A positive electrode lithium supplementing material, a preparation method and application thereof

Abstract

The application provides a positive electrode lithium supplement material, a preparation method and application thereof. The positive electrode lithium supplement material comprises a positive electrode lithium supplement base material and a shell layer existing on at least part of the surface of the positive electrode lithium supplement base material. The shell layer comprises fluorine elements, and the content of the fluorine elements in the shell layer shows an increasing trend along the direction from the positive electrode lithium supplement base material to the shell layer. The positive electrode lithium supplement material provided by the application has high structural stability, is used for a battery, and can improve the cycle performance of the battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and particularly relates to a positive electrode lithium supplement material and a preparation method and application thereof. BACKGROUND

[0002] In the field of battery manufacturing technology, the quality of the positive electrode active material directly affects the performance of the battery, such as energy density, power density, cycle life, etc. However, during the charging and discharging process of the battery, a solid-state electrolyte interface film will be formed on the surface of the positive electrode active material, which will consume part of the active lithium in the positive electrode active material and cannot be recovered, thereby causing problems such as low battery capacity, low first coulomb efficiency, and poor cycle life. The use of a positive electrode lithium supplement material can effectively reduce the irreversible loss of active lithium and simultaneously restore the structure of the positive electrode active material, thereby ensuring the normal performance of the material.

[0003] The commonly used positive electrode lithium supplement material has the problem of poor structural stability during the cycle process, thereby causing the capacity of the battery to decay quickly and the cycle performance to be poor. Therefore, it is urgent to develop a positive electrode lithium supplement material with high structural stability to improve the cycle performance of the battery. SUMMARY

[0004] The main purpose of the present application is to provide a positive electrode lithium supplement material with high structural stability for use in a battery, which can improve the cycle performance of the battery.

[0005] The present application also provides a preparation method of a positive electrode lithium supplement material, which can prepare the above-mentioned positive electrode lithium supplement material and has a simple process and low cost.

[0006] The present application also provides a positive electrode sheet, which comprises the above-mentioned positive electrode lithium supplement material, and therefore, the positive electrode sheet for use in a battery can improve the cycle performance of the battery.

[0007] The present application also provides a battery, which comprises the above-mentioned positive electrode sheet, and therefore, the battery has excellent cycle performance.

[0008] In a first aspect, the present application provides a positive electrode lithium supplement material, which comprises a positive electrode lithium supplement base material and a shell layer existing on at least part of the surface of the positive electrode lithium supplement base material; the shell layer comprises fluorine elements, and the content of the fluorine elements in the shell layer shows an increasing trend along the direction from the positive electrode lithium supplement base material to the shell layer.

[0009] The positive electrode lithium supplement material as described above, the chemical formula of the shell layer is A a ZrF b wherein 0

[0010] and / or, the chemical formula of the positive electrode lithium supplement matrix material is Li x M y O z wherein, 0

[0011] The positive electrode lithium supplement material as described above, the shell layer comprises a first shell layer existing on the surface of the positive electrode lithium supplement matrix material, a second shell layer existing on the side of the first shell layer away from the positive electrode lithium supplement matrix material, and a third shell layer existing on the side of the second shell layer away from the positive electrode lithium supplement matrix material.

[0012] The content of fluorine element in the first shell layer is less than that in the second shell layer, and the content of fluorine element in the second shell layer is less than that in the third shell layer.

[0013] The positive electrode lithium supplement material as described above, the thickness of the first shell layer is 0.05-0.6 μm; the thickness of the second shell layer is 0.3-0.75 μm; and the thickness of the third shell layer is 0.2-1 μm.

[0014] The content of fluorine element in the first shell layer is less than that in the second shell layer, and the content of fluorine element in the second shell layer is less than that in the third shell layer.

[0015] The positive electrode lithium supplement material as described above, the D50 of the positive electrode lithium supplement matrix material is 8-10 μm; and the total thickness d of the shell layer is 1-2.1 μm.

[0016] And / or, through X-ray diffraction analysis, the half-peak width FWHM(003) of the diffraction peak corresponding to the (003) crystal face in the X-ray diffraction pattern of the positive electrode lithium supplement material is 0.25-0.42°; wherein, FWHM(003)=0.0027d 2 +0.13d+0.13, d is the total thickness of the shell layer.

[0017] The positive electrode lithium supplement material as described above, the proportion of the area of the part of the surface of the positive electrode lithium supplement matrix material where the shell layer does not exist to the total area of the surface of the positive electrode lithium supplement matrix material is less than or equal to 5%.

[0018] The positive electrode lithium supplement material as described above has a differential capacity curve in a cycle of 0-200 cycles, wherein a fluctuation range of a phase transition peak I1 in a range of 4.1 V-4.3 V is 0%-2%, and a fluctuation range of a phase transition peak I2 in a range of 3.4 V-3.7 V is 0%-5%.

[0019] In a second aspect, the present application provides a preparation method of the positive electrode lithium supplement material of the first aspect, comprising the following steps:

[0020] 1) performing first sintering on a raw material system comprising a lithium source and an M source under an inert gas atmosphere at 300 DEG C-500 DEG C for 8 h-16 h to obtain a first intermediate;

[0021] 2) performing second sintering on the first intermediate under an inert gas atmosphere at 600 DEG C-800 DEG C for 8 h-16 h to obtain a second intermediate;

[0022] 3) performing first deposition of a redox medium on the surface of the second intermediate to obtain a third intermediate;

[0023] 4) performing second deposition of the redox medium on the surface of the third intermediate to obtain a fourth intermediate;

[0024] 5) performing third deposition of the redox medium on the surface of the fourth intermediate to obtain the positive electrode lithium supplement material.

[0025] The preparation method as described above has the following conditions: the temperature of the first deposition is 400 DEG C-450 DEG C, the deposition rate is 0.01 um / min-0.02 um / min, and the deposition time is 2.5 min-30 min;

[0026] And / or, the temperature of the second deposition is 350 DEG C-400 DEG C, the deposition rate is 0.02 um / min-0.03 um / min, and the deposition time is 10 min-25 min;

[0027] And / or, the temperature of the third deposition is 300 DEG C-350 DEG C, the deposition rate is 0.03 um / min-0.035 um / min, and the deposition time is 6 min-28 min.

[0028] In a third aspect, the present application provides a positive electrode sheet comprising the positive electrode lithium supplement material of the first aspect or the positive electrode lithium supplement material prepared by the preparation method of the second aspect.

[0029] The positive electrode sheet as described above comprises a positive electrode current collector, a positive electrode active material layer existing on the surface of the positive electrode current collector, and a positive electrode lithium supplement layer existing on the side of the positive electrode active material layer away from the positive electrode current collector.

[0030] In a fourth aspect, the present application provides a battery comprising the positive electrode sheet of the third aspect.

[0031] The technical scheme of the present application has the following beneficial effects:

[0032] The positive electrode lithium supplementing material provided by the present application can supplement lithium for a battery, make up for the loss of lithium ion concentration caused by the lithium ion battery during the cycle process, and the content of fluorine element in the shell layer of the positive electrode lithium supplementing material increases in the direction from the positive electrode lithium supplementing matrix material to the shell layer, so that a shell layer with gradually increasing density can be formed, the structural stability of the positive electrode lithium supplementing material is effectively enhanced, and the cycle stability of the battery is improved. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical scheme in the embodiments of the present application or the related art, the drawings needed to be used in the description of the embodiments of the present application or the related art are briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without creating any creative labor.

[0034] Figure 1 A cross-sectional SEM image of the positive electrode lithium supplementing material prepared for the first embodiment of the present application;

[0035] Figure 2 A surface SEM image of the positive electrode lithium supplementing material prepared for the first embodiment of the present application;

[0036] Figure 3 A graph showing the change of the content of fluorine element in the positive electrode lithium supplementing material prepared for the first embodiment of the present application along the distance in the direction from the positive electrode lithium supplementing matrix material to the shell layer;

[0037] Figure 4 A structural schematic diagram of a positive electrode sheet provided by the present application. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical scheme and advantages of the present application more clear, the technical scheme in the embodiments of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creating any creative labor are within the scope of protection of the present application.

[0039] In a first aspect, the present application provides a positive electrode lithium supplementing material, comprising a positive electrode lithium supplementing matrix material and a shell layer existing on at least part of the surface of the positive electrode lithium supplementing matrix material; the shell layer comprises fluorine element, and the content of fluorine element in the shell layer increases in the direction from the positive electrode lithium supplementing matrix material to the shell layer.

[0040] Specifically, the shell layer can be coated on the surface of the positive electrode lithium supplement matrix material, the content of fluorine element in the shell layer increases in the direction from the positive electrode lithium supplement matrix material to the shell layer, that is, in the direction from the positive electrode lithium supplement matrix material to the shell layer, a shell layer with gradually increasing density is formed, and the shell layer can be a redox medium layer. The gradual increase in the density strengthens the combination of the redox medium and the positive electrode lithium supplement matrix material, which is beneficial to improve the transmission of electric charges, that is, the diffusion process of ions. The gradually increasing content of fluorine element can reduce the diffusion impedance of ions, effectively optimize the diffusion of ions, and the gradient distribution makes the diffusion of ions in the positive electrode lithium supplement material more smooth, reduces the diffusion resistance of ions, and at the same time, the outer high-density shell layer can increase the structural stability of the positive electrode lithium supplement material, reduce the degradation of the structure of the positive electrode lithium supplement material and the increase of the interface impedance in the charging and discharging process, thereby prolonging the cycle life of the battery. In addition, the redox medium can also spontaneously react with the dead lithium on the surface of the negative electrode. The reaction is a reversible reaction, which can effectively prolong the cycle life of the battery. Specifically, during the charging process, the oxidized redox medium can spontaneously react with the dead lithium on the surface of the metal lithium negative electrode to become a reduced redox medium, then diffuse to the positive electrode side, and lose electrons to be oxidized to an oxidized redox medium again; that is, it can effectively reduce the influence of dead lithium on the cycle performance of the battery without affecting the performance of the positive electrode lithium supplement matrix material.

[0041] In the present application, the content of fluorine element can be measured by X-ray energy spectrum (EDS) line scanning.

[0042] The positive electrode lithium supplement material of the present application can supplement lithium for the battery, make up for the loss of lithium ion concentration caused by the cycle process of the lithium ion battery, and the content of fluorine element in the shell layer of the positive electrode lithium supplement material in the present application increases in the direction from the positive electrode lithium supplement matrix material to the shell layer, which can form a shell layer with gradually increasing density, effectively enhance the structural stability of the positive electrode lithium supplement material, and further improve the cycle stability of the battery.

[0043] Specifically, the chemical formula of the shell layer is A a ZrF b wherein 0

[0044] In some embodiments, the chemical formula of the positive electrode lithium supplement matrix material is Li x M y O z wherein 0

[0045] Exemplarily, A a ZrF b In the formula, a can be 0.1, 0.5, 1, 1.5, 2, or a range consisting of any two of them, and b can be 4, 4.5, 5, 5.5, 6, or a range consisting of any two of them. x M y O z In the formula, x can be 0.1, 0.5, 1, 1.5, 2, 3, 4, or a range consisting of any two of them, y can be 0.1, 0.5, 1, 1.5, 2, or a range consisting of any two of them, and z can be 0.1, 0.5, 1, 1.5, 2, 3, 4, or a range consisting of any two of them.

[0046] The shell layer in the application is fluorozirconate, which can adjust the kinetics of the reaction by changing the electron density of the electrode surface or changing the chemical environment of the electrode surface as a redox medium. Such adjustment helps to achieve more efficient electron transfer and more uniform electrochemical reaction, thereby improving the energy density and rate performance of the battery. Moreover, the fluorozirconate shell layer can form a stable protective film on the surface of the positive lithium supplement matrix material, reduce the direct contact of the electrolyte with the positive lithium supplement matrix material, and reduce the probability of occurrence of side reactions, thereby improving the structural stability of the positive lithium supplement material and further improving the cycle performance of the battery.

[0047] The use of the above positive lithium supplement matrix material is conducive to the performance of the lithium supplement function, and the coating of fluorozirconate on the surface of the positive lithium supplement matrix material can improve the structural stability thereof, thereby improving the cycle performance of the battery.

[0048] In some embodiments of the application, the shell layer includes a first shell layer present on the surface of the positive lithium supplement matrix material, a second shell layer present on the side of the first shell layer away from the positive lithium supplement matrix material, and a third shell layer present on the side of the second shell layer away from the positive lithium supplement matrix material.

[0049] The content of fluorine in the first shell layer is less than the content of fluorine in the second shell layer, and the content of fluorine in the second shell layer is less than the content of fluorine in the third shell layer.

[0050] In the present application, the shell layer includes a first shell layer, a second shell layer and a third shell layer. Specifically, the first shell layer exists on the surface of the positive electrode lithium supplement matrix material, which can be part of the surface or the entire surface; the second shell layer exists on the side of the first shell layer away from the positive electrode lithium supplement matrix material, which can be part of the surface or the entire surface; and the third shell layer exists on the side of the second shell layer away from the positive electrode lithium supplement matrix material, which can be part of the surface or the entire surface. The first shell layer can provide preliminary protection for the positive electrode lithium supplement matrix material, the second shell layer can further enhance the protection of the positive electrode lithium supplement matrix material, and the third shell layer can provide the strongest protection. This gradient structure can effectively prevent the corrosion of the electrolyte on the positive electrode lithium supplement matrix material, and significantly improve the structural stability of the positive electrode lithium supplement material. Moreover, the gradient shell layer design can alleviate the stress concentration caused by the stress difference between different levels of materials, reduce the mechanical stress and lattice distortion of the material during charging and discharging, thereby improving the mechanical strength and structural stability of the material.

[0051] The content of fluorine element in the first shell layer of the present application is less than that in the second shell layer, and the content of fluorine element in the second shell layer is less than that in the third shell layer. This layer-by-layer increase in the content of fluorine element forms a gradient protection structure. The lower content of fluorine element in the first shell layer helps to maintain good electronic and ionic conductivity, ensuring efficient electrochemical reaction. With the increase of the content of fluorine element, the second shell layer and the third shell layer can provide stronger chemical stability and protection, thereby improving the structural stability of the positive electrode lithium supplement material. In addition, the high content of fluorine element in the third shell layer can form a stable protective film, reduce the side reaction of electrolyte with the positive electrode lithium supplement material, reduce the decomposition of electrolyte and the generation of electrode surface by-products, thereby improving the cycle life of the battery.

[0052] In some embodiments of the present application, the thickness of the first shell layer is 0.05-0.6 μm; the thickness of the second shell layer is 0.3-0.75 μm; and the thickness of the third shell layer is 0.2-1 μm.

[0053] In some embodiments, the content of fluorine element in the first shell layer accounts for 0.01%-1.5% of the mass percentage of the positive electrode lithium supplement material; the content of fluorine element in the second shell layer accounts for 1%-3% of the mass percentage of the positive electrode lithium supplement material; and the content of fluorine element in the third shell layer accounts for 3%-5% of the mass percentage of the positive electrode lithium supplement material.

[0054] Exemplarily, the thickness of the first shell layer can be 0.05 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, or a range consisting of any two of them, the thickness of the second shell layer can be 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, 0.75 μm, or a range consisting of any two of them, and the thickness of the third shell layer can be 0.2 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, or a range consisting of any two of them. The mass percentage of fluorine in the first shell layer with respect to the positive electrode lithium supplement material can be 0.01%, 0.05%, 0.07%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.5%, or a range consisting of any two of them, the mass percentage of fluorine in the second shell layer with respect to the positive electrode lithium supplement material can be 1%, 1.5%, 2%, 2.5%, 3%, or a range consisting of any two of them, and the mass percentage of fluorine in the third shell layer with respect to the positive electrode lithium supplement material can be 3%, 3.5%, 4%, 4.5%, 5%, or a range consisting of any two of them.

[0055] In the present application, the thickness of the first shell layer, the second shell layer and the third shell layer can be obtained by EDS line scanning to measure the content of fluorine in each shell layer. Specifically, after depositing the first shell layer on the positive electrode lithium supplement base material, EDS line scanning is performed, and the thickness of the first shell layer is obtained by testing the thickness of the region with a fluorine mass percentage greater than 0.5%; after depositing the second shell layer on the positive electrode lithium supplement base material, EDS line scanning is performed, and the first thickness is obtained by testing the thickness of the region with a fluorine mass percentage greater than 1.5%, and the second shell layer thickness is obtained by subtracting the first shell layer thickness from the first thickness; after depositing the third shell layer on the positive electrode lithium supplement base material, EDS line scanning is performed, and the second thickness is obtained by testing the thickness of the region with a fluorine mass percentage greater than 3%, and the third shell layer thickness is obtained by subtracting the first thickness from the second thickness.

[0056] In the present application, the thickness of the first shell layer, the second shell layer and the third shell layer, and the mass percentage of fluorine in the first shell layer, the second shell layer and the third shell layer with respect to the positive electrode lithium supplement material are in the above-mentioned ranges, which can further improve the structural stability of the positive electrode lithium supplement material, reduce the increase of interface impedance during charging and discharging, and thus improve the cycle performance of the battery.

[0057] In some embodiments of the present application, the D50 of the positive electrode lithium supplement base material is 8 μm-10 μm; and the total thickness d of the shell layer is 1 μm-2.1 μm.

[0058] In some embodiments, the positive electrode lithium supplement material has a half-peak width FWHM(003) of a diffraction peak corresponding to a (003) crystal face in an X-ray diffraction pattern of 0.25-0.42°, wherein FWHM(003) = 0.0027d 2 +0.13d+0.13, d is the total thickness of the shell layer.

[0059] In some embodiments, the proportion of the area of the part of the surface of the positive electrode lithium supplement matrix material where the shell layer is not present to the total area of the surface of the positive electrode lithium supplement matrix material is less than or equal to 5%.

[0060] Illustratively, the D50 of the positive electrode lithium supplement matrix material can be in a range consisting of 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, or any two thereof, the total thickness d of the shell layer can be in a range consisting of 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.1 μm, or any two thereof, the half-peak width FWHM(003) of a diffraction peak corresponding to a (003) crystal face in an X-ray diffraction pattern of the positive electrode lithium supplement material can be in a range consisting of 0.25°, 0.3°, 0.32°, 0.35°, 0.38°, 0.4°, 0.42°, or any two thereof, and the proportion of the area of the part of the surface of the positive electrode lithium supplement matrix material where the shell layer is not present to the total area of the surface of the positive electrode lithium supplement matrix material can be in a range consisting of 1%, 2%, 3%, 4%, 5%, or any two thereof.

[0061] The D50 of the positive electrode lithium supplement matrix material in the present application is in the above range, which can provide a good specific surface area, help to improve the electrochemical reaction activity and efficiency, and also can balance the electrical conductivity and ion transference rate, ensure that the positive electrode lithium supplement material has good rate performance and energy density, and also help to improve the mechanical strength and structural stability of the positive electrode lithium supplement material, reduce the pulverization and breakage phenomenon in the charging and discharging process. The total thickness d of the shell layer is in the above range, which can provide effective protection for the positive electrode lithium supplement matrix material, prevent the electrolyte from corroding the positive electrode lithium supplement matrix material, reduce the occurrence of side reactions, also help to improve the structural stability of the positive electrode lithium supplement material, reduce the increase of interface impedance in the charging and discharging cycle, and thus improve the cycle performance and rate performance of the battery.

[0062] The total thickness of the shell layer in the present application closely affects the uniformity of the lithium ion deintercalation channel, and the total thickness of the shell layer changing with the gradient can effectively regulate the uniformity of the lithium ion deintercalation channel, and thus regulate the charging and discharging uniformity. A moderate total thickness of the shell layer can reduce the polarization phenomenon of the electrode material in the charging and discharging process, reduce the internal resistance of the battery, and thus improve the energy density and rate performance of the battery, while an excessively thick surface coating can inhibit the reverse deintercalation of lithium ions.

[0063] The proportion of the area of the part without the shell layer on the surface of the positive electrode lithium supplement matrix material to the total area of the surface of the positive electrode lithium supplement matrix material is less than or equal to 5% in the present application, which means that the shell layer has a high coverage rate, can provide comprehensive protection for the positive electrode lithium supplement matrix material, can keep the structure stability of the positive electrode lithium supplement material in the charging and discharging process, prevent the direct contact of the electrolyte and the positive electrode lithium supplement matrix material, reduce the occurrence of side reactions, reduce the increase of the interface impedance in the charging and discharging process, and improve the cycle performance and rate performance of the battery.

[0064] In some embodiments of the present application, the positive electrode lithium supplement material prepared by the preparation method of the battery has a fluctuation range of 0%-2% for the phase transition peak I1 in the 4.1V-4.3V interval and a fluctuation range of 0%-5% for the phase transition peak I2 in the 3.4V-3.7V interval in the differential differential capacity curve of 0-200 cycles of the battery.

[0065] Specifically, the preparation method of the battery in the present application can include the following steps: under the conditions of 25 DEG C and normal pressure (0.1 MPa), the positive electrode active material NCM622, the conductive agent Super P and the binder polyvinylidene fluoride (PVDF) are mixed uniformly in the N-methyl pyrrolidone solvent at a mass ratio of 8:1:1 to obtain a positive electrode slurry with a solid content of 70%. The positive electrode lithium supplement material, the conductive carbon black and the binder polyvinylidene fluoride (PVDF) are mixed uniformly in the N-methyl pyrrolidone solvent at a mass ratio of 4:2:2 to obtain a positive electrode lithium supplement slurry with a solid content of 20%. The positive electrode lithium supplement slurry is coated on the current collector Al foil by the transfer coating, and the face density of the positive electrode supplement slurry is controlled in the range of 13-15 mg / cm 2 -15mg / cm 2 The coating speed is 1 mL / min. After the positive electrode slurry is pre-coated for 400 mm, the slurry nozzle is opened, the positive electrode lithium supplement slurry is sprayed, the spraying pressure is 0.5 MPa, and the spraying speed is 10 mL / min. After coating, the positive electrode sheet is dried in an oven at 110 DEG C-130 DEG C, the negative electrode is graphite, the separator is polypropylene PP, and the electrolyte (the electrolyte composition is 1 mol / L LiPF6, the volume ratio of EC / DMC / DEC is 1:1:1) to form a full battery.

[0066] Under the condition of 25 DEG C, the battery is charged at a charge rate of 1C to 4.35V, charged at a constant voltage of 4.35V to a current rate of 0.5C, then discharged at a discharge rate of 1C to 3.0V, and repeated 200 times of charging and discharging cycles. The collected data is processed, the voltage change (dV) and the charge change (dQ) in each cycle are calculated, the ratio of dQ / dV (the ratio of charge change to voltage change) is taken as the vertical coordinate, and the voltage or capacity is taken as the horizontal coordinate, so as to obtain the standard differential differential capacity (dQ / dV) curve.

[0067] Exemplarily, the fluctuation range of the phase transition peak peak position I1 can be 0%, 0.5%, 1%, 1.5%, 2%, or a range formed by any two of them, and the fluctuation range of the phase transition peak peak position I2 can be 0%, 1%, 2%, 3%, 4%, 5%, or a range formed by any two of them.

[0068] In the present application, the fluctuation range of the phase transition peak peak position I1 in the interval of 4.1V-4.3V and the phase transition peak peak position I2 in the interval of 3.4V-3.7V is in the above range, the surface battery has stable phase change behavior in the cycle process, and the positive electrode lithium supplement material maintains good structural stability and electrochemical stability in the charge and discharge process; the fluctuation range of the phase transition peak peak position is small, which indicates that the battery has low capacity attenuation in the cycle process, can maintain high capacity and energy density in a long time use process, thereby prolonging the cycle life of the battery.

[0069] In a second aspect, the present application provides a preparation method of the positive electrode lithium supplement material of the first aspect, comprising the following steps:

[0070] 1) Sintering the raw material system comprising a lithium source and an M source once at 300-500℃ in an inert gas atmosphere for 8-16h to obtain a first intermediate;

[0071] 2) Sintering the first intermediate twice at 600-800℃ in an inert gas atmosphere for 8-16h to obtain a second intermediate;

[0072] 3) Depositing a redox medium on the surface of the second intermediate once to obtain a third intermediate;

[0073] 4) Depositing a redox medium on the surface of the third intermediate twice to obtain a fourth intermediate;

[0074] 5) Depositing a redox medium on the surface of the fourth intermediate three times to obtain the positive electrode lithium supplement material.

[0075] In the present application, through three times of deposition treatment, the positive electrode lithium supplement material of the first aspect of the present application can be finally prepared.

[0076] Specifically, in step 1), a lithium source, such as lithium hydroxide, and a M source are mixed in a high-speed mixer in a certain ratio for 3h-5h to obtain sample A1; then sample A1 is placed in a ball mill for ball milling at a speed of 500 rpm to obtain sample A2; and the sample A2 is sintered once under an inert gas atmosphere for 8h-16h to obtain a first intermediate. The M source is a compound containing at least one element selected from C, Ni, Co, Mn and Fe. The temperature of the first sintering can be in the range of 300℃, 350℃, 400℃, 450℃, 500℃ or any two of them, and the time of the first sintering can be in the range of 8h, 10h, 12h, 14h, 16h or any two of them.

[0077] In step 2), the first intermediate is cooled and then ball milled again, and then the milled first intermediate is sintered twice under an inert gas atmosphere at 600℃-800℃ for 8h-16h to obtain a second intermediate. The temperature of the second sintering can be in the range of 600℃, 650℃, 700℃, 750℃, 800℃ or any two of them, and the time of the second sintering can be in the range of 8h, 10h, 12h, 14h, 16h or any two of them.

[0078] In step 3), the oxidation-reduction medium is pretreated with an inert atmosphere N2, the flow rate of N2 is 20mL / min, the oxidation-reduction medium is vaporized under vacuum, the vaporization load of the oxidation-reduction medium solution is 5L-10L, and a stepwise gradient deposition is carried out. The oxidation-reduction medium is first deposited on the surface of the second intermediate to obtain a third intermediate with a first shell.

[0079] In step 4), a second deposition is carried out on the surface of the third intermediate to obtain a fourth intermediate with a second shell.

[0080] In step 5), a third deposition is carried out on the surface of the fourth intermediate to obtain the above-mentioned positive electrode lithium supplement material.

[0081] In the present application, by carrying out three times of deposition of the oxidation-reduction medium on the surface of the second intermediate, the positive electrode lithium supplement material with gradient distribution of fluorine elements provided in the first aspect of the present application can be obtained, and the structural stability of the positive electrode lithium supplement material is improved, thereby improving the cycle stability of the battery.

[0082] In some embodiments of the present application, the temperature of the first deposition is 400℃-450℃, the deposition rate is 0.01μm / min-0.02μm / min, and the deposition time is 2.5min-30min.

[0083] In some embodiments, the temperature of the second deposition is 350-400℃, the deposition rate is 0.02-0.03 μm / min, and the deposition time is 10-25 min.

[0084] In some embodiments, the temperature of the third deposition is 300-350℃, the deposition rate is 0.03-0.035 μm / min, and the deposition time is 6-28 min.

[0085] Exemplarily, the temperature of the first deposition can be 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, or a range formed by any two of them, the rate of the first deposition can be 0.01 μm / min, 0.012 μm / min, 0.015 μm / min, 0.018 μm / min, 0.02 μm / min, or a range formed by any two of them, and the time of the first deposition can be 2.5 min, 5 min, 10 min, 20 min, 30 min, or a range formed by any two of them. The temperature of the second deposition can be 350℃, 360℃, 370℃, 380℃, 390℃, 400℃, or a range formed by any two of them, the rate of the second deposition can be 0.02 μm / min, 0.022 μm / min, 0.025 μm / min, 0.028 μm / min, 0.03 μm / min, or a range formed by any two of them, and the time of the second deposition can be 10 min, 15 min, 20 min, 22 min, 25 min, or a range formed by any two of them. The temperature of the third deposition can be 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, or a range formed by any two of them, the rate of the third deposition can be 0.03 μm / min, 0.031 μm / min, 0.032 μm / min, 0.033 μm / min, 0.034 μm / min, 0.035 μm / min, or a range formed by any two of them, and the time of the third deposition can be 6 min, 10 min, 15 min, 20 min, 25 min, 28 min, or a range formed by any two of them.

[0086] The preparation process of the positive electrode lithium supplement material in the present application is simple, and the reaction conditions are mild, thereby expanding the use range of the shell. Different deposition temperatures and deposition rates can form a shell with gradually increasing density in the direction from the positive electrode lithium supplement matrix material to the shell. This gradual transition of density strengthens the combination of the oxidation-reduction medium and the positive electrode lithium supplement matrix material, is conducive to improving the charge transmission and ion diffusion process, and effectively enhances the stability of the positive electrode lithium supplement material, thereby improving the cycle performance of the battery.

[0087] In a third aspect, the present application provides a positive electrode sheet comprising the positive electrode lithium supplementing material of the first aspect or the positive electrode lithium supplementing material prepared by the preparation method of the second aspect.

[0088] In some embodiments of the present application, as shown in Figure 4 The positive electrode sheet comprises a positive electrode current collector, a positive electrode active material layer present on the surface of the positive electrode current collector, and a positive electrode lithium supplementing layer present on the side of the positive electrode active material layer away from the positive electrode current collector.

[0089] The positive electrode sheet of the present application can be prepared by a preparation method comprising the following steps:

[0090] 1) coating a positive electrode slurry comprising a positive electrode active material, a conductive agent, and a binder on at least one functional surface of a positive electrode current collector to obtain a positive electrode sheet precursor;

[0091] 2) coating a positive electrode lithium supplementing slurry comprising a positive electrode lithium supplementing material, a conductive agent, and a binder on the side of the positive electrode sheet precursor away from the positive electrode slurry to obtain the positive electrode sheet.

[0092] The present application does not make special limitations on the specific types of conductive agents and binders, and the components such as conductive agents and binders can be selected from conventional materials in the art. For example, the conductive agent can be selected from one or more of conductive carbon black, carbon nanotube, conductive graphite, and graphene, and the binder can be selected from one or more of polyvinylidene fluoride (PVDF), acrylic modified PVDF, polyacrylate polymer, polyimide, butadiene styrene rubber, and styrene butadiene rubber.

[0093] The present application does not make special limitations on the coating method, and any one of gravure coating, extrusion coating, spraying, and screen printing can be used to realize the coating of the positive electrode active layer slurry.

[0094] The conventional positive electrode lithium supplementing material is used by being uniformly mixed with the positive electrode active material and then coated, and the present application uses the positive electrode lithium supplementing material and the positive electrode active material to be uniformly mixed respectively and then coated in a double-layer coating manner, which can not only fully exert the capacity of the positive electrode lithium supplementing material, but also can not destroy the conductive network of the positive electrode slurry, ensure the stability of lithium ion kinetics, ensure the adhesion between the current collector and the positive electrode slurry, avoid electrical isolation, and ensure the normal transportation of electrons.

[0095] In a fourth aspect, the present application provides a battery comprising the positive electrode sheet of the third aspect.

[0096] The battery of the present application comprises, in addition to the positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte. The composition of the negative electrode sheet can refer to the conventional negative electrode sheet in the art, and the separator can also use the conventional separator in the art, such as a PP film and a PE film.

[0097] The battery of the present application can be prepared by conventional methods in the art. Specifically, the positive electrode sheet, the separator and the negative electrode sheet are sequentially stacked, and then the battery core is obtained by stacking or winding process. Then, the battery is obtained by baking, liquid injection, formation, packaging and other processes.

[0098] The technical solutions of the present application are further illustrated in combination with specific examples.

[0099] Example 1

[0100] The preparation method of the positive electrode sheet of the present embodiment comprises the following steps:

[0101] 1) Lithium hydroxide and oxalic acid containing C element were put into a high-speed mixer at a mass ratio of 1.2:1 and mixed for 5h to obtain sample A1.

[0102] 2) The sample A1 was placed in a ball mill and ball-milled at a speed of 500 rpm to obtain sample A2.

[0103] 3) The sample A2 was sintered once under an inert gas N2 atmosphere, the sintering temperature was 500℃, and the holding time was 8h, to obtain a first intermediate.

[0104] 4) After cooling, the first intermediate was ball-milled again, and the milled first intermediate was sintered again under an inert gas N2 atmosphere, the sintering temperature was 800℃, and the holding time was 10h, to obtain a second intermediate.

[0105] 5) The inert atmosphere N2 was used to pretreat the redox medium K2ZrF6, the N2 flow rate was 20mL / min, the redox medium was vacuum gasified, the redox medium solution gasification load was 6L, and the stepwise gradient deposition was carried out. The first deposition temperature was 450℃, the deposition rate was 0.02μm / min, and the deposition time was 15min; the second deposition temperature was 400℃, the deposition rate was 0.03μm / min, and the deposition time was 16min; the third deposition temperature was 350℃, the deposition rate was 0.035μm / min, and the deposition time was 28min, and the positive electrode lithium supplement material was obtained after the third deposition.

[0106] Li2C2O4, the D50 of the positive electrode lithium supplement matrix material is 9.65 μm, the chemical formula of the shell layer existing on the surface of the positive electrode lithium supplement matrix material is K2ZrF6, and the total thickness d of the shell layer is 1.8 μm. The thickness of the first shell layer existing on the surface of the positive electrode lithium supplement matrix material is 0.3 μm, the mass percentage of fluorine in the first shell layer is 1% of the positive electrode lithium supplement material, and is denoted as ratio 1; the thickness of the second shell layer existing on the side of the first shell layer away from the positive electrode lithium supplement matrix material is 0.5 μm, the mass percentage of fluorine in the second shell layer is 2.5% of the positive electrode lithium supplement material, and is denoted as ratio 2; the thickness of the third shell layer existing on the side of the second shell layer away from the positive electrode lithium supplement matrix material is 1 μm, the mass percentage of fluorine in the third shell layer is 4% of the positive electrode lithium supplement material, and is denoted as ratio 3. Through X-ray diffraction analysis, the half-peak width FWHM(003) of the positive electrode lithium supplement material corresponding to the diffraction peak of the (003) crystal face in the X-ray diffraction pattern is 0.214°; wherein FWHM(003) = 0.0027d 2 + 0.13d + 0.13, d is the total thickness of the shell layer. The area ratio of the part of the surface of the positive electrode lithium supplement matrix material without the shell layer to the total area of the surface of the positive electrode lithium supplement matrix material is 5%, denoted as ratio 4.

[0107] 6) At 25°C and normal pressure (0.1 MPa), the positive electrode active material NCM622, conductive carbon black Super P, and binder polyvinylidene fluoride (PVDF) were mixed uniformly in N-methylpyrrolidone solvent at a mass ratio of 8:1:1 to obtain a positive electrode slurry with a solid content of 70%. The positive electrode lithium supplement material, conductive carbon black, and binder polyvinylidene fluoride (PVDF) in step 5) were mixed uniformly in N-methylpyrrolidone solvent at a mass ratio of 4:2:2 to obtain a positive electrode lithium supplement slurry with a solid content of 20%. The positive electrode lithium supplement slurry was coated on the current collector Al foil by transfer coating, and the positive electrode slurry loading surface density was controlled to be 15 mg / cm 2 2. The coating speed was 1 mL / min. After pre-coating the positive electrode slurry for 400 mm, the slurry nozzle was opened, and the positive electrode lithium supplement slurry was sprayed, with a spraying pressure of 0.5 MPa and a spraying speed of 10 mL / min. The coated positive electrode sheet was dried in an oven at 110°C to obtain a positive electrode sheet. As shown in Figure 4 , the positive electrode sheet includes a positive electrode current collector, a positive electrode active material layer existing on the surface of the positive electrode current collector, and a positive electrode lithium supplement layer existing on the side of the positive electrode active material layer away from the positive electrode current collector.

[0108] Example 2

[0109] Example 2 and the preparation method of the positive electrode sheet of Example 1 are basically the same, except that the one-time sintering temperature in step 5) is changed to 300°C.

[0110] Example 3

[0111] Example 3 and the preparation method of the positive electrode sheet of Example 1 are basically the same, except that the one-time sintering time in step 5) is changed to 16 h.

[0112] Example 4

[0113] Example 4 and the preparation method of the positive electrode sheet of Example 1 are basically the same, except that the secondary sintering temperature in step 5) is changed to 600°C.

[0114] Example 5

[0115] Example 5 and the preparation method of the positive electrode sheet of Example 1 are basically the same, except that the secondary sintering time in step 5) is changed to 16 h.

[0116] Example 6

[0117] Example 6 and the preparation method of the positive electrode sheet of Example 1 are basically the same, except that in step 6) the positive electrode slurry and the positive electrode lithium supplement slurry are mixed uniformly at a mass ratio of 8:2, transfer coating is used, and the loading area density is controlled to be 15 mg / cm 2 , and the coating speed is 1 mL / min. The obtained positive electrode sheet includes a positive electrode active material layer, and the positive electrode lithium supplement material exists in the positive electrode active material layer.

[0118] Examples 7-25

[0119] Examples 7-25 and the preparation method of the positive electrode sheet of Example 1 are basically the same, except that one or more of the preparation conditions are changed.

[0120] Comparative Example 1

[0121] Comparative Example 1 and the preparation method of the positive electrode sheet of Example 1 are basically the same, except that the three-time deposition treatment in step 5) is not performed, and the chemical formula of the obtained positive electrode lithium supplement material is Li2C2O4.

[0122] Comparative Example 2

[0123] Comparative Example 2 and the preparation method of the positive electrode sheet of Example 5 are basically the same, except that the three-time deposition treatment in step 5) is not performed, and the chemical formula of the obtained positive electrode lithium supplement material is Li2C2O4.

[0124] Comparative Example 3

[0125] The preparation method of the positive electrode sheet of Comparative Example 3 is basically the same as that of Example 1, except that in step 5), the first deposition temperature is 350°C, the deposition rate is 0.035 μm / min; the second deposition temperature is 400°C, the deposition rate is 0.03 μm / min; the third deposition temperature is 450°C, the deposition rate is 0.02 μm / min, and the third deposition is ended to obtain the positive electrode lithium supplement material.

[0126] Comparative Example 4

[0127] The preparation method of the positive electrode sheet of Comparative Example 4 is basically the same as that of Example 1, except that in step 5), the first deposition temperature is 450°C, the deposition rate is 0.02 μm / min, the deposition time is 90 min, and the second and third depositions are not performed.

[0128] Comparative Example 5

[0129] The preparation method of the positive electrode sheet of Comparative Example 5 is basically the same as that of Example 1, except that in step 5), the first deposition temperature is 400°C, the deposition rate is 0.03 μm / min, the deposition time is 60 min, and the second and third depositions are not performed.

[0130] Comparative Example 6

[0131] The preparation method of the positive electrode sheet of Comparative Example 6 is basically the same as that of Example 1, except that in step 5), the first deposition temperature is 350°C, the deposition rate is 0.035 μm / min, the deposition time is 51 min, and the second and third depositions are not performed.

[0132] Test Example:

[0133] 1. Fluorine element content: The fluorine element content is measured by linear scanning from the center of the sphere to the outside by an energy dispersive spectrometer (EDS).

[0134] 2. Shell thickness: The shell thickness is measured by linear scanning from the center of the sphere to the outside by an energy dispersive spectrometer (EDS). Specifically, after depositing the first shell on the positive electrode lithium supplement substrate material, EDS line scanning is performed, and the first shell thickness is obtained by measuring the thickness of the region where the fluorine element mass percentage is greater than 0.5%; after depositing the second shell on the positive electrode lithium supplement substrate material, EDS line scanning is performed, and the first thickness is obtained by measuring the thickness of the region where the fluorine element mass percentage is greater than 1.5%; the second shell thickness is obtained by subtracting the first shell thickness from the first thickness; after depositing the third shell on the positive electrode lithium supplement substrate material, EDS line scanning is performed, and the second thickness is obtained by measuring the thickness of the region where the fluorine element mass percentage is greater than 3%; the third shell thickness is obtained by subtracting the first thickness from the second thickness.

[0135] 3. D50: The particle size of the material is measured by a laser particle size analyzer.

[0136] 4. Full width at half maximum (FWHM) of the diffraction peak corresponding to the (003) crystal plane in the XRD pattern: The XRD pattern of the material was tested by X-ray diffraction, and the full width at half maximum (FWHM) of the diffraction peak corresponding to the (003) crystal plane was derived.

[0137] 5. The proportion of the area of ​​the cathode lithium replenishment substrate material without a shell to the total surface area of ​​the cathode lithium replenishment substrate material: The surface coating ratio is obtained by statistically analyzing all identified particles according to their gray values ​​using SEM particle statistical analysis software. The total area is set to 100%, then the uncoated ratio is 100% minus the surface coating ratio.

[0138] 6. Phase transition peak positions: The phase transition peak positions I1 and I2 are obtained by using the differential capacitance (dQ / dV) curve derived from the cycle test of the prepared battery.

[0139] 7. Impedance: The impedance value is obtained by testing the impedance of the prepared battery using a Princeton impedance meter.

[0140] 8. Cyclic Performance: Using the positive electrode sheet and graphite negative electrode from the various embodiments and comparative examples, along with a polypropylene separator and an electrolyte (composition: 1 mol / L LiPF6, solvent: EC / DMC / DEC = v / v / v: 1 / 1 / 1), a full cell was constructed. At 25°C, the cell was charged at a constant current rate of 1C to 4.35V, then charged at a constant voltage of 4.35V to a current rate of 0.5C, and finally discharged at a discharge rate of 1C to 3V. This charge-discharge cycle was repeated 300 times. The discharge capacity Q1 at the first cycle and Q2 at the 300th cycle were measured. 300 The capacity retention rate after 300 cycles is Q = Q 300 / Q1 100%.

[0141] Figure 1 This is a cross-sectional SEM image of the positive electrode lithium replenishment material prepared in Example 1 of the present invention.

[0142] from Figure 1 It can be seen that the fluorine content in the positive electrode lithium replenishment material prepared in Example 1 of the present invention exhibits a gradient distribution.

[0143] Figure 2 This is a surface SEM image of the positive electrode lithium replenishment material prepared in Example 1 of the present invention.

[0144] from Figure 2 It can be seen that the positive electrode lithium replenishment material prepared in Example 1 of the present invention has a uniformly coated shell layer on its surface.

[0145] Figure 3A graph of the change of the content of fluorine element in the positive electrode lithium supplement material prepared in Embodiment 1 along the direction from the positive electrode lithium supplement matrix material to the shell.

[0146] From Figure 3 It can be seen that the content of fluorine element in the positive electrode lithium supplement material prepared in Embodiment 1 along the direction from the positive electrode lithium supplement matrix material to the shell increases.

[0147] Table 1

[0148] Serial number Primary deposition temperature / °C Primary deposition rate / μm / min Primary deposition time / min Secondary deposition temperature / °C Secondary deposition rate / μm / min Secondary deposition time / min Tertiary deposition temperature / °C Tertiary deposition rate / μm / min Tertiary deposition time / min Primary sintering temperature / °C Primary sintering time / h Secondary sintering temperature / °C Secondary sintering time / h Example 1 450 0.02 15 400 0.03 16 350 0.035 28 500 8 800 10 Example 2 450 0.02 15 350 0.03 16 350 0.035 28 300 8 800 10 Example 3 450 0.02 15 400 0.03 16 350 0.035 28 500 16 800 10 Example 4 450 0.02 15 400 0.03 16 350 0.035 28 500 8 600 10 Example 5 450 0.02 15 400 0.03 16 350 0.035 28 500 8 800 16 Example 6 450 0.02 15 400 0.03 16 350 0.035 28 500 8 800 10 Example 7 450 0.01 15 400 0.03 16 350 0.035 28 500 8 800 10 Example 8 450 0.015 15 400 0.03 16 350 0.035 28 500 8 800 10 Example 9 450 0.02 15 400 0.02 16 350 0.035 28 500 8 800 10 Example 10 450 0.02 15 400 0.025 16 350 0.035 28 500 8 800 10 Example 11 450 0.02 15 400 0.03 16 350 0.03 28 500 8 800 10 Example 12 450 0.02 15 400 0.03 16 350 0.032 28 500 8 800 10 Example 13 400 0.02 15 400 0.03 16 350 0.035 28 500 8 800 10 Example 14 420 0.02 15 400 0.03 16 350 0.035 28 500 8 800 10 Example 15 450 0.02 15 350 0.03 16 350 0.035 28 500 8 800 10 Example 16 450 0.02 15 375 0.03 16 350 0.035 28 500 8 800 10 Example 17 450 0.02 15 400 0.03 16 300 0.035 28 500 8 800 10 Example 18 450 0.02 15 400 0.03 16 325 0.035 28 500 8 800 10 Example 19 450 0.02 15 400 0.03 16 350 0.035 6 500 8 800 10 Example 20 450 0.02 15 400 0.03 16 350 0.035 10 500 8 800 10 Example 21 450 0.02 2.5 400 0.03 16 350 0.035 28 500 8 800 10 Example 22 450 0.02 30 400 0.03 16 350 0.035 28 500 8 800 10 Example 23 450 0.02 15 400 0.03 10 350 0.035 28 500 8 800 10 Example 24 450 0.02 15 400 0.03 25 350 0.035 28 500 8 800 10 Example 25 450 0.02 15 400 0.03 16 350 0.035 15 500 8 800 10 Comparative Example 1 / / / / / / / / / 500 8 800 10 Comparative Example 2 / / / / / / / / / 500 8 800 10 Comparative Example 3 350 0.035 15 400 0.03 16 450 0.02 28 500 8 800 10 Comparative Example 4 450 0.02 90 / / / / / / 500 8 800 10 Comparative Example 5 400 0.03 60 / / / / / / 500 8 800 10 Comparative Example 6 350 0.035 51 / / / / / / 500 8 800 10

[0149] Table 2

[0150] Serial number First shell layer thickness / μm Proportion 1 / % Second shell layer thickness / μm Proportion 2 / % Third shell layer thickness / μm Proportion 3 / % Total thickness of shell layers d / μm D50 of positive electrode lithium supplement matrix material / μm FWHM(003) / ° Proportion 4 / % Fluctuation range of phase transition peak peak position I1 / % Fluctuation range of phase transition peak peak position I2 / % Impedance / mΩ Capacity retention rate after 100 cycles / % Example 1 0.3 1 0.5 2.5 1 4 1.8 9.65 0.373 3.65 0.05 0.17 51.2 92.5 Example 2 0.3 1 0.5 2.5 1 4 1.8 9.46 0.373 4.31 0.08 0.2 56.3 91.3 Example 3 0.3 1 0.5 2.5 1 4 1.8 9.88 0.373 3.83 0.06 0.16 53.5 90.3 Example 4 0.3 1 0.5 2.5 1 4 1.8 9.66 0.373 4.25 0.13 0.35 58.3 89.7 Example 5 0.3 1 0.5 2.5 1 4 1.8 9.59 0.373 4.02 0.15 0.42 57.1 88.45 Example 6 0.3 1 0.5 2.5 1 4 1.8 9.49 0.373 4.01 0.2 0.45 60.2 87.3 Example 7 0.15 0.56 0.5 2.82 1 4.3 1.65 9.32 0.352 3.87 0.08 0.25 53.2 90.5 Example 8 0.24 0.73 0.5 2.53 1 4.2 1.74 9.44 0.364 3.65 0.07 0.23 52.5 91.3 Example 9 0.3 1.2 0.37 1.74 1 4.3 1.67 9.33 0.355 6.74 0.07 0.23 54.7 89.5 Example 10 0.3 1.14 0.45 2.32 1 4.12 1.75 9.46 0.366 3.43 0.06 0.21 53 89.9 Example 11 0.3 1.23 0.5 2.62 0.89 3.2 1.69 9.36 0.357 3.68 0.06 0.24 56.2 90.3 Example 12 0.3 1.18 0.5 2.57 0.94 3.7 1.74 9.55 0.364 4.37 0.06 0.21 55.8 91.2 Example 13 0.23 0.76 0.5 2.62 1 4.14 1.73 9.53 0.363 4.2 0.08 0.2 54.2 89.7 Example 14 0.26 0.93 0.5 2.59 1 4.03 1.76 9.57 0.367 4.13 0.07 0.19 53.7 91.5 Example 15 0.3 1.14 0.42 2.16 1 4.15 1.72 9.51 0.362 3.32 0.08 0.21 56.2 90.4 Example 16 0.3 1.09 0.48 2.37 1 4.03 1.78 9.62 0.370 3.28 0.07 0.18 54.7 91.7 Example 17 0.3 1.18 0.5 2.54 1 3.86 1.8 9.67 0.373 3.46 0.08 0.2 55.9 88.3 Example 18 0.3 1.04 0.5 2.35 1 3.94 1.8 9.66 0.373 4.34 0.07 0.18 54.3 90.1 Example 19 0.3 0.87 0.5 1.5 0.2 4.85 1 9.33 0.263 4.51 0.11 0.32 58.3 88.3 Example 20 0.3 0.65 0.5 1.14 0.35 4.93 1.15 9.45 0.283 4.84 0.2 0.38 61.2 87.1 Example 21 0.05 0.05 0.5 2.75 1 4.32 1.55 9.48 0.338 4.39 0.12 0.42 58.9 88.0 Example 22 0.6 1.35 0.5 2.35 1 3.84 2.1 9.48 0.415 4.47 0.13 0.35 59.5 87.9 Example 23 0.3 1.23 0.3 2.15 1 4.2 1.6 9.47 0.345 4.54 0.14 0.4 60.1 87.3 Example 24 0.3 0.81 0.75 2.75 1 3.26 2.05 9.47 0.408 4.61 0.15 0.31 60.7 87.0 Example 25 0.3 0.61 0.5 2.34 0.525 4 1.325 9.46 0.307 4.68 0.15 0.35 61.3 87.7 Comparative Example 1 / / / / / / / 7.5 0.463 / 0.53 0.63 132.5 83.2 Comparative Example 2 / / / / / / / 7.3 0.483 / 0.66 0.72 150.2 80.5 Comparative Example 3 1.3 4.32 0.5 2.42 0.21 0.64 2.01 9.28 0.402 5.88 0.21 0.51 77.5 85.3 Comparative Example 4 1.8 7 / / / / 1.8 9.54 0.373 5.12 0.29 0.58 72.5 84.3 Comparative Example 5 1.8 7 / / / / 1.8 9.56 0.373 5.2 0.29 0.523 77.2 85.7 Comparative Example 6 1.8 7 / / / / 1.8 9.53 0.373 5.18 0.289 0.52 74.3 85.2

[0151] It can be seen from Tables 1-2 that, compared with the comparative examples, the positive electrode lithium supplement material of the present application can supplement lithium for the battery, make up for the loss of lithium ion concentration caused by the cycle process of the lithium ion battery, and the content of fluorine element in the shell of the positive electrode lithium supplement material of the present application increases along the direction from the positive electrode lithium supplement matrix material to the shell, so that a shell with gradually increasing compactness can be formed, the structural stability of the positive electrode lithium supplement material is effectively enhanced, and the cycle stability of the battery is improved.

[0152] It can be seen from the comparison between Embodiment 1 and Comparative Example 1 that the positive electrode lithium supplement material without a shell has poor structural stability, and the dead lithium cannot be effectively activated during the cycle process.

[0153] It can be seen from the comparison between Embodiment 1 and Comparative Example 2 that the positive electrode lithium supplement material without a shell is blended with the positive electrode slurry, and the homogenate coating has poor cycle stability, so that the positive electrode lithium supplement material cannot play a role.

[0154] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed in the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A cathode lithium replenishment material, characterized in that, The cathode lithium replenishment substrate material includes a shell layer present on at least a portion of the surface of the cathode lithium replenishment substrate material; the shell layer includes fluorine, and the fluorine content in the shell layer increases along the direction from the cathode lithium replenishment substrate material to the shell layer; The chemical formula of the shell is A. a Z r F b Where 0 < a ≤ 2, 4 ≤ b ≤ 6, and A is selected from at least one of K, Na, and NH4; The shell layer is a redox medium layer; The shell layer includes a first shell layer existing on the surface of the positive electrode lithium replenishment substrate material, a second shell layer existing on the side of the first shell layer opposite to the positive electrode lithium replenishment substrate material, and a third shell layer existing on the side of the second shell layer opposite to the positive electrode lithium replenishment substrate material; The fluorine content in the first shell is less than the fluorine content in the second shell, and the fluorine content in the second shell is less than the fluorine content in the third shell. The thickness of the first shell layer is 0.05μm-0.6μm; the thickness of the second shell layer is 0.3μm-0.75μm; and the thickness of the third shell layer is 0.2μm-1μm. The fluorine element in the first shell layer accounts for 0.01%-1.5% of the mass of the positive electrode lithium replenishment material; the fluorine element in the second shell layer accounts for 1%-3% of the mass of the positive electrode lithium replenishment material; and the fluorine element in the third shell layer accounts for 3%-5% of the mass of the positive electrode lithium replenishment material.

2. The positive electrode lithium replenishment material according to claim 1, characterized in that, The chemical formula of the positive electrode lithium-filling matrix material is Li. x M y O z Where 0 < x ≤ 4, 0 < y ≤ 2, 0 < z ≤ 4, and M is selected from at least one of C, Ni, Co, Mn, and Fe.

3. The positive electrode lithium replenishment material according to claim 1, characterized in that, The D50 of the positive electrode lithium replenishment substrate material is 8μm-10μm; the total thickness d of the shell layer is 1μm-2.1μm; And / or, according to X-ray diffraction analysis, the full width at half maximum (FWHM) of the diffraction peak corresponding to the (003) crystal plane in the X-ray diffraction pattern of the cathode lithium replenishment material is 0.25°-0.42°; where FWHM(003) = 0.0027d. 2 +0.13d+0.13, where d is the total thickness of the shell; And / or, the area of ​​the portion of the positive electrode lithium-filling substrate material without the shell layer is less than or equal to 5% of the total surface area of ​​the positive electrode lithium-filling substrate material.

4. The positive electrode lithium replenishment material according to any one of claims 1-3, characterized in that, In the differential capacitance curve of the battery prepared by the positive electrode lithium replenishment material after 0-200 cycles, the fluctuation range of the phase transition peak position I1 is 0%-2% in the range of 4.1V-4.3V; and the fluctuation range of the phase transition peak position I2 is 0%-5% in the range of 3.4V-3.7V.

5. A method for preparing a positive electrode lithium replenishment material as described in any one of claims 1-4, characterized in that, Includes the following steps: 1) The raw material system, including lithium source and M source, is sintered for 8h-16h at 300℃-500℃ in an inert gas atmosphere to obtain the first intermediate; 2) The first intermediate is subjected to secondary sintering at 600℃-800℃ in an inert gas atmosphere for 8h-16h to obtain the second intermediate; 3) A redox medium is deposited once on the surface of the second intermediate to obtain the third intermediate; 4) A redox medium is deposited a second time on the surface of the third intermediate to obtain the fourth intermediate; 5) The redox medium is deposited three times on the surface of the fourth intermediate to obtain the positive electrode lithium replenishment material.

6. The preparation method according to claim 5, characterized in that, The temperature of the first deposition is 400℃-450℃, the deposition rate is 0.01μm / min-0.02μm / min, and the deposition time is 2.5min-30min; And / or, the secondary deposition temperature is 350℃-400℃, the deposition rate is 0.02μm / min-0.03μm / min, and the deposition time is 10min-25min; And / or, the temperature of the three depositions is 300℃-350℃, the deposition rate is 0.03μm / min-0.035μm / min, and the deposition time is 6min-28min.

7. A positive electrode plate, characterized in that, This includes the positive electrode lithium replenishment material according to any one of claims 1-4, and the positive electrode lithium replenishment material prepared by the preparation method according to claim 5 or 6.

8. The positive electrode sheet according to claim 7, characterized in that, The positive electrode sheet includes a positive current collector, a positive active material layer on the surface of the positive current collector, and a positive lithium supplement layer on the side of the positive active material layer opposite to the positive current collector.

9. A battery, characterized in that, Includes the positive electrode sheet as described in claim 7 or 8.

Images