Alloy negative electrode material applicable to low external pressure, preparation method and all-solid-state lithium battery

Abstract

The invention provides an alloy negative electrode material applicable to low external pressure, a preparation method and an all-solid-state lithium battery, and relates to the technical field of solid-state lithium batteries. The alloy negative electrode comprises an amorphous lithium-gallium alloy phase and amorphous lithium-silicon alloy particles, wherein the amorphous lithium-silicon alloy particles are dispersed in the amorphous lithium-gallium alloy. The alloy negative electrode is suitable for a solid-state lithium battery with low external pressure (1t, 10MPa) and high surface capacity, and can stably circulate more than 500 circles when being charged and discharged under the conditions of low np ratio and high current density, and lithium dendrites do not grow on the surface of the negative electrode.

Description

Technical Field

[0001] This application relates to the field of solid-state lithium batteries, and in particular to an alloy anode material suitable for low external pressure, a preparation method thereof, and an all-solid-state lithium battery. Background Technology

[0002] In recent years, solid-state batteries have been considered the core development direction of next-generation power battery technology due to their higher energy density and safety. With the rapid development of new energy vehicles and distributed energy storage, all-solid-state lithium batteries using solid electrolytes have attracted widespread attention due to their superior safety. However, the extremely high chemical reactivity of lithium metal makes most sulfide solid electrolytes incompatible with it, leading to severe interfacial reactions and consequently high interfacial impedance. Furthermore, grain boundaries and defects within the solid electrolyte can induce the formation of lithium dendrites. These interfacial side reactions and lithium dendrite growth issues make it difficult for all-solid-state lithium metal batteries to achieve long-term stable cycling at high current densities, which significantly restricts their practical application and commercialization.

[0003] Among them, silicon-based anodes are characterized by low cost and high specific capacity (3579 mAh g). -1 Suitable lithium intercalation potential (0.4V) and excellent safety are considered effective ways to break through the energy density of all-solid-state lithium batteries. However, existing pure silicon anodes and lithium-silicon alloy anodes have defects such as high hardness, high modulus, and low ionic and electronic conductivity. At the same time, their volume expansion is extremely severe during charge and discharge cycles, which makes it easy for electrical contact deactivation to occur at the interface between the anode and the electrolyte and between the anode particles. Typically, a stacking pressure of more than 50MPa is required to stabilize the cycle, which is far beyond the pressure threshold that commercial applications can withstand.

[0004] Patent CN115133011A discloses an anode material, its preparation method, and an all-solid-state lithium battery. The anode material includes a core and an amorphous lithium-silicon alloy layer covering the core. The core includes a glassy solid electrolyte and amorphous lithium-silicon alloy particles dispersed in the glassy solid electrolyte. The amorphous lithium-silicon alloy particles are made of LixSi, where 0 < x ≤ 4.4. The amorphous lithium-silicon alloy layer is made of LiySi, where 0 < y ≤ 4.4. Although the cycle stability of this anode material is improved.

[0005] Patent CN115117331A discloses a composite silicon-based anode material, an anode sheet, and an all-solid-state lithium battery. The anode material includes a core, a first coating layer covering the surface of the core, and a second coating layer covering the surface of the first coating layer. The core comprises a crystalline 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. This composite silicon-based anode material exhibits both good ionic and electronic conductivity, and the contact between the composite silicon-based anode materials is good under pressure, which is beneficial for improving its rate performance and cycle performance. However, the ionic conductivity, electronic conductivity, and cycle stability under low pressure conditions of both pure silicon and lithium-silicon alloy anodes still need improvement.

[0006] Therefore, there is currently no anode material that is stable under low pressure conditions and has excellent ionic and electronic conductivity. Summary of the Invention

[0007] The purpose of this application is to address the shortcomings of existing technologies by providing an alloy anode material, anode sheet, and all-solid-state lithium battery that can be applied under low external pressure. The anode material is prepared by dispersing and encapsulating an amorphous lithium silicon alloy with an amorphous lithium gallium alloy that has low hardness, low modulus, high ionic conductivity, and high electronic conductivity. It has excellent ionic and electronic conductivity and can achieve stable cycling under low pressure conditions (below 10 MPa).

[0008] To achieve the above objectives, the technical solution adopted in this application is as follows: According to one aspect of this application, an alloy anode material suitable for low external pressure is provided, comprising an amorphous lithium gallium alloy and amorphous lithium silicon alloy particles, wherein the amorphous lithium silicon alloy particles are dispersed in the crystalline lithium gallium alloy.

[0009] Furthermore, the mass ratio of lithium to silicon in the amorphous lithium-silicon alloy is (30-50):(50-70), for example, the mass ratio of lithium to silicon can be 30:70, 31:69, 32:68, 33:67, 34:66, 35:65, 36:64, 37:63, 38:62, 39:61, 40:60, 41:59, 42:58, 43:57, 44:56, 45:55, 46:54, 47:53, 48:52, 49:51, 50:50 or any range therebetween.

[0010] Furthermore, the mass ratio of lithium to gallium in the amorphous lithium-gallium alloy is (50-70):(30-50), for example, it can be 50:50, 51:49, 52:48, 53:47, 54:46, 55:45, 56:44, 57:43, 58:42, 59:41, 60:40, 61:39, 62:38, 63:37, 64:36, 65:35, 66:34, 67:33, 68:32, 69:31, 70:30 or any range therefrom.

[0011] Furthermore, the amorphous lithium gallium alloy also contains a dopant element X, which is selected from one or more of silver (Ag), zinc (Zn), magnesium (Mg), and aluminum (Al). The dopant element X accounts for 0 to 3% of the total mass of the alloy anode material. Preferably, the dopant element accounts for 1 to 3% of the total mass of the alloy anode material. For example, it can be 1%, 1.5%, 2%, 2.5%, 3%, or any range between them.

[0012] Preferably, the doping element is selected from Mg and Ag in a mass ratio of 2:1.

[0013] Furthermore, the particle size of the amorphous lithium-silicon alloy particles in the alloy negative electrode is 0.1–1 μm.

[0014] Furthermore, in the alloy anode material applicable to low external pressure, the mass ratio of amorphous lithium gallium alloy to amorphous lithium silicon alloy is (50-60):(40-50).

[0015] When doping elements are added to alloy anode materials suitable for low external pressure, the doping elements will accumulate on the surface of lithium gallium alloys. As a buffer and softening component, it helps to reduce the surface hardness and modulus of lithium gallium alloy particles and improve cycle stability. In particular, when doping elements of Mg and Ag with a mass ratio of 2:1 are added, the best performance can be obtained.

[0016] Furthermore, the lithium-ion conductivity of the alloy anode material suitable for low external pressure is 0.02–3.0 mS / cm, and the lithium-ion diffusion coefficient is 0.04–5.0 × 10⁻⁶. -12 m 2 / s.

[0017] According to another aspect of this application, a method for preparing an alloy negative electrode material suitable for low external pressure is provided, comprising the following steps: (1) Under inert gas protection, lithium metal is heated and melted at 200-300℃, then cooled to 180-200℃, gallium metal is added and allowed to melt completely; then a step cooling method is adopted, first cooling to 100-130℃ at 1-2℃ / min, holding at this temperature for 1-2h, and then cooling to room temperature at a rate of 5-8℃ / min to obtain lithium gallium alloy; (2) The lithium gallium alloy obtained in step (1) is mixed with lithium silicon alloy powder and doped element powder and ball-milled to obtain alloy powder; (3) The alloy powder is doped with PTFE and coated onto a foil, which is then rolled into a foil-shaped electrode to obtain the alloy negative electrode.

[0018] Furthermore, in step (1), after the metal is heated and melted, a stepped cooling mode is adopted. First, the cooling is carried out at a low cooling rate, and then the cooling rate is increased. Adjusting the metal ratio and matching the cooling rate can ensure that the grains in the lithium gallium crystalline alloy are refined to the greatest extent, so that the grain structure is subjected to more uniform force in the subsequent grinding process and avoids local residual crystalline phase.

[0019] Furthermore, in step (2), during the ball milling process, grinding balls made of silicon nitride are used to avoid introducing impurities; an intermittent grinding method of 40 minutes of operation + 20 minutes of shutdown is adopted, that is, ball milling is carried out at a frequency of 40 minutes of grinding and 20 minutes of stopping grinding; the grinding rate is maintained in the range of 500 to 800 r / min during the ball milling process, and the entire ball milling process takes 5 to 15 hours.

[0020] Compared to traditional grinding methods, ball milling employs an intermittent grinding process, controlling the running and stopping times of the ball mill. This ensures sufficient mechanical force is accumulated to disorder the atoms while avoiding the high-energy impacts during grinding that could cause localized high temperatures that would lead to the rearrangement of metal atoms into grains, resulting in amorphization failure. It also ensures a more uniform particle size distribution in the final lithium-gallium amorphous alloy powder and that the lithium-silicon amorphous alloy is uniformly dispersed within the lithium-silicon alloy. The lithium-gallium amorphous alloy possesses high ionic and electronic conductivity, providing a rapid lithium-ion transport path for the lithium-silicon alloy and significantly improving the lithium-ion transport efficiency within the negative electrode. This alloy negative electrode is suitable for solid-state lithium batteries with low external pressure and high areal capacity. Under low np ratio and high current density charging and discharging conditions, it can stably cycle for over 500 cycles without lithium dendrite growth on the negative electrode surface.

[0021] Further, in step (3), the mass ratio of alloy powder to PTFE is 100:0.8, and the foil is any one of copper foil, nickel foil, or stainless steel foil.

[0022] Furthermore, the proportions of gallium metal, lithium metal, silicon powder, and dopant elements are adjusted according to the required proportions of amorphous lithium-gallium alloy, amorphous lithium-silicon alloy, and dopant elements in the alloy anode material, as well as the elemental proportions in the amorphous lithium-silicon alloy and lithium-gallium alloy. For example, if the required alloy anode material satisfies the following conditions: the mass ratio of amorphous lithium-gallium alloy to amorphous lithium-silicon alloy is 50:50, and the total proportion of dopant elements in the alloy anode material is 1%, then the mass ratio of lithium, gallium, and dopant elements in the lithium-gallium alloy is 50:48:2, the mass ratio of lithium and silicon in the lithium-silicon alloy is 50:50, and the required proportions of each metal element are lithium:gallium:silicon:dopant elements = 50:24:25:1.

[0023] According to another aspect of this application, a solid-state lithium battery is provided, comprising the aforementioned alloy negative electrode material suitable for low external pressure, a solid electrolyte, a positive electrode material, and current collectors on both sides of the alloy negative electrode material and the positive electrode material suitable for low external pressure.

[0024] Furthermore, the areal capacity ratio of the alloy negative electrode material and the positive electrode material suitable for low external pressure is 1.05 to 2.5, for example, it can be any range between 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.2, 1.21, 1.22, 1.23, 1.24, 1.25, 1.26, 1.27, 1.28, 1.29, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5 or the range thereof.

[0025] Furthermore, the solid electrolyte is a conventional choice in the art and is not particularly limited, for example, it can be Li6PS5Cl, Li 5.5 PS 4.5 Cl 1.5 Li3PS4, Li 10 GeP2S 12 Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 Li 0.33 La 0.56 TiO3, Li7La3Zr2O 12 Any one or more of Li3InCl6.

[0026] Furthermore, the cathode material is a conventional choice in the art and is not particularly limited; for example, it could be LiNi. x Co y Mn 1-x-yAny one or more of O2, LiCoO2, LiFePO4, LiMn2O4, TiS2, and S.

[0027] Compared with the prior art, this application has the following beneficial effects: 1. The alloy anode material provided in this application introduces a lithium gallium alloy with low hardness and low Young's modulus, and a lithium silicon alloy dispersed in the lithium gallium alloy to form a structure in which the lithium gallium alloy encapsulates the lithium silicon alloy and fills the gaps between the lithium silicon alloy. This makes the overall Young's modulus and hardness of the anode lower than that of sulfide electrolytes represented by Li6PS5Cl, avoiding damage and wear to the electrolyte layer caused by continuous volume changes of the anode. It also achieves good contact between anode particles and between the anode and electrolyte interface under low external pressure, ensuring that the solid-state battery can cycle stably under low external pressure.

[0028] 2. This application achieves a structure in which lithium-silicon alloy is uniformly distributed within lithium-gallium alloy by controlling ball milling conditions. The lithium-gallium alloy possesses high ionic and electronic conductivity, providing a rapid lithium-ion transport path for the lithium-silicon alloy and significantly improving the lithium-ion transport efficiency within the negative electrode. This alloy negative electrode is suitable for solid-state lithium batteries with low external pressure (<10MPa) and high areal capacity. Under low np ratio and high current density charging and discharging conditions, it can stably cycle for over 500 cycles without lithium dendrite growth on the negative electrode surface.

[0029] 3. The alloy anode material provided in this application introduces doping elements, which are enriched on the surface of the lithium gallium alloy. The addition of doping elements helps to reduce the surface hardness and modulus of the lithium gallium alloy particles, and significantly improves the cycle stability under low external pressure.

[0030] 4. A solid-state lithium battery prepared using the alloy anode material provided in this application, employing a high areal capacity LiNi alloy. 0.8 Co 0.1 Mn 0.1 With an O2 cathode, it can exhibit high energy density under low external pressure and high current density, and achieve stable cycling. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of alloy powder being rolled into foil-shaped electrode sheets in Embodiment 3 of this application. Detailed Implementation

[0032] The following non-limiting embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of this application, but do not limit this application in any way. The following content is merely an exemplary description of the scope of protection claimed in this application, and those skilled in the art can make various changes and modifications to the invention based on the disclosed content, which should also fall within the scope of protection claimed in this application.

[0033] The present application will be further described below by way of specific embodiments. Unless otherwise specified, all chemical reagents used in the embodiments of this application are obtained through conventional commercial means.

[0034] Example 1 This embodiment provides a method for preparing an alloy anode material suitable for low external pressure, including the following steps: (1) Heat lithium metal to 200°C to melt it, then cool it down to 180°C, add gallium metal, and wait for it to melt completely; then use a step cooling method, first cool down to 100°C at 1°C / min, continue to hold at this temperature for 1 hour, and then cool down to room temperature at 5°C / min to obtain a lithium-gallium alloy; the mass ratio of lithium to gallium in the lithium-gallium alloy is 50:50; (2) The lithium gallium alloy obtained in step (1) is mixed with the amorphous lithium silicon alloy and placed in a ball mill for grinding. During the grinding process, an intermittent grinding method of 40 min running + 20 min stopping is adopted, the grinding rate is maintained at 500 r / min, and the entire ball milling process takes 15 h to obtain alloy powder. The mass ratio of lithium gallium alloy to amorphous lithium silicon alloy is 60:40. In amorphous lithium-silicon alloys, the mass ratio of lithium to silicon is 30:70. (3) The alloy powder and PTFE are mixed at a ratio of 100:0.8 and then coated onto copper foil. The mixture is then rolled and pressed into foil-shaped electrode sheets.

[0035] Example 2 This embodiment provides a method for preparing an alloy anode material suitable for low external pressure, including the following steps: (1) Heat lithium metal to 300°C to melt it, then cool it down to 200°C, add gallium metal, and wait for it to melt completely; then use a step cooling method, first cool down to 130°C at 2°C / min, continue to hold at this temperature for 2 hours, and then cool down to room temperature at 8°C / min to obtain a lithium-gallium alloy; the mass ratio of lithium to gallium in the lithium-gallium alloy is 70:30; (2) The lithium gallium alloy obtained in step (1) is mixed with the amorphous lithium silicon alloy and placed in a ball mill for grinding. During the grinding process, an intermittent grinding method of 40 min running + 20 min stopping is adopted, the grinding rate is maintained at 800 r / min, and the entire ball milling process takes 5 h to obtain alloy powder. The mass ratio of lithium gallium alloy to amorphous lithium silicon alloy is 50:50. In amorphous lithium-silicon alloys, the mass ratio of lithium to silicon is 70:30. (3) The alloy powder and PTFE are mixed at a ratio of 100:0.8 and then coated onto copper foil. The mixture is then rolled and pressed into foil-shaped electrode sheets.

[0036] Example 3 This embodiment provides a method for preparing an alloy anode material suitable for low external pressure, including the following steps: (1) Heat lithium metal to 300°C to melt it, then cool it down to 200°C, add gallium metal, and wait for it to melt completely; then use a step cooling method, first cool down to 130°C at 2°C / min, continue to hold at this temperature for 2 hours, and then cool down to room temperature at 8°C / min to obtain a lithium-gallium alloy; the mass ratio of lithium to gallium in the lithium-gallium alloy is 70:30; (2) The lithium gallium alloy obtained in step (1) is mixed with the amorphous lithium silicon alloy and the doping element Mg, and then put into a ball mill for grinding. During the grinding process, an intermittent grinding method of 40 min running + 20 min stopping is adopted, the grinding rate is maintained at 800 r / min, and the entire ball milling process takes 15 h to obtain alloy powder. The mass ratio of lithium gallium alloy, amorphous lithium silicon alloy, and doped element Mg is 60:39:1. In amorphous lithium-silicon alloys, the mass ratio of lithium to silicon is 30:70. (3) The alloy powder and PTFE are mixed at a ratio of 100:0.8 and then coated onto copper foil. The mixture is then rolled and pressed into foil-shaped electrode sheets.

[0037] Figure 1 This diagram illustrates the process of rolling alloy powder into foil-shaped electrodes, i.e., alloy amorphous Li, obtained by ball milling and alloying with doping elements. 1.2 In GaX alloys, X represents a doping element; in this embodiment, X is Mg.

[0038] Example 4 This embodiment provides a method for preparing an alloy anode material suitable for low external pressure, including the following steps: (1) Heat lithium metal to 300°C to melt it, then cool it down to 200°C, add gallium metal, and wait for it to melt completely; then use a step cooling method, first cool down to 130°C at 2°C / min, continue to hold at this temperature for 2 hours, and then cool down to room temperature at 8°C / min to obtain a lithium-gallium alloy; the mass ratio of lithium to gallium in the lithium-gallium alloy is 50:50; (2) The lithium gallium alloy obtained in step (1) is mixed with the amorphous lithium silicon alloy and the doping element Mg, and then put into a ball mill for grinding. During the grinding process, an intermittent grinding method of 40 min running + 20 min stopping is adopted, the grinding rate is maintained at 800 r / min, and the entire ball milling process takes 15 h to obtain alloy powder. The mass ratio of amorphous lithium gallium alloy, amorphous lithium silicon alloy, and doped element Mg is 49:49:2. In amorphous lithium-silicon alloys, the mass ratio of lithium to silicon is 50:50. (3) The alloy negative electrode material and PTFE are doped at a ratio of 100:0.8 and coated on copper foil, and then rolled to form a foil electrode sheet.

[0039] Example 5 This embodiment provides a method for preparing an alloy anode material suitable for low external pressure, including the following steps: (1) Heat lithium metal to 300°C to melt it, then cool it down to 200°C, add gallium metal, and wait for it to melt completely; then use a step cooling method, first cool down to 130°C at 2°C / min, continue to hold at this temperature for 2 hours, and then cool down to room temperature at 8°C / min to obtain a lithium-gallium alloy; the mass ratio of lithium to gallium in the lithium-gallium alloy is 50:50; (2) The lithium gallium alloy obtained in step (1) is mixed with the amorphous lithium silicon alloy and the doping element Ag, and then put into a ball mill for grinding. During the grinding process, an intermittent grinding method of 40 min running + 20 min stopping is adopted, the grinding rate is maintained at 800 r / min, and the entire ball milling process takes 15 h to obtain alloy powder. The mass ratio of amorphous lithium gallium alloy, amorphous lithium silicon alloy, and doped element Ag is 50:47:3. In amorphous lithium-silicon alloys, the mass ratio of lithium to silicon is 50:50. (3) The alloy negative electrode material and PTFE are doped at a ratio of 100:0.8 and coated on copper foil, and then rolled to form a foil electrode sheet.

[0040] Example 6 The difference from Example 4 is that the doping elements in this example are replaced with Mg and Ag in a mass ratio of 2:1, while the total amount of doping elements remains unchanged.

[0041] Comparative Example 1 The difference from Example 4 is that the mass ratio of lithium to silicon in the amorphous lithium-silicon alloy is 25:75.

[0042] Comparative Example 2 The difference from Example 4 is that the mass ratio of lithium to gallium in the lithium-gallium alloy is 45:55.

[0043] Comparative Example 3 The difference from Example 4 is that the mass ratio of lithium gallium alloy, amorphous lithium silicon alloy, and dopant element Mg is 45:53:2.

[0044] Comparative Example 4 The difference from Example 4 is that the mass ratio of lithium gallium alloy, amorphous lithium silicon alloy, and dopant element Mg is 63:35:2.

[0045] Comparative Example 5 The difference from Example 4 is that the doping element Mg is replaced with an equal amount of Fe.

[0046] Comparative Example 6 The difference from Example 4 is that the mass ratio of lithium gallium alloy, amorphous lithium silicon alloy, and dopant element Mg is 48:48:4.

[0047] Comparative Example 7 This comparative example provides a method for preparing an alloy anode material suitable for low external pressure, comprising the following steps: (1) Silicon and lithium metals are heated to 300°C and held at that temperature for 2 hours to alloy them. Then, they are cooled to room temperature to obtain a lithium-silicon alloy. (2) The lithium-silicon alloy was mixed with the doping element Mg and ball-milled at a speed of 500 r / min for 15 h to obtain alloy powder; wherein the mass ratio of lithium, silicon and Mg in the alloy anode material was 43:55:2. (3) The alloy powder and PTFE are mixed at a ratio of 100:0.8 and then coated onto copper foil. The mixture is then rolled and pressed into foil-shaped electrode sheets.

[0048] Comparative Example 8 This comparative example provides a method for preparing an alloy anode material suitable for low external pressure, comprising the following steps: (1) Heat lithium metal to 300°C to melt it, then cool it down to 200°C, add gallium metal, and wait for it to melt completely; then use a step cooling method, first cool down to 130°C at 2°C / min, continue to hold at this temperature for 2 hours, and then cool down to room temperature at 8°C / min to obtain a lithium-gallium alloy; the mass ratio of lithium to gallium in the lithium-gallium alloy is 50:50; (2) The lithium gallium alloy was mixed with the doping element Mg and ground in a ball mill. During the grinding process, an intermittent grinding method of 40 min running + 20 min stopping was adopted. The grinding rate was maintained at 800 r / min. The entire ball milling process took 15 h to obtain alloy powder. The mass ratio of lithium gallium alloy to doping element Mg was 98:2. (3) The alloy powder and PTFE were doped at a ratio of 100:0.8 and coated on copper foil. The copper foil was then rolled into a foil-shaped electrode to obtain the LiGaMg alloy negative electrode.

[0049] Comparative Example 9 This comparative example provides a method for preparing an alloy anode material suitable for low external pressure, comprising the following steps: (1) Heat lithium metal to 300°C to melt it, then cool it down to 200°C, add gallium metal, and wait for it to melt completely; then use a step cooling method, first cool down to 130°C at 2°C / min, continue to hold at this temperature for 2 hours, and then cool down to room temperature at 8°C / min to obtain a lithium-gallium alloy; the mass ratio of lithium to gallium in the lithium-gallium alloy is 50:50; (2) Mix micron-sized silicon powder with doping element (Mg) and grind it in a ball mill. During the grinding process, an intermittent grinding method of 40 min running + 20 min stopping is adopted. The grinding rate is maintained at 800 r / min. The entire ball milling process takes 15 h to obtain alloy powder I. In step (1), the lithium gallium alloy is directly ground into powder using a mortar and pestle. Due to the lack of long-term ball milling, the lithium gallium alloy is in a crystalline state at this time. The lithium gallium alloy powder is mixed with alloy powder I to obtain alloy powder II. The mass ratio of amorphous lithium gallium alloy, amorphous lithium silicon alloy, and doped element Mg is 49:49:2. In amorphous lithium-silicon alloys, the mass ratio of lithium to silicon is 50:50. (3) Alloy powder II and PTFE are doped at a ratio of 100:0.8 and coated onto copper foil, and then rolled to form foil-shaped electrode sheets.

[0050] Comparative Example 10 The difference from Example 4 is that in step (1), the cooling rate is 8°C in the step-by-step cooling process.

[0051] Comparative Example 11 The difference from Example 4 is that step (1) adopts a one-stage cooling with a cooling rate of 8°C and no heat preservation is performed in between.

[0052] Comparative Example 12 The difference from Example 4 is that in step (2), an intermittent ball milling method of grinding for 30 minutes and stopping for 30 minutes is used.

[0053] Comparative Example 13 The difference from Example 4 is that in step (2), the ball milling method is a one-stage milling method, and the grinding rate remains unchanged during the grinding process.

[0054] Comparative Example 14 A method for preparing a solid-state lithium-ion battery includes the following steps: A 25 μm thick Li6PS5Cl solid electrolyte membrane with an areal capacity of 5.0 mAh / cm² was used. 2 LiNi 0.8 Co 0.1 Mn 0.1The O2 positive electrode (alloy negative electrode surface capacity / positive electrode surface capacity = 1.24) and the alloy negative electrode obtained in the above embodiment are stacked with Li6PS5Cl and ternary positive electrode to form a multilayer solid-state lithium-ion pouch battery.

[0055] Solid-state lithium-ion batteries were prepared according to the above method. Using a LAND CT 2001C secondary battery performance testing device, under conditions of 298±1K and an external stacking pressure of 10MPa, each battery was first allowed to stand for 120 minutes, and then subjected to charge-discharge cycle testing at a rate of 0.1C: charging to 4.20V at a rate of 0.1C and then discharging to 2.40V at a rate of 0.1C constituted one cycle, and the discharge capacity of the first cycle was recorded. This cycle was repeated 500 times, and the discharge capacity of the 500th cycle was recorded. The capacity retention rate was calculated based on the initial discharge capacity.

[0056] The results are shown in Table 1 below.

[0057] Table 1. Battery performance test results

[0058] The results show that the amorphous lithium-gallium alloy composite amorphous lithium-silicon alloy containing doped elements provided in this application, as the negative electrode active material of all-solid-state batteries, can achieve stable contact with the electrolyte and has interconnected high-speed ion and electron transport channels, enabling all-solid-state batteries to achieve stable cycling under low external pressure. Disassembly of the cycled battery revealed that no lithium dendrites were generated on the alloy negative electrode, and no cracks were found on the electrolyte surface.

[0059] Compared to Example 4, Comparative Example 1 has an excess of silicon in its amorphous lithium-silicon alloy, Comparative Example 2 has an excess of gallium in its amorphous lithium-gallium alloy, and Comparative Example 3 has an excessively low proportion of soft amorphous lithium-gallium alloy in its alloy anode. These conditions make it difficult to form a continuous network of conductive electrons, conductive ions, and mechanical buffers, making it difficult for the anode to maintain stable contact with the electrolyte interface under low external pressure. As a result, the battery has very poor cycle performance. Upon disassembly of the cycled battery, cracks were found on the surface of the electrolyte.

[0060] In Comparative Example 4, increasing the proportion of amorphous lithium-gallium alloy enabled the composite anode to maintain more stable cycling under low external pressure, but the specific capacity of the anode itself was insufficient to meet the high energy density requirements of the full cell. Disassembly of the cycled battery revealed cracks on the electrolyte surface.

[0061] When the doping element in the alloy anode of Comparative Example 5 is replaced with Fe, it reacts with the lithium gallium alloy and increases its hardness and modulus, making it more difficult to deform under low stacking pressure in order to maintain close contact with the lithium silicon particles. The cycle performance of the battery is greatly reduced, and cracks are found on the surface of the electrolyte when the battery is disassembled after cycling.

[0062] In Comparative Example 7, the alloy anode lacks a soft amorphous lithium gallium alloy as a buffer, making it difficult for the lithium silicon alloy to maintain stable contact with the electrolyte interface under low external pressure. As a result, the battery has poor cycle performance. Upon disassembly of the cycled battery, cracks were found on the electrolyte surface.

[0063] In Comparative Example 8, although using only amorphous lithium gallium alloy as the anode could maintain stable cycling under low external pressure, the specific capacity of the anode itself was too low to meet the high energy density requirements of the full cell. Disassembly of the cycled battery revealed no cracks on the electrolyte surface and no dendrite formation on the alloy anode.

[0064] In Comparative Example 9, replacing the low-hardness amorphous lithium gallium alloy with a high-hardness crystalline lithium gallium alloy in the alloy anode also failed to maintain stable interfacial contact. Disassembly of the cycled battery revealed no lithium dendrite formation in the alloy anode, but cracks were present on the electrolyte surface.

[0065] In Comparative Examples 10 and 11, altering the stepped cooling process during lithium-gallium alloy preparation affected the formation of a continuous conductive electron, ion, and mechanical buffer network between the lithium-gallium alloy and the lithium-silicon alloy during subsequent grinding. This made it difficult for the negative electrode to maintain stable contact with the electrolyte interface under low external pressure, resulting in reduced battery cycle performance. The altered intermittent grinding conditions during the grinding processes of Comparative Examples 12 and 13 resulted in the amorphous lithium gallium alloy in the obtained alloy negative electrode not being evenly distributed, failing to maintain stable contact with the electrolyte interface under low external pressure, and thus reducing the battery cycle performance.

[0066] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, this application is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of this application without departing from the scope of this application should be within the protection scope of this application.

Claims

1. An alloy anode material suitable for low external pressure, characterized in that, It includes amorphous lithium gallium alloy and amorphous lithium silicon alloy particles, wherein the amorphous lithium silicon alloy particles are dispersed in the amorphous lithium gallium alloy.

2. The alloy negative electrode material suitable for low external pressure according to claim 1, characterized in that, The mass ratio of lithium to silicon in the amorphous lithium-silicon alloy is (30-50):(50-70); and / or The mass ratio of lithium to gallium in the amorphous lithium-gallium alloy is (50-70):(30-50).

3. The alloy negative electrode material suitable for low external pressure according to claim 2, characterized in that, The amorphous lithium gallium alloy also contains doping elements, which are selected from one or more of Ag, Zn, Mg, and Al, and the doping elements account for 0 to 3% of the total mass of the alloy anode material; preferably, the doping elements account for 1 to 3% of the total mass of the alloy anode material.

4. The alloy negative electrode material suitable for low external pressure according to claim 3, characterized in that, Preferably, the doping element is selected from Mg and Ag in a mass ratio of 2:

1.

5. The alloy negative electrode material suitable for low external pressure according to claim 4, characterized in that, The mass ratio of the amorphous lithium gallium alloy to the amorphous lithium silicon alloy is (50-60):(40-50).

6. The alloy negative electrode material suitable for low external pressure according to any one of claims 1-5, characterized in that, Its lithium-ion conductivity is 0.02–3.0 mS / cm, and its lithium-ion diffusion coefficient is 0.04–5.0 × 10⁻⁶. -12 m 2 / s.

7. The method for preparing the alloy negative electrode material suitable for low external pressure according to any one of claims 1-6, characterized in that, Includes the following steps: (1) Under inert gas protection, lithium metal is heated and melted at 200-300℃, then cooled to 180-200℃, gallium metal is added and allowed to melt completely; then a step cooling method is adopted, first cooling to 100-130℃ at 1-2℃ / min, holding at this temperature for 1-2h, and then cooling to room temperature at a rate of 5-8℃ / min to obtain lithium gallium alloy; (2) The lithium gallium alloy obtained in step (1) is mixed with lithium silicon alloy powder and doped element powder and ball-milled to obtain alloy powder; (3) The alloy powder is doped with PTFE and coated onto a foil, which is then rolled into a foil-shaped electrode to obtain the alloy negative electrode.

8. The preparation method according to claim 7, characterized in that, In step (2), grinding balls made of silicon nitride are used during the ball milling process; an intermittent grinding method of 40 minutes of operation + 20 minutes of shutdown is adopted; the grinding rate is maintained in the range of 500 to 800 r / min during the ball milling process, and the entire ball milling process takes 5 to 15 hours.

9. The preparation method according to claim 7, characterized in that, In step (3), the foil is any one of copper foil, nickel foil, or stainless steel foil.

10. A solid-state lithium battery, characterized in that, It comprises an alloy anode material suitable for low external pressure as described in any one of claims 1-6 or an alloy anode material prepared by the preparation method described in any one of claims 7-9, a solid electrolyte, a cathode material, and current collectors on both sides of the alloy anode material and the cathode material suitable for low external pressure.

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