A nickel-cobalt-manganese ternary positive electrode material with a lithium-deficient and oxygen-deficient rock salt phase structure on the surface

Abstract

The present invention relates to a nickel-cobalt-manganese ternary positive electrode material having a lithium-deficient and oxygen-deficient rock salt phase structure on its surface, belonging to the technical field of chemical energy storage batteries. The material is prepared by adding the nickel-cobalt-manganese ternary positive electrode material to anhydrous ethanol at 50°C to 70°C, maintaining the temperature at 50°C to 70°C, and allowing the material to stand and immerse for 10 to 20 minutes; or adding the nickel-cobalt-manganese ternary positive electrode material to an anhydrous ethanol solution with a pH of 2.8 to 5.5, which is a weak acid or a medium-strong acid, and allowing the material to stand and immerse for 10 to 20 minutes; after the immersion is completed, the solid obtained by washing, filtering, separating, drying, and calcining in an inert gas atmosphere is obtained. The lithium-deficient and oxygen-deficient rock salt phase structure formed on the surface of the material can reduce surface activity, inhibit interfacial side reactions and the resulting transition metal dissolution during the cycle process, improve crystal structure stability and battery cycle stability, and greatly improve battery capacity retention. At the same time, the lithium-deficient and oxygen-deficient secondary phase structure on the surface can also inhibit the deterioration of lithium-nickel mixing and adverse phase changes during the electrochemical process, thereby improving the thermal stability of the material.

Description

Technical Field

[0001] The present invention relates to a nickel-cobalt-manganese ternary positive electrode material having a lithium-deficient and oxygen-deficient rock salt phase structure on its surface, belonging to the technical field of chemical energy storage batteries. Background Art

[0002] New energy vehicles are gradually replacing traditional fuel vehicles, and the related industries are booming. The market for power batteries, a core component, is vast. However, due to the low specific capacity of cathode materials, the energy density of power batteries remains a bottleneck hindering further performance improvements. Currently, the mainstream cathode materials for power batteries are lithium iron phosphate and nickel-cobalt-manganese ternary materials. While lithium iron phosphate offers stable performance and high safety, its low mass-specific capacity and poor rate performance make nickel-cobalt-manganese ternary materials the dominant technology for high-performance, long-range pure electric vehicles in the long term. However, nickel-cobalt-manganese ternary cathode materials suffer from poor long-term cycling stability and are prone to material degradation, leading to performance degradation. Furthermore, they also suffer from poor safety performance. High-nickel ternary cathode materials with higher nickel content are prone to oxygen release and heat release at high temperatures, posing a serious threat to battery safety. These issues have significantly limited their further commercialization.

[0003] Traditional modification processes mostly focus on means such as surface coating and bulk doping, which enhance the surface interface and structural stability of the material by introducing heterogeneous elements or structures. Although these means can effectively improve the electrochemical properties of the material, they often require complex secondary processing of the material, which is cumbersome and has poor repeatability. In addition, the modified medium may fail in the later stage, making it difficult to achieve stable discharge of multiple batches. Chinese patent application CN110054226A discloses a method for preparing a nickel-cobalt-manganese ternary positive electrode material with low surface residual alkali. The method comprises adding the nickel-cobalt-manganese ternary positive electrode material to an ethanol solution of boric acid or citric acid, stirring, rinsing, and secondary calcination in an oxygen atmosphere to obtain a nickel-cobalt-manganese ternary positive electrode material with low surface residual alkali. Although the consistency of the material has been improved to a certain extent, its electrochemical performance and stability still need to be further improved. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a nickel-cobalt-manganese ternary positive electrode material having a lithium-deficient and oxygen-deficient rock salt phase structure on its surface.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] A nickel-cobalt-manganese ternary positive electrode material having a lithium-deficient and oxygen-deficient rock salt phase structure on its surface, wherein the material is prepared by the following method, the method steps comprising:

[0007] Add the nickel-cobalt-manganese ternary positive electrode material to anhydrous ethanol at 50°C to 70°C, maintain the temperature at 50°C to 70°C, and allow to stand and soak for 10 to 20 minutes; or add the nickel-cobalt-manganese ternary positive electrode material to an anhydrous ethanol solution with a weak acid or medium-strong acid at a pH of 2.8 to 5.5, and allow to stand and soak for 10 to 20 minutes;

[0008] After the impregnation is completed, the solid obtained by washing with anhydrous ethanol, filtering and separating is dried, and then calcined under an inert gas atmosphere to obtain a nickel-cobalt-manganese ternary positive electrode material with a lithium-deficient and oxygen-deficient rock salt phase structure on the surface;

[0009] Wherein, the chemical formula of the nickel-cobalt-manganese ternary positive electrode material is LiNi x Co y Mn 1-x-y O2, 0<x<1, 0<y<1, 0<(1-xy)<1;

[0010] The calcination temperature is 480°C to 600°C, and the calcination time is 5h to 10h.

[0011] Preferably, the nickel-cobalt-manganese ternary positive electrode material is prepared by a high-temperature solid-phase reaction of a transition metal hydroxide precursor and a lithium salt.

[0012] Preferably, 0.8≤x<1.

[0013] Preferably, the weak acid or medium-strong acid is polyacrylic acid, formic acid, oleic acid or phosphoric acid.

[0014] Preferably, the pH of the anhydrous ethanol solution of the weak acid or medium-strong acid is 3-5.

[0015] Preferably, the polar solution is an anhydrous ethanol solution of phosphoric acid with a concentration of 1 g / L to 3 g / L.

[0016] Preferably, the solid-liquid ratio during static immersion is 1 g:10-20 mL.

[0017] Preferably, the calcination temperature is 500° C. to 550° C., the calcination time is 6 h to 8 h, and the heating rate is 1° C. / min to 2° C. / min.

[0018] Preferably, the surface layer has a lithium-deficient and oxygen-deficient rock salt phase structure with a thickness of 2 nm to 8 nm.

[0019] A lithium-ion battery, wherein the positive electrode material of the battery adopts the nickel-cobalt-manganese ternary positive electrode material with a lithium-deficient and oxygen-deficient rock salt phase structure on the surface as described in the present invention.

[0020] Beneficial effects

[0021] The present invention provides a nickel-cobalt-manganese ternary cathode material having a lithium-deficient and oxygen-deficient rock salt phase structure on its surface. The material is obtained by adding the nickel-cobalt-manganese ternary cathode material to anhydrous ethanol at 50°C to 70°C or a polar solution with a pH of 2.8 to 5.5, allowing the material to stand for immersion, drying, and then calcining under an inert gas atmosphere. The material's surface undergoes reconstruction, and the resulting lithium-deficient and oxygen-deficient rock salt phase structure reduces surface activity, inhibits interfacial side reactions and the resulting transition metal dissolution during cycling, improves crystal structure stability and battery cycle stability, and significantly enhances battery capacity retention. Furthermore, the lithium-deficient and oxygen-deficient secondary phase structure on the surface inhibits the deterioration of lithium-nickel mixing and adverse phase transitions during the electrochemical process, delays the temperature at which the material releases oxygen and heat, and improves the material's thermal stability.

[0022] The present invention provides a nickel-cobalt-manganese ternary positive electrode material with a lithium-deficient and oxygen-deficient rock salt phase structure on the surface. The layered structure of the nickel-cobalt-manganese ternary positive electrode material is uniformly transformed into a lithium-deficient and oxygen-deficient rock salt phase structure (secondary phase). This secondary phase evolved from the layered structure can make the bulk phase and the surface phase more closely combined, avoiding the interface stress between different phase structures during conventional doping or coating modification. Especially in the high nickel system surface Ni 3+ This interfacial stabilization effect is particularly important when the activity is significantly enhanced.

[0023] The present invention provides a nickel-cobalt-manganese ternary cathode material with a lithium-deficient and oxygen-deficient rock-salt-like structure on its surface. By controlling the impregnation and calcination conditions during the preparation process, the thickness, distribution, and chemical composition (such as the lithium content of the rock-salt-like phase) of the secondary phase can be specifically controlled. The method is simple, stable, and easily industrialized.

[0024] The present invention provides a lithium-ion battery whose positive electrode material utilizes the nickel-cobalt-manganese ternary positive electrode material described herein, which has a lithium-deficient and oxygen-deficient rock salt-like phase structure on its surface. This rock salt-like phase, rather than a pure rock salt phase, ensures unobstructed lithium ion transmission channels during the battery's charge and discharge processes, facilitates lithium ion transport across the interface, and enhances the material's rate performance. Furthermore, the secondary phase is rich in oxygen vacancies, which raises the material's oxygen release energy barrier and delays the exothermic temperature of oxygen release, thereby improving the safety of the assembled battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The X-ray diffraction (XRD) patterns of the materials described in Comparative Example 1 and Example 1 are shown.

[0026] Figure 2 This is a scanning electron microscope (SEM) image of the material described in Comparative Example 1.

[0027] Figure 3 This is the SEM image of the material described in Example 1.

[0028] Figure 4 This is a high-resolution transmission electron microscopy (HRTEM) image of the material described in Example 1.

[0029] Figure 5 This is a comparison chart of the electrochemical performance test results of the materials described in Comparative Example 1 and Example 1.

[0030] Figure 6 This is a comparison chart of the exothermic temperature and the exothermic amount in the differential scanning calorimetry (DSC) test of the materials described in Comparative Example 1 and Example 1. DETAILED DESCRIPTION

[0031] For better understanding the present invention, the present invention is described in further detail below in conjunction with specific embodiment.It should be understood that the specific embodiment described herein is only used to explain the present invention and is not intended to limit the present invention.In addition, the endpoints and any value of the scope disclosed in this article are not limited to this accurate range or value, and these ranges or values ​​should be interpreted as comprising values ​​close to these ranges or values.For numerical ranges, between the endpoint values ​​of each scope, between the endpoint values ​​of each scope and a separate point value, and between the separate point value, can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered as specifically disclosed in this article.

[0032] In the following examples or comparative examples, the material characterization and analysis methods used are as follows:

[0033] (1) X-ray diffraction (XRD) test: X-ray diffractometer, instrument model is Rigaku Ultima IV, Japan.

[0034] (2) Scanning electron microscope (SEM) test: Scanning electron microscope, instrument model is FEI Quanta, the Netherlands.

[0035] (3) High-resolution transmission electron microscopy (HRTEM) test: High-resolution transmission electron microscope, instrument model is JEOL JEM-2100, Japan.

[0036] (4) Differential scanning calorimetry (DSC) test: Differential scanning calorimeter, instrument model is DSC214Polyma, Germany.

[0037] (5) Assembly and testing of CR2025 button cells: The positive electrode material (the final product prepared in the example), acetylene black, and polyvinylidene fluoride (PVDF) were prepared into a slurry at a mass ratio of 8:1:1 and coated on aluminum foil. The dried aluminum foil loaded with the slurry was cut into small discs with a diameter of approximately 1 cm using a cutting machine for use as the positive electrode. A metal lithium sheet was used as the negative electrode, Celgard 2500 was used as the separator, and a 1M carbonate solution was used as the electrolyte (wherein the solvent was a mixed solution of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1:1:1, and the solute was LiPF6). CR2025 button cells were assembled in an argon atmosphere glove box. The charge and discharge current density was 1C = 200 mA / g, and the charge and discharge tester used was Land CT2100A, China.

[0038] Comparative Example 1

[0039] (1) According to the molar ratio of Ni:Co:Mn=8:1:1, 420.56 g, 56.22 g, and 33.804 g of nickel sulfate hexahydrate, cobalt sulfate monohydrate, and manganese sulfate heptahydrate were weighed, respectively, to prepare 1 L of a metal salt solution with a total metal ion concentration of 2 mol / L.

[0040] (2) Weigh 160 g of NaOH powder and add deionized water to prepare 1 L of 4 mol / L NaOH solution. Take 50 mL of 30% ammonia solution and add deionized water to prepare 1 L of ammonia solution.

[0041] (3) Add 1L of deionized water as the reaction base liquid to the coprecipitation reactor, and use a peristaltic pump to slowly and continuously pump the prepared metal salt solution, NaOH solution and ammonia solution into the reactor in the Ar atmosphere at a rate of 200mL / h. Control the pH of the base liquid to be 11, the temperature to be 55℃, and the stirring rate to be 600r / min. After the feeding is completed, the material is aged for 12h. After aging, the material is filtered, washed repeatedly with deionized water until neutral, and placed in an 80℃ oven to dry for 10h to obtain the precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)2. The precursor and LiOH·H2O were dispersed and mixed in anhydrous ethanol at a molar ratio of 1:1.05 until the ethanol was completely volatilized, and then transferred to a tube furnace in an O2 atmosphere. It was pre-calcined at 550℃ for 5h, then heated to 750℃ and kept warm for 15h, and then naturally cooled to room temperature to obtain a nickel-cobalt-manganese ternary positive electrode material, LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0042] Example 1

[0043] Phosphoric acid was added to anhydrous ethanol and stirred to dissolve until the pH value was stable at 3.8 to 4.1 to obtain a phosphoric acid ethanol solution. 0.8 Co 0.1 Mn 0.1 O2 powder was added to 100 mL of ethanolic phosphoric acid solution, allowed to stand and soak for 15 minutes, washed with anhydrous ethanol, filtered and separated to obtain a solid, which was then dried in an 80°C oven for 10 hours. The obtained solid powder was transferred to a tubular furnace and, under the protection of an Ar atmosphere, heated to 500°C at a heating rate of 2°C / min and calcined for 6 hours to reconstruct the surface. After the calcination, the material was naturally cooled to obtain a nickel-cobalt-manganese ternary positive electrode material with a lithium-deficient and oxygen-deficient rock salt phase structure on the surface.

[0044] The XRD test results of the materials described in Comparative Example 1 and Example 1 are as follows Figure 1 As shown in the XRD diffraction spectrum, the materials described in Comparative Example 1 and Example 1 are both typical α-NaFeO2 phases, belonging to the R-3m group. The (003) / (104) ratios are both higher than 1.2, showing a good layered structure. The difference is that the (003) peak of the material described in Example 1 in the range of θ=18-20° is shifted to a higher angle than that of the material described in Comparative Example 1, indicating that there is indeed some Li in the lithium layer of the material described in Example 1. + The crystal shrinks to a certain extent along the c-axis.

[0045] The SEM test results of the materials described in Comparative Example 1 and Example 1 are as follows Figure 2-3 As shown in the figure, it can be seen that compared with the material described in Comparative Example 1, the surface of the material described in Example 1 is smoother, and the residual alkali impurity layer attached to the surface is removed, but the particle morphology is not destroyed, and it is still a spherical secondary particle formed by the agglomeration of complete primary particles.

[0046] The HRTEM test results of the material described in Example 1 are as follows Figure 4 As shown, the results show that the surface structure of the material described in Example 1 is significantly different from the bulk structure, and the internal bulk phase presents a regular layered structure arrangement, while in the area less than 10nm from the surface, the atomic arrangement is significantly different, which is a rock salt phase close to NiO with a thickness of about 5nm.

[0047] Figure 5 Comparison of electrochemical data for button cells assembled with the materials described in Comparative Example 1 and Example 1, cycled at a 1C rate within a cutoff voltage range of 2.8-4.3V. The unmodified material in Comparative Example 1 exhibited a first-cycle 1C discharge capacity of 188.2 mAh / g, with a 50-cycle retention rate of 90.4%. The material in Example 1 exhibited a first-cycle 1C discharge capacity of 191.4 mAh / g, with a 50-cycle retention rate of 95.1%.

[0048] Figure 6 These are the DSC test results of the materials described in Comparative Example 1 and Example 1. Compared with the material described in Comparative Example 1, the exothermic temperature of the material described in Example 1 is delayed from 212°C to 248°C, and the heat release is reduced from 1462 J / g to 651 J / g. The thermal stability of the material is enhanced, which is beneficial to improving the intrinsic safety of the battery.

[0049] Example 2

[0050] Add polyacrylic acid to anhydrous ethanol and stir to dissolve until the pH value is stable at 4.8-5 to obtain polyacrylic acid ethanol solution. 0.8 Co 0.1 Mn 0.1 O2 powder was added to 100 mL of polyacrylic acid ethanol solution, and after standing and soaking for 15 minutes, the solid was washed and filtered to separate with anhydrous ethanol, and then dried in an 80°C oven for 10 hours; the obtained solid powder was transferred to a tubular furnace, and under the protection of Ar gas atmosphere, heated to 530°C at a heating rate of 2°C / min and calcined for 7 hours to reconstruct the surface. After calcination, it was naturally cooled to obtain a nickel-cobalt-manganese ternary positive electrode material with a lithium-deficient and oxygen-deficient rock salt phase structure on the surface.

[0051] XRD test results show that the material is a typical α-NaFeO2 phase, belonging to the R-3m group. The (003) / (104) ratio is higher than 1.2, showing a good layered structure. The (003) peak in the range of θ = 18-20° shifts to a high angle, indicating that there is indeed some Li in the lithium layer of the material described in this example. + The crystal shrinks to a certain extent along the c-axis.

[0052] The SEM test results show that the surface of the material is smooth, and the residual alkali impurity layer attached to the surface has been removed, but the particle morphology is not destroyed and it is still a spherical secondary particle formed by the agglomeration of complete primary particles.

[0053] HRTEM test results show that the surface structure of the material is significantly different from the bulk structure. The internal bulk phase presents a regular layered structure arrangement, while in the area less than 10nm from the surface, the atomic arrangement is significantly different, which is a rock salt phase close to NiO, with a thickness of about 8nm.

[0054] The assembled battery was cycled at a 1C rate in the cut-off voltage range of 2.8 to 4.3 V. The 1C discharge capacity in the first week was 185 mAh / g, and the cycle retention rate was 92% after 50 cycles.

[0055] The DSC test results show that the exothermic temperature of the material is 231° C. and the heat released is 1050 J / g.

[0056] Example 3

[0057] Phosphoric acid was added to anhydrous ethanol and stirred to dissolve until the pH value was stable at 3.8 to 4.1 to obtain a phosphoric acid ethanol solution. 0.8 Co 0.1 Mn 0.1 O2 powder was added to 100 mL of ethanolic phosphoric acid solution, and after standing and immersing for 20 minutes, the solid was washed and filtered to separate with anhydrous ethanol, and then dried in an 80°C oven for 10 hours; the obtained solid powder was transferred to a tubular furnace, and under the protection of Ar gas atmosphere, heated to 550°C at a heating rate of 2°C / min and calcined for 8 hours to reconstruct the surface. After the calcination, it was naturally cooled to obtain a nickel-cobalt-manganese ternary positive electrode material with a lithium-deficient and oxygen-deficient rock salt phase structure on the surface.

[0058] XRD test results show that the material is a typical α-NaFeO2 phase, belonging to the R-3m group. The (003) / (104) ratio is higher than 1.2, showing a good layered structure. The (003) peak in the range of θ = 18-20° shifts to a high angle, indicating that there is indeed some Li in the lithium layer of the material described in this example. + The crystal shrinks to a certain extent along the c-axis.

[0059] The SEM test results show that the surface of the material is smooth, and the residual alkali impurity layer attached to the surface has been removed, but the particle morphology is not destroyed and it is still a spherical secondary particle formed by the agglomeration of complete primary particles.

[0060] HRTEM test results show that the surface structure of the material is significantly different from the bulk structure. The internal bulk phase presents a regular layered structure arrangement, while in the area less than 10nm from the surface, the atomic arrangement is significantly different, which is a rock salt phase close to NiO, with a thickness of about 10nm.

[0061] The assembled battery was cycled at a 1C rate in the cut-off voltage range of 2.8 to 4.3 V. The 1C discharge capacity in the first week was 182 mAh / g, and the 50-week cycle retention rate was 93.1%.

[0062] DSC test results show that the exothermic temperature of the material is 241° C. and the heat released is 785 J / g.

[0063] Example 4

[0064] 10g of the LiNi 0.8 Co 0.1 Mn 0.1O2 powder was added to 100 mL of ethanol solution at 60°C, and the temperature was kept constant at 60°C and allowed to stand for 20 minutes. The solid was then washed and filtered with anhydrous ethanol to separate the solid, which was then dried in an oven at 80°C for 10 hours. The obtained solid powder was transferred to a tubular furnace, and under the protection of an Ar atmosphere, heated to 500°C at a heating rate of 2°C / min and calcined for 6 hours to reconstruct the surface. After the calcination, the material was naturally cooled to obtain a nickel-cobalt-manganese ternary positive electrode material with a lithium-deficient and oxygen-deficient rock salt phase structure on the surface.

[0065] XRD test results show that the material is a typical α-NaFeO2 phase, belonging to the R-3m group. The (003) / (104) ratio is higher than 1.2, showing a good layered structure. The (003) peak in the range of θ = 18-20° shifts to a high angle, indicating that there is indeed some Li in the lithium layer of the material described in this example. + The crystal shrinks to a certain extent along the c-axis.

[0066] The SEM test results show that the surface of the material is smooth, and the residual alkali impurity layer attached to the surface has been removed, but the particle morphology is not destroyed and it is still a spherical secondary particle formed by the agglomeration of complete primary particles.

[0067] HRTEM test results show that the surface structure of the material is significantly different from the bulk structure. The internal bulk phase presents a regular layered structure arrangement, while in the area less than 10nm from the surface, the atomic arrangement is significantly different, which is a rock salt phase close to NiO, with a thickness of about 2nm.

[0068] The assembled battery was cycled at a 1C rate in the cut-off voltage range of 2.8 to 4.3 V. The 1C discharge capacity in the first week was 190 mAh / g, and the cycle retention rate was 92.3% after 50 cycles.

[0069] DSC test results show that the exothermic temperature of the material is 221° C. and the heat released is 1231 J / g.

[0070] Example 5

[0071] Add formic acid to anhydrous ethanol and stir to dissolve until the pH value is stable at 2.8 to 3.3 to obtain an ethanol solution of formic acid. 0.8 Co 0.1 Mn 0.1O2 powder was added to 100 mL of formic acid ethanol solution, allowed to stand and soak for 15 minutes, washed with anhydrous ethanol, filtered and separated to obtain a solid, which was then dried in an 80°C oven for 10 hours. The obtained solid powder was transferred to a tubular furnace and, under the protection of an Ar gas atmosphere, heated to 600°C at a heating rate of 2°C / min and calcined for 10 hours to reconstruct the surface. After calcination, the material was naturally cooled to obtain a nickel-cobalt-manganese ternary positive electrode material with a lithium-deficient and oxygen-deficient rock salt phase structure on the surface.

[0072] XRD test results show that the material is a typical α-NaFeO2 phase, belonging to the R-3m group. The (003) / (104) ratio is higher than 1.2, showing a good layered structure. The (003) peak in the range of θ = 18-20° shifts to a high angle, indicating that there is indeed some Li in the lithium layer of the material described in this example. + The crystal shrinks to a certain extent along the c-axis.

[0073] The SEM test results show that the surface of the material is smooth, and the residual alkali impurity layer attached to the surface has been removed, but the particle morphology is not destroyed and it is still a spherical secondary particle formed by the agglomeration of complete primary particles.

[0074] HRTEM test results show that the surface structure of the material is significantly different from the bulk structure. The internal bulk phase presents a regular layered structure arrangement, while in the area less than 10nm from the surface, the atomic arrangement is significantly different, which is a rock salt phase close to NiO, with a thickness of about 8nm.

[0075] The assembled battery was cycled at a 1C rate in the cut-off voltage range of 2.8 to 4.3 V. The 1C discharge capacity in the first week was 189 mAh / g, and the cycle retention rate was 93.6% after 50 cycles.

[0076] DSC test results show that the exothermic temperature of the material is 235° C. and the heat release is 860 J / g.

[0077] Comparative Example 2

[0078] 10g of the LiNi 0.8 Co 0.1 Mn 0.1 O2 powder was added to 100 mL of ethanol solution at 25°C, allowed to stand and soak for 20 minutes, washed with anhydrous ethanol, filtered and separated to obtain a solid, which was then dried in an oven at 80°C for 10 hours. The obtained solid powder was transferred to a tubular furnace and heated to 450°C at a heating rate of 2°C / min under the protection of an Ar atmosphere and calcined for 5 hours. After calcination, the solution was naturally cooled to obtain a nickel-cobalt-manganese ternary positive electrode material.

[0079] XRD test results show that the material is a typical α-NaFeO2 phase, belonging to the R-3m group. The (003) / (104) ratio is higher than 1.2, showing a good layered structure; the (003) peak in the range of θ = 18-20° has no obvious angular shift, indicating that the lithium layer of the material in this comparative example has a good structure. + No obvious prolapse.

[0080] The SEM test results show that the surface of the material is smooth, and the residual alkali impurity layer attached to the surface has been removed, but the particle morphology is not destroyed and it is still a spherical secondary particle formed by the agglomeration of complete primary particles.

[0081] HRTEM test results show that the surface structure of the material is basically consistent with the bulk phase.

[0082] The assembled battery was cycled at a rate of 1C in the cutoff voltage range of 2.8 to 4.3 V. The 1C discharge capacity in the first week was 188 mAh / g, and the cycle retention rate was 90.8% after 50 weeks. The performance did not change significantly compared with the original material in Comparative Example 1.

[0083] The DSC test results show that the exothermic temperature and the exothermic heat of the material have no significant changes compared with the material described in Comparative Example 1.

[0084] Comparative Example 3

[0085] Phosphoric acid was added to anhydrous ethanol and stirred to dissolve until the pH value was stable at 3.8 to 4.1 to obtain a phosphoric acid ethanol solution. 0.8 Co 0.1 Mn 0.1 O2 powder was added to 100 mL of ethanolic phosphoric acid solution, and after standing and immersing for 40 minutes, the solid was washed and filtered to separate with anhydrous ethanol, and then dried in an 80°C oven for 10 hours; the obtained solid powder was transferred to a tubular furnace, and under the protection of Ar gas atmosphere, heated to 450°C at a heating rate of 2°C / min and calcined for 5 hours to reconstruct the surface. After the calcination, it was naturally cooled to obtain a nickel-cobalt-manganese ternary positive electrode material with a reconstructed surface.

[0086] The XRD test results show that the material is mainly α-NaFeO2 phase, but the (003) / (104) ratio is 1.15, which is lower than 1.2. The layered structure is destroyed to a certain extent. The (003) peak in the range of θ=18-20° has a significant angle shift. Due to the long immersion time, the proton exchange effect causes the Li in the lithium layer of the material to + Excessive release causes structural collapse.

[0087] The SEM test results show that the surface of the material is smooth, and the residual alkali impurity layer attached to the surface has been removed, but the particle morphology is not destroyed and it is still a spherical secondary particle formed by the agglomeration of complete primary particles.

[0088] HRTEM test results show that the surface structure of the material is destroyed and the rock salt phase is unevenly distributed.

[0089] The assembled battery was cycled at a 1C rate in the cut-off voltage range of 2.8 to 4.3 V. The 1C discharge capacity in the first week was 170 mAh / g, and the cycle retention rate was 75% after 50 cycles.

[0090] Comparative Example 4

[0091] Phosphoric acid was added to anhydrous ethanol and stirred to dissolve until the pH value was stable at 3.8 to 4.1 to obtain a phosphoric acid ethanol solution. 0.8 Co 0.1 Mn 0.1 O2 powder was added to 100 mL of ethanolic phosphoric acid solution, allowed to stand and soak for 20 minutes, washed with anhydrous ethanol, filtered and separated to obtain a solid, which was then dried in an oven at 80°C for 10 hours. The obtained solid powder was transferred to a tubular furnace and heated to 500°C at a heating rate of 2°C / min for 6 hours under the protection of an O2 atmosphere. After calcination, the material was naturally cooled to obtain a nickel-cobalt-manganese ternary positive electrode material.

[0092] XRD results indicate that the material is a typical α-NaFeO2 phase belonging to the R-3m group. The (003) / (104) ratio is greater than 1.2, indicating a well-defined layered structure. The (003) peak exhibits no significant angular shift within the θ range of 18 to 20°.

[0093] The SEM test results show that the surface of the material is smooth, and the residual alkali impurity layer attached to the surface has been removed, but the particle morphology is not destroyed and it is still a spherical secondary particle formed by the agglomeration of complete primary particles.

[0094] HRTEM test results show that the surface structure of the material is basically consistent with the bulk phase.

[0095] The assembled battery was cycled at a rate of 1C in the cut-off voltage range of 2.8 to 4.3 V. The 1C discharge capacity in the first week was 190 mAh / g, and the 50-week cycle retention rate was not significantly different from that of comparative example 1.

[0096] The DSC test results show that the exothermic temperature and the exothermic heat of the material have no significant changes compared with the material described in Comparative Example 1.

[0097] Comparative Example 5

[0098] Phosphoric acid was added to anhydrous ethanol and stirred to dissolve until the pH value was stable at 3.8 to 4.1 to obtain a phosphoric acid ethanol solution. 0.8 Co 0.1 Mn 0.1 O2 powder was added to 100 mL of ethanolic phosphoric acid solution, allowed to stand and soak for 20 minutes, washed with anhydrous ethanol, filtered and separated to obtain a solid, which was then dried in an oven at 80°C for 10 hours. The obtained solid powder was transferred to a tubular furnace and heated to 400°C at a heating rate of 2°C / min for 3 hours under the protection of an Ar atmosphere. After calcination, the material was naturally cooled to obtain a nickel-cobalt-manganese ternary positive electrode material.

[0099] XRD results indicate that the material is a typical α-NaFeO2 phase belonging to the R-3m group. However, the (003) / (104) ratio is greater than 1.2, indicating a well-defined layered structure. The (003) peak exhibits no significant angular shift within the θ range of 18 to 20°.

[0100] The SEM test results show that the surface of the material is smooth, and the residual alkali impurity layer attached to the surface has been removed, but the particle morphology is not destroyed and it is still a spherical secondary particle formed by the agglomeration of complete primary particles.

[0101] The HRTEM test results show that the surface layer of the material is still a typical layered phase, and no obvious rock salt phase structure appears.

[0102] The assembled battery was cycled at a rate of 1C in the cut-off voltage range of 2.8 to 4.3 V. The 1C discharge capacity in the first week was 185 mAh / g, and the 50-week cycle retention rate was not significantly different from that of comparative example 1.

[0103] The DSC test results show that the exothermic temperature and the exothermic heat of the material have no significant changes compared with the material described in Comparative Example 1.

[0104] In summary, the invention includes but is not limited to the above embodiments. Any equivalent replacement or partial improvement made under the spirit and principle of the present invention shall be deemed to be within the scope of protection of the present invention.

Claims

1. A nickel-cobalt-manganese ternary cathode material having a lithium-deficient and oxygen-deficient rock salt phase structure on its surface, characterized in that: The material is prepared by the following method, which comprises the following steps: The nickel-cobalt-manganese ternary positive electrode material is added to anhydrous ethanol at 50° C. to 70° C., maintained at 50° C. to 70° C., and allowed to stand and soak for 10 to 20 minutes; or the nickel-cobalt-manganese ternary positive electrode material is added to an anhydrous ethanol solution of a weak acid or a medium-strong acid with a pH of 2.8 to 5.5, and allowed to stand and soak for 10 to 20 minutes; after the impregnation, the solid is washed with anhydrous ethanol, filtered and separated, dried, and then calcined under an inert gas atmosphere to obtain a nickel-cobalt-manganese ternary positive electrode material having a lithium-deficient and oxygen-deficient rock salt phase structure on the surface. Wherein, the chemical formula of the nickel-cobalt-manganese ternary positive electrode material is LiNi x Co y Mn 1-x-y O2, 0<x<1, 0<y<1, 0<(1-xy)<1; The calcination temperature is 480℃~600℃, and the calcination time is 5h~10h; The weak acid or medium-strong acid is polyacrylic acid, formic acid, oleic acid or phosphoric acid.

2. The nickel-cobalt-manganese ternary positive electrode material having a lithium-deficient and oxygen-deficient rock salt phase structure on the surface as claimed in claim 1, characterized in that: The nickel-cobalt-manganese ternary positive electrode material is prepared by a high-temperature solid-phase reaction of a transition metal hydroxide precursor and a lithium salt.

3. The nickel-cobalt-manganese ternary positive electrode material having a lithium-deficient and oxygen-deficient rock salt phase structure on the surface as claimed in claim 1, characterized in that: 0.8≤x＜1。 4. The nickel-cobalt-manganese ternary positive electrode material having a lithium-deficient and oxygen-deficient rock salt phase structure on the surface as claimed in claim 1, characterized in that: The pH of the anhydrous ethanol solution of the weak acid or medium-strong acid is 3-5.

5. The nickel-cobalt-manganese ternary positive electrode material having a lithium-deficient and oxygen-deficient rock salt phase structure on the surface as claimed in claim 1, characterized in that: The solution is an anhydrous ethanol solution of phosphoric acid with a concentration of 1g / L~3g / L.

6. The nickel-cobalt-manganese ternary cathode material having a lithium-deficient and oxygen-deficient rock salt phase structure on the surface as claimed in claim 1, characterized in that: The solid-liquid ratio during static immersion is 1g:10~20mL.

7. The nickel-cobalt-manganese ternary cathode material having a lithium-deficient and oxygen-deficient rock salt phase structure on the surface as claimed in claim 1, characterized in that: The calcination temperature is 500°C~550°C, the calcination time is 6h~8h, and the heating rate is 1°C / min~2°C / min.

8. The nickel-cobalt-manganese ternary positive electrode material having a lithium-deficient and oxygen-deficient rock salt phase structure on the surface as claimed in claim 1, characterized in that: The surface layer has a lithium-deficient and oxygen-deficient rock salt phase structure with a thickness of 2nm to 8nm.

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