and adding a second solvent to obtain the negative electrode slurry.

7. The negative electrode material layer according to claim 6, characterized in that Contains at least one of the following features (1) to (5): (1) Assuming that the total mass of the sodium carboxymethyl cellulose, styrene butadiene rubber, negative electrode active material, conductive agent and battery negative electrode additive is R, the mass of the conductive agent accounts for 0.25% to 0.5% of the total mass R, the total mass of the sodium carboxymethyl cellulose and styrene butadiene rubber accounts for 2.5% to 5% of the total mass R, the mass ratio of the sodium carboxymethyl cellulose to styrene butadiene rubber is (1 to 1.5):2, the mass of the battery negative electrode additive accounts for 0.25% to 0.5% of the total mass R, and the mass of the negative electrode active material accounts for 94% to 97% of the total mass R; (2) The viscosity of the negative electrode slurry is 3000~4000cps; (3) The rotation speed of the first mixing process is: 3000-4000 rpm for rotation and 20-100 rpm for revolution. The time of the first mixing process is 1-2 hours. (4) The rotation speed of the second mixing process is: 3000~4000 rpm for rotation and 20~100 rpm for revolution. The time of the second mixing process is 3~4 hours. (5) The rotation speed of the third mixing process is: 500-700 rpm for rotation and 20-50 rpm for revolution. The time of the third mixing process is 20-35 min.

8. A negative electrode sheet, characterized in that: The negative electrode material layer comprises a negative electrode current collector and a negative electrode material layer provided on at least one side of the negative electrode current collector, wherein the negative electrode material layer is the negative electrode material layer according to any one of claims 4 to 7.

9. A battery, characterized in that: The negative electrode sheet according to claim 8 is included.

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