Monocrystal-polycrystal composite positive electrode material and preparation method thereof, solid-state battery positive electrode layer and solid-state battery

Abstract

The invention provides a single crystal-polycrystal composite positive electrode material and a preparation method thereof, a solid-state battery positive electrode layer and a solid-state battery, the single crystal-polycrystal composite positive electrode material comprises a single crystal positive electrode material, a polycrystal positive electrode material and a solid electrolyte material, the particle size D50 of the polycrystalline positive electrode material is larger than the particle size D50 of the single crystal positive electrode material and is larger than the particle size D50 of the solid electrolyte material; the mass ratio of the polycrystal positive electrode material to the single crystal positive electrode material is less than or equal to 1. According to the invention, through three-level grain composition and control of the mass ratio of the single-crystal positive electrode material to the polycrystalline positive electrode material, the single-crystal particles construct a rigid framework, and the polycrystalline particles and the electrolyte fill gaps, so that the contact area of the active material and the electrolyte is increased, the stack pressure is reduced, and the compaction density is improved; and meanwhile, the problems of poor interface stability, poor rate capability and high cost are solved.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a single-crystal-polycrystalline composite cathode material and its preparation method, a solid-state battery cathode layer and a solid-state battery. Background Technology

[0002] Solid-state batteries have the advantage of high safety compared to liquid batteries. The cathode material is an important component of solid-state batteries. The cathodes of existing all-solid-state batteries are generally divided into pure polycrystalline cathode systems and pure monocrystalline cathode systems. Among them, the pure polycrystalline cathode system uses layered oxide polycrystalline particles as active materials and mixes them with electrolytes (such as sulfide electrolytes) through ball milling and cold pressing to construct a composite cathode. In order to suppress the interfacial side reactions between polycrystalline particles and electrolytes, a coating layer is often used to modify the polycrystalline surface. However, the pure polycrystalline cathode system has the following problems: (1) poor mechanical stability: the volume expansion of polycrystalline particles during charging and discharging does not match the deformation of the solid electrolyte (high brittleness and low elastic modulus), resulting in electrode delamination and electrolyte particle breakage. After 300 cycles, the capacity retention rate is generally less than 60%; (2) violent interfacial reaction: the transition metal at the grain boundary of polycrystalline particles is easy to dissolve and react with the solid electrolyte to generate insulating products. After 100 cycles, the interfacial impedance can reach 5-8 times the initial value; (3) ion transport is hindered: the thickness of the "reaction layer" formed by the grain boundary and the solid electrolyte increases with the cycle. If it increases to 50-100nm, it becomes an ion transport barrier.

[0003] To address the issue of intense reactions at the polycrystalline-electrolyte interface, pure monocrystalline cathode systems utilize boundary-free monocrystalline particles as active materials to reduce reaction sites, coupled with composite electrolytes to lower interfacial impedance. However, existing pure monocrystalline cathode systems suffer from the following problems: ① Interfacial contact failure: Monocrystalline surfaces are smooth and have poor wettability with solid electrolytes, resulting in a lower physical contact area compared to polycrystalline systems of the same volume, necessitating high stacking pressure to maintain the conductive network. ② Cost and processing challenges: Monocrystalline particle synthesis requires high-temperature sintering at 1050-1100℃, making the cathode cost 3-4 times higher than that of pure polycrystalline systems. Furthermore, cold pressing can easily lead to SE agglomeration and uneven particle distribution.

[0004] In summary, pure polycrystalline systems are low in cost but suffer from uncontrolled interfacial reactions, while pure monocrystalline systems offer improved stability but have poor contact performance and are expensive. Existing coating and doping technologies can only delay interfacial reactions and cannot simultaneously solve the problems of poor interfacial stability, low ion transport efficiency, and high cost. Therefore, there is a need to provide a cathode material with high interfacial stability, excellent ion transport performance, and low cost. Summary of the Invention

[0005] The purpose of this invention is to provide a single-crystal-polycrystalline composite cathode material and its preparation method, a solid-state battery cathode layer, and a solid-state battery. The single-crystal-polycrystalline composite cathode material uses a three-level particle gradation and controls the mass ratio of single-crystal cathode material to polycrystalline cathode material, so that single-crystal particles form a rigid framework, and polycrystalline particles and electrolyte fill the gaps, thereby increasing the contact area between the active material and the electrolyte, reducing the stacking pressure, and increasing the compaction density. At the same time, it solves the problems of poor interface stability, poor rate performance, and high cost.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a single-crystal-polycrystalline composite cathode material, wherein the single-crystal-polycrystalline composite cathode material includes a single-crystal cathode material, a polycrystalline cathode material and a solid electrolyte material, wherein the particle size D50 of the polycrystalline cathode material is greater than the particle size D50 of the single-crystal cathode material, and the particle size D50 of the single-crystal cathode material is greater than the particle size D50 of the solid electrolyte material;

[0008] The mass ratio of the polycrystalline cathode material to the single-crystal cathode material is ≤1, for example, it can be 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3 or 0.2.

[0009] The monocrystalline-polycrystalline composite cathode material of this invention is used as the cathode layer material of a solid-state battery. The particle size D50 of the polycrystalline cathode material is greater than that of the monocrystalline cathode material, which is greater than that of the solid electrolyte material. The mass ratio of the polycrystalline cathode material to the monocrystalline cathode material is ≤1. There is a three-level particle size distribution among the polycrystalline cathode material, the monocrystalline cathode material, and the solid electrolyte material. Due to the high rigidity of the monocrystalline cathode material, it forms a rigid framework to resist the brittle fracture of the electrolyte. The polycrystalline particles fill the spaces between the framework formed by the monocrystalline cathode material, while the solid electrolyte material fills the gaps between the monocrystalline and polycrystalline cathode materials. This increases the contact area between the monocrystalline cathode material and the electrolyte and reduces the stacking pressure. Therefore, this invention can simultaneously solve the problems of poor interface stability, poor rate performance, and high cost existing in current technologies, while improving the cycle performance and rate performance of solid-state batteries.

[0010] Preferably, the polycrystalline cathode material includes a polycrystalline substrate and an ion conductor coating layer on the surface of the polycrystalline substrate.

[0011] The polycrystalline cathode material of the present invention is coated with an ion conductor coating layer. By utilizing the interfacial synergistic mechanism, that is, the coating layer on the surface of the polycrystalline particles forms a homogeneous interface with the electrolyte, the interfacial side reactions are reduced.

[0012] Preferably, the particle size D50 of the polycrystalline cathode material is 2μm-10μm, for example, it can be 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 4μm-6μm.

[0013] Preferably, the particle size D50 of the single-crystal cathode material is 1μm-4μm, for example, it can be 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm or 4μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 1.2μm-1.8μm.

[0014] Preferably, the particle size D50 of the solid electrolyte material is 0.2μm-3μm, for example, it can be 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 1.25μm, 1.5μm, 1.75μm, 2μm, 2.25μm, 2.5μm, 2.75μm or 3μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 0.5μm-1.0μm.

[0015] The particle size D50 of the polycrystalline cathode material, the single-crystal cathode material, and the solid electrolyte material of the present invention are preferably within a specific range, which can promote the gradation effect among the three types of particles; otherwise, the gradation effect among the particles will be affected.

[0016] It is understood that, since the particle size D50 of the polycrystalline cathode material of the present invention is larger than that of the monocrystalline cathode material, and the particle size D50 of the monocrystalline cathode material is larger than that of the solid electrolyte material, the particle size D50 of the polycrystalline cathode material and the monocrystalline cathode material do not simultaneously take the same value within 2-4 μm, and the particle size D50 of the monocrystalline cathode material and the solid electrolyte material do not simultaneously take the same value within 1-3 μm.

[0017] Preferably, the difference between the particle size D50 of the polycrystalline cathode material and the particle size D50 of the single-crystal cathode material is ≥1μm (≥1μm, ≤7μm), for example, it can be 1μm, 2μm, 3μm, 4μm, 5μm, 6μm or 7μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0018] Based on the premise that the particle size D50 of the polycrystalline cathode material is 2μm-10μm and the particle size D50 of the single-crystal cathode material is 1μm-4μm, the present invention preferably places the difference between the particle size D50 of the polycrystalline cathode material and the particle size D50 of the single-crystal cathode material within a specific range, thereby further promoting the gradation effect.

[0019] Preferably, the difference between the particle size D50 of the single-crystal cathode material and the particle size D50 of the solid electrolyte material is ≥0.5μm (≥0.5μm, ≤1.8μm), for example, it can be 0.5μm, 0.7μm, 0.9μm, 1.1μm, 1.3μm, 1.5μm, 1.7μm or 1.8μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0020] Based on the premise that the particle size D50 of the single crystal cathode material is 1μm-4μm and the particle size D50 of the solid electrolyte material is 0.2μm-3μm, the present invention preferably places the difference between the particle size D50 of the single crystal cathode material and the particle size D50 of the solid electrolyte material within a specific range, thereby further promoting the gradation effect.

[0021] Preferably, the mass ratio of the polycrystalline cathode material to the single-crystal cathode material is (2-5):(5-8), for example, it can be 2:8, 2.5:7.5, 3:7, 3.5:6.5, 4:6, 4.5:5.5 or 5:5, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] If the mass ratio of the polycrystalline cathode material to the single-crystal cathode material described in this invention is not within the above-mentioned range, such as too little polycrystalline cathode material and too much single-crystal cathode material, the gaps between the single-crystal particles cannot be fully filled, the contact area between the active material and the electrolyte is sharply reduced, the rate performance deteriorates, the electrode porosity is too high, the compaction density is difficult to improve, the stacking stress is concentrated in the single-crystal skeleton, which easily leads to particle fragmentation and interface microcracks, and the cycle stability decreases; if there is too much polycrystalline cathode material and too little single-crystal cathode material, a continuous single-crystal rigid skeleton cannot be formed, the electrode structure strength is insufficient, and it is easy to deform and collapse during compaction and cycling; the intrinsic defects of polycrystalline particles and excessive accumulation lead to increased interface impedance, highlighting the shortcomings in rate performance; at the same time, the production cost increases, weakening the cost advantage of this invention.

[0023] Preferably, the mass ratio of the polycrystalline cathode material to the solid electrolyte material is 1:(0.2-0.8), for example, it can be 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7 or 1:0.8, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] Preferably, the mass ratio of the polycrystalline substrate to the ion conductor coating layer is 1:(0.01-0.03), for example, it can be 1:0.01, 1:0.015, 1:0.02, 1:0.025 or 1:0.03, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] Preferably, the polycrystalline matrix and the single-crystal cathode material include ternary cathode materials.

[0026] Preferably, the ternary cathode material has the general chemical formula LiNi. 1-x-y Co x Mn y O2, where 0 < x ≤ 0.3, for example, it can be 0.05, 0.1, 0.15, 0.2, 0.25 or 0.3, and 0 < y ≤ 0.3, for example, it can be 0.05, 0.1, 0.15, 0.2, 0.25 or 0.3, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] Preferably, the solid electrolyte material includes a sulfide solid electrolyte material, such as Li7P3S. 11 Li6PS5X (X = Cl, Br, or I) or Li 10 GeP2S 12 Or any one or at least a combination of two of Li3PS4.

[0028] Preferably, the ion conductor coating layer comprises LiNbO3 and / or LiPO3.

[0029] Preferably, the single-crystal-polycrystalline composite cathode material further includes a conductive agent.

[0030] Preferably, the mass ratio of the polycrystalline cathode material to the conductive agent is 1:(0.04-0.12), for example, it can be 1:0.04, 1:0.06, 1:0.07, 1:0.1 or 1:0.12, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Preferably, the conductive agent includes VGCF (vapor-grown carbon fiber).

[0032] Preferably, the compaction density of the single-crystal-polycrystalline composite cathode material is 3.0 g / cm³. 3 The above, for example, could be 3.0 g / cm³. 3 3.02g / cm 3 3.04 g / cm 3 3.06 g / cm 3 3.08g / cm 3 3.10 g / cm3 Or 3.12g / cm 3 However, this does not limit the listed values; other unlisted values ​​within the range are also applicable.

[0033] Preferably, the ionic conductivity of the single-crystal-polycrystalline composite cathode material is above 0.6 mS / cm, for example, it can be 0.6 mS / cm, 0.8 mS / cm, 1.0 mS / cm, 1.2 mS / cm, 1.4 mS / cm, 1.6 mS / cm or 1.8 mS / cm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] Preferably, the electronic conductivity of the single-crystal-polycrystalline composite cathode material is above 0.6 mS / cm, for example, it can be 0.6 mS / cm, 0.65 mS / cm, 0.7 mS / cm, 0.75 mS / cm, 0.8 mS / cm, 0.9 mS / cm, 1.0 mS / cm, 1.1 mS / cm, 1.2 mS / cm, 1.3 mS / cm or 1.4 mS / cm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0035] In a second aspect, the present invention provides a method for preparing a single-crystal-polycrystalline composite cathode material as described in the first aspect, the method comprising the following steps:

[0036] The monocrystalline cathode material, polycrystalline cathode material, and solid electrolyte material are mixed to obtain the monocrystalline-polycrystalline composite cathode material.

[0037] Preferably, a conductive agent is also added during the mixing process.

[0038] Thirdly, the present invention provides a solid-state battery cathode layer, which is obtained by cold pressing of a single-crystal-polycrystalline composite cathode material as described in the first aspect.

[0039] Fourthly, the present invention provides a solid-state battery, the solid-state battery comprising a solid electrolyte sheet, a negative electrode layer on one side of the solid electrolyte sheet, and a positive electrode layer on the other side as described in the third aspect.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] This invention utilizes a three-tiered particle size distribution among polycrystalline cathode material, monocrystalline cathode material, and solid electrolyte material. This allows the monocrystalline cathode material to form a rigid framework, resisting brittle fracture of the electrolyte. Polycrystalline particles fill the spaces between these frameworks, while the solid electrolyte material fills the gaps between the monocrystalline and polycrystalline cathode materials. This increases the contact area between the monocrystalline cathode material and the electrolyte, reducing stacking pressure. Simultaneously, the polycrystalline cathode material is coated with an ion-conducting coating layer. Utilizing an interfacial synergistic mechanism, the coating layer on the polycrystalline particle surface forms a homogeneous interface with the electrolyte, reducing interfacial side reactions. Furthermore, this is combined with a monocrystalline cathode material that lacks grain boundaries and reduces transition metal dissolution, allowing the interfacial reaction layer thickness to be controlled at 10-20 nm, more than 70% thinner than pure polycrystalline cathode material. Therefore, this invention simultaneously solves the problems of poor interfacial stability, poor rate performance, and high cost existing in current technologies, while improving the cycle performance and rate performance of solid-state batteries. Detailed Implementation

[0042] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments are merely illustrative of the present invention and should not be considered as specific limitations thereof.

[0043] Example 1

[0044] This embodiment provides a single-crystal-polycrystalline composite cathode material, which includes a single-crystal cathode material, a polycrystalline cathode material, a solid electrolyte material, and VGCF. The particle size D50 of the polycrystalline cathode material is 5 μm, the particle size D50 of the single-crystal cathode material is 1.5 μm, the particle size D50 of the solid electrolyte material is 0.6 μm, the difference between the particle size D50 of the polycrystalline cathode material and the single-crystal cathode material is 3.5 μm, and the difference between the particle size D50 of the single-crystal cathode material and the solid electrolyte material is 0.9 μm.

[0045] The mass ratio of polycrystalline cathode material to monocrystalline cathode material is 3.5:6.5 (mass ratio value is 0.54), the mass ratio of polycrystalline cathode material to solid electrolyte material is 2.48:1 (equivalent to 1:0.4), and the mass ratio of polycrystalline cathode material to VGCF is 14.3:1 (equivalent to 1:0.07).

[0046] The polycrystalline cathode material comprises a polycrystalline matrix with a mass ratio of 1:0.02 and an ion-conducting coating layer on the surface of the polycrystalline matrix. Both the polycrystalline matrix and the single-crystal cathode material have the chemical formula LiNi. 0.83 Co 0.12 Mn 0.05 O2; the ion conductor coating layer includes LiNbO3; the solid electrolyte material is Li6PS5Cl;

[0047] The preparation method of single-crystal-polycrystalline composite cathode material includes the following steps: mixing single-crystal cathode material, polycrystalline cathode material, solid electrolyte material and VGCF to obtain single-crystal-polycrystalline composite cathode material.

[0048] Example 2

[0049] This embodiment provides a single-crystal-polycrystalline composite cathode material, which includes a single-crystal cathode material, a polycrystalline cathode material, a solid electrolyte material, and VGCF. The particle size D50 of the polycrystalline cathode material is 4.5 μm, the particle size D50 of the single-crystal cathode material is 1.8 μm, the particle size D50 of the solid electrolyte material is 0.7 μm, the difference between the particle size D50 of the polycrystalline cathode material and the single-crystal cathode material is 2.7 μm, and the difference between the particle size D50 of the single-crystal cathode material and the solid electrolyte material is 1.1 μm.

[0050] The mass ratio of polycrystalline cathode material to monocrystalline cathode material is 2:8 (mass ratio value is 0.25), the mass ratio of polycrystalline cathode material to solid electrolyte material is 1.42:1 (equivalent to 1:0.7), and the mass ratio of polycrystalline cathode material to VGCF is 8.17:1 (equivalent to 1:0.12).

[0051] The polycrystalline cathode material comprises a polycrystalline matrix with a mass ratio of 1:0.01 and an ion-conducting coating layer on the surface of the polycrystalline matrix. Both the polycrystalline matrix and the single-crystal cathode material have the chemical formula LiNi. 0.83 Co 0.12 Mn 0.05 O2; the ion conductor coating layer includes LiNbO3; the solid electrolyte material is Li6PS5Cl;

[0052] The preparation method of single-crystal-polycrystalline composite cathode material includes the following steps: mixing single-crystal cathode material, polycrystalline cathode material, solid electrolyte material and VGCF to obtain single-crystal-polycrystalline composite cathode material.

[0053] Example 3

[0054] This embodiment provides a single-crystal-polycrystalline composite cathode material, which includes a single-crystal cathode material, a polycrystalline cathode material, a solid electrolyte material, and VGCF. The particle size D50 of the polycrystalline cathode material is 5.5 μm, the particle size D50 of the single-crystal cathode material is 1.2 μm, the particle size D50 of the solid electrolyte material is 0.5 μm, the difference between the particle size D50 of the polycrystalline cathode material and the single-crystal cathode material is 4.3 μm, and the difference between the particle size D50 of the single-crystal cathode material and the solid electrolyte material is 0.7 μm.

[0055] The mass ratio of polycrystalline cathode material to monocrystalline cathode material is 5:5 (mass ratio = 1), the mass ratio of polycrystalline cathode material to solid electrolyte material is 3.55:1 (equivalent to 1:0.28), and the mass ratio of polycrystalline cathode material to VGCF is 20.43:1 (equivalent to 1:0.05).

[0056] The polycrystalline cathode material comprises a polycrystalline matrix with a mass ratio of 1:0.03 and an ion-conducting coating layer on the surface of the polycrystalline matrix. Both the polycrystalline matrix and the single-crystal cathode material have the chemical formula LiNi. 0.83 Co 0.12 Mn 0.05 O2; the ion conductor coating layer includes LiNbO3; the solid electrolyte material is Li6PS5Cl;

[0057] The preparation method of single-crystal-polycrystalline composite cathode material includes the following steps: mixing single-crystal cathode material, polycrystalline cathode material, solid electrolyte material and VGCF to obtain single-crystal-polycrystalline composite cathode material.

[0058] Example 4

[0059] This embodiment provides a single-crystal-polycrystalline composite cathode material. Except that the particle size D50 of the polycrystalline cathode material is 2.0 μm and the difference between the particle size D50 of the polycrystalline cathode material and the single-crystal cathode material is 0.5 μm, the single-crystal-polycrystalline composite cathode material is the same as that in Embodiment 1.

[0060] Example 5

[0061] This embodiment provides a single-crystal-polycrystalline composite cathode material. Except that the particle size D50 of the polycrystalline cathode material is 3.5 μm and the difference between the particle size D50 of the polycrystalline cathode material and the single-crystal cathode material is 2 μm, the single-crystal-polycrystalline composite cathode material is the same as that in Embodiment 1.

[0062] Example 6

[0063] This embodiment provides a single-crystal-polycrystalline composite cathode material. Except that the particle size D50 of the polycrystalline cathode material is 4.0 μm and the difference between the particle size D50 of the polycrystalline cathode material and the single-crystal cathode material is 2.5 μm, the single-crystal-polycrystalline composite cathode material is the same as that in Embodiment 1.

[0064] Example 7

[0065] This embodiment provides a single-crystal-polycrystalline composite cathode material. Except that the particle size D50 of the polycrystalline cathode material is 4.5 μm and the difference between the particle size D50 of the polycrystalline cathode material and the single-crystal cathode material is 3 μm, the single-crystal-polycrystalline composite cathode material is the same as that in Embodiment 1.

[0066] Example 8

[0067] This embodiment provides a single-crystal-polycrystalline composite cathode material. Except that the particle size D50 of the polycrystalline cathode material is 5.5 μm and the difference between the particle size D50 of the polycrystalline cathode material and the single-crystal cathode material is 4 μm, the single-crystal-polycrystalline composite cathode material is the same as that in Example 1.

[0068] Example 9

[0069] This embodiment provides a single-crystal-polycrystalline composite cathode material. Except that the particle size D50 of the polycrystalline cathode material is 6 μm and the difference between the particle size D50 of the polycrystalline cathode material and the single-crystal cathode material is 4.5 μm, the single-crystal-polycrystalline composite cathode material is the same as that in Embodiment 1.

[0070] Example 10

[0071] This embodiment provides a single-crystal-polycrystalline composite cathode material. Except that the particle size D50 of the polycrystalline cathode material is 10.0 μm and the difference between the particle size D50 of the polycrystalline cathode material and the single-crystal cathode material is 8.5 μm, the single-crystal-polycrystalline composite cathode material is the same as that in Embodiment 1.

[0072] Example 11

[0073] This embodiment provides a single-crystal-polycrystalline composite cathode material. Except that the particle size D50 of the single-crystal cathode material is 1.0 μm, the difference between the particle size D50 of the polycrystalline cathode material and the single-crystal cathode material is 4.0 μm, and the difference between the particle size D50 of the single-crystal cathode material and the solid electrolyte material is 0.4 μm, the single-crystal cathode material is the same as that of Example 1.

[0074] Example 12

[0075] This embodiment provides a single-crystal-polycrystalline composite cathode material. Except that the particle size D50 of the single-crystal cathode material is 4.0 μm, the difference between the particle size D50 of the polycrystalline cathode material and the single-crystal cathode material is 1 μm, and the difference between the particle size D50 of the single-crystal cathode material and the solid electrolyte material is 3.4 μm, the single-crystal-polycrystalline composite cathode material is the same as that in Example 1.

[0076] Example 13

[0077] This embodiment provides a single-crystal-polycrystalline composite cathode material. Except for the particle size D50 of the solid electrolyte material being 0.2 μm and the difference between the particle size D50 of the single-crystal cathode material and the particle size D50 of the solid electrolyte material being 1.3 μm, the single-crystal-polycrystalline composite cathode material is the same as that in Embodiment 1.

[0078] Example 14

[0079] This embodiment provides a single-crystal-polycrystalline composite cathode material. Except that the particle size D50 of the single-crystal cathode material is 3.3 μm, the difference between the particle size D50 of the polycrystalline cathode material and the single-crystal cathode material is 1.7 μm, the particle size D50 of the solid electrolyte material is 3.0 μm, and the difference between the particle size D50 of the single-crystal cathode material and the solid electrolyte material is 0.3 μm, the rest are the same as in Example 1.

[0080] Example 15

[0081] This embodiment provides a single-crystal-polycrystalline composite cathode material. Except for the mass ratio of polycrystalline cathode material to single-crystal cathode material being 1:9 (mass ratio value is 0.11), the single-crystal-polycrystalline composite cathode material is the same as that in Embodiment 1.

[0082] Comparative Example 1

[0083] This comparative example provides a single-crystal-polycrystalline composite cathode material. Except for the particle size D50, which is the same as that of the single-crystal cathode material, the single-crystal cathode material is the same as that of Example 1.

[0084] Comparative Example 2

[0085] This comparative example provides a single-crystal-polycrystalline composite cathode material. Except for the fact that the particle size D50 of the single-crystal cathode material and the solid electrolyte material is the same (0.6 μm), the single-crystal-polycrystalline composite cathode material is the same as that in Example 1.

[0086] Comparative Example 3

[0087] This comparative example provides a single-crystal-polycrystalline composite cathode material. Except for the mass ratio of polycrystalline cathode material to single-crystal cathode material being 6:5 (mass ratio value of 1.2), the single-crystal-polycrystalline composite cathode material is the same as that in Example 1.

[0088] In the above embodiments and comparative examples, the particle size D50 of the polycrystalline cathode material (hereinafter referred to as polycrystalline particle size D50), the particle size D50 of the monocrystalline cathode material (hereinafter referred to as monocrystalline particle size D50), the particle size D50 of the solid electrolyte material (hereinafter referred to as electrolyte particle size D50), and the mass ratio of the polycrystalline cathode material to the monocrystalline cathode material (hereinafter referred to as the polycrystalline to monocrystalline mass ratio) are shown in Table 1. The particle size D50 of the corresponding materials was measured using a laser particle size analyzer. The compaction density and ion exchange rate of the monocrystalline-polycrystalline composite cathode materials in the above embodiments and comparative examples are also shown in Table 1. The conductivity and electronic conductivity are shown in Table 1. The compaction density test method is as follows: a certain mass of single-crystal-polycrystalline composite cathode material powder is weighed, placed in a mold, a set pressure is applied using a powder film resistivity meter and held until stable, the thickness and diameter of the film are measured, the film volume is calculated, and the compaction density is obtained by the ratio of mass to volume. The ionic conductivity test method is as follows: a symmetrical battery is prepared by combining the composite cathode material and electrolyte, and electrochemical impedance spectroscopy (EIS) is performed using an electrochemical workstation with a test frequency range of 10 Hz. -2 ~10 8 The ionic conductivity was calculated based on impedance spectral data fitting at Hz. The electronic conductivity was tested by pressing composite cathode material powder into a film, using a powder film resistivity meter to perform a four-probe resistance test on the film, and then using the conductivity calculation formula to obtain the electronic conductivity by combining the film size parameters.

[0089] The monocrystalline-polycrystalline composite cathode material of the above embodiments and comparative examples is evenly spread on the sulfide electrolyte sheet (Li6PS5Cl), and a preset pre-pressure is applied and held for 5 minutes to achieve close contact between the cathode material and the electrolyte sheet; then the negative electrode is attached to the other side of the electrolyte sheet, and the same pre-pressure is applied and held for 5 minutes. After depressurization, the entire cell is encapsulated in an aluminum-plastic film to obtain a solid-state half-cell.

[0090] The cycle performance and rate performance of the solid-state half-cell were tested under the following conditions: constant current charge-discharge test was conducted at room temperature using a battery testing system; the charge-discharge voltage range was 2.8~4.3V; cycle performance test: 100 consecutive charge-discharge cycles were performed at a current density of 0.1C, and the discharge specific capacity and capacity retention rate were recorded for each cycle; rate performance test: charge-discharge was performed sequentially at current densities of 0.1C, 0.2C, 0.5C, 1C, and 2C, with 5 cycles at each current density, and finally the cycle was performed again at a current density of 0.1C for 5 cycles to verify the capacity recovery capability; the test results are detailed in Table 1.

[0091] Table 1

[0092]

[0093] As can be seen from Table 1 above:

[0094] As shown in Example 1 and Comparative Examples 1-2, the present invention, through a three-level particle size distribution among polycrystalline cathode material, monocrystalline cathode material, and solid electrolyte material, enables the monocrystalline-polycrystalline composite cathode material to simultaneously possess high compaction density, ionic conductivity, and electronic conductivity, thereby simultaneously improving the cycle performance and rate performance of the battery. As shown in Examples 1, 15, and General Comparative Example 3, the mass ratio of polycrystalline cathode material to monocrystalline cathode material in the present invention is ≤1, enabling the monocrystalline cathode material to construct a rigid framework, resisting brittle fracture of the electrolyte and improving the stability of the material. Furthermore, the combination of polycrystalline cathode material and monocrystalline cathode material is optimized. The mass ratio of the materials is (2-5):(5-8), thereby improving the gradation effect between particles and ensuring the overall performance of the battery. As can be seen from Examples 1 and 4-10, the present invention preferably has a particle size D50 of polycrystalline cathode material within a specific range, and preferably the difference between the particle size D50 of polycrystalline cathode material and the particle size D50 of single-crystal cathode material is ≥1μm, which can further improve the gradation effect between particles. As can be seen from Examples 1 and 11-14, the present invention preferably has a particle size D50 of single-crystal cathode material and a particle size D50 of solid electrolyte material within a specific range, which can further improve the gradation effect between particles.

[0095] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A single-crystal-polycrystalline composite cathode material, characterized in that, The single-crystal-polycrystalline composite cathode material includes a single-crystal cathode material, a polycrystalline cathode material, and a solid electrolyte material. The particle size D50 of the polycrystalline cathode material is larger than that of the single-crystal cathode material, and the particle size D50 of the single-crystal cathode material is larger than that of the solid electrolyte material. The mass ratio of the polycrystalline cathode material to the monocrystalline cathode material is ≤1.

2. The single-crystal-polycrystalline composite cathode material according to claim 1, characterized in that, The polycrystalline cathode material includes a polycrystalline matrix and an ion-conducting coating layer on the surface of the polycrystalline matrix; Preferably, the particle size D50 of the polycrystalline cathode material is 2μm-10μm, and more preferably 4μm-6μm; Preferably, the particle size D50 of the single-crystal cathode material is 1μm-4μm, and more preferably 1.2μm-1.8μm; Preferably, the particle size D50 of the solid electrolyte material is 0.2μm-3μm, and more preferably 0.5μm-1.0μm; Preferably, the difference between the particle size D50 of the polycrystalline cathode material and the particle size D50 of the monocrystalline cathode material is ≥1μm; Preferably, the difference between the particle size D50 of the single-crystal cathode material and the particle size D50 of the solid electrolyte material is ≥0.5μm.

3. The single-crystal-polycrystalline composite cathode material according to claim 1 or 2, characterized in that, The mass ratio of the polycrystalline cathode material to the single-crystal cathode material is (2-5):(5-8); Preferably, the mass ratio of the polycrystalline cathode material to the solid electrolyte material is 1:(0.2-0.8); Preferably, the mass ratio of the polycrystalline matrix to the ion conductor coating layer is 1:(0.01-0.03).

4. The single-crystal-polycrystalline composite cathode material according to claim 1 or 2, characterized in that, The polycrystalline matrix and single-crystal cathode material include ternary cathode materials; Preferably, the ternary cathode material has the general chemical formula LiNi. 1-x-y Co x Mn y O2, where 0 < x ≤ 0.3, 0 < y ≤ 0.3; Preferably, the solid electrolyte material includes a sulfide solid electrolyte material; Preferably, the ion conductor coating layer comprises LiNbO3 and / or LiPO3.

5. The single-crystal-polycrystalline composite cathode material according to claim 1 or 2, characterized in that, The single-crystal-polycrystalline composite cathode material also includes a conductive agent; Preferably, the mass ratio of the polycrystalline cathode material to the conductive agent is 1:(0.04-0.12); Preferably, the conductive agent comprises VGCF.

6. The single-crystal-polycrystalline composite cathode material according to claim 1 or 2, characterized in that, The compaction density of the monocrystalline-polycrystalline composite cathode material is 3 g / cm³. 3 above; Preferably, the ionic conductivity of the single-crystal-polycrystalline composite cathode material is above 0.6 mS / cm; Preferably, the electronic conductivity of the single-crystal-polycrystalline composite cathode material is above 0.6 mS / cm.

7. A method for preparing a single-crystal-polycrystalline composite cathode material as described in any one of claims 1-6, characterized in that, The preparation method includes the following steps: The monocrystalline cathode material, polycrystalline cathode material, and solid electrolyte material are mixed to obtain the monocrystalline-polycrystalline composite cathode material.

8. The preparation method according to claim 7, characterized in that, A conductive agent was also added during the mixing process.

9. A solid-state battery positive electrode layer, characterized in that, The solid-state battery cathode layer is obtained by cold pressing the single-crystal-polycrystalline composite cathode material as described in any one of claims 1-6.

10. A solid-state battery, characterized in that, The solid-state battery includes a solid electrolyte sheet, a negative electrode layer on one side of the solid electrolyte sheet, and a positive electrode layer on the other side as described in claim 9.

Images