A mixed coating coated nickel-rich layered oxide positive electrode and its application

Abstract

The present invention belongs to the technical field of the preparation of battery cathodes, and particularly relates to a mixed - coated nickel - rich layered oxide cathode and its application. The mixed - coated nickel - rich layered oxide cathode is a cathode material of the NCM system, in which the proportion of Ni material in the NCM ternary system is ≥92 wt%; the proportion of Ni in the mixed - coated nickel - rich layered oxide cathode in the three elements of Ni, Co, and Mn is ≥92 mol%; the mixed - coated nickel - rich layered oxide cathode is coated with Li3PO4 and / or Li3BO3 and / or LiNbO3. The cathode material provided by the present invention can effectively reduce the space - charge layer effect and interfacial side reactions between the cathode and the electrolyte, has a high lithium - ion migration efficiency, and the battery has good cycle performance after assembly.

Description

Technical Field

[0001] The invention belongs to the technical field of battery positive electrode preparation, and specifically relates to a nickel-rich layered oxide positive electrode coated with a mixed coating, and a preparation method and application thereof. Background Art

[0002] The demand for energy storage devices is growing, among which high energy density cathode materials have become a research focus. However, the capacity of traditional cathodes such as lithium iron phosphate is not enough to support the current high energy density demand. To solve this problem, researchers applied high-capacity nickel-rich layered oxide cathodes to sulfide all-solid-state batteries to achieve a breakthrough in higher energy density.

[0003] The nickel-rich layered oxide positive electrodes are mainly NCM811, NCM622, and NCM523. Since nickel ions and lithium ions are easily mixed due to their similar ion radius, nickel-rich electrodes are easily corroded by electrolyte side reactions during cycling and produce microcracks. Therefore, although NCM811 with a high nickel content has a high theoretical capacity (275 mAh g -1 ), but because of the problems between itself and the sulfide solid electrolyte, such as poor interface contact, many interface side reactions and space charge layer effect, its stability is relatively poor, so its actual capacity tends to decrease significantly.

[0004] Although NCM622 and NCM523 have good cycle stability and safety, their theoretical capacity is lower than that of NCM811. The positive electrode materials of NCM622 and NCM523 of the same quality cannot provide more capacity, and the energy density of the assembled energy storage device is insufficient. Among them, it can be seen that the nickel-rich layered oxide positive electrode with high nickel content has a good research prospect.

[0005] In this field, battery modification is carried out by means of doping, core-shell structure construction and surface coating. However, doping will cause the material to lose discharge capacity; the current process cost of the core-shell structure is too high and it is not yet mature. The surface coating can form a protective layer on the surface of the positive electrode material, effectively isolating the direct contact between the positive electrode and the sulfide electrolyte, and reducing the occurrence of harmful side reactions. At the same time, the surface coating can also effectively improve the transmission efficiency of lithium ions, which has a significant improvement in kinetic performance.

[0006] In summary, the current high-capacity nickel-rich layered oxide cathode still cannot withstand long-term cycling, has a short service life, and the highly stable nickel-rich layered oxide cathode does not meet people's demand for high-density energy storage devices. In addition, in order to achieve cost reduction and efficiency improvement, the cathode synthesis process under the ultra-high nickel content system needs to be optimized.

[0007] For example, the prior art CN115954451A discloses a core-shell structure NCM ternary positive electrode material and its application in sulfide solid-state batteries. The material is a LiNi shell with a microporous structure. a Co b Mn 1-a-b O2 material, whose Ni content can reach 80-98%, but although it constructs a core-shell structure to optimize the cycle performance of the high-nickel NCM ternary positive electrode system, it still shows a low capacity, and the performance still needs to be improved. Similarly, CN114824174B also discloses a high-nickel NCM ternary positive electrode material and its preparation method, and its application in sulfide solid-state batteries, which forms an electrolyte concentration gradient by constructing a bipolar sheet system, thereby improving the transmission process of lithium ions, thereby improving its cycle performance, but it still cannot avoid the defect of showing a low specific capacity. It can be seen that with regard to many current technical solutions, it is still difficult to solve the problem of low specific capacity of high-nickel NCM ternary positive electrode materials. Summary of the invention

[0008] Based on the above content, in order to solve the problems of poor cycle stability of battery positive electrode, high preparation process cost and complex preparation process operation, the present invention proposes a mixed coating coated nickel-rich layered oxide positive electrode and its preparation method and application.

[0009] The purpose of the present invention is: 1. To improve the interface problem between the mixed coating-coated nickel-rich layered oxide positive electrode and the sulfide solid electrolyte.

[0010] 2. Enhance the positive electrode cycle stability.

[0011] To achieve the above objectives, the present invention adopts the following technical solutions.

[0012] A hybrid coating is coated on a nickel-rich layered oxide cathode.

[0013] The mixed coating-coated nickel-rich layered oxide positive electrode is a positive electrode material of an NCM system, and the proportion of Ni material in the NCM ternary system is ≥92 wt%.

[0014] The content of Ni in the mixed coating-coated nickel-rich layered oxide positive electrode is ≥92 mol% among the three elements of Ni, Co and Mn.

[0015] The mixed coating-coated nickel-rich layered oxide positive electrode is coated with Li3PO4 and / or Li3BO3 and / or LiNbO3.

[0016] Preferably, the mixed coating-coated nickel-rich layered oxide positive electrode contains 92-95 mol% of Ni material.

[0017] Application of a mixed coating coated nickel-rich layered oxide positive electrode.

[0018] The hybrid coating is used to coat a nickel-rich layered oxide positive electrode for a sulfide all-solid-state battery.

[0019] Commercial lithium-ion batteries mostly use organic electrolytes to transfer lithium ions, which have a high risk of spontaneous combustion. However, there are many interfacial side reactions between the mixed coating-coated nickel-rich layered oxide positive electrode and the commonly used sulfide solid electrolyte, and the electrochemical performance and chemical stability of the assembled battery are poor.

[0020] Compared with the prior art, the present invention increases the nickel content to a rare 92-95 mol%. The nickel-rich positive electrode exhibits good lithium ion diffusivity and high temperature stability. Generally speaking, positive electrode materials with high nickel content have poor stability and their capacity decays rapidly. However, due to the synergistic effect of the substrate components and coating agents on the grains in the present invention, the degree of lithium-nickel mixing is reduced, which significantly enhances the structural stability of the positive electrode material, thereby improving its cycle stability.

[0021] The beneficial effects of the present invention are as follows: (1) The cathode preparation method provided by the present invention can effectively reduce the space charge layer effect and interface side reactions between the cathode and the electrolyte.

[0022] (2) The positive electrode material prepared by the present invention has high lithium ion migration efficiency and good battery cycle performance after assembly.

[0023] (3) The positive electrode material of the present invention is more suitable for sulfide all-solid-state batteries, and the improvement effect is very obvious.

[0024] (4) The positive electrode material prepared by the present invention has high mechanical strength and can effectively alleviate the stress-strain effect generated by the positive electrode during long-term cycling.

[0025] (5) The preparation process of the present invention is simple, requires less raw materials and has low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 These are scanning electron microscope (SEM) images of the positive electrode materials of Examples 1 to 4.

[0027] Figure 2 The 1 C 150 cycle performance curves of the sulfide all-solid-state batteries respectively assembled from the positive electrode materials of Examples 1 to 4 at 55°C.

[0028] Figure 3 0.1 C charge and discharge curves of sulfide all-solid-state batteries assembled from the positive electrode materials of Examples 1 to 4 at 55°C.

[0029] Figure 4The 0.1-10 C rate performance curves of the sulfide all-solid-state batteries respectively assembled from the positive electrode materials of Examples 1-4 at 55°C.

[0030] Figure 5 The sulfide all-solid-state batteries assembled from the cathode materials with different loading amounts in Example 5 were tested at 55°C at 1 C (1.52 mA·cm -2 ) 300-cycle performance curve.

[0031] Figure 6 The sulfide all-solid-state batteries assembled from the cathode materials with different loading amounts in Example 5 were tested at 55°C and 2.03 mA·cm 2 The 0.1~10 C rate performance curve is shown below.

[0032] Figure 7 The sulfide all-solid-state batteries assembled from the cathode materials with different loading amounts in Example 5 were tested at 33°C and 1.52 mA·cm 2 The 0.1~10 C rate performance curve is shown below.

[0033] Figure 8 The sulfide all-solid-state batteries assembled from the cathode materials with different loading amounts in Example 5 were tested at 33°C and 1.52 mA·cm 2 Below is the 1 C 250 cycle performance curve.

[0034] Fig. 9 This is the first cycle charge and discharge curve of a 0.1 C liquid button battery.

[0035] Fig.10 This is the 50-cycle performance curve of a 0.1 C liquid button battery. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below in conjunction with specific embodiments and the accompanying drawings. A person of ordinary skill in the art will be able to implement the present invention based on these descriptions. In addition, the embodiments of the present invention involved in the following description are generally only embodiments of a part of the present invention, rather than all embodiments. Therefore, based on the embodiments of the present invention, all other embodiments obtained by a person of ordinary skill in the art without making creative work should fall within the scope of protection of the present invention.

[0037] Unless otherwise specified, the raw materials used in the examples of the present invention are all commercially available or available to those skilled in the art; unless otherwise specified, the methods used in the examples of the present invention are all methods known to those skilled in the art.

[0038] Unless otherwise specified, the CAS number of LiOH·H2O used in the examples of the present invention is 1310-66-3.

[0039] Example 1: A method for preparing a mixed coating-coated nickel-rich layered oxide positive electrode, the method comprising: taking 100 g of precursor Ni 0.92 Co 0.06 Mn 0.02 (OH)2 and 47.5 g LiOH·H2O were mixed evenly, and the mixed material was placed in a tube furnace, heated to 700 °C in an oxygen atmosphere and kept warm for 10 h, and then crushed into powder to obtain SC-NCM92 positive electrode material.

[0040] Example 2: A method for preparing a mixed coating-coated nickel-rich layered oxide positive electrode, the method comprising: 1) taking 100 g of precursor Ni 0.92 Co 0.06 Mn 0.02 (OH)2 and 47.5 g LiOH·H2O were mixed evenly, and the mixed material was placed in a tube furnace, heated to 700 °C in an oxygen atmosphere and kept warm for 10 h, and then crushed into powder to obtain the SC-NCM92 positive electrode substrate.

[0041] 2) According to the total mass of SC-NCM92 positive electrode substrate, 0.2 wt% Li3PO4 and 0.3 wt% Li3BO3 were added and mixed evenly. The mixture was placed in a coating machine and the speed was set to 4000 rpm. The coating was performed for 15 min. Under an oxygen atmosphere, the mixed material was placed in a tube furnace, heated to 350 °C and kept warm for 10 h to obtain SC-NCM92@LPO+LBO positive electrode material (the abbreviation of the positive electrode material prepared by SC-NCM92 substrate loaded with Li3PO4 and Li3BO3).

[0042] Example 3: A method for preparing a mixed coating-coated nickel-rich layered oxide positive electrode, the method comprising: 1) taking 100 g of precursor Ni 0.92 Co 0.06 Mn 0.02 (OH)2 and 47.5 g LiOH·H2O were mixed evenly, and the mixed material was placed in a tube furnace, heated to 700 °C in an oxygen atmosphere and kept warm for 10 h, and then crushed into powder to obtain the SC-NCM92 positive electrode substrate.

[0043] 2) According to the total mass of the SC-NCM92 positive electrode substrate, 0.2 wt% Li3NbO4 and 0.3 wt% Li3BO3 were added and mixed evenly. The mixture was placed in a coating machine and the speed was set to 4000 rpm. The coating was performed for 15 min. Under an oxygen atmosphere, the mixed material was placed in a tube furnace, heated to 350 °C and kept warm for 10 h to obtain the SC-NCM92@LNO+LBO positive electrode material (the abbreviation of the positive electrode material prepared by loading LiNbO3 and Li3BO3 on the SC-NCM92 substrate).

[0044] Example 4: A method for preparing a mixed coating-coated nickel-rich layered oxide positive electrode, the method comprising: 1) taking 100 g of precursor Ni 0.92 Co 0.06 Mn 0.02 (OH)2 and 47.5 g LiOH·H2O were mixed evenly, and the mixed material was placed in a tube furnace, heated to 700 °C in an oxygen atmosphere and kept warm for 10 h, and then crushed into powder to obtain the SC-NCM95 positive electrode substrate.

[0045] 2) According to the total mass of the SC-NCM95 positive electrode substrate, 0.2 wt% Li3PO4 and 0.3 wt% Li3BO3 were added and mixed evenly. The mixture was placed in a coating machine with a speed set to 4000 rpm and coated for 15 min. Under an oxygen atmosphere, the mixed material was placed in a tube furnace, heated to 350 °C and kept warm for 10 h to obtain the SC-NCM95@LPO+LBO positive electrode material.

[0046] The positive electrode materials prepared in Examples 1 to 4 were subjected to ICP characterization, and the characterization results are shown in the following table.

[0047]

[0048] In the table: the percentages (%) of Ni, Co and Mn are molar percentages (mol%).

[0049] The characterization results show that the mixed coating coated nickel-rich layered oxide positive electrode material product prepared by the present invention retains an extremely high nickel content, wherein the Ni content in the sample SC-NCM92@LPO+LBO prepared in Example 2 and the sample SC-NCM92@LNO+LBO prepared in Example 3 are basically equivalent to the sample SC-NCM92 in Example 1, which shows that the coating material of the present invention does not cause the loss of nickel, cobalt and manganese components. However, from the characterization results of the sample SC-NCM95@LPO+LBO prepared in Example 4, the amount of raw material nickel increased but the nickel content of the product decreased, while the cobalt content and manganese content remained relatively high, which shows that when the raw material nickel content is too high, during the mixing process and the coating process, some high-nickel phases fall off and are not effectively coated, resulting in a decrease in nickel content. However, compared with conventional NCM811 systems or NCM622 and other ternary positive electrode systems, it also has a higher retained nickel content.

[0050] The positive electrode materials prepared in Examples 1 to 4 were characterized by electron microscopy.

[0051] like Figure 1 As shown, scanning electron microscope (SEM) images of SC-NCM92, SC-NCM92@LPO+LBO, SC-NCM92@LNO+LBO and SC-NCM95@LPO+LBO are shown. According to the picture, the SC-NCM92 positive electrode material has obvious agglomeration phenomenon and small particles are accumulated; the size of the SC-NCM92@LNO+LBO positive electrode material becomes smaller and the morphology is more wrinkled. Comparing the results of Example 2 and Example 4, it is found that with the increase of nickel content, the size of the positive electrode material becomes smaller, the agglomerated particles are peeled off from the large spherical particles, and the active specific surface area increases.

[0052] According to research, under certain charging and discharging conditions, squeezing between large grains (grain diameter exceeds 100 nm) will cause voltage hysteresis, especially when the grain diameter exceeds 200 nm, the voltage hysteresis is particularly significant, and there are diffusion-induced stress and surface effects between nano-scale grains (grain radius is less than 100 nm), resulting in material energy loss. The size of the positive electrode material prepared by the present invention reaches about 2 μm. In theory, a small size can alleviate voltage hysteresis. Usually, the particle size of the positive electrode material is controlled at about 100 nm, but this will also lead to a decrease in its capacity. The present invention reduces oxygen loss and inhibits the migration of transition metals by constructing a protective layer on the surface, thereby slowing down voltage hysteresis. Therefore, on the basis of effectively maintaining the capacity of the positive electrode material, the voltage hysteresis phenomenon is further inhibited, so that the positive electrode material also shows good cycle stability.

[0053] Li2S, P2S5 and LiCl were mixed in a molar ratio of 5:1:2 and the speed was set to 600 rpm. Ball milling for 12 h. In an argon atmosphere, the temperature was raised to 550 °C and sintered for 12 h at a heating rate of 5 °C / min. Li6PS5Cl solid electrolyte was obtained by crushing. Then the positive electrode material prepared in this example, Li6PS5Cl and VGCF were mixed evenly in a mass ratio of 60:37:3. 80 mgLi6PS5Cl electrolyte was pressed into a disc with a diameter of 10 mm under a pressure of 124 MPa (1 t). 10 mg of composite positive electrode was placed on one side of SE and pressed at a pressure of 870 MPa (7 t) for 2 min to make the two fit tightly. A 10 mm indium sheet was placed on the other side of SE, and then a 5 mm lithium sheet was attached. It was pressed into a Li-In alloy under a pressure of 124 MPa to assemble a sulfide all-solid-state battery.

[0054] The all-solid-state battery was charged and discharged using a NEWARE BTS610 charge and discharge test machine to characterize its charge and discharge capacity at 0.1 C. The cyclic charge and discharge test was then carried out at a constant current density, with an ambient temperature of 55 °C and a voltage range of 2.1 to 3.7 V. The cathode materials prepared under the same conditions were charged and discharged for 150 cycles at 1.0 C, and the cycle retention rate of the battery capacity was recorded.

[0055] The cyclic charge and discharge test was carried out under constant current density. The test environment temperature was 55 °C and the test voltage range was 2.1-3.7 V. The positive electrode materials prepared under the same conditions were first charged and discharged at 1.0 C for 28 cycles and then at 0.1 C for 28 cycles. The cycle retention rate of the 1 / 0.1C battery capacity was recorded.

[0056] The results are as follows.

[0057]

[0058] According to the results in the table, it can be seen that after adding the coating agent to the substrate, the capacity decay trend of the positive electrode material becomes smaller. After adding the coating agent, during the charge and discharge cycle, the positive electrode material will not quickly release oxygen from the layered structure to the spinel structure and the rock salt structure with no electrochemical activity, resulting in material collapse and irreversible capacity decay. At the same time, the interface side reactions are reduced and the interface problems are improved.

[0059] During the calcination process, the coating agent elements diffuse into the substrate grains, uniformly coat the grains, combine with the oxygen on the surface of the positive electrode material, and reduce the electron migration rate between the electrode material and the electrolyte interface. 2-After being consumed, the charge imbalance drives some trivalent nickel ions to be reduced to divalent nickel ions, reducing the distortion rate of the molecular ensemble with a spatially degenerate electronic ground state; at the same time, some divalent nickel ions migrate into the layered structure, playing a good supporting role, enhancing the structural stability of the positive electrode material, and facilitating the deintercalation and extraction of lithium ions, so that the positive electrode material exhibits good performance.

[0060]

[0061] According to the results in the tables of Example 2 and Example 3, combined with Figure 2 It can be seen that although LiNbO3 can regulate the interface, promote the diffusion of lithium ions, effectively inhibit the mixing of lithium ions and nickel ions, and reduce the lattice changes caused by lithium ion deintercalation, since the bond energy and stability of LiNbO3 are weaker than Li3PO4, the capacity decline trend of the positive electrode material modified with LiNbO3 and Li3BO3 composite coating agents after cycling is greater than that of the positive electrode material modified with Li3PO4 and Li3BO3 composite coating agents, and the attenuation trend of the positive electrode material has not been significantly improved.

[0062]

[0063] Example 4 The coating agent loading on the positive electrode material is 7.6 mg cm -2 According to the results in the tables of Example 2 and Example 4, combined with Figure 2 , Figure 3 It can be seen that the capacity of the positive electrode material with high nickel content increases, and its capacity decay trend is small. The charge and discharge rate of SC-NCM95@LPO+LBO with high nickel content is faster.

[0064] Based on the above tests, the all-solid-state battery was charged and discharged using a NEWARE BTS610 charge and discharge test machine. The test environment temperature was 55 °C, the test voltage range was 2.1-3.7 V, and the assembled all-solid-state battery was placed at 0.1 C, 0.2 C, 0.5 C, 1.0 C, 2.0 C, 5.0 C, and 10.0 C for rate performance testing. The results are as follows: Figure 4 As shown in the figure, combined with the above characterization results, it can be clearly seen that the capacity of the unmodified SC-NCM92 is prone to a "cliff-like" drop, while the cycle performance of the modified material is improved. In all-solid-state batteries, the advantages of the coating are further magnified, and the electrochemical performance of the modified positive electrode material is significantly improved. The all-solid-state battery assembled using SC-NCM92@LPO+LBO has a capacity of 220.5 mAh·g -1 The high discharge capacity and excellent rate performance of SC-NCM95@LPO+LBO with high nickel content (95 wt%) reached a discharge capacity of 253.3 mAh·g -1, while also having excellent rate performance (137.9 mAh g -1 , 10 C) and cycle stability. The surface modification method provided by the present invention can improve the layered structure, reduce lattice distortion, promote the diffusion of lithium ions in the material, and improve the charge and discharge rate and cycle stability of the battery.

[0065] Example 5: Based on Example 4, only the step 1) of "add 0.2 wt% Li3PO4 and 0.3 wt% Li3BO3 according to the total mass of the SC-NCM92 positive electrode substrate and mix evenly" is changed to "add 0.1 wt% Li3PO4 and 0.1 wt% Li3BO3 according to the total mass of the SC-NCM92 positive electrode substrate and mix evenly" to obtain SC-NCM92@LPO+LBO positive electrode material-A.

[0066] Based on Example 4, only the step 1) "add 0.2 wt% Li3PO4 and 0.3 wt% Li3BO3 according to the total mass of the SC-NCM92 positive electrode substrate and mix evenly" was changed to "add 0.2 wt% Li3PO4 and 0.4wt% Li3BO3 according to the total mass of the SC-NCM92 positive electrode substrate and mix evenly" to obtain SC-NCM92@LPO+LBO positive electrode material-B.

[0067] The SC-NCM92@LPO+LBO cathode material-A and SC-NCM92@LPO+LBO cathode material-B were characterized by using a NEWARE BTS610 charge and discharge test machine to perform charge and discharge tests on the above-mentioned all-solid-state battery, characterizing its charge and discharge capacity at 0.1 C, and characterizing the volume expansion rate of the cathode material at a constant current density. Then, a cyclic charge and discharge test was performed at a constant current density, the test environment temperature was 55 °C, and the test voltage range was 2.1-3.7 V. First, multiple cathode materials prepared under the same conditions were charged and discharged at 1.0 C (1.52 mA·cm 2 ) was charged and discharged for 300 cycles to characterize its battery capacity.

[0068] After testing, the coating agent loading on the positive electrode material A in this example is 3.8 mg cm -2 The coating agent loading on the positive electrode material B is 10.2 mg cm -2 .like Figure 5 As shown in the figure, the SC-NCM95 improved by LPO+LBO showed excellent performance under different loading conditions. Among them, at an appropriate amount of coating agent loading, as its loading amount increases, the positive electrode material has a smaller charge and discharge capacity, and more importantly, the attenuation trend becomes smaller, and its cycle stability becomes better; at a larger coating agent loading, the capacity of the material decreases significantly due to the difficulty of lithium ion migration.

[0069] At the same time, based on the detection in Example 4, the assembly method of "take the positive electrode material prepared in this example, Li6PS5Cl and VGCF according to the mass ratio of 60:37:3 and mix them evenly" was changed to "take the positive electrode material prepared in this example, Li6PS5Cl and VGCF according to the mass ratio of 80:37:3 and mix them evenly" to obtain SC-NCM92@LPO+LBO positive electrode material-C.

[0070] The all-solid-state battery assembled with the above SC-NCM92@LPO+LBO cathode material-C was characterized by using a NEWARE BTS610 charge and discharge tester to perform charge and discharge tests on the battery. The test environment temperature was 55 °C, the test voltage range was 2.1 to 3.7 V, and the charge and discharge voltage was 2.03 mA·cm 2 The assembled all-solid-state batteries were placed at 0.1 C, 0.2 C, 0.5 C, 1.0 C, 2.0 C, 5.0 C, and 10.0 C for rate performance testing.

[0071] like Figure 6 As shown, increasing the proportion of positive electrode material in the electrode can increase the battery charge and discharge capacity, but it does not significantly improve the cycle stability. In practical applications, it can be considered in combination with economic benefits.

[0072] The all-solid-state battery assembled with the above SC-NCM92@LPO+LBO cathode material-A was characterized by using a NEWARE BTS610 charge and discharge tester to perform charge and discharge tests on the battery. The test environment temperature was 33 °C, the test voltage range was 2.1-3.7 V, and the voltage at 1.52 mA·cm 2 The assembled all-solid-state batteries were placed at 0.1 C, 0.2 C, 0.5 C, 1.0 C, 2.0 C, 5.0 C, and 10.0 C for rate performance testing.

[0073] like Figure 7 As shown in the figure, at 33 °C, the material has good performance at 0.1-2.0 °C. It can be seen that the SC-NCM95@LPO+LBO cathode material prepared by the present invention also has excellent rate performance under the conditions of high coating agent loading and room temperature. This provides a very valuable reference for the application of ultra-high nickel layered oxide cathode in sulfide all-solid-state batteries.

[0074] The all-solid-state battery assembled with the above SC-NCM92@LPO+LBO cathode material-A was characterized by using a NEWARE BTS610 charge and discharge test machine to perform charge and discharge tests on the above all-solid-state battery. The cyclic charge and discharge tests were performed at a constant current density. The test environment temperature was 55 °C, the test voltage range was 2.1 to 3.7 V, and the test voltage was 1.52 mA cm 2 The assembled all-solid-state battery was charged and discharged at 1.0 C for 250 cycles, and the cycle retention rate of the battery capacity was recorded.

[0075] like Figure 8 As shown, it can be clearly seen that at 33 °C, the SC-NCM92@LPO+LBO cathode material has excellent cycle retention rate.

[0076] Take the positive electrode material of Example 4 and assemble it into a liquid button battery. The assembly method is: mix the positive electrode material, the conductive agent acetylene black, and the adhesive PVDF in a mass ratio of 8:1:1, add NMP reagent after grinding and mix evenly, distribute it evenly on the aluminum foil, press it into an electrode sheet after sufficient drying, place it in an argon atmosphere, use a lithium sheet as the negative electrode, a microporous polypropylene membrane as the diaphragm, and a LiPF6 solution as the electrolyte to assemble it into a liquid button battery, and seal the battery and let it stand.

[0077] The above-mentioned liquid button battery was subjected to charge and discharge tests to characterize its charge and discharge capacity at 0.1 C, and a cyclic charge and discharge test was performed at a constant current density. The test voltage range was 3.0 to 4.3 V. The liquid button battery was charged and discharged at 0.5 C for 50 cycles, and the cycle retention rate of the battery capacity was recorded.

[0078] like Fig. 9 As shown in the figure, the capacity gap under the liquid system is not obvious, and the capacity advantage of SC-NCM95@LPO+LBO is still the most obvious. Fig.10 As shown, the cycle performance gap in the liquid system is also small. This shows that the positive electrode material prepared by the present invention can be well used in all-solid-state batteries and liquid button batteries, and has good application prospects.

[0079] Comparative Example 1: A method for preparing a mixed coating-coated nickel-rich layered oxide positive electrode, the method comprising: 1) taking 100 g of precursor Ni 0.95 Co 0.04 Mn 0.01 (OH)2 and 47.5 g LiOH·H2O were mixed evenly, and the mixed material was placed in a tube furnace, heated to 700 °C in an oxygen atmosphere and kept warm for 10 h, and crushed into powder to obtain the SC-NCM92 positive electrode substrate.

[0080] 2) According to the total mass of the SC-NCM92 positive electrode substrate, 0.2 wt% Li3PO4 and 0.3 wt% Li3BO3 were added and mixed evenly. The mixture was placed in a coating machine with a speed set to 4000 rpm and coated for 15 min. Under an oxygen atmosphere, the mixed material was placed in a tube furnace, heated to 350 °C and kept warm for 10 h to obtain the SC-NCM92@LPO+LBO positive electrode material.

[0081] The SC-NCM92@LPO+LBO positive electrode material prepared in this example was assembled into an all-solid-state battery and subjected to the same performance test as in Example 4. The results are as follows.

[0082]

[0083] Compared with Example 4, this example adds twice as much Co and Mn, and the substrate is evenly distributed with individually nucleated grains, that is, the content of nickel-cobalt-manganese compounds in the positive electrode material is low, and at the same time, its grain boundaries are unclear, a large number of grains are agglomerated, the active surface area of ​​the material is small, and lithium ions are difficult to deintercalate, resulting in a significant deterioration in its performance. According to the results in the table, since cobalt and manganese compounds are easily exposed to oxidation in the air, the continuity of the components in the material is poor, and multi-level phase changes are prone to occur, such as the transformation from monoclinic phase M to rhombohedral phase H1. It can be seen from this that further increasing the amount of Co and Mn will cause the cation binding effect to deteriorate, resulting in the failure to fully form the target heterogeneous layered structure, resulting in a lower capacity of the positive electrode material, easy cracking during application, and a shorter cycle life.

[0084] Comparative Example 2: A method for preparing a nickel-rich layered oxide positive electrode, the method comprising: 1) taking 100 g of precursor Ni 0.92 Co 0.06 Mn 0.02 (OH)2 and 47.5 g LiOH·H2O were mixed evenly, and the mixed material was placed in a tube furnace, heated to 700 °C in an oxygen atmosphere and kept warm for 10 h, and then crushed into powder to obtain the SC-NCM92 positive electrode substrate.

[0085] 2) According to the total mass of SC-NCM92 positive electrode substrate, 0.5 wt% Li3PO4 was added and mixed evenly. The mixture was placed in a coating machine and the speed was set to 4000 rpm. The coating was performed for 15 min. Under an oxygen atmosphere, the mixed material was placed in a tube furnace, heated to 350°C and kept warm for 10 h to obtain SC-NCM92@LPO positive electrode material (the abbreviation of the positive electrode material prepared by SC-NCM92 substrate loaded with Li3PO4).

[0086] Comparative Example 3: A method for preparing a nickel-rich layered oxide positive electrode, the method comprising: 1) taking 100 g of precursor Ni 0.92 Co 0.06Mn 0.02 (OH)2 and 47.5 g LiOH·H2O were mixed evenly, and the mixed material was placed in a tube furnace, heated to 700 °C in an oxygen atmosphere and kept warm for 10 h, and then crushed into powder to obtain the SC-NCM92 positive electrode substrate.

[0087] 2) According to the total mass of SC-NCM92 positive electrode substrate, 0.5 wt% Li3BO3 was added and mixed evenly. The mixture was placed in a coating machine with a speed set at 4000 rpm for coating for 15 min. Under an oxygen atmosphere, the mixed material was placed in a tube furnace, heated to 350°C and kept warm for 10 h to obtain SC-NCM92@LBO positive electrode material (the abbreviation of the positive electrode material prepared by SC-NCM92 substrate loaded with Li3BO3).

[0088] Comparative Example 4: A method for preparing a nickel-rich layered oxide positive electrode, the method comprising: 1) taking 100 g of precursor Ni 0.92 Co 0.06 Mn 0.02 (OH)2 and 47.5 g LiOH·H2O were mixed evenly, and the mixed material was placed in a tube furnace, heated to 700 °C in an oxygen atmosphere and kept warm for 10 h, and then crushed into powder to obtain the SC-NCM92 positive electrode substrate.

[0089] 2) According to the total mass of the SC-NCM92 positive electrode substrate, 0.5 wt% LiNbO3 was added and mixed evenly. The mixture was placed in a coating machine and the speed was set to 4000 rpm. The coating was performed for 15 min. Under an oxygen atmosphere, the mixed material was placed in a tube furnace, heated to 350°C and kept warm for 10 h to obtain the SC-NCM92@LNO positive electrode material (the abbreviation of the positive electrode material prepared by SC-NCM92 substrate loaded with LiNbO3).

[0090] Compared with Example 2, Comparative Examples 2 to 4 all adopted single coating instead of double coating to prepare positive electrode materials, and performed the same characterization as described in Example 4. The characterization results are shown in the following table.

[0091]

[0092] Comparative Example 5: The positive electrode materials prepared in Examples 1 to 4 were used to assemble a liquid lithium-ion battery and the corresponding discharge capacity, 1 / 0.1C battery capacity cycle retention rate and 1.0 C cycle retention rate were characterized.

[0093] The liquid lithium-ion battery is a liquid button battery assembled with the positive electrode material prepared in Examples 1 to 4 directly as the positive electrode, a battery-grade lithium sheet as the negative electrode, and an electrolyte whose main component is LiPF6, and its charge and discharge electrochemical window is 3.0-4.3V.

[0094] The characterization results are shown in the following table.

[0095]

[0096] Comparing the data of this example with the data of Examples 1 to 4, it can be clearly seen that the performance of this example is superior to that of Examples 1 to 4. However, when compared with commercially available liquid lithium-ion batteries and solid batteries, it can be found that the performance improvement of this example is not significant compared to commercially available liquid lithium-ion batteries. When used in sulfide all-solid-state batteries, Examples 1 to 4 show performance far superior to that of commercially available batteries. It can be seen that the positive electrode material of the present invention has unique advantages when used in the field of sulfide all-solid-state batteries.

Claims

1. A mixed coating coated nickel-rich layered oxide positive electrode, characterized in that: The content of Ni in the mixed coating-coated nickel-rich layered oxide positive electrode is ≥ 92 mol% among the three elements of Ni, Co and Mn; The mixed coating coated nickel-rich layered oxide positive electrode is used in sulfide all-solid-state batteries; The mixed coating coated nickel-rich layered oxide positive electrode is coated with Li3PO4 and Li3BO3 or LiNbO3 and Li3BO3.

2. The mixed coating-coated nickel-rich layered oxide positive electrode according to claim 1, characterized in that: The content of Ni in the mixed coating-coated nickel-rich layered oxide positive electrode is 95 mol% among the three elements of Ni, Co and Mn; The mixed coating coated nickel-rich layered oxide positive electrode is coated with Li3PO4 and Li3BO3 or LiNbO3 and Li3BO3.

3. An application of the mixed coating coated with a nickel-rich layered oxide positive electrode as claimed in claim 1 or 2, characterized in that: The hybrid coating is used to coat a nickel-rich layered oxide positive electrode for a sulfide all-solid-state battery.

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