Composite anode materials and their preparation methods, and anode sheets and batteries

Abstract

This invention relates to the field of anode material technology, and discloses a composite anode material, its preparation method, and anode sheet and battery. The composite anode material includes silicon-carbon material and an interface modifier. The silicon-carbon material also contains oxygen, with an oxygen content of 0.1-5 wt% based on the total mass of the silicon-carbon material. The interface modifier has the chemical composition A. a B b H c O d Element A is selected from one or more of Mg, Al, and Ca; element B is selected from one or more of S, P, and C; H is hydrogen; and O is oxygen. At least a portion of the oxygen in the silicon-carbon material forms chemical bonds with element A in the interface modifier. The composite negative electrode material of this invention can utilize chemical bonds to tightly connect the silicon-carbon material and the conductive agent together, thereby reducing electrical contact loss during cycling and significantly improving the cycle capacity retention rate of lithium-ion batteries.

Description

Technical Field

[0001] This invention relates to negative electrode materials, specifically to a composite negative electrode material, its preparation method, and a negative electrode sheet and battery. Background Technology

[0002] As is well known, silicon anode materials suffer from significant volume expansion during charge and discharge. This massive volume expansion not only leads to silicon material cracking, causing continuous electrolyte consumption, but also greatly accelerates the mechanical fracture of the electrode, resulting in a loss of electrical contact between the silicon material and the conductive agent. The capacity loss due to this loss of electrical contact accounts for a considerable portion of the cycle capacity loss of silicon materials. To mitigate the capacity loss caused by this lack of electrical contact, organic materials can be used to coat and modify the silicon material. Although organic materials can adhere well to the silicon surface, the significant volume changes during charge and discharge cycles still cause the organic materials to detach from the silicon surface, creating physical gaps that disrupt the conductive network and ultimately lead to capacity loss.

[0003] Therefore, there is an urgent need to provide a silicon anode material that can enhance the bonding strength with conductive agents. Summary of the Invention

[0004] The purpose of this invention is to overcome the problem of poor adhesion between conductive agents and silicon materials in the prior art, and to provide a composite negative electrode material, its preparation method, and a negative electrode and battery.

[0005] To achieve the above objectives, a first aspect of the present invention provides a composite anode material, wherein the anode material comprises a silicon-carbon material and an interface modifier; wherein the silicon-carbon material further contains oxygen, and the oxygen content is 0.1-5 wt% based on the total mass of the silicon-carbon material; the interface modifier has a chemical composition of A. a B b H c O d Element A is selected from one or more of Mg, Al, and Ca; element B is selected from one or more of S, P, and C; H is hydrogen; O is oxygen; the value of a is 1≤a≤3; the value of b is 1≤b≤3; the value of c is 0≤c≤6; and the value of d is 4≤d≤12. At least a portion of the oxygen in the silicon-carbon material forms chemical bonds with element A in the interface modifier.

[0006] A second aspect of the present invention provides a method for preparing a composite anode material, wherein the method comprises: mixing and reacting the silicon-carbon material described in the first aspect of the present invention, the interface modifier, and optionally the modifying accelerator to obtain the composite anode material.

[0007] A third aspect of the present invention provides a negative electrode sheet, the negative electrode sheet comprising a current collector and a coating layer coated on the current collector, the coating layer comprising a composite negative electrode material, optionally graphite, a conductive agent, and a binder; wherein the composite negative electrode material is the composite negative electrode material described in the first aspect of the present invention or a composite negative electrode material prepared using the preparation method described in the second aspect of the present invention.

[0008] A fourth aspect of the present invention provides a battery comprising the negative electrode sheet described in the third aspect of the present invention.

[0009] The beneficial technical effects achieved by the present invention through the above technical solution are as follows:

[0010] 1) In the composite negative electrode material provided in this invention, element A in the interface modifier can form a chemical bond with oxygen in the silicon-carbon material, and element B can form a chemical bond with hydroxyl groups in the conductive agent added during electrode preparation. Thus, when preparing a negative electrode sheet using the composite negative electrode material of this invention, the composite negative electrode material can form a better bonding strength with the conductive agent. During the charging and discharging process, this negative electrode sheet can avoid or reduce the shedding of the conductive agent from the silicon material surface, preventing the physical gaps formed by the detachment of the conductive agent from damaging the conductive network and causing a loss of contact, thereby improving the cycle capacity retention rate of the lithium-ion battery.

[0011] 2) The preparation method of the composite negative electrode material provided in this invention is simple to operate, the interface modifier used is a general chemical reagent, which is inexpensive and has low production cost. It also has no negative impact on the electrochemical reaction and is suitable for industrial promotion. Attached Figure Description

[0012] Figure 1 This is the XPS-Mg spectrum of the composite anode material prepared in Example 1;

[0013] Figure 2 This is the XPS-S spectrum of the electrode prepared from the composite negative electrode material in Example 1;

[0014] Figure 3 The graph shows the room temperature cycling curves of the lithium-ion batteries prepared using Example 1 and Comparative Example 1. Detailed Implementation

[0015] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0016] A first aspect of the present invention provides a composite anode material, the anode material comprising a silicon-carbon material and an interface modifier; wherein the silicon-carbon material further contains oxygen, and the oxygen content is 0.1-5 wt% based on the total mass of the silicon-carbon material; the interface modifier has a chemical composition of A. a B b H c O d Element A is selected from one or more of Mg, Al, and Ca; element B is selected from one or more of S, P, and C; H is hydrogen; O is oxygen; the value of a is 1≤a≤3; the value of b is 1≤b≤3; the value of c is 0≤c≤6; and the value of d is 4≤d≤12. At least a portion of the oxygen in the silicon-carbon material forms chemical bonds with element A in the interface modifier.

[0017] In a preferred embodiment, the silicon-carbon material contains 30-60 wt% silicon and 35-69.9 wt% carbon, based on the total mass of the silicon-carbon material.

[0018] In this invention, the silicon-carbon material is a composite material of silicon and carbon containing a small amount of oxygen. Silicon undergoes a lithiation reaction with lithium ions, providing high specific capacity; the carbon material has high conductivity, which can improve the ion transfer rate on the electrode material surface, thereby increasing the rate performance of the lithium-ion battery; simultaneously, the carbon substrate can buffer the expansion and pulverization of silicon particles, effectively extending the battery's cycle life. Therefore, appropriate silicon and carbon content helps to improve the specific capacity and cycle stability of the silicon-carbon material.

[0019] In a preferred embodiment, based on the total mass of the silicon-carbon material, the oxygen content is 0.5-3 wt%, the silicon content is 44-55 wt%, and the carbon content is 42-55.5 wt%. At this point, the mass percentages of silicon and carbon are roughly equal, which not only effectively balances the specific capacity and cycle life of the composite anode material but also ensures that the silicon particles are uniformly dispersed within the carbon framework (since the density of silicon is greater than that of carbon, when the masses of silicon and carbon are roughly equal, the volume of carbon is greater than that of silicon). From the perspective of the overall material structure, when uniformly dispersed silicon particles undergo the lithiation reaction, the expansion force on the material as a whole is relatively dispersed, which reduces or alleviates the pulverization phenomenon caused by concentrated expansion of silicon particles, further increasing the cycle stability of the material.

[0020] In this invention, when the oxygen content is >5 wt%, the surface impedance of the composite anode material is too high, affecting the cycle performance of the lithium-ion battery; when the oxygen content is <0.1 wt%, the active sites for the silicon-carbon material to bond with the interface modifier are too few, resulting in reduced bonding strength. When the oxygen content is between 0.5-3 wt%, the composite anode material exhibits optimal cycle performance and low surface impedance.

[0021] In a preferred embodiment, the silicon in the silicon-carbon material comprises amorphous silicon, and the average particle size of the silicon is 0.5-15 nm, preferably 0.8-2 nm.

[0022] In a preferred embodiment, the silicon in the silicon-carbon material further includes silicon grains.

[0023] In this invention, silicon has a small average particle size and a large specific surface area, resulting in numerous contact points for self-reaction with lithium. Furthermore, smaller particles have a smaller volume expansion rate. From the perspective of the overall material structure, uniformly dispersed silicon particles have a small particle size, resulting in a relatively smaller expansion force on the material as a whole. This reduces or alleviates the pulverization caused by concentrated expansion of silicon particles, further increasing the cycling stability of the material.

[0024] In a preferred embodiment, element A is selected from Mg and / or Al, preferably Mg; element B is selected from S and / or P, preferably S.

[0025] In a preferred embodiment, the interface modifier is selected from one or more of MgSO4, AlPO4, CaSO4, Mg(HSO4)2, Mg(H2PO4)2, MgHPO4, Al(HSO4)3, Al(H2PO4)3, Al2(HPO4)3, Al3(SO4)2, and Mg3(PO4)2, preferably MgSO4 and / or Mg3(PO4)2.

[0026] In a preferred embodiment, the content of the silicon-carbon material is 97.5-99.9 wt% and the content of the interface modifier is 0.1-2.5 wt% based on the total mass of the composite anode material.

[0027] In a preferred embodiment, the negative electrode material further includes a modifying accelerator, wherein the modifying accelerator is selected from one or more of ammonium chloride, sodium carbonate, sodium bicarbonate, and sodium acetate, preferably sodium carbonate and / or sodium acetate.

[0028] In this invention, a small amount of modifying accelerator can make it easier for the interface modifier to bond with silicon-carbon materials and conductive agents, thereby further improving the impedance performance of the composite anode material.

[0029] In a preferred embodiment, based on the total mass of the composite anode material, the content of the silicon-carbon material is 91-99.85 wt%, preferably 96.62-99.38 wt%; the content of the interface modifier is 0.05-6.5 wt%, preferably 0.12-2.9 wt%; and the content of the modification accelerator is 0.1-2.5 wt%, preferably 0.48-1.95 wt%.

[0030] In this invention, the content of each component in the composite anode material is based on the amount of feed. When the content of silicon-carbon material is 96.62-99.38 wt%, the content of interface modifier is 0.12-2.9 wt%, and the content of modification accelerator is 0.48-1.95 wt%, the composite anode material can possess the highest specific capacity and the best structural stability, thereby providing the battery with higher energy density and cycle life.

[0031] In a preferred embodiment, the average particle size of silicon in the composite anode material is 0.5-15 nm, preferably 0.8-2 nm. Silicon within this particle size range can alleviate the lithiation scale effect of silicon, thereby mitigating lithiation expansion and increasing the cycle life of the composite anode material.

[0032] In this invention, the average particle size of silicon in the composite anode material is basically the same as the average particle size of silicon in the silicon-carbon raw material used to prepare the composite anode material.

[0033] A second aspect of the present invention provides a method for preparing a composite anode material, wherein the method comprises: mixing and reacting the silicon-carbon material described in the first aspect of the present invention, the interface modifier, and optionally the modifying accelerator to obtain the composite anode material.

[0034] In this invention, the preparation method of the composite anode material can be to mix and react the silicon-carbon material and the interface modifier described in the first aspect of this invention to obtain the composite anode material, or to mix and react the silicon-carbon material, the interface modifier and the modification accelerator described in the first aspect of this invention to obtain the composite anode material.

[0035] In a preferred embodiment, the mixing reaction includes a wet mixing reaction and / or a dry ball milling reaction; wherein the wet mixing reaction includes: adding silicon carbon material, an interface modifier, and optionally a modifying accelerator to an alcohol solution, stirring at 40-60°C for 12-48 hours, followed by filtration and pulverization to obtain a composite anode material; the dry ball milling reaction includes: mixing silicon carbon material, an interface modifier, and optionally a modifying accelerator with grinding balls, and ball milling at a speed of 1000-3000 r / min for 1-10 hours to obtain a composite anode material. The ball milling process generates heat, which is beneficial to the reaction between the silicon carbon material, the interface modifier, and the optionally modifying accelerator.

[0036] A third aspect of the present invention provides a negative electrode sheet, the negative electrode sheet comprising a current collector and a coating layer coated on the current collector, the coating layer comprising a composite negative electrode material, optionally graphite, a conductive agent, and a binder; wherein the composite negative electrode material is the composite negative electrode material described in the first aspect of the present invention or a composite negative electrode material prepared using the preparation method described in the second aspect of the present invention.

[0037] In this invention, element A in the interface modifier has a positive charge and can form covalent bonds with oxygen atoms in the silicon-carbon material, enhancing the connection between the silicon-carbon material and the interface modifier. Element B atoms have unpaired lone pairs of electrons in their outermost shell and have low electronegativity, readily donating electrons and forming hydrogen bonds with hydroxyl groups on the conductive agent. Therefore, the interface modifier acts as a bridge in this invention, directly connecting the conductive agent and the silicon-carbon material through chemical bonds, enhancing the connection strength between the conductive agent and the silicon-carbon material, and reducing electrical contact loss during cycling. Furthermore, the interface modifier selected in this invention does not react with other substances in the battery and will not affect the battery's performance.

[0038] In a preferred embodiment, the B element in the composite negative electrode material is bonded to the hydroxyl group in the conductive agent.

[0039] In a preferred embodiment, the dressing layer comprises 1 part by weight of composite negative electrode material, 0-100 parts by weight of graphite, 0.1-1 parts by weight of conductive agent and 0.5-1.5 parts by weight of binder.

[0040] In a preferred embodiment, the dressing layer comprises 1 part by weight of composite negative electrode material, 8-30 parts by weight of graphite, 0.4-0.6 parts by weight of conductive agent and 0.8-1.2 parts by weight of binder.

[0041] In a preferred embodiment, the conductive agent comprises conductive carbon black and carbon nanotubes; more preferably, the mass ratio of the conductive carbon black to the carbon nanotubes is 1:0.05-0.25. The binder includes, but is not limited to, polyacrylic acid, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium polyacrylate and its modifiers, as well as mixed binders composed of the aforementioned binders in various proportions.

[0042] The present invention will be described in detail below through embodiments.

[0043] The silicon-carbon materials used in the examples and comparative examples were purchased from Group 14 Technologies, Inc., USA. Specifically, silicon-carbon material 1 contained 2.6 wt% oxygen, 49.4 wt% silicon, and 48 wt% carbon. The silicon in the silicon-carbon material included amorphous silicon, and the average particle size of the silicon was 1.0 nm.

[0044] The oxygen content in silicon-carbon material 2 is 0.5 wt%, the silicon content is 49 wt%, and the carbon content is 55.5 wt%. The silicon in silicon-carbon material includes amorphous silicon, and the average particle size of silicon is 1.0 nm.

[0045] The oxygen content in silicon-carbon material 3 is 5 wt%, the silicon content is 48 wt%, and the carbon content is 47 wt%. The silicon in the silicon-carbon material includes shaped silicon, and the average particle size of the silicon is 2.0 nm.

[0046] The oxygen content in silicon-carbon material 4 is 0.15 wt%, the silicon content is 50 wt%, and the carbon content is 49.85 wt%. The silicon in silicon-carbon material includes amorphous silicon, and the average particle size of silicon is 15 nm.

[0047] The oxygen content in silicon-carbon material 5 is 8 wt%, the silicon content is 50 wt%, and the carbon content is 42 wt%. The silicon in silicon-carbon material includes amorphous silicon, and the average particle size of silicon is 18 nm.

[0048] Example 1

[0049] 2 kg of silicon-carbon material 1, 10 g of interface modifier magnesium sulfate and 10 g of modifier accelerator sodium carbonate were added to 10 L of anhydrous ethanol and stirred at 400 r / min at 55 °C for 4 h. After filtration and drying, the composite anode material was obtained.

[0050] Example 2

[0051] Similar to Example 1, except that 2.5g of magnesium sulfate, an interface modifier, and 10g of sodium carbonate, a modification accelerator, were added.

[0052] Example 3

[0053] Similar to Example 1, except that 60g of magnesium sulfate, an interface modifier, and 10g of sodium carbonate, a modifier accelerator, were added.

[0054] Example 4

[0055] Similar to Example 1, except that 1g of magnesium sulfate, an interface modifier, and 10g of sodium carbonate, a modifier accelerator, were added.

[0056] Example 5

[0057] Similar to Example 1, except that 90g of magnesium sulfate, an interface modifier, and 10g of sodium carbonate, a modifier accelerator, were added.

[0058] Example 6

[0059] 2 kg of silicon-carbon material, 1.5 g of interface modifier magnesium phosphate, and 25 g of modifier accelerator sodium acetate were added to 10 L of anhydrous ethanol and stirred at 400 r / min at 55 °C for 4 h. After filtration and drying, the composite anode material was obtained.

[0060] Example 7

[0061] Same as Example 6, except that no modification accelerator is added.

[0062] Example 8

[0063] Similar to Example 6, except that silicon-carbon material 1 is replaced with silicon-carbon material 2 of equal mass.

[0064] Example 9

[0065] Similar to Example 6, except that silicon-carbon material 1 is replaced with silicon-carbon material 3 of equal mass.

[0066] Example 10

[0067] Similar to Example 6, except that silicon-carbon material 1 is replaced with silicon-carbon material 4 of equal mass.

[0068] Example 11

[0069] 2 kg of silicon carbide material, 10 g of magnesium sulfate as an interface modifier, and 40 g of sodium carbonate as a modification accelerator were mixed and placed into a high-energy ball mill jar. 200 g of zirconia grinding balls with diameters of 0.2 mm, 0.5 mm, and 1 mm (the mass ratio of the 0.2 mm, 0.5 mm, and 1 mm zirconia grinding balls was 1:3:5) were added to the ball mill jar. After sealing, the jar was ball-milled at a speed of 2000 r / min for 5 h at a ball milling temperature of 50 °C. After separating the zirconia grinding balls, the composite anode material was obtained.

[0070] Comparative Example 1

[0071] Same as Example 7, except that no interface modifier was added.

[0072] Comparative Example 2

[0073] Same as Example 7, except that silicon-carbon material 1 is replaced with silicon-carbon material 5 of equal mass.

[0074] Comparative Example 3

[0075] Same as Example 7, except that the interface modifier is an equal mass of potassium sulfate.

[0076] Comparative Example 4

[0077] Same as Example 7, except that the interface modifier is an equal mass of magnesium nitrate.

[0078] Based on the calculations based on the amount of feed, the compositions of the composite anode materials prepared in Examples 1-11 and Comparative Examples 1-4 are shown in Table 1:

[0079] Table 1

[0080]

[0081]

[0082] Test Example 1

[0083] The composite anode material prepared in Example 1 was characterized by XPS-Mg, and the results are as follows: Figure 1 As shown.

[0084] Among them, by Figure 1 It can be seen that a side peak appears to one side of the main peak of Mg, indicating that the electron cloud density of some atoms in Mg has changed. This is because Mg atoms have formed at least partial chemical bonds with oxygen atoms in silicon-carbon materials. Since Mg atoms and oxygen atoms have different electronegativity, electrons flow between atoms, indirectly causing the change in the electron cloud density of Mg atoms.

[0085] The composite anode materials prepared in Examples 2-11 were characterized by XPS-Mg, and the characterization results were basically the same as those in Example 1.

[0086] Test Example 2

[0087] The composite negative electrode material prepared in Example 1 was mixed with graphite, a conductive agent (conductive carbon black to carbon nanotubes in a mass ratio of 1:0.1), and polyacrylic acid in a mass ratio of 1:9:0.5:1. An appropriate amount of water was added, and the mixture was kneaded for 1 hour at a solid content of approximately 60%. Water was added to adjust the slurry viscosity to 5000 Pa·s to prepare a negative electrode slurry. This slurry was then coated onto a copper foil current collector, dried, and cold-pressed to obtain the negative electrode sheet. The obtained negative electrode sheet was characterized by XPS-S, and the results are as follows: Figure 2 As shown.

[0088] Among them, by Figure 2 It is known that the XPS peak of sulfur shows a bifurcation. This is because at least some of the sulfur atoms in the modifier reacted chemically with the hydroxyl groups in the conductive agent to form chemical bonds. Due to the difference in electronegativity between the two, their electron-withdrawing abilities differ. Therefore, this bonding causes electrons to flow between the two different atoms, resulting in a change in electron cloud density and thus forming a bifurcation.

[0089] The XPS-Mg and XPS-S characterization results show that the Mg and S elements in the interface modifier can tightly bond the silicon-carbon material and the conductive agent together through chemical bonds. This improves the adhesion strength between the silicon-carbon material and the conductive agent, reduces capacitance loss caused by the lack of electrical contact during lithium-ion battery cycling, and significantly improves the cycle capacity retention rate of the lithium-ion battery. Furthermore, the chemical bonding between the silicon-carbon material and the conductive agent also facilitates electronic conduction between them, reducing resistance and mitigating polarization and heat generation during charging and discharging, thereby further improving battery performance.

[0090] The composite anode materials prepared in Examples 2-11 were characterized by XPS-S, and the characterization results were basically the same as those in Example 1.

[0091] Test Example 3

[0092] The composite anode materials from Examples 1-11 and Comparative Examples 1-4 were used to prepare lithium-ion batteries. The impedance of the lithium-ion batteries was then tested, and room-temperature cycling tests were performed. The test results for the impedance and capacity retention after 1000 cycles are shown in Table 2.

[0093] Lithium-ion batteries are assembled as follows:

[0094] The composite negative electrode materials from Examples 1-11 and Comparative Examples 1-4 were mixed with graphite, a conductive agent (conductive carbon black to carbon nanotubes in a mass ratio of 1:0.1), and polyacrylic acid in a mass ratio of 1:9:0.5:1. An appropriate amount of water was added, and the mixture was kneaded for 1 hour at a solid content of approximately 60%. Water was then added to adjust the slurry viscosity to 5000 Pa·s to prepare the negative electrode slurry. The prepared negative electrode slurry was coated onto a copper foil current collector, dried, and cold-pressed to obtain the negative electrode sheet.

[0095] Lithium cobalt oxide was mixed with a conductive agent (SP) and PVDF in a ratio of 100:1:1, and NMP (N-methylpyrrolidone) was added. The mixture was stirred for 1 hour to obtain a positive electrode slurry with a solid content of approximately 80%. The prepared positive electrode slurry was coated onto an aluminum foil current collector, dried, and cold-pressed to obtain a positive electrode sheet. The positive and negative electrode sheets were cut into 50*90mm sheets. A 25μm thick polyethylene porous membrane with an alumina ceramic layer on its surface was used as a separator. An equal mass mixture of ethylene carbonate and dimethyl carbonate containing 1mol / L lithium hexafluorophosphate was used as the electrolyte. The positive electrode sheet, separator, negative electrode sheet, and electrolyte were assembled into a 3Ah soft-pack stacked battery in an Ar gas glove box with a water content and oxygen content of less than 5ppm.

[0096] Room temperature cycling test method: After capacity grading, the batteries prepared in the above examples and comparative examples were placed in a constant temperature chamber at 25±2℃ and charged and discharged at a current of 1C within a voltage range of 2.8-4.25V for 1000 consecutive cycles. The capacity retention rate (%) is the percentage obtained by dividing the discharge capacity after 1000 cycles by the discharge capacity at the first discharge.

[0097] Battery impedance test method: At room temperature, the impedance of the battery after 1000 cycles was tested using a HIOKI BT3562A battery hitestea instrument.

[0098] Table 2

[0099]

[0100]

[0101] The results of 1000 tests in Example 1 and Comparative Example 1 were plotted as room temperature cycling curves, as shown below. Figure 3 As shown. By Figure 3 It is understood that the composite anode material provided in this invention uses chemical bonds to tightly connect silicon-carbon materials and conductive agents together, which can effectively avoid the damage to the conductive network caused by the detachment of the binder from the silicon anode material during the cycle of lithium-ion batteries, and can significantly improve the cycle performance of lithium-ion batteries.

[0102] Test Example 4

[0103] Referring to Test Example 3, the composite anode material prepared in Example 1 and the composite anode material (i.e., silicon-carbon material 1) in Comparative Example 1 were used to prepare lithium-ion batteries. The difference was that the mass ratio of the composite anode material to graphite was changed. The capacity retention rate and impedance test results of the lithium-ion batteries after 1000 cycles are shown in Table 3.

[0104] Test Example 5

[0105] The composite anode materials prepared in Example 1 and Comparative Example 1 were used to fabricate 2025 coin cells, and then the anode specific capacity of the 2025 coin cells was tested (Note: This anode specific capacity can be understood as the specific capacity of the active material in the 2025 coin cell, that is, the specific capacity of the silicon-carbon anode material and the optional graphite active material; the anode here does not represent the true anode in the 2025 coin cell, but is only for the purpose of consistency with the name in pouch cells). The preparation method of the 2025 coin cell and the anode specific capacity testing method are as follows:

[0106] The silicon-carbon anode material prepared in Example 1 was mixed with graphite, a conductive agent (conductive carbon black to carbon nanotubes in a mass ratio of 1:0.1), and polyacrylic acid in a mass ratio of 1:9:0.5:1. An appropriate amount of water was added, and the mixture was kneaded for 1 hour at a solid content of approximately 60%. Water was then added to adjust the slurry viscosity to 5000 Pa·s to prepare the anode slurry. The prepared anode slurry was coated onto a copper foil current collector, dried, and cold-pressed to obtain the anode sheet.

[0107] A 2025 coin cell was assembled using a 17mm diameter, 1mm thick lithium metal sheet as the negative electrode, a 25μm thick porous polyethylene membrane coated with an alumina ceramic layer as the separator, and an equal mass mixture of ethylene carbonate and dimethyl carbonate containing 1mol / L lithium hexafluorophosphate as the electrolyte. The negative electrode, separator, lithium metal sheet, and electrolyte were assembled in an Ar glove box with both water and oxygen contents less than 5ppm to form a coin cell. The battery was then discharged at 0.05C to 5mV and charged at 0.05C to 1.5V using the charging capacity at this point.

[0108] Referring to Test Example 4, the mass ratio of composite anode material to graphite was changed, and a series of 2025 coin cells were prepared using the silicon-carbon anode material prepared in Example 1. The test results of the anode specific capacity are shown in Table 3.

[0109] Table 3

[0110]

[0111]

[0112] As shown in Table 3, with the increase of graphite content, the specific capacity decreases, the impedance decreases, and the capacity retention rate after 1000 cycles increases. When the mass ratio of composite anode material to graphite is between 1:8 and 30, a battery with relatively large specific capacity, low impedance, and good cycle performance can be obtained.

[0113] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A dressing, characterized in that, The dressing comprises a composite negative electrode material and a conductive agent. The composite negative electrode material comprises a silicon-carbon material and an interface modifier. The conductive agent contains hydroxyl groups. The silicon-carbon material also contains oxygen, with an oxygen content of 0.1-5 wt% based on the total mass of the silicon-carbon material. The interface modifier is selected from one or more of MgSO4, AlPO4, CaSO4, Mg(HSO4)2, Mg(H2PO4)2, MgHPO4, Al(HSO4)3, Al(H2PO4)3, Al2(HPO4)3, Al3(SO4)2, and Mg3(PO4)2. At least a portion of the oxygen in the silicon-carbon material forms chemical bonds with the Mg, Al, and Ca elements in the interface modifier.

2. The dressing according to claim 1, wherein, Based on the total mass of the silicon-carbon material, the silicon content is 30-60 wt% and the carbon content is 35-69.9 wt%.

3. The dressing according to claim 1, wherein, Based on the total mass of the silicon-carbon material, the oxygen content is 0.5-3 wt%, the silicon content is 44-55 wt%, and the carbon content is 42-55.5 wt%.

4. The dressing according to claim 1, wherein, The average particle size of silicon in the silicon-carbon material is 0.5-15 nm.

5. The dressing according to claim 1, wherein, The average particle size of silicon in the silicon-carbon material is 0.8-2 nm.

6. The dressing according to claim 1 or 2, wherein, The interface modifier is selected from MgSO4 and / or Mg3(PO4)2.

7. The dressing according to any one of claims 1-3, wherein, Based on the total mass of the composite anode material, the content of the silicon-carbon material is 97.5-99.9 wt%, and the content of the interface modifier is 0.1-2.5 wt%.

8. The dressing according to any one of claims 1-4, wherein, The composite negative electrode material further includes a modifying accelerator; wherein the modifying accelerator is selected from one or more of ammonium chloride, sodium carbonate, sodium bicarbonate, and sodium acetate.

9. The dressing according to claim 8, wherein, The modifying accelerator is sodium carbonate and / or sodium acetate.

10. The dressing according to claim 8, wherein, Based on the total mass of the composite anode material, the content of the silicon-carbon material is 91-99.85 wt%, the content of the interface modifier is 0.05-6.5 wt%, and the content of the modification accelerator is 0.1-2.5 wt%.

11. The dressing according to claim 8, wherein, Based on the total mass of the composite anode material, the content of silicon-carbon material is 96.62-99.38 wt%; the content of interface modifier is 0.12-2.9 wt%; and the content of modification accelerator is 0.48-1.95 wt%.

12. The dressing according to claim 1, wherein, The average particle size of silicon in the composite anode material is 0.5-15 nm.

13. The dressing according to claim 12, wherein, The average particle size of silicon in the composite anode material is 0.8-2 nm.

14. A method for preparing a dressing, characterized in that, The method includes preparing the composite anode material according to the following process: mixing and reacting the silicon-carbon material according to any one of claims 1-13, the interface modifier, and optionally the modifying accelerator to obtain the composite anode material.

15. The method for preparing the dressing according to claim 14, wherein, The mixing reaction includes wet mixing reaction and / or dry ball milling reaction.

16. The method for preparing the dressing according to claim 15, wherein, The wet mixing process includes: adding the silicon-carbon material, the interface modifier, and optionally the modifying accelerator to an alcohol solution, stirring at 40-60°C for 12-48 hours, followed by filtration and pulverization to obtain the composite anode material.

17. The method for preparing the dressing according to claim 15, wherein, The dry ball milling process includes: mixing the silicon-carbon material, the interface modifier, and optionally the modification accelerator with grinding balls, and ball milling at a speed of 1000-3000 r / min for 1-10 h to obtain the composite anode material.

18. A negative electrode sheet, characterized in that, The negative electrode sheet includes a current collector and a dressing layer coated on the current collector, the dressing layer including the dressing as described in any one of claims 1-13 or the dressing prepared by the preparation method described in any one of claims 14-17, optional graphite and binder.

19. The negative electrode sheet according to claim 18, wherein, The conductive agent includes conductive carbon black and carbon nanotubes.

20. The negative electrode sheet according to claim 19, wherein, The mass ratio of the conductive carbon black to carbon nanotubes is 1:0.05-0.

25.

21. The negative electrode sheet according to claim 18, wherein, The dressing layer comprises 1 part by weight of composite negative electrode material, 0-100 parts by weight of graphite, 0.1-1 parts by weight of conductive agent and 0.5-1.5 parts by weight of binder.

22. The negative electrode sheet according to claim 18, wherein, The dressing layer comprises 1 part by weight of composite negative electrode material, 8-30 parts by weight of graphite, 0.4-0.6 parts by weight of conductive agent and 0.8-1.2 parts by weight of binder.

23. A battery, characterized in that, The battery contains a negative electrode sheet as described in any one of claims 18-22.

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