Composite negative electrode sheet and use thereof in solid-state battery

Abstract

The present disclosure provides a composite negative electrode sheet and a use thereof in a solid-state battery. The composite negative electrode sheet comprises a silicon active material and a metal compound, and in the process of silicon lithiation, a ternary Zintl phase Li-M-Si and an ionic conductive phase lithium compound are formed, wherein the mass ratio of the metal compound to the silicon active material is 5%-30%. According to the technical solution, by compounding the silicon active material with the metal compound, the ternary Zintl phase Li-M-Si can be formed in situ within a silicon-based negative electrode. The ternary Zintl phase has a stable structure, which can alleviate the volume expansion problem of silicon and enhance cycle stability. In addition, the lithium compound is formed to act as an ionic conductive phase, accelerating ion transport, enhancing lithium-ion transport kinetics, and improving the rate performance of batteries.

Description

A composite negative electrode sheet and its application in solid-state batteries Technical Field

[0001] The embodiments of the present disclosure generally relate to the field of lithium-ion battery technology, and more specifically, to a composite negative electrode sheet and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries (LIBs) have become the most important energy supply device supporting the normal operation of portable devices such as mobile phones, laptops, and cameras. Currently, lithium-ion batteries have safety issues due to the use of flammable organic electrolytes. Compared with organic electrolytes, solid-state electrolytes have many advantages, such as higher safety, better thermal stability, and good machinability. All-solid-state batteries have become the future development direction. Solid-state electrolytes have attracted widespread attention due to their high ionic conductivity and processability. At the same time, with the development of new solid electrolyte materials, electrode design has a great influence on the electrochemical performance of solid-state electrodes. In particular, with the development of electric vehicles, the demand for high-energy-density batteries is increasing. However, the low specific capacity of the negative electrode currently limits the development of high-energy-density batteries.

[0003] Silicon anode active materials are widely recognized as one of the next generation of advanced anode materials due to their ultra-high theoretical specific capacity, superior safety compared to lithium metal, vast natural reserves, widespread accessibility, and low cost. In liquid batteries, ion transport is excellent due to the presence of electrolyte infiltration. However, with solid electrolytes, the solid-solid interface between the silicon and solid electrolyte results in sluggish ion dynamics at the interface. Furthermore, the dramatic volume changes during lithiation and delithiation of the silicon anode can cause cracks in the silicon anode active material, leading to stress concentration at the interface between the silicon and solid electrolyte, and consequently, cracks within the electrolyte, resulting in poor cycling stability. Current improvement strategies include size and shape control of the silicon active material, carbon doping, and surface coating. Alternatively, direct introduction of Si and Na can first form a NaSi compound with a Zinter phase, followed by de-Na removal from the NaSi compound to form a sodium-silicon inclusion complex crystalline phase. This can mitigate the volume expansion of silicon during charge and discharge by intercalating and deintercalating metal ions. However, the known methods are highly complex, for example, they require sealing under an argon atmosphere, heat treatment at 700°C for 20 hours, crushing the obtained NaSi compound, and heat treatment under vacuum (about 0.1 Pa) at 450°C for 5 hours to remove Na. Summary of the Invention

[0004] In order to solve or at least partially solve the above-mentioned defects, according to the embodiments of the present disclosure, a composite negative electrode plate and its preparation method and application are provided, which can effectively alleviate the volume expansion problem of silicon-based negative electrodes, improve cycle stability, and enhance the lithium ion transmission of the electrode, so that the silicon gram capacity is higher.

[0005] In a first aspect of the present disclosure, a composite negative electrode plate is provided. The composite negative electrode plate comprises a silicon active material and a metal compound, and during the silicon lithiation process, a ternary Zinter phase Li-M-Si and an ion-conducting phase lithiated material are formed; wherein:

[0006] The mass ratio of the metal compound to the silicon active material is 5%-30%, for example, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%.

[0007] When the content of the metal compound is lower than 5%, the content of the Zinter phase and the high ion conductive phase formed is relatively small, which cannot effectively restrain the volume expansion and improve the ion transport. When the content of the metal compound is higher than 30%, the in-situ complete lithiation to the Li-Mg-Si phase is limited due to the high content of the metal compound, and a large amount of residual metal compound is not conducive to lithium ion transport. The most preferred range is 10%-25%.

[0008] According to the aspects and any possible implementation described above, an implementation is further provided, wherein the metal of the metal compound is selected from at least one of the group II, group III, group IV, group I, group II and group VIII, and the non-metal is selected from P or N.

[0009] According to the aspects and any possible implementation described above, an implementation is further provided, wherein the metal compound is selected from at least one of X3Y2 (X=Mg, Ca, Sr, Ba, Zn; Y=P, N), XY (X=Al, Ga, In, Ti, Ge, Sn, Pb, Y=P, N), and X2Y (X=Ni, Y=P, N).

[0010] According to the above aspects and any possible implementation, an implementation is further provided, wherein the silicon active material is selected from at least one of Si, SiO, and Si—C.

[0011] According to the above aspects and any possible implementation, there is further provided an implementation, wherein the composite negative electrode plate further comprises an electrolyte, a conductive agent, and a binder.

[0012] According to the above aspects and any possible implementation, there is further provided an implementation, wherein the Young's modulus of the electrolyte is ≤500 GPa, preferably ≤200 GPa.

[0013] The electrolyte is specifically selected from at least one of a sulfide electrolyte, an oxide electrolyte, a halide electrolyte, a polymer electrolyte, and a borohydride electrolyte.

[0014] According to the above aspects and any possible implementation, an implementation is further provided, wherein the conductive agent is selected from at least one of SuperP, SuperS, 350G, acetylene black, carbon fiber, carbon nanotubes, Ketjen black, graphite and graphene.

[0015] According to the aspects and any possible implementations described above, an implementation is further provided, wherein the binder is selected from at least one of polyvinylidene fluoride, polyacrylic acid, sodium polyacrylate, styrene-butadiene rubber, nitrile rubber, polytetrafluoroethylene, alginic acid, sodium alginate, carboxymethyl cellulose or sodium carboxymethyl cellulose.

[0016] According to the above aspects and any possible implementation, an implementation is further provided, wherein the solvent is selected from one of N-methylpyrrolidone, toluene, xylene, acetone, hexane and heptane, butyl butyrate and benzyl acetate, or any combination thereof in any proportion.

[0017] According to the above aspects and any possible implementation, an implementation is further provided, wherein the current collector is selected from copper foil and stainless steel.

[0018] In a second aspect of the present disclosure, a method for preparing a composite negative electrode sheet is provided. The method comprises the following steps:

[0019] dissolving the binder in a solvent;

[0020] According to the mass ratio of the metal compound to the silicon active material being 5% to 30%, the silicon active material and the metal compound are added to the solvent mixed with the binder, and the mixture is stirred to obtain a mixed slurry;

[0021] The mixed slurry is coated on the surface of a current collector (eg, copper foil), heated and dried to obtain a composite negative electrode sheet.

[0022] In some embodiments, an electrolyte and a conductive agent are added when the metal compound and the silicon active material are mixed.

[0023] In a third aspect of the present disclosure, a method for preparing a composite negative electrode sheet is provided. The method comprises the following steps:

[0024] The mass ratio of the metal compound to the silicon active material is 5%-30%, and the silicon active material and the metal compound are directly ground and rolled into sheets;

[0025] The dry electrode sheet is compounded with a current collector via a conductive adhesive to obtain a composite negative electrode sheet.

[0026] In some embodiments, an electrolyte and a conductive agent are added when the metal compound and the silicon active material are mixed.

[0027] In the fourth aspect of the present disclosure, there is provided an application of a composite negative electrode sheet based on the composite negative electrode sheet as described in the first aspect of the present disclosure or a composite negative electrode sheet prepared by the preparation method of the second and third aspects of the present disclosure in an all-solid-state battery, that is, an all-solid-state battery is prepared by the preparation method of the second and third aspects of the present disclosure, which contains the composite negative electrode sheet as described in the first aspect of the present disclosure.

[0028] The present disclosure provides a composite negative electrode plate, a preparation method, and an application thereof. By compounding a silicon active material and a metal compound, a Li-M-Si ternary Zinter phase is formed in situ in the silicon-based negative electrode system. The ternary Zinter phase has a stable structure, can alleviate the volume expansion problem of silicon, and improve cycle stability. At the same time, the interfacial lithium compounds (Li3P, Li3N) formed have high ionic conductivity and can serve as an ion conductive phase to accelerate ion transport, enhance lithium ion transport kinetics, and improve the rate performance of the composite plate.

[0029] It should be understood that the contents described in the disclosure section are not intended to limit the key or important features of the embodiments of the present disclosure, nor are they intended to limit the scope of the present disclosure. Other features of the present disclosure will become readily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a structural diagram for testing the ionic conductivity of composite negative electrode materials.

[0031] FIG2 is an XPS spectrum of Si 2p in the first cycle charge state of Example 2.

[0032] FIG3 is an XPS spectrum of P 2p in the first cycle charge state of Example 2. DETAILED DESCRIPTION

[0033] To make the purpose, technical solutions, and advantages of the embodiments of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure are clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present disclosure, not all of the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present disclosure.

[0034] In this document, the term "and / or" simply describes a relationship between related objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, or B exists alone. Furthermore, the character " / " in this document generally indicates that the related objects are in an "or" relationship.

[0035] The present disclosure provides a composite negative electrode sheet, a preparation method thereof, and an application thereof. Metal compounds, such as metal phosphides Mg3P2, Ca3P2, Zn3P2, Sn4P3, AlP, and metal nitrides Mg3N2, Ca3N2, Zn3N2, and AlN, are added to the silicon negative electrode to form a Li-M-Si ternary Zinter phase (M = Ca, Mg, Zn, Al, Sn, etc.) in situ during the lithiation process. Due to the high structural stability of the ternary Zinter phase, the volume expansion of silicon can be alleviated, and the cycle stability of the silicon negative electrode can be improved. At the same time, the lithium compounds Li3P and LiN formed at the interface are high ionic conductivity phases, which enhance the lithium ion transport of the electrode and improve the battery rate performance. Compared with directly introducing the Zinter phase into the negative electrode active material, in-situ lithiation directly binds the silicon in the Zinter phase, which can better alleviate the volume expansion problem of silicon.

[0036] The mass ratio of the metal compound to the silicon active material is 5%-30%, and the preferred mass ratio is 10%-25%.

[0037] The embodiments of the present disclosure are described in detail below. The composite negative electrode provided by the embodiment of the first aspect of the present disclosure is composed of a ternary Zintl phase Li-M-Si, an ion-conductive phase lithium compound, a silicon active material, and a binder. It may also include an electrolyte and a conductive agent. The metal compound accounts for 5% to 30% by mass of the silicon active material, with a preferred mass ratio of 10% to 25%.

[0038] The silicon active material is at least one selected from Si, a silicon-oxygen composite material (SiO), and a silicon-carbon composite material (Si—C).

[0039] The metal of the metal compound is selected from at least one of Group II, Group III, Group IV, Group I, Group II, and Group VIII, and the non-metal is selected from phosphorus (P) or nitrogen (N). Furthermore, the metal compound is selected from at least one of X3Y2 (X = Mg, Ca, Sr, Ba, Zn; Y = P, N), XY (X = Al, Ga, In, Ti, Ge, Sn, Pb, Y = P, N), and X2Y (X = Ni, Y = P, N).

[0040] During the silicon lithiation process, Si is first lithiated to LiSi, and then the metal phase is inserted into the LiSi phase to form a ternary Zinter phase Li-M-Si (M is a metal compound), and at the same time, a high ionic conductivity phase lithium compound Li3P or LiN is introduced.

[0041] Furthermore, the Young's modulus of the electrolyte is ≤500 GPa, preferably ≤200 GPa, and the electrolyte is specifically selected from at least one of a sulfide electrolyte, an oxide electrolyte, a halide electrolyte, a polymer electrolyte, and a borohydride electrolyte. Preferably, the electrolyte is selected from zLi2S·(100-z)P2S5 (0≤z≤100), Li3PS4, Li7P3S 11 、Li6PS5X (X=C1、Br、I) and its derivative systems、Li 10 M'P2S 12 (M'=Ge, Sn), Li 3.25 Ge 0.25 P 0.75 S4、Li4GeS4、Li 11 Sn2PS 12 、Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 、Li3InCl6 and its derivative systems、Li 0.388 Ta 0.238 La 0.475 Cl3 and its derivative systems, Li5X3M"2O 12 (M" = Ta and Nb), Li7La3Zr2O 12 and its derivative systems 、 La 2 / 3-x Li 3x At least one of TiO3 and its derivative systems, NaZr2(PO4)3 and its derivative systems, PEO base and its derivatives, polymers PPC, PAN, PDMS, PVDF and PMMA, LiBH4 and its derivatives.

[0042] The conductive agent is selected from at least one of acetylene black, carbon fiber, carbon nanotube, Ketjen black, graphite and graphene.

[0043] The binder is selected from one of polyvinylidene fluoride, polyacrylic acid, sodium polyacrylate, styrene-butadiene rubber, nitrile rubber, alginic acid, sodium alginate, carboxymethyl cellulose or sodium carboxymethyl cellulose, or any combination thereof in any proportion.

[0044] The solvent is selected from one of N-methylpyrrolidone, toluene, xylene, acetone, hexane and heptane, butyl butyrate and benzyl acetate, or any combination thereof in any proportion.

[0045] The current collector is selected from one of stainless steel and copper foil.

[0046] The second aspect of the present disclosure provides a method for preparing a composite negative electrode sheet, comprising the following steps:

[0047] 1) Dissolve the binder in the solvent and stir for 5 hours.

[0048] 2) According to the mass ratio of metal compound to silicon active material being 5%-30%, silicon active material, metal compound, optional electrolyte, and optional conductive agent are added to the above solvent mixed with binder, and mixed and stirred to obtain a mixed slurry.

[0049] Preferably, the mass ratio of the metal compound to the silicon active material is 10%-25%, the stirring speed is 2000 rpm, and the stirring is performed for 2 hours.

[0050] 3) Applying the mixed slurry to the current collector, heating and drying it to obtain a composite negative electrode sheet.

[0051] Preferably, the mixed slurry is coated on a copper foil, heated at 60° C. for 2 hours, and then heated to 120° C. and kept for 6-15 hours for drying.

[0052] The third aspect of the present disclosure provides a method for preparing a composite negative electrode sheet, comprising the following steps:

[0053] 1) The mass ratio of the metal compound to the silicon active material is 5%-30%. The silicon active material, the metal compound, the optional electrolyte and the optional conductive agent are mixed uniformly.

[0054] 2) The mixed sample was fibrillated at 100°C.

[0055] 3) The fibrillated sample was rolled into a sheet.

[0056] 4) Compounding the dry-process electrode sheet with a current collector via a conductive adhesive to obtain a composite negative electrode sheet.

[0057] Based on the above method for preparing the composite negative electrode sheet, the present disclosure has the following embodiments, and the following comparative examples are made to compare and analyze the performance of the composite negative electrode sheet of the present disclosure:

[0058] [Example 1]

[0059] 1) Dissolve the binder nitrile rubber in toluene solvent, rotate at 800 rpm, and stir for 5 hours.

[0060] 2) Add the above silicon active material, metal compound, electrolyte, and conductive agent to a solvent at a solid content of 50% according to the mass ratio of active material silicon: metal compound: electrolyte: conductive agent: binder = Si: Mg3N2: Li6PS5Cl: Super P: nitrile rubber = 75:15:5:3:2, and mix and stir at a speed of 2000 rpm for 2 hours to obtain a mixed slurry.

[0061] 3) The mixed slurry was coated on copper foil, heated at 60°C for 2 hours, and then baked at 120°C for 10 hours.

[0062] [Example 2]

[0063] Example 2 includes the following steps:

[0064] 1) Dissolve the binder nitrile rubber in toluene solvent, rotate at 800 rpm, and stir for 5 hours.

[0065] 2) Add the silicon active material, metal compound, electrolyte, and conductive agent to a solvent at a solid content of 50% according to the mass ratio of active material silicon: metal compound: electrolyte: conductive agent: binder = Si: Mg3P2: Li6PS5Cl: Super P: nitrile rubber = 75:15:5:3:2, and mix and stir at a speed of 2000 rpm for 2 hours to obtain a mixed slurry.

[0066] 3) The mixed slurry was coated on copper foil, heated at 60°C for 2 hours, and then baked at 120°C for 10 hours.

[0067] The electrode was assembled into a solid-state battery and cycled at 0.1C for 3 cycles. The battery was stopped in the lithium-intercalation state on the third cycle. The battery was then disassembled, the negative electrode was peeled off, and sent for XPS testing. The test results are shown in Figures 2 and 3.

[0068] [Example 3]

[0069] Example 3 includes the following steps:

[0070] 1) Dissolve the binder styrene-butadiene rubber and sodium hydroxymethyl cellulose in deionized water solvent at 800 rpm and stir for 5 hours.

[0071] 2) According to the mass ratio of active material silicon: metal compound: electrolyte: conductive agent: binder = Si: Zn3N2: Li 0.388 Ta 0.238 La 0.475 Cl3: carbon nanotube: binder = 75:15:5:3:2. Add the above-mentioned silicon active material, metal compound, electrolyte, and conductive agent to the solvent with a solid content of 50%, mix and stir at a speed of 2000 rpm for 2 hours to obtain a mixed slurry.

[0072] 3) The mixed slurry was coated on copper foil, heated at 60°C for 2 hours, and then baked at 120°C for 10 hours.

[0073] [Example 4]

[0074] Example 4 includes the following steps:

[0075] 1) Dissolve the adhesive styrene-butadiene rubber in toluene solvent at 800 rpm and stir for 5 hours.

[0076] 2) Add the above silicon active material, metal compound, electrolyte, and conductive agent to a solvent according to the mass ratio of active material silicon: metal compound: electrolyte: conductive agent: binder = Si: Sn4P3: Li3PS4: graphene: nitrile rubber = 75:15:5:3:2, with a solid content of 50%, mix and stir at a speed of 2000 rpm for 2 hours to obtain a mixed slurry.

[0077] 3) The mixed slurry was coated on copper foil, heated at 60°C for 2 hours, and then baked at 120°C for 10 hours.

[0078] [Example 5]

[0079] Example 5 includes the following steps:

[0080] 1) Dissolve the binder nitrile rubber in toluene solvent, rotate at 800 rpm, and stir for 5 hours.

[0081] 2) Add the silicon active material, metal compound, electrolyte, and conductive agent to a solvent at a solid content of 50% according to a mass ratio of active material silicon: metal compound: electrolyte: conductive agent: binder = Si: AlN: Li6PS5Cl: Super P: nitrile rubber = 75:15:5:3:2, and mix and stir at a speed of 2000 rpm for 2 hours to obtain a mixed slurry.

[0082] 3) The mixed slurry was coated on copper foil, heated at 60°C for 2 hours, and then baked at 120°C for 10 hours.

[0083] [Example 6]

[0084] Example 6 includes the following steps:

[0085] 1) Dissolve the binder nitrile rubber in toluene solvent, rotate at 800 rpm, and stir for 5 hours.

[0086] 2) Add the silicon active material, metal compound, electrolyte, and conductive agent to a solvent at a solid content of 50% according to a mass ratio of active material silicon: metal compound: electrolyte: conductive agent: binder = Si: Ni2P: Li6PS5Cl: Super P: nitrile rubber = 75:15:5:3:2, and mix and stir at a speed of 2000 rpm for 2 hours to obtain a mixed slurry.

[0087] 3) The mixed slurry was coated on copper foil, heated at 60°C for 2 hours, and then baked at 120°C for 10 hours.

[0088] [Example 7]

[0089] Example 7 includes the following steps:

[0090] 1) Dissolve the binder nitrile rubber in toluene solvent, rotate at 800 rpm, and stir for 5 hours.

[0091] 2) Add the above silicon active material and metal compound to the solvent according to the mass ratio of active material silicon: metal compound: binder = Si: Mg3N2: nitrile rubber = 76:22:2, with a solid content of 50%, mix and stir at a speed of 2000 rpm for 2 hours to obtain a mixed slurry.

[0092] 3) The mixed slurry was coated on copper foil, heated at 60°C for 2 hours, and then baked at 120°C for 10 hours.

[0093] [Example 8]

[0094] Example 8 includes the following steps:

[0095] 1) The silicon active material, metal compound, electrolyte, and conductive agent were uniformly mixed in a mortar according to the mass ratio of silicon active material: metal compound: electrolyte: conductive agent: binder = SiO:Mg3N2:LiBH4:Super P: polytetrafluoroethylene = 75:15:5:3:2, and fibrillated in a heating mantle at 100°C.

[0096] 2) The fibrillated sample was rolled into a sheet on a roller press.

[0097] 3) The dry-process electrode is laminated with a copper foil current collector through a conductive adhesive to prepare a composite negative electrode.

[0098] [Example 9]

[0099] Example 9 includes the following steps:

[0100] 1) Dissolve the binder nitrile rubber in toluene solvent, rotate at 800 rpm, and stir for 5 hours.

[0101] 2) Add the above silicon active material, metal compound, electrolyte, and conductive agent to a solvent in a mass ratio of silicon active material: metal compound: electrolyte: conductive agent: binder = SiC:Mg3N2: LiTaOCl4: Super P: polyvinylidene fluoride = 75:15:5:3:2, with a solid content of 50%. Mix and stir at a speed of 2000 rpm for 2 hours to obtain a mixed slurry.

[0102] 3) The mixed slurry was coated on copper foil, heated at 60°C for 2 hours, and then baked at 120°C for 10 hours.

[0103] [Comparative Example 1]

[0104] Comparative Example 1 comprises the following steps:

[0105] 1) Dissolve the binder nitrile rubber in toluene solvent, rotate at 800 rpm, and stir for 5 hours.

[0106] 2) Add the silicon active material, metal compound, electrolyte, and conductive agent to a solvent at a solid content of 50% according to the mass ratio of active material silicon: metal compound: electrolyte: conductive agent: binder = Si: TiP: Li6PS5Cl: Super P: nitrile rubber = 75:15:5:3:2, and mix and stir at a speed of 2000 rpm for 2 hours to obtain a mixed slurry.

[0107] 3) The mixed slurry was coated on copper foil, heated at 60°C for 2 hours, and then baked at 120°C for 10 hours.

[0108] [Comparative Example 2]

[0109] Comparative Example 2 comprises the following steps:

[0110] 1) Dissolve the binder nitrile rubber in toluene solvent, rotate at 800 rpm, and stir for 5 hours.

[0111] 2) The silicon active material, Zinter phase, electrolyte, and conductive agent were added to a solvent at a solid content of 50% according to a mass ratio of active material silicon: Zinter phase: electrolyte: conductive agent: binder = Si: Li-Si-Mg: Li6PS5Cl: Super P: nitrile rubber = 75:15:5:3:2. The mixture was stirred at 2000 rpm for 2 hours to obtain a mixed slurry.

[0112] 3) The mixed slurry was coated on copper foil, heated at 60°C for 2 hours, and then baked at 120°C for 10 hours.

[0113] [Comparative Example 3]

[0114] Comparative Example 3 comprises the following steps:

[0115] 1) Dissolve the binder nitrile rubber in toluene solvent, rotate at 800 rpm, and stir for 5 hours.

[0116] 2) Add the silicon active material, metal sulfide, electrolyte, and conductive agent to a solvent at a mass ratio of active material silicon: metal sulfide: electrolyte: conductive agent: binder = Si:MgS:Li6PS5Cl:Super P: nitrile rubber = 75:15:5:3:2 to a solid content of 50%. Mix and stir at 2000 rpm for 2 hours to obtain a mixed slurry.

[0117] 3) The mixed slurry was coated on copper foil, heated at 60°C for 2 hours, and then baked at 120°C for 10 hours.

[0118] [Comparative Example 4]

[0119] Comparative Example 4 comprises the following steps:

[0120] 1) Dissolve the binder nitrile rubber in toluene solvent, rotate at 800 rpm, and stir for 5 hours.

[0121] 2) Add the silicon active material, metal fluoride, electrolyte, and conductive agent to a solvent at a mass ratio of active material silicon: metal fluoride: electrolyte: conductive agent: binder = Si: MgF2: Li6PS5Cl: Super P: nitrile rubber = 75:15:5:3:2 to obtain a 50% solid content. Mix and stir at 2000 rpm for 2 hours to obtain a mixed slurry.

[0122] 3) The mixed slurry was coated on copper foil, heated at 60°C for 2 hours, and then baked at 120°C for 10 hours.

[0123] [Comparative Example 5]

[0124] Comparative Example 5 comprises the following steps:

[0125] 1) Dissolve the binder nitrile rubber in toluene solvent, rotate at 800 rpm, and stir for 5 hours.

[0126] 2) Add the silicon active material, electrolyte, and conductive agent to a solvent at a mass ratio of active material silicon: electrolyte: conductive agent: binder = Si: Li6PS5Cl: Super P: nitrile rubber = 90:5:3:2, with a solid content of 50%. Mix and stir at 2000 rpm for 2 hours to obtain a mixed slurry.

[0127] 3) The mixed slurry was coated on copper foil, heated at 60°C for 2 hours, and then baked at 120°C for 10 hours.

[0128] [Comparative Example 6]

[0129] Comparative Example 6 comprises the following steps:

[0130] 1) Dissolve the binder nitrile rubber in toluene solvent, rotate at 800 rpm, and stir for 5 hours.

[0131] 2) The silicon active material was added to a solvent at a mass ratio of active material silicon: binder = Si: nitrile rubber = 98:2, with a solid content of 50%. The mixture was stirred at 2000 rpm for 2 hours to obtain a mixed slurry.

[0132] 3) The mixed slurry was coated on copper foil, heated at 60°C for 2 hours, and then baked at 120°C for 10 hours.

[0133] For the composite negative electrodes obtained in Examples 1-9 and Comparative Examples 1-6, Li-In alloy was used as the counter electrode to test the battery rate, cycle performance, and expansion rate of the delithiation state relative to the uncycled state after 50 cycles at 0.1C.

[0134] [Compound electrode ion conductivity test]

[0135] The negative electrode ion conductivity test was performed on Examples 1-3 and Comparative Examples 1-4. First, the composite electrode sheet / Li-In battery was cycled for 2 cycles. The battery with the negative electrode sheet in the third cycle delithiated was stopped. The composite negative electrode material was peeled off from the current collector to prepare for the ion conductivity test. In the present disclosure, the ion conductivity parameter was measured using a DC polarization method. Specifically, the ion conductivity was tested as follows: 100 mg of the sample to be tested was first pressed into a sheet at a pressure of 360 MPa. Li6PS5Cl was placed on both sides at a pressure of 360 MPa. Then, LiIn alloy was placed on both sides and pressed at a pressure of 200 MPa. Finally, stainless steel sheets were placed on both sides of the LiIn alloy at a pressure of 200 MPa. The battery was assembled in a mold and calculated according to formula (1) (2): R = U / I (1) σ = L / (R×S) (2)

[0136] Where U is a constant voltage of 0.1 V, I is the steady-state current, and the ionic resistance value R can be obtained. According to formula (2), R is the ionic resistance of the sample, and L and S are the thickness and area of ​​the composite negative electrode sample. The specific test structure is shown in Figure 1.

[0137] Thus, the ionic conductivity of the negative electrode with different metal compounds or direct addition of Zintel was obtained, and the test results are shown in Table 1.

[0138] The XPS spectra of Si in Example 2 (Figures 2 and 3) confirmed that after a certain number of cycles, a Li-Mg-Si phase was generated in the composite negative electrode, while the XPS spectra of P confirmed that a highly ionic conductive phase Li3P was also generated in the composite negative electrode.

[0139] Table 1

[0140] As shown in Table 1, in Examples 1 and 2 of the present disclosure, the metal compound and the silicon active material react to form the high ion conductive phase Li3N(10 -3 S / cm), Li3P(10 -4 S / cm) to improve the ionic conductivity of the electrode; Comparative Example 1 cannot form the Zinter phase, TiP cannot be lithiated, and the high ionic conductive phase Li3P cannot be formed. Comparative Example 2 directly adds the Zinter phase, and there is no high ionic conductive phase Li3P, Li3N. Using other metal compounds, such as metal sulfides and metal fluorides (Comparative Examples 3 and 4), the ionic conductivity of the formed Li2S and LiF is ≤10 -7 S / cm, which reduces the ionic conductivity of the negative electrode.

[0141] [Rate performance and cycle performance test]

[0142] Constant current charge and discharge tests were conducted using a Xinwei charge and discharge tester. Based on a nominal specific capacity of 3100 mAh / g for Si, 1500 mAh / g for silicon-oxygen, and 2000 mAh / g for silicon-carbon, the battery was tested over a voltage window of 0.01-1.5 V (for Li) at various rates: 0.05C / 0.05C, 0.1C / 0.1C, 0.2C / 0.2C, 0.5C / 0.5C, and 1C / 1C. The voltage window was 0.01-1.5 V. The test results are shown in Table 2.

[0143] Table 2

[0144] The test voltage window was 0.01-1.5 (for Li), with constant current charge and discharge at 0.1C / 0.1C to test and analyze the cycling performance. The test results are shown in Table 3.

[0145] Table 3

[0146] From Table 3 we can see that:

[0147] The addition of metal nitrides to the silicon anode forms a highly ionic conductive phase Li3N(10 -3S / cm), which is superior to adding metal phosphides to the negative electrode. Therefore, batteries with metal nitrides in the negative electrode have the best rate performance. Compared to adding other metal compounds, the addition of metal nitrides and phosphides significantly improves the rate performance of the battery; this is true whether they are added to a self-diffusion negative electrode or a conventional negative electrode. Comparing Example 1 with Comparative Example 1 shows that when silicon is added with metal nitrides, metal phosphides, metal sulfides, and metal fluorides, a Zinter phase can form, which can restrain the volume expansion of silicon. The cycling performance is better than the combination of silicon plus TiP, which cannot form a Zinter phase, and the combination of directly adding the Zinter phase.

[0148] It can be seen that the silicon-based negative electrode in the embodiment of the present disclosure has a high specific capacity, excellent rate performance, and good cycle performance.

[0149] [Expansion rate test]

[0150] The test voltage window was 0.005-1.5V, with constant current charge and discharge at 0.1C / 0.1C. After 50 cycles, the volume stability of the negative electrode was measured by measuring the change in the expansion rate of the delithiation state relative to the uncycled negative electrode. The test results are shown in Table 4.

[0151] Table 4

[0152] Comparing Example 1 with Comparative Example 1 in Table 4 shows that the negative electrode capable of forming a ternary Zinter phase has a stable structure and a significantly lower expansion rate than the negative electrode without Zinter phase formation. Comparative Example 2 shows that directly adding Zinter phase to the negative electrode does not effectively bind the original active material silicon and is not as effective as in-situ Zinter phase formation, which can better mitigate silicon volume expansion.

[0153] It can be seen that the present invention introduces a metal compound into the silicon-based negative electrode, Si is first lithiated to LiSi, and then the metal phase is inserted into the LiSi phase to form a ternary Zinter phase Li-M-Si in situ. Due to its stable structure, it can effectively reduce the volume expansion of the silicon-based negative electrode and improve the cycle stability. The introduced high ionic conductivity interface phases Li3P and Li3N have high ionic conductivity, which improves the interface ion transport and makes the battery have better rate performance.

[0154] In this specification, the terms "connect," "install," and "fix" should be understood broadly. For example, "connect" can refer to a fixed connection, a detachable connection, or an integral connection; it can refer to a direct connection or an indirect connection through an intermediary. Those skilled in the art will understand the specific meanings of these terms in this application based on the specific circumstances.

[0155] Throughout this specification, terms such as "one embodiment," "some embodiments," and the like indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present application. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0156] The above is only a preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, various modifications and variations of the present application are possible. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A composite negative electrode sheet, characterized in that, Containing a ternary Zintl phase Li-M-Si and an ionic conductive phase lithium compound; wherein M is a metal, and the ionic conductivity of the ionic conductive phase lithium compound is ≥ 10 -5 S / cm.

2. The composite negative electrode sheet according to claim 1, wherein the metal is selected from at least one of Group II, Group III, Group IV, Group I, Group II and Group VIII of the periodic table, and the ionic conductive phase lithium compound is selected from nitrides or phosphides.

3. The composite negative electrode sheet according to claim 1, wherein The ternary Zintl phase Li-M-Si and the ionic conductive phase lithium compound are formed by the silicon active material and the metal compound during the lithiation of silicon.

4. The composite negative electrode sheet according to claim 3, wherein the metal compound is selected from at least one of the following materials: X3Y2, where X = Mg, Ca, Sr, Ba, Zn and Y = P, N; XY, where X = Al, Ga, In, Ti, Ge, Sn, Pb and Y = P, N; X2Y, where X = Ni and Y = P, N; and / or, the silicon active material is selected from at least one of Si, SiO, and Si-C; and / or, the mass ratio of the metal compound to the silicon active material is 5% - 30%.

5. The composite negative electrode sheet according to claim 1, wherein, It is composed of a ternary Zintl phase Li-M-Si, an ionic conductive phase lithium compound, a silicon active material, and a binder.

6. The composite negative electrode sheet according to claim 5, wherein, The composite negative electrode sheet further contains a solid electrolyte and a conductive agent.

7. The composite negative electrode sheet according to claim 6, wherein the Young's modulus of the electrolyte is ≤ 500 GPa, preferably the Young's modulus is ≤ 200 GPa, and / or, the electrolyte is selected from at least one of sulfide electrolytes, oxide electrolytes, halide electrolytes, polymer electrolytes, and borohydride electrolytes.

8. A method for preparing the composite negative electrode sheet according to any one of claims 1 to 7, characterized in that, Comprising the following steps: Dissolve the binder in a solvent; According to the mass ratio of the metal compound to the silicon active material of 5% - 30%, add the silicon active material and the metal compound to the above solvent mixed with the binder, mix and stir to obtain a mixed slurry; Coat the mixed slurry on a current collector, heat and dry to obtain a composite negative electrode sheet.

9. A preparation method for preparing the composite negative electrode sheet according to any one of claims 1 to 7, characterized in that, Comprising the following steps: The mass ratio of the metal compound to the silicon active material is 5% - 30%, and the silicon active material and the metal compound are directly ground and roll-pressed into a sheet; The dry electrode sheet is compounded with a current collector through a conductive adhesive to obtain a composite negative electrode sheet.

10. The preparation method according to claim 8 or 9, characterized in that, When the metal compound and the silicon active material are mixed, a solid electrolyte and a conductive agent are further added.

11. Application of a composite negative electrode sheet prepared based on the composite negative electrode sheet according to any one of claims 1 to 7 or the preparation method according to any one of claims 8 to 10 in a solid-state battery.

Images