Preparation method of gradient-doped zn and zn o coated layered oxide cathode for sodium ion battery

Abstract

The application discloses a preparation method of a gradient-doped Zn and ZnO-coated layered oxide positive electrode for a sodium ion battery. The application comprises the following steps: S1, a precursor is obtained by using a coprecipitation method; S2, the obtained precursor is continuously mixed with different concentrations of zinc-containing metal liquid intermittently by using the coprecipitation method to obtain a layered oxide precursor coated with a gradient of zinc salt; and S3, the layered oxide precursor is mixed with a sodium salt and zinc oxide, and then is calcined in an oxidizing atmosphere in stages, and the layered oxide is obtained after cooling and grinding. The modification method provided by the application integrates gradient structure design, element doping and metal oxide coating, effectively improves the comprehensive performance, the gradient doping method ensures the structural stability while reasonably reducing the use of zinc to ensure the capacity performance, the zinc oxide coating effectively improves the air stability, reduces the side reaction with an electrolyte, and the modification method is simple and suitable for commercialization.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of sodium ion batteries, and specifically designs a gradient doped Zn and ZnO coated sodium ion battery layered oxide, a preparation method and a battery. BACKGROUND

[0002] As an important technical supplement of lithium ion batteries, sodium ion batteries are restricted by the distribution of lithium resources, and the abundance is far less than that of sodium. The price of lithium carbonate, the main raw material, also restricts it. Sodium ion batteries have relatively low cost and are suitable for supplementing lithium ion batteries in energy storage, small cars and other scenarios. The cathode material greatly affects the overall performance of the battery. The current layered oxide material has become the mainstream cathode material in the market due to its simple synthesis method, excellent electrical performance and other characteristics. However, due to its poor air stability, low cycle performance and capacity performance, it hinders its commercial development. The current modification methods including element doping, material coating and structure design cannot simultaneously consider all problems, so a simple multi-effect modification method is still needed. SUMMARY

[0003] The purpose of the present application is to overcome the shortcomings of the prior art and provide a gradient doped Zn and ZnO coated sodium ion battery layered oxide, a preparation method and a battery. The present application uses a simple co-precipitation method to complete the structure design, element doping and metal oxide coating in one step, achieving the effect of multiple performance improvements.

[0004] To achieve the above-mentioned effects, the present application provides a preparation method of a gradient doped Zn and ZnO coated sodium ion battery layered oxide in the first aspect, which specifically includes the following steps:

[0005] Step 1: Obtain the precursor by co-precipitation method, mix and dissolve the metal salt in water, and obtain metal liquid A after clarification; prepare the alkali solution, dissolve the alkali in another aqueous solution, add the complexing agent and mix and dissolve in the aqueous solution, and obtain the alkali solution B after stirring to clarification. Add metal liquid A and alkali solution B to the heating reaction kettle under inert gas protection at a fixed rate, keep the pH of the mixed solution constant, and preliminarily obtain the layered oxide precursor.

[0006] Step 2, preparation of metal liquid C1, which contains metal liquid A and a first concentration of zinc salt; preparation of metal liquid C2 by the same method only changing the concentration of zinc salt (i.e. the second concentration of zinc salt replaces the first concentration of zinc salt), preparation of metal liquid C3 only containing a third concentration of zinc salt; preparation of corresponding alkali liquid B1, B2, B3 in a certain proportion. In the preliminary layered oxide precursor, first add alkali liquid B1 and metal liquid C1 in a certain rate, secondly add alkali liquid B2 and metal liquid C2, finally add alkali liquid B3 and metal liquid C3. During the process, the pH is controlled to be constant, and after aging, filtering, washing and drying steps, the zinc gradient doped layered oxide precursor is obtained.

[0007] Further, the alkali liquid B1 and metal liquid C1 are the first group, the alkali liquid B2 and metal liquid C2 are the second group, and the alkali liquid B3 and metal liquid C3 are the third group; the molar ratio of alkali liquid to metal liquid in each group is fixed, for example, the molar ratio of alkali liquid B1 to metal liquid C1 is a fixed value.

[0008] The metal elements in the metal liquid A include the main discharge metals and doping metal elements of the layered oxide, and usually include one or more of Ni, Mn, Fe, Zn, Cu, Ca, Al, W, Sb, Nb, Sn, Li, K, Ag, Zr, Ti, Mo, Cr, Sr, Y, Cd, Ce.

[0009] The complexing agent is preferably one or more of ammonia, dihydrogen phosphate, monohydrogen phosphate, citric acid, oxalic acid, tartaric acid.

[0010] The temperature of the reaction kettle is preferably 40-70℃, the dropwise addition rate ratio of A liquid and B liquid is preferably (1-1.2):(1.8-3), the pH control in the reaction kettle is preferably 8-12, and the aging time is preferably 4-6h.

[0011] The zinc salt is preferably one or more of zinc sulfate, zinc oxalate, zinc chloride, zinc nitrate, zinc phosphate, zinc acetate.

[0012] The ratio of the concentration of zinc ions in the metal liquid C1 to the concentration of other metals (the sum of the concentrations of all metals other than zinc ions in the metal liquid C1) is preferably 0.05:1-0.1:1.

[0013] The ratio of the concentration of zinc ions in the metal liquid C2 to the concentration of other metals (the sum of the concentrations of all metals other than zinc ions in the metal liquid C2) is preferably 0.1:1-0.2:1.

[0014] The concentration of zinc ions in the metal liquid C3 is preferably 0.5-2mol / L.

[0015] The total metal ion concentration in the metal liquid A in step 1 is 0.5-3 mol / L, preferably 0.5-2 mol / L; the OH - concentration in the alkali solution B is preferably 1-3 mol / L.

[0016] The molar ratio of the total amount of substances after mixing the metal liquid A with the metal liquids C1, C2 and C3 is preferably 1:0.05-1:0.2.

[0017] Further, the zinc ion concentration of the metal liquids C1, C2 and C3 has an increasing trend, and the increasing ratio of the zinc ion concentration is preferably (0.3-0.6):1:(1.5-2).

[0018] The second aspect of the present application provides a gradient-doped Zn and ZnO-coated sodium-ion battery layered oxide, and the steps include mixing the layered oxide precursor, a sodium source and zinc oxide uniformly, and two-step calcination to obtain a gradient-zinc-doped and zinc oxide-coated layered oxide.

[0019] The two-step calcination is carried out in an oxidizing atmosphere, including a first-step calcination and a second-step calcination, the first-step calcination temperature is between 300-550 DEG C, and the isothermal sintering time is 3-5 h; the second-step calcination temperature is between 750-950 DEG C, and the isothermal sintering time is 8-15 h. The calcination heating rate is preferably 1-5 DEG C / min.

[0020] The mass ratio of the zinc oxide to the layered oxide precursor is preferably 0.01-0.08:1.

[0021] In the third aspect, the present application provides a positive electrode sheet comprising the zinc-doped and zinc oxide-coated layered oxide prepared by the above preparation method.

[0022] In the fourth aspect, the present application relates to a sodium-ion secondary battery comprising the positive electrode sheet of the third aspect.

[0023] Compared with the prior art, the layered oxide material disclosed in the present application has the characteristics of high stability, good rate performance, excellent high-low temperature performance and excellent cycle performance, and the modification method has a wide application range and can be used for modifying various layered oxide materials including P2 and O3.

[0024] The modification method provided in the present application combines gradient structure design, element doping and metal oxide coating in one, effectively improves the comprehensive performance, the gradient doping method ensures the structural stability while reasonably reducing the use of zinc to ensure the capacity performance, and the zinc oxide coating effectively improves the air stability and reduces the side reaction with the electrolyte, and the modification method is simple and suitable for commercialization.

[0025] The modification method provided in the present application combines gradient structure design, element doping and metal oxide coating in one, effectively improves the comprehensive performance, the gradient doping method ensures the structural stability while reasonably reducing the use of zinc to ensure the capacity performance, and the zinc oxide coating effectively improves the air stability and reduces the side reaction with the electrolyte, and the modification method is simple and suitable for commercialization. DETAILED DESCRIPTION

[0026] The meanings understood by those of ordinary skill in the art of the technical field of the present application are identical. The terms used in the specification of the present application are only for the purpose of describing the specific embodiments and are not intended to limit the present application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. The following is specifically set forth with respect to the embodiments and comparative examples.

[0027] Comparative Example 1:

[0028] 0.9336 g of NiSO4 and 0.9878 g of MnSO4 were weighed and a 2 mol / L metal aqueous solution was prepared. Ammonia water and NaOH were weighed in a molar ratio of 2:1 and a 1 mol / L OH - solution was prepared. The metal solution and the alkali solution were injected into a reaction kettle under nitrogen protection under the driving of a peristaltic pump, the pH was maintained at 10-11, and aging was performed for 5 hours. After filtration and drying, Na2CO3 was added in a molar ratio of 1.02:1 of sodium carbonate to nickel oxide, and the mixture was ball-milled for 6 hours to fully mix. The solid mixture fully mixed was placed in a tube furnace, high-purity air was passed, and sintering was performed at 500°C at a temperature rising rate of 2°C / min for 4 hours. The temperature was continuously increased to 900°C at a temperature rising rate of 2°C / min, and sintering was performed for 15 hours, and then the temperature was decreased to room temperature. A P2-type sodium nickel titanate layered oxide was obtained.

[0029] Comparative Example 2:

[0030] 0.1 mol of NiSO4, 0.2 mol of MnSO4, 0.05 mol of CuSO4, and 0.007 mol of ZnSO4 were weighed and dissolved in water to prepare a 2 mol / L metal solution. Ammonia water and Na2CO3 were weighed in a molar ratio of 2:1 to prepare a 1 mol / L CO3 2- solution. The metal solution and the alkali solution were synchronously injected into a reaction kettle under nitrogen protection under the driving of a peristaltic pump, the pH was maintained at 9.5-10.5, and aging was performed for 5 hours. After filtration and drying, a carbonate precursor was obtained. Na2CO3 was added in a molar ratio of 3.55:1 of sodium carbonate to nickel oxide, and 3% of ZnO based on the mass of the precursor was ball-milled for 6 hours to fully mix. The solid mixture fully mixed was placed in a tube furnace, high-purity air was passed, and sintering was performed at 500°C at a temperature rising rate of 2°C / min for 4 hours. The temperature was continuously increased to 900°C at a temperature rising rate of 2°C / min, and sintering was performed for 15 hours, and then the temperature was decreased to room temperature. A zinc-doped and zinc-coated O3-type sodium nickel titanate layered oxide was obtained.

[0031] Comparative Example 3:

[0032] Take 0.1 mol NiSO4, 0.2 mol MnSO4, 0.05 mol CuSO4, dissolve in water, prepared into 2 mol / L metal liquid A1, take 0.1 mol NiSO4, 0.2 mol MnSO4, 0.05 mol CuSO4, 0.005 mol ZnSO4, dissolve in water, prepared into 2 mol / L metal liquid A2, take 0.1 mol NiSO4, 0.2 mol MnSO4, 0.05 mol CuSO4, 0.009 mol ZnSO4, dissolve in water, prepared into 2 mol / L metal liquid A3, with CO3 2- The total mole ratio of 2:1, take ammonia and 0.051 mol Na2CO3 respectively corresponding to the preparation of 1 mol / L CO3 2- The alkali B1, B2, B3, under the drive of peristaltic pump, gradually injected into the reaction kettle under the protection of nitrogen, according to the order of A1, B1 to A2, B2 to A3, B3, gradually reacted, maintained pH 9.5-10.5, after aging 5h, dried by filtration to obtain carbonate precursor, and with the molar ratio of sodium carbonate to nickel oxide of 3.55:1, Na2CO3 was added and ball milled for 6h to make it fully mixed, the mixed solid mixture was placed in a tube furnace, high-purity air was passed through, and sintered at 500℃ with a temperature rising rate of 2℃ / min for 4h, then continued to rise to 900℃ with a temperature rising rate of 2℃ / min for 15h, and then cooled to room temperature. Gradient zinc doped O3 type sodium nickel manganese copper zinc layered oxide was obtained.

[0033] Example 1:

[0034] Take 0.9336 g NiSO4, 0.9878 g MnSO4, prepare 2 mol / L metal solution A1, take 0.9336 g NiSO4, 0.9878 g MnSO4, 0.0463 g ZnSO4, prepare 2 mol / L metal aqueous solution A2, take 0.9336 g NiSO4, 0.9878 g MnSO4, 0.0842 g ZnSO4, prepare 2 mol / L metal aqueous solution A3, take ammonia and NaOH in a molar ratio of 2:1, respectively, to prepare 1 mol / L lye B1, B2, B3, under the drive of a peristaltic pump, inject the metal solution and lye into the reaction kettle protected by nitrogen, A1, A2, A3 are sequentially dropped at a speed of 0.2 L / h, B1, B2, B3 are sequentially dropped at a speed of 0.4 L / h at the same time, wherein A1, B1 is dropped for 0.5 h, A1, B2 is dropped for 0.2 h, A1, B2 is dropped for 0.05 h. Keep pH at 10-11, age for 5 hours, after drying, add Na2CO3 and 0.3038 g ZnO in a molar ratio of 1.02:1 of sodium carbonate to nickel oxide, ball mill for 6 h to fully mix, place the fully mixed solid mixture in a tube furnace, pass high-purity air, and sinter at 500℃ at a temperature rising rate of 2℃ / min for 4 h, continue to rise to 900℃ at a temperature rising rate of 2℃ / min for 15 h, and then reduce to room temperature to obtain zinc oxide coated P2 type sodium nickel titanate layered oxide.

[0035] Example 2:

[0036] Take 0.1 mol NiSO4, 0.1 mol MnSO4, prepare 2 mol / L metal solution A1, take 0.1 mol NiSO4, 0.1 mol MnSO4, 0.0001 mol ZnSO4, prepare 2 mol / L metal aqueous solution A2, take ammonia and NaOH in a mass ratio of ammonia:NaOH=0.8:1, respectively, to prepare 1 mol / L lye B1, B2, under the drive of a peristaltic pump, inject the metal solution and lye into the reaction kettle protected by nitrogen, A1, A2 are sequentially dropped at a speed of 0.2 L / h, B1, B2 are sequentially dropped at a speed of 0.4 L / h at the same time, wherein A1, B1 is dropped for 0.5 h, A1, B2 is dropped for 0.15 h. Keep pH at 10-11, age for 5 hours, after drying, add 0.051 mol Na2CO3 and 3% ZnO of the mass of the precursor to the ethanol solution and stir to mix, then dry and grind to obtain a precursor powder, place the fully mixed solid mixture in a tube furnace, pass high-purity air, and sinter at 500℃ at a temperature rising rate of 2℃ / min for 4 h, continue to rise to 950℃ at a temperature rising rate of 2℃ / min for 15 h, and then reduce to room temperature to obtain O3 type sodium nickel manganese oxide layered oxide coated with zinc oxide and gradient doped with zinc.

[0037] Sample Name Voltage Range First Cycle Capacity (mAh / g) Capacity Retention (%) Comparative Example 1 2-4V 82.3(1C) 80.5 (200 cycles) Example 1 2-4V 94.5(1C) 94.2 (200 cycles) Comparative Example 1 2-4.3V 134.3(1C) 42.3 (200 cycles) Example 1 2-4.3V 116.8(1C) 88.3 (200 cycles) Comparative Example 2 2-4V 119.2(1C) 76.5 (200 cycles) Comparative Example 3 2-4V 136.6(1C) 88.7 (200 cycles) Example 3 2-4V 128.3.(1C) 92.3 (200 cycles) Comparative Example 2 2-4.3V 135.7(1C) 78.2 (200 cycles) Comparative Example 3 2-4.3V 146.2(1C) 81.3 (200 cycles) Example 3 2-4.3V 140.8(1C) 84.3 (200 cycles)

[0038] Conclusion: From Comparative Example 1 and Example 1, it can be seen that after introducing gradient zinc doping and zinc oxide coating in the P-type material, the capacity and cycle stability are both improved under the conventional 2-4V voltage, which is due to the fact that zinc doping widens the sodium ion diffusion channel to a certain extent, and the column effect of zinc and the protective layer of zinc oxide effectively delay the structure phase transition and reduce the occurrence of side reactions. Under 2-4.3V, Example 1 provides additional first-cycle capacity due to the participation of oxygen in redox, but the generation of oxygen leads to structural distortion, and the cycle stability decreases significantly. However, the gradient zinc doping and zinc coating effectively inhibit the generation of oxygen and structural distortion, and obtain a material with excellent stability.

[0039] From Comparative Example 2, Comparative Example 3 and Example 3, it can be seen that under 2-4V, when only zinc doping and coating are used in O-type, due to non-gradient doping, the non-electrochemically active element zinc has some influence on the overall electrochemical performance, while gradient zinc doping can make full use of zinc to achieve a layer-by-layer progressive structure of internal high electrochemical activity and external high stability to inhibit phase transition, effectively improving the comprehensive performance. When only gradient zinc doping is used, the stability is slightly inferior without coating. Under 2-4.3V, the oxygen is all inhibited to a certain extent, and the material with gradient zinc doping and coating achieves the best comprehensive performance.

Claims

1. A method for the preparation of gradient doped Zn and ZnO coated layered oxide cathodes for sodium-ion batteries, characterized in that, The method comprises the following steps: Step 1: obtaining a precursor by co-precipitation, dissolving metal salts in water by stirring, obtaining a metal solution A after clarification; preparing an alkali solution, dissolving an alkali in another aqueous solution, adding a complexing agent to the aqueous solution, dissolving by stirring until clarification, obtaining an alkali solution B; adding the metal solution A and the alkali solution B into a heating reaction kettle under inert gas protection at a fixed rate, keeping the pH of the mixed solution constant to obtain a layered oxide precursor; Step 2: preparing a metal solution C1 containing the metal solution A and a first concentration of zinc salt; preparing a metal solution C2 by changing the concentration of the zinc salt according to the same method, i.e. replacing the first concentration of zinc salt with a second concentration of zinc salt, and preparing a metal solution C3 containing only a third concentration of zinc salt; preparing corresponding alkali solutions B1, B2 and B3 according to a certain proportion; adding the alkali solution B1 and the metal solution C1 first, then the alkali solution B2 and the metal solution C2, and finally the alkali solution B3 and the metal solution C3 into the layered oxide precursor obtained in step 1 at a certain rate; controlling the pH to be constant during the process, and obtaining a zinc gradient doped layered oxide precursor through aging, filtration, washing and drying steps; Step 3: mixing the layered oxide precursor obtained in step 2 with a sodium salt and zinc oxide, and calcining in stages under an oxidizing atmosphere, and obtaining the layered oxide after cooling and grinding.

2. The production method according to claim 1, characterized by The concentration of metal liquid A in the coprecipitation method is 0.5-2 mol / L; the concentration of OH - in the alkali liquid B is 1-3 mol / L; and the molar ratio of the complexing agent to the total mass of each metal is 0.5:1-5:

1.

3. The preparation method according to claim 1, characterized in that The concentration ratio of zinc ions to other metal ions in the metal solution C1 is 0.05:1-0.1:1; the concentration ratio of zinc ions to other metal ions in the metal solution C2 is 0.1:1-0.2:1; and the concentration of zinc ions in the metal solution C3 is 0.5-2 mol / L.

4. The method of claim 1, wherein, The total molar ratio of the metal solution A and the metal solutions C1, C2 and C3 after mixing is 1:0.05-1:0.

2.

5. The preparation method according to claim 1, characterized in that The zinc ion concentrations of the metal solutions C1, C2 and C3 show an increasing trend, and the increasing ratio of the zinc ion concentrations is (0.3-0.6):1:(1.5-2).

6. The method of claim 1, wherein The alkali solution B1 and the metal solution C1 form a first group, the alkali solution B2 and the metal solution C2 form a second group, and the alkali solution B3 and the metal solution C3 form a third group; the molar ratio of the alkali solution to the metal solution in each group is fixed.

7. The preparation method according to claim 1, characterized in that: The mass ratio of the zinc oxide to the layered oxide precursor is 0.01-0.08:

1.

8. The method of claim 1, wherein the step of forming the first and second layers is performed by a process selected from the group consisting of: sputtering, evaporation, and chemical vapor deposition. The calcination in stages comprises a first step calcination and a second step calcination, the first step calcination temperature is 300-550℃, the isothermal sintering time is 3-5h, the second step calcination temperature is 750-950℃, and the isothermal sintering time is 8-15h; and the calcination heating rate is 1-5℃ / min.

9. A positive electrode sheet characterized by comprising: The layered oxide prepared by the preparation method of any one of claims 1-8.

10. A sodium-ion secondary battery, characterized by, The positive electrode sheet obtained by the method of claim 9.