High-nickel NCM positive electrode with continuous coating layer containing amorphous glass phase and preparation method of high-nickel NCM positive electrode

Abstract

The invention discloses a surface modification method of a high-nickel layered oxide positive electrode material for a sulfide solid electrolyte all-solid-state battery, the positive electrode material and the battery. According to the method, boric acid, lithium tetrafluoroborate and a small amount of cobalt tetrafluoroborate are used as a coating system, and firstly, the boric acid, the lithium tetrafluoroborate and the cobalt tetrafluoroborate are refined and premixed to improve the subsequent continuous film forming capacity; then mixing with LiNi < x > Co < y > Mn < 1-x-y > O < 2 > (x is greater than or equal to 0.8) positive electrode powder to enable the coating precursor to form continuous distribution on the surfaces of the particles; then carrying out segmented heat treatment in an oxygen atmosphere, so that lithium tetrafluoroborate is melted, wetted and spread in a medium-temperature region to form a continuous precursor film, promoting boric acid dehydration and interface rearrangement in a higher-temperature region, and constructing an amorphous / glass phase continuous coating layer containing a Li-B-O-F component in the presence of fluorine-containing active species; meanwhile, Co introduced by cobalt tetrafluoroborate forms a Co-enriched surface modification / reconstruction area on the surface layer of the particle and / or is distributed in a coating layer; and finally cooling to obtain the modified positive electrode material. Through the method, a continuous and compact composite interface modification layer which is filled with lithium and inhibits interface side reaction can be obtained, the interface impedance increase of sulfide is reduced, and the cycling stability and rate capability of the all-solid-state battery are improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion all-solid-state battery technology, and more particularly to a surface modification method for a high-nickel layered oxide cathode material suitable for sulfide solid electrolyte systems, as well as the cathode material obtained by the method and an all-solid-state battery containing the cathode material. Background Technology

[0002] Sulfide solid-state electrolytes possess high lithium-ion conductivity and good compressibility, making them a crucial electrolyte system for achieving high-energy-density all-solid-state batteries. However, sulfide solid-state electrolytes, along with high-nickel layered oxide cathode materials such as NCM and LiNi... x Co y Mn 1-x-y When O2 (x≥0.8) is in direct contact, interfacial side reactions are likely to occur and cause an increase in interfacial impedance. At the same time, during electrochemical cycling and heat treatment, the surface of high-nickel cathode is prone to structural reconstruction, local karyolysis and microcrack propagation, which further leads to deterioration of interfacial contact and performance degradation, resulting in capacity decay, reduced rate performance and shortened cycle life.

[0003] To improve the interfacial stability between sulfide electrolytes and high-nickel cathodes, existing technologies typically employ inorganic coatings, solution deposition, or solid-phase coating to construct an isolation / interfacial layer on the cathode particle surface. However, these methods may still present the following problems in practical applications: First, the coating layer is prone to island-like aggregation or localized insufficient coverage, making it difficult to form a continuous, dense, and controllable thickness coating layer, thus hindering the effective suppression of interfacial side reactions. Second, some coating processes require the introduction of multiple precursors or complex solvent systems, resulting in lengthy processes and limited scalability and consistency. Third, high-nickel cathodes may experience increased surface oxygen depletion / oxygen release tendency during heat treatment in vacuum or strongly inert atmospheres, leading to excessive surface reconstruction, which is detrimental to interfacial impedance control and structural stability.

[0004] Therefore, there is still an urgent need for a surface modification method that has a simple raw material system, can be scaled up, can construct a continuous coating layer on the surface of high-nickel NCM cathode particles, and takes into account the surface stability of high-nickel cathodes, so as to reduce sulfide interfacial side reactions and impedance growth, and improve the cycle and rate performance of all-solid-state batteries. Summary of the Invention

[0005] In view of the defects and deficiencies of the existing technology, the present invention provides, firstly, a method for preparing a cathode material; secondly, a cathode material; and thirdly, an all-solid-state battery.

[0006] In a first aspect, the present invention provides a method for preparing a cathode material, comprising the following steps:

[0007] Step 1: Boric acid, lithium tetrafluoroborate and cobalt tetrafluoroborate are refined and mixed to form a coating precursor mixture to improve the ability to form a continuous coating on the surface of the cathode particles.

[0008] Step 2: Mix the coating precursor mixture obtained in Step 1 with the high-nickel layered oxide cathode powder, so that the coating precursor forms a continuous precursor coating on the surface of the cathode particles, to obtain the mixture to be processed; wherein the high-nickel layered oxide is LiNi. x Co y Mn 1-x-y O2 and x≥0.8;

[0009] Step 3: The mixture to be treated obtained in Step 2 is subjected to segmented heat treatment in an oxygen atmosphere, so that lithium tetrafluoroborate melts in the medium temperature zone and wets and spreads on the surface of the positive electrode particles to form a continuous precursor film, and boric acid is dehydrated and the interface rearrangement is promoted in the higher temperature zone, and an amorphous or glassy phase continuous coating layer containing Li-BOF components is formed on the surface of the positive electrode particles with the participation of fluorine-containing active species.

[0010] Step 4: Cool the material after heat treatment in step 3 to obtain the modified positive electrode active material; wherein cobalt tetrafluoroborate is used as a Co source, so that Co forms a Co-enriched surface modification / reconstruction region on the surface of the positive electrode particles and / or is distributed in the coating layer during the heat treatment process.

[0011] Preferably, in step 1, the refining process includes dry grinding and ball milling.

[0012] Preferably, in step 1, the refining process reduces the D50 particle size of the coated precursor mixture to 0.2-10 μm.

[0013] Preferably, in step 2, the mixing is a dry mixing process, and the mixing time is 10-120 min.

[0014] Preferably, in step 2, based on the mass of the positive electrode powder, the amount of lithium tetrafluoroborate added is 0.5-1.5 wt%, the amount of boric acid added is 0.2-1.0 wt%, and the amount of cobalt tetrafluoroborate added is 0.02-0.1 wt% based on the element Co.

[0015] Preferably, in step 3, the segmented heat treatment includes: a first stage of holding at 100-150℃ for 0.5-3 hours; a second stage of holding at 300-360℃ for 0.25-2 hours; and a third stage of holding at 360-450℃ for 5-120 minutes.

[0016] Preferably, in step 3, the heating rate of the segmented heat treatment is 1-10℃ / min.

[0017] Preferably, in step 3, the heat treatment is carried out in a covered or semi-closed container to suppress component drift caused by the volatilization of fluorine-containing boron species and promote the formation of a continuous coating layer.

[0018] Preferably, in step 4, the cooling rate is 1-10℃ / min, and the heat treatment is carried out in an oxygen atmosphere.

[0019] Secondly, the present invention also provides a cathode material, which is prepared by the method described in the first aspect, and is a LiNi with x ≥ 0.8. x Co y Mn 1-x-y The O2 high-nickel cathode particles have an amorphous / glassy continuous coating layer containing Li-BOF components on their surface, and the particle surface has a Co-enriched surface modification / reconstruction region, which is located inside the coating layer or overlaps with the coating layer.

[0020] Thirdly, the present invention provides a battery comprising the above-described positive electrode material or the positive electrode material prepared by the above-described preparation method. Compared with the prior art, the present invention has the following significant advantages:

[0021] This invention constructs an inorganic interface on the surface of the positive electrode active material that enables continuous ion transport and reduces interfacial side reactions. This significantly improves the continuity and conductivity of lithium-ion transport at the positive electrode interface while effectively suppressing electron cross-interface transport and reducing the risk of oxidative decomposition of sulfide solid electrolytes on the positive electrode side. As a result, it achieves a synergistic improvement in interface stability, ionic conductivity, and chemical reliability.

[0022] This invention forms a continuous precursor film by melting and wetting LiBF4 in the mid-temperature region, and promotes boric acid dehydration and interfacial rearrangement in the higher temperature region to construct an amorphous / glassy phase continuous coating layer containing Li-BOF components, thereby achieving interface control of lithium passage / side reaction inhibition.

[0023] This invention can also enhance the surface stability of high nickel by introducing a Co source through a small amount of Co(BF4)2, forming a Co-enriched modified region on the particle surface or distributing Co in the coating layer, thereby improving the surface structure stability of high nickel NCM and synergistically suppressing the growth of sulfide interface impedance. Attached Figure Description

[0024] Figure 1 XRD patterns of Example 1 and the uncoated positive electrode; Figure 2 This is a TEM image of the positive electrode after coating in Example 1; Figure 3 The diagram shows the cycle of the examples and comparative examples. Detailed Implementation

[0025] In a first aspect, the present invention provides a method for preparing a high-nickel layered oxide positive electrode active material for a sulfide solid electrolyte system, comprising the following steps:

[0026] Step 1: Boric acid, lithium tetrafluoroborate and cobalt tetrafluoroborate are refined and mixed to form a coating precursor mixture to improve the ability to form a continuous coating on the surface of the cathode particles.

[0027] Step 2: Mix the coating precursor mixture obtained in Step 1 with the high-nickel layered oxide cathode powder, so that the coating precursor forms a continuous precursor coating on the surface of the cathode particles, to obtain the mixture to be processed; wherein the high-nickel layered oxide is LiNi. x Co y Mn 1-x-y O2 and x≥0.8;

[0028] Step 3: The mixture to be treated obtained in Step 2 is subjected to segmented heat treatment in an oxygen atmosphere, so that lithium tetrafluoroborate melts in the medium temperature zone and wets and spreads on the surface of the positive electrode particles to form a continuous precursor film, and boric acid is dehydrated and the interface rearrangement is promoted in the higher temperature zone, and an amorphous or glassy phase continuous coating layer containing Li-BOF components is formed on the surface of the positive electrode particles with the participation of fluorine-containing active species.

[0029] Step 4: Cool the material after heat treatment in step 3 to obtain the modified positive electrode active material; wherein cobalt tetrafluoroborate is used as a Co source, so that Co forms a Co-enriched surface modification / reconstruction region on the surface of the positive electrode particles and / or is distributed in the coating layer during the heat treatment process.

[0030] Through research, the inventors discovered that the various steps of the preparation method described in this invention work together to form a synergistic effect: by refining and premixing boric acid, lithium tetrafluoroborate, and cobalt tetrafluoroborate and achieving continuous precursor coverage with high-nickel layered oxide cathode powder, the dispersibility and film continuity of the coating system are significantly improved; further, segmented heat treatment is carried out under an oxygen atmosphere, utilizing the melt wetting and spreading of lithium tetrafluoroborate and the dehydration and rearrangement of boric acid, an amorphous / glassy phase continuous coating layer containing Li-BOF components is constructed in situ with the participation of fluorine-containing active species, while the introduced Co forms a Co-enriched surface modification / reconstruction region on the particle surface and / or is distributed in the coating layer; finally, after cooling and solidification, a continuous, dense, lithium-through composite interface modification layer that can suppress sulfide interface side reactions and impedance growth is obtained, thereby synergistically improving the interface stability, structural stability, and cycle performance of the high-nickel cathode in the sulfide all-solid-state system.

[0031] Preferably, in step 1, the refining process includes dry grinding and ball milling.

[0032] Preferably, in step 1, the refining process reduces the D50 particle size of the coated precursor mixture to 0.2-10 μm.

[0033] Through research, the inventors discovered that the optimal conditions in step 1 are essentially achieved by dry grinding and ball milling to fully premix and reduce particle size, thereby controlling the D50 of the coating precursor mixture to 0.2-10μm, thus laying a stable foundation for the subsequent formation of a uniform and continuous coating on the surface of the cathode particles.

[0034] Preferably, in step 2, the mixing is a dry mixing process, and the mixing time is 10-120 min.

[0035] Preferably, in step 2, based on the mass of the positive electrode powder, the amount of lithium tetrafluoroborate added is 0.5-1.5 wt%, the amount of boric acid added is 0.2-1.0 wt%, and the amount of cobalt tetrafluoroborate added is 0.02-0.1 wt% based on the element Co.

[0036] Through research, the inventors discovered that the optimal conditions for step 2 are reflected in the process control of coating formation and proportioning window: dry mixing for 10-120 minutes is used to achieve uniform distribution of the coating precursor on the surface of high-nickel cathode particles and form a continuous coating; at the same time, the addition amounts of LiBF4, H3BO3 and Co(BF4)2 (calculated as Co) are limited to the ranges of 0.5-1.5wt%, 0.2-1.0wt%, and 0.02-0.1wt%, respectively, which can ensure the continuity of the coating while taking into account the compositional stability required for subsequent film formation, thereby improving the repeatability and consistency of the coating layer formation after heat treatment.

[0037] Preferably, in step 3, the segmented heat treatment includes: a first stage of holding at 100-150℃ for 0.5-3 hours; a second stage of holding at 300-360℃ for 0.25-2 hours; and a third stage of holding at 360-450℃ for 5-120 minutes.

[0038] Preferably, in step 3, the heating rate of the segmented heat treatment is 1-10℃ / min.

[0039] Preferably, in step 3, the heat treatment is carried out in a covered or semi-closed container to suppress component drift caused by the volatilization of fluorine-containing boron species and promote the formation of a continuous coating layer.

[0040] Through research, the inventors discovered that the optimal conditions for step 3 are essentially the standardization of the thermal range window and sample loading method: the process is divided into controllable stages by using three-stage heat treatment (100-150℃, 300-360℃, 360-450℃), and the heating rate is limited to 1-10℃ / min to reduce process fluctuations; at the same time, using a covered or semi-closed container for sample loading can reduce component drift caused by volatilization, further improve the stability of the coating layer formation, and make it easier to obtain a continuous and uniform Li-BOF amorphous / glass phase coating layer on the surface of the cathode particles.

[0041] In step 4, the cooling rate is 1-10℃ / min, and the heat treatment is carried out in an oxygen atmosphere.

[0042] Through research, the inventors discovered that by controlling the cooling rate at 1-10℃ / min and completing the cooling and solidification process after heat treatment in an oxygen atmosphere in step 4, the amorphous / glass phase coating layer containing Li-BOF components formed in step 3 can be solidified more stably and maintain continuity. At the same time, the oxygen atmosphere helps to reduce the risk of surface oxygen depletion and excessive reconstruction of the high-nickel cathode during heat treatment / cooling, thereby improving the interfacial stability and process repeatability of the modified cathode material.

[0043] Secondly, the present invention provides a high-nickel layered oxide positive electrode active material for sulfide solid electrolyte systems, which is prepared by the above-described preparation method.

[0044] The inventors discovered through research that the positive electrode active material is LiNi x Co y Mn 1-x-y O2 (x≥0.8) is the main component, and an amorphous or glassy continuous coating layer containing Li-BOF components is formed on the particle surface. The particle surface has Co-enriched surface modification / reconstruction regions, which are located inside the coating layer or overlap with it. This structure, without changing the high-nickel cathode energy density, helps to reduce interfacial side reactions and interfacial impedance growth caused by direct contact between the sulfide solid electrolyte and the cathode, and improves interfacial contact stability and cycle consistency, thereby achieving a synergistic improvement in the cycle stability and rate performance of the all-solid-state battery.

[0045] Thirdly, the present invention provides an all-solid-state battery, comprising a sulfide solid electrolyte and a positive electrode, characterized in that the positive electrode comprises the above-mentioned positive electrode active material or comprises a positive electrode active material prepared by the above-mentioned preparation method.

[0046] To make the technical problems, technical solutions and technical advantages of the present invention clearer, a detailed description will be given below with reference to specific examples. However, the scope of protection of the present invention is not limited to the following specific embodiments.

[0047] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0048] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0049] Example 1:

[0050] A method for preparing a high-performance cathode material includes the following steps:

[0051] Step 1: Weigh boric acid (H3BO3), lithium tetrafluoroborate (LiBF4), and cobalt tetrafluoroborate (Co(BF4)2), and use 10g LiNi 0.8 Co 0.1 Mn 0.1 For O2 cathode powder, take 0.1g LiBF4, 0.05g H3BO3, and 0.01g Co(BF4)2. Add the above three raw materials to a ball mill jar and dry ball mill for 90 minutes to obtain a coated precursor mixture; adjust the ball milling conditions to make the D50 of the obtained coated precursor mixture 0.2-10μm.

[0052] Step 2: Mix the coated precursor mixture obtained in Step 1 with LiNi 0.8 Co 0.1 Mn 0.1 The O2 cathode powder was dry-mixed for 30 minutes to obtain the mixture to be treated.

[0053] Step 3: Load the mixture obtained in Step 2 into a covered ceramic boat and place it in an oxygen-filled tube furnace for segmented heat treatment under an oxygen atmosphere. The heating rate is set to 3℃ / min and the cooling rate is set to 5℃ / min. The heat treatment procedure is as follows: First stage: heat up to 120℃ and hold for 1 hour; Second stage: continue to heat up to 330℃ and hold for 1 hour; Third stage: continue to heat up to 400℃ and hold for 30 minutes.

[0054] Step 4: Cool to 100℃, collect the material, and grind it for later use.

[0055] Example 2:

[0056] A method for preparing a high-performance cathode material includes the following steps:

[0057] Step 1: Weigh boric acid (H3BO3), lithium tetrafluoroborate (LiBF4), and cobalt tetrafluoroborate (Co(BF4)2), and use 10g LiNi 0.8 Co0.1 Mn 0.1 For O2 cathode powder, take 0.1g LiBF4, 0.05g H3BO3, and 0.02g Co(BF4)2. Add the above three raw materials to a ball mill jar and dry ball mill for 90 minutes to obtain a coated precursor mixture; adjust the ball milling conditions to make the D50 of the obtained coated precursor mixture 0.2-10μm.

[0058] Step 2: Mix the coated precursor mixture obtained in Step 1 with LiNi 0.8 Co 0.1 Mn 0.1 The O2 cathode powder was dry-mixed for 60 minutes to obtain the mixture to be treated.

[0059] Step 3: Load the mixture obtained in Step 2 into a covered ceramic boat and place it in an oxygen-filled tube furnace for segmented heat treatment under an oxygen atmosphere. The heating rate is set to 3℃ / min and the cooling rate is set to 5℃ / min. The heat treatment procedure is as follows: First stage: heat up to 120℃ and hold for 1 hour; Second stage: continue to heat up to 330℃ and hold for 1 hour; Third stage: continue to heat up to 400℃ and hold for 30 minutes.

[0060] Step 4: Cool to 100℃, collect the material, and grind it for later use.

[0061] Example 3:

[0062] A method for preparing a high-performance cathode material includes the following steps:

[0063] Step 1: Weigh boric acid (H3BO3), lithium tetrafluoroborate (LiBF4), and cobalt tetrafluoroborate (Co(BF4)2), and use 10g LiNi 0.8 Co 0.1 Mn 0.1 For O2 cathode powder, take 0.1g LiBF4, 0.05g H3BO3, and 0.01g Co(BF4)2. Add the above three raw materials to a ball mill jar and dry ball mill for 30 minutes to obtain a coated precursor mixture; adjust the ball milling conditions to make the D50 of the obtained coated precursor mixture 2-10μm.

[0064] Step 2: Mix the coated precursor mixture obtained in Step 1 with LiNi 0.8 Co 0.1 Mn 0.1 The O2 cathode powder was dry-mixed for 30 minutes to obtain the mixture to be treated.

[0065] Step 3: Load the mixture obtained in Step 2 into a covered ceramic boat and place it in an oxygen-filled tube furnace for segmented heat treatment under an oxygen atmosphere. The heating rate is set to 3℃ / min and the cooling rate is set to 5℃ / min. The heat treatment procedure is as follows: First stage: heat up to 120℃ and hold for 1 hour; Second stage: continue to heat up to 330℃ and hold for 1 hour; Third stage: continue to heat up to 400℃ and hold for 30 minutes.

[0066] Step 4: Cool to 100℃, collect the material, and grind it for later use.

[0067] Comparative Example 1:

[0068] A method for preparing a positive electrode includes the following steps:

[0069] Step 1: Weigh lithium tetrafluoroborate (LiBF4) and cobalt tetrafluoroborate (Co(BF4)2). Using 10g of LiNi0.8Co0.1Mn0.1O2 cathode powder, take 0.1g of LiBF4 and 0.01g of Co(BF4)2. Add both raw materials to a ball mill jar and dry ball mill for 90 minutes to obtain a coated precursor mixture. Adjust the ball milling conditions to achieve a D50 of 0.2-10μm for the resulting coated precursor mixture.

[0070] Step 2: Mix the coated precursor mixture obtained in Step 1 with LiNi 0.8 Co 0.1 Mn 0.1 The O2 cathode powder was dry-mixed for 60 minutes to obtain the mixture to be treated.

[0071] Step 3: Load the mixture obtained in Step 2 into a covered ceramic boat and place it in an oxygen-filled tube furnace for segmented heat treatment under an oxygen atmosphere. The heating rate is set to 3℃ / min and the cooling rate is set to 5℃ / min. The heat treatment procedure is as follows: First stage: heat up to 120℃ and hold for 1 hour; Second stage: continue to heat up to 330℃ and hold for 1 hour; Third stage: continue to heat up to 400℃ and hold for 30 minutes.

[0072] Step 4: Cool to 100℃, collect the material, and grind it for later use.

[0073] Comparative Example 2:

[0074] A method for preparing a positive electrode includes the following steps:

[0075] Step 1: Weigh boric acid (H3BO3) and lithium tetrafluoroborate (LiBF4), and use 10g LiNi 0.8 Co 0.1 Mn 0.1For O2 cathode powder, take 0.1g LiBF4 and 0.05g H3BO3. Add the above two raw materials to a ball mill jar and dry ball mill for 90min to obtain a coated precursor mixture; adjust the ball milling conditions so that the D50 of the obtained coated precursor mixture is 0.2-10μm.

[0076] Step 2: Mix the coated precursor mixture obtained in Step 1 with LiNi 0.8 Co 0.1 Mn 0.1 The O2 cathode powder was dry-mixed for 60 minutes to obtain the mixture to be treated.

[0077] Step 3: Load the mixture obtained in Step 2 into a covered ceramic boat and place it in an oxygen-filled tube furnace for segmented heat treatment under an oxygen atmosphere. The heating rate is set to 3℃ / min and the cooling rate is set to 5℃ / min. The heat treatment procedure is as follows: First stage: heat up to 120℃ and hold for 1 hour; Second stage: continue to heat up to 330℃ and hold for 1 hour; Third stage: continue to heat up to 400℃ and hold for 30 minutes.

[0078] Step 4: Cool to 100℃, collect the material, and grind it for later use.

[0079] Comparative Example 3:

[0080] A method for preparing a positive electrode includes the following steps:

[0081] Step 1: Weigh boric acid (H3BO3), lithium tetrafluoroborate (LiBF4), and cobalt tetrafluoroborate (Co(BF4)2), and use 10g LiNi 0.8 Co 0.1 Mn 0.1 O2 cathode powder, take 0.1g LiBF4, 0.05g H3BO3, and 0.01g Co(BF4)2.

[0082] Step 2: Combine all the precursors obtained in Step 1 with LiNi 0.8 Co 0.1 Mn 0.1 The O2 cathode powder was dry-mixed for 30 minutes to obtain the mixture to be treated.

[0083] Step 3: Load the mixture obtained in Step 2 into a covered ceramic boat and place it in an oxygen-filled tube furnace for segmented heat treatment under an oxygen atmosphere. The heating rate is set to 3℃ / min and the cooling rate is set to 5℃ / min. The heat treatment procedure is as follows: First stage: heat up to 120℃ and hold for 1 hour; Second stage: continue to heat up to 330℃ and hold for 1 hour; Third stage: continue to heat up to 400℃ and hold for 30 minutes.

[0084] Step 4: Cool to 100℃, collect the material, and grind it for later use.

[0085] Comparative Example 4:

[0086] Step 1: Weigh boric acid (H3BO3), lithium tetrafluoroborate (LiBF4), and cobalt tetrafluoroborate (Co(BF4)2), and use 10g LiNi 0.8 Co 0.1 Mn 0.1 For O2 cathode powder, take 0.1g LiBF4, 0.05g H3BO3, and 0.01g Co(BF4)2. Add the above three raw materials to a ball mill jar and dry ball mill for 90 minutes to obtain a coated precursor mixture; adjust the ball milling conditions to make the D50 of the obtained coated precursor mixture 0.2-10μm.

[0087] Step 2: Mix the coated precursor mixture obtained in Step 1 with LiNi 0.8 Co 0.1 Mn 0.1 The O2 cathode powder was dry-mixed for 30 minutes to obtain the mixture to be treated.

[0088] Step 3: Load the mixture obtained in Step 2 into a covered ceramic boat and place it in an oxygen-filled tube furnace for segmented heat treatment in an oxygen atmosphere; set the heating rate to 3℃ / min and the cooling rate to 5℃ / min, and the heat treatment procedure is as follows: heat to 400℃ and hold for 30min.

[0089] Step 4: Cool to 100℃, collect the material, and grind it for later use.

[0090] Comparative Example 5:

[0091] A method for preparing a positive electrode includes the following steps:

[0092] Step 1: Weigh boric acid (H3BO3), lithium tetrafluoroborate (LiBF4), and cobalt tetrafluoroborate (Co(BF4)2), and use 10g LiNi 0.8 Co 0.1 Mn 0.1 For O2 cathode powder, take 0.1g LiBF4, 0.05g H3BO3, and 0.01g Co(BF4)2. Add the above three raw materials to a ball mill jar and dry ball mill for 90 minutes to obtain a coated precursor mixture; adjust the ball milling conditions to make the D50 of the obtained coated precursor mixture 0.2-10μm.

[0093] Step 2: Mix the coated precursor mixture obtained in Step 1 with LiNi 0.8 Co 0.1 Mn 0.1The O2 cathode powder was dry-mixed for 30 minutes to obtain the mixture to be treated.

[0094] Step 3: Load the mixture obtained in Step 2 into a ceramic boat and place it in an oxygen-filled tube furnace for segmented heat treatment under an oxygen atmosphere. The heating rate is set to 3℃ / min and the cooling rate is set to 5℃ / min. The heat treatment procedure is as follows: First stage: heat up to 120℃ and hold for 1 hour; Second stage: continue to heat up to 330℃ and hold for 1 hour; Third stage: continue to heat up to 400℃ and hold for 30 minutes.

[0095] Step 4: Cool to 100℃, collect the material, and grind it for later use.

[0096] The cathode materials obtained in Examples 1-3 and Comparative Examples 1-5, and uncoated commercial LiNi were processed using the following method. 0.8 Co 0.1 Mn 0.1 O2 (NCM) is assembled into a battery.

[0097] PEEK cell mold batteries were assembled in a glove box filled with argon atmosphere and containing less than 0.1 ppm of water and oxygen. First, the positive electrode composite layer was prepared. The positive electrode material, Li6PS5Cl sulfide solid electrolyte powder, and VGCF were thoroughly mixed in a mortar at a mass ratio of 90:9:1. 70 mg of Li6PS5Cl powder was evenly spread on a designated area of ​​the PEEK cell mold. A tablet press was started, applying a pressure of 4 tons and holding for 30 seconds to press into a dense electrolyte sheet. On one side of the pressed Li6PS5Cl electrolyte sheet, 10 mg of the positive electrode composite layer material was evenly spread, ensuring the material coverage area matched the electrolyte sheet. Then, a tablet press was used to apply a pressure of 3 tons to tightly press the positive electrode composite layer material and the electrolyte sheet together. Indium foil was punched into a circle with a diameter of 10 mm, and lithium foil was punched into a circle with a diameter of 4 mm. A circular indium foil of mm diameter is first laid flat on the other side of the unpressed positive electrode of the Li6PS5Cl electrolyte sheet. Then, a circular lithium foil is placed in the center of the indium foil, ensuring that the lithium foil is aligned with the indium foil and the electrolyte sheet. A pressure of 1 t is applied to the overall structure inside the mold, and the layers are pressed and held for a period of time to ensure tight adhesion. After standing for 8 hours, cyclic tests are performed at a voltage of 2.18-3.68V (LiIn as the reference electrode) and a test temperature of 30℃, with current densities of 0.1 C and 1 C, respectively.

[0098] Table 1. Electrochemical performance data of batteries assembled from the cathode materials prepared in Examples 1-3 and Comparative Examples 1-5.

[0099]

[0100] Based on the data in Table 1, the inventors concluded that the high-nickel cathode material prepared by the surface modification method of this invention, when used in a sulfide solid electrolyte all-solid-state battery, can significantly improve the cycle stability and capacity retention of the battery at different rates. The capacity decay during cycling is effectively suppressed, demonstrating more reliable interface stability and more continuous lithium-ion transport. This indicates that the composite interface modification layer constructed by this invention can effectively reduce the side reactions and interface impedance growth at the sulfide electrolyte / high-nickel cathode interface, thereby enabling the battery to obtain better long-term cycle performance and rate adaptability.

[0101] The above-described embodiments are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope of the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-nickel layered oxide positive electrode active material for a sulfide solid electrolyte system, characterized in that, The process includes the following steps: Step 1, refining boric acid, lithium tetrafluoroborate, and cobalt tetrafluoroborate to form a coating precursor mixture, thereby improving the ability to form a continuous coating on the surface of the cathode particles; Step 2, mixing the coating precursor mixture obtained in Step 1 with high-nickel layered oxide cathode powder, so that the coating precursor forms a continuously distributed precursor coating on the surface of the cathode particles, obtaining the mixture to be processed; wherein the high-nickel layered oxide is LiNi. x Co y Mn 1-x-y O2 and x≥0.8; Step 3, the mixture to be treated obtained in Step 2 is subjected to segmented heat treatment in an oxygen atmosphere, so that lithium tetrafluoroborate melts in the medium temperature zone and wets and spreads on the surface of the positive electrode particles to form a continuous precursor film, and in the higher temperature zone, boric acid dehydration and interface rearrangement are promoted, and an amorphous or glassy phase continuous coating layer containing Li-BOF components is formed on the surface of the positive electrode particles with the participation of fluorine-containing active species; Step 4, the material after heat treatment in Step 3 is cooled to obtain the modified positive electrode active material; wherein cobalt tetrafluoroborate is used as a Co source, so that Co forms a Co-enriched surface modification / reconstruction region on the surface of the positive electrode particles and / or is distributed in the coating layer during the heat treatment process.

2. The method according to claim 1, characterized in that, The refining process described in step 1 includes one or more of dry grinding and ball milling.

3. The method according to claim 1 or 2, characterized in that, The refining process described in step 1 reduces the D50 particle size of the coated precursor mixture to 0.2-10 μm.

4. The method according to any one of claims 1-3, characterized in that, The mixing in step 2 is a dry mixing process, and the mixing time is 10-120 min.

5. The method according to any one of claims 1-4, characterized in that, Based on the mass of the cathode powder, the amount of lithium tetrafluoroborate added is 0.5-1.5 wt%, the amount of boric acid added is 0.2-1.0 wt%, and the amount of cobalt tetrafluoroborate added is 0.02-0.1 wt% based on the elemental Co.

6. The method according to any one of claims 1-5, characterized in that, Step 3 describes the segmented heat treatment, which includes: a first stage of holding at 100-150℃ for 0.5-3 hours; a second stage of holding at 300-360℃ for 0.25-2 hours; and a third stage of holding at 360-450℃ for 5-120 minutes.

7. The method according to claim 6, characterized in that, The heating rate of the segmented heat treatment in step 3 is 1-10℃ / min, and the cooling rate is 1-10℃ / min.

8. The method according to any one of claims 1-7, characterized in that, The heat treatment described in step 3 is carried out in a covered or semi-closed container to suppress component drift caused by the volatilization of fluorine-containing boron species and to promote the formation of a continuous coating layer.

9. A high-nickel layered oxide positive electrode active material for sulfide solid electrolyte systems, characterized in that, The positive electrode active material is LiNi. x Co y Mn 1-x-y O2 and x≥0.8; its particle surface has a continuous coating layer, the coating layer containing an amorphous or glassy phase of Li-BOF component; and the particle surface has a Co-enriched surface modification / reconstruction region, the Co-enriched region being located inside the coating layer or overlapping with the coating layer.

10. An all-solid-state battery, comprising a sulfide solid electrolyte and a positive electrode, characterized in that, The positive electrode comprises the positive electrode active material as described in claim 9, and the sulfide solid electrolyte is selected from one or more of Li6PS5Cl sulfide solid electrolyte and LGPS sulfide solid electrolyte.

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