Negative electrode material, preparation method thereof and secondary battery

Abstract

The invention relates to the technical field of batteries, in particular to a negative electrode material, a preparation method thereof and a secondary battery. The invention provides a negative electrode material, the negative electrode material is a silicon-based alloy, and the silicon-based alloy comprises silicon, magnesium and indium; in the silicon-based alloy, the mass ratio of the magnesium to the indium is (0.5 to 1.5): (0.5 to 1.5); in the silicon-based alloy, the mass ratio of the magnesium is 8%-25%; the mass ratio of the indium is 8%-25%. According to the negative electrode material, the preparation method thereof and the secondary battery, magnesium and indium are introduced for a silicon-based negative electrode to prepare a ternary alloy, the electronic conductivity can be improved and the silicon expansion rate can be reduced while magnesium and indium metal elements are introduced, and the magnesium and indium metal with high conductivity not only improves the rate capability of the battery, but also enhances the cycling stability of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a negative electrode material, a preparation method thereof and a secondary battery. BACKGROUND

[0002] Lithium ion batteries, as indispensable energy storage devices in modern portable electronic devices and electric vehicles, their performance depends largely on the properties of electrode materials. The negative electrode material, as an important component of secondary batteries, directly affects the energy density, cycle life, rate performance and safety of the battery. The traditional graphite negative electrode has been developed to the limit theoretical specific capacity (372 mAh / g), and it is urgent to find a replacement material. Among the many negative electrode materials, silicon (Si) is very promising to realize high energy density and power density secondary batteries due to its ultra-high theoretical specific capacity (4200 mAh / g), suitable lithium intercalation / deintercalation potential (0.2~0.4V (vs. Li / Li + ) ), natural abundance and other advantages.

[0003] However, the large volume change (~300%) of silicon during lithium intercalation / deintercalation will generate a huge internal stress, causing vertical cracks in the silicon negative electrode, increasing the curvature of the lithium ion transport path, and increasing the internal resistance of the battery. With the continuous operation of the battery, it will eventually lead to the failure of the battery. At the same time, the low electrical conductivity and ion diffusion coefficient of silicon will also make it difficult for the silicon negative electrode to deliver capacity at high current density. These two problems hinder the application of silicon negative electrode in secondary batteries. In view of these two problems, researchers have proposed strategies such as nanocrystallization, porosity, surface modification and compounding. Nanocrystallization and porous Si can alleviate the volume expansion of Si, but the high cost restricts its commercial application; surface modification alone cannot solve the internal expansion problem of Si negative electrode; Si / C negative electrode has mature technology but has low specific capacity.

[0004] Therefore, there is still room for improvement in the optimization of silicon-based negative electrodes. SUMMARY

[0005] The purpose of the present application is to provide a negative electrode material, a preparation method thereof and a secondary battery, which can improve the rate performance, cycle performance and safety performance of the secondary battery.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows: The first aspect of the present application provides a negative electrode material, the negative electrode material is a silicon-based alloy, the silicon-based alloy includes silicon, magnesium and indium; in the silicon-based alloy, the mass ratio of the magnesium and the indium is (0.5~1.5):(0.5~1.5); in the silicon-based alloy, the mass percentage of the magnesium is 8%~25%; the mass percentage of the indium is 8%~25%.

[0007] In some embodiments, the mass ratio of silicon, magnesium and indium in the silicon-based alloy is (4-5):(0.5-1.5):(0.5-1.5).

[0008] The second aspect of the present application provides a preparation method of the above negative electrode material, comprising: mixing silicon powder, magnesium powder, indium powder and a solvent in an inert gas atmosphere to obtain a silicon-based alloy raw material; ball milling the silicon-based alloy raw material, and then performing sintering treatment.

[0009] In some embodiments, the solvent comprises one or more of ethanol, ethylene glycol, propanol, acetone, butanone, and N,N-dimethylformamide.

[0010] In some embodiments, the mass percentage of the solvent in the silicon-based alloy raw material is 10wt%-30wt%.

[0011] In some embodiments, the ball milling is performed in a forward-reverse alternating mode.

[0012] In some embodiments, the forward-reverse alternating mode comprises a program of forward rotation for 10-30 minutes, reverse rotation for 10-30 minutes, and interval for 5-10 minutes.

[0013] In some embodiments, the mass ratio of the ball milling beads to the silicon-based alloy raw material is (25-50):1.

[0014] In some embodiments, the ball milling time is 2-8 hours, and the rotation speed is 300-600 rpm.

[0015] In some embodiments, the sintering treatment comprises sintering the ball-milled material in an inert gas atmosphere, the sintering temperature is 400-600℃, and the sintering time is 2-4 hours.

[0016] In some embodiments, the sintering treatment is performed at a heating rate of 3-5℃ / min from room temperature to 400-600℃, and after the sintering is completed, the temperature is decreased to room temperature at a cooling rate of 5-20℃ / min.

[0017] In some embodiments, the preparation method of the negative electrode material comprises: mixing micron-sized silicon powder, micron-sized magnesium powder, micron-sized indium powder and ethanol in an inert gas atmosphere to obtain a silicon-based alloy raw material, ball milling the silicon-based alloy raw material; the mass percentage of the ethanol in the silicon-based alloy raw material is 10wt%-30wt%; the mass ratio of the micron-sized silicon powder, the micron-sized magnesium powder and the micron-sized indium powder is (4-5):(0.5-1.5):(0.5-1.5). The ball milling process adopts a forward-reverse alternating mode; the forward-reverse alternating mode includes: forward rotation for 10-30 min, reverse rotation for 10-30 min, and interval of 5-10 min; The sintering process of the material after ball milling is carried out under an inert gas atmosphere; the sintering process is carried out at a temperature rising rate of 3-5 ℃ / min from room temperature to 400-600 ℃, and after sintering, the temperature is lowered to room temperature at a temperature lowering rate of 5-20 ℃ / min; The sintered material is ground, and the ground material is sieved through a 200-mesh sieve.

[0018] The third aspect of the present application provides a secondary battery, which comprises a negative electrode sheet, the negative electrode sheet comprising a negative electrode film layer and a current collector, and the negative electrode film layer comprising the above-mentioned negative electrode material.

[0019] The present application has the following beneficial effects: The negative electrode material, the preparation method thereof and the secondary battery disclosed by the present application introduce magnesium and indium to prepare a silicon-based alloy for a silicon-based negative electrode, reduce the expansion rate by introducing magnesium metal elements, inhibit lithium dendrite formation by introducing indium metal elements, and high-conductivity magnesium and indium metal not only improves the rate performance of the battery but also enhances the cycle stability of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 Figure 3 is an XRD diagram of the silicon-magnesium-indium ternary alloy prepared in Example 1 of the present application.

[0021] Figure 2 Figure 4 is an SEM-EDS diagram of the silicon-magnesium-indium ternary alloy prepared in Example 1 of the present application, wherein Figure A is an element distribution diagram of the micro-morphology of the silicon-magnesium-indium ternary alloy, Figure B is a Si element distribution diagram of the silicon-magnesium-indium ternary alloy, Figure C is a Mg element distribution diagram of the silicon-magnesium-indium ternary alloy, and Figure D is an In element distribution diagram of the silicon-magnesium-indium ternary alloy. DETAILED DESCRIPTION

[0022] The embodiments of the present application will be described below with reference to the accompanying drawings and preferred embodiments, and other advantages and effects of the present application can be easily understood by those skilled in the art from the disclosure herein. The present application can also be implemented or applied in other different specific embodiments, and various modifications or changes can be made to the details in the specification based on different viewpoints and applications without departing from the spirit of the present application. It should be understood that the preferred embodiments are only for illustrating the present application, and are not intended to limit the protection scope of the present application.

[0023] Currently, among the modification methods of Si, alloying with Si can maintain the high specific capacity of the base Si and reduce the expansion rate and improve the electrical conductivity by introducing alloying elements. Patent application CN119920850A discloses alloying Si by mixing metal powder, silicon powder and phosphorus powder, adding conductive additives to obtain a uniform negative electrode slurry, and coating the slurry on the surface of the current collector to obtain a silicon alloy negative electrode sheet. However, the introduction of P element reduces the specific capacity of Si alloy, the complex electrode sheet preparation process increases the production cost, and the introduction of non-conductive P cannot improve the electronic conductivity of Si, and the rate performance is poor. Patent application CN119361705A discloses the preparation of lithium-silicon alloy by over-prelithiation and the introduction of conductive carbon to improve the cycle performance and rate performance of the silicon-based negative electrode. However, the lithium-rich compound (such as LiH) has extremely high reactivity, which is easy to cause thermal runaway risk during production and transportation. The introduction of conductive carbon will cause the decomposition of sulfide electrolyte, leading to side reactions at the negative electrode interface, and is not suitable for sulfide full solid-state batteries. Other common binary silicon alloys have poor lithium storage performance (such as silicon-iron alloy) and high cost (such as silicon-germanium alloy). Therefore, the current silicon alloy negative electrode material cannot balance safety, storage, cycle and rate performance.

[0024] The present application finds that the introduction of magnesium and indium in the silicon-based negative electrode can improve the electronic conductivity and volume expansion rate of the obtained silicon-magnesium-indium alloy as a negative electrode material. The increase in configurational entropy of the ternary silicon alloy negative electrode material improves the intrinsic stability of the material, and can balance the improvement of rate performance and cycle life.

[0025] Based on this, the present application provides a kind of negative electrode material and its preparation method and secondary battery, specifically: In a first aspect, the present application provides a negative electrode material, which is a silicon-based alloy, comprising silicon, magnesium and indium. In the silicon-based alloy, the mass ratio of magnesium to indium is (0.5-1.5):(0.5-1.5). In the silicon-based alloy, the mass fraction of magnesium is 8%-25%, and the mass fraction of indium is 8%-25%.

[0026] Traditional binary silicon alloys have poor lithium storage performance (such as silicon-iron alloy) and high cost (such as silicon-germanium alloy). The present application finds that the silicon-magnesium-indium silicon-based alloy negative electrode material not only can solve the above problems, but also can improve the thermodynamic stability of the material by increasing the configurational entropy. By controlling the mass ratio of magnesium and indium within the above range, both the local aggregation of lithium ions during charging and the single-element enrichment leading to single function can be avoided, and finally the stability of the silicon alloy negative electrode material during charging and discharging is synergistically enhanced, and the cycle life is improved.

[0027] Exemplarily, the mass ratio of the magnesium and the indium can be 1:1, 0.5:1.5, 0.5:1, 1.5:1 or 1.5:0.5, or a ratio range with any two of the above as the end points.

[0028] In some embodiments, the silicon-based alloy is composed of silicon, magnesium, indium and inevitable impurities. In the present application, the "inevitable impurities" are defined as elements that are unintentionally added to the composition of the powder and contributed by other elements. For example, these inevitable impurities can come from alloy raw materials, ball milling equipment, etc.

[0029] In some embodiments, the mass percentage of the inevitable impurities in the silicon-based alloy is 0.1% or less.

[0030] In the present application, magnesium metal is introduced as the negative electrode material. Magnesium has a high theoretical specific capacity (2150 mAh / g). The elastic Li-Mg alloy formed after lithium intercalation can effectively improve the interface stability and inhibit the volume expansion of silicon, which is beneficial to improve the cycle life. At the same time, magnesium metal forms a continuous metal conductive framework in the bulk phase, which can effectively improve the electronic conductivity of the silicon negative electrode material compared to pure silicon with semiconductor characteristics. Therefore, controlling the mass percentage of magnesium in the silicon-based alloy within the above range is beneficial to balance the improvement of the cycle performance and rate performance of the battery.

[0031] Exemplarily, the mass percentage of the magnesium in the silicon-based alloy can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, or a ratio range with any two of the above as the end points.

[0032] The electronic conductivity of indium at room temperature is about 10 orders of magnitude higher than that of silicon, which can significantly improve the electronic conductivity of silicon and help to achieve large-rate charging and discharging of solid-state batteries. At the same time, the ductility of indium promotes the lateral extension of lithium dendrites instead of vertical penetration of the electrolyte, which can reduce the loss of active lithium and inhibit the growth of lithium dendrites to pierce the sulfide solid-state electrolyte film, thereby reducing the risk of thermal runaway of the battery and greatly improving the safety of the solid-state battery. In addition, during the charging and discharging process of the battery, since In can achieve the intercalation and deintercalation of Li ions by forming an alloy with Li, the incorporation of In can form an electron-ion dual channel between Si particles, thereby enhancing the fast-charging performance of the negative electrode. Moreover, the lithium-indium alloy formed by In and Li has the characteristics of low modulus and high ductility, which can form a flexible buffer layer between silicon particles to effectively absorb the stress generated by volume expansion. Therefore, by controlling the mass percentage of indium in the silicon-based alloy within the above range, it is beneficial to balance the improvement of the safety performance and rate performance of the battery.

[0033] Exemplarily, the mass percentage of the indium in the silicon-based alloy can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, or a range with any two of the above values as the end points.

[0034] In some embodiments, the mass ratio of the silicon, magnesium and indium in the silicon-based alloy is (4-5):(0.5-1.5):(0.5-1.5). Exemplarily, the mass ratio of the magnesium and the indium can be 4:1:1, 4:0.5:1.5, 4:0.5:1, 4:1.5:0.5, 4:1.5:1.5, 5:1:1, 5:0.5:1.5, 5:0.5:1, 5:1.5:0.5 or 5:1.5:1.5, or a range with any two of the above values as the end points. By controlling the amount of the three elements in the silicon-based alloy to be within the above range, the local agglomeration of lithium ions during charging is avoided, and the rate performance and cycle performance of the silicon-based alloy anode material during charging and discharging are synergistically enhanced. At the same time, the growth of lithium dendrites to pierce the sulfide solid electrolyte film is inhibited, and the safety of the solid-state battery is greatly improved. Optionally, the mass ratio of the silicon, magnesium and indium is 4:(0.8-1.2):(0.8-1.2).

[0035] The second aspect of the present application provides a preparation method of the above anode material.

[0036] In some embodiments, the anode material is prepared by a ball milling-annealing method.

[0037] In some embodiments, the preparation method (i.e., the ball milling-annealing method) comprises: mixing silicon powder, magnesium powder, indium powder and a solvent under an inert gas atmosphere to obtain a silicon-based alloy raw material; and ball milling the silicon-based alloy raw material and then performing sintering treatment.

[0038] The present application finds that, compared with conventional alloying methods, the ball milling-annealing method can significantly enhance the electrical conductivity of the material, and inhibit the volume expansion of Si during lithium intercalation, thereby improving the electrochemical stability of the anode material.

[0039] In the present application, the inert gas can be one or more of nitrogen, argon and helium.

[0040] In some embodiments, the solvent comprises one or more of ethanol, ethylene glycol, propanol, acetone, butanone and N,N-dimethylformamide.

[0041] In some embodiments, the silicon powder, the magnesium powder and the indium powder are each independently nanoscale or microscale. Preferably, the silicon powder, the magnesium powder and the indium powder are all microscale, which is advantageous for avoiding agglomeration.

[0042] In some embodiments, the mass percentage of the solvent in the silicon-based alloy raw material is 10wt%-30wt%. Illustratively, the mass percentage of the solvent is 10wt%, 15wt%, 20wt%, 25wt%, or 30wt%, or a numerical range with any two of the above values as endpoints.

[0043] In some embodiments, the ball milling is performed in a forward-reverse alternating mode.

[0044] In some embodiments, the forward-reverse alternating mode includes a procedure of forward rotation for 10-30min, reverse rotation for 10-30min, and interval for 5-10min. Illustratively, the forward rotation time can be 10min, 15min, 20min, 25min, or 30min, or a numerical range with any two of the above values as endpoints; the reverse rotation time can be 10min, 15min, 20min, 25min, or 30min, or a numerical range with any two of the above values as endpoints; and the interval time can be 5min, 6min, 7min, 8min, 9min, or 10min, or a numerical range with any two of the above values as endpoints. The present application has found that the above ball milling mode can promote the deformation of magnesium and indium into ribbon-like objects around the silicon particles during ball milling, thereby helping to improve the electrical conductivity of the material and also inhibiting the volume expansion of Si during lithium intercalation, thereby improving the electrochemical stability of the anode material.

[0045] In some embodiments, the mass ratio of the ball milling beads to the silicon-based alloy raw material is (25-50):1. Illustratively, the mass ratio of the ball milling beads to the silicon-based alloy raw material can be 25:1, 30:1, 35:1, 40:1, 45:1, or 50:1, or a ratio range with any two of the above values as endpoints.

[0046] In some embodiments, the ball milling time is 2h-8h, and the rotation speed is 300rpm-600rpm. Illustratively, the ball milling time can be 2h, 3h, 4h, 5h, 6h, 7h, or 8h, or a numerical range with any two of the above values as endpoints; and the rotation speed can be 300rpm, 350rpm, 400rpm, 450rpm, 500rpm, 550rpm, or 600rpm, or a numerical range with any two of the above values as endpoints.

[0047] In some embodiments, the annealing process comprises: sintering the ball-milled material under an inert gas atmosphere, the sintering temperature being 400-600℃, and the sintering time being 2-4h. Illustratively, the sintering temperature can be 400℃, 450℃, 500℃, 550℃ or 600℃, or a range defined by any two of the above values as endpoints; and the sintering time can be 2h, 3h or 4h, or a range defined by any two of the above values as endpoints.

[0048] In the present application, the ball-milling method can be selected by the skilled person according to the actual situation, for example, the ball-milling can be performed using a ball mill, which is not limited herein.

[0049] In some embodiments, the sintering process is performed at a temperature increasing rate of 3-5℃ / min from room temperature to 400-600℃, and after the sintering is completed, the temperature is decreased at a rate of 5-20℃ / min to room temperature. In the present application, the above-mentioned relatively slow temperature increasing rate can avoid excessive thermal expansion stress during high-temperature sintering and ensure uniform heating of the surface and the internal body phase; and after the material is sintered into a shape, the temperature change has a relatively small effect on the material, and the above-mentioned relatively fast temperature decreasing rate can improve the efficiency.

[0050] Illustratively, the temperature increasing rate of the sintering can be 3℃ / min, 4℃ / min, 5℃ / min, or a range defined by any two of the above values as endpoints; and the temperature decreasing rate of the sintering can be 5℃ / min, 10℃ / min, 15℃ / min or 20℃ / min, or a range defined by any two of the above values as endpoints.

[0051] In some embodiments, the method for preparing the negative electrode material comprises: micron-sized silicon powder, micron-sized magnesium powder, micron-sized indium powder and ethanol are mixed under an inert gas atmosphere to obtain a silicon-based alloy raw material, and the silicon-based alloy raw material is ball-milled; the mass fraction of the ethanol in the silicon-based alloy raw material is 10-30wt%; and the mass ratio of the micron-sized silicon powder, the micron-sized magnesium powder and the micron-sized indium powder is (4-5):(0.5-1.5):(0.5-1.5). During the ball-milling, a forward-reverse alternating mode is adopted; the forward-reverse alternating mode comprises: forward rotation for 10-30min, reverse rotation for 10-30min, and an interval of 5-10min. The ball-milled material is subjected to a sintering process under an inert gas atmosphere; the sintering process is performed at a temperature increasing rate of 3-5℃ / min from room temperature to 400-600℃, and after the sintering is completed, the temperature is decreased at a rate of 5-20℃ / min to room temperature. The sintered material is ground, and the ground material is sieved through a 200-mesh screen.

[0052] When magnesium and indium are introduced into the silicon-based negative electrode material, compared with other alloying methods, the use of the ball milling-annealing process helps to improve the conductivity of the negative electrode material, and can inhibit the volume expansion of silicon during the lithium intercalation process, improve the cycle stability of the negative electrode material, and prolong the battery life.

[0053] The third aspect of the present application provides a negative electrode material prepared using the preparation method of the second aspect.

[0054] The fourth aspect of the present application provides a secondary battery, which comprises a negative electrode sheet, the negative electrode sheet comprising a negative electrode film layer and a current collector, and the negative electrode film layer comprising the negative electrode material described above.

[0055] The secondary battery in the present application can be a solid-state battery, such as a sulfide full solid-state battery.

[0056] The embodiments of the present application are specifically described below in combination with examples and drawings. It can be understood that the following examples are only exemplary to illustrate the present application, and should not be understood as limiting the present application.

[0057] If a specific technique or condition is not specified in the examples, the technique or condition described in the literature in the art or according to the product manual is used. If the manufacturer of the reagent or instrument is not specified, it is a conventional product that can be obtained by purchase.

[0058] Example 1 Preparation of the negative electrode material The present embodiment provides a silicon-magnesium-indium ternary silicon alloy negative electrode material, and a preparation method thereof, which comprises the following steps: Step 1: high-purity Si powder (99.9%), Mg powder (99.9%), In powder (99.9%) and anhydrous ethanol (chromatographically pure) are used as starting materials. The particle size of the Si powder is 1-30 μm, the particle size of the Mg powder is 10-50 μm, and the particle size of the In powder is 1-20 μm.

[0059] In an Ar-filled glove box, 4 g of the above-mentioned Si powder, 1 g of the Mg powder, 1 g of the In powder and 2 g of anhydrous ethanol are respectively loaded into a stainless steel ball milling jar, and 200 g of zirconium dioxide milling beads with a diameter of 1-2 mm are added to the ball milling jar.

[0060] Step Two: Place the sealed stainless steel container in a planetary ball mill (model YXQM-2L) for ball milling. Set the ball mill to alternate forward and reverse operation, using a program of 20 minutes forward rotation, 20 minutes reverse rotation, and an 8-minute interval. The ball mill should grind the raw material for 3 hours at a speed of 600 rpm. To ensure thorough and uniform mixing, after 1 hour of ball milling, scrape off the powder adhering to the container wall in the glove box before continuing ball milling.

[0061] Step 3: The ball-milled material is sintered in an argon atmosphere at a heating rate of 4℃ / min, from room temperature to a sintering temperature of 500℃, for 3 hours. Then, the material is cooled to room temperature at a cooling rate of 10℃ / min. The resulting material is ground into powder and passed through a 200-mesh sieve.

[0062] Testing of negative electrode materials The negative electrode material prepared in Example 1 was subjected to XRD testing, and the spectrum is shown below. Figure 1 As shown. For Figure 1 XRD analysis revealed that the synthesized anode material contained silicon-magnesium alloy (PDF#35-0773) as well as elemental Si and In.

[0063] The surface morphology of the powder sample from Example 1 was observed using SEM-EDS. Before the experiment, the sample was vacuum dried to ensure it was free of agglomerates. The accelerating voltage was set to 3 kV. The SEM-EDS spectra are shown below. Figure 2 SEM images show that the prepared silicon-magnesium-indium ternary silicon alloy anode material has uniform particle size and no obvious agglomeration. EDS spectra show that the elements in the material are uniformly distributed. Further XRD analysis confirms the successful synthesis of the silicon-magnesium-indium ternary alloy.

[0064] Example 2 This embodiment provides a silicon-magnesium-indium ternary silicon alloy anode material, which differs from Embodiment 1 only in that: in the preparation method of the silicon-magnesium-indium ternary silicon alloy anode material, the total mass of Si powder, Mg powder and In powder remains unchanged, and the mass ratio of Si powder, Mg powder and In powder is 4:0.5:1.5.

[0065] Example 3 This embodiment provides a silicon-magnesium-indium ternary silicon alloy anode material, which differs from Embodiment 1 only in that: in the preparation method of the silicon-magnesium-indium ternary silicon alloy anode material, the total mass of Si powder, Mg powder and In powder remains unchanged, and the mass ratio of Si powder, Mg powder and In powder is 4:1.5:0.5.

[0066] Example 4 The embodiment provides a silicon-magnesium-indium ternary silicon alloy negative electrode material, which is different from the embodiment 1 only in that in a preparation method of the silicon-magnesium-indium ternary silicon alloy negative electrode material, the total mass of Si powder, Mg powder and In powder is unchanged, and the mass ratio of the Si powder, the Mg powder and the In powder is 4:1.6:1.6.

[0067] Embodiment 5 The embodiment provides a silicon-magnesium-indium ternary silicon alloy negative electrode material, which is different from the embodiment 1 only in that the preparation method is a melting and pouring method. Specifically, the method comprises the following steps: A graphite crucible is preheated to 300 DEG C, 10g of Mg powder is put into the crucible, and then a layer of RJ-2 type flux is scattered. From room temperature, the temperature is raised to 750 DEG C at a temperature raising rate of 10 DEG C / min and is kept for 30 min, and 40g of Si powder and 10g of In powder are slowly added for many times. Stirring is continuously carried out under the protection of the flux until the solid is completely melted. The graphite crucible containing the alloy liquid is taken out with a crucible clamp, and is quickly poured into a mold preheated to 200 DEG C, and after cooling, the flux and the oxide skin on the surface are removed, and finally the silicon-magnesium-indium ternary silicon alloy is obtained.

[0068] Comparative Example 1 The comparative example provides a silicon-phosphorus-indium ternary silicon alloy negative electrode material, and the preparation method is different from the embodiment 1 only in that the magnesium powder is replaced by an equal amount of phosphorus powder.

[0069] Comparative Example 2 The comparative example provides a silicon-iron-indium ternary silicon alloy negative electrode material, and the preparation method is different from the embodiment 1 only in that the magnesium powder is replaced by an equal amount of iron powder.

[0070] Comparative Example 3 The comparative example provides a silicon-tin-indium ternary silicon alloy negative electrode material, and the preparation method is different from the embodiment 1 only in that the magnesium powder is replaced by an equal amount of tin powder.

[0071] Comparative Example 4 The comparative example provides a silicon-magnesium-yttrium ternary silicon alloy negative electrode material, and the preparation method is different from the embodiment 1 only in that the indium powder is replaced by an equal amount of yttrium powder.

[0072] Comparative Example 5 The comparative example provides a silicon-magnesium binary silicon alloy negative electrode material, and the preparation method is different from the embodiment 1 only in that high-purity Si powder (99.9%), Mg powder (99.9%) and In powder (99.9%) are replaced by an equal amount of high-purity Si powder (99.9%) and Mg powder (99.9%), and the mass ratio of the high-purity Si powder and the Mg powder is 4:1.

[0073] Comparative Example 6 The comparative example provides a silicon-indium binary silicon alloy negative electrode material, and the preparation method is only different from that of example 1 in that the high-purity Si powder (99.9%), Mg powder (99.9%) and In powder (99.9%) are replaced with equal amounts of high-purity Si powder (99.9%) and In powder (99.9%), and the mass ratio of the high-purity Si powder and the In powder is 4:1.

[0074] Examples 2-5 and comparative examples 1-6 provide negative electrode materials, which are different from example 1 in that the raw materials and methods of the negative electrode materials are adjusted according to table 1.

[0075] Table 1

[0076] Preparation of a sulfide all-solid-state lithium ion battery Preparation of a composite positive electrode: 75 mg of NCM811 powder, 22 mg of Li 5.5 PS 4.5 Cl 1.5 The electrolyte powder, 3 mg of VGCF (carbon fiber) powder, was ground in a mortar for 30 min until the above powders were uniformly mixed, and was prepared for use.

[0077] Preparation of a current collector: the positive electrode current collector aluminum foil was punched into a circular sheet with a diameter of 10 mm, and was prepared for use; the negative electrode current collector copper foil was punched into a circular sheet with a diameter of 10 mm, and was prepared for use.

[0078] Assembly of a pressure battery: in an argon-filled glove box, 100 mg of Li 5.5 PS 4.5 Cl 1.5 The electrolyte powder was placed in a pressure battery mold with a diameter of 10 mm, and the electrolyte powder was rotated and flattened by a rotating stainless steel column. The powder was pressed into a sheet on a tablet press in two steps. First, the pressure was 120 MPa, and the pressure was maintained for 2 min. Then, the pressure was increased to 370 MPa, and the pressure was maintained for 2 min. 30 mg of the above composite positive electrode powder was weighed and placed on the surface of the Li 5.5 PS 4.5 Cl 1.5 The electrolyte sheet was placed on the surface of the Li 5.5 PS 4.5 Cl 1.5 The other side of the electrolyte sheet was the negative electrode side, and 7.7 mg of the negative electrode material was placed on the negative electrode side. After assembly, a pressure of 120 MPa was applied to the pressure battery and the pressure was maintained, and a sulfide all-solid-state lithium ion battery was obtained.

[0079] Battery performance test The sulfide full solid-state lithium ion batteries prepared in the examples and comparative examples were tested by using a new Wei battery test system, equipment model: CT-4000, using 0.1C-0.33C-1C-2C-0.1C rate charge-discharge steps, and the discharge capacity of the sulfide full solid-state lithium ion battery was tested. Table 2 is a rate performance comparison table; Table 3 is the cycle number of the discharge capacity decay to 80% of the initial capacity at 0.33C rate.

[0080] Table 2

[0081] According to Table 2, silicon-magnesium-indium, silicon-phosphorus-indium, silicon-iron-indium, silicon-tin-indium, silicon-magnesium-yttrium, silicon-magnesium, and silicon-indium alloys were synthesized by ball milling-annealing process. Under the premise of using the same positive electrode and electrolyte and mold battery preparation process, the test results of SiMgIn alloy and other alloys showed that the silicon-magnesium-indium alloy had better charge and discharge performance. In addition, under the premise of the same mass ratio, silicon-magnesium-indium alloy negative materials were prepared by ball milling-annealing method (Example 1) and melting pouring method (Example 5), respectively. Under the premise of using the same positive electrode and electrolyte and mold battery preparation process, the silicon-magnesium-indium alloy negative material prepared by the ball milling-annealing method had obvious advantages. This is because the silicon-based alloy prepared by the melting pouring method is a dense whole. In the charge and discharge process, the material repeatedly expands and shrinks, and the stress cannot be dispersed, resulting in the breakage and pulverization of the particles themselves, and finally showing relatively poor electrical performance.

[0082] Table 3

[0083] According to Tables 2-3, under the premise of using the same positive electrode and electrolyte and mold battery preparation process, the test results of SiMgIn alloy and other alloys show that the SiMgIn alloy has better charge and discharge performance. At the same time, under the condition of 0.33C charge and discharge cycle, the capacity decay results of the examples and the comparative examples are compared, and the cycle cutoff condition is set to 80% SOH. Compared with Comparative Examples 1-6 and Example 1, the cycle performance of the silicon-magnesium-indium alloy is significantly higher than that of other silicon-based alloys; the reason is that Y can form a YSi2 structure with Si to inhibit the expansion of Si during lithium intercalation, but it cannot provide dynamic buffering like lithium-indium alloy, and the effect of relieving volume expansion is limited, which still causes the silicon particles to gradually pulverize during repeated charge and discharge, thereby affecting the cycle performance of the battery. Metal Fe is a good electronic conductor that can effectively improve the electronic conductivity of the Si negative electrode. At the same time, Fe has a certain mechanical strength, which can effectively constrain the volume expansion of Si. However, Fe has no activity to Li, and the incorporation of Fe will reduce the specific capacity of the Si negative electrode. Metal Sn forms a conductive network in Si, which can inhibit the volume expansion of Si up to 300% and improve the cycle performance. However, the 260% volume expansion of Sn itself still limits the performance of the Si negative electrode. Doping P in the Si negative electrode material can enhance the structural stability of the silicon negative electrode and relieve the expansion of the Si negative electrode during lithium intercalation. However, in terms of process, uneven P doping will lead to inconsistent performance within the silicon material, resulting in poor battery consistency. If P is uniformly doped by processes such as vapor deposition, the cost of commercial application is increased; in terms of materials, the introduction of non-conductive P cannot improve the electronic conductivity of Si to enhance the rate performance, nor can it form an alloy with Li like Mg to achieve the effect of lithium storage. P, which does not store lithium, reduces the mass specific capacity of the Si negative electrode.

[0084] At the same time, the ductility of In promotes the lateral extension of lithium dendrites rather than the vertical penetration of the electrolyte, which can inhibit the growth of lithium dendrites to pierce the sulfide solid electrolyte membrane and reduce the risk of battery thermal runaway, so the intrinsic safety of the silicon-magnesium-indium alloy battery is higher than that of other silicon-based alloys.

[0085] The above is only an embodiment of the present application and is not intended to limit the protection scope of the present application. Any modifications, equivalent replacements and improvements made within the spirit and scope of the present application are included in the protection scope of the present application.

Claims

1. A negative electrode material, characterized in that, The negative electrode material is a silicon-based alloy, which includes silicon, magnesium, and indium; in the silicon-based alloy, the mass ratio of magnesium to indium is (0.5~1.5):(0.5~1.5); in the silicon-based alloy, the mass percentage of magnesium is 8%~25%; and the mass percentage of indium is 8%~25%.

2. The negative electrode material according to claim 1, characterized in that, In the silicon-based alloy, the mass ratio of silicon, magnesium, and indium is (4~5):(0.5~1.5):(0.5~1.5).

3. The method for preparing the negative electrode material according to claim 1 or 2, characterized in that, include: Silicon powder, magnesium powder, indium powder and solvent are mixed in an inert gas atmosphere to obtain silicon-based alloy raw material; the silicon-based alloy raw material is ball-milled and then sintered.

4. The method for preparing the negative electrode material according to claim 3, characterized in that, The solvent includes one or more of ethanol, ethylene glycol, propanol, acetone, butanone, and N,N-dimethylformamide.

5. The method for preparing the negative electrode material according to claim 4, characterized in that, In the silicon-based alloy raw material, the solvent accounts for 10wt% to 30wt% by mass.

6. The method for preparing the negative electrode material according to claim 3, characterized in that, During the ball milling process, an alternating forward and reverse rotation mode is adopted; the alternating forward and reverse rotation mode includes a program of forward rotation for 10 min to 30 min, reverse rotation for 10 min to 30 min, and an interval of 5 min to 10 min.

7. The method for preparing the negative electrode material according to claim 3, characterized in that, During the ball milling process, the mass ratio of the milling balls to the silicon-based alloy raw material is (25~50):

1.

8. The method for preparing the negative electrode material according to claim 3, characterized in that, During the ball milling process, the milling time is 2 hours to 8 hours, and the milling speed is 300 rpm to 600 rpm.

9. The method for preparing the negative electrode material according to claim 3, characterized in that, The sintering process includes: sintering the ball-milled material in an inert gas atmosphere at a sintering temperature of 400℃~600℃ for 2h~4h.

10. The method for preparing the negative electrode material according to claim 9, characterized in that, The sintering process involves raising the temperature from room temperature to 400℃~600℃ at a heating rate of 3℃ / min~5℃ / min, and then lowering the temperature to room temperature at a cooling rate of 5℃ / min~20℃ / min after sintering.

11. The method for preparing the negative electrode material according to claim 3, characterized in that, include: In an inert gas atmosphere, micron-sized silicon powder, micron-sized magnesium powder, micron-sized indium powder, and ethanol are mixed to obtain a silicon-based alloy raw material. The silicon-based alloy raw material is then ball-milled. The mass percentage of ethanol in the silicon-based alloy raw material is 10wt%~30wt%. The mass ratio of the micron-sized silicon powder, the micron-sized magnesium powder, and the micron-sized indium powder is (4~5):(0.5~1.5):(0.5~1.5). During the ball milling process, an alternating forward and reverse rotation mode is adopted. The alternating forward and reverse rotation mode includes a program of forward rotation for 10min~30min, reverse rotation for 10min~30min, and an interval of 5min~10min. The ball-milled material is then sintered in an inert gas atmosphere. The sintering process involves heating from room temperature to 400℃~600℃ at a heating rate of 3℃ / min~5℃ / min, and cooling down to room temperature at a cooling rate of 5℃ / min~20℃ / min after sintering. The sintered material is then crushed and sieved through a sieve of 200 mesh or finer.

12. A secondary battery, characterized in that, The secondary battery includes a negative electrode sheet, which includes a negative electrode film and a current collector. The negative electrode film includes the negative electrode material according to claim 1 or 2 or the negative electrode material prepared by the preparation method according to any one of claims 3 to 11.

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