A pre-lithiation method for preparing lithium alloy electrodes, applications, and sulfide all-solid-state batteries

Abstract

The present invention belongs to the field of new energy battery technology and provides a pre-lithiation method, application and sulfide all-solid-state battery for preparing lithium alloy electrodes. The pre-lithiation method comprises the following steps: S1, in an inert gas environment, uniformly mixing lithium powder with one or more metal element powders selected from Sn powder, Si powder, Se powder, Ag powder, Zn powder and Mg powder to obtain a mixed powder; S2, spreading the mixed powder on the surface of a current collector, heating the current collector to 160-200°C, rolling the current collector multiple times, and cooling it to room temperature to obtain a lithium alloy electrode. The electrode has a loose, porous structure inside, which can effectively alleviate the volume expansion of the electrode, facilitate uniform transmission of lithium ions, inhibit the irregular growth of lithium dendrites, and improve battery capacity and cycle stability.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy batteries, and in particular to a pre-lithiation method for preparing lithium alloy electrodes, applications thereof, and a sulfide all-solid-state battery. Background Art

[0002] With the continuous growth of global energy demand and the improvement of environmental awareness, battery technology, especially solid-state battery technology, has become a research hotspot. Solid-state batteries can effectively improve the safety, energy density and service life of batteries by using solid electrolytes instead of traditional liquid electrolytes. Therefore, solid-state batteries, especially solid-state batteries based on sulfide electrolytes, have become an ideal choice for the next generation of battery technology due to their high ionic conductivity and wide electrochemical stability window. However, although sulfide solid-state batteries have excellent performance in theory, they still face a series of technical challenges in practical applications, especially in terms of the stability and conductivity of the electrode-electrolyte interface.

[0003] Among them, lithium metal anode materials are widely considered to be the most promising anode materials for solid-state batteries due to their high energy density and lightweight properties. However, the volume expansion and growth of lithium dendrites during the cycle of lithium metal anodes often lead to shortened cycle life, reduced efficiency, and even safety hazards. Therefore, how to improve the stability of lithium metal anodes and reduce the growth of lithium dendrites has become a key issue in solid-state battery technology. To address the above issues, people currently use a lithium alloy substitution method to optimize solid-state lithium metal batteries.

[0004] Lithium alloys, as negative electrode materials, have become an important research direction in the field of solid-state batteries in recent years due to their lower risk of dendrite growth and better cycling stability compared to pure lithium metal. Although lithium alloy negative electrodes have good performance, they still face certain challenges in interfacial reactions with sulfide electrolytes. In particular, during the initial charge and discharge process of the battery, the lithium alloy negative electrode may be affected by uneven lithium deposition, resulting in performance degradation.

[0005] CN 116093242 A discloses a lithium-indium alloy electrode, its preparation method, and application. By adjusting the lithium content in the lithium-indium alloy, the production efficiency and cycle stability of the battery are effectively improved. However, after the metal sheet is pressed, the alloy morphology cannot be effectively controlled.

[0006] CN202410104830.2 discloses a method for preparing a lithium metal negative electrode with a pre-lithiation interface layer of a multi-element alloy. It uses a multi-element alloy composite material coated with carbon nanotubes to induce the formation of a 3D conductive network skeleton, effectively inhibiting the generation of lithium dendrites and "dead lithium" and improving the cycle stability of the battery; however, during the preparation process, the alloy particles need to be added to a solvent for dissolution, which will cause partial reactions and reduce the capacity of the final alloy negative electrode.

[0007] CN 116072824 A proposes a method for preparing a Li-M alloy negative electrode for a sulfide solid-state battery. This method utilizes high-energy ball milling to prepare a lithium alloy negative electrode material with high specific capacity and energy density. However, the preparation process requires the addition of solvents and binders. Solvents can cause Li to deteriorate, affecting the alloying process between Li and metals and reducing the alloy capacity. Binders themselves have low electrical conductivity, and when introduced into the alloy negative electrode, they increase its resistance, raising the impedance of the entire battery and causing a decrease in cycle stability. Furthermore, high-energy ball milling has high kinetic energy, which causes a large amount of Li powder to adhere to the inner wall of the ball mill and the milling beads during mixing, wasting a large amount of material and resulting in incomplete alloying of Li and metal materials. The present invention eliminates the effects of solvents and binders, and eddy current mixing, compared to high-energy ball milling, has lower external kinetic energy, eliminating material waste and allowing Li powder to be fully mixed with other metal powders.

[0008] Therefore, studying an effective pre-lithiation method for metal materials, which can optimize the initial lithiation process of lithium alloy negative electrodes and enhance their interfacial contact with sulfide electrolytes, has become an effective means to solve problems in solid-state battery technology. Summary of the Invention

[0009] To address the shortcomings of the prior art, the present invention aims to provide a pre-lithiation method for preparing lithium alloy electrodes, its application, and a sulfide all-solid-state battery. This method uses lithium powder and elemental metal powder as raw materials, directly mixing the metal powders and pressing them to produce a lithium alloy negative electrode. This method allows for more convenient adjustment of the ratio of lithium powder to other metal powders, thereby producing different alloy types.

[0010] During the preparation process, the lithium powder and the metal element powder are effectively mixed by high-speed and long-term oscillation in a vortex mixer. The mixed powder is then pressed at high temperature to promote full lithiation of the metal element powder and make it tightly adhere to the copper current collector to serve as the lithium alloy negative electrode of the sulfide solid-state battery.

[0011] Furthermore, the present invention eliminates the influence of solvents during the electrode preparation process, thereby ensuring battery stability without reducing battery capacity.

[0012] The purpose of the present invention can be achieved by the following solutions:

[0013] <First Aspect>

[0014] A pre-lithiation method for preparing a lithium alloy electrode comprises the following steps:

[0015] S1. Under an inert gas environment, lithium powder is uniformly mixed with one or more metal element powders selected from Sn powder, Si powder, Se powder, Ag powder, Zn powder, and Mg powder to obtain a mixed powder; the mixing is thoroughly oscillated using a vortex mixer;

[0016] S2. Spread the mixed powder on the surface of a current collector, heat the current collector to 160-200° C., roll-press the current collector multiple times, and cool it to room temperature to obtain a lithium alloy electrode.

[0017] In S2, the mixed powder is shaken through a mesh to perform three-dimensional spatial discretization processing to break up the agglomerates, and is spread flat on the surface of the current collector. The current collector is then heated to 160-200°C to melt the surface of the low-melting-point component. Under the capillary action of the molten liquid phase, the current collector is continuously rolled multiple times to achieve interlayer densification to a theoretical density of >95%. Finally, it is cooled to room temperature and the solid-state phase change volume shrinkage effect is used to dynamically compensate for the micro-cracks caused by thermal stress to obtain a pre-lithiation lithium alloy electrode.

[0018] In S1, the mass ratio of lithium powder to metal powder is 0.8-1.2:1. Excessive lithium powder may cause irregular growth of lithium dendrites and severe side reactions at the interface between the negative electrode and the electrolyte, resulting in a short circuit. A small amount of lithium powder may lead to low negative electrode conductivity, preventing sufficient lithium ion release from the negative electrode, reducing battery discharge efficiency and hindering stable long-term battery cycling.

[0019] The lithium powder includes one or more of nano-scale lithium powder and micron-scale lithium powder.

[0020] Preferably, the lithium powder comprises nano-scale lithium powder, and the particle size of the lithium powder is 80-100 nm.

[0021] The particle size of the metal element powder is 40-100 nm.

[0022] In S1, the frequency of the vortex mixer is 800-1200 rpm, and the oscillation time is 2-6 hours;

[0023] And / or, in S2, the roller pressing pressure is 300 MPa to 400 MPa, the temperature is 180 to 200° C., and the rotation speed is 50 to 80 rpm.

[0024] In some embodiments, the inert gas is argon.

[0025] <Second Aspect>

[0026] The present invention also provides a lithium alloy electrode prepared by the above-mentioned pre-lithiation method.

[0027] <Third Aspect>

[0028] The present invention also provides a negative electrode application of the lithium alloy electrode as described above in a sulfide all-solid-state battery.

[0029] <Fourth Aspect>

[0030] The present invention also provides a sulfide all-solid-state battery, comprising a lithium alloy electrode, a sulfide solid electrolyte, and a ternary material composite positive electrode sheet arranged in sequence.

[0031] The sulfide solid electrolyte is selected from Li2SP2S5, Li7P3S 11 、Li6PS5Cl、Li 5.5 PS 4.5 Cl 1.5 、Li6PS5Br、Li6PS5I、Li 11 Si2PS 12 、Li 9.54 Si 1.74 P 1.44 S 11.7 Cl, Li 10 SnP2S 12 、Li 10 GeP2S 12 One or more of .

[0032] And / or, the ternary material composite positive electrode sheet includes a positive electrode active material, a sulfide electrolyte, and a conductive agent;

[0033] Alternatively, the positive electrode active material may be selected from one or more of NCM111, NCM424, NCM523, NCM622, and NCM811. The positive electrode, electrolyte, and negative electrode are pressed together in this order to form an all-solid-state battery. This battery effectively improves safety, interfacial resistance, capacity, cyclability, and rate capabilities.

[0034] The traditional method is to directly press lithium sheets and metal single-substance sheets to pre-lithiate the metal material to form a lithium alloy electrode. However, the electrode prepared by this method will cause irreversible cracks to appear inside the electrode due to continuous changes in volume during the long cycle of the battery. Subsequently, lithium ions will concentrate at the cracks, thereby forming irregular lithium dendrites, and eventually causing the battery to short-circuit. The present invention uses a vortex mixer to fully mix lithium powder and metal powder, and then presses at high temperature to obtain a lithium alloy electrode. The interior of the electrode has a loose, porous structure, which can effectively alleviate the volume expansion of the electrode, facilitate the uniform transmission of lithium ions, inhibit the irregular growth of lithium dendrites, and improve the battery capacity and cycle stability.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. The method provided by the present invention is to use a vortex mixer to mix lithium powder and metal element powder, shake the mixed powder through a mesh screen to perform three-dimensional spatial discretization processing to break up the agglomerates, and spread it flat on the surface of the current collector. Then, the current collector is heated to 160-200°C to melt the surface of the low-melting point component. Under the capillary action generated by the molten liquid phase, the current collector is continuously rolled multiple times to achieve interlayer densification to a theoretical density of more than 95%. Finally, it is cooled to room temperature and the micro-cracks caused by thermal stress are dynamically compensated by the solid-state phase change volume shrinkage effect to obtain a pre-lithiated lithium alloy electrode.

[0037] 2. The mixed powder is composed of lithium powder and metal powder. The lithium powder is 80~100nm, and the metal powder particle size is 50~70nm. The lithium alloy electrode formed by high-temperature pressing has a loose and porous structure. Unlike the alloy electrode obtained by direct pressing of metal sheets, which has a dense and solid structure, this structure cannot effectively alleviate the volume expansion of the electrode. The space reserved inside the porous structure can serve as a buffer zone for volume expansion. At the same time, lithium ions can move freely in these spaces, improving the electrode conductivity, which is conducive to improving the capacity and long-cycle stability of solid-state batteries. In addition, the lithium alloy negative electrode has good compatibility with the sulfide electrolyte interface, forming a stable SEI layer, reducing the internal resistance of the battery, and improving the battery cycle life.

[0038] 3. The present invention uses high-temperature roller pressing technology to fully alloy lithium powder and metal element powder, thereby preventing the lithium metal from losing contact with the electrolyte when the volume expands significantly during the battery cycle (volume expansion during lithium insertion / delithiation), thereby increasing the battery impedance and reducing the stability.

[0039] 4. The protective layer of the present invention has excellent initial charge and discharge efficiency, stability with sulfide electrolytes, and low volume change, and can cope with lithium metal sheets of different sizes; at the same time, the preparation process is simple and fast and can be prepared on a large scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0041] Figure 1 This is a SEM image of the pre-lithiated lithium alloy electrode prepared in Example 1;

[0042] Figure 2 This is the SEM image of the Li-Sn alloy prepared by ball milling in Comparative Example 3. DETAILED DESCRIPTION

[0043] The present invention will be described in detail below with reference to the examples. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that those skilled in the art may make several adjustments and improvements without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0044] In the following embodiments and comparative examples:

[0045] The lithium powder and metal powder used in the present embodiment and the comparative example are all simple substances.

[0046] Example 1

[0047] In an argon-filled glove box, approximately 0.5 g of Li powder (50 nm) and 0.5 g of Sn powder (50 nm) were mixed and placed in equal amounts in two 50 mL black-capped glass bottles. These bottles were then placed symmetrically in a vortex mixer and shaken at high speed for 4 hours at 1000 rpm to obtain a mixed powder. Weigh 500 mg of the above mixed powder and spread it flat (use a mesh screen to continuously shake, use mechanical shaking to achieve three-dimensional spatial discretization of the powder, break the agglomerates, and disperse the powder on the current collector) on the copper current collector. When the stainless steel is heated to 180°C (the low-melting-point component produces surface melting, and the molten liquid phase forms a capillary action to promote the rearrangement of the powder particles), start the roller press at a speed of 50 rpm (matching the rheological properties of the melt), and roll it repeatedly (rolling temperature 180°C, pressure 300 MPa) to achieve interlayer densification (theoretical density > 95%). Then cool it to room temperature, use the solid-state phase change volume shrinkage effect (Li alloy cooling shrinkage rate is about 2-3%) to dynamically compensate for the micro-cracks caused by thermal stress and inhibit dendrite growth to obtain a pre-lithiated lithium alloy electrode. The SEM image is as follows Figure 1 .

[0048] 15 mg of composite cathode (70% NCM811-29% Li6PS5Cl-1% VGCF) (all weight ratios) was uniformly pressed onto the surface (0.7 mm) of 100 mg of Li6PS5Cl electrolyte at a pressure of 300 MPa. A lithium alloy electrode was placed on the other side of the electrolyte and maintained at a pressure of 50 MPa for 15-20 minutes to ensure close contact between the cathode and electrolyte.

[0049] The composite cathode / sulfide electrolyte / lithium alloy electrode is assembled in a pressure battery to obtain a sulfide all-solid-state battery.

[0050] Example 2

[0051] The difference between this embodiment and embodiment 1 is that Sn powder is replaced by Si powder.

[0052] The specific method is: in a glove box also filled with argon, prepare a sulfide all-solid-state battery according to the method in Example 1.

[0053] Example 3

[0054] The difference between this embodiment and embodiment 1 is that Sn powder is replaced by Ag powder.

[0055] The specific method is: in a glove box also filled with argon, prepare a sulfide all-solid-state battery according to the method in Example 1.

[0056] Example 4

[0057] The difference between this embodiment and embodiment 1 is that Sn powder is replaced by Mg powder.

[0058] The specific method is: in a glove box also filled with argon, prepare a sulfide all-solid-state battery according to the method in Example 1.

[0059] Example 5

[0060] The preparation method of this embodiment is basically the same as that of Example 1, except that the oscillation time is replaced from 4 h to 2 h, the oscillation speed is replaced from 1000 rpm to 800 rpm, the high-temperature roller pressing temperature is replaced from 180°C to 190°C, and the holding time remains unchanged to prepare a sulfide all-solid-state battery.

[0061] Example 6

[0062] The preparation method of this embodiment is basically the same as that of Example 1, except that the oscillation time is replaced from 4 h to 6 h, the oscillation speed is replaced from 1000 rpm to 1200 rpm, the high-temperature roller pressing temperature is replaced from 180°C to 200°C, and the holding time remains unchanged to prepare a sulfide all-solid-state battery.

[0063] Example 7

[0064] The preparation method of this embodiment is basically the same as that of Example 1, except that the pressure holding time is replaced from 15 min to 20 min to prepare a sulfide all-solid-state battery.

[0065] Comparative Example 1

[0066] The preparation method of this comparative example is basically the same as that of Example 1, except that the oscillation time is replaced with 30 minutes to prepare a sulfide all-solid-state battery.

[0067] Comparative Example 2

[0068] The preparation method of this comparative example is basically the same as that of Example 1, except that the oscillation speed is replaced with 100 rpm to prepare a sulfide all-solid-state battery.

[0069] Comparative Example 3

[0070] The preparation method of this comparative example is basically the same as that of Example 1, except that eddy current mixing is replaced by ball milling to prepare the sulfide all-solid-state battery.

[0071] Comparative Example 4

[0072] The preparation method of this comparative example is basically the same as that of Example 1, except that the high-temperature pressing temperature is replaced with room temperature to prepare a sulfide all-solid-state battery.

[0073] Comparative Example 5

[0074] The preparation method of this comparative example is basically the same as that of Example 1, except that Li powder and Sn powder are replaced by Li sheets and Sn sheets, which are then directly pressed.

[0075] Comparative Example 6

[0076] The preparation method of this comparative example is basically the same as that of Example 1, except that Sn powder is replaced with Ge powder to prepare a sulfide all-solid-state battery.

[0077] Comparative Example 7

[0078] The preparation method of this comparative example is basically the same as that of Example 1, except that the particle size of the Sn powder is 50 microns to prepare a sulfide all-solid-state battery.

[0079] Performance Testing

[0080] First efficiency: The all-solid-state battery was tested using the Xinwei battery testing system (model: CT-4000). A 0.1C / 0.1C charge and discharge cycle was used to test the first charge and discharge capacity of the solid-state lithium battery. First efficiency (%) = first discharge capacity / first charge capacity × 100%.

[0081] Full battery cycling stability: All-solid-state batteries were tested using a Xinwei battery testing system (model: CT-4000) using a 0.5C / 0.5C charge / discharge cycle. Capacity retention after cycling was measured. Capacity retention (%) = 100-cycle discharge capacity / initial discharge capacity × 100%. Table 1 shows the performance test results for the Examples and Comparative Examples:

[0082] Table 1

[0083]

[0084] The test results in Table 1 show that the sulfide all-solid-state batteries of Examples 1-7 exhibit high initial charge-discharge specific capacity and efficiency, as well as good cycling stability at high currents. The lithium alloy anode provides the battery with high capacity while stabilizing the anode-electrolyte interface and reducing electrolyte degradation. The lithium alloy anode is composed of powder, forming a loose, porous structure that helps mitigate volume expansion and enhance the battery's cycle life.

[0085] In Comparative Examples 1 and 2, the oscillation time is insufficient and the frequency is too slow, so that the lithium powder and the metal powder cannot be fully mixed, resulting in lithium agglomeration. During the battery charging and discharging process, lithium dendrites grow, causing a significant decrease in battery capacity and a short circuit.

[0086] In Comparative Example 3, the powders were mixed by ball milling, which resulted in a large amount of lithium powder agglomerating due to the huge kinetic energy impact and could not be fully mixed with other metal powders. Figure 2 , which makes the prepared electrode unable to effectively suppress lithium dendrites, is not conducive to battery cycling and causes battery short circuit.

[0087] In Comparative Example 4, the rolling temperature is replaced with room temperature, which prevents the lithium powder from effectively forming an alloy with other metal powders. The electrodes are simply lithium and other metals. This not only makes it easy for the negative electrode and the electrolyte to undergo side reactions, resulting in a decrease in the initial charge and discharge efficiency of the battery, but also the volume expansion problem is not solved, resulting in a decrease in cycle stability and a low capacity retention rate.

[0088] In Comparative Example 5, the powder is replaced with metal sheets. Although the initial charge and discharge capacity and efficiency are close to those of the embodiment, due to the tight and solid structure inside the electrode, the volume continues to change as the battery cycles, and irreversible cracks are generated inside. These cracks will reduce the lithium ion transmission rate and reduce the escape of lithium ions, resulting in a decrease in the long-cycle capacity retention rate.

[0089] The lithium-germanium alloy used in Comparative Example 6 has relatively low mechanical strength. Under high pressure, the electrode is severely deformed and cracks appear, which promotes irregular transmission of lithium ions, accelerates the growth of lithium dendrites, and reduces the battery capacity and stability.

[0090] The micron-sized metal powder used in Comparative Example 7 is not conducive to forming a porous structure with lithium powder, and the resulting electrode cannot fully suppress volume expansion, resulting in reduced battery cycle stability.

[0091] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various variations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A pre-lithiation method for preparing a lithium alloy electrode, characterized in that: The following steps are involved: S1. Under an inert gas environment, lithium powder is uniformly mixed with one or more metal element powders selected from Sn powder, Si powder, Se powder, Ag powder, Zn powder, and Mg powder to obtain a mixed powder; the mixing is thoroughly oscillated using a vortex mixer; In S1, the vortex mixer frequency is 800-1200 rpm, and the oscillation time is 2-6 hours; the lithium powder includes nano-scale lithium powder; the particle size of the lithium powder is 80-100 nm; the particle size of the metal element powder is 40-100 nm; S2. Spread the mixed powder on the surface of a current collector, heat the current collector to 160-200° C., roll-press the current collector multiple times, and cool it to room temperature to obtain a lithium alloy electrode.

2. The pre-lithiation method according to claim 1, wherein In S1, the mass ratio of the lithium powder to the metal element powder is 0.8-1.2:

1.

3. The pre-lithiation method according to claim 1, wherein And / or, in S2, the roller pressing pressure is 300 MPa to 400 MPa, the temperature is 180 to 200° C., and the rotation speed is 50 to 80 rpm.

4. A lithium alloy electrode prepared using the pre-lithiation method according to any one of claims 1 to 3.

5. Use of the lithium alloy electrode according to claim 4 as a negative electrode in a sulfide all-solid-state battery.

6. A sulfide all-solid-state battery, characterized in that: It comprises a lithium alloy electrode, a sulfide solid electrolyte and a ternary material composite positive electrode sheet arranged in sequence; the lithium alloy electrode is prepared by the pre-lithiation method according to any one of claims 1 to 3.

7. The sulfide all-solid-state battery according to claim 6, characterized in that: The sulfide solid electrolyte is selected from Li2SP2S5, Li7P3S 11 、Li6PS5Cl、Li 5.5 PS 4.5 Cl 1.5 、Li6PS5Br、Li 11 Si2PS 12 、Li 10 P2S 12 One or more of; And / or, the ternary material composite positive electrode sheet comprises a positive electrode active material, a sulfide electrolyte and a conductive agent; And / or, the positive electrode active material is selected from one or more of NCM111, NCM424, NCM523, NCM622, and NCM811.

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