Negative electrode, preparation method and all-solid-state battery

Abstract

The invention belongs to the technical field of lithium battery production, and relates to a negative electrode, a preparation method and an all-solid-state battery, the negative electrode comprises a negative electrode active material, and the negative electrode active material comprises porous silicon carbon and nanometer silicon; the nano silicon is attached to the particle surface of the porous silicon carbon; the surface of the nano silicon is subjected to oxidation treatment; the oxygen content of the surface of the nano silicon is 0.1%-3%. According to the method, the surface of the nano silicon is subjected to oxidation treatment, so that the surface of the nano silicon is subjected to micro-oxidation to form substances such as silicon dioxide and silicon monoxide, and agglomeration of the nano silicon is prevented, so that the problems of polarization increase, capacity and energy density reduction, relatively large local expansion stress of the agglomerated nano silicon, circulation degradation and the like caused by overhigh local current density can be effectively prevented.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery production, and particularly relates to a negative electrode and a preparation method and a full solid-state battery. BACKGROUND

[0002] Silicon material is expected to be used as a negative electrode of a full solid-state battery due to its high theoretical specific capacity. In current research, in order to inhibit the expansion of silicon, the size of silicon is usually reduced, and nano-silicon is used as a negative electrode active material. However, nano-silicon is prone to agglomeration, and a large amount of binder needs to be used, which reduces the energy density of the battery.

[0003] When a combination of porous silicon carbon and nano-silicon is used, the nano-silicon acts as a conductor for transferring lithium ions. When the nano-silicon agglomerates, the lithium ion transmission path is discontinuous, and needs to detour a long distance, which increases the interface impedance, and at the same time, causes local overpotential, and accelerates the reaction of the internal side reaction of the battery. SUMMARY

[0004] In order to solve the above problems, the present application discloses a negative electrode and a preparation method and a full solid-state battery. The technical scheme of the present application is as follows:

[0005] The first aspect of the present application provides a negative electrode, which comprises a negative electrode active material and a negative electrode binder, and the negative electrode active material comprises porous silicon carbon and nano-silicon.

[0006] The surface of the porous silicon carbon particles is attached with nano-silicon.

[0007] The surface of the nano-silicon is subjected to an oxidation treatment.

[0008] The oxygen content of the surface of the nano-silicon is 0.1% to 3%.

[0009] In an embodiment, the oxygen content of the surface of the nano-silicon is 0.1% to 0.5%.

[0010] In an embodiment, the particle size D50 of the nano-silicon is 30 nm to 100 nm.

[0011] The particle size D50 of the porous silicon carbon is 2 microns to 10 microns.

[0012] The particle size D50 of the nano-silicon is greater than the pore size of the porous silicon carbon.

[0013] In an embodiment, the mass ratio of the porous silicon carbon to the nano-silicon is (1.5 to 9) to 1.

[0014] In an embodiment, the surface of the porous silicon carbon particles is provided with a coating layer.

[0015] The coating layer is a silicon layer.

[0016] In an embodiment, the negative electrode further comprises a negative solid-state electrolyte.

[0017] The solid-state electrolyte is a sulfide solid-state electrolyte.

[0018] In an embodiment, the negative electrode further comprises a negative electrode binder and a negative electrode conductive agent.

[0019] A second aspect of the present application discloses a preparation method of a negative electrode, the method being used for preparing the negative electrode disclosed in the first aspect of the present application, and the method comprises the following steps:

[0020] S1, performing an oxidation treatment on the surface of the nanosilicon;

[0021] S2, adding the porous silicon carbon and the nanosilicon to a solution containing a binder to prepare a negative electrode slurry, and coating the negative electrode slurry on a negative electrode current collector to obtain the negative electrode.

[0022] In an embodiment, in the step S1, the oxidation treatment step comprises surface passivation of the nanosilicon by introducing an oxidizing gas, and the oxidizing gas comprises O2.

[0023] A third aspect of the present application discloses an all-solid-state battery, the all-solid-state battery comprising a positive electrode, a solid-state electrolyte film and the negative electrode disclosed in the first aspect of the present application.

[0024] The advantages of the present application are as follows:

[0025] The present application performs an oxidation treatment on the surface of the nanosilicon, forms silicon dioxide and silicon monoxide and other substances on the surface of the nanosilicon by micro-oxidation, prevents the nanosilicon from agglomerating, and thus effectively prevents problems such as polarization increase, capacity and energy density decrease, local swelling stress of the agglomerated nanosilicon, and cycle degradation caused by too large local current density. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only one embodiment of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0027] Figure 1 The SEM image of the negative electrode active material in the embodiment 1 of the present application. As the only drawing of the present application, this drawing is also designated as the summary drawing. DETAILED DESCRIPTION

[0028] In the all-solid-state battery, when the combination of the porous silicon carbon and the nanosilicon is adopted, the nanosilicon acts as a conductor for transferring lithium ions. When the nanosilicon agglomerates, the lithium ion transmission path is discontinuous, needs to detour a long distance, increases the interface impedance, and at the same time, causes local overpotential and accelerates the occurrence of the internal side reaction of the battery.

[0029] To solve the above problems, the present application provides a technical scheme.

[0030] The first aspect of the present application provides a negative electrode, which comprises a negative electrode active material, and the negative electrode active material comprises porous silicon-carbon and nano-silicon.

[0031] The surface of the porous silicon-carbon particles is attached with nano-silicon.

[0032] The surface of the nano-silicon is subjected to an oxidation treatment.

[0033] The oxygen content of the surface of the nano-silicon is 0.1% to 3%.

[0034] In a full solid-state battery, nano-silicon in the negative electrode is prone to agglomeration, and a major reason is that there are dangling bonds on the surface of the nano-silicon, which easily combine adjacent nano-silicon through the dangling bonds, causing agglomeration of the nano-silicon. By slightly oxidizing the surface of the nano-silicon, agglomeration of the nano-silicon can be effectively prevented. By passivating the nano-silicon, silicon dioxide and silicon monoxide and the like can be formed on the surface of the nano-silicon. During charging, the nano-silicon is lithiated, and the silicon dioxide and silicon monoxide are converted into lithium silicate. Lithium silicate is a fast ion conductor, which is conducive to promoting the transmission of lithium ions and conducive to forming a good lithium ion transmission path in the negative electrode of the full solid-state battery.

[0035] In specific applications, the oxygen content of the surface of the nano-silicon can be selected as 0.1%, 0.2%, 0.3%, 0.5%, 0.7%, 1%, 1.1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.1%, 2.5%, 2.8%, 3%, and the like. The above listed values are only examples and are not limited, and within the understanding range of those skilled in the art, those skilled in the art can freely implement any value within the range of 0.1% to 3%.

[0036] In some preferred embodiments, the oxygen content of the surface of the nano-silicon is 0.1% to 0.5%.

[0037] In practical applications, the oxygen content of the surface of the nano-silicon can be controlled to be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, and the like. The above listed values are only examples and are not limited, and within the understanding range of those skilled in the art, those skilled in the art can freely implement any value within the range of 0.1% to 0.5%.

[0038] In some embodiments, the particle size D50 of the nano-silicon is 30 nm to 100 nm.

[0039] The particle size D50 of the porous silicon-carbon is 2 μm to 10 μm.

[0040] The particle size D50 of the nanosilicon is greater than the pore size of the porous silicon-carbon.

[0041] The present application controls the particle size of the nanosilicon so that it can be attached to the surface of the porous silicon-carbon, contributing to the capacity while transmitting lithium ions.

[0042] It can be understood that the porous silicon-carbon in the present application refers to the deposition of silicon in the pores of the porous carbon, and the pore size of the porous silicon-carbon refers to the pore size of the porous carbon. The pore size of the porous carbon in the present application is 1 nm to 15 nm.

[0043] In specific applications, the particle size D50 of the nanosilicon can be selected as 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, etc. The above listed values are only examples and are not limited, and within the understanding range of those skilled in the art, those skilled in the art can freely implement any value within the range of 30 nm to 100 nm.

[0044] The particle size D50 of the porous silicon-carbon can be selected as 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc. The above listed values are only examples and are not limited, and within the understanding range of those skilled in the art, those skilled in the art can freely implement any value within the range of 2 μm to 10 μm.

[0045] In some embodiments, the mass ratio of the porous silicon-carbon to the nanosilicon is (1.5-9):1.

[0046] It has been tested that when the mass ratio of the porous silicon-carbon to the nanosilicon is greater than the range, the mass proportion of the nanosilicon is small, which is not conducive to the formation of a continuous and stable lithium ion channel in the negative electrode, and when the mass ratio is less than the range, the negative electrode is prone to swelling, and the cycle performance of the battery is deteriorated. Therefore, the mass ratio of the porous silicon-carbon to the nanosilicon is controlled within the range of (1.5-9):1.

[0047] In specific applications, the mass ratio of the porous silicon-carbon to the nanosilicon can be selected as 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, etc. The above listed value ratios are only examples and are not limited, and within the understanding range of those skilled in the art, those skilled in the art can freely implement any value ratio within the range of (1.5-9):1.

[0048] In some embodiments, the surface of the particles of the porous silicon-carbon is provided with a coating layer;

[0049] The coating layer is a silicon layer.

[0050] In some embodiments, the coating layer is prepared by depositing silicon on the surface of the porous carbon.

[0051] In some embodiments, at least part of the nano-silicon is attached to the surface of the coating layer.

[0052] In some embodiments, the negative electrode further comprises a negative solid-state electrolyte;

[0053] The solid-state electrolyte is a sulfide solid-state electrolyte.

[0054] The sulfide solid-state electrolyte can synergize with the nano-silicon to build an efficient lithium ion transmission channel in the negative electrode.

[0055] In specific applications, the sulfide solid-state electrolyte includes Li2S-P2S5, Li2S-P2S5-MSx (wherein M is Si, Ge and Sn and 0≤x≤2), Li 3.4 Si 0.4 P 0.6 S4, Li 10 GeP2S 11.7 O 0.3 , Li 9.6 P3S 12 , Li7P3S 11 , Li9P3S9O3, Li 10.35 Si 1.35 P 1.65 S 12 , Li 9.81 Sn 0.81 P 2.19 S 12 , Li 10 (Si 0.5 Ge 0.5 )P2S 12 , Li(Ge 0.5 Sn 0.5 )P2S 12 , Li(Si 0.5 Sn 0.5 )PsS 12 , Li 10 GeP2S 12 (LGPS), Li6PS5X (wherein X is Cl, Br or I), Li7P2S8I, Li1 0.35 Ge 1.35 P 1.65 S 12 , Li 3.25 Ge 0.25 P 0.75 S4, Li 10 SnP2S12 Li 10 SiP2S 12 Li 9.54 Si 1.74 P 1.44 S 11.7 C l0.3 , or a combination of at least two of them, typical but non-limiting combinations include Li2S-P2S5 and Li2S-P2S5-MSx (where M is Si, Ge and Sn and 0≤x≤2), Li 3.4 Si 0.4 P 0.6 S4 and Li 10 GeP2S 11.7 O 0.3 Li7P3S 11 , Li9P3S9O3 and Li 10.35 Si 1.35 P 1.65 S 12 , or Li 9.81 Sn 0.81 P 2.19 S 12 , Li 10 (Si 0.5 Ge 0.5 )P2S 12 , Li(Ge 0.5 Sn 0.5 )P2S 12 and Li(Si 0.5 Sn 0.5 )PsS 12 .

[0056] In some embodiments, the negative electrode further comprises a negative electrode binder and a negative electrode conductive agent.

[0057] In specific applications, the negative electrode binder comprises one or more of carboxymethyl cellulose, nitrile rubber, styrene butadiene rubber, linear three-embedded copolymer SEBS, polytetrafluoroethylene, PVDF.

[0058] In the negative electrode, the mass fraction of the negative electrode binder is 0.1% to 10%.

[0059] In specific applications, the mass fraction of the negative electrode binder can be selected as 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 2.8%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 7%, 7.5%, 8%, 9%, 10%, etc. The above listed values are only examples and are not limiting, and within the scope of understanding of those skilled in the art, those skilled in the art can freely implement any value within the range of 0.1% to 10%.

[0060] In specific applications, the negative electrode conductive agent includes one or more of conductive carbon black, ketjen black, acetylene black, conductive graphite, vapor grown carbon fiber, carbon nanotube or graphene.

[0061] In the negative electrode, the mass percentage of the negative electrode conductive agent is 0.1% to 20%.

[0062] In specific applications, the mass percentage of the negative electrode conductive agent can be selected as 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 7%, 7.5%, 8%, 9%, 10%, 11%, 12%, 15%, 18%, 20%, etc. The above listed values are only examples and are not limiting, and within the scope of understanding of those skilled in the art, those skilled in the art can freely implement any value within the range of 0.1% to 20%.

[0063] In some embodiments, the negative electrode further includes other active materials, such as at least one of graphite, vapor-deposited silicon-carbon, sand-milled silicon, metallic tin, silicon-tin alloy and silicon-iron alloy.

[0064] A second aspect of the present application discloses a preparation method of a negative electrode, which is used to prepare the negative electrode disclosed in the first aspect of the present application, and the method comprises the following steps:

[0065] S1, performing oxidation treatment on the surface of the nano-silicon;

[0066] S2, adding the porous silicon-carbon and the nano-silicon to a solution containing a binder to prepare a negative electrode slurry, and coating the negative electrode slurry on a negative electrode current collector to obtain the negative electrode.

[0067] In specific applications, the preparation method of the nano-silicon can be one of a vapor deposition method, a vacuum evaporation method or a pulsed laser deposition method.

[0068] In some embodiments, in step S1, the oxidation treatment step includes surface passivation of the nano-silicon by introducing an oxidizing gas, and the oxidizing gas includes O2.

[0069] In some embodiments, the oxidizing gas includes a mixture of O2 and N2.

[0070] In some embodiments, in step S1, the oxidation treatment step includes high-temperature oxidation treatment at a temperature of 500 to 800°C.

[0071] In some embodiments, in step S1, the oxidation treatment step includes oxidation of the nano-silicon using an oxidizing agent. Exemplarily, the oxidizing agent can be hydrogen peroxide, which is not limited by the present application.

[0072] In some embodiments, step S2 further comprises adding a conductive agent to the solution.

[0073] In some embodiments, step S2 further comprises adding a solid-state electrolyte to the solution.

[0074] In some embodiments, step S2 further comprises adding a solid-state electrolyte to the solution.

[0075] The solid-state electrolyte film comprises a sulfide solid-state electrolyte.

[0076] The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one side surface of the positive electrode current collector.

[0077] The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one side surface of the positive electrode current collector.

[0078] As an example, the positive electrode current collector has two opposite surfaces in the thickness direction thereof, and the positive electrode active material layer is disposed on either one or both of the two opposite surfaces of the positive electrode current collector.

[0079] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be used. The composite current collector can comprise a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0080] In some embodiments, the positive electrode active material can use a positive electrode active material known in the art for a battery. As an example, the positive electrode active material can comprise at least one of the following materials: lithium-containing phosphate with olivine structure, lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive electrode active material for a battery can also be used. These positive electrode active materials can be used alone or in combination with two or more. Among them, examples of lithium transition metal oxides can include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (which can also be referred to as NCM 333 ), LiNi0.5 Co 0.2 Mn 0.3 O2(also can be referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2(also can be referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2(also can be referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2(also can be referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2), and modified compounds thereof. Examples of lithium-containing phosphates of olivine structure can include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4(also can be referred to as LFP)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite of lithium manganese iron phosphate and carbon.

[0081] In some embodiments, the positive active material layer can also optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), sodium carboxymethylcellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), styrene-ethylene-butylene-styrene copolymer (SEBS), styrene-butadiene-styrene copolymer (SBS), polyacrylic acid (PAA), lithium polyacrylate (LiPAA), sodium polyacrylate (NaPAA), sodium alginate, and lithium alginate.

[0082] In some embodiments, the positive active material layer can also optionally include a conductive agent. As an example, the conductive agent can include at least one of super P, acetylene black, conductive carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0083] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive active material, the conductive agent, and the binder, in a solvent to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector, and after processes such as drying, cold pressing, etc., the positive electrode sheet can be obtained.

[0084] Solid-state electrolyte membrane:

[0085] In some embodiments, the solid-state electrolyte film includes a solid-state electrolyte and a binder. As an example, the binder can include at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polypropylene, polyethylene, polyimide.

[0086] In some embodiments, the solid-state electrolyte is an inorganic solid-state electrolyte including one or more of an oxide solid-state electrolyte, a sulfide solid-state electrolyte, a halide solid-state electrolyte, a hydride solid-state electrolyte, a boride solid-state electrolyte, a nitride solid-state electrolyte.

[0087] The oxide solid-state electrolyte includes one or more of garnet ceramics, LISICON-type oxides, NASICON-type oxides, and perovskite-type ceramics. For example, the one or more garnet ceramics include, but are not limited to, Li 6.5 La3Zr 1.75 Te 0.25 O 12 , Li7La3Zr2O 12 , Li 6.2 Ga 0.3 La 2.95 Rb 0.05 Zr2O 12 , Li 6.85 La 2.9 Ca 0.1 Zr 1.75 Nb 0.25 O 12 , Li 6.25 Al 0.25 La3Zr2O 12 , Li 6.75 La3Zr 1.75 Nb 0.25 O 12 . The one or more LISICON-type oxides include, but are not limited to, Li 14 Zn(GeO4)4, Li 3+x (P 1-x Si x )O4 (where 0 < x < 1), Li 3+x Ge x V 1-x O4 (where 0 < x < 1). The one or more NASICON-type oxides can be defined by LiMM'(PO4)3, where M and M' are independently selected from Al, Ge, Ti, Sn, Hf, Zr, and La. For example, in certain variations, the one or more NASICON-type oxides include, but are not limited to, Li 1+x Al x Ge2-x (PO4)3(LAGP) (wherein 0 < x < 2), Li 1+x Al x Ti 2-x (PO4)3(LATP) (wherein 0 < x < 2), Li 1+ x Y x Zr 2-x (PO4)3(LYZP) (wherein 0 < x < 2), Li 1.3 Al 0.3 Ti 1.7 one or more of LiTi2(PO4)3, LiGeTi(PO4)3, LiGe2(PO4)3, LiHf2(PO4)3. One or more perovskite-type ceramics include, but are not limited to, Li 3.3 La 0.53 TiO3, LiSr 1.65 Zr 1.3 Ta 1.7 O9, Li 2x-y Sr 1-x Ta y Zr 1-y O3 (wherein x = 0.75y and 0.60 < y < 0.75), Li 3 / 8 Sr 7 / 16 Nb 3 / 4 Zr 1 / 4 O3, Li 3x La (2 / 3-x) TiO3 (wherein 0 < x < 0.25).

[0088] Sulfide solid state electrolytes include, but are not limited to, Li2S-P2S5, Li2S-P2S5-MS x (wherein M is Si, Ge, and Sn and 0 < x < 2), Li 3.4 Si 0.4 P 0.6 S4, Li 10 GeP2S 11.7 O 0.3 , Li 9.6 P3S 12 , Li7P3S 11 , Li9P3S9O3, Li 10.35 Si 1.35 P 1.65 S 12 , Li 9.81 Sn 0.81 P 2.19 S 12 , Li 10 (Si 0.5 Ge0.5 )P2S 12 、Li(Ge 0.5 Sn 0.5 )P2S 12 、Li(Si 0.5 Sn 0.5 )PsS 12 、Li 10 GeP2S 12 (LGPS), Li6PS5X (where X is selected from Cl, Br, or I), Li7P2S8I, Li 10.35 Ge 1.35 P 1.65 S 12 、Li 3.25 Ge 0.25 P 0.75 S4, Li 10 SnP2S 12 、Li 10 SiP2S 12 、Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 、 (1-x) P2S 5-x Li2S (where 0.5 ≤ x ≤ 0.7) or more of them.

[0089] Halide solid electrolytes include but are not limited to Li2CdC l4 、Li2MgC l4 、Li2Cd I4 、Li2ZnI4, Li3OCl, LiI, Li5ZnI4, Li3OCl 1-x Br x (where 0 < x < 1) or more of them.

[0090] Boride solid electrolytes include but are not limited to Li2B4O7, Li2O-(B\(_2\)O\(_3\))-(P\(_2\)O\(_5\)) or more of them.

[0091] Nitride solid electrolytes include but are not limited to Li3N, Li7PN4, LiSi2N3, LiPON or more of them.

[0092] Hydride solid electrolytes include but are not limited to Li3AlH6, LiBH4, LiBH4-LiX (where X is one of Cl, Br, and I), LiNH2, Li2NH, LiBH4-LiNH2 or more of them.

[0093] In some embodiments, the inorganic solid-state electrolyte can also be one or more metal oxide particles or lithium-containing compounds, including but not limited to one or more of Al2O3, SiO2, TiO2, LiNbO3, Li4Ti5O4, Li3PO4.

[0094] In some embodiments, the solid-state electrolyte further comprises a partial polymer solid-state electrolyte, and the polymer solid-state electrolyte and the inorganic solid-state electrolyte form a composite solid-state electrolyte. In the embodiments of the present application, the mass ratio of the inorganic solid-state electrolyte and the polymer solid-state electrolyte in the composite solid-state electrolyte is not particularly required, and the user can design it according to the actual needs. Among them, the polymer solid-state electrolyte can be at least one of polyvinyl chloride (PVC), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), and polyethylene oxide (PEO).

[0095] The embodiments of the present application will be described more specifically below through examples and comparative examples. It should be noted that the embodiments of the present application are not limited only to these examples.

[0096] In addition, in order to reduce errors, the same process is used in the preparation method of all the all-solid-state batteries in the embodiments and comparative examples of the present application, and the positive electrode and the solid-state electrolyte film are also completely the same. Specifically as follows:

[0097] Step one, preparation of the positive electrode:

[0098] 97.8wt% LiCoO2, 0.8wt% polyvinylidene fluoride and 1.4wt% conductive carbon black were mixed and added to the solvent N-methyl pyrrolidone to form a positive electrode slurry. The positive electrode slurry was coated on both sides of the positive electrode current collector aluminum foil, and after drying and rolling, the positive electrode sheet was obtained.

[0099] Step two, preparation of the solid-state electrolyte film:

[0100] The sulfide solid-state electrolyte Li6PS5Cl and polytetrafluoroethylene were mixed in a mass ratio of 96:4 to obtain a mixture, which was ground for 30 min to obtain a sulfide solid-state electrolyte sheet. The obtained sulfide solid-state electrolyte sheet was hot-rolled to prepare a solid-state electrolyte film.

[0101] Oxygen content characterization method: LC-Elementrac ONH-p oxygen nitrogen hydrogen analyzer was used for testing. Specifically, the following steps were included: 10 mg of the sample to be tested (oxidized nano-silicon) was placed in a nickel capsule, which was placed in a graphite crucible through a gas lock, and the crucible was placed on a detection base. The test software was started for testing.

[0102] Example 1:

[0103] Preparation of the negative electrode:

[0104] S1, oxidizing the surface of nanosilicon: nanosilicon is prepared by chemical vapor deposition, and high-temperature oxidation passivation is performed after the preparation of nanosilicon is completed. Oxygen gas is introduced during the oxidation process. The specific process is as follows:

[0105] The temperature is slowly increased to 600 DEG C within 30 min, the mixed gas O2 / N2 is introduced, the oxygen concentration in the mixed gas is 1%, the flow rate is 0.1 mL / min, and the temperature is kept for 120 min. The surface-oxidized nanosilicon is prepared.

[0106] The oxygen content on the surface of the prepared nanosilicon is 0.1%.

[0107] S2, porous silicon carbon and nanosilicon are added to the N-methyl-2-pyrrolidone solution of PVDF and mixed to form a slurry. The weight ratio of the negative electrode active material to PVDF is 99:1, and the negative electrode slurry is prepared by mixing. The negative electrode slurry is coated on the negative electrode current collector copper foil, dried, and sliced to obtain the negative electrode. The average particle size D50 of the nanosilicon is 35 nm, and the average particle size D50 of the porous silicon carbon is 4 μm. The mass ratio of the porous silicon carbon to the nanosilicon is 3:1.

[0108] The negative electrode prepared in this embodiment, the solid electrolyte membrane obtained in step two, and the positive electrode prepared in step one are stacked in order to assemble a battery cell. After the tab welding of the battery cell, the battery cell is placed in an aluminum plastic film, vacuumized, and then thermoplastic sealed. After sealing, the above-mentioned battery cell is subjected to isostatic pressing treatment under an ultra-high pressure of 500 MPa for 5 min, so that the components in the battery cell have good solid-solid interface contact. A full solid-state battery is obtained.

[0109] Example 2:

[0110] The process of preparing the negative electrode and the process of preparing the full solid-state battery in this embodiment are basically the same as those in Example 1, and the only difference is that in this embodiment, the oxygen concentration in the mixed gas is adjusted to 2%, so that the oxygen content on the surface of the nanosilicon is 0.2%.

[0111] Example 3:

[0112] The process of preparing the negative electrode and the process of preparing the full solid-state battery in this embodiment are basically the same as those in Example 1, and the only difference is that in this embodiment, the oxygen concentration in the mixed gas is adjusted to 3%, so that the oxygen content on the surface of the nanosilicon is 0.3%.

[0113] Example 4:

[0114] The process of preparing the negative electrode and the process of preparing the full solid-state battery in this embodiment are basically the same as those in Example 1, and the only difference is that in this embodiment, the oxygen concentration in the mixed gas is adjusted to 4%, so that the oxygen content on the surface of the nanosilicon is 0.4%.

[0115] Example 5:

[0116] The process of preparing the negative electrode and the process of preparing the full solid-state battery in this example are basically the same as those in Example 1, except that in this example, the oxygen concentration in the mixed gas is adjusted to 5%, so that the oxygen content on the surface of the nano-silicon is 0.5%.

[0117] Example 6:

[0118] The process of preparing the negative electrode and the process of preparing the full solid-state battery in this example are basically the same as those in Example 1, except that in this example, the oxygen concentration in the mixed gas is adjusted to 10%, so that the oxygen content on the surface of the nano-silicon is 1%.

[0119] Example 7:

[0120] The process of preparing the negative electrode and the process of preparing the full solid-state battery in this example are basically the same as those in Example 1, except that in this example, the oxygen concentration in the mixed gas is adjusted to 20%, so that the oxygen content on the surface of the nano-silicon is 2%.

[0121] Example 8:

[0122] The process of preparing the negative electrode and the process of preparing the full solid-state battery in this example are basically the same as those in Example 1, except that in this example, the oxygen concentration in the mixed gas is adjusted to 30%, so that the oxygen content on the surface of the nano-silicon is 3%.

[0123] Example 9:

[0124] The process of preparing the negative electrode and the process of preparing the full solid-state battery in this example are basically the same as those in Example 5, except that in this example, the average particle size D50 of the nano-silicon is 50 nm.

[0125] Example 10:

[0126] The process of preparing the negative electrode and the process of preparing the full solid-state battery in this example are basically the same as those in Example 5, except that in this example, the average particle size D50 of the nano-silicon is 150 nm.

[0127] Comparative Example 1:

[0128] Preparation of the negative electrode:

[0129] The porous silicon carbon and the nano-silicon with a mass ratio of 3:1 were added to a PVDF-containing N-methyl-2-pyrrolidone solution and mixed to form a slurry. Among them, the weight ratio of the negative electrode active material to PVDF is 99:1. And mixed to prepare the negative electrode slurry, the negative electrode slurry was coated on the negative electrode current collector graphite, dried, and sliced to obtain the negative electrode. Among them, the average particle size D50 of the nano-silicon is 35 nm, and the average particle size D50 of the porous silicon carbon is 4 μm.

[0130] The negative electrode prepared in this example, the solid-state electrolyte film obtained in step two, and the positive electrode prepared in step one are stacked in order to assemble a battery cell. After welding the tabs of the battery cell, the battery cell is placed in an aluminum plastic film, vacuumized, and heat sealed. After sealing, the battery cell is subjected to isostatic pressing at an ultra-high pressure of 500 MPa for 5 min, so that the components in the battery cell have good solid-solid interface contact, and a full solid-state battery is obtained.

[0131] Comparative Example 2:

[0132] The process of preparing the negative electrode in this example and the process of preparing the full solid-state battery are basically the same as in Example 5, except that in this example, the surface oxygen content of the nano-silicon is 8%.

[0133] Comparative Experiment:

[0134] Twelve groups of full solid-state battery samples were taken from Examples 1-10 and Comparative Examples 1-2, and were respectively subjected to the following tests.

[0135] 300-cycle capacity retention rate test:

[0136] At a temperature of 25°C (room temperature), the battery was charged to a charge cut-off voltage of 4.25V at a current of 1C, converted to constant voltage charging until the cut-off current was 0.05C, rested for 0.5h, then discharged to a cut-off voltage of 3.0V at a current of 1C, rested for 0.5h, and entered the next charge-discharge cycle. This was repeated for a total of 300 charge-discharge cycles. The capacity retention rate = the discharge capacity after the 300th cycle / the initial discharge capacity.

[0137] 2. Rate performance:

[0138] At a temperature of 45°C, the fully charged battery was discharged to a cut-off voltage of 3.0V at a current of 0.1C, and the capacity obtained was C0.

[0139] At a temperature of 45°C, the fully charged battery was discharged to a cut-off voltage of 3.0V at a current of 1C, and the capacity obtained was C1. C1 / C0 was the 1C / 0.1C discharge capacity retention rate.

[0140] The test results are shown in the following table:

[0141]

[0142] From the above table, it can be seen that:

[0143] Comparative Example 1-Example 8, by oxidation treatment of nano-silicon, when the surface oxygen content of nano-silicon is 0.1% to 3%, it is beneficial to improve the cycle performance and rate performance, when the surface oxygen content of nano-silicon is 1% to 3%, the improvement effect decreases, the possible reason is that the increase of the surface oxygen content of nano-silicon leads to the generation of silicon dioxide on the surface of nano-silicon, which leads to the increase of the impedance of the battery and the decrease of the improvement effect of the rate performance.

[0144] Comparative Example 1, Comparative Example 1 and Comparative Example 2, the surface of nano-silicon is not treated by oxidation, the cycle performance and rate performance are not good, but if the surface oxygen content of nano-silicon exceeds 3%, it will affect the cycle performance and rate performance of the all-solid-state battery. Therefore, the surface oxygen content of nano-silicon should be controlled within a certain range (0.1% to 3%).

[0145] Comparative Example 5, Example 9 and Example 10, the increase of the particle size of nano-silicon will reduce the cycle performance and rate performance, because the increase of the particle size of nano-silicon leads to the decrease of the contact area of nano-silicon and porous silicon carbon and the expansion of nano-silicon itself.

[0146] It should be noted that the above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A negative electrode comprising a negative electrode active material and a negative electrode binder, characterized in that, The negative active material comprises porous silicon-carbon and nano-silicon; The surface of the porous silicon-carbon particles is attached with the nano-silicon; The surface of the nano-silicon is subjected to an oxidation treatment; The oxygen content of the surface of the nano-silicon is 0.1%-3%.

2. The negative electrode according to claim 1, characterized by The oxygen content of the surface of the nano-silicon is 0.1%-0.5%.

3. The negative electrode according to claim 1, characterized by The particle size D50 of the nano-silicon is 30nm-100nm; The particle size D50 of the porous silicon-carbon is 2um-10um; The particle size D50 of the nano-silicon is greater than the pore size of the porous silicon-carbon.

4. The negative electrode according to claim 1, characterized by The mass ratio of the porous silicon-carbon to the nano-silicon is (1.5-9):

1.

5. The negative electrode according to claim 1, wherein The surface of the porous silicon-carbon particles is provided with a coating layer; The coating layer is a silicon layer.

6. The negative electrode according to claim 1, wherein The negative electrode further comprises a negative electrode solid electrolyte, and the negative electrode solid electrolyte is a sulfide solid electrolyte.

7. The negative electrode according to claim 1, wherein The negative electrode further comprises a negative electrode conductive agent.

8. A method for producing a negative electrode, characterized by The method comprises the following steps: S1, performing an oxidation treatment on the surface of the nano-silicon; S2, adding the porous silicon-carbon and the nano-silicon to a solution containing a binder to prepare a negative electrode slurry, and coating the negative electrode slurry on a negative electrode current collector to obtain a negative electrode.

9. The method of claim 8, wherein, In step S1, the oxidation treatment step comprises surface passivation of the nano-silicon by introducing an oxidizing gas, and the oxidizing gas comprises O2.

10. An all-solid battery comprising a positive electrode, a solid electrolyte film, characterized by, The negative electrode as claimed in any one of claims 1-7. The negative electrode as claimed in any one of claims 1-7.

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