Composite negative electrode, and electrochemical device and electronic device comprising same

Abstract

The invention discloses a composite negative electrode and an electrochemical device and an electronic device comprising the same, and belongs to the technical field of electrochemical energy storage. According to the composite negative electrode provided by the invention, a first coating, a second coating and a third coating are sequentially introduced on the surface of a current collector, the first coating is limited to comprise silicon, a conductive agent and a first binder, the second coating comprises a modified sulfide electrolyte, and the third coating comprises a halide electrolyte and a second binder; the structural design of the interface separation function can effectively improve the initial discharge specific capacity, the first coulombic efficiency and the cycle performance of the subsequently prepared solid-state battery.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, and in particular to composite negative electrodes and electrochemical and electronic devices containing them. Background Technology

[0002] Lithium-ion batteries are one of the most widely used electrochemical energy storage technologies, but safety issues posed by organic electrolytes are hindering their development. Solid-state electrolytes, with their high decomposition temperature, non-volatility, and non-flammability, can significantly reduce battery safety risks. Furthermore, solid-state electrolytes exhibit good compatibility with high-energy-density lithium metal anodes, making all-solid-state batteries with matching lithium metal anodes a promising candidate for high-energy-density and high-safety electrochemical energy storage. In recent years, various types of solid-state electrolyte materials have been developed, among which sulfide electrolytes are considered one of the most promising solid-state electrolyte systems due to their ionic conductivity comparable to organic electrolytes and their excellent processing performance.

[0003] Among various sulfide electrolytes (SSEs), sulfides such as LPSCI, which possess high ionic conductivity and good mechanical deformability, have attracted widespread attention. However, SSEs are easily reduced at the negative electrode, and the resulting solid electrolyte interface (SEI) containing low ionic conductivity Li₂S and other materials can hinder lithium-ion transport. Summary of the Invention

[0004] The purpose of this application is to solve the technical problems of low initial discharge specific capacity, reduced first coulombic efficiency and poor cycle performance of electrochemical devices obtained by using corresponding composite anodes in the prior art. It proposes a composite anode with good initial discharge specific capacity and first coulombic efficiency and excellent cycle performance, as well as an electrochemical device and an electrical device containing the anode.

[0005] To achieve the above objectives, a first aspect of this application provides a composite negative electrode, the composite negative electrode comprising a negative electrode current collector and a first coating, a second coating and a third coating sequentially disposed on the surface of the negative electrode current collector; The first coating comprises silicon, a conductive agent, and a first binder; The second coating includes a modified sulfide electrolyte; The third coating comprises a halide electrolyte and a second binder.

[0006] As an embodiment of this application, the composite negative electrode satisfies 0.05≤H≤0.6; Where H = H3 / (H1+H2); H1 μm is the thickness of the first coating; H2 μm is the thickness of the second coating; H3 μm represents the thickness of the third coating.

[0007] As an embodiment of this application, the H1 μm is 20-35.

[0008] As an embodiment of this application, the H2 μm is 10-30.

[0009] As an embodiment of this application, the H3 μm is 5-20.

[0010] As an embodiment of this application, the modified sulfide electrolyte satisfies log(σe / σi) ≤ -4; Wherein, σe is the electronic conductivity of the modified sulfide electrolyte under the conditions of 25℃ / 350MPa; σi is the ionic conductivity of the modified sulfide electrolyte at 25℃ / 350MPa.

[0011] As an embodiment of this application, the modified sulfide electrolyte is obtained by ball milling a mixture of sulfide electrolyte and modifying material; the sulfide electrolyte includes Li6PS5Cl (LPSCl), Li 10 GeP2S 12 (LGPS), Li7P3S 11 At least one of the following: The modified material includes at least one of GeS2, SnS2, Ta2O5, Nb2O5, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium chloride, lithium fluoride, etc.

[0012] As an embodiment of this application, the halide electrolyte includes at least one of lithium-rare earth metal halides, lithium-transition metal halides, and their doped solid solutions.

[0013] As an embodiment of this application, the silicon has a Dv50 of 2-8 μm.

[0014] As an embodiment of this application, in the first coating, the mass percentage of silicon is 88-92% and the mass percentage of conductive agent is 2-8%.

[0015] As an embodiment of this application, the third coating contains 95-98% by mass of halide electrolyte.

[0016] As an embodiment of this application, the first adhesive and the second adhesive are each independently selected from at least one of water-based adhesives and oil-based adhesives.

[0017] A second aspect of this application provides an electrochemical device comprising the composite negative electrode described in this application.

[0018] In a third aspect, this application provides an electronic device, which includes the electrochemical device described in this application.

[0019] Compared with the prior art, the beneficial effects of this application are: The composite negative electrode provided in this application sequentially introduces a first coating, a second coating, and a third coating on the surface of the current collector. The first coating includes silicon, a conductive agent, and a first binder; the second coating includes a modified sulfide electrolyte; and the third coating includes a halide electrolyte and a second binder. This interfacial separation structure effectively isolates silicon from the halide electrolyte and prevents direct contact between the sulfide electrolyte and the positive electrode in the subsequent electrochemical device, thereby alleviating interfacial side reaction problems and electrolyte separation problems. It effectively improves the initial discharge specific capacity, initial coulombic efficiency, and cycle performance of the solid-state battery prepared subsequently, specifically improving the capacity retention rate before and after cycling and reducing the interfacial impedance before and after cycling. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] The term "polymer" refers to a polymeric compound prepared by polymerizing the same or different types of monomers. The general term "polymer" includes the terms "homopolymer," "copolymer," "trimer," and "interpolymer."

[0022] The term "binder" refers to a substance used to bind inorganic fillers to or to porous substrate materials.

[0023] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0024] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0025] As used herein, the terms “approximately,” “generally,” “substantially,” and “about” are used to describe and indicate small variations. When used in conjunction with an event or situation, the terms may refer to examples in which the event or situation occurred precisely and examples in which the event or situation occurred very approximately. For example, when used in conjunction with numerical values, the terms may refer to a range of variation less than or equal to ±10% of the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. For example, if the difference between two values ​​is less than or equal to ±10% of the average of the values ​​(e.g., less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%), then the two values ​​can be considered "substantially" the same.

[0027] Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format in this document. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only the numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0028] In the detailed description and claims, a list of items connected by the terms "one of," "among," "a kind of," or other similar terms may mean any of the listed items. For example, if items A and B are listed, then the phrase "one of A and B" means only A or only B. In another example, if items A, B, and C are listed, then the phrase "one of A, B, and C" means only A; only B; or only C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0029] In the detailed description and claims, the list of items connected by the term "at least one of" can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C.

[0030] In the following description, all figures disclosed in this application are approximate values, regardless of whether the terms "about" or "approximately" are used in conjunction. They may vary by 1%, 2%, 5%, or sometimes 10% to 20%. Whenever a range of values ​​with a lower limit (RL) and an upper limit (RU) is disclosed, any values ​​falling within that range are specifically disclosed. Specifically, the following values ​​within this range are specifically disclosed: R = RL + k × (RU - RL), where k is a variable with a 1% increment from 1% to 100%, i.e., k is 1%, 2%, 3%, 4%, 5%, ..., 50%, 51%, 52%, ..., 95%, 96%, 97%, 98%, 99%, or 100%. Furthermore, any range of values ​​defined by the two R values ​​as defined above are also specifically disclosed.

[0031] Throughout this specification, references to "implementation," "partial implementation," "one implementation," "another implementation," "specific method," or "partial method" mean that at least one implementation or embodiment in this application includes the specific features, structures, materials, or characteristics described in that implementation or embodiment.

[0032] In this application, numerical ranges are involved. Unless otherwise specified, the numerical ranges mentioned above are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form a range not explicitly stated.

[0033] Unless otherwise specified, all reagents or instruments used in this application are commercially available products.

[0034] In one embodiment of this application, a first aspect of this application provides a composite negative electrode, the composite negative electrode comprising a negative electrode current collector and a first coating, a second coating and a third coating sequentially disposed on the surface of the negative electrode current collector; The first coating comprises silicon, a conductive agent, and a first binder; The second coating includes a modified sulfide electrolyte; The third coating comprises a halide electrolyte and a second binder.

[0035] The composite negative electrode provided in this application sequentially introduces a first coating, a second coating, and a third coating on the surface of the current collector. The first coating includes silicon, a conductive agent, and a first binder; the second coating includes a modified sulfide electrolyte; and the third coating includes a halide electrolyte and a second binder. This interfacial separation structure effectively isolates silicon from the halide electrolyte and prevents direct contact between the sulfide electrolyte and the positive electrode in the subsequent electrochemical device, thereby alleviating interfacial side reaction problems and electrolyte separation problems. It effectively improves the initial discharge specific capacity, initial coulombic efficiency, and cycle performance of the solid-state battery prepared subsequently, specifically improving the capacity retention rate before and after cycling and reducing the interfacial impedance before and after cycling.

[0036] Specifically, the first coating includes silicon, which can effectively ensure that the resulting solid-state battery has a high initial discharge specific capacity; the modified sulfide electrolyte included in the second coating can improve the initial coulombic efficiency of the subsequently prepared solid-state battery to a certain extent; the third coating includes a halide electrolyte, which can reduce volume expansion, thereby effectively stabilizing the interface, reducing interfacial side reactions, and improving the cycle performance of the solid-state battery.

[0037] In one embodiment, the composite negative electrode satisfies 0.05 ≤ H ≤ 0.6; Where H = H3 / (H1+H2); H1 μm is the thickness of the first coating; H2 μm is the thickness of the second coating; H3 μm represents the thickness of the third coating.

[0038] It should be noted that the thickness of the first, second, and third coatings was tested as follows: a clean cross-section was prepared by argon ion polishing of the composite negative electrode. Finally, the thickness of each coating was observed using a scanning electron microscope (SEM) in backscatter mode, and the thickness was measured and statistically analyzed at multiple points.

[0039] For example, H can be any point value between 0.05 and 0.6 or a range value between any two points, such as 0.05, 0.08, 0.1, 0.12, 0.15, 0.18, 0.2, 0.22, 0.25, 0.28, 0.3, 0.32, 0.35, 0.38, 0.4, 0.42, 0.45, 0.48, 0.5, 0.52, 0.55, 0.58, 0.6, etc.

[0040] In one embodiment, the composite negative electrode satisfies 0.14 ≤ H ≤ 0.44. For example, it can be 0.14, 0.16, 0.18, 0.2, 0.22, 0.24, 0.26, 0.28, 0.3, 0.32, 0.34, 0.36, 0.38, 0.4, 0.42, 0.44, etc.

[0041] This study found that the thicknesses of the first, second, and third coatings of the composite anode satisfy the above-mentioned relationship. In particular, by further selecting H to be 0.14-0.44, it is possible to ensure that the third coating can form a continuous and dense protective layer, effectively blocking the oxidation of the high-voltage cathode. At the same time, its thickness is within a suitable range, thereby avoiding excessive negative impact on the overall ionic conductivity of the solid-state battery, achieving a balance between high voltage stability and high rate performance. That is, it can maximize the proportion of active material and minimize ion transport impedance while ensuring the stability of interface structure and chemical stability. As a result, the solid-state battery prepared subsequently has a high initial discharge specific capacity and first coulombic efficiency, as well as excellent cycle capacity retention and a low rate of increase in interfacial internal resistance before and after cycling.

[0042] In one embodiment, the H1 μm is 20-35.

[0043] For example, H1 μm can be any point value between 20 and 35 or a range value between any two points, such as 20, 22, 25, 28, 30, 32, 35, etc.

[0044] In one embodiment, the H1 μm is 25-30. For example, it can be 25, 26, 27, 28, 29, 30, etc.

[0045] This study found that the thickness of the first coating affects the initial discharge specific capacity of the subsequently fabricated solid-state battery, as well as the interfacial impedance and ion diffusion efficiency. When H1 is selected within the above-mentioned range, especially within a further preferred range, the resulting solid-state battery exhibits a high initial discharge specific capacity and first coulombic efficiency, along with excellent cycle capacity retention and a low rate of increase in interfacial internal resistance before and after cycling. In one embodiment, the H2 μm is 10-30.

[0046] For example, H2 μm can be any point value between 10 and 30 or a range value between any two points, such as 10, 12, 15, 18, 20, 22, 25, 28, 30, etc.

[0047] In one embodiment, the H2 μm is 15-25. For example, it can be 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, etc.

[0048] This study found that the thickness of the second coating affects the interfacial resistance and ion transport efficiency, as well as the mechanical stability of the coating. When the thickness of the second coating is selected within the above-mentioned range, especially within a further preferred range, the resulting solid-state battery has a higher initial coulombic efficiency and better cycle performance.

[0049] In one embodiment, the H3 μm is 5-20.

[0050] For example, H3 μm can be any point value between 5 and 20 or a range value between any two points, such as 5, 10, 15, 20, etc.

[0051] In one embodiment, the H3 μm is 8-17. For example, it can be 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, etc.

[0052] This study found that the thickness of the third coating affects the overall chemical stability of the composite anode and the degree of side reactions. When the thickness of the third coating is further selected within the above-mentioned range, especially within the more preferred range, the cycle performance of the obtained solid-state battery is better.

[0053] In one embodiment, the modified sulfide electrolyte satisfies log(σe / σi) ≤ -4; Where σe is the electronic conductivity of the modified sulfide electrolyte at 25℃ / 350MPa; σi is the ionic conductivity of the modified sulfide electrolyte at 25℃ / 350MPa.

[0054] It should be noted that the test method for the electronic conductivity and ionic conductivity of the modified sulfide electrolyte at 25℃ / 350MPa is as follows: The modified sulfide electrolyte is cold-pressed into a dense thin sheet (10mm in diameter, 0.2mm thick) in an inert atmosphere glove box, placed between two blocking electrodes, and assembled into a symmetrical cell. Long-term DC polarization is performed under a constant small voltage (10 mV), and the electronic conductivity is calculated by measuring the steady-state current. The same electrolyte sheet is then placed between the blocking electrodes to assemble a symmetrical cell. An electrochemical workstation is used to perform AC impedance testing at a set temperature (25℃) within a frequency range of 0.1 Hz to 1 MHz. The ionic conductivity and electronic conductivity are calculated by fitting the characteristics of the high-frequency region intercept (volume resistance) and the low-frequency sloping line in the Nyquist plot.

[0055] In one embodiment, the modified sulfide electrolyte satisfies -6 ≤ log(σe / σi) ≤ -4.

[0056] For example, log(σe / σi) can be any value between (-6) and (-4) or a range between any two points, such as -6, -5.8, -5.6, -5.4, -5.2, -5, -4.8, -4.6, -4.4, -4.2, -4, etc. This application research found that when the modified sulfide electrolyte satisfies log(σe / σi) ≤ -4, especially -6 ≤ log(σe / σi) ≤ -4, it can systematically reduce its electronic conductivity without significantly sacrificing ionic conductivity. This effectively suppresses electron migration to the electrolyte layer, thereby fundamentally reducing the side reaction of electrolyte reduction by silicon at low potentials, significantly improving interface stability, and thus improving the cycle performance of solid-state batteries.

[0057] In one embodiment, the modified sulfide electrolyte is obtained by ball milling a mixture of sulfide electrolyte and a modifying material; the sulfide electrolyte includes Li6PS5Cl (LPSCl), Li 10 GeP2S 12 (LGPS), Li7P3S 11 At least one of the following: The modified material includes at least one of GeS2, SnS2, Ta2O5, Nb2O5, lithium bis(fluorosulfonyl)imide (LTFSI), lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium chloride, and lithium fluoride.

[0058] This study found that different types of modified sulfide electrolytes and modifying materials result in differences in ionic and electronic conductivity, which affects the capacity and ion transport efficiency of solid-state batteries. When the modified sulfide electrolyte is further selected to include the above-mentioned types of materials, the resulting solid-state battery has a higher initial discharge specific capacity and first coulombic efficiency, and the resulting solid-state battery has excellent cycle performance.

[0059] In some embodiments, the mass percentage of the modified material is 2-8% based on the sum of the masses of the sulfide electrolyte and the modified material.

[0060] In some embodiments, the ball milling temperature is 15-35°C and the time is 8-10 hours.

[0061] It should be noted that the modified sulfide electrolyte log(σe / σi) can be changed by adjusting the type and amount of modified material, as well as the temperature and time of ball milling.

[0062] In one embodiment, the halide electrolyte includes at least one of lithium-rare earth metal halides, lithium-transition metal halides, and their doped solid solutions.

[0063] In one embodiment, the halide electrolyte includes Li3YCl6, Li3YBr6, Li3InCl6, Li3InBr6, Li2ZrCl6, and Li 6.25 La3Zr 1.75 Ta 0.25 O 12 At least one of Cl.

[0064] This study found that the type of halide electrolyte affects ionic conductivity and capacity utilization. When the halide electrolyte is further selected to include the above-mentioned types of substances, the resulting solid-state battery has higher initial discharge specific capacity and initial coulombic efficiency, as well as better cycle performance.

[0065] In one embodiment, the silicon has a Dv50 of 2-8 μm.

[0066] It should be noted that the Dv50 test method for the silicon is as follows: the composite negative electrode is soaked in a specific solvent (such as water) to dissolve the binder, and then pure silicon-based active material powder is obtained through centrifugation and washing. The following operations are then performed: S1. Sample dispersion: The extracted powder is placed in pure water and thoroughly ultrasonically dispersed to ensure that the particles deagglomerate and are in a native dispersed state. S2. Instrument Testing: A laser diffraction particle size analyzer was used for testing. The well-dispersed sample suspension was circulated through the instrument's measuring cell. The instrument analyzed and calculated the volumetric particle size distribution of the sample based on the diffraction pattern of the particles to the laser.

[0067] For example, the Dv50 of the silicon can be any point value between 2 and 8 μm or a range value between any two points, such as 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, etc.

[0068] This study found that the Dv50 particle size of silicon affects its volume expansion capability and also affects the ion diffusion path. When the Dv50 of silicon is further selected within the above range, the first discharge specific capacity of the solid-state battery can be effectively improved, and the cycle performance of the solid-state battery can also be improved.

[0069] It should be noted that the Dv50 of the silicon can be adjusted by ball milling and sieving.

[0070] In one embodiment, the mass percentage of silicon in the first coating is 88-92%.

[0071] It should be noted that the test method for the mass percentage of silicon in the first coating is as follows: Take the composite negative electrode and carefully peel the first coating off the current collector or the second coating using a scraper or blade. Collect the peeled coating material powder and record it as m1 (total mass). Remove the organic binder (loss on ignition): Take a portion of the sample (approximately 0.5g, accurately weighed, recorded as m2) and place it in a ceramic crucible that has been constant-weighted at high temperature. Place the crucible in a tube furnace and ignite at 600°C for 2 hours in an air or oxygen atmosphere. Under these conditions, the binder and conductive agent are completely oxidized to CO2 and H2O and removed, leaving silicon oxide (SiO2) as the remaining solid residue. After cooling, accurately weigh the residue and record it as m3. This step allows for the calculation of the total amount of organic components in the coating.

[0072] For example, in the first coating, the mass percentage of silicon can be any point value between 88-92% or a range between any two points, such as 88%, 89%, 90%, 91%, 92%, etc.

[0073] This application study found that when the mass percentage of silicon is within the above range, it can provide sufficient energy for solid-state batteries.

[0074] In one embodiment, the halide electrolyte in the third coating is 95-98% by mass.

[0075] It should be noted that the test method for the mass percentage of halide electrolyte in the third coating is as follows: take the composite negative electrode, scrape off the third coating, weigh it as m1, dissolve it in xylene, filter, dry, weigh it as m2, and m2 / m1×100% is the mass percentage of halide electrolyte.

[0076] For example, in the third coating, the mass percentage of the halide electrolyte can be any point value between 95-98% or a range between any two points, such as 95%, 96%, 97%, 98%, etc.

[0077] This study found that when the mass percentage of halide electrolytes is within the above range, they can provide a certain ionic conductivity and help with capacity utilization.

[0078] In one embodiment, the first adhesive and the second adhesive are each independently selected from at least one of water-based adhesives and oil-based adhesives.

[0079] In some embodiments, the water-based adhesive includes at least one of polyacrylic acid, styrene-butadiene rubber, sodium alginate, and polyacrylonitrile.

[0080] In some embodiments, the oil-based binder includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, and polymethyl methacrylate.

[0081] This application does not have any special requirements for the selection of the first conductive agent; any conductive agent conventionally available in the art can be selected. For example, the first conductive agent may be at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon nanotubes, activated carbon, and mesoporous carbon.

[0082] In one embodiment, the method for preparing the composite negative electrode includes the following steps: (1) Silicon, conductive agent and first binder are mixed and added to deionized water to obtain a first slurry with a solid content of 15-30%. The first slurry is coated on the surface of the negative electrode current collector and then dried and cold-pressed to obtain a first coating. (2) After mixing the modified sulfide electrolyte and the binder, add them to xylene to obtain a second slurry with a solid content of 40-55%. After coating the second slurry onto the surface of the first coating, dry it to obtain the second coating. (3) After mixing the halide electrolyte and the second binder, add them to xylene to obtain a third slurry with a solid content of 35-55%. After coating the third slurry onto the surface of the second coating, dry it to obtain a composite negative electrode.

[0083] It should be noted that the thickness of the first, second, and third coatings can be controlled by controlling the slurry solid content and the coating gap.

[0084] In a second aspect, this application provides an electrochemical device including the composite negative electrode described in this application.

[0085] In one embodiment, the electrochemical device further includes a positive electrode sheet, the positive electrode sheet comprising a current collector and a positive active material layer disposed on at least one surface of the current collector, the positive active material layer comprising a positive active material, a positive conductive agent, and a positive binder.

[0086] This application does not have any special requirements for the selection of the positive electrode active material; conventionally available positive electrode active materials in the art can be used. For example, the positive electrode active material may be selected from LiCoO2, LiNiO2, or LiNi. x Mn y O2, Li 1+z Ni x Mn y Co 1-x- y O2, LiNi x Co y Al zThe group consisting of O2, LiV2O5, LiTiS2, LiMoS2, LiMnO2, LiCrO2, LiMn2O4, Li2MnO3, LiFeO2, LiFePO4, LiMnPO4, and combinations thereof, wherein each x is independently 0.2 to 0.9; each y is independently 0.1 to 0.45; and each z is independently 0 to 0.2. The positive electrode active material of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as positive electrode active materials.

[0087] Alternatively, the positive electrode active material can be selected from LiCoO2, LiNiO2, or LiNi. x Mn y O2, Li 1+z NixMnyCo 1-x-y O2, LiNi x Co y Al z The group consisting of O2, LiV2O5, LiTiS2, LiMoS2, LiMnO2, LiCrO2, LiMn2O4, LiFeO2, LiFePO4 and combinations thereof, wherein each x is independently 0.4 to 0.6; each y is independently 0.2 to 0.4; and each z is independently 0 to 0.1.

[0088] Or the positive electrode active material is Li 1+x Ni a Mn b Co c Al (1-a-b-c) O2; where -0.2≤x≤0.2, 0≤a<1, 0≤b<1, 0≤c<1 and a+b+c≤1.

[0089] Or the positive electrode active material is Li 1+x Ni a Mn b Co c Al (1-a-b-c) O2, where 0.33≤a≤0.92, 0.33≤a≤0.9, 0.33≤a≤0.8, 0.5≤a≤0.92, 0.5≤a≤0.9, 0.5≤a≤0.8, 0.6≤a≤0.92 or 0.6≤a≤0.9; 0≤b≤0.5, 0≤b≤0.3, 0.1≤b≤0.5, 0.1≤b≤0.4, 0.1≤b≤0.3, 0.1≤b≤0.2 or 0.2≤b≤0.5; 0≤c≤0.5, 0≤c≤0.3, 0.1≤c≤0.5, 0.1≤c≤0.4, 0.1≤c≤0.3, 0.1≤c≤0.2 or 0.2≤c≤0.5.

[0090] In some embodiments, the positive electrode active material is doped with a dopant selected from the group consisting of Fe, Ni, Mn, Al, Mg, Zn, Ti, La, Ce, Sn, Zr, Ru, Si, Ge, and combinations thereof. In some embodiments, the dopant is not Fe, Ni, Mn, Mg, Zn, Ti, La, Ce, Ru, Si, or Ge. In some embodiments, the dopant is not Al, Sn, or Zr.

[0091] In some embodiments, the positive electrode active material may include LiNi. 0.33 Mn 0.33 Co 0.33 O2, LiNiO2, LiNi 0.4 Mn 0.4 Co 0.2 O2, LiNi 0.5 Mn 0.3 Co 0.2 O2, LiNi 0.6 Mn 0.2 Co 0.2 O2, LiNi 0.7 Mn 0.15 Co 0.15 O2, LiNi 0.8 Mn 0.1 Co 0.1 O2, LiNi 0.92 Mn 0.04 Co 0.04 O2, LiNi 0.8 Co 0.15 Al 0.05 At least one of O2.

[0092] This application does not have specific requirements for the selection of the positive electrode binder; conventionally available positive electrode binders in the art can be used. Exemplarily, the positive electrode binder may be at least one of the following: polyvinylidene fluoride (PVDF), poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polyvinyl butyral, polyisobutylene, polyvinylpyrrolidone (PVP), acrylic acid-acrylonitrile-acrylamide copolymer, and acrylic acid-acrylonitrile-acrylate copolymer. The positive electrode binder in this application is not limited to the above materials and also includes other materials that can be used as battery positive electrode binders.

[0093] This application does not have any special requirements for the selection of the positive electrode conductive agent; conventionally available positive electrode conductive agents in the art can be used. Exemplarily, the positive electrode conductive agent may be at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon nanotubes, activated carbon, and mesoporous carbon. The positive electrode conductive agent in this application is not limited to the above materials and also includes other materials that can be used as positive electrode conductive agents in batteries.

[0094] In a third aspect, this application provides an electronic device, which includes the electrochemical device described in this application.

[0095] Example 1 This application provides a composite negative electrode and a solid-state battery. The preparation method of the composite negative electrode and the secondary battery includes the following steps: (1) Preparation of modified sulfide electrolyte The modified sulfide electrolyte (Li6PS5Cl) and the modified material (GeS2) were ball-milled at 25°C for 12 hours at a mass ratio of 97:3 to obtain the modified sulfide electrolyte. (2) Preparation of positive electrode sheet The positive electrode material (lithium cobalt oxide), sulfide electrolyte (LPSCl), positive electrode conductive agent (carbon nanofiber), and positive electrode binder (polyisobutylene) are thoroughly mixed in xylene at a mass ratio of 80:16:2:2 and then coated onto aluminum foil. After drying and slitting, the positive electrode sheet is obtained. All the above operations are carried out in a glove box. (3) Preparation of composite negative electrode Silicon (Dv50 of 5μm), conductive carbon fiber, and first binder (polyacrylic acid) are mixed evenly in deionized water at a mass ratio of 90:5:5 to obtain a first slurry with a solid content of 20%; then the first slurry is coated on copper foil, dried at 100°C and cold-pressed to obtain a first coating with a thickness of 30μm. The modified sulfide electrolyte and binder (polyisobutylene) were mixed evenly in xylene at a mass ratio of 95:5 to obtain a second slurry with a solid content of 45%. This slurry was coated on the first coating and dried at 100°C to obtain a second coating with a thickness of 25 μm. The halide electrolyte (Li3YCl6) and the second binder (polyisobutylene) were mixed evenly in p-xylene at a mass ratio of 97:3 to obtain a third slurry with a solid content of 50%. The third slurry was then coated on the second coating and dried at 80°C to form a third coating with a thickness of 8μm, thus forming a composite negative electrode. (5) Preparation of solid-state batteries The prepared positive electrode and composite negative electrode are stacked at 500 MPa to obtain a solid-state battery.

[0096] Examples 2-4 This application provides a composite negative electrode and a solid-state battery. The difference from Embodiment 1 is that the coating amount of the first coating, the second coating and the third coating are adjusted to achieve the parameters in Table 1.

[0097] Examples 5-6 This application provides a composite negative electrode and a solid-state battery. The difference from Embodiment 1 is that the coating amount of the first coating is adjusted to achieve the parameters in Table 1.

[0098] Examples 7-8 This application provides a composite negative electrode and a solid-state battery. The difference from Embodiment 1 is that the amount of the second coating is adjusted to achieve the parameters in Table 1.

[0099] Examples 9-10 This application provides a composite negative electrode and a solid-state battery. The difference from Embodiment 1 is that the coating amount of the third coating is adjusted to achieve the parameters in Table 1.

[0100] Examples 11-13 This application provides a composite negative electrode and a solid-state battery. The difference from Example 1 is that the preparation of the modified sulfide electrolyte is adjusted to achieve the parameters in Table 1. In Example 11, the modified sulfide electrolyte (Li6PS5Cl) and the modified material (LTFSI) were ball-milled at 25°C for 12 hours at a mass ratio of 97:3 to obtain the modified sulfide electrolyte. In Example 12, a modified sulfide electrolyte (Li6PS5Cl) and a modified material (SnS2) were ball-milled at 25°C for 12 hours at a mass ratio of 97:3 to obtain the modified sulfide electrolyte. In Example 13, a modified sulfide electrolyte (Li6PS5Cl) and a modified material (Ta2O5) were ball-milled at 25°C for 12 hours at a mass ratio of 97:3 to obtain the modified sulfide electrolyte.

[0101] Example 14 This application provides a composite negative electrode and solid-state battery, which differs from Embodiment 1 in that the type of halide electrolyte is adjusted to achieve the parameters in Table 1.

[0102] Examples 15-16 This application provides a composite negative electrode and a solid-state battery. The difference from Embodiment 1 is that the Dv50 of silicon is adjusted to achieve the parameters in Table 1.

[0103] Examples 17-18 This application provides a composite negative electrode and a solid-state battery. The difference from Embodiment 1 is that the amount of components added in the first coating and the third coating is adjusted to achieve the parameters in Table 1. In Example 17, the mass ratio of silicon, conductive agent and binder in the first coating is 92:4:4; In Example 18, the mass ratio of silicon, conductive agent and binder in the first coating is 88:6:6.

[0104] Comparative Example 1 This application provides a composite negative electrode and a solid-state battery, which differs from Example 1 in that it does not have a second coating.

[0105] Comparative Example 2 This application provides a composite negative electrode and a solid-state battery, which differs from Example 1 in that it does not have a third coating.

[0106] Comparative Example 3 This application provides a composite negative electrode and a solid-state battery in comparison. The difference between this application and Example 1 is that the sulfide electrolyte is not modified.

[0107] Comparative Example 4 This application provides a composite negative electrode and a solid-state battery, which differs from Example 1 in that the positions of the second and third coatings are interchanged.

[0108] In the solid-state batteries prepared in the examples, H, H1 μm, H2 μm, H3 μm, L=log(σe / σi), sulfide electrolyte, modified materials, halide electrolyte, silicon Dv50 μm, the mass percentage of silicon in the first coating W1% and the mass percentage of halide electrolyte in the third coating W2% are shown in Table 1. Table 1 The performance of the composite anodes and solid-state batteries prepared in the examples and comparative examples is shown in Table 2; the testing methods include the following steps: 1. Charge and discharge test: In an environment of 25℃, the solid-state battery is charged to 4.5V at a constant current rate of 0.1C, and the initial charge capacity (C_charge1) is recorded; then it is discharged to 2.5V at a constant current rate of 0.1C, and the initial discharge capacity (C_discharge1) is recorded. Initial discharge specific capacity = C_discharge1 / mass of positive electrode active material (LCO) (mAh / g); Initial Coulomb efficiency = (C_discharge1 / C_charge1) × 100%.

[0109] 2. Cyclic performance test: After the first charge and discharge, 100 cycles were performed at a charge rate of 0.5C / discharge rate, and the discharge capacity (C_discharge100) of the 100th cycle was recorded. Capacity retention rate after 100 cycles = (C_discharge100 / C_discharge1) × 100%; Interfacial impedance testing: Electrochemical impedance spectroscopy (EIS) was performed after 100 cycles of the solid-state battery; The results are shown in Table 2. Table 2 As shown in Table 2, when the technical solution provided in this application is adopted, the obtained solid-state battery has a high initial discharge specific capacity and initial coulombic efficiency, as well as high cycle capacity retention and low interface impedance before and after cycling. Specifically, the obtained solid-state battery has an initial discharge specific capacity of over 154 mAh / g, an initial coulombic efficiency of over 72.2%, a capacity retention of over 72.5% after 100 cycles, and an interface impedance of over 87 Ω·cm after 100 cycles. 2 the following; As can be seen from Examples 1-18 and Comparative Examples 1-2 and 4, the effects of this application can be achieved when the second and third coatings of this application are simultaneously present and the coating sequence of this application is adopted; as can be seen from Examples 1-18 and Comparative Example 3, the effects of this application can be achieved when the modified sulfide electrolyte of this application is used.

[0110] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of this application and not to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A composite negative electrode, characterized by, The composite negative electrode comprises a negative electrode current collector and a first coating layer, a second coating layer and a third coating layer arranged in sequence on the surface of the negative electrode current collector; The first coating layer comprises silicon, a conductive agent and a first binder; The second coating layer comprises a modified sulfide electrolyte; The third coating layer comprises a halide electrolyte and a second binder.

2. The composite negative electrode according to claim 1, characterized by The composite negative electrode satisfies 0.05≤H≤0.6; wherein H=H3 / (H1+H2); H1 μm is the thickness of the first coating layer; H2 μm is the thickness of the second coating layer; H3 μm is the thickness of the third coating layer.

3. The composite negative electrode according to claim 2, characterized by The H1 μm is 20-35; and / or, the H2 μm is 10-30; and / or, the H3 μm is 5-20.

4. The composite anode according to claim 1, wherein The modified sulfide electrolyte satisfies log(σe / σi)≤-4; wherein σe is the electronic conductivity of the modified sulfide electrolyte at 25℃ / 350Mpa; σi is the ionic conductivity of the modified sulfide electrolyte at 25℃ / 350Mpa.

5. The composite anode according to claim 1, wherein The modified sulfide electrolyte is obtained by mixing a sulfide electrolyte and a modifying material by ball milling; the sulfide electrolyte comprises at least one of Li6PS5Cl (LPSCl), Li 10 GeP2S 12 (LGPS), Li7P3S 11 Cl5, Li7P3S12, Li10GeP2S12, Li10SnP2S12, Li10Ta2O5P2S12, Li10Nb2O5P2S12, Li3V2(P0.9S1.1)3, Li3V2(P0.8S1.2)3, Li3V2(P0.7S1.3)3, Li3V2(P0.6S1.4)3, Li3V2(P0.5S1.5)3, Li3V2(P0.4S1.6)3, Li3V2(P0.3S1.7)3, Li3V2(P0.2S1.8)3, Li3V2(P0.1S1.9)3, Li3V2PS3, Li3V2(P0.9S1.1)3, Li3V2(P0.8S1.2)3, Li3V2(P0.7S1.3)3, Li3V2(P0.6S1.4)3, Li3V2(P0.5S1.5)3, Li3V 6. The composite anode according to claim 1, wherein The halide electrolyte comprises at least one of lithium-rare earth metal halide, lithium-transition metal halide and their doped solid solution.

7. The composite anode according to claim 1, wherein The Dv50 of the silicon is 2-8 μm.

8. The composite anode according to claim 1, wherein In the first coating layer, the mass percentage of silicon is 88-92%; and / or, in the third coating layer, the mass percentage of halide electrolyte is 95-98%; and / or, the first binder and the second binder are each independently selected from at least one of water-based binder and oil-based binder.

9. An electrochemical device, characterized by The electrochemical device comprises the composite negative electrode according to any one of claims 1-8.

10. An electrical device, characterized by The electric device comprises the electrochemical device according to claim 9.

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