Solid-state battery composite cathode based on particle size distribution and step mixing process and preparation method thereof

Abstract

This invention discloses a solid-state battery composite cathode based on particle gradation and stepwise mixing technology, and its preparation method. This composite cathode is prepared by grading micron-sized and nano-sized solid electrolytes in a specific ratio (e.g., 4:1) and employing an innovative mixing process: first, the micron-sized electrolyte is mixed with active materials to construct the framework; then, the nano-sized electrolyte is premixed with a conductive agent to form a bifunctional filler; finally, the two are composited. This method utilizes the conductive agent to enhance the dispersibility and slippage ability of nanoparticles, making them easier to fill the framework voids, and simultaneously constructing a highly efficient ion-electron hybrid conduction network. This significantly reduces interfacial impedance and porosity, greatly improving the ionic conductivity and electrochemical performance of the composite cathode.

Description

Technical Field

[0001] This invention belongs to the field of solid-state lithium battery technology, specifically relating to a solid-state battery composite cathode based on particle gradation and stepwise mixing process and its preparation method. Background Technology

[0002] All-solid-state lithium-ion batteries are considered an ideal choice for next-generation energy storage devices due to their high safety and high energy density. However, the commercial application of solid-state batteries still faces many challenges, one of which is the solid-solid interface problem. In composite cathodes, active materials (such as ternary materials NCM, lithium iron phosphate LFP, etc.), solid electrolytes, and conductive agents mix to form a network for ion and electron conduction. Because the contact between the solid electrolyte and the cathode active material is rigid, the limited contact area results in high interfacial ion transport impedance, becoming a rate-limiting step in the internal reaction of the battery.

[0003] Existing composite cathodes typically employ solid electrolyte powders of a single particle size. While using micron-sized electrolytes offers good flowability and ease of preparation, the large particle size fails to adequately fill the gaps between the cathode active material particles, resulting in high internal porosity and long, discontinuous ion conduction paths. Using nano-sized electrolytes, while providing a large specific surface area and more contact points, leads to nanoparticle agglomeration, making dispersion difficult during mixing. Furthermore, the excessively high specific surface area may increase side reactions with the cathode active material, and the process is costly. Moreover, existing mixing processes often involve a simple one-step mixing of different powder components or pre-mixing electrolytes of different particle sizes. These traditional mixing methods fail to effectively address the agglomeration problem of nanomaterials and cannot actively construct an optimal ion-electron hybrid conduction network in the composite cathode, resulting in limited performance improvement even with particle size distribution.

[0004] Therefore, how to design a composite cathode structure that can ensure good ionic conductivity, reduce interfacial impedance, and simultaneously consider process feasibility and cost has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the aforementioned issues, the primary objective of this invention is to provide a method for preparing a solid-state battery composite cathode based on particle gradation and stepwise mixing technology. This method optimizes the microstructure of the cathode through a unique micro / nano particle gradation scheme, and simultaneously constructs an ion-electron hybrid conduction network in advance through a unique stepwise mixing sequence, thereby improving the processing performance of nanoparticles and solving the problem of nanoelectrolyte agglomeration.

[0006] Another object of the present invention is to provide a composite cathode prepared by the above method, which has the characteristics of low porosity, low interfacial impedance and high ionic conductivity.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] On the one hand, this invention proposes a method for preparing a solid-state battery composite cathode based on particle gradation and stepwise mixing technology, comprising the following steps:

[0009] S1: First premixing step: Micron-sized solid electrolyte powder and positive electrode active material are mixed to obtain a first mixture;

[0010] S2: Second premixing step: The nano-scale solid electrolyte powder and the conductive agent are mixed for the second time to obtain the second mixture.

[0011] S3: Main mixing step: The first mixture and the second mixture are mixed in a third step to obtain the main mixture, thereby achieving a uniform composite of micron-scale framework and nano-scale filler;

[0012] S4: Material preparation step: Add a binder to the main mixture and stir to form positive electrode material;

[0013] S5: Compression molding step: After kneading the positive electrode material into a ball, it is hot-rolled to the target thickness to obtain a dense composite positive electrode.

[0014] Furthermore, the mass ratio of the micron-sized solid electrolyte powder to the nano-sized solid electrolyte powder is (2~5):1, preferably 4:1.

[0015] Furthermore, the median particle size D50 of the micron-sized solid electrolyte powder is 0.5 μm to 3.0 μm, preferably 1 μm to 2 μm. The median particle size D50 of the nano-sized solid electrolyte powder is 100 nm to 600 nm, preferably 200 nm to 400 nm.

[0016] Preferably, the solid electrolyte is at least one of oxide-based, sulfide-based, or halide-based solid electrolytes, such as LLZO (garnet type), LATP (NASICON type), LPSCl (silver germanite type), or Li3InCl6 (chloride electrolyte).

[0017] Preferably, the positive electrode active material is at least one of lithium transition metal oxide, lithium iron phosphate, and lithium-rich manganese-based materials. The conductive agent is at least one of Super P, acetylene black, Ketjen black, carbon nanotubes, and graphene; and the binder is PTFE binder.

[0018] On the other hand, the present invention also proposes a solid-state battery composite cathode based on particle gradation and stepwise mixing process, which is prepared by the preparation method described above, including cathode active material, solid electrolyte, conductive agent and binder. The solid electrolyte includes micron-sized solid electrolyte powder and nano-sized solid electrolyte powder, and the mass ratio of micron-sized solid electrolyte powder to nano-sized solid electrolyte powder is (2-5):1. Furthermore, the nano-sized solid electrolyte powder and the conductive agent form a composite unit in the microstructure, which is uniformly distributed and fills the pores of the skeleton formed by the micron-sized solid electrolyte powder and the cathode active material.

[0019] Furthermore, in the composite positive electrode, the positive electrode active material accounts for 70% to 90% of the total mass, the solid electrolyte accounts for 10% to 25% of the total mass, the conductive agent accounts for 1% to 4% of the total mass, and the binder accounts for 1% to 3% of the total mass.

[0020] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0021] (1) Synergistic filling effect: Micron-sized electrolyte particles serve as the framework, constructing the main framework for ion conduction; nano-sized electrolyte particles effectively fill the gaps between micron-sized particles and positive electrode active material particles. This "coarse particle framework + fine particle filling" gradation mode significantly reduces the porosity of the composite positive electrode.

[0022] (2) Increase the contact area: Nanoscale electrolyte particles have a huge specific surface area, which can connect micron-sized electrolytes and positive electrode active materials, greatly increasing the effective contact points between the three, providing more and shorter migration paths for lithium ions, thereby significantly reducing the interface impedance.

[0023] (3) Optimization of ionic conductivity: Experiments have shown that when the micron-sized and nano-sized electrolytes are graded at a mass ratio of (2~5):1 (preferably 4:1), the composite cathode exhibits the highest ionic conductivity. At this ratio, the nanoparticles can fully fill the gaps without blocking the ion channels due to excessive aggregation, thus maximizing the ion transport efficiency.

[0024] (4) Construction of a dual-continuous conduction network: The innovative stepwise mixing method of this invention has unique advantages. First, the nanoscale electrolyte and conductive agent are pre-mixed, which allows the high specific surface area nanoparticles to be effectively dispersed and "supported" by the conductive agent (such as carbon nanotubes, Ketjen black, etc.), forming a "dual-functional composite unit" that can conduct both lithium ions and electrons. When mixed with the micron-scale framework in the subsequent process, this "dual-functional composite unit" can be more uniformly embedded in the gaps, which reduces the ion transport impedance and optimizes the electron conduction path, realizing the in-situ synchronous construction of the ion / electron conduction network.

[0025] (5) Improved processability: The introduction of conductive agents significantly improves the dispersibility and slippage ability of nano-sized electrolyte powders. Nanoparticles are prone to agglomeration due to van der Waals forces, while the addition of conductive agents reduces the direct contact and friction between nanoparticles, making them easier to flow and disperse during mixing and slurry stirring. This allows them to fill the gaps in the framework composed of micron-sized electrolytes and active substances more effectively, achieving a more extreme densification effect. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the solid-state battery composite cathode based on particle gradation and stepwise mixing process of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0028] The solid electrolyte used in the following examples is a sulfide-based solid electrolyte LPSClBr (Li6PS5Cl). 0.5 Br 0.5 The positive electrode active material is ternary material LiNi. 0.8 Co 0.1 Mn 0.1 O2 (NCM811), the conductive agent is vapor-grown carbon fiber (VGCF), and the binder is polytetrafluoroethylene (PTFE). However, it should be understood that these specific materials are not intended to limit the invention.

[0029] Example 1: Using the innovative stepwise mixing method of this invention

[0030] First premix: Select LPSClBr micron-sized powder with a median particle size D50 of 1.3 μm and mix it with the positive electrode active material (NCM811) at a certain mass ratio to obtain the first mixture.

[0031] Second premix: Select LPSClBr nanoparticles with a D50 of 300nm and mix them with a conductive agent (VGCF) at a certain mass ratio to obtain the second mixture.

[0032] Main mixing: The first mixture and the second mixture are dry mixed, wherein the final mass ratio of micron-sized LPSClBr to nano-sized LPSClBr is 4:1.

[0033] Preparation of composite cathode material: Add binder (PTFE) to the mixture obtained in the main mixing step, and stir to form a uniform cathode material.

[0034] Pressing step: After kneading the obtained composite cathode material into a ball, hot roller pressing is performed to the target thickness to obtain a dense composite cathode.

[0035] Figure 1 This is a schematic diagram of the structure of the solid-state battery composite cathode based on particle gradation and stepwise mixing process of the present invention. As can be seen from the figure, the skeleton is composed of micron-sized solid electrolyte and cathode active material, and the structure is filled in the gaps of the skeleton by bifunctional units composed of nano-sized solid electrolyte and conductive agent.

[0036] Example 2: Using the innovative stepwise mixing method of this invention

[0037] The process is basically the same as in Example 1, except that the final mass ratio of micron-sized LPSClBr to nano-sized LPSClBr in the solid electrolyte of the main mixing step is 5:1.

[0038] Comparative Example 1: All using micron-sized electrolytes

[0039] The process is basically the same as in Example 1, except that all solid electrolytes used are LPSClBr micron-sized powders with a D50 of 1.3 μm.

[0040] Comparative Example 2: All using nanoscale electrolytes

[0041] The example is basically the same as Example 1, except that the solid electrolyte is made of LPSClBr nanoparticles with a D50 of 300 nm.

[0042] Comparative Example 3: Using a traditional particle size distribution method but without optimized mixing

[0043] This comparative example uses the exact same raw materials and ratios as Example 1 (i.e., micron-scale: nano-scale = 4:1), but adopts the traditional mixing sequence:

[0044] Electrolyte premixing: Micron-sized LPSClBr powder and nano-sized LPSClBr powder are first dry-mixed at a mass ratio of 4:1 to obtain a graded electrolyte mixture.

[0045] Conventional mixing: The graded electrolyte mixture obtained in the previous step is dry-mixed with the conductive agent (VGCF) at the required mass ratio to obtain the first mixture. The first mixture is then dry-mixed with the positive electrode active material (NCM811) to obtain the second mixture.

[0046] Preparation of composite cathode material: Add binder (PTFE) to the second mixture obtained in the previous mixing step, and stir to form a uniform cathode material.

[0047] Subsequent steps: Same as in Example 1.

[0048] Performance testing:

[0049] A Li-SE-composite cathode-SE-Li battery configuration (symmetric battery structure) was assembled using the blocked electrode method. The ionic conductivity of the composite cathodes obtained in the above embodiments and comparative examples was calculated through constant current charging tests. The porosity of the composite cathodes obtained in the above embodiments and comparative examples was tested using isostatic compaction. The results are shown in the table below:

[0050]

[0051] The test results show that the composite cathode using the particle gradation technology of this invention exhibits significantly higher ionic conductivity than the control sample with a single particle size. In particular, when micron-sized and nano-sized electrolytes are mixed in a 4:1 ratio (Example 1), the ionic conductivity reaches its maximum value, increasing by approximately 38% compared to the pure micron-sized sample and approximately 44% compared to the pure nano-sized sample. This demonstrates that the "skeleton-filler" structure effectively improves density and ion transport efficiency, fully proving the effectiveness of the technical solution and the scientific validity of the optimal ratio of this invention.

[0052] Comparison of Comparative Example 3 and Example 1: Both used the exact same raw materials and proportions; the only difference was the mixing process. Comparative Example 3 used a traditional method of first mixing the electrolyte, resulting in a significantly lower ionic conductivity than Example 1, which used the stepwise mixing method of this invention, and limited improvement in porosity. This demonstrates that nanoparticles severely agglomerate in traditional mixing processes, failing to provide a filling effect and instead blocking ion channels. In contrast, this invention, by premixing the nano-electrolyte with the conductive agent, constructs a highly efficient ion-electron dual continuous conduction network, a key factor in improving the performance of the composite cathode. This process alters the dispersion state and processing behavior of the nanoparticles, thereby achieving a significant performance improvement. This fully demonstrates the effectiveness of the stepwise mixing process of this invention.

[0053] In summary, this invention, through the core process of "stepwise premixing to construct a dual-functional unit and then combining it with the framework," synergistically optimizes the microstructure, conduction network, and processing performance of the composite cathode, providing an efficient, feasible, and highly innovative technical solution for solving the cathode interface problem in all-solid-state batteries.

[0054] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a solid-state battery composite cathode based on particle size distribution and step-mixing process, characterized in that, Includes the following steps: S1: First premixing step: Micron-sized solid electrolyte powder and positive electrode active material are mixed to obtain a first mixture; S2: Second premixing step: The nano-scale solid electrolyte powder and the conductive agent are mixed for the second time to obtain the second mixture. S3: Main mixing step: The first mixture and the second mixture are mixed for the third time to obtain the main mixture, so as to achieve uniform composite of micron-level skeleton and nano-level filler; the nano-level solid electrolyte powder and the conductive agent form composite units in the microstructure, which are uniformly distributed and fill the gaps in the skeleton composed of the micron-level solid electrolyte powder and the positive electrode active material. S4: Material preparation step: Add a binder to the main mixture and stir to form positive electrode material; S5: Compression molding step: After kneading the positive electrode material into a ball, it is hot-rolled to the target thickness to obtain a dense composite positive electrode; The mass ratio of the micron-sized solid electrolyte powder to the nano-sized solid electrolyte powder is (2~5):1; The median particle size D50 of the micron-sized solid electrolyte powder is 0.5 μm to 3.0 μm, and the median particle size D50 of the nano-sized solid electrolyte powder is 100 nm to 600 nm.

2. The method of claim 1, wherein the method is characterized by: The median particle size D50 of the micron-sized solid electrolyte powder is 1 μm to 2 μm, and the median particle size D50 of the nano-sized solid electrolyte powder is 200 nm to 400 nm.

3. The method for preparing a solid-state battery composite cathode based on particle gradation and stepwise mixing process according to claim 1, characterized in that, The solid electrolyte is at least one of oxide-based, sulfide-based, or halide-based solid electrolytes.

4. The method of claim 1, wherein the method is characterized by: The positive electrode active material is at least one of lithium iron phosphate and lithium-rich manganese-based materials.

5. The method of claim 1, wherein the method is characterized by: The conductive agent is at least one of Super P, acetylene black, Ketjen black, carbon nanotubes, and graphene; the binder is PTFE binder.

6. A solid-state battery composite cathode based on particle gradation and stepwise mixing process, prepared by the preparation method according to any one of claims 1-5, characterized in that, It includes a positive electrode active material, a solid electrolyte, a conductive agent, and a binder. The solid electrolyte includes micron-sized solid electrolyte powder and nano-sized solid electrolyte powder, and the mass ratio of the micron-sized solid electrolyte powder to the nano-sized solid electrolyte powder is (2-5):

1.

7. A solid-state battery composite cathode based on particle gradation and stepwise mixing process according to claim 6, characterized in that, In the composite positive electrode, the positive electrode active material accounts for 70% to 90% of the total mass, the solid electrolyte accounts for 10% to 25% of the total mass, the conductive agent accounts for 1% to 4% of the total mass, and the binder accounts for 1% to 3% of the total mass.

Images