Sodium secondary battery and preparation and application of high-voltage single-crystal oxide active material thereof

Abstract

The application belongs to the field of sodium ion batteries, and particularly relates to a preparation method of a high-voltage oxide positive electrode material. x Ni a Mn b M 1‑a‑b O2 material and a first auxiliary agent are mixed, and then a first-stage calcination is performed under an oxygen-containing atmosphere to obtain a first-stage calcination material; the first-stage calcination material and a second auxiliary agent are mixed, and then a second-stage calcination is performed under an oxygen-free atmosphere to obtain a high-voltage single-crystal oxide active material. The application also provides application of the material. The material has excellent air stability and excellent high-voltage performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of batteries, in particular to the field of sodium secondary battery cathode material technology. BACKGROUND

[0002] Sodium secondary batteries such as sodium ion battery systems have received extensive attention in recent years due to their abundant resources, low price, environmental friendliness, and similar electrochemical properties to lithium ion batteries, thus providing a new option for electrochemical energy storage. Sodium ion batteries are similar to lithium ion batteries in terms of reversible storage and migration mechanisms, and the abundance of sodium elements in the earth's crust and seawater is completely unrestricted by resources and regions, thus having high resource security, and thus being favored by researchers. Currently, layered metal oxide cathode materials are considered to be a promising sodium ion battery cathode material system due to their high specific capacity, high voltage platform, and excellent comprehensive performance. However, sodium ion battery layered oxide cathode materials still cannot meet the current energy density requirements and cost requirements, and the average voltage and discharge specific capacity of layered oxide cathode materials must be further improved. Therefore, the working voltage of layered oxide cathode materials must be improved to highlight the cost and performance advantages of sodium ion batteries and further promote the development of sodium ion batteries. However, at high voltage (≥4.2V), the layered oxide cathode material will undergo severe P3-O3' irreversible phase transition and lattice oxygen loss, causing the structure to rapidly decay, and the cathode material gradually cracks and powders. In addition, due to the instability of the electrolyte at high voltage, continuous side reactions occur with the cathode material, causing the CEI film to thicken, transition metal dissolution, and other problems, which exacerbate the structure decay and performance decline. Therefore, strategies need to be taken to modify and develop high-voltage layered metal oxide cathode materials for sodium ion batteries with excellent performance.

[0003] Compared with polycrystalline materials, single crystal oxide positive electrode materials can better inhibit the harm caused by phase transition and relieve the generation of cracks due to higher mechanical strength. In addition, single crystal oxide positive electrode materials have smaller surface area and less side reaction with electrolyte. However, single crystal oxide positive electrode materials still cannot avoid lattice oxygen loss, performance attenuation at high voltage and continuous corrosion of electrolyte. In addition, alkaline substances such as NaOH and Na2CO3 exist on the surface of the single crystal oxide positive electrode materials, and are easy to react with electrolyte, causing problems such as gas production of the battery, which seriously threatens the safety performance of sodium ion batteries at high voltage. One of the most effective ways to improve the high-voltage performance of the material in the existing technology is surface modification, which usually uses some metal oxides for surface coating / surface doping. Although this method can improve the structure collapse and interface side reaction of the positive electrode material during the cycle process at high voltage to some extent, the coating effect is difficult to control due to the high melting point of the metal oxide. If the coating amount is large, the coating layer will be too thick, which will reduce the electron and ion transmission, increase the sodium ion transfer impedance and reduce the rate performance of the material. If the coating amount is small, the coating will be uneven and the coating effect will be poor, which cannot play an obvious role. Therefore, how to design a sodium ion battery oxide positive electrode material with excellent high-voltage performance still needs further research. SUMMARY

[0004] In view of the problems of unsatisfactory air stability of the oxide active material of the sodium ion battery and difficulty in adapting to the high-voltage application requirements, the first object of the present application is to provide a preparation method of a high-voltage single crystal oxide active material of a sodium secondary battery, which aims to prepare a positive electrode active material with excellent air stability and high-voltage performance.

[0005] The second object of the present application is to provide a high-voltage single crystal oxide active material prepared by the preparation method and the application thereof in a sodium secondary battery.

[0006] The third object of the present application is to provide a sodium secondary battery comprising the high-voltage single crystal oxide active material, a positive electrode and a positive electrode material thereof.

[0007] Most of the single crystal oxides of the sodium secondary battery are suitable for the application requirements of 4.0V, and are difficult to adapt to the high-voltage application requirements of 4.2V or more, and are difficult to exhibit good electrochemical performance at high voltage. In addition, there are also problems of unsatisfactory air stability, easy to deteriorate in air, etc. In view of this problem, the present application provides the following improvement scheme after in-depth research:

[0008] The preparation method of the high-voltage single crystal oxide active material of the sodium secondary battery comprises the following steps: x Ni a Mn b M 1-a-bThe O2 material and the first auxiliary agent are mixed to perform a first-stage calcination under an oxygen-containing atmosphere at a temperature T1 to obtain a first-stage calcination material; and then the first-stage calcination material and a second auxiliary agent are mixed to perform a second-stage calcination under an oxygen-free atmosphere at a temperature T2 to obtain the high-voltage single-crystal oxide active material;

[0009] The Na x Ni a Mn b M 1-a-b In the O2 material, the M includes at least one of Fe, Co, Zn, Al, Mg, Ti, Cu, Li, Ca, K, Y, Zr, Nb, W, Mo, Ta, Ba and Sr, 0.5≤x≤1.2, 0

[0010] The first auxiliary agent is a metal ammonium salt of an oxygen-containing acid;

[0011] The second auxiliary agent is a non-metal ammonium salt of an oxygen-containing acid;

[0012] The temperature T1 is 350-800 DEG C, and the temperature T2 is greater than 250 DEG C and less than or equal to 0.8T1.

[0013] In view of the problems that the single-crystal Na x Ni a Mn b M 1-a-b The O2 material is pre-calcined in the first-stage calcination with the assistance of the first auxiliary agent, and then is pre-calcined in the second-stage calcination with the assistance of the second auxiliary agent, and based on the joint control of the auxiliary agent composition and the temperature mechanism parameters of the two-stage calcination processes, the synergistic effect can be unexpectedly achieved, the physical and chemical characteristics such as the oxygen defect, the sodium conduction path, the surface and the interface structure suitable for the high-voltage application can be constructed, the high-voltage performance can be exhibited, and the air stability can be improved.

[0014] In the application, as an optional scheme, the single-crystal Na x Ni a Mn b M 1-a-b In the O2 material, 0.90≤x≤1, 0.2≤a≤0.4 and 0.2≤b≤0.4; further preferably, x=1, a=0.33 and b=0.33; and the M is one or more of Fe, Al, Mg, Ti, Li, Ca, Zr, Nb and Sr.

[0015] In the application, the single-crystal Na x Ni a Mn b M 1-a-bThe O2 material can be prepared by known processes, for example, by sintering of mixed raw materials capable of providing stoichiometric amounts of each metal.

[0016] In the present application, the first stage calcination assisted by the first additive and the second stage calcination of the second additive thereafter, and the combined control of the additive composition and the gradient temperature are the key to synergistically improving the high-voltage performance and air stability of the prepared material.

[0017] In the present application, the first additive includes but is not limited to one or more of ammonium tungstate, ammonium metatungstate, ammonium paratungstate, ammonium molybdate, ammonium vanadate, ammonium metavanadate, ammonium niobate, ammonium chromate, ammonium permanganate, ammonium metaaluminate, ammonium ferrite, ammonium perrhenate, ammonium tellurate; preferably one or more of ammonium tungstate, ammonium metatungstate, ammonium paratungstate, ammonium vanadate, ammonium metavanadate, ammonium niobate, ammonium metaaluminate; further preferably one or more of ammonium tungstate, ammonium metatungstate, ammonium paratungstate;

[0018] Preferably, the first additive is single-crystal Na x Ni a Mn b M 1-a-b 0.02-5wt.% of the O2 material; preferably 0.05-2wt.%; further preferably 0.5-1.5wt.%.

[0019] In the present application, the oxygen-containing atmosphere comprises at least one of oxygen and air;

[0020] In the present application, the oxygen-containing atmosphere further comprises a dilution gas, and the dilution gas comprises at least one of nitrogen and an inert gas;

[0021] Preferably, the temperature T1 is 400-800℃, preferably 600-800℃, further 720-770℃;

[0022] Preferably, the holding time at the temperature T1 is 4-8h, preferably 5-6h.

[0023] In the present application, the second additive includes but is not limited to one or more of ammonium sulfate, ammonium borate, ammonium carbonate, ammonium bicarbonate, ammonium oxalate, ammonium acetate, ammonium tartrate, ammonium hydrogen tartrate, ammonium sulfite, ammonium bisulfite, ammonium formate, ammonium citrate, ammonium hydrogen citrate, ammonium succinate, ammonium benzoate; preferably one or more of ammonium sulfate, ammonium borate, ammonium sulfite, ammonium bisulfite; further preferably one or more of ammonium sulfate, ammonium borate;

[0024] Preferably, the second additive is Na x Ni a Mn b M 1-a-b0.02-3 wt.%, preferably 0.1-1.5 wt.%, further preferably 0.2-1 wt.%, further 0.3-0.7 wt.% of the weight of the O2 material.

[0025] In the present application, the oxygen-free atmosphere is at least one of nitrogen, inert gas, hydrogen-inert gas mixture.

[0026] Preferably, the temperature T2 is greater than or equal to 300°C and less than or equal to 0.75T1; further, the temperature T2 is 300-500°C.

[0027] Preferably, the holding time at temperature T2 is 0.5-4 h; further preferably, 1-2 h.

[0028] The present application also provides a high-voltage single-crystal oxide active material prepared by the preparation method.

[0029] In the present application, the preparation method can impart the material with physicochemical characteristics suitable for high-voltage application requirements, and the material prepared by the preparation method has excellent electrochemical performance and air resistance stability at high voltage.

[0030] The present application also provides a positive electrode material of a sodium secondary battery, comprising a positive electrode active material, a binder and a conductive agent, wherein the positive electrode active material comprises a high-voltage single-crystal oxide active material prepared by the preparation method of the present application.

[0031] In the present application, in addition to the positive electrode active material comprising the high-voltage single-crystal oxide active material of the present application, other components and types and contents can be conventional.

[0032] The present application also provides a positive electrode of a sodium secondary battery, comprising a current collector and a positive electrode material complexed on the surface thereof, wherein the positive electrode material is a positive electrode material comprising the high-voltage single-crystal oxide active material of the present application.

[0033] The present application also provides a sodium secondary battery comprising the positive electrode comprising the high-voltage single-crystal oxide active material of the present application.

[0034] Advantages:

[0035] The present application innovatively combines single-crystal Na x Ni a Mn b M 1-a-bThe O2 material is pre-calcined in the first stage with the assistance of a first auxiliary agent, and then pre-calcined in the second stage with the assistance of a second auxiliary agent, and based on the joint control of the auxiliary agent composition and the temperature mechanism parameters of the two-stage calcination process, the synergistic effect can be achieved, the harmful phase change of the prepared active material can be effectively inhibited, the lattice oxygen can be stabilized, the sodium conduction ability can be improved, the appropriate oxygen defects can be constructed, and the appropriate layered to spinel phase transition can be induced, the interface side reaction between the bulk material and the electrolyte can be synergistically reduced, and the reversibility of the anion redox reaction is improved.

[0036] The combined process adopted by the application not only solves the uniformity problem of surface doping and surface coating, but also forms a composite phase structure of the surface and the subsurface. Thanks to the design of the application, the material prepared by the application has excellent mechanical properties and interlayer slip resistance, which is beneficial to alleviate the lattice stress and micro-crack caused by P3-O3' phase transition during high-voltage charging and discharging; has a stable positive electrode interface structure, reduces the interface side reaction and surface structure decay under high voltage; has a reversible anion redox reaction, and stabilizes the lattice oxygen. Therefore, the material prepared by the application solves many problems under high voltage, and realizes high capacity and high cycle stability of the positive electrode material under high voltage. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 is the SEM diagram of the material finally prepared in Example 1.

[0038] Figure 2 is the SEM diagram of the material finally prepared in Example 4.

[0039] Figure 3 is the 0.1C first charge-discharge curve diagram of the material finally prepared in Example 1 and Comparative Example 1 under 2-4.2V.

[0040] Figure 4 is the cycle performance comparison diagram of the material finally prepared in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0041] The technical solutions of the application will be further described below in combination with specific embodiments, but are not limited thereto.

[0042] The preparation method of one exemplary high-voltage single-crystal oxide active material of the application comprises the following steps:

[0043] Step S1, mix the sodium source, nickel source, iron source and manganese source according to a certain mass ratio, put them into a kiln for high-temperature sintering, and after cooling, perform jaw breaking, roller, sieving and air breaking to obtain a single-crystal oxide positive electrode material for sodium ion batteries, and prepare a single-crystal Na xNi a Mn b Fe 1-a-b O2 cathode material;

[0044] Step S2, the cathode material obtained in step S1 is mixed with ammonium metal oxoacid in a certain proportion, put into a kiln and calcined at a temperature of 350-800℃ in an oxygen-containing atmosphere, and after cooling, the jaw breaking, roller and sieving are carried out to obtain the first ammonium salt treated cathode material.

[0045] Step S3, the cathode material obtained in step S2 is mixed with ammonium nonmetal oxoacid in a certain proportion, put into a kiln and calcined at a temperature of 250-650℃ in an oxygen-free atmosphere, and after cooling, the jaw breaking, roller and sieving are carried out to obtain the second ammonium salt treated cathode material, i.e. the sodium ion battery high-voltage oxide cathode material.

[0046] The nickel source in step S1 includes but is not limited to one or more of NiO, Ni2O3, Ni3O4, Ni(OH)2, nickel sulfate, nickel chloride, nickel nitrate, and nickel carbonate; preferably, one or more of NiO, Ni2O3, Ni3O4, Ni(OH)2; further preferably, one or more of NiO, Ni(OH)2.

[0047] The iron source in step S1 includes but is not limited to one or more of FeO, Fe2O3, Fe3O4, Fe(OH)2, Fe(OH)3, iron sulfate, iron chloride, iron nitrate, and iron carbonate; preferably, one or more of FeO, Fe2O3, Fe3O4, Fe(OH)2, Fe(OH)3; further preferably, one or more of FeO, Fe2O3.

[0048] The manganese source in step S1 includes but is not limited to one or more of MnO, Mn2O3, Mn3O4, MnO2, Mn2O7, Mn(OH)2, manganese sulfate, manganese chloride, manganese nitrate, and iron carbonate; preferably, one or more of MnO, Mn2O3, Mn3O4, MnO2, Mn(OH)2; further preferably, one or more of MnO, MnO2.

[0049] The sodium source in step S1 includes but is not limited to one or more of Na2CO3, NaOH, NaHCO3, CH3COONa, sodium oxalate, sodium fluoride, sodium borate, and sodium phosphate; preferably, one or more of Na2CO3, NaOH, NaHCO3; further preferably, one or more of Na2CO3, NaOH.

[0050] In step S1, the sintering atmosphere is one of air and oxygen; preferably, air; further preferably, dehumidified air.

[0051] In step S1, the high-temperature calcination process is: the temperature rising rate is 1-10℃ / min, the first-stage calcination temperature is 600-900℃, the holding time is 3-7h, the second-stage calcination temperature is 900-1100℃, and the holding time is 10-16h; preferably, the temperature rising rate is 2-5℃ / min; further preferably, 4-5℃ / min; preferably, the first-stage calcination temperature is 700-900℃, the holding time is 4-6h, the second-stage calcination temperature is 1000-1100℃, and the holding time is 10-14h; further preferably, the first-stage calcination temperature is 800-850℃, the holding time is 4.5-5.5h, the second-stage calcination temperature is 1050-1080℃, and the holding time is 12-13h.

[0052] In step S2, the metal ammonium oxoacid includes but is not limited to one or more of ammonium tungstate, ammonium metatungstate, ammonium paratungstate, ammonium molybdate, ammonium vanadate, ammonium metavanadate, ammonium niobate, ammonium chromate, ammonium permanganate, ammonium metaaluminate, ammonium ferrate, ammonium perrhenate, and ammonium tellurate; preferably, one or more of ammonium tungstate, ammonium metatungstate, ammonium paratungstate, ammonium vanadate, ammonium metavanadate, ammonium niobate, and ammonium metaaluminate; further preferably, one or more of ammonium tungstate, ammonium metatungstate, and ammonium paratungstate.

[0053] In step S2, the ratio of the metal ammonium oxoacid salt to the positive electrode material is 0.02%-5%wt; preferably, 0.05%-2%wt; further preferably, 0.5%-1.5%wt.

[0054] In step S2, the sintering atmosphere is one of air and oxygen; preferably, oxygen.

[0055] In step S2, the high-temperature calcination process is: the temperature rising rate is 1-10℃ / min, preferably, the temperature rising rate is 2-5℃ / min; further preferably, 4-5℃ / min; preferably, the calcination temperature is 400-800℃, and the holding time is 4-8h; further preferably, the calcination temperature is 600-800℃, further 720-770℃, and the holding time is 5-6h.

[0056] In step S3, the non-metal ammonium oxoacid includes but is not limited to one or more of ammonium sulfate, ammonium borate, ammonium carbonate, ammonium bicarbonate, ammonium oxalate, ammonium acetate, ammonium tartrate, ammonium bitartrate, ammonium sulfite, ammonium bisulfite, ammonium formate, ammonium citrate, ammonium citrate dihydrogen, ammonium succinate, and ammonium benzoate. Preferably, one or more of ammonium sulfate, ammonium borate, ammonium sulfite, and ammonium bisulfite; further preferably, one or more of ammonium sulfate and ammonium borate.

[0057] The ratio of the non-metallic oxyacid ammonium salt to the positive electrode material in step S3 is 0.02% to 3% wt; preferably, 0.1% to 1.5% wt; further preferably, 0.2 to 1% wt.

[0058] In step S3, the sintering atmosphere is one of nitrogen, argon, and hydrogen-argon mixed gas; preferably, one of nitrogen and argon; further preferably, nitrogen.

[0059] In step S3, the high-temperature calcination process is as follows: the heating rate is 1 to 10℃ / min, the calcination temperature is 300 to 500℃, and the holding time is 0.5 to 4h; preferably, the heating rate is 2 to 5℃ / min; further preferably, 4 to 5℃ / min; preferably, the calcination temperature is 450 to 520℃, and the holding time is 1 to 2h.

[0060] The mixing method in steps S1, S2, and S3 is dry mixing or wet mixing. Preferably, it is dry mixing, and a mixer is used for mixing.

[0061] The kiln in steps S1, S2, and S3 includes but is not limited to one of a box furnace, a push plate kiln, a roller kiln, and a rotary kiln.

[0062] The application also provides a sodium-ion battery positive electrode sheet, which comprises a current collector and a positive electrode material layer coated on the current collector, wherein the positive electrode material layer comprises the positive electrode material, a conductive additive, and a binder.

[0063] The conductive additive is one or more of conductive carbon black, acetylene black, Ketjen black, and Super P; and the binder is polyvinylidene fluoride.

[0064] Example 1:

[0065] NaNi 0.33 Fe 0.34 Mn 0.33 The modification method of the O2 single-crystal layered oxide comprises the following steps:

[0066] In step (1), NiO2, Fe2O3, MnO2, and Na2CO3 are weighed according to the stoichiometric ratio, mixed uniformly in a vertical mixer, and then put into an agglomeration box and placed in a roller kiln. The temperature is raised to 800℃ at a rate of 3℃ / min, and then held for 5h. Then the temperature is raised to 1050℃ at the same rate, and then held for 12h. After natural cooling to 150℃, the mixture is taken out, crushed, and NaNi 0.33 Fe 0.34 Mn 0.33 O2 layered oxide single-crystal positive electrode material.

[0067] Step (2), take the positive electrode material obtained in step (1), take 1%wt of ammonium tungstate (first additive) according to the positive electrode material, mix uniformly, then put into the roller kiln, pass in oxygen, with a heating rate of 5℃ / min to 750℃ (marked as T1), keep for 6h, and naturally cool to 150℃. The cooled material is sequentially subjected to jaw breaking, roller, 200 mesh screening, and air breaking to obtain the first treated positive electrode material.

[0068] Step (3), take the positive electrode material obtained in step (2), take 0.5%wt of ammonium borate (second additive) according to the positive electrode material, mix uniformly, then put into the roller kiln, pass in nitrogen, with a heating rate of 5℃ / min to 500℃ (marked as T2), keep for 2h, and naturally cool to 150℃. The cooled material is sequentially subjected to jaw breaking, roller, 200 mesh screening, and air breaking to obtain the high-voltage oxide positive electrode material.

[0069] Example 2

[0070] Compared with Example 1, the only difference is that in step (2), the first additive is replaced by ammonium molybdate, and other preparation conditions are the same as those in Example 1.

[0071] Example 3

[0072] Compared with Example 1, the only difference is that in step (2), the amount of ammonium tungstate is replaced by 4%wt of the positive electrode material, and other preparation conditions are the same as those in Example 1.

[0073] Example 4

[0074] Compared with Example 1, the only difference is that in step (3), the second additive is replaced by ammonium oxalate, and other preparation conditions are the same as those in Example 1.

[0075] Example 5

[0076] Compared with Example 1, the only difference is that in step (3), the amount of ammonium borate is replaced by 2%wt of the positive electrode material, and other preparation conditions are the same as those in Example 1.

[0077] Example 6

[0078] Compared with Example 1, the only difference is that in step 2, the temperature of T1 is 450℃, and the holding time at this temperature is 8h; and in step (3), the calcination temperature T2 is replaced by 300℃, and the holding time at this temperature is 3h; and other preparation conditions are the same as those in Example 1.

[0079] Comparative Example 1

[0080] Compared with Example 1, the only difference is that steps 2 and 3 are missing, and the material prepared in step 1 is directly used as the positive electrode active material.

[0081] Comparative Example 2

[0082] Comparative Example 2 is the same as Example 1 except that the product of Step 1 is directly subjected to Step 3 without the treatment of Step 2.

[0083] Comparative Example 3

[0084] Comparative Example 3 is the same as Example 1 except that the first additive is replaced by the second additive in Step 2.

[0085] Comparative Example 4

[0086] Comparative Example 4 is the same as Example 1 except that the product of Step 2 is directly used as the positive active material without the treatment of Step 3.

[0087] Comparative Example 5

[0088] Comparative Example 5 is the same as Example 1 except that the second additive is replaced by the first additive in Step 3.

[0089] Comparative Example 6

[0090] Comparative Example 6 is the same as Example 1 except that the order of Steps 2 and 3 is reversed, i.e., Step 1 is followed by Step 3 and then Step 2.

[0091] Comparative Example 7

[0092] Comparative Example 7 is the same as Example 1 except that the first additive and the second additive are used simultaneously in Step 2, i.e., the second additive in Step 3 is used in Step 2 together with the first additive and the positive active material from Step 1, and then subjected to the subsequent temperature Tl and temperature T2 without additional second additive.

[0093] Comparative Example 8

[0094] Comparative Example 8 is the same as Example 1 except that the first additive is replaced by sodium tungstate and the second additive is replaced by sodium borate.

[0095] Comparative Example 9

[0096] Comparative Example 9 is the same as Example 1 except that the sintering atmosphere in Step 3 is replaced by oxygen.

[0097] Comparative Example 10

[0098] The difference compared with Example 1 is that the sintering temperature T2 and temperature T1 in step (3) are the same, 750℃, and other preparation conditions are the same as those in Example 1.

[0099] Sodium secondary battery performance test:

[0100] The active material (freshly prepared or stored in Ar atmosphere after preparation) of each case, acetylene black (AB) and polyvinylidene fluoride (PVDF) in a molar ratio of 8:1:1 were added to an n-methyl-2-pyrrolidone (NMP) solution, ground and dispersed, and then the slurry was uniformly coated on an aluminum foil. The coated aluminum foil was dried in a vacuum oven at 80℃ for more than 10h to prepare a positive electrode sheet. The acetylene black was a conductive additive, the polyvinylidene fluoride was a binder, and the aluminum foil was a current collector. The positive electrode surface loading was about 2.5mg / cm 2 .

[0101] 2032 button cells were assembled in an argon-filled glove box with H2O and O2 concentrations less than 0.1ppm. The electrolyte was a solution of 1M NaPF6 in propylene carbonate (PC) and 5% fluoroethylene carbonate (PEC). A metal sodium foil was used as the negative electrode, and a glass fiber membrane was used as the separator of the half-cell to assemble a CR2032 button cell. The test was performed using a constant current charge and discharge mode, and the test cabinet temperature was 25℃ (cycling test temperature). The charge cut-off voltage was 4.2V, and the discharge cut-off voltage was 2.0V. The results are shown in Table 1.

[0102] Air stability test:

[0103] The materials prepared in each case were stored in an air environment at 25℃, 30RH% for 7 days, and then assembled into CR2032 button cells according to the above sodium secondary battery performance test method. The results are shown in Table 1.

[0104] Table 1 Electrochemical test results

[0105]

[0106]

[0107] Analysis:

[0108] According to Table 1, the comparison of Example 1 and Comparative Example 1 shows that the high voltage performance of the material based on the application is effectively improved, and the discharge specific capacity and cycle performance are greatly improved. The comparison of Example 1 and Comparative Examples 2, 3, 4, 5, 6, 7 and 8 shows that the process sequence and the selection of additives in the combined process are necessary conditions for achieving excellent high voltage performance. The comparison of Example 1 and Comparative Examples 9 and 10 shows that the calcination conditions have a key influence on the realization of excellent performance.

Claims

1. A method for producing a high-voltage single crystal oxide active material of a sodium secondary battery, characterized by, The single crystal Na x Ni a Mn b M 1-a-b After mixing the O2 material and the first additive, the first-stage calcination is carried out in an oxygen-containing atmosphere at a temperature T1 to obtain a first-stage calcined material. mixing a second additive, and then performing a second calcination treatment under an oxygen-free atmosphere at a temperature T2 to obtain the high-voltage single-crystal oxide active material; The Na x Ni a Mn b M 1-a-b In the O2 material, the M includes at least one of Fe, Co, Zn, Al, Mg, Ti, Cu, Li, Ca, K, Y, Zr, Nb, W, Mo, Ta, Ba, Sr, 0.5≤x≤1.2, 0<a≤0.5, 0<b≤0.

5. the first additive is an ammonium salt of a metal oxoacid; the second additive is an ammonium salt of a non-metal oxoacid; the temperature T1 is 350-800°C, and the temperature T2 is greater than 250°C and less than or equal to 0.8T1.

2. The production method according to claim 1, wherein The single crystal Na x Ni a Mn b M 1-a-b O2 material is obtained by sintering a mixed raw material capable of providing stoichiometric amounts of each metal.

3. The production method according to claim 1, wherein the first additive comprises one or more of ammonium tungstate, ammonium metatungstate, ammonium paratungstate, ammonium molybdate, ammonium vanadate, ammonium metavanadate, ammonium niobate, ammonium chromate, ammonium permanganate, ammonium metaaluminate, ammonium ferrate, ammonium perrhenate, and ammonium tellurate.

4. The production method according to claim 1, wherein The first additive is single-crystal Na x Ni a Mn b M 1-a-b 0.02 to 5 wt. % of the weight of the O2 material.

5. The production method according to claim 4, wherein The first additive is single-crystal Na x Ni a Mn b M 1-a-b 0.05 to 2 wt. % based on the weight of the O2 material.

6. The production method according to claim 4, wherein The first additive is single-crystal Na x Ni a Mn b M 1-a-b 0.5-1.5 wt. % of the weight of the O2 material.

7. The production method according to claim 1, wherein The oxygen-containing atmosphere comprises at least one of oxygen and air.

8. The production method according to claim 7, wherein The oxygen-containing atmosphere further comprises a dilution gas, which comprises at least one of nitrogen and an inert gas.

9. The production method according to claim 1, wherein The temperature T1 is 400-800°C.

10. The production method according to claim 1, wherein The temperature T1 is 600-800°C.

11. The production method according to claim 1, wherein The temperature T1 is 720-770°C.

12. The production method according to claim 1, wherein The temperature T1 is 720-770°C.

13. The production method according to claim 1, wherein The temperature T1 is 720-770°C.

14. The production method according to claim 1, wherein The temperature T1 is 720-770°C.

15. The production method according to claim 1, wherein The second additive is Na x Ni a Mn b M 1-a-b 0.02 to 3 wt. % of the weight of the O2material.

16. The production method according to claim 15, wherein The second additive is Na x Ni a Mn b M 1-a-b 0.1 to 1.5 wt. % of the weight of the O2material.

17. The production method according to claim 16, wherein The second additive is Na x Ni a Mn b M 1-a-b 0.2 to 1 wt. % of the weight of the O2material.

18. The production method according to claim 1, wherein The second additive comprises one or more of ammonium sulfate, ammonium borate, ammonium carbonate, ammonium bicarbonate, ammonium oxalate, ammonium acetate, ammonium tartrate, ammonium bitartrate, ammonium sulfite, ammonium bisulfite, ammonium formate, ammonium citrate, ammonium hydrogen citrate, ammonium succinate, and ammonium benzoate.

19. The production method according to claim 1, wherein The oxygen-free atmosphere comprises at least one of nitrogen, an inert gas, and hydrogen-inert gas mixture.

20. The production method according to claim 1, wherein The temperature T2 is greater than 300°C and less than or equal to 0.75T1.

21. The production method according to claim 20, wherein The temperature T2 is greater than 300°C and less than or equal to 0.75T1. The temperature T2 is greater than 300°C and less than or equal to 0.75T1.

23. A positive electrode material of a sodium secondary battery, comprising a positive electrode active material, a binder, and a conductive agent, characterized by, 22. A high-voltage single-crystal oxide active material prepared by the preparation method of any one of claims 1-21.

24. A positive electrode of a sodium secondary battery comprising a current collector and a positive electrode material complexed on a surface thereof, characterized by, The positive active material comprises the high-voltage single-crystal oxide active material prepared by the preparation method of any one of claims 1-21.

25. A sodium secondary battery characterized in that, The positive active material is the positive active material of claim 23. The positive electrode comprises the positive active material of claim 24.

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