Composite silicon-based negative electrode materials, negative electrode sheets and all-solid-state lithium batteries

Abstract

The present application provides a composite silicon-based negative electrode material, comprising a core, a first coating layer coated on the surface of the core, and a second coating layer coated on the surface of the first coating layer, wherein the core comprises a lithium-silicon alloy, the first coating layer comprises at least one of Li3N and Li3P, and the second coating layer is an amorphous lithium-silicon alloy. The composite silicon-based negative electrode material has good ionic conductivity and electronic conductivity at the same time, and the contact between the composite silicon-based negative electrode materials is good under pressure, which is conducive to improving its rate performance and cycle performance. The present application also provides a negative electrode sheet and an all-solid-state lithium battery using the composite silicon-based negative electrode material.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a composite silicon-based negative electrode material, a negative electrode sheet and an all-solid-state lithium battery. Background Art

[0002] In recent years, all-solid-state lithium batteries using solid electrolytes have received widespread attention due to their high safety. Among them, silicon negative electrode materials with high theoretical specific capacity and high safety are considered to be an effective way to break through the energy density of all-solid-state lithium batteries. However, the two types of silicon negative electrode materials, silicon element and silicon oxide, have poor ion conductivity and electron conductivity, and usually require the addition of a large amount of solid electrolytes and conductive agents for assistance. However, the large amount of these additives that are not electrochemically active will reduce the capacity of the negative electrode and the energy density of the entire all-solid-state lithium battery. Although the electronic conductivity and ionic conductivity of lithium-silicon alloys are higher than those of the above two types of silicon negative electrode materials, the ion conductivity of lithium-silicon alloys is still relatively low, and the electrochemical performance is poor, which cannot meet the increasingly stringent electrochemical performance requirements of all-solid-state lithium batteries. Summary of the invention

[0003] In view of this, the present application provides a composite silicon-based negative electrode material. By sequentially coating a first coating layer with high ionic conductivity and an amorphous lithium-silicon alloy layer on the surface of a lithium-silicon alloy, the composite silicon-based negative electrode material can have good ionic conductivity and electronic conductivity at the same time, thereby improving its rate and cycle performance, and making the contact between particles good, thereby making it possible to add no solid electrolyte material and conductive agent to the negative electrode sheet made therefrom.

[0004] Specifically, in the first aspect, the present application provides a composite silicon-based negative electrode material, comprising a core, a first coating layer coated on the surface of the core, and a second coating layer coated on the surface of the first coating layer, wherein the core comprises a lithium silicon alloy, the first coating layer comprises at least one of Li3N and Li3P, and the second coating layer is an amorphous lithium silicon alloy.

[0005] The composite silicon-based negative electrode material provided in the first aspect of the present application, by coating the surface of the lithium silicon alloy with a material including a first coating layer of Li3N and / or Li3P, based on the fact that both Li3N and Li3P have very high ionic conductivity, can be beneficial to improving the transmission capacity of lithium ions in the composite silicon-based negative electrode material; coating an amorphous lithium silicon alloy layer outside the first coating layer, the outer surface of the composite silicon-based negative electrode material can have a certain conductivity and a certain deformation capacity, so that the composite silicon-based negative electrode material can achieve good contact between particles when contacting each other under pressure, can avoid poor contact caused by the presence of crystal phases or grain boundaries, reduce the impedance between particles, and facilitate the conduction of electrons / ions between particles. Therefore, the composite silicon-based negative electrode material has good rate performance and cycle stability.

[0006] Optionally, the thickness of the first coating layer is 2nm-200nm.

[0007] Optionally, the mass of the first coating layer accounts for 0.5%-10% of the sum of the mass of the core and the first coating layer.

[0008] Optionally, the second coating layer has a thickness of 5nm-500nm.

[0009] Optionally, the mass of the second coating layer accounts for 0.5%-10% of the mass of the composite silicon-based negative electrode material.

[0010] Optionally, the particle size of the amorphous lithium silicon alloy does not exceed 50 nm.

[0011] Optionally, the size of the core is 10 nm-1 μm.

[0012] Optionally, the particle size of the composite silicon-based negative electrode material is 17nm-1.7μm.

[0013] In a second aspect, the present application further provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode material layer disposed on the negative electrode current collector, wherein the negative electrode material layer comprises the composite silicon-based negative electrode material as described in the first aspect of the present application.

[0014] Wherein, the negative electrode material layer does not contain a conductive agent and a solid electrolyte material. In this case, the specific capacity of the negative electrode sheet is large and the energy density of the all-solid-state lithium battery is high.

[0015] Optionally, the negative electrode material layer further contains a binder. Further, the binder has a mass percentage of 0.5-5% in the negative electrode material layer.

[0016] The negative electrode sheet provided in the second aspect of the embodiment of the present application, because it contains the above-mentioned composite silicon-based negative electrode material with good ionic conductivity and electronic conductivity, can establish good electronic and ion pathways in the negative electrode sheet, and make the contact between adjacent composite silicon-based negative electrode material particles in the negative electrode sheet good, the density of the negative electrode sheet is high, and the gaps are small. It can also increase the mass proportion of the composite silicon-based negative electrode material in the negative electrode sheet, which is beneficial to improve the rate performance, cycle performance, energy density, etc. of the battery made of the negative electrode sheet.

[0017] In a third aspect, the present application further provides an all-solid-state lithium battery, comprising a positive electrode sheet, a negative electrode sheet, and a solid electrolyte layer located between the positive electrode sheet and the negative electrode sheet, wherein the negative electrode sheet is as described in the second aspect of the present application.

[0018] The all-solid-state lithium battery provided by the third aspect of the present application has excellent electrochemical performance due to the use of the above-mentioned negative electrode sheet, for example, it has a relatively high capacity, strong cycle stability, and high energy density. Description of the Drawings

[0019] Figure 1 It is a schematic structural diagram of a composite silicon-based negative electrode material provided by an embodiment of the present application;

[0020] Figure 2 It is a schematic structural diagram of a negative electrode sheet provided by an embodiment of the present application;

[0021] Figure 3 It is a schematic structural diagram of an all-solid-state lithium battery provided by an embodiment of the present application. Detailed Embodiments

[0022] Hereinafter, the technical solutions in the embodiments of the present application will be described in detail with reference to the accompanying drawings in the embodiments of the present application.

[0023] Please refer to Figure 1 , an embodiment of the present application provides a composite silicon-based negative electrode material 100, which includes a core 101, a first coating layer 102 coated on the surface of the core 101, and a second coating layer 103 coated on the surface of the first coating layer 102. Among them, the core 101 includes a lithium-silicon alloy, the first coating layer 102 includes at least one of Li3N and Li3P, and the second coating layer 103 is an amorphous lithium-silicon alloy (that is, a non-crystalline lithium-silicon alloy).

[0024] Among them, the chemical composition of the lithium-silicon alloy of the core 101 can be represented by Li x Si, and the chemical composition of the amorphous lithium-silicon alloy in the second coating layer 103 can be represented by Li y Si, where 0 < x ≤ 4.4 and 0 < y ≤ 4.4. The values of x and y can be the same or different.

[0025] When a pure lithium-silicon alloy is used as the negative electrode active material of an all-solid-state lithium-ion battery, its ion conductivity is not high, its rate performance is poor, and its cycle performance is not good. When the negative electrode active material is a crystalline lithium-silicon alloy, the contact between the particles is still poor due to the presence of a large grain boundary resistance. When the surface of the lithium-silicon alloy is coated with Li3N and / or Li3P with high ion conductivity as the first coating layer, it is beneficial to improve the transmission capacity of lithium ions in the composite silicon-based negative electrode material 100 (i.e., improve ion conductivity), which is beneficial to improve its rate performance. The amorphous lithium-silicon alloy is coated on the outside of the first coating layer 102 as the second coating layer 103. The interior of the second coating layer 103 does not have a grain boundary. When multiple composite silicon-based negative electrode material 100 particles are pressed and contacted (for example, during the pressing process of the negative electrode sheet, the pressing process of the negative electrode sheet and the solid electrolyte layer or the positive electrode sheet), the second coating layer 103 can make the contact between two adjacent composite silicon-based negative electrode material 100 particles good, avoiding the poor contact caused by the presence of crystal phases or grain boundaries in the contact outer layer; in addition, the second coating layer 103 can also make the outer surface of the composite silicon-based negative electrode material 100 have a certain conductivity and "toughness", improve the tightness of the contact between adjacent composite silicon-based negative electrode materials 100, reduce the impedance between particles, etc., which is conducive to reducing the conduction resistance of electrons or lithium ions between the composite silicon-based negative electrode materials 100 and improving the cycle performance. Therefore, compared with the bare lithium-silicon alloy material, the rate performance of the composite silicon-based negative electrode material is improved, and the cycle stability is improved. In addition, the first coating layer 102 also has a certain rigidity, which can effectively suppress the volume change of the core 101 during the charge and discharge process and improve its cycle stability.

[0026] In the embodiment of the present application, the core 101 can be a crystalline lithium silicon alloy, or an amorphous lithium silicon alloy (i.e., an amorphous lithium silicon alloy), or a mixture of the two. Among them, the crystalline lithium silicon alloy has a clearly distinguishable XRD (X-Ray Diffraction) sharp peak, the crystal is long-range ordered, and has anisotropy; and the XRD spectrum of the amorphous lithium silicon alloy is basically a bulge, without a clearly distinguishable sharp diffraction peak. Among them, the amorphous lithium silicon alloy has a smaller volume change during the charge and discharge process than the crystalline lithium silicon alloy, and the cycle performance is better; the capacity of the crystalline lithium silicon alloy is higher than that of the amorphous lithium silicon alloy. In some embodiments, the core 101 is a crystalline lithium silicon alloy. At this time, under the action of the aforementioned first coating layer and the material of the amorphous lithium silicon alloy, the obtained composite silicon-based negative electrode material 100 can take into account both high capacity and good cyclability.

[0027] In the embodiment of the present application, the thickness of the first coating layer 102 is 2nm-200nm. Li3N and Li3P have high ionic conductivity, but poor electronic conductivity. Controlling the thickness of the first coating layer in this range can effectively improve the ionic conductivity of the composite silicon-based negative electrode material 100 without significantly reducing its conductivity. Specifically, the thickness of the first coating layer 102 is 5nm, 10nm, 20nm, 25nm, 40nm, 50nm, 60nm, 80nm, 100nm, 120nm, 150nm, 180nm or 200nm. In some embodiments, the thickness of the first coating layer 102 is 10nm-90nm.

[0028] Optionally, the first coating layer 102 is uniformly coated on the surface of the core 101 .

[0029] In the embodiment of the present application, the mass of the first coating layer 102 accounts for 0.5%-10% of the sum of the mass of the core 101 and the first coating layer 102. This mass ratio can ensure that the thickness of the first coating layer 102 is appropriate, and the ionic conductivity of the overall material will not be effectively improved due to the low mass of the coating layer 102, nor will the coating layer be too thick due to the high mass of the coating layer, which will deteriorate the electronic conductivity of the composite silicon-based negative electrode material 100 and reduce the mass ratio of the lithium silicon alloy. Specifically, the mass ratio can be 0.6%, 1%, 1.5%, 2%, 3%, 3.5%, 4%, 5%, 6%, 8% or 9%. In some embodiments, the mass ratio is 0.5%-5%, preferably 0.5%-2%.

[0030] In the present application, an amorphous lithium-silicon alloy is selected as the second coating layer 103, which is a metal material and can be squeezed and deformed to a certain extent. When multiple composite negative electrode materials 100 are in contact under pressure, the second coating layer 103 can be deformed under pressure, increasing the contact between the composite negative electrode materials 100, reducing the existence of particle boundaries, reducing the resistance between particles, etc., and based on the absence of grain boundaries in the amorphous lithium-silicon alloy, metal elements are easier to diffuse, so that adjacent composite solid electrolyte material particles can achieve better contact. Optionally, the amorphous lithium-silicon alloy is uniformly coated on the surface of the first coating layer 102.

[0031] Amorphous lithium silicon alloy can be prepared by a variety of methods, such as in-situ lithiation, high temperature solid phase reaction, or high energy ball milling of crystalline lithium silicon alloy. In one embodiment, when the amorphous lithium silicon alloy is prepared by high energy ball milling of crystalline lithium silicon alloy, the rotation speed of the high energy ball milling is above 200r / min, for example, 350r / min or 400r / min, and the time of high energy ball milling can be 20min-60min. The particle size of the amorphous lithium silicon alloy is smaller than that of the crystalline lithium silicon alloy. Optionally, the amorphous lithium silicon alloy in the second coating layer 103 does not exceed 50nm, for example, 5nm-50nm, or 10nm-50nm.

[0032] In the embodiment of the present application, the thickness of the second coating layer 103 is 5nm-500nm. The second coating layer thickness of 5nm-500nm can make the outermost layer of the composite silicon-based negative electrode material 100 have a certain conductivity, and will not reduce the ionic conductivity of the overall composite silicon-based negative electrode material due to excessive thickness. Specifically, the thickness of the second coating layer 103 is 7nm, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 80nm, 100nm, 150nm, 180nm, 200nm, 300nm, 400nm or 500nm. In some embodiments, the thickness of the second coating layer 103 is 10nm-200nm.

[0033] In the embodiment of the present application, the mass of the second coating layer 103 accounts for 4%-35% of the mass of the composite silicon-based negative electrode material 100. This mass ratio can ensure that the thickness of the second coating layer 103 is appropriate and the coating integrity of the core 101 is high, and the first coating layer will not be completely coated due to low mass, nor will the coating layer be too thick due to high mass, which will deteriorate the ion conductivity of the composite silicon-based negative electrode material 100. In some embodiments, the mass ratio of the second coating layer 103 in the composite silicon-based negative electrode material 100 can be 5%-20%. For example, it can be 5%, 8%, 10%, 12%, 15%, 17% or 19%.

[0034] In the embodiment of the present application, the size of the core 101 is 10nm-1μm. A core with a suitable particle size is easier to prepare and is beneficial to the capacity of the composite silicon-based negative electrode material 100. When the core 101 is an amorphous lithium-silicon alloy, its particle size is usually 10nm-50nm.

[0035] In the embodiment of the present application, the particle size of the composite silicon-based negative electrode material 100 is 17 nm-1.7 μm. In some embodiments, the particle size is 20 nm-1.5 μm.

[0036] In the embodiment of the present application, the ionic conductivity of the composite silicon-based negative electrode material 100 at room temperature is 10 -7 -10-4 S cm -1 The electronic conductivity is within the range of 10 -2 -10 2 S cm -1 within the range.

[0037] Accordingly, the present application also provides a method for preparing a composite silicon-based negative electrode material, comprising:

[0038] forming a first coating layer on the surface of the core material;

[0039] A second coating layer is formed on the surface of the first coating layer to obtain a composite silicon-based negative electrode material; wherein the core includes a crystalline lithium-silicon alloy, the first coating layer includes at least one of Li3N and Li3P, and the second coating layer is an amorphous lithium-silicon alloy.

[0040] In the embodiment of the present application, the formation methods of the first coating layer and the second coating layer are not limited to solid-liquid coating method, solid-solid coating method, solvent thermal reaction method, high temperature solid phase reaction method, coating method, physical vapor deposition (such as evaporation or sputtering), chemical vapor deposition, etc. Among them, the difference between the solid-liquid coating method and the solid-solid coating method is that there is a suitable solvent in the material, and the equipment used in these two methods can be the same, such as a ball mill, a fusion machine or other coating equipment (such as Nobilta particle composite equipment, vibration modification equipment, dry impact mixing equipment, etc.).

[0041] In some embodiments of the present application, the first coating layer can be prepared by a high-temperature solid-phase reaction method. Exemplarily, the first coating layer made of Li3N is formed by the following method: placing a lithium silicon alloy in a sealed container, introducing nitrogen, and reacting at 90-200°C for 1 hour under a pressure of 200 kPa to obtain a Li3N-coated lithium silicon alloy.

[0042] Exemplarily, in some embodiments of the present application, the second coating layer is formed by the following method: the lithium silicon alloy coated with the first coating layer is mixed with the amorphous lithium silicon alloy, and processed by a ball mill or other solid-solid coating equipment to form a second coating layer made of lithium silicon alloy on the first coating layer. These two processes for forming coating layers are relatively simple and easy to control, and are suitable for industrial mass production. Optionally, the rotation speed of the ball mill is in the range of 30-300rpm (for example, 50rpm, 150rpm); the rotation speed of the solid-solid coating equipment can be in the range of 1000-5000rpm (for example, 3000rpm) to obtain a better coating effect.

[0043] See also Figure 2The embodiment of the present application further provides a negative electrode sheet 10 , including a negative electrode current collector 11 and a negative electrode material layer 12 disposed on the negative electrode current collector 11 , wherein the negative electrode material layer 12 contains the above-mentioned composite silicon-based negative electrode material 100 .

[0044] The negative electrode sheet 10 provided in the embodiment of the present application, because it contains the above-mentioned composite silicon-based negative electrode material 100 with good ionic conductivity and electronic conductivity, can establish good electronic and ion pathways in the negative electrode sheet, and make the contact between adjacent composite silicon-based negative electrode material particles in the negative electrode sheet 10 good, the density of the negative electrode sheet is high, and the gaps are small. It can also increase the mass proportion of the composite silicon-based negative electrode material in the negative electrode sheet, which is beneficial to improve the rate performance, cycle performance, energy density, etc. of the battery made of the negative electrode sheet.

[0045] Among them, the negative electrode material layer 12 does not contain a conductive agent and a solid electrolyte material. At this time, the specific capacity of the negative electrode sheet is large and the energy density of the all-solid-state lithium battery is high. In this way, the mass proportion of the electrochemically active composite silicon-based negative electrode material 100 in the negative electrode material layer 12 is large, which is conducive to improving the specific capacity of the negative electrode sheet 10 and improving the energy density of the all-solid-state lithium battery.

[0046] In some embodiments of the present application, the negative electrode material layer 12 may contain a binder 121 to facilitate better molding of the composite silicon-based negative electrode material 100, so that the obtained negative electrode material layer 12 is firmly fixed on the negative electrode current collector 11. Further, the mass percentage of the binder 121 in the negative electrode material layer 12 is 0.5-5%, for example, 1-5%, or 2-4%.

[0047] Optionally, the thickness of the negative electrode material layer 12 is 5-50 μm. When the negative electrode material layer 12 is thicker, the negative electrode sheet 10 still has good and stable electrochemical performance.

[0048] Among them, the binder 121 used in the negative electrode material layer can be one or more of polythiophene (PT), polypyrrole (PPy), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene (PE), polypropylene (PP), polystyrene (PS), polyacrylamide (PAM), ethylene-propylene-diene copolymer, styrene-butadiene rubber, polybutadiene, fluororubber (FPM), polyvinyl pyrrolidone (PVP), polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol (PVA), carboxypropyl cellulose (HPC), ethyl cellulose (EC), polyethylene oxide (PEO), sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR).

[0049] See also Figure 3The embodiment of the present application also provides an all-solid-state lithium battery 200 , including a negative electrode sheet 10 , a positive electrode sheet 20 , and a solid electrolyte layer 30 located between the positive electrode sheet 20 and the negative electrode sheet 10 .

[0050] Since the all-solid-state lithium battery 200 uses the negative electrode sheet 20 having the composite silicon-based negative electrode material 100, the battery has excellent electrochemical performance, such as high capacity, strong cycle stability, and high energy density.

[0051] In the embodiment of the present application, the positive electrode sheet 20 may include a positive electrode current collector 21 and a positive electrode material layer 22 disposed on the positive electrode current collector 21. Among them, the positive electrode material layer 22 may include a positive electrode active material, a conductive agent, a positive electrode solid electrolyte material and a positive electrode binder. The composition of the solid electrolyte layer 30 includes a solid electrolyte material. In some embodiments, the solid electrolyte layer 30 may also contain a binder.

[0052] Among them, the material of the binder contained in the solid electrolyte layer 30 can be the same as or different from the binder 121 in the negative electrode material layer 12, and can be selected arbitrarily from the several binders listed above. Similarly, the positive electrode binder can be the same as or different from the material of the binder 121 in the negative electrode material layer 12. For example, the positive electrode binder can be one or more of fluorine-containing resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), polyolefin, etc. The conductive agent in the positive electrode material layer 22 is not particularly limited, and conventional materials in the art can be used, such as one or more of conductive carbon black (such as acetylene black, Ketjen black), carbon nanotubes, carbon fibers, graphite and furnace black. Optionally, the mass percentage content of the positive electrode binder in the positive electrode material layer 22 is 0.1-10%. Further, it can be 0.2-5%. Optionally, the mass percentage content of the conductive agent in the positive electrode material layer 22 is 0.1-20%. Further, it can be 1-10%.

[0053] The solid electrolyte material for the positive electrode sheet 20 and the solid electrolyte material in the solid electrolyte layer 30 can be independently selected from one or more of a sodium fast ion conductor (NASICON) solid electrolyte, a garnet-type solid electrolyte, a perovskite-type solid electrolyte, and a sulfur-based solid electrolyte. For example, the solid electrolyte layer 30 selects a reduction-resistant solid electrolyte material to protect the composite silicon-based negative electrode material on the negative electrode sheet 10 and further improve its cycle stability; the solid electrolyte material for the positive electrode is selected to have a higher ionic conductivity. Further, when preparing the solid electrolyte layer 30 and the positive electrode material layer 22, the particle size of the solid electrolyte material used can be 20nm-5μm.

[0054] Specifically, the NASICON-type solid electrolyte can be one or more of LiM2(PO4)3 and its dopants, wherein M is Ti, Zr, Ge, Sn or Pb, and the doping elements used in the dopant are selected from one or more of Mg, Ca, Sr, Ba, Sc, Al, Ga, In, Nb, Ta and V.

[0055] The chemical formula of the garnet-type solid electrolyte is Li 7+p-q-3u Al u La 3-p X p Zr 2-q Y q O 12 , wherein 0≤p≤1, 0≤q≤1, 0≤u≤1, X is selected from one or more of La, Ca, Sr, Ba and K, and Y is selected from one or more of Ta, Nb, W and Hf.

[0056] The chemical formula of the perovskite solid electrolyte is A 1 x1 B 1 y1 TiO3、A 2 x2 B 2 y2 Ta2O6、A 3 x3 B 3 y3 Nb2O6 or A j E k D V Ti w O3, where x1+3y1=2, 0<x1<2, 0<y1<2 / 3; x2+3y2=2, 0<x2<2, 0<y2<2 / 3; x3+3y3=2, 0<x3<2, 0<y3<2 / 3; j+2k+5v+4w=6, j, k, v, w are all greater than 0; A 1 , A 2 , A 3 , A is independently selected from at least one of Li and Na, B 1 , B 2 , B 3 is independently selected from at least one of La, Ce, Pr, Y, Sc, Nd, Sm, Eu and Gd, E is selected from at least one of Sr, Ca, Ba, Ir and Pt, and D is selected from at least one of Nb and Ta.

[0057] The sulfide-type solid electrolyte may include one or more of crystalline sulfide, glassy sulfide, ceramic glass ceramic sulfide and dopants thereof. Optionally, the doping element in the dopant is selected from one or more of Mg, Ca, Sr, Ba, Sc, Al, Ga, In, Nb, Ta and V. The chemical composition of the crystalline sulfide can be expressed as Li d Q e P f S g (Q is one or more of Si, Ge, Sn, where d+4e+5f=2g, 0≤e≤1.5). When Q is Ge, g=4, e+f=1, the crystalline sulfide is a thio-lithium fast ion conductor (thio-LISICON) type. Glassy sulfide solid electrolytes are usually composed of at least one network former such as P2S5, SiS2, B2S3, and a network modifier Li2S. Among them, the glassy Li2S-P2S5 system can include Li7P3S 11 Products composed of Li2S and P2S5 in different weight ratios, such as 3.5Li2S-1.5P2S5, 75Li2S-25P2S5, 70Li2S-30P2S5, etc. Glass-ceramic sulfides include glass-ceramic Li2S-P2S5, etc.

[0058] In the embodiment of the present application, the positive electrode active material is not limited to one or more of oxide type, sulfide type, polyanion type and composites of the above materials. Optionally, the particle size of the positive electrode active material is 100nm-500μm, for example, 100nm-100μm, 100nm-50μm, or 500nm-50μm.

[0059] Specifically, the oxide-type positive electrode active material may include TiO2, Cr3O8, V2O5, MnO2, NiO, WO3, LiMn2O4 (lithium manganate), Li2CuO2, LiCo m Ni 1-m O2(0≤m≤1), LiCo a Ni 1-a-b Al b O2、LiFe c Mn d G e O4、Li 1+ f L 1－g－h H g R h At least one of O2, etc. wherein the LiCo a Ni 1-a-b Al bIn O2, 0≤a≤1, 0≤b≤1. c Mn d G e In O4, G is selected from at least one of Al, Mg, Ga, Cr, Co, Ni, Cu, Zn and Mo, and 0≤c≤1, 0≤d≤1, 0≤e≤1, c+d+e=1. 1+f L 1－g－h H g R h In O2, L, H and R are independently selected from at least one of Li, Co, Mn, Ni, Fe, Al, Mg, Ga, Ti, Cr, Cu, Zn, Mo, F, I, S and B, and L, H and R are different elements, and -0.1≤f≤0.2, 0≤g≤1, 0≤h≤1, 0≤g+h≤1. The sulfide-type positive electrode active material may include TiS2, V2S3, FeS, FeS2, WS2, LiJS i (J is selected from at least one of Ti, Fe, Ni, Cu and Mo, and 1≤i≤2.5), etc. The polyanionic positive electrode active material may specifically include at least one of LiFePO4 (lithium iron phosphate), Li3V2(PO4)3 (lithium vanadium phosphate), and LiVPO4F.

[0060] In addition, in some embodiments of the present application, the surface of the positive electrode active material may also have a coating layer to optimize the interface between it and the solid electrolyte layer 30, reduce the interface impedance, and improve the cycle stability. Specifically, the coating layer on the surface of the positive electrode active material may be LiNbO3, LiTaO3, Li3PO4, Li4Ti5O 12 At least one of the above.

[0061] The negative electrode current collector 11 and the positive electrode current collector 21 are independently selected from metal foil or alloy foil. Among them, the metal foil includes copper, titanium, aluminum, platinum, iridium, ruthenium, nickel, tungsten, tantalum, gold or silver foil, and the alloy foil includes stainless steel, or an alloy containing at least one element of copper, titanium, aluminum, platinum, iridium, ruthenium, nickel, tungsten, tantalum, gold and silver. For example, the negative electrode current collector 11 can be specifically copper foil, and the positive electrode current collector 21 can be specifically aluminum foil. The thickness and surface roughness of the negative electrode current collector 11 and the positive electrode current collector 21 of the present application can be adjusted according to actual needs.

[0062] In one embodiment of the present application, there is also provided a Figure 3 The method for preparing the all-solid-state lithium battery shown comprises the following steps:

[0063] S101, preparing a negative electrode sheet 10: in the presence of a protective gas, the composite silicon-based negative electrode material 100 is mixed with a negative electrode binder and a first solvent to obtain a negative electrode slurry; the negative electrode slurry is coated on a negative electrode current collector 11, and after drying and pressing, a negative electrode material layer 12 is formed on the negative electrode current collector 11 to obtain a negative electrode sheet 10;

[0064] S102, preparing a solid electrolyte layer 30: in the presence of a protective gas, uniformly mixing a solid electrolyte material, a binder and a second solvent to obtain a solid electrolyte slurry, coating the solid electrolyte slurry on the negative electrode material layer 12 of the negative electrode sheet 10, and drying to form a solid electrolyte layer 30;

[0065] S103, preparing the positive electrode sheet 20: uniformly mixing the positive electrode active material, the positive electrode solid electrolyte material, the conductive agent, the positive electrode binder and the third solvent to obtain a positive electrode slurry; coating the positive electrode slurry on the positive electrode collector 21, and after drying and pressing, forming a positive electrode material layer 22 on the positive electrode collector 21 to obtain the positive electrode sheet 20;

[0066] S104, in the presence of a protective gas, the negative electrode sheet 10 with the solid electrolyte layer 30 is laminated to the positive electrode sheet 20 so that the positive electrode material layer 22 is in contact with the solid electrolyte layer 30, and after a pressing process, an all-solid-state lithium battery 100 is obtained.

[0067] Wherein, the first solvent, the second solvent and the third solvent are conventionally selected in the art, for example, they can be independently selected from at least one of water, ethanol, N-methylpyrrolidone (NMP), acetone, acetonitrile, toluene, xylene, anisole, heptane, decane, ethyl acetate, ethyl propionate, butyl butyrate, etc. The amount of each solvent can generally be 50-400wt% of the mass of the dry material in the corresponding mixed slurry. For example, the mass of the first solvent accounts for 50-400wt% of the sum of the mass of the composite solid electrolyte material, the negative electrode active material, and the negative electrode binder.

[0068] In step S104, the pressing process may include at least one of roller pressing, hot pressing, isostatic pressing, etc. In some embodiments, the pressing process includes hot pressing and isostatic pressing in sequence. The temperature of the hot pressing process may be, but is not limited to, about 100°C, and the hot pressing process time is 0.5-3 hours. The pressure of the isostatic pressing is above 100MPa, for example, the pressure is 100-300MPa; the time of the isostatic pressing process is 3-10min.

[0069] The above-mentioned method for preparing the all-solid-state lithium battery has a simple process, is easy to control, and can be mass-produced.

[0070] The following is a further description of the embodiments of the present application with reference to a number of embodiments.

[0071] Example 1

[0072] A preparation method of an all-solid-state lithium battery comprises the following steps:

[0073] (1) Preparation of negative electrode

[0074] First, prepare the composite silicon-based negative electrode material:

[0075] a. In an argon atmosphere, 1000 g of crystalline Li 4.4 Si (average particle size of 100 nm) was placed in a closed reaction chamber. After evacuation, N2 was slowly filled into the chamber until the pressure was 200 kPa (about 100 kPa higher than atmospheric pressure). Then, an electric heating furnace surrounding the reaction chamber was used to heat the chamber to 373 K at a rate of 2 K / min. The reaction was continued for 1 h. After cooling to room temperature, LiN coated with a layer of Li3N was obtained. 4.4 Si material; wherein the thickness of the Li3N coating layer is about 5nm, the particle size is about 100nm, and the mass proportion of the coating layer is about 2%;

[0076] b. Preparation of amorphous Li 4.4 Si material: 250g of crystalline Li 4.4 The Si material was placed in a ball mill, and an appropriate amount of ZrO2 ball milling beads were added. The amorphous Li 4.4 Si material;

[0077] The Li3N-coated Li prepared in step a 4.4 1000g Si material and 200g amorphous Li in step b 4.4 Si material and 1000g toluene solvent were placed in a ball mill, and an appropriate amount of ZrO2 ball milling beads were added. The ball milling was carried out at a speed of 50rpm for 30min to form an amorphous Li3N layer with a thickness of about 20nm. 4.4 Si coating layer to obtain a composite silicon-based negative electrode material.

[0078] Then, 1000 g of the composite silicon-based negative electrode material and 30 g of the binder SBR were added to 1000 mL of toluene solvent, and then stirred in a blender to form a stable and uniform negative electrode slurry; the negative electrode slurry was evenly and intermittently coated on a copper foil (copper foil size: width 160 mm, thickness 16 μm), and then dried at 100°C, and pressed by a roller press to form a negative electrode material layer on the copper foil to obtain a negative electrode sheet.

[0079] (2) Fabrication of solid electrolyte layer

[0080] Under a protective atmosphere, 600 g of 70Li2S·30P2S5 glassy sulfur-based solid electrolyte material is placed in 1200 g of toluene solution containing 30 g of butadiene rubber binder, and heated and stirred to obtain a uniform and stable slurry; the slurry is continuously coated on the negative electrode sheet obtained in step (1), and then dried at 100°C to form a solid electrolyte layer with a thickness of 35 μm on the negative electrode sheet.

[0081] (3) Production of positive electrode

[0082] Take 1000g of positive electrode active material TiS2, 150g of Li 10 GeP2S 12 Solid electrolyte material, 30 g of butadiene rubber adhesive, 20 g of acetylene black, and 20 g of carbon fiber are added to 1500 g of toluene solvent, and then stirred in a vacuum mixer to form a stable and uniform positive electrode slurry; the positive electrode slurry is uniformly and intermittently coated on an aluminum foil (the size of the aluminum foil is: width 160 mm, thickness 16 μm), and then dried at 120° C. After being pressed by a roller press, a positive electrode material layer with a thickness of 35 μm is formed on the aluminum foil to obtain a positive electrode sheet;

[0083] (4) Assembly of all-solid-state lithium batteries

[0084] Under a protective atmosphere, the positive electrode sheet in step (3) and the negative electrode sheet with a solid electrolyte layer in step (2) are aligned and placed in a tablet press, the tabs are attached, hot pressed at 100° C. for 1 h, vacuum-sealed with an aluminum-plastic film, and pressed at 200 MPa for 300 s in an isostatic press to obtain the following: Figure 3 The all-solid-state lithium battery shown.

[0085] Example 2

[0086] A preparation method of a composite silicon-based negative electrode material, comprising:

[0087] In an argon atmosphere, 1000 g of crystalline Li 4.4 Si (average particle size of 100 nm) and an appropriate amount of white phosphorus were placed separately in a closed reaction chamber. After evacuation, the temperature was raised to 573 K at a rate of 2 K / min using an electric heating furnace surrounding the reaction chamber. The reaction was continued for 8 h. After cooling to room temperature, Li3P coated with a layer of Li was obtained. 4.4 Si material; wherein the thickness of the Li3P coating layer is about 5nm, the particle size is about 100nm, and the mass proportion of the Li3P coating layer is about 5%;

[0088] The prepared Li3P-coated Li 4.4 1000g Si material and 200g amorphous Li 4.4Si material and 1000g toluene solvent were placed in a ball mill, and an appropriate amount of ZrO2 ball milling beads were added. The ball milling was carried out at a speed of 60rpm for 30min to form an amorphous Li layer with a thickness of about 20nm outside the Li3P layer. 4.4 Si coating layer to obtain a composite silicon-based negative electrode material.

[0089] According to the preparation method of the all-solid-state lithium battery described in Example 1, the composite silicon-based negative electrode material of Example 2 is prepared into an all-solid-state lithium battery.

[0090] Example 3

[0091] A composite silicon-based negative electrode material, including crystalline Li 4.4 Si core (particle size is 30nm), a first coating layer wrapping the core, and a second coating layer wrapping the first coating layer, wherein the first coating layer is Li3N, the thickness of the first coating layer is 2nm, and the mass of the first coating layer accounts for 2% of the sum of the mass of the core and the first coating layer; the second coating layer is amorphous Li 3.75 Si, its usage is 100g, the coating thickness is 30nm, and the mass of the second coating layer accounts for 9% of the mass of the composite silicon-based negative electrode material.

[0092] According to the preparation method of the all-solid-state lithium battery described in Example 1, the composite silicon-based negative electrode material of Example 3 is prepared into an all-solid-state lithium battery.

[0093] Example 4

[0094] A composite silicon-based negative electrode material, including crystalline Li 4.4 Si core (particle size is 500nm), a first coating layer wrapping the core, and a second coating layer wrapping the first coating layer, wherein the first coating layer is Li3N, the thickness of the first coating layer is 20nm, and the mass of the first coating layer accounts for 2% of the sum of the mass of the core and the first coating layer; the second coating layer is amorphous Li 2.33 Si, its usage is 300g, the coating thickness is 35nm, and the mass of the second coating layer accounts for 23% of the mass of the composite silicon-based negative electrode material.

[0095] According to the preparation method of the all-solid-state lithium battery described in Example 1, the composite silicon-based negative electrode material of Example 4 is prepared into an all-solid-state lithium battery.

[0096] Example 5

[0097] A composite silicon-based negative electrode material, which differs from Example 1 in that the core is an amorphous Li 4.4 Si material, other parameters are the same.

[0098] Example 6

[0099] A composite silicon-based negative electrode material, including crystalline Li 4.4 Si (average particle size of 100nm), a first coating layer wrapping the core, a second coating layer wrapping the first coating layer, wherein the first coating layer is Li3N and Li3P, the thickness of the first coating layer is 5nm, and the mass of the first coating layer accounts for 4% of the sum of the mass of the core and the first coating layer; the second coating layer is amorphous Li 4.4 Si, the coating thickness is 20nm, and the mass of the second coating layer accounts for 16% of the mass of the composite silicon-based negative electrode material.

[0100] The preparation method of the composite silicon-based negative electrode material is as follows: (1) 1000g of crystalline Li 4.4 Si (average particle size of 100 nm) and an appropriate amount of white phosphorus are placed in a closed reaction chamber. After evacuation, N2 is slowly filled in until the pressure in the chamber reaches 50 kPa (i.e., about 50 kPa lower than the atmospheric pressure). Then, an electric heating furnace surrounding the reaction chamber is used to heat the chamber to 573 K at a rate of 2 K / min. The reaction is carried out for 6 hours. After cooling to room temperature, crystalline Li coated with the first coating layer (Li3N and Li3P) is obtained. 4.4 Si material; (2) the above-mentioned Li3N and Li3P coated crystalline Li 4.4 1000g Si material and 200g amorphous Li 4.4 The Si material is ball-milled to obtain the above-mentioned composite silicon-based negative electrode material.

[0101] According to the preparation method of the all-solid-state lithium battery described in Example 1, the composite silicon-based negative electrode material of Example 6 is prepared into an all-solid-state lithium battery.

[0102] In order to highlight the beneficial effects of the embodiments of the present application, the following comparative examples are provided:

[0103] Comparative Example 1

[0104] A preparation of an all-solid-state lithium battery, which differs from Example 1 in that: when preparing the negative electrode sheet, carbon-coated Si is used as the negative electrode active material; when preparing the negative electrode sheet, LiNbO3-coated LiCoO2 is used as the positive electrode active material instead of TiS2.

[0105] Among them, the preparation method of carbon-coated Si is as follows: 1000g of Si and 240g of sucrose are placed in 1000mL of deionized water and stirred evenly, and then heated to 100°C during stirring, and after the water evaporates, the solid is taken out and heated to 300°C under an inert atmosphere to obtain a carbon-coated Si negative electrode material.

[0106] The preparation process of LiNbO3-coated LiCoO2 positive electrode material is as follows: 1000g of LiCoO2, 51mL of ethanol niobium, 12g of ethanol lithium, 1000mL of deionized water and 1000mL of ethanol are fully mixed, and under continuous stirring, ammonia water is added dropwise to adjust the pH to 10, the solution is evaporated to dryness, and the obtained powder is heated at 400°C for 8h to obtain a LiCoO2 positive electrode active material with LiNbO3 coated on the surface.

[0107] Comparative Example 2

[0108] The invention discloses a preparation method for an all-solid-state lithium battery, which is different from Comparative Example 1 in that when preparing the negative electrode sheet, not only Si coated with carbon is used as the negative electrode active material, but also a solid electrolyte material and a conductive agent are added.

[0109] The negative electrode slurry used to prepare the negative electrode sheet specifically includes: 1000g of carbon-coated Si negative electrode material, 400g of 70Li2S·30P2S5 glassy fixed electrolyte material, 100g of acetylene black conductive agent, 30g of binder SBR and 1000mL of toluene solvent.

[0110] Comparative Example 3

[0111] An all-solid-state lithium battery, which differs from Example 1 in that the negative electrode active material used is only crystalline Li 4.4 Si, it is not coated.

[0112] Comparative Example 4

[0113] An all-solid-state lithium battery, which differs from Example 1 in that the negative electrode active material used is only Li3N-coated Li 4.4 Si material is not re-coated with amorphous lithium-silicon alloy.

[0114] Comparative Example 5

[0115] An all-solid-state lithium battery, which differs from Example 2 in that the negative electrode active material used is only Li3P-coated Li 4.4 Si material is not re-coated with amorphous lithium-silicon alloy.

[0116] It should be noted that the negative electrode active materials used in Examples 1-6 and Comparative Examples 3-5 are lithium-containing lithium-silicon alloys, and the positive electrode active material of the battery is TiS2 that does not contain lithium; the negative electrode active material used in Comparative Examples 1-2 is a silicon material that does not contain lithium, and accordingly, the positive electrode active material used is lithium-containing, so LiCoO2 is used.

[0117] In order to strongly support the beneficial effects brought about by the technical solutions of the embodiments of the present application, electrochemical performance tests were carried out on the all-solid-state lithium batteries of Examples 1-6 and Comparative Examples 1-5, and the test results are summarized in Table 1 below.

[0118] The test method is as follows: 20 samples of all-solid-state lithium batteries prepared in each embodiment and comparative example are taken, and each battery is subjected to a charge-discharge cycle test at a rate of 0.1C at 298±1K on a LANDCT 2001C secondary battery performance test device: leave it for 10 minutes, charge at a constant voltage until 3V / 0.05C is cut off; leave it for 10 minutes; discharge at a constant current until 1V is one cycle, and record the first cycle discharge capacity (for batteries using LiNbO3-coated LiCoO2 material as the positive electrode active material, the upper and lower voltage limits are 4.25V / 0.05C and 3V, respectively, and the other conditions are the same). Repeat the above cycle steps, and when the battery capacity is lower than 80% of the initial discharge capacity during the cycle, the cycle is terminated, and the number of cycles at the end of the cycle is the cycle life of the battery, and the average value is taken for each group.

[0119] Table 1: Cycle performance test results of each group of battery samples

[0120]

[0121]

[0122] It can be seen from Table 1 that in Comparative Example 1 of the carbon-coated silicon negative electrode material commonly used in lithium batteries using electrolyte, since no solid electrolyte material is added to the negative electrode sheet, there is no ion channel in the negative electrode sheet, and it cannot perform normal charge and discharge cycles, indicating that the negative electrode material alone is not suitable for all-solid-state lithium batteries; but after the carbon-coated silicon negative electrode material is mixed with the solid electrolyte material and the conductive agent (Comparative Example 2), the performance of the obtained battery is improved compared with that of Comparative Example 1, but it is still far inferior to the performance of the all-solid-state lithium battery of the embodiment of the present application, especially the cycle performance. From the comparison of Comparative Examples 3-4 with Example 1 and from the comparison of Comparative Example 5 with Example 2, it can be seen that when the lithium silicon alloy is not coated or only Li3N or Li3P is used for coating, the cycle performance of the obtained battery is deviated, and the first discharge specific capacity is also low. Therefore, the lithium-silicon alloy with a specific multi-layer coating layer provided in the embodiment of the present application is used as the negative electrode active material of the all-solid-state lithium battery. It has excellent electronic conductivity and ionic conductivity, so that the use of solid electrolyte materials and conductive agents in the negative electrode sheet can be avoided, thereby making the electrochemical performance of the battery better, for example, the negative electrode has a higher discharge specific capacity and the battery has better cycle stability.

[0123] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A composite silicon-based negative electrode material, characterized in that: It includes an inner core, a first coating layer coated on the surface of the inner core, and a second coating layer coated on the surface of the first coating layer, wherein the inner core includes a crystalline lithium silicon alloy, the first coating layer includes at least one of Li3N and Li3P, and the second coating layer is an amorphous lithium silicon alloy.

2. The composite silicon-based negative electrode material according to claim 1, characterized in that: The thickness of the first coating layer is 2nm-200nm.

3. The composite silicon-based negative electrode material according to claim 2, characterized in that: The mass of the first coating layer accounts for 0.5%-10% of the sum of the mass of the core and the first coating layer.

4. The composite silicon-based negative electrode material according to claim 1, characterized in that: The thickness of the second coating layer is 5nm-500nm.

5. The composite silicon-based negative electrode material according to claim 4, characterized in that: The mass of the second coating layer accounts for 4%-35% of the mass of the composite silicon-based negative electrode material.

6. The composite silicon-based negative electrode material according to claim 1, characterized in that: The size of the core is 10 nm-1 μm.

7. The composite silicon-based negative electrode material according to any one of claims 1 to 6, characterized in that: The particle size of the composite silicon-based negative electrode material is 17nm-1.7μm.

8. A negative electrode sheet, comprising a negative electrode current collector and a negative electrode material layer disposed on the negative electrode current collector, wherein the negative electrode material layer comprises the composite silicon-based negative electrode material according to any one of claims 1 to 7 and does not contain a conductive agent and a solid electrolyte material.

9. The negative electrode sheet according to claim 8, characterized in that: The negative electrode material layer further contains a binder.

10. An all-solid-state lithium battery, characterized in that: It comprises a positive electrode sheet, a negative electrode sheet as described in any one of claims 8 to 9, and a solid electrolyte layer located between the positive electrode sheet and the negative electrode sheet.

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