Solid-state lithium battery composite positive electrode material and preparation method thereof

Abstract

The embodiment of the specification provides a solid-state lithium battery composite positive electrode material, the composite positive electrode material comprises positive electrode active particles, a solid electrolyte and a conductive adhesive, and the conductive adhesive comprises a conductive substrate and a coating buffer layer. The embodiment of the invention also provides a preparation method of the solid-state lithium battery composite positive electrode material. The preparation method comprises the following steps: adding the conductive substrate and the auxiliary raw materials into a solvent; carrying out stirring treatment on the solution; the stirred solution is dried to obtain a conductive adhesive, and the conductive adhesive comprises the conductive substrate and a coating buffer layer; and mixing and pressing the conductive adhesive, the positive active particles and the solid electrolyte to obtain the composite positive electrode material.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a solid-state lithium battery composite positive electrode material and a preparation method thereof. Background Art

[0002] The global demand for lithium batteries is growing significantly due to their high energy and power density advantages. For example, nickel-based oxides (e.g., single crystal high nickel NCM (nickel cobalt manganese oxide)) as lithium battery cathode materials have become important candidates for solid-state lithium batteries due to their reasonable cost and high energy density. However, achieving high area capacity and current density on the cathode at high voltage remains a challenge. Specifically, compared with liquid electrolytes, solid composite cathodes inherently exhibit more complex ion percolation networks. Therefore, it is crucial to optimize the microstructure of solid cathodes. In addition, the cathode active particles are prone to planar slip during delithiation, resulting in phase transition aggregation, which in turn generates microcracks at high voltages. These microcracks form isolated areas in the composite electrode, resulting in reduced utilization of the active material. Furthermore, the local non-uniformity of the cathode leads to the generation of stress, but these stresses cannot be effectively and uniformly transmitted through the rigid solid electrolyte, resulting in the accumulation of internal stress, which in turn leads to the rupture of the physical contact between the cathode active material and the solid electrolyte, as well as the rupture and crushing of the active material particles, ultimately limiting the diffusion of lithium ions.

[0003] Therefore, it is necessary to provide an improved solid-state lithium battery composite positive electrode material and a preparation method thereof to improve ion transport within the composite positive electrode material and protect its mechanical integrity, thereby improving the overall performance of the solid-state battery. Summary of the invention

[0004] The embodiments of the present specification provide a solid-state lithium battery composite positive electrode material, the composite positive electrode material comprising: positive electrode active particles; a solid electrolyte; a conductive adhesive, the conductive adhesive comprising a conductive matrix and a coating buffer layer.

[0005] In some embodiments, the coating buffer layer is prepared from polyethylene glycol and LiTFSI.

[0006] In some embodiments, the mass ratio of polyethylene glycol to LiTFSI is 1:0.5 to 1:5.

[0007] In some embodiments, the mass ratio of the coating buffer layer to the conductive substrate is 1-20%.

[0008] In some embodiments, the thickness of the coating buffer layer is 1-20 nm.

[0009] In some embodiments, the mass ratio of the conductive adhesive in the composite positive electrode material is 1-10%.

[0010] In some embodiments, the sulfide electrolyte and the conductive adhesive form a mixed interface for conducting ions and electrons.

[0011] The embodiments of the present specification also provide a method for preparing a composite cathode material for a solid-state lithium battery. The preparation method includes: adding a conductive matrix and auxiliary raw materials into a solvent; performing a stirring treatment on the above solution; performing a drying treatment on the stirred solution to obtain a conductive adhesive, where the conductive adhesive includes the conductive matrix and a coating buffer layer; mixing and pressing the conductive adhesive, cathode active particles, and solid electrolyte to obtain a composite cathode material.

[0012] In the embodiments of the present specification, by introducing a conductive adhesive including a conductive matrix and a coating buffer layer, on the one hand, the initial ionic conductivity in the composite cathode can be enhanced, the tortuosity of the ion channels can be reduced, and uniform ion flow can be promoted; on the other hand, the adhesive surface of the conductive adhesive serves as an adhesive for the composite cathode, enhancing the interaction force between the cathode active particles and the solid electrolyte particles, thereby resisting the expansion and slippage of the cathode active particles, improving the adaptability of the cathode particles to stress and strain, increasing the specific capacity and cycle life of the all-solid-state lithium battery at high voltages, and correspondingly improving the overall performance of the battery. Description of the Drawings

[0013] The present specification will be further described by way of exemplary embodiments, and these exemplary embodiments will be described in detail through the drawings. These embodiments are not restrictive. In these embodiments, the same numbers represent the same structures, where:

[0014] Figure 1 is a flowchart of an exemplary method for preparing a composite cathode material for a solid-state lithium battery according to some embodiments of the present specification.

[0015] Figure 2 is a schematic diagram of an exemplary composite cathode material according to some embodiments of the present specification.

[0016] Figure 3 is the test result of the ionic conductivity corresponding to the sulfide solid electrolyte in the comparative example and Examples 1 to 3.

[0017] Figure 4 is the SEM morphology image of the Li6PS5Cl sulfide solid electrolyte in the comparative example and Examples 1 to 3.

[0018] Figure 5 is the test result of the electronic conductivity of CB, LCCB-5, LCCB-10, and LCCB-15 in the comparative example and Examples 1 to 3.

[0019] Figure 6 Nyquist plots of (a) CB and (b) LCCB-10 tested in the five-layer electrode as described in the comparative example and Example 2.

[0020] Figure 7 SEM morphological images of CB and LCCB-10 particles as described in the comparative example and Example 2.

[0021] Figure 8 Test results of charge-discharge curves and specific capacities at 0.1C of batteries based on CB, LCCB-5, LCCB-10, and LCCB-15 as described in the comparative example and Examples 1-3.

[0022] Figure 9 XCT 2D cross-sectional views of the composite cathodes in the CB battery and LCCB-10 battery as described in the comparative example and Example 2.

[0023] Figure 10 XCT characterization results of the composite cathodes based on CB-CL and LCCB-10-CL after cycling as described in the comparative example and Example 2.

[0024] Figure 11 PFIB-SEM morphological images of the surfaces and cross-sections of CB-CL and LCCB-CL after cycling as described in the comparative example and Example 2.

[0025] Figure 12 HAADF image results of CB-CL and LCCB-CL after PFIB as described in the comparative example and Example 2.

[0026] Figure 13 Test results of the cycling performance of the batteries based on CB and LCCB-10 at 0.3C and 7 mg cm-2 as described in the comparative example and Example 2. Detailed implementation manners

[0027] To more clearly illustrate the technical solutions of the embodiments of this specification, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some examples or embodiments of this specification. For those of ordinary skill in the art, without creative efforts, this specification can also be applied to other similar scenarios based on these drawings. Unless obvious from the language context or otherwise stated, the same reference numerals in the figures represent the same structure or operation.

[0028] It should be understood that the "system", "device", "unit", and / or "module" used herein is a method for distinguishing different components, elements, parts, portions, or assemblies at different levels. However, if other words can achieve the same purpose, the said words can be replaced by other expressions.

[0029] As shown in this specification and the claims, unless the context clearly indicates otherwise, words such as "a", "an", "one", and / or "the" are not specifically singular and may also include the plural. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of the steps and elements that have been clearly identified, and these steps and elements do not constitute an exclusive list. The method or device may also include other steps or elements.

[0030] Flowcharts are used in this specification to illustrate the operations performed by the system according to the embodiments of this specification. It should be understood that the previous or subsequent operations do not necessarily need to be performed precisely in sequence. On the contrary, the steps can be processed in reverse order or simultaneously. At the same time, other operations can also be added to these processes, or one or more steps can be removed from these processes.

[0031] Figure 1 It is a flowchart of a method for preparing a composite positive electrode material for a solid-state lithium battery as shown in some embodiments of this specification. In some embodiments, process 100 can be automatically executed by a control system. For example, process 100 can be implemented through control instructions, and the control system controls each component to complete each operation of process 100 based on the control instructions. In some embodiments, process 100 can be semi-automatically executed. For example, one or more operations of process 100 can be manually performed by an operator. In some embodiments, when process 100 is completed, one or more additional operations not described can be added, and / or one or more operations discussed here can be deleted. Additionally, Figure 1 the order of the operations shown is not restrictive. As Figure 1 shown, process 100 may include the following steps.

[0032] Step 110, adding a conductive matrix and auxiliary raw materials into a solvent.

[0033] In some embodiments, the conductive matrix is carbon black, the auxiliary raw materials include a polymer and a lithium salt, and the solvent is an NMP solution.

[0034] In some embodiments, the polymer may include polyethylene glycol (PEG), cellulose ether, a derivative of PEG such as PEOz, polyether, polyethylenephosphonate (PEEP), etc. In the embodiments of this specification, PEG is taken as an example for specific description.

[0035] In some embodiments, the lithium salt may include LiTFSI, LiFSI, LiBOB, etc. In the embodiments of this specification, LiTFSI is taken as an example for specific description.

[0036] Specifically, add NMP solvent into a container (such as a centrifuge tube, a screw-cap bottle, etc.), and then add polyethylene glycol into the NMP solution. During the addition of polyethylene glycol, continuously shake or stir the container. Further, add LiTFSI into the above solution, and continuously shake or stir the container during the addition process. Finally, add carbon black into the above solution, and continuously shake or stir the container during the addition process. After adding the above materials into the NMP solution, a suspension to a certain extent is formed.

[0037] In some embodiments, the process of adding the conductive matrix and auxiliary raw materials into the solvent needs to be carried out under a protective atmosphere (such as argon).

[0038] Step 120, perform a stirring treatment on the above solution.

[0039] In some embodiments, after adding the above conductive matrix, polyethylene glycol and LiTFSI into the container, seal the container and seal the above suspension in the container.

[0040] After completing the sealing treatment, perform a stirring treatment on the suspension. For example, it can be stirred for a preset time (such as 5 hours) by a magnetic stirrer to make the above materials mix as fully and evenly as possible.

[0041] Step 130, perform a drying treatment on the solution after the stirring treatment to obtain a conductive adhesive.

[0042] In some embodiments, after completing the foregoing stirring treatment, perform a drying treatment on the solution after the stirring treatment. For example, quickly place the solution after the stirring treatment in a vacuum drying oven to complete the drying treatment. For example, the drying temperature is 80 °C and the drying time is 1 h.

[0043] In some embodiments, after the stirring treatment and the drying treatment, a conductive adhesive can be prepared. The conductive adhesive prepared through the above process includes a conductive matrix and a coating buffer layer. Specifically, the conductive adhesive includes carbon black and a coating buffer layer coated on the outer layer of the carbon black.

[0044] As an example, such as Figure 2As shown, the coating buffer layer is coated on the outer layer of the conductive matrix (e.g., carbon black). The lithium salt in the coating buffer layer can enhance the ionic conductivity, and the polymer can play a role in wrapping and buffering, effectively reducing the oxidation and structural damage of the cathode particles. After introducing this coating buffer layer in the preparation of the composite cathode material, on the one hand, it can enhance the initial conductivity of ions in the composite cathode, reduce the tortuosity of ion channels, and promote uniform ion flow; on the other hand, the adhesive surface of the conductive binder serves as an adhesive for the composite cathode, enhancing the interaction force between the cathode active particles and the solid electrolyte particles, thereby resisting the expansion and slippage of the cathode active particles, improving the adaptability of the cathode particles to stress and strain, increasing the specific capacity and cycle life of the all-solid-state lithium battery at high voltages, and correspondingly improving the overall performance of the battery.

[0045] In some embodiments, in order to maximize the ionic conductivity of the coating buffer layer, it is necessary to control the mass ratio of polyethylene glycol and LiTFSI within a preset range. In some embodiments, the mass ratio of polyethylene glycol and LiTFSI is 1:0.5 to 1:5. In some embodiments, the mass ratio of polyethylene glycol and LiTFSI is 1:0.6 to 1:4. In some embodiments, the mass ratio of polyethylene glycol and LiTFSI is 1:0.7 to 1:3. In some embodiments, the mass ratio of polyethylene glycol and LiTFSI is 1:0.7 to 1:2. In some embodiments, the mass ratio of polyethylene glycol and LiTFSI is 1:0.8 to 1:1.5. In some embodiments, the mass ratio of polyethylene glycol and LiTFSI is 1:09 to 1:1.2. In some embodiments, the mass ratio of polyethylene glycol and LiTFSI is 1:0.95 to 1:1.05. In some embodiments, the mass ratio of polyethylene glycol and LiTFSI is 1:1 to 1:1.1. In some specific embodiments, the mass ratio of polyethylene glycol and LiTFSI is 1:1.

[0046] In some embodiments, in order to control the balance between the ionic conductivity and electronic conductivity of the coating buffer layer and the conductive matrix, it is necessary to control the mass ratio of the coating buffer layer to the conductive matrix within a preset range. In some embodiments, the mass ratio of the coating buffer layer to the conductive matrix is 1 - 20%. In some embodiments, the mass ratio of the coating buffer layer to the conductive matrix is 2 - 18%. In some embodiments, the mass ratio of the coating buffer layer to the conductive matrix is 3 - 15%. In some embodiments, the mass ratio of the coating buffer layer to the conductive matrix is 5 - 10%.

[0047] In some embodiments, to effectively achieve the above effects, it is necessary to control the thickness of the coating buffer layer. If the thickness is too large, the electronic conductivity of the conductive matrix will be reduced. If the thickness is too small, the optimal ionic conductivity cannot be guaranteed. In addition, only an appropriate thickness can effectively resist the expansion and slippage of the positive active particles. In some embodiments, the thickness of the coating buffer layer is controlled to be 1 - 20 nm. In some embodiments, the thickness of the coating buffer layer is controlled to be 1 - 10 nm. In some embodiments, the thickness of the coating buffer layer is controlled to be 1 - 5 nm. In some embodiments, the thickness of the coating buffer layer is controlled to be 1 - 2 nm.

[0048] In some embodiments, to control the thickness of the coating buffer layer within a suitable range (so as to ensure the subsequent improvement of the ionic transport performance and mechanical integrity of the composite cathode material by the coating buffer layer), it is necessary to control the conditions of the above stirring treatment and drying treatment. Specifically, the conditions of the stirring treatment and / or drying treatment should be controlled.

[0049] In some embodiments, the speed of the stirring treatment is 10 - 60 ° / S.

[0050] In some embodiments, the time of the stirring treatment is 5 - 24 hours.

[0051] In some embodiments, the drying temperature is 40 - 100 °C

[0052] In some embodiments, the drying time is 5 - 24 hours.

[0053] Step 140, mix the conductive binder, the positive active particles and the solid electrolyte and perform a pressing treatment to obtain the composite cathode material.

[0054] In some embodiments, after mixing the conductive binder, the positive active particles and the solid electrolyte, the composite cathode material can be obtained by pressing.

[0055] In some embodiments, the pressing pressure is 5 - 15 MPa. In some embodiments, the holding time of the pressing is 5 - 15 min.

[0056] In some embodiments, the solid electrolyte can be a sulfide electrolyte. In some embodiments, the sulfide electrolyte can be Li6PS5Cl. As an example, the preparation process of Li6PS5Cl can be: under a protective atmosphere (for example, an argon atmosphere), grind a stoichiometric mixture of Li2S, P2S5 and LiCl for a certain time (for example, 30 minutes) (for example, by hand grinding in an agate mortar). After grinding, seal the mixture in a glass tube and perform an annealing treatment (for example, anneal at 550 °C for 10 hours).

[0057] In some embodiments, to ensure the performance of the composite cathode material and enable the conductive binder to effectively achieve the above effects, it is necessary to control the mass ratio of the cathode active particles, solid electrolyte, and conductive binder within a preset range, especially to control the proportion of the conductive binder in the composite cathode material. In some embodiments, the mass ratio of the conductive binder in the composite cathode material is 1-10%. In some embodiments, the mass ratio of the conductive binder in the composite cathode material is 2-8%. In some embodiments, the mass ratio of the conductive binder in the composite cathode material is 3-7%. In some embodiments, the mass ratio of the conductive binder in the composite cathode material is 4-5%.

[0058] Combined with the above, since the outer layer of the conductive matrix is coated with a coating buffer layer, during the charge and discharge process of the composite cathode, the solid electrolyte and the conductive binder form a mixed interface for guiding ions and electrons. Through this mixed interface, the electron and ion transport efficiency is effectively enhanced. At the same time, the coating buffer layer can protect the mechanical integrity of the composite cathode material, thereby effectively suppressing irreversible phase transformation and interfacial side reactions, and improving the specific capacity and cycle life of the solid-state lithium-ion battery at high voltages.

[0059] It should be noted that the above description of process 100 is only for illustration and explanation, and does not limit the scope of application of this application. For those skilled in the art, various modifications and changes can be made to process 100 under the guidance of this application. However, these modifications and changes are still within the scope of this application.

[0060] Comparative Example

[0061] Under a protective gas atmosphere, a stoichiometric mixture of Li2S, P2S5, and LiCl was manually ground in an agate mortar for 30 minutes. Next, the mixture was sealed in a glass tube under an argon atmosphere and annealed at 550°C for 10 hours. A reference composite cathode (denoted as CB-CL) was prepared by manually grinding NCM, Li6PS5Cl, and conductive agent carbon black with a mass ratio of 60:37:3.

[0062] Example 1

[0063] Carbon black (CB), PEG, and LiTFSI were added to the NMP solvent. The mass ratio of PEG to LiTFSI was 1:1. The mass ratio of carbon black to PEG was 100:5. The suspension was stirred in air for 5 hours and dried in a vacuum oven at 80°C to obtain a conductive binder (LCCB). A composite cathode 1 (denoted as LCCB-5-CL) was prepared by manually grinding NCM, Li6PS5Cl, and LCCB with a mass ratio of 60:37:3.

[0064] Example 2

[0065] Carbon black (CB), PEG, and LiTFSI were added to the NMP solvent. The mass ratio of PEG to LiTFSI was 1:1. The mass ratio of carbon black to PEG was 100:10. The suspension was stirred in air for 5 hours and dried in a vacuum oven at 80 °C to obtain a conductive binder (LCCB). Composite cathode 2 (denoted as LCCB-10-CL) was prepared by manually grinding NCM, Li6PS5Cl, and LCCB with a mass ratio of 60:37:3.

[0066] Example 3

[0067] Carbon black (CB), PEG, and LiTFSI were added to the NMP solvent. The mass ratio of PEG to LiTFSI was 1:1. The mass ratio of carbon black to PEG was 100:15. The suspension was stirred in air for 5 hours and dried in a vacuum oven at 80 °C to obtain a conductive binder (LCCB). Composite cathode 3 (denoted as LCCB-15-CL) was prepared by manually grinding NCM, Li6PS5Cl, and LCCB with a mass ratio of 60:37:3.

[0068] Performance test:

[0069] (1) The sulfide solid electrolyte material Li6PS5Cl described in the comparative example and the example was pressed into a thin sheet with a diameter of 10 mm and a thickness of about 1 mm at 8 MPa, and stainless steel disks were used as blocking electrodes on both sides to form a symmetric cell SS / sulfide solid electrolyte material / SS. Electrochemical impedance spectroscopy (EIS) was tested, and the test frequency range was 10 Hz - 1 MHz. The test was carried out in an argon atmosphere. The EIS test results are shown in Figure 3 , and the morphology diagram of Li6PS5Cl is shown in Figure 4 .

[0070] (2) The electronic conductivity of the conductive binders (such as CB, LCCB-5, LCCB-10, and LCCB-15) of the above comparative example and example was tested by chronoamperometry on a stainless steel / carbon / stainless steel electrode, and the applied bias voltage was 15 mV. The test results are shown in Figure 5 . As Figure 5 shown, the electronic conductivity of CB was the highest, at 2.24 S cm-1. When the mass ratio of carbon black to PEG was 100:5, denoted as LCCB-5, the electronic conductivity decreased slightly, to 2.19 S cm-1. When the mass ratio of carbon black to PEG was 100:10, denoted as LCCB-10, the electronic conductivity decreased to 2.06 S cm-1. When the mass ratio of carbon black to PEG was 100:15, denoted as LCCB-15, the electronic conductivity decreased to 1.63 S cm-1. It means that when the proportion of polyethylene glycol exceeds 10%, the electronic conductivity begins to decrease.

[0071] (3) The ionic conductivity of the conductive adhesives of the above comparative examples and examples was measured by electrochemical impedance spectroscopy (EIS) in the frequency range of 1 MHz to 1 Hz. Using a lithium / solid-state electrolyte (SSE) / sample / SSE / lithium five-layer electrode, 50 mg of the sample was pressed into a tablet at 240 Mpa. Then, 100 mg of Li6PS5Cl was pressed on both sides of the tablet at a pressure of 240 Mpa. Finally, lithium foils were placed on both sides of the composite tablet. The test results are shown in Figure 6 . As Figure 6 shown, the Nyquist plot of CB is random, indicating that it cannot conduct ions. In contrast, the normal semi-circle of LCCB-10 shows its lithium-ion conduction ability, exhibiting suitable electronic and ionic conductivities for coaxial conduction of ions and electrons, and the conductivity is calculated to be 8×10-5 S cm-1. It can be seen that the presence of high-concentration lithium salts and low-molecular-weight polymers promotes ionic conductivity. In addition, the morphological images of the conductive adhesives of the above comparative examples and examples were taken by SEM. As Figure 7 shown, compared with the fine powder state of CB, LCCB-10 shows an aggregated state, and the particle sizes of both samples are about 50 nm.

[0072] (4) The above composite cathode was prepared by manually grinding NCM, Li6PS5Cl and conductive adhesive with a mass ratio of 60:37:3. A comparative composite cathode without a conductive agent was also prepared, containing NCM and Li6PS5Cl with a mass ratio of 60:40. To assemble a all-solid-state lithium-ion battery, the composite cathode and Li6PS5Cl powder were successively pressed into two layers of granules at 320 Mpa, and In-Li alloy (placing a small piece of Li metal on In metal) was pressed to the other side at a pressure of 100 Mpa. Finally, two stainless steel disks were connected to both sides of the battery as current collectors. All the above manufacturing processes were carried out in an argon atmosphere. Charge-discharge tests were performed on the above batteries, and the test results are shown in Figure 8 .

[0073] As Figure 8 shown, the multiple advantages of LCCB improve the electrochemical performance of the composite cathode. At a rate of 0.1 C, the battery without a conductive agent shows the lowest specific capacity (105.8 mAh g-1), indicating insufficient electron conduction in the composite cathode and the need for a conductive agent. The specific discharge capacities of the composite cathodes including CB, LCCB-5, LCCB-10 and LCCB-15 are 138.0, 142.9, 154.4 and 122.5 mAh g-1 respectively. The specific capacity of the battery initially increases with the increase of the polymer percentage, and after the polymer content exceeds 10%, the specific capacity of the battery begins to gradually decrease. This decrease is attributed to the insufficient electronic conductivity caused by the too thick buffer layer.

[0074] (5) The microstructure of the composite cathode was detected using X-ray computed tomography (XCT). Due to the different X-ray absorption capabilities of atoms, different gray-scale contrasts were shown. The dark regions (low X-ray absorption) represent low-density microcracks, while the high-density cathode active particles (CAM particles) uniformly distributed in the composite cathode layer are represented by the brightest spots. The remaining gray regions can be attributed to the SSE. The results are as Figure 9 and Figure 10 shown.

[0075] As Figure 9 shown, after long-term electrochemical cycling, the CB-based cathode layer (CB-CL) has more large-sized dark spots than the LCCB-10-based cathode layer (LCCB-CL). This difference indicates that during repeated charge and discharge processes, CB-CL is more likely to generate microcracks.

[0076] As Figure 10 shown, based on the contrast difference between the background and SSE / CAM, threshold segmentation and 3D rendering were used to extract the high-density parts of CB-CL and LCCB-CL. It was found that LCCB-CL is relatively compact, while CB-CL has a large number of cracks extending inwards. The two-dimensional cross-sectional view of the XZ plane shows that compared with about 10 μm of LCCB-CL, CB-CL has more microcracks with sizes up to 50 μm. More microcrack density leads to a loose structure, which is not conducive to tortuous lithium-ion transport and increases the possibility of heterogeneous electrochemical reactions.

[0077] (6) PFIB-SEM was performed to visualize the depth cross-sectional information of the composite cathode (CAM), and the results are as Figure 11 . As Figure 11 shown, the surface morphologies of the two cathodes show obvious differences. Contrary to the CB-CL with obvious depressions and protrusions, the surface morphology of the cycled LCCB-CL is much flatter. The cross-sectional view shows that there are almost no microcracks distributed in LCCB-CL (at least on the side facing the current collector). However, in CB-CL, the microcracks in the SSE and CAM are clearly shown by the yellow and orange dashed lines respectively. These strip-shaped microcracks indicate the existence of contact failure, which will lead to different lithiation states of CAM, higher ion diffusion impedance, and more concentrated stress.

[0078] (7) PFIB-STEM technology was used to detect the structural fracture and lattice degradation of CAM, and the results are as Figure 12 . As Figure 12As shown, during the PFIB thinning process, due to the nucleation and growth of microcracks during cycling, the cyclic CB-CL cannot maintain its integrity. High-resolution HAADF images show that the main CAM shows the ideal lattice edges composed of NCM materials in the LCCB-CL, while the cyclic Ni83 cathode with CB-CL has undergone severe surface structure reconstruction, transforming from an ordered layered structure to an electrochemically inert Ni-O rock salt or spinel structure with a thickness exceeding 15 nm (as shown by the yellow dashed line in the figure). In addition, the dark areas and uneven contrast in the figure indicate that the loss of lattice oxygen and transition metals due to non-uniform reactions and stress / strain leads to the formation of micropores. In contrast, in the areas with closer contact, the structural degradation is much smaller, only showing a thin (about 1 nm) spinel layer.

[0079] (8) The cyclic performance of the aforementioned battery was tested, and the test results are as Figure 13 shown. As Figure 13 shown, significant capacity degradation will occur when ion conduction is insufficient at a higher current density. At 0.3C and 7 mg cm-2, the capacity gap between the LCCB-10 and CB batteries becomes larger. More importantly, the LCCB-10 battery exhibits an excellent discharge specific capacity of over 120.0 mAh g-1 after 1000 cycles, indicating that almost no capacity decay occurs after long-term electrochemical processes. However, the CB battery fails after approximately 150 cycles, with a significant decrease in capacity and CE, which is basically due to the structural degradation of the electrode particles.

[0080] The beneficial effects that may be brought about by the embodiments of this application include, but are not limited to: by introducing a conductive adhesive including a conductive matrix and a coating buffer layer, on the one hand, the initial conductivity of ions in the composite cathode can be enhanced, the tortuosity of ion channels can be reduced, and uniform ion flow can be promoted; on the other hand, the adhesive surface of the conductive adhesive serves as an adhesive for the composite cathode, enhancing the interaction force between the cathode active particles and the solid electrolyte particles, thereby resisting the expansion and slip of the cathode active particles, improving the adaptability of the cathode particles to stress and strain, increasing the specific capacity and cycle life of the all-solid-state lithium battery at high voltages, and correspondingly improving the overall performance of the battery.

[0081] It should be noted that the beneficial effects that may be produced by different embodiments are different. In different embodiments, the beneficial effects that may be produced can be a combination of any one or several of the above, or any other beneficial effects that may be obtained.

[0082] The basic concepts have been described above. Obviously, for those skilled in the art, the above detailed disclosure is only an example and does not constitute a limitation to this specification. Although not explicitly stated here, those skilled in the art may make various modifications, improvements, and corrections to this specification. Such modifications, improvements, and corrections are suggested in this specification, so such modifications, improvements, and corrections still fall within the spirit and scope of the exemplary embodiments of this specification.

[0083] Meanwhile, this specification uses specific terms to describe the embodiments of this specification. Such as "one embodiment", "an embodiment", and / or "some embodiments" mean a certain feature, structure, or characteristic related to at least one embodiment of this specification. Therefore, it should be emphasized and noted that the "one embodiment" or "an embodiment" or "an alternative embodiment" mentioned twice or more at different positions in this specification does not necessarily refer to the same embodiment. In addition, certain features, structures, or characteristics in one or more embodiments of this specification can be appropriately combined.

[0084] In addition, unless clearly stated in the claims, the order of the processing elements and sequences, the use of numerical letters, or the use of other names in this specification are not used to limit the order of the processes and methods of this specification. Although some currently considered useful embodiments of the invention are discussed through various examples in the above disclosure, it should be understood that such details only serve the purpose of illustration. The appended claims are not limited to the disclosed embodiments. On the contrary, the claims are intended to cover all modifications and equivalent combinations that conform to the essence and scope of the embodiments of this specification. For example, although the system components described above can be implemented by hardware devices, they can also be implemented only through software solutions, such as installing the described system on existing servers or mobile devices.

[0085] Similarly, it should be noted that, in order to simplify the expression of the disclosure of this specification and thus help the understanding of one or more embodiments of the invention, in the previous description of the embodiments of this specification, sometimes multiple features are merged into one embodiment, drawing, or its description. However, this disclosure method does not mean that the features required by the object of this specification are more than those mentioned in the claims. In fact, the features of the embodiments are fewer than all the features of the individual embodiments disclosed above.

[0086] In some embodiments, numbers are used to describe components and quantitative attributes. It should be understood that such numbers used in the description of embodiments are modified by the modifiers "about", "approximately" or "substantially" in some examples. Unless otherwise specified, "about", "approximately" or "substantially" indicate that the said numbers are allowed to vary by ±20%. Accordingly, in some embodiments, the numerical parameters used in the specification and claims are approximate values, which may vary according to the characteristics required by individual embodiments. In some embodiments, the numerical parameters should consider the specified significant digits and adopt the method of retaining general digits. Although the numerical ranges and parameters used in some embodiments of this specification to confirm the breadth of their scope are approximate values, in specific embodiments, such numerical settings are as precise as possible within the feasible range.

[0087] For each patent, patent application, patent application publication, and other materials cited in this specification, such as articles, books, specifications, publications, documents, etc., their entire contents are hereby incorporated into this specification by reference. This excludes the application history files that are inconsistent with or conflict with the content of this specification, and also excludes the files that limit the broadest scope of the claims of this specification (currently or subsequently attached to this specification). It should be noted that if there are inconsistencies or conflicts between the descriptions, definitions, and / or uses of terms in the attached materials of this specification and the content described in this specification, the descriptions, definitions, and / or uses of terms in this specification shall prevail.

[0088] Finally, it should be understood that the embodiments described in this specification are only used to illustrate the principles of the embodiments of this specification. Other variations may also fall within the scope of this specification. Therefore, by way of example and not limitation, alternative configurations of the embodiments of this specification may be considered to be consistent with the teachings of this specification. Accordingly, the embodiments of this specification are not limited to the embodiments explicitly introduced and described in this specification.

Claims

1. A composite cathode material for a solid-state lithium battery, characterized in that The composite cathode material includes: Cathode active particles; Solid electrolyte; A conductive binder, which includes a conductive matrix and a coating buffer layer.

2. The composite cathode material according to claim 1, wherein The coating buffer layer is prepared from polyethylene glycol and LiTFSI.

3. The composite cathode material according to claim 2, wherein The mass ratio of polyethylene glycol to LiTFSI is 1:0.5 to 1:

5.

4. The composite cathode material according to claim 1, characterized in that, The thickness of the coating buffer layer is 1-20 nm.

5. The composite cathode material according to claim 1, wherein The mass ratio of the coating buffer layer to the conductive matrix is 1-20%.

6. The composite cathode material according to claim 1, wherein The mass ratio of the conductive binder in the composite cathode material is 1-10%.

7. The composite cathode material according to claim 1, characterized in that, The solid electrolyte and the conductive binder form a mixed interface for conducting ions and electrons.

8. A preparation method of a composite cathode material for a solid-state lithium battery, characterized in that, The preparation method includes: Adding the conductive matrix and auxiliary materials into a solvent; Stirring the above solution; Drying the stirred solution to obtain a conductive binder, which includes the conductive matrix and the coating buffer layer; Mixing and pressing the conductive binder, cathode active particles and solid electrolyte to obtain a composite cathode material.

9. The preparation method according to claim 8, characterized in that, The auxiliary materials include polyethylene glycol and LiTFSI.

10. The preparation method according to claim 9, characterized in that, The mass ratio of polyethylene glycol to LiTFSI is 1:0.5 to 1:5.

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