Modified lithium nickel cobalt manganese oxide cathode material, preparation method thereof, cathode sheet and lithium ion battery

Abstract

The application relates to the technical field of lithium ion batteries, in particular to a modified lithium nickel cobalt manganese oxide positive electrode material, a preparation method thereof, a positive electrode sheet and a lithium ion battery. The method comprises the following steps: dissolving a lanthanum source in an organic solvent to obtain a lanthanum salt solution; placing lithium nickel cobalt manganese oxide in the lanthanum salt solution, stirring, filtering and drying to obtain an intermediate powder; and performing ultrafast joule heat treatment on the intermediate powder to obtain the modified lithium nickel cobalt manganese oxide positive electrode material, wherein the temperature of the ultrafast joule heat treatment is 400 DEG C-800 DEG C, the heating rate is 20 DEG C / s-100 DEG C / s, and the holding time is 10 s-10 min. Lithium ions are replaced by lanthanum ions at the surface interface of the lithium nickel cobalt manganese oxide, the modified positive electrode material is improved, the cycle life and safety performance of the modified positive electrode material are improved, and the production cost is greatly reduced; lanthanum doping leaves lithium vacancies at the surface interface of the modified positive electrode material, provides more migration space for lithium ions in initial charging and discharging, and improves the rate performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, and particularly relates to a modified lithium nickel cobalt manganese oxide positive electrode material, a preparation method thereof, a positive electrode sheet and a lithium ion battery. BACKGROUND

[0002] High-nickel positive electrode materials are widely used in the fields of electric vehicles and energy storage systems due to their high energy density characteristics, but as the nickel content in the high-nickel positive electrode material increases, the low-valence Ni ions in the high-nickel positive electrode material are oxidized to unstable high-oxidation-state Ni 4+ during the charging process, accompanied by volume expansion and contraction and oxygen release process. The high-nickel positive electrode material is prone to collapse of the layered structure, further exacerbating the phase transition irreversibility of the high-nickel positive electrode material and the occurrence of side reactions with the electrolyte, so that the structure of the high-nickel positive electrode material is easily degraded during the cycle process, and microcracks are generated due to the accumulation of internal stress, the electrochemical performance is rapidly attenuated, and the risk of thermal runaway of the battery is increased, resulting in reduced safety performance of the lithium ion battery. SUMMARY

[0003] In view of this, the present application provides a modified lithium nickel cobalt manganese oxide positive electrode material, a preparation method thereof, a positive electrode sheet and a lithium ion battery, which can solve at least one of the above technical problems.

[0004] In a first aspect, the present application provides a preparation method of a modified lithium nickel cobalt manganese oxide positive electrode material, comprising the following steps: dissolving a lanthanum source in an organic solvent to obtain a lanthanum salt solution; placing lithium nickel cobalt manganese oxide in the lanthanum salt solution, and after the processes of stirring, filtering and drying, an intermediate powder is obtained; and subjecting the intermediate powder to ultrafast joule heat treatment to obtain the modified lithium nickel cobalt manganese oxide positive electrode material, wherein the temperature of the ultrafast joule heat treatment is 400-800 DEG C, the heating rate is 20-100 DEG C / s, and the holding time is 10 s-10 min.

[0005] The present application adopts ion exchange method and ultrafast joule heat treatment method to dope lanthanum in lithium nickel cobalt manganese oxide, and controls the temperature, the heating rate and the holding time of the ultrafast joule heat treatment in the above range. In the ion exchange process, the lithium ions at the surface interface of the lithium nickel cobalt manganese oxide are replaced by lanthanum ions, and the lithium nickel cobalt manganese oxide is modified. The lanthanum ions occupy the position of the lithium ions in the form of +3 valence to obtain the modified lithium nickel cobalt manganese oxide positive electrode material. Since the lanthanum in the modified lithium nickel cobalt manganese oxide positive electrode material does not change in valence during lithium storage, it has strong bonding ability with oxygen atoms, can reduce the release of oxygen, and thus plays a role in stabilizing the lattice structure of the modified lithium nickel cobalt manganese oxide positive electrode material, improves the cycle life and safety performance of the modified lithium nickel cobalt manganese oxide positive electrode material; and the charge of the modified lithium nickel cobalt manganese oxide positive electrode material remains neutral, so that the surface interface of the modified lithium nickel cobalt manganese oxide positive electrode material leaves lithium vacancies, provides more migration space for lithium ions for the initial charge and discharge of the modified lithium nickel cobalt manganese oxide positive electrode material, and improves the rate performance of the modified lithium nickel cobalt manganese oxide positive electrode material; at the same time, the ultrafast joule heat treatment method shortens the synthesis cycle of the modified lithium nickel cobalt manganese oxide positive electrode material, reduces the energy consumption, and greatly reduces the production cost.

[0006] In some embodiments, the temperature of the ultrafast joule heat treatment is 400-600℃, the heating rate is 20-60℃ / s, and the holding time is 10s-10min. The heating rate, temperature and holding time of the ultrafast joule heat treatment in the present application in the above range can further improve the doping effect of the lanthanum element.

[0007] In some embodiments, the doping amount of the lanthanum source in the lithium nickel cobalt manganese oxide is 0.02%-2.00% of the molar amount of the lithium nickel cobalt manganese oxide. The doping amount of the lanthanum source in the above range can reduce the cationic disordering caused by lanthanum doping, ensure the structural stability of the modified lithium nickel cobalt manganese oxide positive electrode material after lanthanum doping, reduce the release of oxygen and provide more lithium vacancies to improve the cycle performance and rate performance of the material.

[0008] In some embodiments, the molecular formula of the lithium nickel cobalt manganese oxide is LiNi a Co b Mn c O2, 0.8≤a≤0.96, 0≤b≤0.2, 0≤c≤0.2.

[0009] In some embodiments, the lithium nickel cobalt manganese oxide includes LiNi 0.83 Co 0.11 Mn 0.06 O2, LiNi 0.8 Mn 0.2 O2, LiNi 0.8 Co 0.2 O2, LiNi 0.92 Co0.056 Mn 0.024 O2or LiNi 0.96 Co 0.02 Mn 0.02 at least one of O2.

[0010] In some embodiments, the lanthanum source comprises at least one of lanthanum nitrate and hydrates thereof, lanthanum chloride and hydrates thereof. The lanthanum source of the above-mentioned kind is selected for its wide availability and low cost of doping.

[0011] In some embodiments, the organic solvent comprises at least one of ethanol, methanol and isopropanol. The organic solvent of the above-mentioned kind is selected for its effectiveness in dissolving the lanthanum source and obtaining a lanthanum salt solution with high uniformity.

[0012] In a second aspect, the present application provides a modified lithium nickel cobalt manganese oxide positive electrode material prepared by the preparation method of the modified lithium nickel cobalt manganese oxide positive electrode material according to any one of the first aspect. The molecular formula of the modified lithium nickel cobalt manganese oxide positive electrode material is Li 1-3z Ni 1-x-y Co x Mn y La z O2, wherein 0.02≤x≤0.2, 0.02≤y≤0.2, 0.0002≤z≤0.02.

[0013] In a third aspect, the present application provides a positive electrode sheet, comprising a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises the modified lithium nickel cobalt manganese oxide positive electrode material according to the second aspect.

[0014] In a fourth aspect, the present application provides a lithium ion battery, comprising an electrode assembly comprising a separator and a negative electrode sheet, and the positive electrode sheet according to the third aspect, wherein the separator is provided between the positive electrode sheet and the negative electrode sheet. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 A transmission electron microscope image of the modified lithium nickel cobalt manganese oxide positive electrode material provided in Example 1 of the present application.

[0016] Figure 2 A zoomed-in view of the region I. Figure 1

[0017] Figure 3 A zoomed-in view of the region II. Figure 1

[0018] Figure 4 A zoomed-in view of the region II. Figure 1

[0019] A zoomed-in view of the region II.​​Figure 5 For Figure 1 The Fourier transform diffraction pattern of the middle II region.

[0020] Figure 6 The energy spectrum of the modified nickel cobalt lithium manganate positive electrode material provided in Embodiment 1 of the present application.

[0021] Figure 7 The cycle performance of the modified nickel cobalt lithium manganate positive electrode material provided in Embodiment 1 and the unmodified nickel cobalt lithium manganate positive electrode material provided in Comparative Example 1.

[0022] Figure 8 The rate performance of the modified nickel cobalt lithium manganate positive electrode material provided in Embodiment 1 and the unmodified nickel cobalt lithium manganate positive electrode material provided in Comparative Example 1.

[0023] Figure 9 The scanning electron microscope image of the modified nickel cobalt lithium manganate positive electrode material provided in Embodiment 13 and the unmodified nickel cobalt lithium manganate positive electrode material provided in Comparative Example 3.

[0024] Figure 10 The cycle performance of the modified nickel cobalt lithium manganate positive electrode material provided in Embodiment 13 and the unmodified nickel cobalt lithium manganate positive electrode material provided in Comparative Example 3.

[0025] Figure 11 The rate performance of the modified nickel cobalt lithium manganate positive electrode material provided in Embodiment 13 and the unmodified nickel cobalt lithium manganate positive electrode material provided in Comparative Example 3.

[0026] Figure 12 The electrode cross-section scanning electron microscope images of the unmodified nickel cobalt lithium manganate positive electrode material provided in Comparative Example 3 before and after cycling, a and b, and the electrode cross-section scanning electron microscope images of the modified nickel cobalt lithium manganate positive electrode material provided in Embodiment 13 before and after cycling, c and d. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments.

[0028] In view of the problems of deterioration of the electrochemical performance and safety performance of the existing high-nickel positive electrode material, the present application provides a preparation method of a modified nickel cobalt lithium manganate positive electrode material, which improves the safety performance, cycle performance and rate performance of the modified nickel cobalt lithium manganate positive electrode material while reducing the doping cost.

[0029] The present application provides a preparation method of a modified nickel cobalt lithium manganate positive electrode material, comprising the following steps:

[0030] Step S10, dissolving the lanthanum source in an organic solvent to obtain a lanthanum salt solution.

[0031] In some embodiments, the lanthanum source includes at least one of lanthanum nitrate and hydrates thereof, lanthanum chloride and hydrates thereof, and the type of lanthanum source can be selected as required. The above-mentioned types of lanthanum source are widely available, and can reduce the cost of doping.

[0032] In some embodiments, the organic solvent includes at least one of ethanol, methanol and isopropyl alcohol, and the type of organic solvent and the ratio of organic solvent to lanthanum source can be selected as required. The above-mentioned types of organic solvent can effectively dissolve the lanthanum source, and obtain a lanthanum salt solution with good dispersion uniformity.

[0033] In some embodiments, the amount of lanthanum source added is not limited, and it can be understood that under the same ultrafast joule heat treatment conditions, the amount of lanthanum source added is increased, and the amount of lanthanum doped in the modified lithium nickel cobalt manganese oxide positive electrode material is also increased, and the amount of lanthanum source added can be selected as required.

[0034] In step S20, the lithium nickel cobalt manganese oxide is placed in the lanthanum salt solution, and after stirring, filtering and drying processes, an intermediate powder is obtained.

[0035] In step S20, stirring can ensure sufficient contact between the lithium nickel cobalt manganese oxide and the lanthanum salt solution, so that the lanthanum ions are uniformly dispersed on the surface of the lithium nickel cobalt manganese oxide and in the solvent, and the preliminary doping amount of lanthanum ions in the lithium nickel cobalt manganese oxide is increased; filtering can separate the solid phase and the liquid phase in the mixed solution, such as the doped lithium nickel cobalt manganese oxide and the organic solvent, to obtain a modified lithium nickel cobalt manganese oxide positive electrode material preliminarily doped with lanthanum; and drying can remove the residual organic solvent in the solid phase after filtering, to obtain a dried intermediate powder, and the process parameters of stirring and drying can be selected as required.

[0036] In some embodiments, the lithium nickel cobalt manganese oxide used in the present application has a molecular formula of LiNi a Co b Mn c O2, wherein 0.8≤a≤0.96, 0≤b≤0.2, and 0≤c≤0.2, and the type of lithium nickel cobalt manganese oxide can be selected as required. Optionally, the lithium nickel cobalt manganese oxide can be LiNi 0.83 Co 0.11 Mn 0.06 O2, LiNi 0.8 Mn 0.2 O2, LiNi 0.8 Co 0.2 O2, LiNi 0.92 Co 0.056 Mn 0.024 O2, or LiNi 0.96 Co 0.02 Mn 0.02 O2, etc.

[0037] In step S30, the intermediate powder is subjected to ultrafast joule heat treatment to obtain the modified lithium nickel cobalt manganese oxide positive electrode material, wherein the temperature of the ultrafast joule heat treatment is 400-800℃, the heating rate is 20-100℃ / s, and the holding time is 10s-10min.

[0038] The temperature of the ultrafast joule heat treatment can be 400℃, 500℃, 600℃, 700℃, 800℃, or other values within the range, which can be selected according to actual needs.

[0039] The heating rate of the ultrafast joule heat treatment can be 20℃ / s, 30℃ / s, 40℃ / s, 50℃ / s, 60℃ / s, 70℃ / s, 80℃ / s, 90℃ / s, 100℃ / s, or other values within the range, which can be selected according to actual needs.

[0040] The holding time of the ultrafast joule heat treatment can be 10s, 1min, 3min, 6min, 9min, 10min, or other values within the range, which can be selected according to actual needs.

[0041] The temperature of the ultrafast joule heat treatment affects the solid solubility of the lanthanum element, and in turn affects the amount of lanthanum element doped, if the temperature of the ultrafast joule heat treatment is too low, i.e. lower than 400℃, the solid solubility of the lanthanum element is small, the amount of lanthanum doped is small, and the performance improvement of the lithium nickel cobalt manganese oxide is limited; if the temperature of the ultrafast joule heat treatment is too high, i.e. higher than 800℃, the high-valence nickel Ni 3+ is reduced to low-valence nickel Ni 2+ , lattice oxygen is released to generate a large number of oxygen vacancies, causing the performance of the modified lithium nickel cobalt manganese oxide positive electrode material to deteriorate; at the same time, if the temperature of the ultrafast joule heat treatment is too high, the structure of the lithium nickel cobalt manganese oxide is easily destroyed, making it difficult for the lanthanum source to be doped, and the performance of the modified lithium nickel cobalt manganese oxide positive electrode material is further deteriorated.

[0042] The heating rate of the ultrafast joule heat treatment affects the dispersion uniformity of the lanthanum element, if the heating rate of the ultrafast joule heat treatment is too fast, i.e. higher than 100℃ / s, it will cause the lanthanum element to rapidly accumulate on the surface of the lithium nickel cobalt manganese oxide rather than diffuse; if the heating rate is less than 20℃ / s, it will exacerbate lithium evaporation, and the capacity of the modified lithium nickel cobalt manganese oxide positive electrode material will decrease.

[0043] The holding time of the ultrafast joule heat treatment affects the doping depth and doping amount of the lanthanum element. If the holding time is too long, i.e. the holding time is greater than 10 min, the doping amount or the doping depth of the lanthanum element is too high, which easily causes grain coarsening, blocks ion transmission channels, and also increases the cation mixing in the positive electrode material to some extent. If the holding time is too short, i.e. the holding time is less than 10 s, the doping amount of the lanthanum element is small or the doping region is shallow, which is difficult to meet the doping depth requirement. Moreover, the short holding time not only removes the by-products such as water on the surface of the modified lithium nickel cobalt manganese oxide positive electrode material, but also maximizes the reduction of the migration of transition metals in kinetics, i.e. the cation mixing, which makes the electrochemical performance of the modified lithium nickel cobalt manganese oxide positive electrode material further play, and the cycle performance of the modified lithium nickel cobalt manganese oxide positive electrode material is reduced.

[0044] The holding time, the heating rate, and the holding time and the addition amount of the lanthanum source of the ultrafast joule heat treatment cooperatively affect the doping uniformity, the doping depth, and the doping amount of the lanthanum element. In the present application, the lanthanum ion exchange method and the ultrafast joule heat treatment method are used to dope lanthanum in lithium nickel cobalt manganese oxide, and by controlling the heating rate and the temperature of the ultrafast joule heat treatment method within the above range, the lanthanum ion can diffuse and migrate to the lithium site of the surface interface of the lithium nickel cobalt manganese oxide and replace the lithium ion there. At this time, the lanthanum ion stably occupies the position of the lithium ion in the form of +3 valence to obtain the modified lithium nickel cobalt manganese oxide positive electrode material. Since the valence of lanthanum does not change during the lithium storage process of the modified lithium nickel cobalt manganese oxide positive electrode material, the bonding ability with oxygen atoms is strong, which can reduce the release of oxygen, and thus plays a role in stabilizing the lattice structure of the modified lithium nickel cobalt manganese oxide positive electrode material, improves the cycle life and safety performance of the modified lithium nickel cobalt manganese oxide positive electrode material; and the charge of the modified lithium nickel cobalt manganese oxide positive electrode material remains neutral, which makes the surface interface of the modified lithium nickel cobalt manganese oxide positive electrode material have lithium vacancies, provides more migration space for lithium ions for the initial charge and discharge of the modified lithium nickel cobalt manganese oxide positive electrode material, and improves the rate performance thereof. At the same time, the ultrafast joule heat treatment method makes the synthesis cycle of the modified lithium nickel cobalt manganese oxide positive electrode material short, the energy consumption is low, and the production cost is greatly reduced.

[0045] Preferably, the temperature of the ultrafast joule heat treatment is 400-600℃, the heating rate is 20-60℃ / s, and the holding time is 30 s-6 min. The temperature of the ultrafast joule heat treatment affects the solid solubility of the doping element, and thus affects the doping amount of the lanthanum element. The heating rate affects the doping uniformity of the lanthanum element. The holding time affects the doping depth of the lanthanum ion doping. The heating rate, the temperature, and the holding time of the ultrafast joule heat treatment in the present application are within the above range, which can further improve the doping effect of the lanthanum element, and obtain the modified lithium nickel cobalt manganese oxide positive electrode material with better safety performance, cycle life, and rate performance.

[0046] In some embodiments, the amount of the lanthanum source incorporated in the lithium nickel cobalt manganese oxide is 0.02%-2.00% of the molar amount of the lithium nickel cobalt manganese oxide. Optionally, the amount of the lanthanum source incorporated in the lithium nickel cobalt manganese oxide can be specifically 0.02%, 0.05%, 0.10%, 0.50%, 1.00%, 1.50%, or 2.00% of the molar amount of the lithium nickel cobalt manganese oxide, or other values within the range, which can be selected according to actual needs. The amount of the lanthanum source incorporated within the above range can reduce the cationic disordering caused by lanthanum doping, ensure the structural stability of the modified lithium nickel cobalt manganese oxide cathode material after lanthanum doping, reduce the release of oxygen, and provide more lithium vacancies to improve the cycle performance and rate performance of the material.

[0047] Another embodiment of the present application provides a modified lithium nickel cobalt manganese oxide cathode material prepared by the preparation method of step S10, step S20, and step S30. The modified lithium nickel cobalt manganese oxide cathode material obtained by lanthanum doping has a molecular formula of Li 1-3z Ni 1-x- y Co x Mn y La z O2, wherein 0.02≤x≤0.2, 0.02≤y≤0.2, and 0.0002≤z≤0.02, i.e., a high-nickel cathode material. The specific type of the modified lithium nickel cobalt manganese oxide cathode material can be selected according to actual needs.

[0048] Another embodiment of the present application provides a positive electrode sheet, which comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, and the positive electrode active material layer comprises the modified lithium nickel cobalt manganese oxide cathode material.

[0049] Another embodiment of the present application further provides a lithium ion battery, which comprises an electrode assembly, and the electrode assembly comprises a separator, a negative electrode sheet, and a positive electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet serves as a lithium ion source, releases lithium ions during discharging, and absorbs lithium ions during charging. The negative electrode sheet embeds lithium ions during discharging and de-embeds lithium ions during charging. The separator allows the lithium ions to pass freely through the microporous structure while physically isolating the electrons to prevent short circuiting. The three components work together to realize the operation of the battery.

[0050] The scheme of the present application will be explained below in combination with examples. Those skilled in the art will understand that the examples below are only used to explain the present application and cannot be understood as a limitation of the present application. Unless otherwise indicated, the reagents, software, and instruments not specifically indicated in the following examples are all conventional commercially available products or open source.

[0051] The test method of the doping amount of the lanthanum source is as follows: the modified positive electrode material is dissolved in an acid solution, and the content of lanthanum in the modified lithium nickel cobalt manganese oxide positive electrode material is detected by an inductively coupled plasma spectrometer.

[0052] Example 1:

[0053] (1) A proper amount of La(NO3)3 is weighed and dissolved in ethanol to obtain a lanthanum salt solution;

[0054] (2) A single crystal LiNi 0.83 Co 0.11 Mn 0.06 O2 is weighed and added to the above lanthanum salt solution to obtain a mixed solution, and the mixed solution is fully stirred, filtered and dried to obtain an intermediate powder;

[0055] (3) The intermediate powder is transferred to a Ni foil sample loading platform of an ultrafast joule heat equipment, and rapid heat treatment is performed to obtain a modified lithium nickel cobalt manganese oxide positive electrode material, wherein the ultrafast joule heat treatment temperature is 400℃, the heating rate is 20℃ / s, the holding time is 10 min, and the doping amount of the lanthanum source is 0.02% of the molar amount of the modified lithium nickel cobalt manganese oxide positive electrode material.

[0056] Examples 2 to 5:

[0057] Examples 2 to 5 are different from Example 1 in that the temperature, the heating rate and the holding time of the ultrafast joule heat treatment are adjusted, and the remaining steps are the same as those of Example 1 except that the preparation parameters are adjusted according to Table 1.

[0058] Examples 6 to 7:

[0059] Examples 6 to 7 are different from Example 1 in that the amount of the lanthanum source is adjusted, and the doping amount of the lanthanum source is adjusted accordingly, and the remaining steps are the same as those of Example 1 except that the preparation parameters are adjusted according to Table 1.

[0060] Examples 8 to 10:

[0061] Examples 8 to 10 are different from Example 1 in that the type of the lanthanum source is adjusted, and the remaining steps are the same as those of Example 1 except that the preparation parameters are adjusted according to Table 1.

[0062] Examples 11 to 14:

[0063] Examples 11 to 14 are different from Example 1 in that the types of the lanthanum source and the lithium nickel cobalt manganese oxide are adjusted, and the remaining steps are the same as those of Example 1 except that the preparation parameters are adjusted according to Table 1.

[0064] Comparative Examples 1 to 4:

[0065] Comparative Examples 1 to 4 differ from Example 1 in that no doping modification is performed.

[0066] Comparative Example 5:

[0067] Comparative Example 5 differs from Example 1 in that a common heat treatment process is used.

[0068] Comparative Examples 6 to 7:

[0069] Comparative Examples 6 to 7 differ from Example 1 in that the temperature, heating rate and holding time of the ultrafast Joule heat treatment are adjusted, and the remaining steps are the same as those of Example 1 except for adjusting the preparation parameters according to Table 1.

[0070] Table 1. Preparation parameters of Examples 1-14 and Comparative Examples 1-7 of the present application.

[0071]

[0072] Preparation of lithium ion button half-cells:

[0073] Vinyl carbonate / dimethyl carbonate (EC / DMC, volume ratio 1:1) containing 5 vol.% of fluoroethylene carbonate (FEC) mixed solution dissolved in 1 mol / L LiPF6 is used as the electrolyte, a 7 μm polypropylene / polyethylene composite separator is used, lithium sheet is used as the counter electrode, and 1.0 g of the positive electrode material of Examples 1-14 and Comparative Examples 1-7 is used as the positive electrode to prepare the electrode sheet by slurry coating process, and the button half-cells are assembled in a glove box.

[0074] Test:

[0075] The button half-cells obtained in Examples 1-14 and Comparative Examples 1-7 are subjected to charge-discharge cycling under the conditions of a set voltage of 3V to 4.5V and different current densities.

[0076] (1) The lithium ion battery is placed in a 25°C environment for 720 minutes, and then subjected to charge-discharge in the following steps: 0.2C constant current charging to 4.5V, then standing for 5 minutes, constant current discharging to 3.0V, to obtain the first discharge specific capacity (0.2C), which is one cycle, and the initial discharge capacity C0 of the lithium ion battery is recorded, and then the cycle is repeated 100 times. Among them, the first discharge specific capacity = discharge capacity / mass of modified nickel-cobalt-manganese lithium oxide positive electrode material. According to the above cycle steps, the discharge capacity C1 of the button half-cell after 200 cycles is measured, and the capacity retention rate = C1 / C0 x 100%.

[0077] (2) The lithium-ion battery was placed in an environment of 25°C and left to stand for 720 minutes. Then, it was charged and discharged according to the following steps: 0.2C constant current charging to 4.5V, followed by standing for 5 minutes, constant current discharging to 3.0V, and repeated 3 times; then standing for 5 minutes, 1C constant current charging to 4.5V, followed by standing for 5 minutes, constant current discharging to 3.0V, to obtain the first discharge specific capacity (1C). This is one cycle. The initial discharge capacity C0 of the lithium-ion battery was recorded, and then the cycle was repeated 100 times. Wherein, the first discharge specific capacity = discharge capacity / mass of modified nickel cobalt manganese oxide cathode material. After 100 cycles according to the above cyclic steps, the discharge capacity C1 of the coin cell after 100 cycles was measured, and the capacity retention rate = C1 / C0×100%.

[0078] Table 2. Test results of the first discharge specific capacity and multiple charge-discharge capacity retention rate of Examples 1-14 and Comparative Examples 1-7 of this application.

[0079]

[0080] Test Result Analysis:

[0081] Compared with Comparative Example 1: Example 1:

[0082] Please refer to Figures 1-5 The phase layer structure of the lanthanum-doped modified lithium nickel cobalt manganese oxide cathode material remains intact. Figure 1 In region II), the surface structure changes somewhat due to the incorporation of lithium sites into lanthanum, but selected area electron diffraction reveals that its layered structure is still well preserved. Figure 1 (Region I); also, please refer to Figure 6 The energy spectrum shows that the modified lithium nickel cobalt manganese oxide cathode material obtained by ion exchange and ultrafast Joule heat treatment exhibits good uniformity of lanthanum dispersion at the interface.

[0083] Please refer to Figure 7 Under conditions of 3V to 4.5V and 0.2C, the initial discharge specific capacity of Comparative Example 1 was 201mAh / g, and the capacity retention rate after 200 cycles was 57.7%. The initial discharge specific capacity of Example 1 was 195mAh / g, and the capacity retention rate after 200 cycles was 78.3%. The modified nickel-cobalt-manganese oxide cathode material obtained after lanthanum doping showed good cycle performance; and referring to... Figure 8 The lanthanum-doped cathode material, at a current density of 10C, at 10C (2000 mAg) -1 At a current density of ), the specific capacities of the cathode materials before and after modification are 66.5 mAh g, respectively. -1 and 102.1 mAhg -1The specific capacity retention rate is increased from 33.1% to 51.7%, indicating that the cycle performance of the modified lithium nickel cobalt manganese oxide positive electrode material is improved after the lanthanum ion doping in example 1.

[0084] Examples 2 to 5 compared with Comparative Example 1:

[0085] Under the condition of 3V to 4.5V and 0.2C, compared with Comparative Example 1, after the lanthanum ion doping and the temperature of the ultrafast joule heat treatment satisfying 400℃-800℃, the heating rate satisfying 20℃ / s-100℃ / s, and the holding time satisfying 10s-10min, the rate performance is improved, and the cycle performance of the modified lithium nickel cobalt manganese oxide positive electrode material is improved. Furthermore, when the temperature of the ultrafast joule heat treatment further satisfies 400℃-600℃, the heating rate further satisfies 20℃ / s-60℃ / s, and the holding time further satisfies 30s-6min, the cycle performance of the modified lithium nickel cobalt manganese oxide positive electrode material is further improved.

[0086] Examples 6 to 7 compared with Comparative Example 1:

[0087] Under the condition of 3V to 4.5V and 0.2C, compared with Comparative Example 1, after changing the adding amount of the lanthanum source, the lanthanum doping amount of the modified lithium nickel cobalt manganese oxide positive electrode material is increased, and when the doping amount of the lanthanum source satisfies 0.02%-2.00%, the rate performance is improved, and the cycle performance of the modified lithium nickel cobalt manganese oxide positive electrode material is improved.

[0088] Examples 8 to 10

[0089] According to the test data of examples 8 to 10, by selecting different kinds of lanthanum sources, the rate performance is improved, and the cycle performance of the modified lithium nickel cobalt manganese oxide positive electrode material is improved.

[0090] Examples 11 to 12

[0091] According to the test data of examples 11 to 12, by selecting different kinds of lithium nickel cobalt manganese oxides, the rate performance is improved, and the cycle performance of the modified lithium nickel cobalt manganese oxide positive electrode material is improved.

[0092] Example 13 compared with Comparative Example 3:

[0093] Please refer to Figure 9 The morphology of the modified lithium nickel cobalt manganese oxide positive electrode material obtained by lanthanum doping in the embodiment does not change obviously, and the structure remains intact. Please refer to Figure 10 The first discharge specific capacity of the modified lithium nickel cobalt manganese oxide positive electrode material after lanthanum doping in example 13 reaches 199mAhg -1 under the condition of 3V to 4.5V and 1C (200mAg -1, the capacity retention rate is 88.9% after 100 charge-discharge cycles, while the specific discharge capacity of the modified lithium nickel cobalt manganese oxide cathode material without lanthanum doping in Comparative Example 3 is 200 mAhg -1 , the capacity retention rate is 80.2% after 100 charge-discharge cycles, and after lanthanum doping, the rate performance is improved, and the cycle performance of the modified lithium nickel cobalt manganese oxide cathode material is also improved.

[0094] Please refer to Figure 11 , the specific capacity of the cathode material after lanthanum doping is increased to 152.6 mAhg -1 , which is nearly 18.7% higher than that of Comparative Example 3 without lanthanum doping.

[0095] Please refer to Figure 12 By comparing the cross-section observation of materials with and without lanthanum doping, it is found that lanthanum doping can stabilize the spherical structure of the secondary particles of the modified lithium nickel cobalt manganese oxide cathode material.

[0096] Example 14

[0097] According to the test data of Example 14, by selecting different types of lanthanum sources and lithium nickel cobalt manganese oxides, the cycle performance of the lithium nickel cobalt manganese oxide cathode material is effectively improved after lanthanum doping.

[0098] Comparative Examples 1 to 4

[0099] From the test data of Comparative Examples 1 to 4, compared with Example 1 and Examples 11, 13 and 14, without lanthanum doping, the cycle performance of the obtained cathode material is reduced.

[0100] Example 1 compared with Comparative Example 5:

[0101] Comparative Example 5 uses a common heat treatment method for the lanthanum doping process, and the heat treatment time is too long, which will increase the cation mixing of the cathode material to a certain extent, resulting in poor performance of the cathode material. While Example 1 uses an ultra-fast joule heat shock method, because the heat treatment time is short, it maximizes the removal of water and other by-products on the surface of the modified lithium nickel cobalt manganese oxide cathode material, while minimizing the migration of transition metals, i.e. cation mixing, which enables the electrochemical performance of the modified lithium nickel cobalt manganese oxide cathode material to be further improved. The cycle performance of the modified lithium nickel cobalt manganese oxide cathode material obtained by the ultra-fast joule heat treatment method of the present application is significantly improved.

[0102] Example 1 compared with Comparative Examples 6 to 7:

[0103] Compared with Example 1, the temperature, the temperature rising rate and the holding time of the ultrafast joule heat treatment in Comparative Example 6 do not meet the requirements of 400-800℃, 20-100℃ / s and 10s-10min, and the first discharge specific capacity and the capacity retention rate after 100 cycles are both decreased, that is, the cycle performance of the modified lithium nickel cobalt manganese oxide positive electrode material is decreased; in Comparative Example 7, the temperature of the ultrafast joule heat treatment is too high, which destroys the structure of the lithium nickel cobalt manganese oxide, and makes it difficult for the lanthanum source to be doped, and the performance of the modified lithium nickel cobalt manganese oxide positive electrode material is poor.

[0104] In addition, those skilled in the art should recognize that the above embodiments are only used to illustrate the present application, and are not used as a limitation to the present application, and as long as the above embodiments are appropriately changed and changed within the scope of the spirit of the present application, they fall within the scope of the disclosure of the present application.

Claims

1. A method for preparing a modified lithium nickel cobalt manganese oxide cathode material, characterized in that, The method comprises the following steps: dissolving a lanthanum source in an organic solvent to obtain a lanthanum salt solution; The lithium nickel cobalt manganese oxide is placed in the lanthanum salt solution, and after stirring, filtering and drying processes, an intermediate powder is obtained; the molecular formula of the lithium nickel cobalt manganese oxide is LiNi a Co b Mn c O2, 0.8≤a≤0.96, 0≤b≤0.2, 0≤c≤0.2; subjecting the intermediate powder to ultrafast joule heat treatment to obtain the modified lithium nickel cobalt manganese oxide positive electrode material, wherein the temperature of the ultrafast joule heat treatment is 400-800 DEG C, the heating rate is 20-100 DEG C / s, and the holding time is 10 s-10 min; the amount of the lanthanum source incorporated in the lithium nickel cobalt manganese oxide is 0.02-2.00% of the molar amount of the lithium nickel cobalt manganese oxide.

2. The method for preparing the modified lithium nickel cobalt manganese oxide cathode material according to claim 1, characterized in that, The temperature of the ultrafast joule heat treatment is 400-600 DEG C, the heating rate is 20-60 DEG C / s, and the holding time is 30 s-6 min.

3. The method of claim 1, wherein the modified nickel-cobalt-manganese lithium cathode material is prepared by the steps of: mixing a lithium source, a nickel source, a cobalt source, and a manganese source to form a mixture; and heating the mixture to form the modified nickel-cobalt-manganese lithium cathode material. LiNi 0.83 Co 0.11 Mn 0.06 O2, LiNi 0.8 Mn 0.2 O2, LiNi 0.8 Co 0.2 O2, LiNi 0.92 Co 0.056 Mn 0.024 O2, or LiNi 0.96 Co 0.02 Mn 0.02 O2.

4. The method of claim 1, wherein the modified nickel-cobalt-manganese lithium cathode material is prepared by the steps of: mixing a lithium source, a nickel source, a cobalt source, and a manganese source to form a mixture; and heating the mixture to form the modified nickel-cobalt-manganese lithium cathode material. The lanthanum source comprises at least one of lanthanum nitrate and its hydrate and lanthanum chloride and its hydrate.

5. The method of claim 1, wherein the modified nickel-cobalt-manganese lithium cathode material is prepared by the steps of: mixing a lithium source, a nickel source, a cobalt source, and a manganese source to form a mixture; and heating the mixture to form the modified nickel-cobalt-manganese lithium cathode material. The organic solvent comprises at least one of ethanol, methanol and isopropyl alcohol.

6. A modified lithium nickel cobalt manganese oxide cathode material prepared by the method of preparing a modified lithium nickel cobalt manganese oxide cathode material according to any one of claims 1 to 5, characterized in that, The modified nickel-cobalt-manganese lithium cathode material has a molecular formula of Li 1- 3z Ni 1-x-y Co x Mn y La z O2, wherein 0.02≤x≤0.2, 0.02≤y≤0.2, 0.0002≤z≤0.

02.

7. A positive electrode sheet comprising a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector, characterized in that, The positive electrode active material layer comprises the modified lithium nickel cobalt manganese oxide positive electrode material of claim 6.

8. A lithium-ion battery comprising an electrode assembly, the electrode assembly comprising a separator film and a negative electrode sheet, characterized by, The lithium ion battery further comprises the positive electrode sheet of claim 7, and the separator film is arranged between the positive electrode sheet and the negative electrode sheet.

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