CN114927658B - Device and method for modifying surface of positive electrode material based on ion exchange membrane - Google Patents

Abstract

The invention relates to a device for surface modification of positive electrode materials based on an ion exchange membrane and a method for surface modification of positive electrode materials. The device for surface modification of positive electrode materials based on ion exchange membranes includes: a cation chamber containing a cation solution; an anion chamber containing an anion solution; for physical separation of the anion chamber and the cation chamber. The ion exchange membrane includes a cation exchange membrane and an anion exchange membrane; and a stirring system respectively provided at the bottom of the cation chamber and the bottom of the anion chamber or/and a flow system respectively connected to the cation chamber and the anion chamber.

Description

A device and cathode material for surface modification of cathode materials based on ion exchange membrane Surface modification methods

Technical field

The present invention relates to surface modification of lithium ion electrode materials, specifically to a device for surface modification of lithium ion positive electrode materials and a surface modification method of positive electrode materials, and belongs to the field of chemical energy storage batteries.

Background technique

The rapid development of new energy vehicles has placed higher requirements on the specific capacity and safety of cathode materials used in power batteries. Among the currently commercialized spinel-type, olivine-type and layered cathode materials, the ternary layered cathode material has attracted widespread attention due to its excellent specific capacity. Although the increase in nickel content can improve the specific capacity and Reduce costs, but as the amount of nickel increases, the cycle performance, thermal stability and safety of the ternary cathode material will deteriorate sharply, seriously restricting its practical application. The root cause of the above problems stems from the material properties of the high-nickel ternary cathode, including the dissolution of metal elements and the side reaction of Ni ⁴⁺ , which is highly oxidizing in the charged state, with the electrolyte and surface reconstruction, resulting in high impedance. NiO phase and releases active oxygen, causing battery gas production and thermal runaway. At present, domestic and foreign scholars mainly solve the above shortcomings by coating the surface of ternary materials to inhibit the dissolution of transition metals and isolating the direct contact between highly active Ni ⁴⁺ and the electrolyte.

At present, the main surface coating methods for cathode materials include co-precipitation, sol-gel, hydrothermal, chemical vapor deposition, atomic deposition, solid-phase ball milling, etc. However, there are still problems such as high cost and insufficient coating. Uniformity and other issues. The precursor salts of the sol-gel method and the hydrothermal method are expensive and have low yields; the chemical vapor deposition method and the atomic deposition method have long processing times, are highly toxic and have complex processes, and the solid-phase ball milling method is difficult to obtain a uniform coating layer. The key to uniform coating lies in the control of the coating layer. The key point of the control of the coating layer lies in the slow deposition of the coating material on the surface of the coated material, and through diffusion control to avoid the formation of two separated phases. At present, the uniform control strategies of the coating layer mainly include buffer solution, slow release by precipitation, catalyst assistance, charge interaction, etc. The above strategy can effectively achieve precise control of the coating layer and significantly improve the performance of the cathode material, but it also has problems such as low universality and complex operation. Therefore, it is of great significance to develop a method that is easy to operate and uniformly coats the cathode material.

Contents of the invention

To address the above problems, the present invention provides a device and method for surface modification of cathode materials based on ion exchange membranes.

In a first aspect, the present invention provides a device for surface modification of cathode materials based on ion exchange membranes, including:

a cation chamber containing a cation solution;

an anion chamber containing an anion solution;

An ion exchange membrane used to physically separate the anion chamber and the cation chamber, the ion exchange membrane includes a cation exchange membrane and an anion exchange membrane;

And a stirring system respectively provided at the bottom of the cation chamber and the bottom of the anion chamber or/and a flow system respectively connecting the cation chamber and the anion chamber.

In the present invention, based on the ion exchange effect of the ion exchange membrane, surface modification is performed on the lithium ion cathode material to improve its electrochemical performance and safety, reduce modification costs, and improve coating uniformity. This method is easy to operate, evenly coated, and easy to expand production.

Preferably, the flow system includes:

A cation solution storage tank, a flow pump and a flow pipeline connecting the cation chamber and the cation solution storage tank;

An anion solution storage tank, a flow pump and a flow pipeline connecting the anion chamber and the anion solution storage tank.

Preferably, the cation chamber and the anion chamber are each equipped with a stirring device, wherein the stirring device includes at least one of a magnetic stirring device, a mechanical stirring device, an ultrasonic stirring device and other stirring devices.

Preferably, the active groups in the cation exchange membrane include at least one of a sulfonic acid group, a phosphate group, a carboxylic acid group, a phenol group, an arsenic acid group and a selenate group; the active groups in the anion exchange membrane include At least one of the amino and aromatic amino groups of the four primary, secondary, tertiary and quaternary amines.

Preferably, the cathode material includes lithiated cathode material and cathode precursor material;

The lithiated cathode material includes LiNi _b Co _c Mn _1-bc O ₂ (where 0≤b≤1, 0≤c≤1); and _LiNim Co _n Al _1-mn O ₂ (0≤m≤1 ,0≤n≤1);

The positive electrode precursor material includes Ni _(1-yz) Co _y Mn _z (OH) ₂ (where 0≤y≤1, 0≤z≤1) and Ni _(1-ad) Co _a Al _d (OH) ₂ (where 0≤a≤1, 0≤d≤1).

Preferably, the solute in the cationic solution is selected from Al(NO ₃ ) ₃ , Al ₂ (SO ₄ ) ₃ , AlCl ₃ , MnCl ₃ , Co(NO ₃ ) ₃ , Co ₂ (SO ₄ ) ₃ , Fe( NO ₃ ) ₃ , Fe ₂ (SO ₄ ) ₃ , FeCl ₃ , Cr(NO ₃ ) ₃ , Cr ₂ (SO ₄ ) ₃ , CrCl ₃ , Zr(NO ₃ ) ₄ , ZrCl ₄ , Zn(NO ₃ ) ₃ , at least one of TiBr ₄ .

Preferably, the solvent in the cationic solution includes at least one of distilled water, methanol, ethanol, isopropanol, n-butanol, isobutanol, cycloethanol, acetone, cyclohexanone, glycerol and ethyl acetate.

Preferably, the concentration of the cationic solution is 0.01 mol/L to 10 mol/L.

Preferably, the solute in the anionic solution is selected from the group consisting of KOH, NaOH, LiOH, (NH ₄ ) ₂ HPO ₄ , NH ₄ H ₂ PO ₄ , H ₃ PO ₄ , NH ₃ ·H ₂ O, LiF, and KF in NaF. of at least one.

Preferably, the solvent in the anionic solution includes at least one of distilled water, methanol, ethanol, isopropanol, n-butanol, isobutanol, cycloethanol, acetone, cyclohexanone, glycerol and ethyl acetate. The concentration of the anion solution is 0.01 mol/L to 10 mol/L.

Preferably, the device for surface modification of cathode materials based on ion exchange membranes also includes an external power supply connected to the cation chamber and the anion chamber.

In a second aspect, the present invention provides a surface modification method for cathode materials, including:

(1) Disperse the cathode material in the cation solution or anion solution in the above-mentioned device for surface modification of cathode materials based on ion exchange membranes, and combine the anion solution with the cation solution through a stirring system or flow system to cause a precipitation reaction or redox reaction. Precipitates are generated to form coating substances on the surface of the cathode material or in the particle pores of the cathode material. After separation and drying, a cathode material with coating substances distributed on the surface is obtained;

(4) Heat-treat the cathode material with coating substances distributed on its surface to obtain a surface-modified cathode material.

In the present invention, with a unique device structure, an ion exchange membrane is used to isolate the anions and cations of the coating or filling material, without the need for an external power supply, so that the anions and cations slowly combine to cause a precipitation reaction or a redox reaction to generate precipitation, thereby obtaining coating material. Of course, it is also possible to apply an external power supply, that is, the charge ions migrate faster under concentration diffusion and electric field. Since the process of generating precipitation is controlled by the diffusion rate of ions in the ion exchange membrane, the supersaturation of the coating material in the positive electrode material mixed liquid system is always maintained at a low level, inhibiting the process of forming separated particles between the coating material and the positive electrode material. , promote its heterogeneous nucleation and growth on the surface of the cathode material, and achieve uniform coating or filling on the surface of the cathode material particles under the action of stirring. Through subsequent heat treatment, multiple surface modifications such as surface coating of the cathode material, primary particle grain boundary filling, and surface element doping are achieved to improve the stability of the cathode material.

Preferably, when the ion exchange membrane is a cation exchange membrane, the positive electrode material is dispersed in the anion chamber; when the ion exchange membrane is an anion exchange membrane, the positive electrode material is dispersed in the cation chamber; the particle size of the positive electrode material is 1 ~ 100μm.

Preferably, the cationic solution or anionic solution and the positive electrode material are mixed to obtain a mixed liquid; the solid content of the positive electrode material in the mixed liquid is 2wt% to 20wt%.

Preferably, the temperature of the precipitation reaction or the redox reaction is 20-100°C, and the time is 0.5-36 hours.

Preferably, the coating substances in the cathode material with coating substances distributed on the surface include Mn(OH) ₂ , Co(OH) ₂ , AlPO ₄ , Mn ₃ (PO ₄ ) ₂ , FePO ₄ , Li ₃ PO ₄ , AlF ₃ , LiAlO ₂ , Li ₂ ZrO ₃ , Li ₄ Ti ₅ O1 ₂ , Al ₂ O ₃ , TiO ₂ , ZrO ₂ , one or more of ZnO, Al(OH) ₃ and Zr(OH) ₄ ; The mass of the coating material is 0.1% to 10% of the mass of the positive electrode material (before modification). Among them, drying includes natural drying, oven drying, and vacuum drying, the drying temperature is 20 to 150°C, and the drying time is 24 to 48 hours.

Preferably, when the cathode material is a lithiated cathode material, the heat treatment temperature is 600-800°C, the heat treatment time is 2-10 hours, and the heat treatment atmosphere is pure oxygen or air. Alternatively, when the positive electrode material is a positive electrode precursor material, the obtained positive electrode material with coating material distributed on the surface and lithium oxide are mixed and sintered to obtain a surface modified positive electrode material; the lithium-containing oxide includes LiOH·H ₂ O , at least one of LiNO ₃ , Li ₂ CO ₃ , Li ₂ O and Li ₂ O ₂ , the molar ratio of the cathode material with coating material distributed on the surface and the lithium-containing oxide is 1: (1.01～1.10) .

Preferably, the sintering process includes: one-step sintering or two-step sintering; the atmosphere of the sintering process is pure oxygen or air.

Wherein, the one-step sintering includes: the sintering temperature is 600-850°C, the holding time is 10h-20h, and the temperature rise rate of the one-step sintering is preferably 2-5°C/min;

The two-step sintering includes: the first step sintering temperature is 300-500°C and the holding time is 2h-4h; the second step sintering temperature is 700-850°C and the holding time is 10h-20h; the preferred temperature rise rate of the two-step sintering is It is 2~5℃/min.

In a third aspect, the present invention provides a surface-modified cathode material prepared according to the above-mentioned surface modification method.

In a fourth aspect, the present invention provides a lithium ion battery, including: a negative electrode material, the above-mentioned surface-modified positive electrode material, and a separator or solid electrolyte that separates the surface-modified positive electrode material and the negative electrode material; preferably, the separator includes Polypropylene separator (PP), celgard separator, the solid electrolyte includes garnet solid electrolyte, NASICON solid electrolyte, sulfide solid electrolyte, perovskite solid electrolyte; preferably, the negative electrode material is graphite, silicon carbon , silicon dioxide, silicon alloy, tin oxide, lithium metal or lithium alloy.

Beneficial effects:

The present invention uses an ion exchange membrane to selectively diffuse anions or cations, so that anions and cations slowly combine to cause a precipitation reaction or a redox reaction to generate precipitation, thereby obtaining a coated substance. The device and method keep the supersaturation degree of the coating material in the positive electrode material mixed liquid system at a low level, suppress the process of the coating material forming particles separated from the precursor material due to homogeneous nucleation and growth, and promote Heterogeneous nucleation and growth of the coating material on the surface of the precursor material, thereby achieving uniform coating on the surface of the cathode material under the action of solid-liquid phase shear force provided by stirring;

The present invention performs in-situ reaction on the surface of the precursor to achieve uniform coating, and can achieve surface coating of the cathode material through heat treatment steps, primary particle grain boundary filling, surface element doping and other multiple surface modifications, thereby achieving various synergistic effects. Further improve the stability of active materials;

The basic driving force for coating in the present invention comes from ion diffusion, no additional energy is required, the principle is simple, the required drugs and solvents are cheap and easy to obtain, and it is environmentally friendly. Therefore, the invention has strong versatility, easy operation, green and environmental protection, and has high industrial application value.

Description of drawings

Figure 1 is a device for surface modification of cathode materials in the present invention. In the figure: 1-cation chamber, 2-anion chamber, 3-ion exchange membrane, 4-stirrer;

Figure 2 is an X-ray diffraction (XRD) pattern of the cathode material, which includes surface-modified Example 1 and non-surface-modified Comparative Example 1;

Figure 3 is the dQ/dV curve of the cathode material at different numbers of cycles. The material includes surface-modified Example 1 (B) and non-surface-modified Comparative Example 1 (A);

Figure 4A and Figure 4B are cycle stability comparison diagrams of Examples 1-3 that have been surface modified and Comparative Example 1 that has not been surface modified;

Figure 5 is a comparison chart of the rate performance of Example 1 with surface modification and Comparative Example 1 without surface modification;

Figure 6 is a scanning electron microscopy image (SEM) of the cross section of the cathode particle before and after cycling of the cathode material. The material includes Example 1 that has been surface modified and Comparative Example 1 that has not been surface modified (both scale bars are 5 μm ).

Detailed ways

The present invention will be further described below through the following embodiments. It should be understood that the following embodiments are only used to illustrate the present invention but not to limit the present invention.

In this disclosure, a device for surface modification of cathode materials based on ion exchange membranes: includes a cation chamber and an anion chamber, and a cation exchange membrane that separates the anion chamber and the cation chamber; wherein both the cation chamber and the anion chamber are equipped with stirring devices. . When the device of the present invention is used, the positive electrode material mixture and the cationic substance solution are first prepared, and then the positive electrode material mixture and the cationic substance solution are injected into the anion chamber and the cation chamber respectively, and stirring is always turned on during coating.

In the present invention, an anionic material solution and a cationic material solution are configured, and the anions and cations constituting the coating material are placed in the anion chamber and the cation chamber respectively, and the positive electrode material is optionally placed in the anion chamber or the cation chamber to obtain a positive electrode material mixture. . The ion exchange membrane is used to isolate the anions and cations of the coating material, control the diffusion of anions or cations, and slowly combine the anions and cations, causing a precipitation reaction or a redox reaction to generate precipitation, thereby obtaining the coating material on the surface of the cathode material or in the pores of the particles. . The obtained modified cathode material is separated, dried, and heat treated to obtain a surface-modified cathode material. The following describes in detail the surface modification method of cathode materials using this device.

Prepare anionic solution. A soluble substance that can provide anions of the coating material is dissolved in a solvent to obtain an anionic solution. Optionally, the positive electrode material is dispersed into the anion solution to obtain a positive electrode material mixture. More preferably, the positive electrode material mixture is injected into the anion chamber, and the cation solution is injected into the cation chamber. Then, the positive electrode material is coated. After the coating is completed, the anion chamber mixture is centrifuged and dried to obtain the coated positive electrode material. During the coating process, agitation is always used in the anion and cation chambers. The centrifugal speed can be 3000~8000rpm, and the centrifugation time can be 3~5 minutes. Drying is or vacuum drying, the drying temperature is 20~150℃, and the drying time is 24~48h.

Prepare cationic solution. A soluble substance that can provide cations to the coating material is dissolved in a solvent, anionic solution. Optionally, the positive electrode material is dispersed into the cationic solution to obtain a positive electrode material mixture. More preferably, the positive electrode material mixture is injected into the cation chamber, and the anion solution is injected into the anion chamber. Then yes. The positive electrode material is coated, and after the coating is completed, the anion chamber mixture is centrifuged and dried to obtain the coated positive electrode material. During the coating process, agitation is always used in the anion and cation chambers. The centrifugal speed can be 3000~8000rpm, and the centrifugation time can be 3~5 minutes. Drying is or vacuum drying, the drying temperature is 20~150℃, and the drying time is 24~48h.

When the coated material is a lithiated cathode material, the resulting coated cathode material is heat treated. After the heat treatment process, the cathode material regains its electrochemical activity, and the coating material coating the surface of the cathode material will become the cathode material through heat treatment. Surface coating and/or elemental doping.

When the coated material is a positive electrode precursor material, mix the obtained coated positive electrode precursor material with a lithium-containing compound such as LiOH·H ₂ O according to a molar ratio of 1:x (1.01 to 1.10) (for example, ball milling to mix thoroughly), After sintering treatment, during the sintering process, the cathode precursor material and the lithium-containing oxide undergo a high-temperature solid phase reaction to form the cathode material, and the coating material coating the surface of the cathode precursor material will be formed at high temperature. Surface coating and/or elemental doping of cathode materials.

In the present invention, the cathode material includes lithiated cathode material and cathode precursor material. The particle size of the positive electrode material is 1 to 100 μm. In an optional embodiment, the dispersion method for dispersing the positive electrode material into the cationic solution or the anionic solution to obtain the positive electrode material mixture is ultrasonic dispersion, the ultrasonic power is 100-500W, and the ultrasonic time is 1-180 minutes.

In the present invention, the lithium ion battery includes: a positive electrode, a negative electrode, and a separator or solid electrolyte that separates the positive and negative electrode materials. The cathode material of the battery is the surface-modified cathode material based on the surface modification of the ion exchange membrane according to the present invention. The separator or solid electrolyte includes PP, celgard, garnet solid electrolyte, NASICON solid electrolyte, sulfide solid electrolyte, and perovskite solid electrolyte. The negative electrode is graphite, silicon carbon, silicon dioxide, silicon alloy, tin oxide, metallic lithium or lithium alloy.

Specifically, the surface-modified cathode material is evenly mixed with conductive carbon and binder to form a slurry and coated on aluminum foil. The dried aluminum foil carrying the slurry is cut into small discs using a cutting machine to be used as the cathode. . A full cell was assembled and tested and characterized.

The following further examples are given to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above contents of the present invention all belong to the present invention. scope of protection. The specific process parameters in the following examples are only an example of the appropriate range, that is, those skilled in the art can make selections within the appropriate range through the description herein, and are not limited to the specific values exemplified below.

Example 1

Assemble the device diagram shown in Figure 1. The ion exchange membrane used in the device is Nafion 117, a proton exchange membrane produced by DuPont. Before use, the Nafion 117 membrane was boiled in a 5 wt% H ₂ O ₂ aqueous solution at 80°C for 1 hour to remove organic impurities in the membrane. Secondly, rinse the membrane repeatedly with deionized water, soak it in deionized water at 80°C and boil it for 1 hour to completely remove the remaining H ₂ O ₂ . The membrane was again immersed in a 5wt% H ₂ SO ₄ solution at 80°C and boiled for 1 hour. Finally, the membrane was rinsed repeatedly with deionized water, and then soaked in deionized water at 80°C for heat treatment for 1 hour to completely remove the remaining H ₂ SO ₄ in the membrane. The purpose of proton exchange membrane Nafion 117 treatment is to activate the proton exchange membrane so that it can have cation exchange function.

Step 1): Weigh NaOH and dissolve it in the aqueous solution, and prepare a NaOH aqueous solution with a concentration of 0.1 mol/L as an anion solution. Mix 4g of nickel-cobalt-manganese ternary precursor material (Ni _0.83 Co _0.12 Mn _0.05 (OH) ₂ ) and the obtained anion solution at a mass ratio of 1:20, and disperse the mixed solution using ultrasound for 10 minutes to obtain a positive electrode. Material mixture.

Step 2): Dissolve MnCl ₂ in water to prepare a 0.1 mol/L MnCl ₂ solution (80 mL) as a cationic solution.

Step 3): Inject the positive electrode material mixture obtained in step 1) and the cationic solution obtained in step 2) into the anion chamber and the cation chamber respectively, keep the stirring of the anion chamber and the cation chamber always turned on, and perform surface coating on the precursor. The coating time is 4h, and the coating temperature is 25℃. After the coating is completed, the anion chamber mixture is centrifuged at a centrifugal speed of 3000 rpm and a centrifugation time of 3 minutes. The solid material obtained by centrifugation was dried in a vacuum oven at a drying temperature of 80°C and a drying time of 24 hours. The surface Mn(OH) _2- coated ternary cathode precursor material was obtained.

Step 4): Mix the coated ternary precursor material obtained in step 3) and LiOH·H ₂ O thoroughly by ball milling at a molar ratio of 1:1.05, and then sinter in two steps under a pure oxygen atmosphere: First step sintering temperature The sintering temperature is 400℃, the holding time is 2h; the sintering temperature in the second step is 750℃, the holding time is 12h; the heating rate is 3℃/min. Surface-modified cathode materials were obtained.

The obtained surface-modified cathode material is used as a cathode active material to prepare an electrode and assemble a button battery. Assembly and testing of CR2025 button battery: Make the surface-modified cathode material, conductive carbon (Super P:VGCF=1:1), and polyvinylidene fluoride (PVDF) into a slurry according to the mass ratio of 8:1:1. Coated on aluminum foil, use a cutting machine to cut the dried aluminum foil loaded with slurry into small discs with a diameter of 1.2cm and use them as positive electrodes. Use metal lithium sheets as negative electrodes, Celgard as separators, and 1M carbonate solution. Electrolyte (where the solvent is a mixed solution of ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) with a volume ratio of 1:1:1, and the solute is LiPF ₆ ), in argon A CR2025 button battery is assembled in the air glove box.

Example 2

Step 1): Weigh NaOH and dissolve it in the aqueous solution to prepare a 0.1 mol/L anion solution. Mix 4g of nickel-cobalt-manganese ternary precursor material (Ni _0.83 Co _0.12 Mn _0.05 (OH) ₂ ) and the obtained anion solution at a mass ratio of 1:20, and disperse the mixed solution using ultrasound for 10 minutes to obtain a positive electrode. Material mixture;

Step 2): Dissolve Mn(C ₂ O ₂ H ₃ ) ₂ in water to prepare a Mn(C ₂ O ₂ H ₃ ) ₂ solution (80 mL) with a concentration of 0.2 mol/L as a cationic solution;

Step 3): Inject the precursor mixed solution obtained in step 1) and the cationic solution obtained in step 2) into the anion chamber and the cation chamber respectively, keep stirring in the anion chamber and cation chamber always turned on, and perform surface coating on the precursor. The coating time is 4h, the coating temperature is 25℃. After the coating is completed, the anion chamber mixture is centrifuged at a centrifugal speed of 3000 rpm and a centrifugation time of 3 minutes. The solid material obtained by centrifugation was dried in a vacuum oven at a drying temperature of 80°C and a drying time of 24 hours. Obtain the surface Mn(OH) _2- coated ternary cathode precursor material;

Step 4): Mix the coated ternary precursor material obtained in step 3) and LiOH·H ₂ O thoroughly by ball milling at a molar ratio of 1:1.05, and then sinter in two steps under a pure oxygen atmosphere: First step sintering temperature The sintering temperature is 400℃, the holding time is 2h; the sintering temperature in the second step is 750℃, the holding time is 12h; the heating rate is 3℃/min. A surface-modified cathode material was obtained; the surface-modified cathode material was prepared into an electrode and a button battery was assembled. The preparation process was the same as in Example 1.

Example 3

Step 1): Weigh NaOH and dissolve it in the aqueous solution to prepare a 0.1 mol/L anion solution. Mix 4g of nickel-cobalt-manganese ternary precursor material (Ni _0.83 Co _0.12 Mn _0.05 (OH) ₂ ) and the obtained anion solution at a mass ratio of 1:20, and disperse the mixed solution using ultrasound for 10 minutes to obtain a positive electrode. Material mixture;

Step 2): Dissolve Co(C ₂ O ₂ H ₃ ) ₂ in water to prepare a Co(C ₂ O ₂ H ₃ ) ₂ solution (80 mL) with a concentration of 0.2 mol/L as a cationic solution;

Step 3): Inject the precursor mixed solution obtained in step 1) and the cationic solution obtained in step 2) into the anion chamber and the cation chamber respectively, keep stirring in the anion chamber and cation chamber always turned on, and perform surface coating on the precursor. The coating time is 4h, the coating temperature is 25℃. After the coating is completed, the anion chamber mixture is centrifuged at a centrifugal speed of 3000 rpm and a centrifugation time of 3 minutes. The solid material obtained by centrifugation was dried in a vacuum oven at a drying temperature of 80°C and a drying time of 24 hours. Obtain the surface Co(OH) _2- coated ternary cathode precursor material;

Step 4): Mix the coated ternary precursor material obtained in step 3) and LiOH·H ₂ O thoroughly by ball milling at a molar ratio of 1:1.05, and then sinter in two steps under a pure oxygen atmosphere: First step sintering temperature The sintering temperature is 400℃, the holding time is 2h; the sintering temperature in the second step is 750℃, the holding time is 12h; the heating rate is 3℃/min. A surface-modified cathode material was obtained; the surface-modified cathode material was prepared into an electrode and a button battery was assembled. The preparation process was the same as in Example 1.

Example 4

Step 1): Weigh NaOH and dissolve it in the aqueous solution to prepare a 0.1 mol/L anion solution. 4g of nickel-cobalt-manganese ternary precursor material (Ni _0.83 Co _0.12 Mn _0.05 (OH) ₂ ) and the obtained anion salt solution were mixed according to a mass ratio of 1:20, and the mixed solution was dispersed using ultrasound for 10 minutes to obtain Cathode material mixture.

Step 2): Dissolve MnCl ₂ and Co(NO ₃ ) ₂ in water at a molar ratio of 1:1 to prepare a 0.1 mol/L cation solution (80 mL).

Step 3): Inject the precursor mixed solution obtained in step 1) and the cationic solution obtained in step 2) into the anion chamber and the cation chamber respectively, keep stirring in the anion chamber and cation chamber always turned on, and perform surface coating on the precursor. The coating time is 4h, the coating temperature is 25℃. After the coating is completed, the anion chamber mixture is centrifuged at a centrifugal speed of 3000 rpm and a centrifugation time of 3 minutes. The solid material obtained by centrifugation was dried in a vacuum oven at a drying temperature of 80°C and a drying time of 24 hours. A ternary cathode precursor material coated with surface Mn _f Co _g (OH) ₂ (f+g=1) was obtained.

Step 4): Mix the coated ternary precursor material obtained in step 3) and LiOH·H ₂ O thoroughly by ball milling at a molar ratio of 1:1.05, and then sinter in two steps under a pure oxygen atmosphere: First step sintering temperature The sintering temperature is 400℃, the holding time is 2h; the sintering temperature in the second step is 750℃, the holding time is 12h; the heating rate is 3℃/min. Surface-modified cathode materials were obtained.

The obtained surface-modified cathode material was prepared into an electrode and a button battery was assembled. The process was the same as in Example 1.

Example 5

Step 1): Weigh (NH ₄ ) ₂ HPO ₄ and dissolve it in the aqueous solution to prepare a 0.1 mol/L anion solution. Mix 4g of nickel-cobalt-manganese ternary precursor material (Ni _0.83 Co _0.12 Mn _0.05 (OH) ₂ ) and the obtained anion solution at a mass ratio of 1:20, and disperse the mixed solution using ultrasound for 10 minutes to obtain a positive electrode. Material mixture;

Step 2): Dissolve Al(NO ₃ ) ₃ ·9H ₂ O in water to prepare a 0.1mol/L cation solution (80mL);

Step 3): Inject the precursor mixed solution obtained in step 1) and the cationic solution obtained in step 2) into the anion chamber and the cation chamber respectively, keep stirring in the anion chamber and cation chamber always open, and coat the precursor. The coating time is 4 hours. , the coating temperature is 25℃. After the coating is completed, the anion chamber mixture is centrifuged at a centrifugal speed of 3000 rpm and a centrifugation time of 3 minutes. The solid material obtained by centrifugation was dried in a vacuum oven at a drying temperature of 80°C and a drying time of 24 hours. Obtain AlPO _4- coated ternary cathode precursor material;

Step 4): Mix the coated ternary precursor material obtained in step 3) and LiOH·H ₂ O thoroughly by ball milling at a molar ratio of 1:1.05, and then sinter in two steps under a pure oxygen atmosphere: First step sintering temperature The sintering temperature is 400℃, the holding time is 2h; the sintering temperature in the second step is 750℃, the holding time is 12h; the heating rate is 3℃/min. Surface-modified cathode materials were obtained.

The surface-modified cathode material was prepared into an electrode and a button battery was assembled. The process was the same as in Example 1.

Example 6

Step 1): Weigh LiOH·H ₂ O and dissolve it in the aqueous solution to prepare a 0.1 mol/L anion solution. Mix 4g of nickel-cobalt-manganese ternary precursor material (Ni _0.83 Co _0.12 Mn _0.05 (OH) ₂ ) and the obtained anion solution at a mass ratio of 1:20, and disperse the mixed solution using ultrasound for 10 minutes to obtain a positive electrode. Material mixture;

Step 2): Dissolve Al(NO ₃ ) ₃ ·9H ₂ O in water to prepare a 0.1mol/L cation solution (80mL);

Step 3): Inject the precursor mixed solution obtained in step 1) and the cationic solution obtained in step 2) into the anion chamber and the cation chamber respectively, keep stirring in the anion chamber and cation chamber always open, and coat the precursor. The coating time is 4 hours. , the coating temperature is 25℃. After the coating time is over, the anion chamber mixture is centrifuged at a centrifugal speed of 3000 rpm and a centrifugation time of 3 minutes. The solid material obtained by centrifugation was dried in a vacuum oven at a drying temperature of 80°C and a drying time of 24 hours. Obtain LiAlO _2- coated ternary cathode precursor material;

Step 4): Mix the coated ternary precursor material obtained in step 3) and LiOH·H ₂ O thoroughly by ball milling at a molar ratio of 1:1.05, and then sinter in two steps under a pure oxygen atmosphere. The sintering temperature in the first step The sintering temperature is 400℃, the holding time is 2h; the sintering temperature in the second step is 750℃, the holding time is 12h; the heating rate is 3℃/min. Surface-modified cathode materials were obtained.

The obtained surface-modified cathode material was prepared into an electrode and a button battery was assembled. The process was the same as in Example 1.

Example 7

Step 1): Weigh LiOH·H ₂ O and dissolve it in the aqueous solution to prepare a 0.1 mol/L anion solution. Mix 4g of nickel-cobalt-manganese ternary precursor material (Ni _0.83 Co _0.12 Mn _0.05 (OH) ₂ ) and the obtained anion solution at a mass ratio of 1:20, and disperse the mixed solution using ultrasound for 10 minutes to obtain a positive electrode. Material mixture;

Step 2): Dissolve 0.49g of ZrO(NO ₃ ) ₂ ·5H ₂ O in water to prepare a 0.1mol/L cation solution (80mL);

Step 3): Inject the precursor mixed solution obtained in step 1) and the cationic solution obtained in step 2) into the anion chamber and the cation chamber respectively, keep the stirring in the anion chamber and cation chamber turned on at all times, and coat the precursor with ZrO _2. The coating time is 4h, and the coating temperature is 25℃. After the coating time is over, the anion chamber mixture is centrifuged at a centrifugal speed of 3000 rpm and a centrifugation time of 3 minutes. The solid material obtained by centrifugation was dried in a vacuum oven at a drying temperature of 80°C and a drying time of 24 hours. Obtain ZrO _2- coated ternary cathode precursor material;

Step 4): Mix the coated ternary precursor material obtained in step 3) and LiOH·H ₂ O thoroughly by ball milling at a molar ratio of 1:1.05, and then sinter in two steps under a pure oxygen atmosphere: First step sintering temperature The sintering temperature is 400℃, the holding time is 2h; the sintering temperature in the second step is 750℃, the holding time is 12h; the heating rate is 3℃/min. Surface-modified cathode materials were obtained.

The obtained surface-modified cathode material was prepared into an electrode and a button battery was assembled. The process was the same as in Example 1.

Comparative example 1

The nickel-cobalt-manganese ternary precursor material (Ni _0.83 Co _0.12 Mn _0.05 (OH) ₂ ) is directly ball-milled and mixed with LiOH·H ₂ O according to a molar ratio of 1:1.05, and then sintered in two steps under a pure oxygen atmosphere: the first The sintering temperature in the first step is 400°C and the holding time is 2h; the sintering temperature in the second step is 750°C and the holding time is 12h; the heating rate is 3°C/min. Surface-modified cathode materials were obtained.

The obtained surface-modified cathode material was prepared into an electrode and a button battery was assembled. The process was the same as in Example 1.

Figure 1 respectively shows a device for surface modification of the positive electrode. The device is mainly divided into cation chamber, anion chamber, ion exchange membrane and stirring or flow system. During use, the anions and cations that make up the coating material are placed in the anion chamber and the cation chamber respectively, and the positive electrode material is optionally placed in the anion chamber or the cation chamber according to the type of ion exchange membrane selected to obtain a positive electrode material mixture. The components in the figures are not to scale, emphasis instead being placed upon the principles of the examples, embodiments, and arrangements presented. It is to be understood that the application is not limited to the details or methodology set forth in the specification or illustrated in the drawings. It is also to be understood that the terminology used in the present disclosure is for the purpose of description only and should not be regarded as limiting.

Figure 2 shows the X-ray diffraction (XRD) pattern of the positive electrode. The positive electrode material includes Example 1 with surface modification and Comparative Example 1 without surface modification. All diffraction peaks match well with the typical hexagonal a- _NaFeO2 structure (JCPDF card number 01-089-4533, space group R-3m), which represents the main phase of NCM. The a-NaFeO ₂ -type crystal structure is an ordered rock salt type, with Li and Me ions occupying alternating (111) layers. NCM has a _layered NaFeO structure, R-3m space group, with alternating layers of _LiO and MO _octahedrons . As can be seen from Figure 1, the main diffraction peaks of all samples match well with the JCPDF card with R-3m space group. It shows that surface modification by the method of the present invention does not change the layered structure of NCM materials.

Figure 3 shows the dQ/dV curves of cathode materials at different numbers of cycles, including surface-modified Example 1 (B) and non-surface-modified Comparative Example 1 (A). The dQ/dV curve shows that after cycling, the peak position of the dQ/dV curve of Comparative Example 1 has been severely shifted, and the charging peak has moved to the right, indicating that the material has been severely polarized during the cycle; the phase change peak at high voltage H2-H3 gradually disappears, indicating that the high-voltage cathode material has undergone a serious phase change. In contrast, the position of the peak in Example 1 did not shift significantly, indicating that the polarization and phase change of the cathode material during the cycle was small. It is fully demonstrated that the surface modification method of nickel-cobalt-manganese ternary cathode material based on ammonolysis reaction is beneficial to suppress the polarization and phase change during the cycle of cathode materials.

Figures 4A and 4B compare the cycle performance of the cathode materials obtained in Example 1, Example 2 and Example 3 after surface modification and Comparative Example 1 without surface modification. The results show that the cycle performance of the surface-modified cathode material using the method of the present invention is significantly improved. After cycling under the same conditions, the capacity retention rate of the surface-modified cathode material is significantly higher than that of the cathode material without surface modification, indicating that The surface modification implemented by the present invention can significantly improve the cycle stability of the cathode material. This fully demonstrates the effectiveness of the device and method for surface modification of cathode materials based on ion exchange membranes.

Figure 5 shows a magnification comparison chart of the cathode material, which includes Example 1 with surface modification and Comparative Example 1 without surface modification. The results show that the device and method for surface modification of cathode materials based on ion exchange membranes have significantly improved the rate performance of the nickel cobalt manganese cathode material after surface modification, and can release more capacity under high rate conditions, which fully demonstrates that based on ions Devices and methods for surface modification of cathode materials of exchange membranes can improve the rate performance of cathode materials.

Figure 6 shows SEM images of cross-sections of cathode particles before and after cycling of cathode materials, including surface-modified Example 1 and unmodified Comparative Example 1. The results show that both Example 1 and Comparative Example 1 are secondary particles formed by agglomeration of primary particles. Before circulation, the primary particles are tightly combined, and there are no obvious cracks between the secondary particles. After 1C magnification and 150 cycles, Example 1 maintained the complete spherical secondary particle morphology, while the positive electrode particles of Comparative Example 1 were obviously broken. It is shown that the device and method for surface modification of cathode materials based on ion exchange membranes can suppress particle breakage of cathode materials during circulation.

The above-described embodiments are only preferred embodiments to fully illustrate the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are within the protection scope of the present invention. The protection scope of the present invention shall be determined by the claims.

Claims (12)

1. A method for modifying a surface of a positive electrode material, comprising:

(1) Dispersing the positive electrode material in an anion solution in an anion chamber in a device based on surface modification of the positive electrode material of an ion exchange membrane, combining the anion solution and the cation solution through a stirring system or a flowing system, generating precipitation through precipitation reaction, forming coating substances on the surface of the positive electrode material or at particle pores of the positive electrode material, and separating and drying to obtain the positive electrode material with the coating substances distributed on the surface; the positive electrode material is a positive electrode precursorA bulk material; the positive electrode precursor material is Ni _(1-y-z) Co _y Mn _z (OH) ₂ Wherein y is more than or equal to 0 and less than or equal to 1, and z is more than or equal to 0 and less than or equal to 1; the coating substance in the positive electrode material with the coating substance distributed on the surface is Mn (OH) ₂ 、Co(OH) ₂ 、AlPO ₄ 、LiAlO ₂ And ZrO(s) ₂ One of the following; the device for modifying the surface of the positive electrode material based on the ion exchange membrane comprises: a cation chamber containing a cation solution therein; an anion chamber containing an anion solution having a solute selected from the group consisting of NaOH, liOH and (NH) ₄ ) ₂ HPO ₄ The method comprises the steps of carrying out a first treatment on the surface of the The positive electrode material is dispersed in an anionic solution; the ion exchange membrane is used for physically separating the anion chamber from the cation chamber, and is a cation exchange membrane; the active group in the cation exchange membrane is a sulfonic group; and stirring systems respectively arranged at the bottom of the cation chamber and the bottom of the anion chamber or/and flow systems respectively communicated with the cation chamber and the anion chamber; the flow system includes: a flow pump and a flow pipeline for communicating the cation chamber with the cation solution storage tank; a flow pump and a flow pipeline which are communicated with the anion chamber and the anion solution storage tank;

(2) Mixing the obtained positive electrode material with the surface distributed with the coating substance and lithium oxide, and performing sintering treatment to obtain a surface modified positive electrode material; the lithium oxide is LiOH.H ₂ O、LiNO ₃ 、Li ₂ CO ₃ 、Li ₂ O and Li ₂ O ₂ At least one of them.

2. The method for surface modification of a positive electrode material according to claim 1, wherein the positive electrode material has a particle diameter of 1 to 100 μm.

3. The method for surface modification of a positive electrode material according to claim 1, wherein the anionic solution and the positive electrode material are mixed to obtain a mixed solution; the solid content of the positive electrode material in the mixed solution is 2-20wt%;

the temperature of the precipitation reaction is 20-100 ℃ and the time is 0.5-36 hours.

4. The method for modifying the surface of a positive electrode material according to claim 1, wherein the mass of the coating substance is 0.1 to 10% of the mass of the positive electrode material.

5. The method for surface modification of a positive electrode material according to any one of claims 1 to 4, wherein the solute in the cationic solution is selected from Al (NO ₃ ) ₃ 、MnCl ₂ And Co (NO) ₃ ) ₂ 。

6. The method for surface modification of a positive electrode material according to any one of claims 1 to 4, wherein the molar ratio of the positive electrode material having the coating substance distributed on the surface thereof to the lithium oxide is 1: (1.01-1.10).

7. The method for surface modification of a positive electrode material according to claim 6, wherein the sintering treatment comprises: one-step sintering or two-step sintering; the sintering treatment atmosphere is pure oxygen or air

Wherein the one-step sintering comprises: the sintering temperature is 600-850 ℃, and the heat preservation time is 10-20 hours;

the two-step sintering comprises: the sintering temperature in the first step is 300-500 ℃, and the heat preservation time is 2-4 hours; the sintering temperature in the second step is 700-850 ℃, and the heat preservation time is 10-20 h.

8. The surface modification method of a positive electrode material according to claim 7, wherein the one-step sintering has a temperature rise rate of 2 to 5 ℃/min; the temperature rising rate of the two-step sintering is 2-5 ℃/min.

9. The method for surface modification of a positive electrode material according to any one of claims 1 to 4, wherein the stirring system comprises at least one of a magnetic stirring device, a mechanical stirring device and an ultrasonic stirring device, which are provided at the bottom of the anion chamber and the bottom of the anion chamber, respectively.

10. The method for surface modification of a positive electrode material according to any one of claims 1 to 4, wherein the solvent in the cationic solution is at least one of distilled water, methanol, ethanol, isopropanol, n-butanol, isobutanol, cyclo-ethanol, acetone, cyclohexanone, glycerin, and ethyl acetate;

the concentration of the cationic solution is 0.01mol/L to 10mol/L.

11. The method for surface modification of a positive electrode material according to any one of claims 1 to 4, wherein the solvent in the anionic solution is at least one of distilled water, methanol, ethanol, isopropanol, n-butanol, isobutanol, cyclo-ethanol, acetone, cyclohexanone, glycerin and ethyl acetate;

the concentration of the anionic solution is 0.01mol/L to 10mol/L.

12. The method for surface modification of a positive electrode material according to claim 11, wherein the device for surface modification of a positive electrode material based on an ion exchange membrane further comprises an external power source connected to the cation chamber and the anion chamber.