A battery positive electrode material, a preparation method and application thereof

Abstract

The application discloses a battery positive electrode material and a preparation method and application thereof. The battery positive electrode material comprises a bulk phase layer and an inert layer coated on the bulk phase layer. The bulk phase layer comprises a transition metal layered oxide material, and the inert layer comprises a transition metal oxide generated by irreversible phase change of the transition metal layered oxide material. In the preparation, the transition metal layered oxide material is first made into a positive electrode, and then assembled into a battery. The battery is activated at high voltage to generate the battery positive electrode material with a specific coating structure. Experiments show that the battery positive electrode material has high cycle stability, and the preparation process is simple and low in energy consumption. The battery positive electrode material can be directly fused into the formation process of an existing battery, and provides a feasible technical path for large-scale production and commercial application of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrochemical devices, in particular to a positive electrode material for sodium-ion batteries and lithium-ion batteries, and specifically to a battery positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] Sodium-ion batteries (SIBs) have attracted extensive attention due to their abundant resources, high cycle efficiency and significant energy conversion efficiency. These characteristics make sodium-ion batteries a beneficial supplement to lithium-ion batteries (LIBs) and suitable for low-speed vehicles and grid-scale energy storage. The positive electrode material is one of the key factors that determine the performance and cycle stability of the battery. Transition metal layered oxide positive electrodes Na x MO2 (M = Ti, V, Cr, Mn, Fe, Co, Ni) have the advantages of good safety, simple structure and easy synthesis. However, during the charge-discharge cycle of the transition metal layered oxide material, the deintercalation of Na will cause the collision and contraction of the layered structure, and further cause the collapse and phase transition of the layered structure, resulting in cycle capacity decay; at the same time, when the charge exceeds the cut-off voltage, it will severely limit the capacity performance, for example, when NaCrO2 is charged to more than 3.8V (Na 1-x CrO2, x > 0.5), NaCrO2 undergoes irreversible phase transition and Cr ion migration, resulting in poor cycle stability. In order to solve the problem of poor cycle stability, patent CN117038873A discloses a layered oxide electrode material coated with surface pitch. Although this surface pitch coating method improves the cycle stability of the material to some extent, the preparation method of the material is too complicated. SUMMARY

[0003] The purpose of the present application is to overcome one or more of the deficiencies in the prior art, and to provide an improved battery positive electrode material and a preparation method thereof, which has high cycle stability and a simple preparation process that can be directly integrated into the existing battery formation process.

[0004] The present application also provides a battery positive electrode sheet and a preparation method thereof, and a battery and a preparation method thereof. When the improved battery positive electrode material and the preparation method thereof are used, the method is simple and the cost is low, and the cycle stability of the battery can be greatly improved. In particular, the preparation process of the positive electrode material of the present application can be directly integrated into the existing battery formation process, providing a feasible technical path for large-scale production and commercial application of ion batteries.

[0005] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0006] A battery cathode material, comprising a bulk layer, an inert layer coated on the bulk layer, the bulk layer comprising a transition metal layered oxide material, the inert layer comprising a transition metal oxide generated from the transition metal layered oxide material by an irreversible phase transition.

[0007] In some embodiments of the present application, the transition metal layered oxide material in the inert layer that generates the transition metal oxide is from a surface portion of the transition metal layered oxide material in the bulk layer.

[0008] In some embodiments of the present application, the thickness of the inert layer is 1-10 nm, further 2-6 nm.

[0009] According to some specific aspects of the present application, the inert layer is a rock salt phase inert layer.

[0010] In some embodiments of the present application, the transition metal layered oxide material in the bulk layer, the transition metal layered oxide material in the inert layer are respectively unmodified, or coated and / or doped modified materials.

[0011] In some embodiments of the present application, the chemical composition of the transition metal layered oxide material is Na x MO2, M is selected from transition metals.

[0012] Further, M is selected from a combination of one or more of Ti (titanium), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni).

[0013] In some embodiments of the present application, in the inert layer, the ratio of the content of Na to M is 0.2-0.4:1; in the bulk layer, the ratio of the content of Na to M is 0.5-1:1.

[0014] According to some preferred aspects of the present application, the irreversible phase transition comprises subjecting the transition metal layered oxide material to an electrochemical transformation under voltage.

[0015] Further, the inert layer is constructed in situ by an electrochemical method.

[0016] The present application provides still another technical solution: a preparation method of the battery cathode material described above, the preparation method comprising:

[0017] subjecting a battery to voltage activation, the battery comprising a cathode comprising a transition metal layered oxide material;

[0018] after the voltage activation, generating the battery cathode material;

[0019] The voltage activation includes charging the battery to an activation voltage, and discharging after standing.

[0020] In some embodiments of the present application, the preparation process of the positive electrode includes: mixing the transition metal layered oxide material, the conductive agent, the binder and the solvent uniformly, coating the mixture on a current collector, and drying to obtain the positive electrode.

[0021] Further, the conductive agent includes, but is not limited to, acetylene black (SP) and the like.

[0022] Further, the binder includes, but is not limited to, polyvinylidene fluoride (PVDF) and the like.

[0023] Further, the solvent includes, but is not limited to, organic solvents such as N-methyl pyrrolidone (NMP) and the like.

[0024] Further, the mass ratio of the transition metal layered oxide material, the conductive agent and the binder is 85-95:1-10:1-10.

[0025] According to some specific aspects of the present application, the current collector includes, but is not limited to, aluminum foil.

[0026] According to some specific aspects of the present application, in the preparation process of the positive electrode, the drying can be performed in a vacuum oven at 100-130°C.

[0027] According to some specific aspects of the present application, in the preparation process of the positive electrode, the intermediate after drying can be punched to obtain the positive electrode.

[0028] In some embodiments of the present application, the positive electrode can be prepared according to the above method or commercially available.

[0029] In some embodiments of the present application, in the preparation process of the battery positive electrode material, the battery includes button half-cell or full-cell, soft package battery. Further, the NP ratio of the soft package battery is 0.9-1.2.

[0030] In some embodiments of the present application, in the preparation process of the battery positive electrode material, the negative electrode of the battery includes, but is not limited to, commercially available hard carbon and the like.

[0031] According to some preferred aspects of the present application, the number of times of voltage activation is 1-15. Further, the number of times of voltage activation is 1-8.

[0032] In some embodiments of the present application, during the voltage activation, the charging is carried out at a constant current and constant voltage of 0.01-1C, and the discharging is carried out at a constant current.

[0033] In some embodiments of the present application, when the transition metal layered oxide material is an O3-NaCrO2 material, the activation voltage is 3.65-3.77V; when the transition metal layered oxide material is an O3-NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 material, the activation voltage is 4.15-4.27V.

[0034] In some embodiments of the present application, the battery cathode material is obtained by disassembling the battery after the voltage activation.

[0035] In some embodiments of the present application, under the voltage activation, the transition metal layered oxide material undergoes phase transition from the surface, and an inert layer is generated in situ, thereby generating the battery cathode material with a coating structure.

[0036] In some embodiments of the present application, the battery cathode material is a particle with a size of 0.5-1 μm, and the particle has a regular morphology and a planar-angulation shape.

[0037] In some embodiments of the present application, the O3-NaCrO2 material can be commercially available or prepared by the following method:

[0038] High-temperature solid-phase synthesis: Na2CO3 and Cr2O3 are mixed in a stoichiometric ratio of x:1, wherein x is 1±0.02. The raw materials are ground finely and then placed in a tube furnace for calcination under an inert atmosphere, and then cooled.

[0039] Further, the sintering rate is 1-10℃ / min, the calcination temperature is 900-1000℃, the calcination atmosphere is an inert atmosphere such as argon atmosphere, the calcination time is 9-15 hours, and further preferably, the calcination time is 12-15 hours. Finally, the temperature is decreased to 400-600℃ at a rate of 1-10℃ / min, and then naturally cooled to room temperature to obtain the O3-NaCrO2 material.

[0040] Another technical solution provided by the present application is a battery cathode material, which is generated by electrochemically transforming a transition metal layered oxide material under an activation voltage, wherein the activation voltage is greater than the cutoff voltage of the transition metal layered oxide material and less than the voltage platform at which the transition metal layered oxide material undergoes irreversible phase transition.

[0041] The application provides another technical scheme: a battery positive plate, which comprises the battery positive material.

[0042] The application provides another technical scheme: a preparation method of a battery positive plate, which comprises the following steps:

[0043] (1) assembling a positive electrode comprising a transition metal layered oxide material into a battery;

[0044] (2) performing voltage activation on the battery; wherein the voltage activation comprises charging the battery to an activation voltage, and discharging after standing; the activation voltage is greater than the cut-off voltage of the transition metal layered oxide material and less than the voltage platform at which the transition metal layered oxide material undergoes irreversible phase transition;

[0045] (3) disassembling the battery treated in step (2) to obtain the battery positive plate.

[0046] The application provides another technical scheme: a battery, which comprises the battery positive plate or the battery positive plate prepared by the preparation method.

[0047] Further, the battery can be a lithium ion battery or a sodium ion battery.

[0048] The application provides another technical scheme: a preparation method of a battery, which comprises a formation process of the battery, and the formation process comprises the following steps:

[0049] performing voltage activation on the battery; wherein the voltage activation comprises charging the battery to an activation voltage, and discharging after standing; the activation voltage is greater than the cut-off voltage of the transition metal layered oxide material and less than the voltage platform at which the transition metal layered oxide material undergoes irreversible phase transition;

[0050] The battery comprises a positive electrode containing a transition metal layered oxide material.

[0051] Thanks to the above technical scheme, the application has the following advantages compared with the prior art:

[0052] In the process of a large number of experimental researches, it is found that the inert layer coated positive material can be directly generated by using the irreversible phase transition of the transition metal layered oxide material, so that the bulk phase layer and the inert layer of the positive material are directly combined and matched better, thereby not only the cycle stability can be significantly improved, but also the inert layer can be directly generated by in-situ construction because the precursor material of the inert layer is the same as the bulk phase layer or even part of the bulk phase layer, so that the production process is greatly simplified.

[0053] Further, the inventors of the present application overcome the technical prejudice that transition metal layered oxide materials cannot be charged above the cut-off voltage; the present application creatively first uses charging above the cut-off voltage to activate the surface layer phase transition of the transition metal layered oxide material, realizes in-situ electrochemical method construction of the inert layer, which not only does not reduce the cycle performance of the material, but also makes the cycle capacity of the material be kept with high efficiency, and especially, the method overcomes the defect that the existing preparation of the coating layer needs high-temperature calcination, greatly reduces the energy consumption, and the operation is relatively simple, can be directly integrated into the formation process of the existing battery, and provides a feasible technical path for large-scale production and commercial application of sodium ion batteries or lithium ion batteries. BRIEF DESCRIPTION OF DRAWINGS

[0054] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below.

[0055] Figure 1 The first circle high-voltage activation range of O3-NaCrO2;

[0056] Figure 2 The first circle voltage-specific capacity curve of Example 1 and Comparative Example 1 at 0.5C in the range of 2-3.6V;

[0057] Figure 3 The cycle test curve of Example 1 and Comparative Example 1 at 0.5C;

[0058] Figure 4 The cycle test curve of Example 2, Example 3 and Comparative Example 2 at 0.5C;

[0059] Figure 5 The cycle test curve of Example 1, Example 4 and Example 5 at 0.5C;

[0060] Figure 6 The STEM image of NaCrO2 activated by high voltage in Example 6;

[0061] Figure 7 The STEM image of NaCrO2 not activated by high voltage in Comparative Example 3;

[0062] Figure 8 The first circle voltage-specific capacity curve of Example 6 activated by high voltage and the first circle voltage-specific capacity curve of Comparative Example 3 not activated by high voltage;

[0063] Figure 9 The cycle test curve of Example 6 and Comparative Example 3 at 0.5C;

[0064] Figure 10First cycle voltage vs. specific capacity curve of Example 7 with high voltage activation and first cycle voltage vs. specific capacity curve of Comparative Example 4 without high voltage activation.

[0065] Figure 11 Cycle test curve of Example 7 and Comparative Example 4 at 0.5C. DETAILED DESCRIPTION

[0066] The above solutions are further described below in conjunction with specific examples. It should be understood that the examples are used to illustrate the basic principles, main features and advantages of the present application, and the present application is not limited in scope by the examples below; the implementation conditions used in the examples can be further adjusted according to specific requirements, and the implementation conditions not noted are usually the conditions in conventional experiments.

[0067] In the following examples, all raw materials are from commercial sources or prepared by conventional methods in the art, unless otherwise specified.

[0068] In the following, the O3-NaCrO2 material can be prepared by the following method:

[0069] High-temperature solid-phase synthesis: Na2CO3 (purchased from Shanghai Titan Science and Technology Co., Ltd., brand: 60035F), Cr2O3 (purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd., brand 10006918, Shanghai test batch number: 20220826) were mixed in a stoichiometric ratio of 1:1. The raw materials were ground finely and placed in a tube furnace for calcination under an argon atmosphere. The calcination temperature was raised at a rate of 5°C / min to 1000°C, and the calcination time was 12 hours. Finally, the temperature was lowered to 500°C at a rate of 5°C / min, and then naturally cooled to room temperature to obtain the O3-NaCrO2 material.

[0070] Example 1: Sodium chromite positive electrode, coin half-cell, 3.75V in-situ construction

[0071] The present example provides a preparation method of a battery positive electrode material, a battery positive electrode material prepared by the method, and a positive electrode comprising the battery positive electrode material and a battery comprising the positive electrode.

[0072] Specifically:

[0073] Preparation of the positive electrode: 3.6 grams of O3-NaCrO2 material, 0.2 grams of acetylene black (SP), and 4 grams of 5% polyvinylidene fluoride (PVDF) glue solution (with N-methyl pyrrolidone (NMP) as the solvent, and 0.2 grams of PVDF) were uniformly mixed, 0.2 grams of organic solvent N-methyl pyrrolidone (NMP) was added, and then uniformly coated on an aluminum foil. After being baked in a 120°C vacuum oven for 12 hours, the positive electrode was punched.

[0074] Preparation of sodium ion button-type half cell: the above prepared positive electrode is assembled into a sodium ion button-type half cell; from the negative electrode shell, the button-type half cell is sequentially placed with a spring, a gasket, a sodium sheet (negative electrode), a diaphragm, a positive electrode sheet, and a positive electrode shell; after the assembly is completed, the positive and negative electrode shells are aligned and pressed tightly, and then a sealing machine is used for pressure sealing. After the assembly is completed, it is left to stand for 4 h to ensure that the electrolyte is fully soaked into the electrode and the diaphragm.

[0075] High-voltage activation: then the sodium ion button-type half cell is subjected to constant current and constant voltage charging at 0.1C, and charged to 3.75V; after standing, constant current discharging is performed to 2V, and then the sodium sodium chromite positive electrode material coated with an inert layer is obtained by disassembly.

[0076] In this example, the sodium ion button-type half cell after high-voltage activation can be directly subjected to charge and discharge cycle test without disassembly, and the specific operation is as follows: the charge and discharge cycle test is performed at 0.5C in the range of 2-3.6V.

[0077] It is measured that the specific capacity of the first cycle in the range of 2-3.6V is 114.25 mAh / g, and the capacity retention rate is 89.17% after 200 cycles at a current of 0.5C; it is shown that the positive electrode material of the application can make the battery have excellent cycle stability, and it is further shown that the inert layer is generated in situ on the surface of the positive electrode material particles, the bulk structure is stabilized, and the occurrence of side reactions is reduced.

[0078] Example 2: sodium chromite positive electrode, button-type half cell, 3.65V in-situ construction, cycle 3 times

[0079] The example provides a preparation method of a battery positive electrode material, a battery positive electrode material prepared by the method, a positive electrode containing the battery positive electrode material, and a battery containing the positive electrode.

[0080] The embodiment is basically the same as example 1, and the difference is that the charging voltage in high-voltage activation is 3.65V, and the high-voltage charge and discharge cycle is repeated 3 times.

[0081] Example 3: sodium chromite positive electrode, button-type half cell, 3.7V in-situ construction, cycle 3 times

[0082] The example provides a preparation method of a battery positive electrode material, a battery positive electrode material prepared by the method, a positive electrode containing the battery positive electrode material, and a battery containing the positive electrode.

[0083] The embodiment is basically the same as example 1, and the difference is that the charging voltage in high-voltage activation is 3.7V, and the high-voltage charge and discharge cycle is repeated 3 times.

[0084] Example 4: sodium chromite positive electrode, button-type half cell, 3.75V in-situ construction, cycle 3 times

[0085] The example provides a preparation method of a battery positive electrode material, a battery positive electrode material prepared by the method, a positive electrode containing the battery positive electrode material, and a battery containing the positive electrode.

[0086] The embodiment is basically the same as embodiment 1, except that the high-voltage activation involves repeating the high-voltage charge-discharge cycle 3 times.

[0087] Example 5: Sodium chromite positive electrode, button half-cell, 3.75V in-situ construction, 5 cycles of cycling

[0088] The example provides a preparation method of a battery positive electrode material, a battery positive electrode material prepared by the method, a positive electrode containing the battery positive electrode material, and a battery containing the positive electrode.

[0089] The embodiment is basically the same as embodiment 1, except that the high-voltage activation involves repeating the high-voltage charge-discharge cycle 5 times,

[0090] Example 6: Sodium chromite positive electrode, soft-pack full-cell, in-situ construction

[0091] The example provides a preparation method of a battery positive electrode material, a battery positive electrode material prepared by the method, a positive electrode containing the battery positive electrode material, and a battery containing the positive electrode.

[0092] Specifically:

[0093] Preparation of the positive electrode: 9 grams of O3-NaCrO2 material, 0.5 grams of acetylene black (SP), and 10 grams of 5% polyvinylidene fluoride (PVDF) glue solution (with N-methyl pyrrolidone (NMP) as the solvent, and 0.5 grams of PVDF) are uniformly mixed and then uniformly coated on an aluminum foil. After being baked in a 120°C vacuum oven for 12 hours, the positive electrode is punched.

[0094] Preparation of the soft-pack full-cell: the NP ratio is determined to be 1.1, and the sodium chromite is matched as the positive electrode and the hard carbon is matched as the negative electrode. The laminated sheets are packaged with an aluminum plastic film, electrolyte is injected, the package is left to soak, and then sealed.

[0095] High-voltage activation: the soft-pack full-cell is then subjected to constant-current constant-voltage charging at 0.1C until the voltage reaches 3.6V. After being left to stand, the cell is subjected to constant-current discharging until the voltage reaches 1.5V. The inert layer-coated sodium chromite positive electrode material is obtained by disassembling the cell.

[0096] In the example, the soft-pack full-cell subjected to high-voltage activation can be directly subjected to charge-discharge cycling at 0.5C within the range of 1.5-3.5V (considering the hard carbon).

[0097] It is measured that the capacity retention rate of the battery is 90% after 1500 cycles at 0.5C. Figure 6As can be seen from the STEM data, about 4 nm of the inert layer of rock salt phase is generated in situ on the surface of the positive electrode material particles in this example, which can stabilize the bulk structure and reduce side reactions.

[0098] Example 7: Nickel-iron-manganese sodium acid positive electrode, button half cell, 4.15V in-situ construction

[0099] This example provides a preparation method of a battery positive electrode material, a battery positive electrode material prepared by the method, a positive electrode comprising the battery positive electrode material, and a battery comprising the positive electrode.

[0100] Specifically,

[0101] Preparation of the positive electrode: 3.6 grams of NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 (purchased from Hefei Kejing Material Technology Co., Ltd., brand) and 0.2 grams of acetylene black (SP), 4 grams of 5% polyvinylidene fluoride (PVDF) glue solution were uniformly mixed, 0.2 grams of organic solvent N-methyl pyrrolidone (NMP) was added, and then uniformly mixed and coated on an aluminum foil. After being baked in a 120°C vacuum oven for 12 hours, the positive electrode was punched into a positive electrode;

[0102] Preparation of a sodium ion button half cell: the positive electrode prepared above was assembled into a sodium ion button half cell; starting from the negative electrode shell, a spring, a gasket, a sodium sheet (negative electrode), a separator, a positive electrode sheet, and a positive electrode shell were sequentially placed, and after assembly, the positive and negative electrode shells were aligned and pressed tightly, and then a sealing machine was used for pressure sealing. After assembly, it was left to stand for 4 hours to ensure that the electrolyte was fully soaked into the electrode and the separator.

[0103] High-voltage activation: then the sodium ion button half cell was subjected to constant current and constant voltage charging at 0.1C, and charged to 4.15V. After standing, constant current discharge was performed to 2V, and then the nickel-iron-manganese sodium acid positive electrode material coated with an inert layer was obtained by disassembly.

[0104] In this example, the sodium ion button half cell subjected to high-voltage activation can be directly subjected to charge and discharge cycling in the range of 2-4V at 0.5C without disassembly.

[0105] It was measured that the specific capacity in the first cycle was 122.81 mAh / g in the range of 2-4V, and the capacity retention rate was 88.58% after 100 cycles at a current of 0.5C.

[0106] Comparative Example 1: Sodium dichromate positive electrode, button half cell, without high-voltage activation treatment

[0107] This example provides a preparation method of a battery positive electrode material, a battery positive electrode material prepared by the method, a positive electrode comprising the battery positive electrode material, and a battery comprising the positive electrode.

[0108] The same as example 1, except that: no high-voltage activation treatment, constant current and constant voltage charging to 3.6V at 0.1C, after standing, constant current discharging to 2V;

[0109] Then, the charge and discharge cycle in the range of 2-3.6V at 0.5C is carried out.

[0110] Comparative example 2: sodium chromite positive electrode, button half-cell, 3.8V in-situ construction

[0111] The example provides a preparation method of a battery positive electrode material, a battery positive electrode material prepared by the method, a positive electrode containing the battery positive electrode material, and a battery containing the positive electrode.

[0112] The same as example 1, except that: the charging voltage in high-voltage activation is 3.8V.

[0113] Practice shows that 3.8V exceeds the upper limit of high-voltage activation of the battery, the material changes unexpectedly, and the performance of the battery decreases sharply.

[0114] Comparative example 3: sodium chromite positive electrode, soft package full battery, no high-voltage activation treatment

[0115] The example provides a preparation method of a battery positive electrode material, a battery positive electrode material prepared by the method, a positive electrode containing the battery positive electrode material, and a battery containing the positive electrode.

[0116] The same as example 6, except that: no high-voltage activation treatment, constant current and constant voltage charging to 3.5V at 0.1C, after standing, constant current discharging to 1.5V;

[0117] Then, the charge and discharge cycle in the range of 1.5-3.5V (considering hard carbon) at 0.5C is carried out.

[0118] From the STEM data of Figure 7 It can be seen that, compared with example 6, comparative example 3 has a part of active material dissolved on the surface, and no rock salt phase inert layer is generated, so the cycle stability is poor.

[0119] Comparative example 4: nickel-iron-manganese sodium acid positive electrode, button half-cell, no high-voltage activation treatment

[0120] The example provides a preparation method of a battery positive electrode material, a battery positive electrode material prepared by the method, a positive electrode containing the battery positive electrode material, and a battery containing the positive electrode.

[0121] The same as example 7, except that: no high-voltage activation treatment, constant current and constant voltage charging to 4V at 0.1C, after standing, constant current discharging to 2V;

[0122] Then, the charge and discharge cycle in the range of 2-4V at 0.5C is carried out.

[0123] Experiments show that compared with Example 7, Comparative Example 4 did not undergo high voltage treatment and had poor cycle stability.

[0124] Performance testing:

[0125] (1) The cycle performance test data of Examples 1-7 and Comparative Examples 1-4 are shown in Table 1.

[0126] Table 1

[0127]

[0128] (2) See Figure 1 As shown in Figure 1, it is a high-voltage first-cycle activation range diagram of O3-NaCrO2. It can be seen that the voltage platform of O3-NaCrO2 is 3.8V; the charging voltage for voltage activation should be before the irreversible voltage platform of the transition metal layered oxide material (before the 3.8V platform, because after charging to the 3.8V platform, the reversible capacity of the material drops sharply), and higher than the cut-off voltage of the positive electrode material (3.6V);

[0129] Figure 2 The voltage-specific capacity curve of the first cycle of 2-3.6V at 0.5C for Example 1 and Comparative Example 1 (the voltage-specific capacity curve of the activation cycle of 3.75V is shown in FIG. Figure 1 The first cycle voltage-specific capacity curve of Example 1 after one cycle of 3.75V high voltage activation shows that due to the 3.75V activation, an inert layer is formed in situ on the surface, resulting in a slight attenuation of the capacity.

[0130] Figure 3 Figure 2 is a cycling test curve of Example 1 and Comparative Example 1 at 0.5C. After one cycle of high voltage activation at 3.75V, Example 1 cycled in the 2-3.6V range, with a 200-cycle cycle stability of 89.17%. Comparative Example 1, which was not activated by high voltage, had a 200-cycle cycle stability of 84.34%, a significant decrease compared to Example 1.

[0131] Figure 4 The cycle test curves of Example 2, Example 3 and Comparative Example 2 at 0.5C (the voltage-specific capacity curve of the activation circle is shown in FIG. Figure 1 ). Example 2 is charged to 3.65V and activated for one cycle, and then tested for cycling within the range of 2-3.6V. The cycling is relatively stable. Example 3 is charged to 3.7V and activated for one cycle, and then tested for cycling within the range of 2-3.6V. The cycling is relatively stable. Comparative Example 2 is charged to 3.8V and activated for one cycle, and then tested for cycling within the range of 2-3.6V. Since the capacity of the material decays when charged to the irreversible voltage platform, it is necessary to control the upper limit of high voltage activation to be lower than the irreversible voltage platform;

[0132] Figure 5Cycle test curves of Example 1, Example 4, Example 5 at 0.5C. The cycle performance of the material was tested for 1 cycle, 3 cycles, 5 cycles of high voltage activation at 3.75V respectively. The cycle stability is the best after the material is activated for 5 cycles, but the thickness of the inert layer generated by the material increases due to the phase change of the surface to the inert layer for each cycle of activation, and the high voltage cycle for 5 cycles, so the specific capacity of the material decreases slightly; according to the data in Table 1, although the construction of the inert layer is too thick, a part of the specific capacity is lost, but the cycle stability is obviously improved;

[0133] Figure 6 STEM image of NaCrO2 activated by high voltage for Example 6, from which it can be seen that a 4nm-thick rock salt phase inert layer is generated on the surface of the material; Figure 6

[0134] Figure 7 STEM image of NaCrO2 not activated by high voltage for Comparative Example 3. STEM provides high-resolution atomic-level images suitable for element contrast and structure analysis. The heavy element region is shown as a bright spot, and the white dot region is the Cr-O layered structure of the layered oxide NaCrO2, and the bright spot is the Cr atom, from which it can be seen that there is no rock salt phase inert layer on the surface of the material; Figure 7

[0135] Figure 8 Voltage-specific capacity curve of the first cycle of Example 6 under high voltage activation and voltage-specific capacity curve of the first cycle of Comparative Example 3 without high voltage activation. Example 6 is a NaCrO2 / / HC soft pack battery, and the positive electrode material is NaCrO2 coated with an inert layer, and the high voltage activation method is charging to above the cutoff voltage and below the irreversible voltage platform (3.6V vs HC), and the inert layer is constructed in situ;

[0136] Figure 9 Cycle test curves of Example 6 and Comparative Example 3 at 0.5C. The cycle stability of Example 6 is good due to the presence of the rock salt phase inert layer, and the capacity retention rate is 92.1% after 1500 cycles, which is significantly higher than the 83.4% of Comparative Example 3;

[0137] Figure 10 Voltage-specific capacity curve of the first cycle of Example 7 under high voltage activation and voltage-specific capacity curve of the first cycle of Comparative Example 4 without high voltage activation. The positive electrode material of Example 7 is NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 coated with an inert layer, and the high voltage activation method is charging to above the cutoff voltage and below the irreversible voltage platform (4.15V), and the inert layer is constructed in situ;

[0138] Figure 11 ​​The graph of the cycle test at 0.5C for Example 7 and Comparative Example 4. Example 7 has better cycle stability due to the existence of the rock salt phase inert layer, and the capacity retention rate after 100 cycles is 88.6%, which is significantly higher than 81.9% of Comparative Example 3.

[0139] The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable the person skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the spirit and essence of the present application shall be covered within the protection scope of the present application.

[0140] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not, in some cases, critical to the technical concept of the application. The endpoints of the ranges and any values are provided as approximations only, and are understood to encompass values approximately the same as the value stated. Any numerical range recited is intended to include all sub-ranges subsumed therein. For example, a range of "1 to 2" is intended to include "1 to 1.5", "1.75 to 2", and any other sub-range within the same.

Claims

1. A battery cathode material, characterized in that, The battery cathode material comprises a bulk layer and an inert layer coated on the bulk layer, the bulk layer comprises a transition metal layered oxide material, and the inert layer comprises a transition metal oxide generated by irreversible phase transition of the transition metal layered oxide material; The chemical composition of the transition metal layered oxide material is Na x MO2, M selected from transition metals.

2. The battery cathode material of claim 1, wherein, The transition metal layered oxide material generating the transition metal oxide in the inert layer is from a surface portion of the transition metal layered oxide material in the bulk layer.

3. The battery cathode material of claim 1, wherein, The thickness of the inert layer is 1-10 nm; and / or, the inert layer is a rock salt phase inert layer.

4. The battery cathode material of claim 1, wherein, The thickness of the inert layer is 2-6 nm.

5. The battery cathode material of claim 1, wherein, The transition metal layered oxide material in the bulk layer and the transition metal layered oxide material in the inert layer are respectively unmodified or coated and / or doped modified materials.

6. The battery cathode material of claim 1, wherein, M is selected from one or more combinations of Ti, V, Cr, Mn, Fe, Co, and Ni.

7. The battery cathode material of claim 1, wherein, In the inert layer, the ratio of the content of Na to M is 0.2-0.4:1; in the bulk layer, the ratio of the content of Na to M is 0.5-1:

1.

8. The battery cathode material of claim 1, wherein, The transition metal layered oxide material is an O3-NaCrO2 material or an O3-NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 material.

9. The battery cathode material of claim 1, wherein, The irreversible phase transition comprises subjecting the transition metal layered oxide material to an electrochemical transformation under voltage.

10. A method of producing the positive electrode material as claimed in any one of claims 1 to 9, characterized by, The preparation method comprises: subjecting a battery to voltage activation, the battery comprising a cathode comprising a transition metal layered oxide material; after the voltage activation, generating the battery cathode material; wherein the voltage activation comprises charging the battery to an activation voltage, and discharging after standing; the activation voltage is greater than the cut-off voltage of the transition metal layered oxide material and less than the voltage plateau at which the transition metal layered oxide material undergoes irreversible phase transition.

11. The method for preparing a positive electrode material for a battery according to claim 10, wherein: The preparation process of the cathode comprises: uniformly mixing the transition metal layered oxide material, a conductive agent, a binder, and a solvent, and then coating the mixture on a current collector and drying to obtain the cathode.

12. The method for preparing a positive electrode material for a battery according to claim 10, wherein: The number of times of voltage activation is 1-15; and / or, during the voltage activation, the charging is carried out at a constant current and a constant voltage at 0.01-1 C, and the discharging is constant current discharging.

13. The method for preparing a positive electrode material for a battery according to claim 10, wherein: The number of times of voltage activation is 1-8.

14. The method for preparing a positive electrode material for a battery according to claim 10, wherein: when the transition metal layered oxide material is O3-NaCrO2 material, the activation voltage is 3.65-3.77V; when the transition metal layered oxide material is O3-NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 material, the activation voltage is 4.15-4.27V; and / or, the battery cathode material is obtained by splitting the battery after the voltage activation; and / or, under the voltage activation, the transition metal layered oxide material undergoes phase transition from the surface, and an inert layer is generated in situ, generating the battery cathode material with a coating structure.

15. A battery cathode material, characterized in that, The battery cathode material is generated by electrochemically transforming a transition metal layered oxide material at an activation voltage greater than the cutoff voltage of the transition metal layered oxide material and less than the voltage plateau at which the transition metal layered oxide material undergoes an irreversible phase change, the transition metal layered oxide material having a chemical composition of Na x M02, M being selected from transition metals.

16. A battery positive electrode sheet, characterized by, The battery cathode sheet comprises the battery cathode material according to any one of claims 1-9 or 15.

17. A method for producing a battery positive electrode sheet, characterized by, The preparation method comprises: (1) Assembling a positive electrode comprising a transition metal layered oxide material having a chemical composition of Na x MO2, M being selected from transition metals, into a battery. (2) Assembling a positive electrode comprising a transition metal layered oxide material having a chemical composition of Na x MO2, M being selected from transition metals, into a battery. (3) Assembling a positive electrode comprising a transition metal layered oxide material having a chemical composition of Na x MO2, M being (2) subjecting the battery to voltage activation; wherein the voltage activation comprises charging the battery to an activation voltage, and discharging after standing; the activation voltage is greater than the cut-off voltage of the transition metal layered oxide material and less than the voltage plateau at which the transition metal layered oxide material undergoes irreversible phase transition; (3) splitting the battery treated in step (2) to obtain the battery cathode sheet.

18. A battery, characterized by The battery comprises the battery cathode sheet according to claim 16 or the battery cathode sheet prepared by the preparation method according to claim 17.

19. The battery of claim 18, wherein, The battery comprises a sodium ion battery or a lithium ion battery.

20. A method for producing a battery, the method comprising a formation process of the battery, characterized by, The formation process comprises: subjecting a battery to voltage activation, the voltage activation comprising: charging the battery to an activation voltage, and discharging after standing; The battery includes a cathode comprising a transition metal layered oxide material having a chemical composition of Na x MO2, M selected from transition metals; The activation voltage is greater than a cutoff voltage of the transition metal layered oxide material and less than a voltage plateau at which the transition metal layered oxide material undergoes an irreversible phase transition. The activation voltage is greater than a cutoff voltage of the transition metal layered oxide material and less than a voltage plateau at which the transition metal layered oxide material undergoes an irreversible phase transition.

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