Composite negative electrode, preparation method thereof and all-solid-state lithium battery

Abstract

The invention provides a composite negative electrode, a preparation method thereof and an all-solid-state lithium battery, and belongs to the technical field of all-solid-state lithium ion batteries. The composite negative electrode provided by the invention comprises a negative electrode material and a nano silicon coating arranged on the surface of the negative electrode material, and the negative electrode material is one or more of Al, Sn, Ge, In, Mg and Ag. The negative electrode material in the composite negative electrode provided by the invention can avoid serious side reaction between the negative electrode and a sulfide solid electrolyte interface, reduce the risk of lithium dendrites at the interface, and ensure the electrochemical performance of the all-solid-state lithium battery; the nano-silicon coating forms a Li-Si alloy layer after the first lithiation, and has high lithium ion conduction characteristic and lower Young modulus, so that good interface contact is formed between the composite negative electrode and a solid electrolyte, a high-diffusivity transmission channel and stable dynamic guarantee are provided for the reversible lithiation / lithium removal process of the composite negative electrode, and the composite negative electrode can be applied to the lithium ion battery. And the electrochemical performance of the all-solid-state lithium battery is further improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of all-solid-state lithium-ion batteries, and particularly relates to a composite negative electrode, a preparation method thereof, and an all-solid-state lithium battery. Background Art

[0002] Traditional liquid lithium-ion batteries have the disadvantages of being flammable, prone to leakage and corrosion, and have relatively large potential safety hazards. The electrode materials and electrolyte materials of all-solid-state lithium batteries are both solids, which make up for the disadvantages of liquid lithium-ion batteries. At present, solid electrolytes mainly include inorganic solid electrolytes, polymer solid electrolytes, and composite solid electrolytes of the two. Among them, sulfide solid electrolytes in inorganic solid electrolytes have ultra-high conductivity, close to that of liquid electrolytes, and have broad application prospects in the research and development of high-safety and high-energy-density batteries.

[0003] When preparing an all-solid-state lithium battery using a sulfide solid electrolyte, the negative electrode usually uses a graphite negative electrode or a metallic lithium negative electrode. Among them, the graphite negative electrode has a low energy density and lacks application prospects. Although the metallic lithium negative electrode has a high energy density, it is prone to side reactions with sulfide solid electrolytes, and non-uniform deposition of metallic lithium at the interface is likely to generate lithium dendrites, which will cause rapid decline in battery performance. At present, the problem of mismatch between the negative electrode and the sulfide solid electrolyte has become an important issue affecting the electrochemical performance of all-solid-state lithium batteries. Therefore, there is an urgent need for a negative electrode that can improve the electrochemical performance of all-solid-state lithium batteries. Summary of the Invention

[0004] The purpose of the present invention is to provide a composite negative electrode, a preparation method thereof, and an all-solid-state lithium battery. The all-solid-state lithium battery prepared from the composite negative electrode provided by the present invention has good electrochemical performance, and has a relatively high initial Coulomb efficiency and cycle stability.

[0005] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a composite negative electrode, including a negative electrode material and a nano-silicon coating provided on the surface of the negative electrode material; the negative electrode material is one or more of Al, Sn, Ge, In, Mg, and Ag.

[0007] Preferably, the thickness of the nano-silicon coating is 1-20 μm, and the thickness of the negative electrode material is 5-100 μm.

[0008] Preferably, the nano-silicon coating includes nano-silicon powder and a binder.

[0009] Preferably, the mass ratio of the nano-silicon powder to the binder is (98-90):(2-10).

[0010] Preferably, the binder is one or more of polyacrylic acid, bacterial cellulose, polyvinylidene fluoride, sodium carboxymethyl cellulose, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, and modified SBR rubber.

[0011] Preferably, the particle size of the nano-silicon powder is 20 - 300 nm.

[0012] The present invention also provides a preparation method of the composite electrode described in the above technical solution, including: mixing nano-silicon powder, binder and solvent to obtain a slurry; coating the slurry on the negative electrode material, and drying to obtain a composite negative electrode.

[0013] Preferably, the solvent is one or more of deionized water, benzene, toluene, and N-methylpyrrolidone.

[0014] Preferably, the addition amount of the solvent is 60 - 95% of the total mass of the slurry.

[0015] The present invention also provides a all-solid-state lithium battery, including a positive electrode, a sulfide solid electrolyte, and a negative electrode. The negative electrode is the composite negative electrode described in the above technical solution or the composite negative electrode prepared by the preparation method described in the above technical solution. The nano-silicon coating of the composite negative electrode is in contact with the sulfide solid electrolyte.

[0016] The present invention provides a composite negative electrode, comprising a negative electrode material and a nano-silicon coating disposed on the surface of the negative electrode material; the negative electrode material is one or more of Al, Sn, Ge, In, Mg, and Ag. In the composite negative electrode provided by the present invention, the negative electrode material can undergo a lithium alloying reaction at a potential slightly higher than the lithium deposition potential, and lithium ions can diffuse and transport in the negative electrode material, avoiding the direct deposition of lithium at the electrolyte interface. While ensuring the energy density advantage of the all-solid-state battery, it avoids serious side reactions between the negative electrode and the sulfide solid electrolyte and reduces the risk of lithium dendrite formation due to non-uniform lithium deposition at the interface; the nano-silicon coating on the surface of the negative electrode material forms a Li-Si alloy layer after the first lithiation. This alloy layer has both high lithium ion conduction characteristics and a relatively low Young's modulus, and forms a good interfacial contact between the composite negative electrode and the solid electrolyte through plastic deformation, providing a highly diffusible transport channel and stable kinetic guarantee for the reversible lithiation / delithiation process of the composite negative electrode; under the synergistic effect of the negative electrode material and the nano-silicon coating, the electrochemical performance of the battery is improved, enabling the assembled all-solid-state lithium battery to have a high initial coulombic efficiency and cycle stability. Experimental results show that the initial discharge specific capacity of the all-solid-state lithium battery assembled with the composite negative electrode provided by the present invention as the negative electrode is 205.08 mAh / g, and the initial coulombic efficiency is as high as 83.06%. After 50 charge-discharge cycles, the discharge specific capacity is still as high as 83.96 mAh / g; for the all-solid-state lithium battery assembled with the composite negative electrode provided by the present invention as the negative electrode, when the battery operating pressure is 50 MPa, the initial discharge specific capacity and charge specific capacity are 1298.74 mAh / g and 881.12 mAh / g respectively, and the initial coulombic efficiency can reach 67.84%, still having a high initial coulombic efficiency under low-pressure operating conditions. Description of the Drawings

[0017] Figure 1 It is a cyclic performance graph of the all-solid-state battery prepared in Example 3 of the present invention under a battery operating pressure of 100 MPa;

[0018] Figure 2 It is a cyclic performance graph of the all-solid-state battery prepared in Comparative Example 1 of the present invention under a battery operating pressure of 100 MPa;

[0019] Figure 3 It is a charge-discharge curve graph of the all-solid-state battery prepared in Example 4 of the present invention under a battery operating pressure of 100 MPa;

[0020] Figure 4 It is a charge-discharge curve graph of the all-solid-state battery prepared in Example 4 of the present invention under a battery operating pressure of 50 MPa;

[0021] Figure 5The charge-discharge curve of the all-solid-state battery prepared in Comparative Example 2 of the present invention under a battery operating pressure of 100 MPa;

[0022] Figure 6 The charge-discharge curve of the all-solid-state battery prepared in Comparative Example 2 of the present invention under a battery operating pressure of 50 MPa;

[0023] Figure 7 The charge-discharge curve of the all-solid-state battery prepared in Comparative Example 3 of the present invention under a battery operating pressure of 50 MPa;

[0024] Figure 8 The charge-discharge curve of the all-solid-state battery prepared in Comparative Example 4 of the present invention under a battery operating pressure of 50 MPa. Detailed implementation mode

[0025] The present invention provides a composite negative electrode, comprising a negative electrode material and a nano-silicon coating disposed on the surface of the negative electrode material; the negative electrode material is one or more of Al, Sn, Ge, In, Mg, and Ag.

[0026] The composite negative electrode provided by the present invention includes a negative electrode material. In the present invention, the negative electrode material is one or more of Al, Sn, Ge, In, Mg, and Ag, preferably one, two, three, four, or six. As an implementation mode of the present invention, the negative electrode material may be a simple substance; the simple substance may be aluminum foil, tin foil, germanium foil, indium foil, magnesium foil, or silver foil; it may also be a binary alloy; the binary alloy may be an Al-Sn alloy, an Al-In alloy, a Ge-Al alloy, a Mg-Al alloy, a Sn-Ge alloy, a Mg-Sn alloy, a Ge-In alloy, a Mg-In alloy, or an In-Ag alloy; it may also be a ternary alloy; the ternary alloy may be an Al-Mg-Sn alloy, an Al-Sn-Ge alloy, an Al-Mg-In alloy, or an Al-Sn-Ag alloy; it may also be a quaternary alloy; the quaternary alloy may be an Al-Mg-In-Ge alloy; it may also be a hexavalent alloy; the hexavalent alloy may be an Al-Ag-In-Mg-Ge-Sn alloy. The selection of the raw materials of the above negative electrode material can enable the negative electrode material to undergo an alloying reaction with lithium at a potential slightly higher than the lithium deposition potential, and when the alloying reaction with lithium occurs, lithium ions can diffuse and transport in the alloy negative electrode, which can avoid the direct deposition of lithium at the electrolyte interface to generate lithium dendrites.

[0027] In the present invention, the thickness of the negative electrode material is preferably 5-100 μm, more preferably 5-15 μm, and further preferably 5-10 μm. By controlling the thickness of the negative electrode material within the above range, the present invention is beneficial to avoiding an increase in the resistance of lithium ion transmission and electrochemical reaction to generate more heat, thereby further improving the electrochemical performance of the all-solid-state lithium battery.

[0028] The composite negative electrode provided by the present invention further includes a nano-silicon coating disposed on the surface of the negative electrode material. In the present invention, the nano-silicon coating preferably includes nano-silicon powder and a binder.

[0029] In the present invention, the purity of the nano-silicon powder is preferably not less than 99.5 wt%; the particle size of the nano-silicon powder is preferably 20 - 300 nm, and more preferably 20 - 80 nm.

[0030] In the present invention, the binder is preferably one or more of polyacrylic acid, bacterial cellulose, polyvinylidene fluoride, sodium carboxymethyl cellulose, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, and modified SBR rubber. In the embodiments of the present invention, the binder is bacterial cellulose.

[0031] In the present invention, the mass ratio of the nano-silicon powder to the binder is preferably (90 - 98):(2 - 10), and more preferably 98:2. By controlling the mass ratio of the nano-silicon powder and the binder within the above range, the present invention helps to obtain a uniform coating.

[0032] In the present invention, the thickness of the nano-silicon coating is preferably 1 - 20 μm, and more preferably 1 - 5 μm. By controlling the thickness of the nano-silicon coating within the above range, the present invention can not only avoid coating rupture and effectively protect silicon particles, but also provide a buffer space to avoid hindering lithium ion transmission, which is beneficial to balancing buffering and ion transmission and further improving the electrochemical performance of all-solid-state lithium batteries.

[0033] The composite negative electrode provided by the present invention can improve the electrochemical performance of the battery under the synergistic action of the negative electrode material and the nano-silicon coating, so that the assembled all-solid-state lithium battery has a high initial Coulomb efficiency and cycle stability.

[0034] The present invention also provides a preparation method of the composite negative electrode described in the above technical solution, including: mixing nano-silicon powder, a binder, and a solvent to obtain a slurry; coating the slurry on the negative electrode material and drying to obtain the composite negative electrode.

[0035] In the present invention, the solvent is preferably one or more of deionized water, benzene, toluene, and N-methylpyrrolidone. In the embodiments of the present invention, the solvent is deionized water. During the drying process of the coating, the volatilization of the above solvent can cause components such as nano-silicon particles and the binder to gradually aggregate, forming a nano-silicon coating with good adhesion and mechanical properties.

[0036] In the present invention, the addition amount of the solvent is preferably 60-95% of the total mass of the slurry, more preferably 90-95%. By controlling the solvent amount within the above range, the structure of the nano-silicon coating can be made dense and stable, which is beneficial to further improving the electrochemical performance of the all-solid-state lithium battery.

[0037] The present invention has no special limitation on the mixing operation of the nano-silicon powder, binder and solvent, and it can be evenly mixed by adopting the technical solutions well-known to those skilled in the art.

[0038] The present invention has no special limitation on the coating amount of the slurry, and it can be determined according to the thickness of the required nano-silicon coating based on the common technical knowledge in the art.

[0039] In the present invention, the drying is preferably carried out in a vacuum drying oven; the drying temperature is preferably 30-100 °C, more preferably 60-100 °C; the drying time is preferably 6-24 h, more preferably 12-24 h. By controlling the drying temperature and time, the nano-silicon powder and the binder can be fully contacted and tightly combined, and a uniform, dense and strong-binding nano-silicon coating can be obtained.

[0040] The composite negative electrode prepared by the above method in the present invention can make the negative electrode material and the nano-silicon coating in the composite negative electrode tightly combined, and a nano-silicon coating with good performance can be obtained.

[0041] The present invention also provides an all-solid-state lithium battery, which includes a positive electrode, a sulfide solid electrolyte and a negative electrode. The negative electrode is the composite negative electrode described in the above technical solution or the composite negative electrode prepared by the preparation method described in the above technical solution, and the nano-silicon coating of the composite negative electrode is in contact with the sulfide solid electrolyte.

[0042] The present invention has no special limitation on the operation of preparing the all-solid-state lithium battery, and it can be assembled by adopting the methods well-known to those skilled in the art.

[0043] In the present invention, the nano-silicon coating of the composite negative electrode is in contact with the sulfide solid electrolyte, which can enable the all-solid-state lithium battery to form a Li-Si alloy layer after the first lithiation of the nano-silicon coating during the first charge and discharge. This alloy layer has both high lithium ion conduction characteristics and a relatively low Young's modulus. Through plastic deformation, a good interfacial contact is formed between the composite negative electrode and the solid electrolyte, providing a highly diffusible transport channel and stable kinetic guarantee for the reversible lithiation / delithiation process of the composite negative electrode, and enabling the all-solid-state lithium battery to have a high first Coulomb efficiency and cycle stability.

[0044] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0045] Example 1

[0046] Composite negative electrode: It consists of a negative electrode material and a nano-silicon coating disposed on the surface of the negative electrode material; the negative electrode material is an aluminum foil with a thickness of 5 μm, and the thickness of the nano-silicon coating is 5 μm; in the nano-silicon coating: the purity of the nano-silicon powder is 99.5 wt%, the particle size is 80 nm, the binder is bacterial cellulose, and the mass ratio of the nano-silicon powder to the binder is 98:2.

[0047] The preparation method of the composite negative electrode is as follows: Weigh the nano-silicon powder and the binder accurately according to the mass ratio. First, dissolve the binder in part of the deionized water to prepare a binder solution with a mass fraction of 0.5%. Then, mix the nano-silicon powder binder solution with the remaining part of the deionized water to obtain a slurry. The total addition amount of deionized water is 90% of the total mass of the slurry. Use a spatula to evenly coat the slurry on the surface of the aluminum foil negative electrode material, transfer it to a vacuum drying oven and dry it at 60 °C for 12 h. After drying, the composite negative electrode is obtained. Finally, cut the composite negative electrode into circular pieces with a diameter of 10 mm, weigh the mass and put them into a glove box for standby.

[0048] Example 2

[0049] The difference from Example 1 is that the negative electrode material of the composite negative electrode is an aluminum foil with a thickness of 15 μm, and the other operating conditions are the same as those in Example 1.

[0050] Example 3

[0051] All-solid-state battery, which is assembled by a positive electrode, a sulfide solid electrolyte and a negative electrode;

[0052] The positive electrode is a composite positive electrode sheet. The preparation method of the composite positive electrode sheet is as follows: In a glove box, mix the active material layered nickel cobalt manganese oxide material (abbreviated as NCM9), the sulfide electrolyte LPSCl, the conductive agent and the binder with a mixer at 2000 r / min for 10 min. Roll the mixture at 100 °C to obtain a composite positive electrode dry film. Weigh an appropriate mass of the film and press it into circular pieces with a diameter of 9.5 mm for standby;

[0053] The preparation method of the sulfide solid electrolyte is as follows: First, weigh 60 mg of the sulfide electrolyte LPSCl, add it to a polyether ether ketone (PEEK) battery mold with a diameter of 10 mm, and press it at a pressure of 1 t for 5 s to obtain a preliminarily formed sulfide solid electrolyte layer;

[0054] The negative electrode is the composite negative electrode prepared in Example 1, and the nano-silicon coating of the composite negative electrode is arranged in contact with the sulfide solid electrolyte.

[0055] The preparation method of the all-solid-state battery is as follows: a negative electrode is added to one side of the sulfide solid electrolyte layer so that the negative electrode is in contact with the sulfide solid electrolyte, and a positive electrode is placed on the other side of the solid electrolyte layer. Then, it is pressed under a pressure of 4 t for 15 min using a press to obtain an all-solid-state lithium battery (AlSi||LPSCl||NCM9).

[0056] Example 4

[0057] The all-solid-state battery is assembled from a positive electrode, a sulfide solid electrolyte, and a negative electrode;

[0058] The positive electrode is a lithium-indium alloy positive electrode sheet (the mass of lithium element accounts for 5% of the total mass);

[0059] The preparation method of the sulfide solid electrolyte is the same as that in Example 3;

[0060] The negative electrode is the composite negative electrode prepared in Example 2, and the nano-silicon coating of the composite negative electrode is arranged in contact with the sulfide solid electrolyte.

[0061] The difference between the preparation method of the all-solid-state battery and the preparation method of the all-solid-state battery in Example 3 is that: it is pressed under a pressure of 2 t for 10 min using a press to obtain an all-solid-state lithium battery (AlSi||LPSCl||Li-In), and the remaining operations are the same as those in Example 3.

[0062] Comparative Example 1

[0063] The all-solid-state battery is assembled from a positive electrode, a sulfide solid electrolyte, and a negative electrode;

[0064] The positive electrode and the sulfide solid electrolyte are the same as those in Example 3;

[0065] The preparation method of the negative electrode is as follows: an aluminum foil with a thickness of 10 μm is cut into a circular sheet with a diameter of 10 mm, weighed, and then placed in a glove box for standby.

[0066] The preparation method of the all-solid-state battery is the same as that in Example 3 to obtain an all-solid-state lithium battery (Al||LPSCl||NCM9).

[0067] Comparative Example 2

[0068] The all-solid-state battery is assembled from a positive electrode, a sulfide solid electrolyte, and a negative electrode;

[0069] The positive electrode is the same as that in Example 4;

[0070] The preparation method of the sulfide solid electrolyte is the same as that in Example 3;

[0071] The preparation method of the negative electrode is as follows: Cut an aluminum foil with a thickness of 15 μm into circular pieces with a diameter of 10 mm, weigh the mass, and then place it in a glove box for standby.

[0072] The preparation method of the all-solid-state battery is the same as that of Example 4, and an all-solid-state lithium battery (Al||LPSCl||Li-In) is obtained.

[0073] Comparative Example 3

[0074] The all-solid-state battery is assembled from a positive electrode, a sulfide solid electrolyte, and a negative electrode;

[0075] The positive electrode is the same as that of Example 4;

[0076] The preparation method of the sulfide solid electrolyte is the same as that of Example 3;

[0077] The preparation method of the negative electrode is as follows: Accurately weigh graphite, conductive agent SuperP, binder CMC, and binder SBR according to a mass ratio of 95.8:1:1.4:1.8, add a dispersant, and mix them into a uniform slurry. Use a scraper to evenly coat the slurry on the surface of the copper foil, then transfer it to a vacuum drying oven and dry it at 60 °C for 12 h. Finally, cut the dried electrode sheet into circular pieces with a diameter of 10 mm, weigh the mass, and place it in a glove box for standby.

[0078] The preparation method of the all-solid-state battery is the same as that of Example 4, and an all-solid-state lithium battery (Graphite (graphite)||LPSCl||Li-In) is obtained.

[0079] Comparative Example 4

[0080] The all-solid-state battery is assembled from a positive electrode, a sulfide solid electrolyte, and a negative electrode;

[0081] The positive electrode is the same as that of Example 4;

[0082] The preparation method of the sulfide solid electrolyte is the same as that of Example 3;

[0083] The preparation method of the negative electrode is as follows: Cut a 50-μm lithium foil into circular pieces with a diameter of 9 mm in a glove box, weigh the mass, and then set it aside.

[0084] The preparation method of the all-solid-state battery is the same as that of Example 4, and the all-solid-state lithium battery (Li||LPSCl||Li-In) is obtained.

[0085] Perform constant current charge and discharge tests on the all-solid-state lithium batteries obtained in Example 3 and Comparative Example 1 in the voltage range of 2 to 4.25 V. The test temperature is 30 °C, and the battery operating pressure is 100 MPa. In Example 3, the loading of the positive electrode active material NCM9 is 13 mg / cm 2, the loading of the negative electrode active material AlSi is 1.85 mg / cm 2 (calculated from the weight of the negative electrode sheet / the area of the negative electrode sheet). In Comparative Example 1, the loading of the positive electrode active material NCM9 is 12 mg / cm 2 , and the loading of the negative electrode active material Al is 2.5 mg / cm 2 .

[0086] Figure 1 Figure showing the cycling performance of the all-solid-state battery obtained in Example 3 at a current density of 0.25 mA / cm 2 (0.1C), with the battery operating pressure at 100 MPa. Among them, the white dots represent the curve of Coulomb efficiency versus the number of cycles, corresponding to the right vertical axis, and the black dots represent the curve of discharge capacity versus the number of cycles, corresponding to the left vertical axis. As can be seen from Figure 1 , the initial discharge specific capacity of this battery is 205.08 mAh / g (calculated based on the positive electrode active material), and the initial Coulomb efficiency is 83.06%. After cycling 2 times at 0.1C, the discharge specific capacity of the battery at 1C is 158.45 mAh / g. After 50 charge-discharge cycles, the discharge specific capacity can still reach 83.96 mAh / g, demonstrating that the nano-silicon coating effectively improves the initial Coulomb efficiency of the alloy negative electrode aluminum foil, provides stable kinetic guarantee for the reversible lithiation / delithiation process of the alloy negative electrode, and at the same time provides a higher specific capacity for the negative electrode.

[0087] Figure 2 Figure showing the cycling performance of the all-solid-state battery obtained in Comparative Example 1 at a current density of 0.24 mA / cm 2 (0.1C), with the battery operating pressure at 100 MPa. Among them, the white dots represent the curve of Coulomb efficiency versus the number of cycles, corresponding to the right vertical axis, and the black dots represent the curve of discharge capacity versus the number of cycles, corresponding to the left vertical axis. As can be seen from Figure 2 , the initial discharge specific capacity of this battery is 134.86 mAh / g (calculated based on the positive electrode active material), and the initial Coulomb efficiency is only 54.57%. After cycling 2 times at 0.1C, the discharge specific capacity of the battery at 1C is 68.42 mAh / g. After 50 charge-discharge cycles, the discharge specific capacity of the battery is 69.17 mAh / g. The results show that the initial Coulomb efficiency of the alloy negative electrode aluminum foil is relatively low and the reversibility is poor during the cycling process.

[0088] The all-solid-state lithium batteries obtained in Example 4 and Comparative Examples 2 to 4 were subjected to constant current charge and discharge tests in the voltage range of 0 to 1.5 V. The test temperature was 30 °C. The operating pressures of the battery in Example 4 were 100 MPa and 50 MPa respectively. The operating pressures of the battery in Comparative Example 2 were 100 MPa and 50 MPa respectively. The operating pressures of the batteries in Comparative Examples 3 to 4 were 50 MPa. In Example 4, the loading of the negative electrode active material AlSi was 4.4 mg / cm 2 , in Comparative Example 2, the loading of the negative electrode active material Al was 3.8 mg / cm 2 , in Comparative Example 3, the loading of the negative electrode active material Graphite was 8.1 mg / cm 2 , in Comparative Example 4, the loading of the negative electrode active material Li was 2.8 mg / cm 2 .

[0089] Figure 3 Fig. is the charge and discharge curve of the all-solid-state battery obtained in Example 4 at a battery operating pressure of 100 MPa and a current density of 0.25 mA / cm 2 . The first line 1 in the figure st represents the first cycle, the second line 2 nd represents the second cycle, and the third line 3 rd represents the third cycle. For all the 1 st , 2 nd , 3 rd in the three-line graph, the lower one is the discharge curve, and the abscissa corresponding to the end is the discharge specific capacity. The upper line is the charge curve, and the abscissa corresponding to the end is the charge specific capacity. It can be seen from Figure 3 that the first discharge specific capacity and charge specific capacity of this battery are 1303.58 mAh / g and 1012.99 mAh / g respectively. By comparing the first discharge specific capacity and the first charge specific capacity, the first Coulomb efficiency is 77.71%. The discharge specific capacity and charge specific capacity of the second cycle of this battery are 1062.46 mAh / g and 945.15 mAh / g respectively. The Coulomb efficiency of the second cycle is calculated to be 88.96%. The discharge specific capacity and charge specific capacity of the third cycle of this battery are 941.25 mAh / g and 974.22 mAh / g respectively. The Coulomb efficiency of the third cycle is calculated to be 103.5%. Compared with Example 3, it shows that after the thickness of the alloy negative electrode foil increases, the kinetics of the de-lithiation process becomes worse, and the first Coulomb efficiency decreases slightly, but it still shows good lithiation / delithiation kinetic performance.

[0090] Figure 4 Fig. is the charge and discharge curve of the all-solid-state battery obtained in Example 4 at a battery operating pressure of 50 MPa and a current density of 0.25 mA / cm 2 . The first line 1 in the figure stRepresents the first cycle, the second line 2 nd Represents the first cycle, the third line 3 rd Represents the third cycle, all 1 st , 2 nd , 3 rd In the graph of the three lines, the lower one is the discharge curve, and the abscissa corresponding to the end is the discharge specific capacity. The upper line is the charge curve, and the abscissa corresponding to the end is the charge specific capacity. From Figure 4 it can be seen that the first discharge specific capacity and charge specific capacity of this battery are 1298.74 mAh / g and 881.12 mAh / g respectively. By comparing the first discharge specific capacity and the first charge specific capacity, the first Coulomb efficiency is 67.84%; the discharge specific capacity and charge specific capacity of the second cycle of this battery are 916.87 mAh / g and 734.19 mAh / g respectively, and the Coulomb efficiency of the second cycle is calculated to be 80.08%; the discharge specific capacity and charge specific capacity of the third cycle of this battery are 725.1 mAh / g and 787.46 mAh / g respectively, and the Coulomb efficiency of the third cycle is calculated to be 108.6%. It shows that the decrease in the stacking pressure during the battery operation process makes the interface contact condition worse, and the first Coulomb efficiency of the battery decreases, but the composite anode still shows good lithiation / delithiation kinetic performance under the condition of lower stacking pressure.

[0091] Figure 5 The all-solid-state battery obtained in Comparative Example 2, at a battery operation pressure of 100 MPa, the charge-discharge curve diagram at a current density of 0.25 mA / cm 2 The first line 1 in the figure st Represents the first cycle, the second line 2 nd Represents the second cycle, the third line 3 rd Represents the third cycle, all 1 st , 2 nd , 3 rd In the graph of the three lines, the lower one is the discharge curve, and the abscissa corresponding to the end is the discharge specific capacity. The upper line is the charge curve, and the abscissa corresponding to the end is the charge specific capacity. From Figure 5 it can be seen that the first discharge specific capacity and charge specific capacity of this battery are 1042.95 mAh / g and 527.5 mAh / g respectively. By comparing the first discharge specific capacity and the first charge specific capacity, the first Coulomb efficiency is 50.58%; the discharge specific capacity and charge specific capacity of the second cycle of this battery are 551.07 mAh / g and 495.37 mAh / g respectively, and the Coulomb efficiency of the second cycle is calculated to be 89.89%; the discharge specific capacity and charge specific capacity of the third cycle of this battery are 493.25 mAh / g and 449.02 mAh / g respectively, and the Coulomb efficiency of the third cycle is calculated to be 91.03%.

[0092] Figure 6 The all-solid-state battery obtained in Comparative Example 2, at a battery operating pressure of 50 MPa, and at a current density of 0.25 mA / cm 2 The charge-discharge curve diagram. The first line 1 in the figure st represents the first cycle, the second line 2 nd represents the second cycle, and the third line 3 rd represents the third cycle. For all the 1 st 、2 nd 、3 rd In the diagram of the three lines, the lower one is the discharge curve, and the abscissa corresponding to the end is the discharge specific capacity. The upper line is the charge curve, and the abscissa corresponding to the end is the charge specific capacity. It can be seen from the figure that the first discharge specific capacity and the first charge specific capacity of this battery are 1025.18 mAh / g and 457.64 mAh / g respectively. By comparing the first discharge specific capacity with the first charge specific capacity, the first Coulomb efficiency is 44.64%; the discharge specific capacity and the charge specific capacity of the second cycle of this battery are 480.56 mAh / g and 457.25 mAh / g respectively, and the Coulomb efficiency of the second cycle is calculated to be 95.15%; the discharge specific capacity and the charge specific capacity of the third cycle of this battery are 461.82 mAh / g and 443.51 mAh / g respectively, and the Coulomb efficiency of the third cycle is calculated to be 96.04%.

[0093] Figure 7 The all-solid-state battery obtained in Comparative Example 3, at a battery operating pressure of 50 MPa, and at a current density of 0.25 mA / cm 2 The charge-discharge curve diagram. The first line 1 in the figure st represents the first cycle, the second line 2 nd represents the second cycle, and the third line 3 rd represents the third cycle. For all the 1 st 、2 nd 、3 rd In the diagram of the three lines, the lower one is the discharge curve, and the abscissa corresponding to the end is the discharge specific capacity. The upper line is the charge curve, and the abscissa corresponding to the end is the charge specific capacity. From Figure 7It can be seen from [the figure] that the initial discharge specific capacity and the initial charge specific capacity of the battery are 48.88 mAh / g and 23.71 mAh / g respectively. By comparing the initial discharge specific capacity with the initial charge specific capacity, the initial Coulombic efficiency is 48.5%; the discharge specific capacity and the charge specific capacity of the battery in the second cycle are 33.13 mAh / g and 26.05 mAh / g respectively, and the calculated Coulombic efficiency in the second cycle is 78.62%; the discharge specific capacity and the charge specific capacity of the battery in the third cycle are 31.65 mAh / g and 27.02 mAh / g respectively, and the calculated Coulombic efficiency in the third cycle is 85.38%. The results show that the specific capacity of the graphite anode is low under a pressure of 50 MPa, and the interfacial lithium ion transport kinetics is poor, resulting in a low initial Coulombic efficiency.

[0094] Figure 8 The all-solid-state battery obtained as Comparative Example 4, with the battery operating pressure of 50 MPa, at a current density of 0.25 mA / cm 2 The charge-discharge curve diagram under [the current density], from Figure 8 It can be seen that there are voltage fluctuations during the initial charging process of the battery, that is, the phenomenon of micro-short circuit, indicating that at a pressure of 50 MPa on the lithium anode, non-uniform lithium deposition occurs at the interface to generate lithium dendrites, resulting in battery failure.

[0095] From the performance test data of the above examples and comparative examples, it can be seen that when the composite anode provided by the present invention is used to prepare an all-solid-state lithium battery, the prepared all-solid-state lithium battery has good electrochemical performance, a high initial Coulombic efficiency and cycle stability, and still exhibits good lithiation / delithiation kinetic performance after the thickness of the anode material is increased or under relatively low stacking pressure conditions.

[0096] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can still be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A composite negative electrode, comprising a negative electrode material and a nano-silicon coating provided on the surface of the negative electrode material; the negative electrode material is one or more of Al, Sn, Ge, In, Mg, and Ag.

2. The composite negative electrode according to claim 1, characterized in that, The thickness of the nano-silicon coating is 1 to 20 μm, and the thickness of the negative electrode material is 5 to 100 μm.

3. The composite negative electrode according to claim 1 or 2, characterized in that, The nano-silicon coating comprises nano-silicon powder and a binder.

4. The composite negative electrode according to claim 3, wherein, The mass ratio of the nano-silicon powder to the binder is (98 - 90):(2 - 10).

5. The composite negative electrode according to claim 3, wherein The binder is one or more of polyacrylic acid, bacterial cellulose, polyvinylidene fluoride, sodium carboxymethyl cellulose, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, and modified SBR rubber.

6. The composite negative electrode according to claim 3, wherein, The particle size of the nano-silicon powder is 20 to 300 nm.

7. The preparation method of the composite electrode according to any one of claims 1 to 6, characterized in that, Comprising: Mixing nano-silicon powder, a binder, and a solvent to obtain a slurry; coating the slurry on the negative electrode material and drying to obtain the composite negative electrode.

8. The preparation method according to claim 7, characterized in that, The solvent is one or more of deionized water, benzene, toluene, and N-methylpyrrolidone.

9. The preparation method according to claim 7 or 8, characterized in that, The addition amount of the solvent is 60 to 95% of the total mass of the slurry.

10. A all-solid-state lithium battery, comprising a positive electrode, a sulfide solid electrolyte and a negative electrode, characterized in that, The negative electrode is the composite negative electrode according to any one of claims 1 to 6 or the composite negative electrode prepared by the preparation method according to any one of claims 7 to 9, and the nano-silicon coating of the composite negative electrode is in contact with a sulfide solid electrolyte.

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