Composite negative electrode material, preparation method thereof, negative electrode sheet and solid-state battery

Abstract

This invention relates to the field of battery technology, and in particular to a composite anode material and its preparation method, an anode sheet, and a solid-state battery. The composite anode material includes a core and a shell; the core comprises the anode material; and the shell comprises a lithium composite oxide. This invention, by coating the surface of the anode material with a lithium composite oxide protective layer, effectively mitigates the volume change of the anode material during charging and discharging, maintains good contact between the electrode and the solid electrolyte, reduces interfacial impedance, and improves battery performance.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a composite negative electrode material and its preparation method, a negative electrode sheet, and a solid-state battery. Background Technology

[0002] All-solid-state batteries have attracted widespread attention due to their superior safety, longer cycle life, and higher energy density. In all-solid-state batteries, a solid electrolyte replaces the liquid electrolyte, resulting in higher thermal stability and stronger cycle stability compared to traditional liquid lithium-ion batteries. However, all-solid-state batteries also face some technical challenges, particularly the interface problem between the solid electrolyte and electrode materials. The application of negative electrode materials in all-solid-state batteries, especially high-capacity materials (such as silicon and lithium metal), can lead to poor contact between the solid electrolyte and the electrode due to significant volume changes during charging and discharging, thus affecting battery performance and cycle life. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings and defects of the prior art and to provide a composite anode material, its preparation method, anode sheet, and solid-state battery.

[0004] To achieve the above objectives, this application adopts the following solution: A composite anode material includes a core and a shell; the core includes an anode material; the shell includes a lithium composite oxide.

[0005] The lithium composite oxide is a sintered product of lithium carbonate and metal oxide; the metal oxide includes one or more of Al2O3, TiO2, ZnO, SnO2, CeO2, MgO, V2O5, ZrO2, Y2O3, SrO, Bi2O3, Ga2O3, WO3, Dy2O3, Cr2O3, MoO3, and La2O3; preferably, the lithium composite oxide accounts for 0.1%-10% of the total mass of the composite anode material.

[0006] The anode material includes one or more of carbon-based anode materials, silicon-based anode materials, titanium-based anode materials, lithium and lithium alloy materials, and transition metal anode materials; the carbon-based anode material includes one or more of graphite, hard carbon, or soft carbon; the silicon-based anode material includes one or more of silicon oxide or silicon carbon; the titanium-based anode material includes one or more of lithium titanate or titanium dioxide; and the transition metal anode material includes one or more of transition metal oxides, transition metal sulfides, or transition metal phosphides.

[0007] The present invention also includes a method for preparing the composite anode material, comprising the following steps: 1) coating a metal oxide onto a cathode material to obtain a metal oxide-coated cathode material; 2) mixing the metal oxide-coated cathode material with lithium carbonate and then sintering to obtain the composite anode material.

[0008] The amount of metal oxide coating relative to the negative electrode material in step 1) is 1-6 wt%; preferably 3 wt%.

[0009] In step 1), the molar ratio of the metal oxide-coated anode material to lithium carbonate is 1:(1-1.5); preferably, the sintering temperature is 600-1000℃, and the sintering time is 6-24h.

[0010] The present invention also includes a negative electrode sheet, comprising the aforementioned composite negative electrode material, negative electrode electrolyte, negative electrode conductive agent, and negative electrode binder.

[0011] The mass ratio of the composite negative electrode material, negative electrode electrolyte, negative electrode conductive agent, and negative electrode binder is 60-95:0-30:0-10:0.1-10; Preferably, the negative electrode electrolyte includes one or more of sulfide electrolytes, oxide electrolytes, polymer electrolytes, and halide electrolytes; The sulfide electrolytes include Li2S-P2S5, Li3PS4, and Li7P3S. 11 Li4SiS4, Li 10 GeP2S 12 One or more of (LGPS) and Li6PS5Cl; The oxide electrolytes include LLZO, LLTO, LATP, and Li. 14 One or more of Zn(GeO4)4; The polymer electrolyte includes one or more of polyoxyethylene electrolyte, polyvinylidene fluoride electrolyte, and polyacrylonitrile-based electrolyte; The halide electrolytes mentioned are one or more of Li3InCl6, Li3YCl6, and Li2ZrCl6; Preferably, the conductive agent includes one or more of carbon-based conductive agents, metal-based conductive agents, conductive polymers, and composite conductive agents: carbon-based conductive agents include one or more of carbon black, graphene, carbon nanotubes, carbon fibers, and graphite. Metal-based conductive agents include one or more of copper powder, nickel powder, silver powder, copper nanowires, silver nanowires, and metal coatings; Conductive polymers include one or more of polyaniline, polypyrrole, and polythiophene; Composite conductive agents include one or more of the following: carbon black-graphene composite materials, carbon nanotube-metal nanowire composite materials, and conductive polymer-carbon-based material composite materials; Preferably, the negative electrode binder includes one or more of polymer binders, water-based binders, and composite binders; Polymer binders include one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyethylene oxide, polyacrylic acid, and polyacrylonitrile; Waterborne adhesives include one or more of carboxymethyl cellulose, styrene-butadiene rubber, and polyvinyl alcohol; Composite adhesives include one or more of the following: composites of PVDF and PEO, composites of CMC and SBR, and composites of bio-based adhesives and polymer adhesives.

[0012] The present invention also includes a solid-state battery, comprising the aforementioned negative electrode, solid electrolyte membrane, and positive electrode.

[0013] The present invention also includes a method for preparing the solid-state battery, comprising the following steps: stacking a negative electrode, a solid electrolyte membrane, and a positive electrode in sequence, or transferring the solid electrolyte membrane onto the surface of the positive or negative electrode by in-situ synthesis or calendering and then stacking them to obtain a battery cell; wrapping the battery cell with a protective layer and placing it in an aluminum-plastic shell and encapsulating it to obtain a solid-state battery.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Improve the interfacial stability between the electrode and the solid electrolyte: By coating the surface of the negative electrode material with a lithium composite oxide protective layer, the volume change of the negative electrode material during charging and discharging can be effectively mitigated, good contact between the electrode and the solid electrolyte can be maintained, the interfacial impedance can be reduced, and the performance of the battery can be improved.

[0015] (2) Improve interfacial reaction: Interfacial reaction between solid electrolyte and negative electrode material may lead to irreversible structural changes or a decrease in conductivity. By designing a lithium composite oxide coating, the occurrence of interfacial reaction can be suppressed, thereby enhancing the cycle stability of the battery.

[0016] (3) Improve the conductivity of the negative electrode: Coating lithium composite oxide can improve the conductivity of the negative electrode in the all-solid-state battery, enhance the rate performance of the battery, and effectively improve the power density of the battery, especially during high current charging and discharging.

[0017] (4) Improve safety: Coating lithium composite oxide can also effectively prevent the dendrite growth of lithium metal in all-solid-state batteries, reduce the risk of short circuit inside the battery, and improve the safety of all-solid-state batteries. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0019] Example 1: A method for preparing a composite anode material (a composite graphite anode coated with lithium composite oxide), comprising the following steps: 1) A metal oxide-coated negative electrode material is obtained by coating the negative electrode material with metal oxide; firstly, 600 mL of a 0.5 mol / L solution is prepared (using Al...). 3+ A solution of aluminum nitrate (Al(NO3)3•9H2O) was prepared. 510 g of graphite particles (5-20 μm) were placed in the aluminum nitrate solution and stirred at 50°C for 2 hours (to achieve a final alumina coating of 3%). Then, ammonia solution was added dropwise until excess. The solution was stirred at 80°C for 4 hours to allow Al(OH)3 to fully adsorb onto the graphite surface. After filtration, the solution was washed successively with deionized water and anhydrous ethanol until the pH of the filtrate was neutral. The solution was then dried at 110°C for 12 hours. The solution was then heated to 600°C at a rate of 1°C / min under air atmosphere and held for 5 hours to obtain alumina-coated graphite.

[0020] 2) A composite anode material was obtained by mixing a metal oxide-coated anode material with lithium carbonate and then sintering the mixture. Alumina-coated graphite and lithium carbonate were uniformly mixed at a molar ratio of 1:1.1 and sintered at 800℃ for 12 hours. This yielded a graphite anode coated with lithium aluminate.

[0021] Example 2: The difference between Example 2 and Example 1 is that the molar ratio of aluminum oxide to lithium carbonate is 1:1.2.

[0022] Example 3: The difference between Example 3 and Example 1 is that the molar ratio of aluminum oxide to lithium carbonate is 1:1.3.

[0023] Example 4: The difference between Example 4 and Example 1 is that the molar ratio of alumina and lithium carbonate is 1:1.5.

[0024] Example 5: The difference between Example 4 and Example 1 is that the coating amount of alumina is 6%, and the molar ratio of alumina to lithium carbonate is 1:1.5.

[0025] Comparative Example 1: A method for preparing a lithium-added graphite anode, comprising directly and uniformly mixing graphite and lithium carbonate (3% by mass of graphite and a molar ratio of lithium carbonate of 1:1.2), and sintering at a temperature of 800℃ for 12 hours. A lithium-added graphite anode is obtained.

[0026] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that only step 1) is performed to obtain alumina-coated graphite.

[0027] Preparation of negative electrode sheet: The composite negative electrode material prepared in the examples and comparative examples, the conductive agent carbon nanotubes, the binder polyvinylidene fluoride (PVDF), and the solid electrolyte LLZO are mixed thoroughly in N-methylpyrrolidone solvent at a mass ratio of 85:2:5:10. The mixture is then coated onto copper foil, dried, and cold-pressed to obtain the negative electrode sheet.

[0028] Preparation of positive electrode sheet: The positive electrode active material (ternary material), conductive agent (carbon black), binder (polyvinylidene fluoride), and solid electrolyte (Li6PS5Cl) are mixed thoroughly in an organic solvent (NMP) at a mass ratio of 80:2:3:15, coated onto aluminum foil, dried, and cold-pressed.

[0029] Preparation of electrolyte membrane: The electrolyte (Li6PS5Cl) and binder (polyvinylidene fluoride) are mixed thoroughly in an organic solvent (NMP) at a mass ratio of 99:1. The mixture is then coated onto an aluminum foil and dried. After coating, the aluminum foil is placed in a vacuum dryer at 80°C for 12 hours to obtain a dry electrolyte membrane. The membrane is then rolled to make it dense, resulting in a solid electrolyte membrane.

[0030] The cells are stacked in the following order: negative electrode, solid electrolyte membrane, and positive electrode. After being wrapped with a protective layer, the cells are placed in an outer packaging shell and encapsulated to obtain an all-solid-state battery. Then, isostatic pressing (100 MPa) is performed, followed by placing the battery in a constant temperature chamber at 50°C for 48 hours.

[0031] Performance testing of all-solid-state batteries: Cyclic capacity retention test: Take one battery from each of the examples and comparative examples, and perform charge-discharge cycles on the lithium-ion batteries through the following steps, and calculate the discharge capacity retention rate of the lithium-ion batteries.

[0032] Charge and discharge were performed at 45°C. Constant current and constant voltage charging was conducted at a charging current of 0.1C until the upper limit voltage reached 4.2V and the cutoff current was 0.02C. The system was then allowed to rest for 10 minutes. Next, constant current discharge was performed at a discharging current of 0.1C until 2.5V was reached. Cycle capacity retention rate test = (Discharge capacity of the nth cycle / Discharge capacity of the first cycle) multiplied by 100%.

[0033] The results are shown in Table 1: Table 1

[0034] As can be seen from the first-cycle coulombic efficiency data of Examples 1, 2, 3, and 4 in Table 1, with the Al2O3 coating amount remaining constant, the first-cycle coulombic efficiency improves with the increase of lithium carbonate content during high-temperature sintering. This may be due to more Al2O3 in the coating layer being converted into lithium aluminate when the lithium carbonate content increases. Increasing the Al2O3 coating amount while simultaneously increasing the amount of lithium carbonate during high-temperature sintering further improves the first-cycle coulombic efficiency. As can be seen from the capacity retention data of Examples 1, 2, 3, and 4 in Table 1, the capacity retention decreases with the increase of coating amount. This may be because a thicker coating layer increases the resistance to lithium-ion insertion and extraction during subsequent cycles, thus degrading the cycle performance. By comparing Examples 4 and 5, with the lithium-aluminum molar ratio fixed at 1:1.5, when the alumina coating amount increases from 3% to 6%, the capacity retention decreases from 95.81% to 95.26%. This also proves that an excessively thick coating layer (6%) slightly degrades the cycle performance.

[0035] Comparative Example 1: Because it was not coated with metal oxide, lithium carbonate and graphite were directly mixed and sintered, resulting in uneven lithium replenishment, numerous interfacial side reactions, and easy damage to the graphite structure, leading to low coulombic efficiency in the first cycle and poor cycle capacity retention.

[0036] Comparative Example 2 illustrates that while simple metal oxide (Al2O3) coating provides some protection, it has serious drawbacks: Low initial efficiency: During the first charge, Al2O3 consumes active lithium ions to form a lithium-conducting interface, resulting in a significant decrease in the first-cycle coulombic efficiency (only 80.20%). Poor ion conduction capability: Compared to the "lithium composite oxide" generated in this invention, the simple oxide layer has lower ionic conductivity and higher interface impedance, resulting in a cycle retention rate (85.69%) that is far lower than other embodiments of this invention (>93%).

[0037] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of the equivalents of the claims be included within the invention.

[0038] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A composite negative electrode material, characterized in that, It includes a core and a shell; the core includes a negative electrode material; the shell includes a lithium composite oxide.

2. The composite negative electrode material according to claim 1, characterized in that, The lithium composite oxide is a sintered product of lithium carbonate and metal oxide; the metal oxide includes one or more of Al2O3, TiO2, ZnO, SnO2, CeO2, MgO, V2O5, ZrO2, Y2O3, SrO, Bi2O3, Ga2O3, WO3, Dy2O3, Cr2O3, MoO3, and La2O3; preferably, the lithium composite oxide accounts for 0.1%-10% of the total mass of the composite anode material.

3. The composite negative electrode material according to claim 1, characterized in that, The anode material includes one or more of carbon-based anode materials, silicon-based anode materials, titanium-based anode materials, lithium and lithium alloy materials, and transition metal anode materials; the carbon-based anode material includes one or more of graphite, hard carbon, or soft carbon; the silicon-based anode material includes one or more of silicon oxide or silicon carbon; the titanium-based anode material includes one or more of lithium titanate or titanium dioxide; and the transition metal anode material includes one or more of transition metal oxides, transition metal sulfides, or transition metal phosphides.

4. A method for preparing the composite negative electrode material according to any one of claims 1-3, characterized in that, The process includes the following steps: 1) coating a metal oxide onto a negative electrode material to obtain a metal oxide-coated negative electrode material; 2) mixing the metal oxide-coated negative electrode material with lithium carbonate and then sintering the mixture to obtain a composite negative electrode material.

5. The preparation method according to claim 4, characterized in that, The amount of metal oxide coating relative to the negative electrode material in step 1) is 1-6 wt%; preferably 3 wt%.

6. The preparation method according to claim 4, characterized in that, In step 1), the molar ratio of the metal oxide-coated anode material to lithium carbonate is 1:(1-1.5); preferably, the sintering temperature is 600-1000℃, and the sintering time is 6-24h.

7. A negative electrode sheet, characterized in that, It includes the composite negative electrode material, negative electrode electrolyte, negative electrode conductive agent, and negative electrode binder as described in any one of claims 1-3.

8. The negative electrode sheet according to claim 7, characterized in that, The mass ratio of the composite negative electrode material, negative electrode electrolyte, negative electrode conductive agent, and negative electrode binder is 60-95:0-30:0-10:0.1-10; Preferably, the negative electrode electrolyte includes one or more of sulfide electrolytes, oxide electrolytes, polymer electrolytes, and halide electrolytes; The sulfide electrolytes include Li2S-P2S5, Li3PS4, and Li7P3S. 11 Li4SiS4, Li 10 GeP2S 12 One or more of (LGPS) and Li6PS5Cl; The oxide electrolytes include LLZO, LLTO, LATP, and Li. 14 One or more of Zn(GeO4)4; The polymer electrolyte includes one or more of polyoxyethylene electrolyte, polyvinylidene fluoride electrolyte, and polyacrylonitrile-based electrolyte; The halide electrolytes mentioned are one or more of Li3InCl6, Li3YCl6, and Li2ZrCl6; Preferably, the conductive agent includes one or more of carbon-based conductive agents, metal-based conductive agents, conductive polymers, and composite conductive agents: carbon-based conductive agents include one or more of carbon black, graphene, carbon nanotubes, carbon fibers, and graphite. Metal-based conductive agents include one or more of copper powder, nickel powder, silver powder, copper nanowires, silver nanowires, and metal coatings; Conductive polymers include one or more of polyaniline, polypyrrole, and polythiophene; Composite conductive agents include one or more of the following: carbon black-graphene composite materials, carbon nanotube-metal nanowire composite materials, and conductive polymer-carbon-based material composite materials; Preferably, the negative electrode binder includes one or more of polymer binders, water-based binders, and composite binders; Polymer binders include one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyethylene oxide, polyacrylic acid, and polyacrylonitrile; Waterborne adhesives include one or more of carboxymethyl cellulose, styrene-butadiene rubber, and polyvinyl alcohol; Composite adhesives include one or more of the following: composites of PVDF and PEO, composites of CMC and SBR, and composites of bio-based adhesives and polymer adhesives.

9. A solid-state battery, comprising the negative electrode, solid electrolyte membrane, and positive electrode as described in claim 7 or 8.

10. A method for preparing a solid-state battery according to claim 9, characterized in that, The process includes the following steps: stacking the negative electrode, solid electrolyte membrane, and positive electrode in sequence, or transferring the solid electrolyte membrane onto the surface of the positive or negative electrode through in-situ synthesis or calendering and then stacking them to obtain a battery cell; wrapping the battery cell with a protective layer and placing it in an aluminum-plastic shell for encapsulation to obtain a solid-state battery.

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