All-solid-state composite positive plate as well as cold sintering preparation method and application thereof

Abstract

The invention provides an all-solid-state composite positive plate and a cold sintering preparation method and application thereof.According to the all-solid-state composite positive plate, a positive electrode material and a solid electrolyte are mixed, and a mixed material is obtained; and sintering the mixed material under the conditions that the pressure is 200-250 MPa and the temperature is 200-250 DEG C, so as to obtain the composite material. According to the preparation method, a low-temperature and low-pressure cold sintering process is adopted, efficient densification of the all-solid-state composite positive plate is achieved, the compactness of the all-solid-state composite positive plate can be effectively improved, and the structural stability and the cycle performance of the all-solid-state composite positive plate can also be improved.

Description

Technical Field

[0001] The present application relates to the technical field of battery materials, and particularly relates to an all-solid composite positive electrode sheet, a cold sintering preparation method thereof, and an application thereof. Background Art

[0002] With the increasing demand for high energy density and high safety batteries in new energy vehicles and energy storage devices, solid-state batteries have become a current research hotspot due to their superior stability and safety. Compared with traditional liquid electrolyte batteries, all-solid-state batteries have become the core development direction of batteries due to their intrinsically non-flammable characteristics and wide electrochemical windows. In the design of solid-state batteries, an all-solid composite positive electrode sheet is composed of a positive electrode material and a solid electrolyte, and a synergistic conduction system of an electron conductive network and an ion transport channel is constructed. Among them, the densification degree of the composite positive electrode directly determines the utilization rate of active substances and the interfacial charge transfer efficiency.

[0003] However, the solid-solid interface contact defects of the all-solid composite positive electrode pose multiple challenges to its densification process: due to the differences in surface roughness and mechanical modulus mismatch between the rigid positive electrode active particles and the solid electrolyte, micron-scale pores (porosity > 15%) are formed during cold pressing or sintering, resulting in discontinuous fracture of the ion transport path; at the same time, the stress concentration effect caused by the volume expansion (ΔV≥4%) of the positive electrode material during charge and discharge further exacerbates the interfacial peeling and significantly increases the interfacial impedance. Summary of the Invention

[0004] In view of this, in order to solve at least one of the above technical problems, the present application provides a cold sintering preparation method for an all-solid composite positive electrode sheet.

[0005] In addition, the present application also provides an all-solid composite positive electrode sheet prepared by the cold sintering preparation method of the foregoing all-solid composite positive electrode sheet, a preparation method for an all-solid battery, and an all-solid battery obtained by this preparation method.

[0006] The embodiment of the present application provides a cold sintering preparation method for an all-solid composite positive electrode sheet, and the preparation method includes: Mixing a positive electrode material and a solid electrolyte to obtain a mixed material; and Sintering the mixed material under a pressure of 200 MPa to 250 MPa and a temperature condition of 200 °C to 250 °C to obtain the all-solid composite positive electrode sheet.

[0007] In some possible embodiments, the sintering time is 30 s to 60 s.

[0008] In some possible embodiments, the mass ratio of the positive electrode material to the solid electrolyte in the mixed material is (1 to 5):1.

[0009] In some possible embodiments, the positive electrode material is a layered positive electrode material.

[0010] In some possible embodiments, the layered positive electrode material includes at least one of lithium cobaltate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, and lithium-rich manganese oxide.

[0011] In some possible embodiments, the solid-state electrolyte includes at least one of a halide solid-state electrolyte and a sulfide solid-state electrolyte.

[0012] In some possible embodiments, the halide solid-state electrolyte includes at least one of a chloride solid-state electrolyte and a fluoride solid-state electrolyte. Among them, the chloride solid-state electrolyte includes at least one of lithium indium chloride, lithium yttrium chloride, and lithium scandium chloride, and the fluoride solid-state electrolyte includes at least one of lithium yttrium chloro-fluoride, lithium scandium fluoride, and lithium gallium fluoride; The sulfide solid-state electrolyte includes at least one of lithium phosphorus sulfide and lithium germanium phosphorus sulfide.

[0013] The embodiment of the present application also provides a fully solid-state composite positive electrode sheet, which is prepared by the cold sintering preparation method of the fully solid-state composite positive electrode sheet described above.

[0014] The embodiment of the present application also provides a preparation method of a fully solid-state battery, including: mixing a positive electrode material and a solid-state electrolyte to obtain a mixed material; under a temperature condition of 200°C to 250°C, pressing the mixed material onto a solid-state electrolyte separator at a pressure of 200 MPa to 250 MPa to form a fully solid-state composite positive electrode sheet on one side of the solid-state electrolyte separator; and assembling a negative electrode sheet on the side of the solid-state electrolyte separator away from the fully solid-state composite positive electrode sheet to obtain the fully solid-state battery.

[0015] The embodiment of the present application also provides a fully solid-state battery, which is prepared by the preparation method of the fully solid-state battery described above.

[0016] Compared with the prior art, the all-solid composite cathode sheet provided by the embodiments of the present application realizes the high-efficiency densification of the composite cathode sheet for all-solid-state batteries by adopting a cold sintering process at low temperature and low pressure, cold sintering the cathode material and the solid electrolyte at a low pressure of 200 MPa to 250 MPa and a low temperature of 200 °C to 250 °C. This preparation method can not only effectively improve the densification of the all-solid composite cathode sheet, but also reduce the risks of problems such as cracking and interfacial side reactions of the all-solid composite cathode sheet due to high pressure and high temperature, thereby improving the stability and rate performance of the all-solid-state battery. In addition, during the low-pressure cold sintering process, certain internal stresses are formed in the all-solid composite cathode sheet, which can effectively relieve the volume stress generated during the charge and discharge process of the all-solid composite cathode sheet and effectively improve the cycling performance of the all-solid composite cathode sheet. This innovative process provides a new solution for the preparation of all-solid composite cathode sheets and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a process flow chart of a cold sintering preparation method for an all-solid composite cathode sheet provided by an embodiment of the present application.

[0018] Figure 2 It is a SEM comparison diagram of all-solid composite cathode sheets in Embodiment 2 and Comparative Example 2 of the present application, where Figure 2 a is the SEM diagram of the all-solid composite cathode sheet in Comparative Example 2, Figure 2 b is the SEM diagram of the all-solid composite cathode sheet in Embodiment 2.

[0019] Figure 3 It is an XRD comparison diagram of the cathode materials in the all-solid composite cathode sheets of Embodiment 2 and Comparative Example 2 of the present application.

[0020] Figure 4 It is a long-cycle performance comparison diagram of all-solid-state batteries in Embodiment 2 and Comparative Example 2 of the present application.

[0021] Figure 5 It is a rate performance comparison diagram of all-solid-state batteries in Embodiment 2 and Comparative Example 2 of the present application.

[0022] Figure 6 It is a long-cycle performance diagram of the all-solid-state battery prepared from the all-solid composite cathode sheet in Embodiment 3 of the present application.

[0023] Figure 7 It is a rate performance comparison diagram of all-solid-state batteries prepared from all-solid composite cathode sheets in Embodiment 3 and Comparative Example 3 of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] The following will clearly and completely describe the technical solutions in the embodiments of the present application in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments.

[0025] Please refer to Figure 1 , the embodiments of the present application provide a cold sintering preparation method for an all-solid composite cathode sheet, and the preparation method includes: Step S101, mixing a cathode material and a solid electrolyte to obtain a mixed material.

[0026] In some embodiments, the mass ratio of the cathode material to the solid electrolyte in the mixed material can be (1-7):1. By adjusting the mass ratio of the cathode material to the solid electrolyte, the conductivity and ion conduction efficiency of the all-solid composite cathode sheet are optimized, and the energy density is increased. The mass ratio of the two can exemplarily be 1:1, 1.5:1, 1.7:1, 2:1, 2.3:1, 2.5:1, 3:1, 3.5:1, 3.7:1, 4:1, 4.2:1, 4.5:1, 4.7:1, 5:1, 6:1, 7:1 or any value within the range composed of any two of the above values. Further, it can be (1-5):1.

[0027] In some embodiments, the cathode material can be a layered cathode material, which can effectively increase the intercalation space of lithium ions, thereby improving the energy density of the all-solid composite cathode sheet. At the same time, the layered structure provides a good electron conduction channel, which helps to improve the rate performance of the all-solid composite cathode sheet.

[0028] Furthermore, the layered cathode material can include at least one of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, and lithium-rich manganese oxide, etc. The above-mentioned layered cathode materials have advantages such as high energy density, excellent cycle performance, and high stability, and can be applied to high-performance batteries.

[0029] In some embodiments, the solid electrolyte can include at least one of halide solid electrolytes and sulfide solid electrolytes, etc. The above-mentioned solid electrolytes have excellent ion conductivity and chemical stability, and compounding with the cathode material can effectively improve the ion conductivity and safety of the all-solid composite cathode sheet.

[0030] In some embodiments, the halide solid electrolyte can include at least one of chloride solid electrolytes and fluoride solid electrolytes. Among them, the chloride solid electrolyte includes at least one of lithium indium chloride, lithium yttrium chloride, and lithium scandium chloride, etc., and the fluoride solid electrolyte includes at least one of lithium yttrium chloro fluoride, lithium scandium fluoride, and lithium gallium fluoride, etc.

[0031] In some embodiments, the sulfide solid electrolyte may include at least one of lithium phosphorus sulfide and lithium germanium phosphorus sulfide, etc. Further, the lithium phosphorus sulfide may include lithium phosphorus sulfur chloride (LPSCl), and the lithium germanium phosphorus sulfide may include lithium germanium phosphorus sulfur (LGPS).

[0032] Step S102, sinter the above mixed materials under the conditions of a pressure of 200 MPa to 250 MPa and a temperature of 200 °C to 250 °C to obtain a fully solid composite positive electrode sheet.

[0033] Traditional preparation methods usually adopt a sintering process of high temperature and high pressure, mainly based on two types of technical routes: (1) High-pressure tablet densification: By applying an ultra-high pressure above 350 MPa to press the composite positive electrode material for a long time, the solid-solid contact area between the positive electrode material and the solid electrolyte is forced to increase. The inventors of the present application have found that although this process can reduce the interfacial porosity of the composite positive electrode material, the mechanical strength of the positive electrode material is limited, and the ultra-high pressure will increase the risk of particle breakage and reduce the particle integrity.

[0034] (2) High-temperature sintering densification: By a temperature above 500 °C, the surface energy of the material is thermally activated to promote the diffusion bonding between the solid electrolyte and the positive electrode material particles, and high-density composite positive electrodes can be achieved in an oxide solid electrolyte system (such as LLZO / LCO). However, the inventors of the present application have found that this process has fundamental limitations for sulfide and halide solid electrolyte systems. Sulfides (such as Li 10 GeP 2 S 12 ) and halides (such as Li 3 InCl 6 ) electrolytes react violently with layered oxide positive electrode materials (such as NCM811 or LCO) at high temperatures. For example, Li 10 GeP 2 S 12 undergoes a sulfur-oxygen exchange reaction with NCM811 at a temperature higher than 250 °C to generate insulating phases such as Li 2 S, Ni x S y , etc., blocking lithium ion transport; Li 3 InCl 6 reacts with the lattice oxygen on the surface of the positive electrode material at a temperature higher than 250 °C (such as ), generating a high-impedance LiCl / In 2 O 3 composite layer, resulting in a sharp increase in interfacial impedance. Moreover, the thermal stability of sulfides and halides is insufficient, and the thermal decomposition temperatures of sulfide and halide electrolytes are significantly lower than those of oxides (for example, the decomposition temperature of LGPS is 350 °C, while that of LLZO is 800 °C), and they are prone to bulk decomposition during the high-temperature sintering process (such as ), resulting in the collapse of the electrolyte structure and the loss of ionic conductivity.

[0035] The high-pressure compaction densification process falls into a vicious cycle of "high-pressure densification - cathode material damage" in sulfide / halide systems. The fundamental reason lies in the mechanical property mismatch between sulfide / halide electrolytes and cathodes. Traditional processes cannot break through this physical limitation, and there is an urgent need to achieve a synergistic improvement in densification and material integrity through non-high-pressure-driven interface optimization strategies. The high-temperature sintering process is only applicable to oxide systems with excellent chemical / thermal stability, while sulfide / halide composite cathodes inevitably face the irreconcilable contradiction of "densification - interface deterioration" at high temperatures. There is an urgent need to develop a new non-thermal-driven densification strategy. Therefore, the existing high-temperature and high-pressure sintering processes have certain defects and lack universality, and cannot achieve the efficient densification of all-solid-state composite cathode sheets of sulfide solid electrolytes and halide solid electrolytes.

[0036] In this application, a cold sintering process with low temperature and low pressure is adopted in this step to control the pressure and temperature of the cold sintering of the mixed material to prepare an all-solid-state composite cathode sheet. Due to the low temperature of this process, the cathode material and the solid electrolyte have a good binding effect and a stable structure, and the surface energy of the mixed material particles is reduced by low temperature to improve the density of the all-solid-state composite cathode sheet; and due to the small pressure, it is beneficial to the structural stability of the all-solid-state composite cathode sheet. In addition, there is an internal stress adjustment for the all-solid-state composite cathode sheet during the cold sintering process. The all-solid-state composite cathode sheet forms a certain internal stress at low temperature and low pressure, which can effectively offset the volume stress caused by the expansion and contraction of the cathode material during the charge and discharge process of the prepared battery, maintaining the structural stability, so that the prepared battery can achieve stable electrochemical cycling at a relatively low pressure (2 MPa). This process effectively solves the problems of unstable solid-solid interfaces, structural damage, and electrochemical performance failure of the above-mentioned all-solid-state composite cathode sheets.

[0037] The cold sintering process with low temperature and low pressure not only realizes the efficient densification of the all-solid-state composite cathode sheet, forms a stable solid-solid interface between the cathode material and the solid electrolyte, but also improves the structural stability and cycling stability of the all-solid-state composite cathode sheet.

[0038] Among them, the pressure can be exemplarily 200 MPa, 210 MPa, 220 MPa, 230 MPa, 240 MPa, 250 MPa or any value within the range composed of any two of the above values. The temperature can be exemplarily 200 °C, 210 °C, 220 °C, 230 °C, 240 °C, 250 °C or any value within the range composed of any two of the above values.

[0039] In some embodiments, the sintering time can be from 30 s to 60 s. By controlling the sintering time within one minute, the desired densification effect can be quickly achieved, the exposure time of the all-solid composite cathode sheet at the sintering temperature can be reduced, thereby further reducing the occurrence of interfacial side reactions, which is beneficial to improving the cycle life and rate performance of the all-solid composite cathode sheet. At the same time, the morphology and grain size of the all-solid composite cathode sheet can be controlled. In addition, the production efficiency can be improved and the energy consumption can be reduced. Exemplarily, the sintering time can be 30 s, 35 s, 40 s, 45 s, 50 s, 55 s, 60 s or any value within the range composed of any two of the above values. Further, the sintering time can be from 30 s to 50 s.

[0040] In some embodiments, the mixed material can be placed in a sintering mold for the above-mentioned sintering. The mold can provide a uniform pressure distribution and an accurate sintering temperature, which is beneficial to further improving the overall densification and structural stability of the all-solid composite cathode sheet. Exemplarily, the sintering mold can include an upper ejector rod, a lower ejector rod, a zirconia ceramic inner liner, a sealed metal outer shell, and a heating sleeve.

[0041] Compared with the prior art, the cold sintering preparation method of the all-solid composite cathode sheet provided by the embodiments of the present application has the following beneficial effects: 1. By using the synergistic effect of a lower sintering temperature and a lower sintering pressure, the surface energy of the mixed material of the cathode material and the solid electrolyte can be reduced during the sintering process. The reduction of the particle surface energy helps to achieve the densification of the all-solid composite cathode sheet. The low-pressure cold sintering process can reduce the porosity inside the all-solid composite cathode sheet, make the ion / electron conduction channels more unobstructed, and effectively improve the ionic conductivity and electronic conductivity of the all-solid composite cathode sheet.

[0042] 2. Under low-temperature conditions, the interfacial side reactions caused by high temperature are effectively reduced, the generation of ion-insulating phases is reduced, a stable solid-solid interface between the cathode material and the solid electrolyte is formed, and the electrochemical performance and cycle stability of the all-solid composite cathode sheet are improved.

[0043] 3. Under low-pressure conditions, the deformation of the solid electrolyte and the cathode material in the all-solid composite cathode sheet is small, which is beneficial to keeping the structures of the two intact, reducing the risk of particle cracking caused by high-pressure compression, and improving the cycle performance of the all-solid composite cathode sheet.

[0044] 4. During the sintering process, due to the densification of the all-solid composite cathode sheet, certain internal stresses will be generated in the all-solid composite cathode sheet. These internal stresses can effectively offset the solid-solid contact failure caused by the volume stress generated by the expansion and contraction of the cathode material during the charge and discharge process of the prepared battery, and improve the cycle life and stability of the battery.

[0045] 5. The preparation method has simple process, short time consumption, low cost, and easy control during the production process, and is suitable for large-scale industrial production of all-solid composite positive electrode sheets.

[0046] An embodiment of the present application also provides an all-solid composite positive electrode sheet, which is prepared by the cold sintering preparation method of the all-solid composite positive electrode sheet described above. Due to the low-temperature and low-pressure cold sintering process adopted by the all-solid composite positive electrode sheet, it has good interface stability between the positive electrode material and the solid electrolyte and high density, thus having advantages such as good ionic conductivity, electronic conductivity, energy density, cycle stability, and structural stability.

[0047] Based on the same inventive concept, an embodiment of the present application also provides a preparation method of an all-solid battery, including: Step S201: Mix the positive electrode material and the solid electrolyte to obtain a mixed material.

[0048] The specific operation is the same as that of the aforementioned step S101 to obtain a mixed material of the positive electrode material and the solid electrolyte.

[0049] Step S202: Under the temperature condition of 200°C to 250°C, press the mixed material onto the solid electrolyte separator at a pressure of 200 MPa to 250 MPa to form an all-solid composite positive electrode sheet on one side of the solid electrolyte separator.

[0050] Referring to the aforementioned step S102, the difference between step S202 and step S102 is only that the low-temperature and low-pressure sintering of the mixed material is carried out on the solid electrolyte separator instead of the sintering mold. In this way, not only can an all-solid composite positive electrode sheet be formed, but also the assembly step of transferring the prepared all-solid composite positive electrode sheet to the solid electrolyte separator can be omitted, realizing the simultaneous preparation and assembly of the all-solid composite positive electrode sheet, which is beneficial to optimizing the preparation process of the all-solid battery.

[0051] Step S203: Assemble a negative electrode sheet on the side of the solid electrolyte separator away from the all-solid composite positive electrode sheet to obtain the all-solid battery.

[0052] Specifically, assemble the negative electrode sheet again, such as a lithium-containing electrode sheet, to obtain a fully assembled all-solid battery.

[0053] It can be understood that the all-solid battery can also be directly assembled by using the aforementioned separately prepared all-solid composite positive electrode sheet, the solid electrolyte separator, and the negative electrode sheet.

[0054] The embodiment of the present application also provides a all-solid-state battery, which is prepared by the preparation method of the all-solid-state battery described above. Since the all-solid-state battery includes an all-solid-state composite positive electrode sheet with good electrochemical performance and stable structure, the energy density, cycle life, rate performance and safety of the all-solid-state battery are improved.

[0055] The all-solid-state composite positive electrode sheet, its cold sintering preparation method and application described above are further illustrated by specific embodiments below.

[0056] Example 1 Step S201: Grind and mix the cathode material LiCoO 2 and Li 3 InCl 6 solid electrolyte (LIC) in a mass ratio of 70:30 for 20 min to obtain a mixed material.

[0057] Step S202: At a temperature of 200 °C, press 10 mg of the mixed material onto an 80 mg solid electrolyte separator at a pressure of 200 MPa for 30 s to form an all-solid-state composite positive electrode sheet on one side of the solid electrolyte separator. The solid electrolyte separator is obtained by placing 80 mg of solid electrolyte powder LIC into a battery mold with a diameter of 10 mm and pressing it under a pressure of 2 t.

[0058] Step S203: Assemble a Li-In foil on the side of the solid electrolyte separator away from the all-solid-state composite positive electrode sheet and press it into a negative electrode sheet at a pressure of 0.5 t to obtain an all-solid-state battery.

[0059] Example 2 Step S201: Grind and mix the NCM811 cathode material and Li 3 InCl 6 solid electrolyte (LIC) in a mass ratio of 70:30 for 20 min to obtain a mixed material.

[0060] Step S202: At a temperature of 200 °C, press 10 mg of the mixed material onto an 80 mg solid electrolyte separator at a pressure of 250 MPa for 40 s to form an all-solid-state composite positive electrode sheet on one side of the solid electrolyte separator. The solid electrolyte separator is obtained by placing 80 mg of solid electrolyte powder LIC into a battery mold with a diameter of 10 mm and pressing it under a pressure of 2 t.

[0061] Step S203: Assemble a Li-In foil on the side of the solid electrolyte separator away from the all-solid-state composite positive electrode sheet and press it into a negative electrode sheet at a pressure of 0.5 t to obtain an all-solid-state battery.

[0062] Example 3 Step S101: Mix NCM811 cathode material with Li 6 PS 5 Cl sulfide solid electrolyte (LPSCl) in a mass ratio of 70:30 to obtain a mixed material.

[0063] Step S102: Place the above mixed material in a sintering mold for sintering. Among them, the sintering pressure is 250 MPa, the sintering temperature is 200 °C, and sinter for 30 s to obtain a all-solid composite cathode sheet.

[0064] Assemble the all-solid composite cathode sheet, solid electrolyte separator, and anode sheet in sequence to obtain an all-solid battery.

[0065] Comparative Example 1 Step S201: Grind and mix LiCoO 2 cathode material with Li 3 InCl 6 solid electrolyte (LIC) in a mass ratio of 70:30 for 20 min to obtain a mixed material.

[0066] Step S202: At room temperature, press 10 mg of the mixed material onto an 80 mg solid electrolyte separator at a pressure of 375 MPa for 30 s to form an all-solid composite cathode sheet on one side of the solid electrolyte separator. Among them, the solid electrolyte separator is obtained by putting 80 mg of solid electrolyte powder LIC into a battery mold with a diameter of 10 mm and pressing it under a pressure of 2 t.

[0067] Step S203: Assemble a Li-In foil on the side of the solid electrolyte separator away from the all-solid composite cathode sheet and press it into an anode sheet at a pressure of 0.5 t to obtain an all-solid battery.

[0068] Comparative Example 2 Step S201: Grind and mix NCM811 cathode material with Li 3 InCl 6 solid electrolyte (LIC) in a mass ratio of 70:30 for 20 min to obtain a mixed material.

[0069] Step S202: At room temperature, press 10 mg of the mixed material onto an 80 mg solid electrolyte separator at a pressure of 375 MPa for 40 s to form an all-solid composite cathode sheet on one side of the solid electrolyte separator. Among them, the solid electrolyte separator is obtained by putting 80 mg of solid electrolyte powder LIC into a battery mold with a diameter of 10 mm and pressing it under a pressure of 2 t.

[0070] Step S203: Assemble a Li-In foil on the side of the solid electrolyte separator away from the all-solid composite positive electrode sheet, and press it into a negative electrode sheet under a pressure of 0.5 t to obtain an all-solid-state battery.

[0071] Comparative Example 3 Step S101: Mix NCM811 positive electrode material with Li 6 PS 5 PSCl sulfide solid electrolyte (LPSCl) in a mass ratio of 70:30 to obtain a mixed material.

[0072] Step S102: Place the above mixed material in a sintering mold and press it into a sheet at room temperature using a tablet press. The pressing pressure is 375 MPa to obtain an all-solid composite positive electrode sheet.

[0073] Assemble the all-solid composite positive electrode sheet, solid electrolyte separator, and negative electrode sheet in sequence to obtain an all-solid-state battery.

[0074] Perform the following tests on the all-solid composite positive electrode sheets and all-solid-state batteries obtained in Examples 1-3 and Comparative Examples 1-3, and obtain the corresponding test results.

[0075] 1. Scanning electron microscopy (SEM): Use a JSM-IT210 model scanning electron microscope. This model instrument has high-resolution imaging ability and can clearly observe the microscopic morphology and structural characteristics of the positive electrode material. The acceleration voltage is 5.00 kV, and the magnification is 5000 times.

[0076] 2. X-ray diffraction test: Use a Rigaku SmartLab SE model X-ray diffractometer made in Japan, equipped with a Cu Kα radiation source (λ = 1.5418 Å), scanning range 10°–80° (2θ), step size 0.02°, scanning rate 1° / min. Analyze the crystal structure and phase purity of the composite positive electrode material, and perform phase calibration based on the ICSD database to detect the interfacial by-products between the solid electrolyte and the positive electrode active material.

[0077] 3. Apparent density test. The test method is as follows: Use a JSM-IT210 model scanning electron microscope (acceleration voltage 5.00 kV, magnification 5000×) to obtain the microscopic morphology image of the composite positive electrode cross-section, perform gray-scale threshold segmentation and binary processing through ImageJ 1.53t software (threshold range: 0–85), and quantify the proportion of the internal pore area of the material. The apparent density calculation formula is: In the formula, A pores is the total pixel area of the pore region, A total is the total pixel area of the selected region. The analysis result takes the average value of 5 different fields of view, and the standard deviation ≤ 1.5%.

[0078] 4. The all-solid-state battery is prepared and electrochemically tested as follows: (1) Long cycle performance test method: At room temperature of 25 °C, the battery is charged and discharged at a current density of 0.5C within the charge-discharge range of 2.8 - 4.5V to obtain the specific capacity and Coulombic efficiency of the battery. The lithium-ion battery is charged at a constant current of 0.5C (C represents the current rate, 1C = 180 mA / g) to 4.5V, and the charging capacity is recorded; then it is discharged at 0.5C to the cut-off voltage of 2.8V, and the discharge capacity is recorded. This cycle is repeated 1000 times. The 0.5C specific capacity of the positive electrode material is calculated based on the discharge capacity, and the Coulombic efficiency of the battery is calculated according to the following formula: Coulombic efficiency = (discharge capacity / charging capacity) * 100%.

[0079] (2) Rate performance test method: At room temperature of 25 °C, the battery is charged and discharged at current densities of 0.1C / 0.2C / 0.5C / 1C / 2C / 4C / 6C / 0.5C within the charge-discharge range of 2.8 - 4.5V to obtain the specific capacity of the battery. The lithium-ion battery is charged at a constant current of 0.1C / 0.2C / 0.5C / 1C / 2C / 4C / 6C / 0.5C (C represents the current rate, 1C = 180 mA / g) to 4.5V, and the charging is stopped; then it is discharged at 0.1C / 0.2C / 0.5C / 1C / 2C / 4C / 6C / 0.5C to the cut-off voltage of 2.8V, and the discharge capacity is recorded.

[0080] The test results show that: Figure 2 For the comparative diagrams of the electron microscope scans of the all-solid-state composite positive electrode sheets in Example 2 and Comparative Example 2, where Figure 2 a in Figure 2 is the SEM image of the all-solid-state composite positive electrode sheet in Comparative Example 2, Figure 2 b in Figure 2 is the SEM image of the all-solid-state composite positive electrode sheet in Example 2. It can be seen that

[0081] Figure 3 a in

[0082] is the all-solid-state composite positive electrode sheet with room-temperature pressing. There are obvious gaps between the positive electrode material particles and the solid electrolyte particles, and these gaps hinder the transport of ions / electrons in the all-solid-state composite positive electrode sheet; while in Example 2 ( Figure 2 b), through the cold sintering process, the gaps between the solid electrolyte and the positive electrode material particles are eliminated, forming a dense all-solid-state composite positive electrode sheet, effectively increasing the transport efficiency of ions / electrons in the all-solid-state composite positive electrode sheet.

[0081] Figure 3 For the X-ray diffraction comparison diagrams of the positive electrode materials in the all-solid-state batteries of Example 2 and Comparative Example 2, it can be seen by comparison that no impurity phase is generated in the positive electrode material in the all-solid-state composite positive electrode sheet, indicating that no side reaction occurs between the positive electrode material and the solid electrolyte during the cold sintering process.

[0082] After density tests, due to the low-temperature and low-pressure cold sintering process, the all-solid composite cathode sheets in Examples 1-3 have good compactness. The density of the all-solid composite cathode sheet in Example 1 reached 98.7%, that in Example 2 was as high as 99.0%, and that in Example 3 was also as high as 99.2%, while those in Comparative Examples 1-3 were only about 82%. Combining with Figure 2 and Figure 3 it can be seen that the all-solid composite cathode sheets obtained in Examples 1-3 have high compactness and structural stability.

[0083] Figure 4 Figure 8 is a comparison chart of the long-term cycling performance of all-solid-state batteries in Example 2 and Comparative Example 2. The results show that within the voltage range of 2.8~4.5V, at 25°C and a rate of 0.5C, compared with Comparative Example 2, the all-solid-state battery obtained in Example 2 shows more excellent cycling stability. This is because the low-pressure cold sintering process in Example 2 effectively improves the interfacial stability and structural stability between the cathode material and the solid electrolyte in the all-solid composite cathode sheet, thereby improving the cycling performance of the all-solid-state battery. Figure 5 Figure 9 is a comparison chart of the rate performance of all-solid-state batteries in Example 2 and Comparative Example 2. The results show that compared with Comparative Example 2, the all-solid-state battery in Example 2 has more excellent rate performance. This is because the low-pressure cold sintering process can reduce the porosity inside the all-solid composite cathode sheet, making the ion / electron conduction channels more unobstructed, and effectively improving the rate performance of the all-solid-state battery.

[0084] Figure 6 Figure 14 is the long-term cycling performance chart of the all-solid-state battery prepared from the all-solid composite cathode sheet in Example 3. The results show that the cold sintering process also has an obvious effect in the sulfide solid electrolyte system. After 500 cycles, the capacity retention rate of the all-solid-state battery is still as high as 98.9%.

[0085] Figure 7 Figure 18 is a comparison chart of the rate performance of all-solid-state batteries prepared from all-solid composite cathode sheets in Example 3 and Comparative Example 3. The results show that the cold sintering process also improves the ion / electron conductivity of the all-solid composite cathode sheet in the sulfide solid electrolyte system, effectively improving the rate performance of the all-solid-state battery. Compared with Comparative Examples 1-3, due to the high density of the all-solid composite cathode sheets in Examples 1-3, the all-solid-state batteries show more excellent cycling performance and rate performance.

[0086] It can be understood that the above embodiments are merely exemplary embodiments adopted to illustrate the principle of the present invention. However, the present invention is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also regarded as the protection scope of the present invention.

Claims

1. A cold sintering method for preparing an all-solid composite positive electrode sheet, characterized in that: include: mixing the positive electrode material with the solid electrolyte to obtain a mixed material; as well as The mixed material is sintered under the conditions of a pressure of 200MPa-250MPa and a temperature of 200°C-250°C to obtain the all-solid composite positive electrode sheet.

2. The cold sintering preparation method of the all-solid composite positive electrode sheet according to claim 1, characterized in that: The sintering time is 30s to 60s.

3. The cold sintering preparation method of the all-solid composite positive electrode sheet according to claim 1, characterized in that: The mass ratio of the positive electrode material to the solid electrolyte in the mixed material is (1-7):

1.

4. The cold sintering preparation method of the all-solid composite positive electrode sheet according to claim 1, characterized in that: The positive electrode material is a layered positive electrode material.

5. The cold sintering preparation method of the all-solid composite positive electrode sheet according to claim 4, characterized in that: The layered positive electrode material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and lithium-rich manganese oxide.

6. The cold sintering preparation method of the all-solid composite positive electrode sheet according to claim 1, characterized in that: The solid electrolyte includes at least one of a halide solid electrolyte and a sulfide solid electrolyte.

7. The cold sintering preparation method of the all-solid composite positive electrode sheet according to claim 6, characterized in that: The halide solid electrolyte includes at least one of a chloride solid electrolyte and a fluoride solid electrolyte, wherein the chloride solid electrolyte includes at least one of lithium indium chloride, lithium yttrium chloride and lithium scandium chloride, and the fluoride solid electrolyte includes at least one of lithium yttrium chlorofluoride, lithium scandium fluoride and lithium gallium fluoride; and / or The sulfide solid electrolyte includes at least one of lithium phosphosulfide and lithium germanium phosphosulfide.

8. An all-solid composite positive electrode sheet, characterized in that: The all-solid composite positive electrode sheet is prepared by the cold sintering preparation method of any one of claims 1 to 7.

9. A method for preparing an all-solid-state battery, characterized in that: include: mixing the positive electrode material with the solid electrolyte to obtain a mixed material; Under the temperature condition of 200° C. to 250° C., pressing the mixed material onto a solid electrolyte membrane at a pressure of 200 MPa to 250 MPa to form an all-solid composite positive electrode sheet on one side of the solid electrolyte membrane; as well as The negative electrode sheet is assembled on the side of the solid electrolyte membrane away from the all-solid composite positive electrode sheet to obtain the all-solid-state battery.

10. An all-solid-state battery, characterized in that: Prepared by the preparation method of the all-solid-state battery according to claim 9.

Images