A quasi-single-crystal ternary positive electrode material and preparation and application thereof

Abstract

The application discloses a quasi-single-crystal ternary positive electrode material and a preparation and application thereof. 1+a Ni x Co y Mn z HbO2; wherein, 0

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery materials, and particularly relates to a kind of single-crystal-like ternary positive electrode material and its preparation and application. BACKGROUND

[0002] With the rapid development of electronic devices and electric vehicles, etc., the performance of the positive electrode material is required to be higher and higher. As the core component of the battery, the positive electrode material needs to have many excellent performances. First of all, the positive electrode material must have good stability, which includes structural stability during charging and discharging and chemical stability under different environmental conditions, to ensure that the battery can work reliably for a long time. Secondly, the positive electrode material needs to have a high capacity, which can store and release more electric energy in unit mass or unit volume, thereby improving the energy density of the battery. In addition, good cycle performance is also essential, that is, after many charging and discharging cycles, it can still maintain a high capacity retention rate and stable performance. At the same time, in order to improve the charging and discharging efficiency and power performance of the battery, the positive electrode material should have a low impedance, so that lithium ions can quickly diffuse and transport, reducing energy loss. Finally, the positive electrode material also needs to have good thermal stability to ensure the safety and reliability of the battery during use.

[0003] Although some progress has been made in the research and development of positive electrode materials, there are still some technical problems that are difficult to meet the growing demand for high performance. First of all, the stability of the existing positive electrode material is still not ideal. In the long-term use process, the positive electrode material is easily affected by factors such as volume change during charging and discharging, corrosion of electrolyte, etc., leading to structural damage and performance decline. Secondly, in terms of cycle performance, many positive electrode materials have a rapid capacity decay after many charging and discharging cycles, which cannot maintain stable output performance, limiting the service life and application range of the battery. In addition, the existing positive electrode material has a high impedance, and the diffusion speed of lithium ions is slow, which not only affects the charging and discharging efficiency of the battery, but also limits its application in high-power devices. Moreover, the thermal stability of some positive electrode materials is insufficient under harsh conditions such as high temperature, which poses a safety hazard, such as overheating, fire, and even explosion risk. These problems comprehensively result in the existing positive electrode material being unable to simultaneously achieve good stability, high capacity, excellent cycle performance, low impedance, and high thermal stability, etc.

[0004] Therefore, a technical solution is needed to simultaneously achieve good stability, high capacity, excellent cycle performance, low impedance, and high thermal stability of the positive electrode material. SUMMARY

[0005] Therefore, the application provides a quasi-single-crystal ternary positive electrode material and a preparation and application thereof, and aims at solving the problem of how to realize good stability, high capacity, excellent cycle performance, low impedance and high thermal stability of the positive electrode material.

[0006] To achieve the above technical purposes, the application adopts the following technical solutions.

[0007] In a first aspect, the application provides a quasi-single-crystal ternary positive electrode material, which comprises a base material and a coating layer coated on the base material; the chemical formula of the base material is Li 1+a Ni x Co y Mn z HbO2; wherein 0

[0008] Preferably, the mass of the coating layer is 0.001-0.5% of the base material.

[0009] Preferably, the D50 of the quasi-single-crystal ternary positive electrode material is 2.0-6.0 μm; and / or, the specific surface area of the quasi-single-crystal ternary positive electrode material is 0.5-1.5 m2 / g.

[0010] In a second aspect, the application provides a preparation method of a quasi-single-crystal ternary positive electrode material, which comprises the following steps:

[0011] The nickel-cobalt-manganese hydroxide, the lithium source and the dopant are mixed and then subjected to primary roasting to obtain the base material; the base material and the coating agent are mixed and then subjected to secondary roasting to obtain the quasi-single-crystal ternary positive electrode material.

[0012] Preferably, in the dopant, the proportion of Na is 0.01-0.5 wt%, and the proportion of K is 0.01-0.5 wt%.

[0013] Preferably, in the coating agent, the proportion of Rb is 0.001-0.5 wt%, and the proportion of Cs is 0.001-0.5 wt%.

[0014] Preferably, the temperature of the primary roasting is 800-1000℃, the time of the primary roasting is 6-12 h, and the atmosphere of the primary roasting is 60-100 vt% oxygen atmosphere; the loading amount of the primary roasting is 4-8 kg.

[0015] Preferably, the temperature of the secondary calcination is 500-700℃, the time of the secondary calcination is 6-12h, the atmosphere of the secondary calcination is air or compressed air; the loading of the secondary calcination is 8-12kg.

[0016] Preferably, the molar ratio of the nickel-cobalt-manganese hydroxide to the lithium source is 1: (1.0-1.2).

[0017] In a third aspect, the present application provides a positive electrode tab, which comprises the single-crystal-like ternary positive electrode material.

[0018] The beneficial effects of the present application are as follows: the present application modifies the positive electrode material by using specific coating agents and dopants, thereby improving the stability of the positive electrode material, increasing the diffusion radius of Li ions in the positive electrode material and improving the diffusion speed of Li ions, reducing the impedance of the positive electrode material, and improving the electrical performance; the present application obtains the single-crystal-like positive electrode material through secondary sintering, thereby ensuring the capacity and cycle performance of the positive electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 SEM image of the single-crystal-like positive electrode material obtained in Example 1;

[0020] Figure 2 XRD images of the single-crystal-like positive electrode material obtained in Example 1 before and after 50 cycles;

[0021] Figure 3 Cross-sectional image of the single-crystal-like positive electrode material obtained in Example 1 after 50 cycles. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application is further described in detail below with reference to examples. It should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the present application.

[0023] The present application provides a single-crystal-like ternary positive electrode material, which comprises a base material and a coating layer coated on the base material; the chemical formula of the base material is Li 1+a Ni x Co y Mn z HbO2; wherein, 0

[0024] In the present application, the bulk structure of Zr, Y, W, Al, Co, Ti, Sr and the like used for modifying NCM anode-like single crystal materials is used for core doping and coating of the positive electrode material to obtain the effect of ensuring the cycle performance of the material under the premise of unchanged capacity, while also improving the thermal stability of the material, thereby improving the overall electrochemical performance of the LMRO anode; in addition, Na and K elements are added during core doping, and Rb and Cs elements are added during coating to modify to expand the Li ion channel radius, and the ionic radius is Li + <Na + <K + <Rb + <Cs + , by doping Na and K elements into the inner layer of the single crystal, and by coating Rb and Cs elements into the outer layer of the single crystal, a gradient Li ion diffusion radius is formed, the internal resistance of the material is reduced, the migration speed of Li ions is greatly enhanced, and the high-voltage electrochemical performance of the single-crystal-like ternary positive electrode material is enhanced.

[0025] In some embodiments, the mass of the coating layer is 0.001-0.5% of the base material.

[0026] In this embodiment, if the amount of the coating layer is too much, it will affect the transmission and diffusion of lithium ions; if the amount of the coating layer is too little, the material surface will have a side reaction with the electrolyte.

[0027] In some embodiments, the D50 of the single-crystal-like ternary positive electrode material is 2.0-6.0 μm; and / or, the specific surface area of the single-crystal-like ternary positive electrode material is 0.5-1.5 m2 / g.

[0028] In this embodiment, under the limited D50 and specific surface area, the smaller the particle size of the single-crystal-like ternary positive electrode material, the higher the capacity, but the cycle retention rate is low, the larger the particle size, the lower the capacity, but the cycle retention rate is high, in order to balance the capacity and cycle, the particle size of 2.0-6.0 μm is appropriate; the smaller the BET, the lower the capacity, but the cycle retention rate is high, the larger the BET, the higher the capacity, but the cycle retention rate is low, in order to balance the capacity and cycle, the BET of 0.5-1.5 m 2 / g is appropriate.

[0029] The present application provides a preparation method of a single-crystal-like ternary positive electrode material, comprising the following steps:

[0030] Mixing nickel-cobalt-manganese hydroxide, lithium source and dopant, and then performing first roasting to obtain base material Li 1+ a Ni 0.6 Co 0.3 Mn 0.1 H bO2; the base material is mixed with the coating agent and then secondarily sintered to obtain the single-crystal-like ternary positive electrode material.

[0031] In the application, the single-crystal-like ternary positive electrode material is prepared by doping the base material through primary sintering and coating the base material through secondary sintering. The secondary sintering process improves the capacity and cycle performance of the positive electrode material under the premise of forming a single-crystal-like material. The dopant and the coating agent improve the stability of the positive electrode material, increase the diffusion radius of Li ions in the positive electrode material, and improve the diffusion speed of Li ions.

[0032] In some embodiments, the proportion of Na in the dopant is 0.01-0.5 wt%, and the proportion of K is 0.01-0.5 wt%.

[0033] In this embodiment, if the amount of Na is too much, the material capacity is low, and the internal resistance is large. If the amount of Na is too little, there is no obvious improvement effect. If the amount of K is too much, the capacity is low, and the internal resistance is large. If the amount of K is too little, there is no obvious improvement effect.

[0034] In some embodiments, the proportion of Rb in the coating agent is 0.001-0.5 wt%, and the proportion of Cs is 0.001-0.5 wt%.

[0035] In this embodiment, if the amount of Rb is too much, the capacity is low, and the internal resistance is large. If the amount of Rb is too little, there is no obvious improvement effect. If the amount of Cs is too much, the capacity is low, and the internal resistance is large. If the amount of Cs is too little, there is no obvious improvement effect.

[0036] In some embodiments, the temperature of the primary sintering is 800-1000℃, the time of the primary sintering is 6-12h, and the atmosphere of the primary sintering is 60-100vt% oxygen atmosphere. The loading amount of the primary sintering is 4-8kg.

[0037] In some embodiments, the temperature of the secondary sintering is 500-700℃, the time of the secondary sintering is 6-12h, and the atmosphere of the secondary sintering is air or compressed air. The loading amount of the secondary sintering is 8-12kg.

[0038] In the application, by adjusting the process conditions of the primary sintering and the secondary sintering, the positive electrode material in a single-crystal-like morphology and within the target range of D50 and specific surface area can be finally obtained. If the temperature of the primary sintering is too high, the primary grain becomes large, and the capacity becomes low. If the temperature of the primary sintering is too low, the material crystallinity is not enough, and the cycle stability is poor. If the temperature of the secondary sintering is too high, the primary grain becomes large, and the capacity becomes low. If the temperature of the secondary sintering is too low, the coating agent cannot be effectively coated.

[0039] In some embodiments, the molar ratio of the nickel cobalt manganese hydroxide to the lithium source is 1: (1.0-1.2).

[0040] The application provides a positive electrode tab, which comprises a quasi-single-crystal ternary positive electrode material.

[0041] The application is further described below through specific examples.

[0042] Example 1

[0043] A preparation method of a quasi-single-crystal ternary positive electrode material comprises the following steps:

[0044] Ni 0.6 Co 0.1 Mn 0.3 (OH)2 (purchased from Green Eco-Material Technology Co., Ltd.), Li2CO3 is weighed according to a lithium metal molar ratio Li / Me (Me is the total molar amount of Ni, Co and Mn) of 1:1, and then Ni 0.6 Co 0.1 Mn 0.3 (OH)2 and Li2CO3 are added with 0.1% of a dopant in total mass, wherein the dopant comprises a mixture of zirconium oxide, yttrium oxide and tungsten oxide in a mass ratio of 1:1:1, and sodium carbonate and potassium carbonate, wherein the amount of Na accounts for 0.3wt% of the amount of the dopant, and the amount of K accounts for 0.2wt% of the amount of the dopant, the mixture is put into a high-speed mixer for mixing, then put into a box body, the loading amount is 4kg, and then the box body is placed in a muffle furnace for primary roasting at 1000℃ for 8h in an air atmosphere containing 60vt% oxygen, and then naturally cooled, crushed and sieved to obtain a base material with a D50 of 3.5μm;

[0045] The base material is mixed with a coating agent, wherein the mass of the coating layer is 0.1% of the mass of the base material, and the coating agent comprises tungsten oxide, aluminum oxide and cobalt oxide in a mass ratio of 1:1:1 and in a content of 0.1wt%, wherein Rb (0.2% of the mass of the coating agent) and Cs (0.1% of the mass of the coating agent) are added in the form of carbonates, the mixture is put into a box body, the loading amount is 12kg, and then placed in a muffle furnace for secondary roasting at 500℃ for 6h in an air atmosphere, and then cooled to obtain a quasi-single-crystal ternary positive electrode material with a D50 of 3.0μm; and the specific surface area of the quasi-single-crystal ternary positive electrode material is 1.0 m2 / g.

[0046] Example 2

[0047] A preparation method of a quasi-single-crystal ternary positive electrode material, and other contents are the same as those in Example 1, except that in the dopant, the amount of Na accounts for 0.5wt%, and the amount of K accounts for 0.5wt%.

[0048] Example 3

[0049] A preparation method of a quasi-single-crystal ternary positive electrode material, other contents are the same as those in Example 1, except that the proportion of Na in the dopant is 0.01wt%, and the proportion of K is 0.01wt%.

[0050] Example 4

[0051] A preparation method of a quasi-single-crystal ternary positive electrode material, other contents are the same as those in Example 1, except that the proportion of Rb in the coating agent is 0.5wt%, and the proportion of Cs is 0.5wt%.

[0052] Example 5

[0053] A preparation method of a quasi-single-crystal ternary positive electrode material, other contents are the same as those in Example 1, except that the proportion of Rb in the coating agent is 0.001wt%, and the proportion of Cs is 0.001wt%.

[0054] Comparative Example 1

[0055] A preparation method of a positive electrode material, other contents are the same as those in Example 1, except that the proportion of Na in the dopant is 0.

[0056] Comparative Example 2

[0057] A preparation method of a positive electrode material, other contents are the same as those in Example 1, except that the proportion of K in the dopant is 0.

[0058] Comparative Example 3

[0059] A preparation method of a positive electrode material, other contents are the same as those in Example 1, except that the proportion of Rb in the coating agent is 0.

[0060] Comparative Example 4

[0061] A preparation method of a positive electrode material, other contents are the same as those in Example 1, except that the proportion of Cs in the coating agent is 0.

[0062] Comparative Example 5

[0063] A preparation method of a positive electrode material, other contents are the same as those in Example 1, except that the proportion of Rb in the coating agent is 0 and the proportion of Cs is 0.

[0064] Test and evaluation

[0065] The quasi-single-crystal positive electrode material obtained in Example 1 was tested by SEM, and the results are shown in FIG. 1. Figure 1 The final product is shown in FIG. 1, and it can be seen that the particle size D50 of the quasi-single-crystal positive electrode material obtained in Example 1 is 4.2μm, and the specific surface area is 1.0 m 2XRD patterns of the single-crystal-like positive electrode material of Test Example 1 before and after 50 cycles are shown in FIG. 6. As shown in FIG. 6, it can be seen that there is no difference in the single-crystal-like positive electrode material of Example 1 before and after the cycles, and the material has good stability. Figure 2 FIG. 7 is a cross-sectional view of the single-crystal-like positive electrode material of Example 1 after 50 cycles. As shown in FIG. 7, it can be seen that the single-crystal-like positive electrode material of Example 1 has no cracks after the cycles, which also indicates that the material has good stability. Figure 3 FIG. 7 is a cross-sectional view of the single-crystal-like positive electrode material of Example 1 after 50 cycles. As shown in FIG. 7, it can be seen that the single-crystal-like positive electrode material of Example 1 has no cracks after the cycles, which also indicates that the material has good stability.

[0066] The positive electrode materials obtained in the above examples and comparative examples were assembled into batteries and subjected to a discharge test, and the specific method was as follows:

[0067] The positive electrode materials, acetylene black and polyvinylidene fluoride (PVDF) obtained in the above examples and comparative examples were weighed according to a mass ratio of 90:5:5, NMP (N-methyl pyrrolidone) was added, and the slurry was prepared by high-speed mixing for 15 min through a defoaming machine, then uniformly coated on an aluminum foil with a doctor blade scale of 100 μm to prepare an electrode sheet; then the electrode sheet was placed in a vacuum drying oven at 80°C for baking, and after drying, the electrode sheet was cut into a positive electrode sheet with a diameter of 14 mm by tabletting, punching and cutting; according to the order of a negative electrode shell, a lithium sheet, 3 drops of DEC / EC (volume ratio of 1:1) electrolyte added by a syringe, a celgard 2500 separator, 3 drops of DEC / EC (volume ratio of 1:1) electrolyte added by a syringe, a positive electrode sheet and a positive electrode shell, a discharge battery was assembled in an argon-filled glove box to prepare lithium ion batteries,

[0068] The lithium ion batteries prepared were subjected to a specific capacity test, a cycle performance test and an impedance test, and the above tests were briefly described as follows:

[0069] Specific capacity test: at 25°C, the charge and discharge performance of the material was studied by constant current charging and discharging (0.1C), and the voltage range was 3.0V-4.55V; the first charge and discharge efficiency was calculated according to the specific charge and discharge capacity.

[0070] Cycle performance test: at 25°C, the battery was charged to 4.50V at 0.1C constant current and constant voltage, the cutoff current was 0.05C, then discharged to 3.0V at 0.1C constant current, and the cycle was repeated; the capacity retention rate at the 50th cycle was calculated after 50 cycles of charge and discharge.

[0071] The calculation formula was: the capacity retention rate at the 50th cycle (%) = (the discharge capacity at the 50th cycle / the discharge capacity at the first cycle) x 100%.

[0072] Impedance test (DCR): EIS data was collected at room temperature by using an IVIUM STAT impedance analyzer, the amplitude was 5mA, the frequency range was 102-105Hz, and the impedance data was fitted by using Zview software.

[0073] Thermal stability test (TR): Differential scanning calorimetry (DSC) analysis was carried out under the condition that the SOC of the material was 80%, and the highest temperature at which the material decomposed thermally was TR. The higher the TR, the better the thermal stability of the material.

[0074] The test results of the capacity test, the cycle performance test and the impedance test are shown in Table 1.

[0075] Table 1 Test results

[0076]

[0077] From the above results, it can be seen that the positive electrode material prepared in the application has a large capacity, low impedance, good cycle stability and strong thermal stability. In the comparative examples, the element types of the dopant or the coating agent are changed, and the capacity, impedance, cycle stability and thermal stability are difficult to balance development, and the electrical and thermal properties of the obtained battery are poor.

[0078] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A quasi-single-crystal ternary cathode material, characterized in that, Includes a matrix material and a coating layer covering the matrix material; The chemical formula of the matrix material is Li 1+a Ni x Co y Mn z H b O2; where 0 < a ≤ 0.2, 0 < x ≤ 0.8, 0 ≤ y ≤ 0.4, 0 ≤ z ≤ 0.4, 0 < b ≤ 0.01, and a + x + y + z + b = 1; H contains Na and K elements, and at least one of the elements Zr, Y, W, Al, Co, Ti, Sr; The chemical composition of the coating layer includes Rb and Cs elements, and at least one of Zr, Y, W, Al, Co, Ti, and Sr elements; the matrix material and the coating agent are mixed and then calcined twice to obtain the quasi-single-crystal ternary cathode material, wherein the proportion of Rb in the coating agent is 0.001-0.5wt%, and the proportion of Cs is 0.001-0.5wt%.

2. The quasi-single-crystal ternary cathode material according to claim 1, characterized in that, The mass of the coating layer is 0.001-0.5% of the matrix material.

3. The quasi-single-crystal ternary cathode material according to claim 1, characterized in that, The D50 of the quasi-single-crystal ternary cathode material is 2.0-6.0 μm; and / or, the specific surface area of ​​the quasi-single-crystal ternary cathode material is 0.5-1.5 m². 2 / g.

4. A method for preparing a quasi-single-crystal ternary cathode material as described in any one of claims 1-3, characterized in that, Includes the following steps: The matrix material is obtained by mixing nickel cobalt manganese hydroxide, lithium source, and dopant and then calcining it once. The matrix material is mixed with the coating agent and then subjected to a second calcination to obtain the quasi-monocrystalline ternary cathode material.

5. The method for preparing the quasi-single-crystal ternary cathode material according to claim 4, characterized in that, In the dopant, the proportion of Na is 0.01-0.5 wt%, and the proportion of K is 0.01-0.5 wt%.

6. The method for preparing the quasi-single-crystal ternary cathode material according to claim 4, characterized in that, The temperature of the first roasting is 800-1000℃, the roasting time is 6-12h, and the roasting atmosphere is 60-100vt% oxygen atmosphere; the amount of potting material in the first roasting is 4-8kg.

7. The method for preparing the quasi-single-crystal ternary cathode material according to claim 4, characterized in that, The secondary roasting temperature is 500-700℃, the secondary roasting time is 6-12h, and the secondary roasting atmosphere is air; the amount of food in the secondary roasting pot is 8-12kg.

8. The method for preparing the quasi-single-crystal ternary cathode material according to claim 4, characterized in that, The molar ratio of the nickel cobalt manganese hydroxide to the lithium source is 1:(1.0-1.2).

9. A positive electrode sheet, characterized in that, It includes a quasi-single-crystal ternary cathode material obtained by the preparation method according to any one of claims 4-8.

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