Monocrystal-like ternary positive electrode material and preparation and application thereof

Abstract

The invention discloses a single-crystal-like ternary positive electrode material as well as preparation and application thereof. The single-crystal-like ternary positive electrode material comprises a base material and a coating layer coating the base material, the chemical formula of the base material is Li < 1 + a > Ni < x > Co < y > Mn < z > H O < 2 >; wherein 0 lt; a is less than or equal to 0.2, 0lt; 0 < = x < = 0.8, 0 < = y < = 0.4, 0 < = z < = 0.4, 0 lt; b < = 0.01, and a + x + y + z + b = 1; h contains Na and k elements and contains at least one of Zr, Y, W, Al, Co, Ti and Sr elements; the chemical composition of the coating layer comprises Rb and Cs elements, and comprises at least one of Zr, Y, W, Al, Co, Ti and Sr elements; the positive electrode material is modified through the coating agent and the doping agent, so that the stability of the positive electrode material is improved, the diffusion radius of Li ions in the positive electrode material is increased, the diffusion speed of the Li ions is increased, the impedance of the positive electrode material is reduced, and the electrical property is improved; and through secondary sintering, the positive electrode material with the monocrystal-like morphology is obtained, and the capacity and the cycle performance of the positive electrode material are ensured.

Description

Technical Field

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

[0002] With the rapid development of fields such as electronic devices and electric vehicles, higher and higher requirements are put forward for the performance of cathode materials. As the core component of the battery, the cathode material needs to have excellent performance in many aspects. First of all, the cathode material must have good stability, which includes structural stability during charge and discharge processes and chemical stability under different environmental conditions, to ensure that the battery can work reliably for a long time. Secondly, the cathode material needs to have a high capacity, capable of storing and releasing more electrical energy per unit mass or unit volume, thereby improving the energy density of the battery. In addition, good cycle performance is also essential, that is, after multiple charge and discharge cycles, it can still maintain a high capacity retention rate and stable performance. At the same time, in order to improve the charge and discharge efficiency and power performance of the battery, the cathode material should have a low impedance, enabling lithium ions to diffuse and transport quickly, reducing energy loss. Finally, the cathode material also needs to have good thermal stability to ensure the safety and reliability of the battery during use.

[0003] Although certain progress has been made in the research and development of cathode materials at present, there are still some technical problems and it is difficult to meet the growing high-performance requirements. First of all, the stability of existing cathode materials is still not ideal enough. During long-term use, the cathode material is easily affected by factors such as volume change during charge and discharge and erosion of the electrolyte, resulting in structural damage and performance degradation. Secondly, in terms of cycle performance, many cathode materials have a relatively fast capacity decay after multiple charge and discharges and cannot maintain stable output performance, which limits the service life and application range of the battery. In addition, the impedance of existing cathode materials is high and the diffusion rate of lithium ions is slow, which not only affects the charge and discharge efficiency of the battery but also limits its application in high-power devices. Moreover, some cathode materials have insufficient thermal stability under harsh conditions such as high temperature, posing safety hazards such as overheating, catching fire or even explosion. These problems comprehensively lead to the inability of existing cathode materials to simultaneously meet the performance requirements of good stability, high capacity, excellent cycle performance, low impedance and high thermal stability.

[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 cathode material. Summary of the Invention

[0005] In view of this, the present application provides a quasi-single crystal ternary cathode material and its preparation and application, which are used to solve the problem of how to simultaneously achieve good stability, high capacity, excellent cycle performance, low impedance and high thermal stability of the cathode material.

[0006] To achieve the above technical objectives, the present application adopts the following technical solutions: In the first aspect, the present application provides a quasi-single crystal ternary cathode material, including a matrix material and a coating layer coated on the matrix material; the chemical formula of the matrix material is Li 1+a Ni x Co y Mn z HbO 2 ; wherein, 0 < a ≤ 0.2, 0 < x ≤ 0.8, 0 ≤ y ≤ 0.4, 0 ≤ z ≤ 0.4, 0 < b ≤ 0.01, a + x + y + z + b = 1; H contains Na and K elements, and contains at least one of Zr, Y, W, Al, Co, Ti, Sr elements; the chemical composition of the coating layer contains Rb and Cs elements, and contains at least one of Zr, Y, W, Al, Co, Ti, Sr elements.

[0007] Preferably, the mass of the coating layer is 0.001 - 0.5% of the matrix material.

[0008] Preferably, 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 / g.

[0009] In the second aspect, the present application provides a preparation method of a quasi-single crystal ternary cathode material, including the following steps: Mix nickel cobalt manganese hydroxide, lithium source, and dopant, and then perform a first roasting to obtain the matrix material; mix the matrix material with the coating agent and then perform a second roasting to obtain the quasi-single crystal ternary cathode material.

[0010] 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%.

[0011] 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%.

[0012] Preferably, the temperature of the first roasting is 800 - 1000 °C, the time of the first roasting is 6 - 12 h, the atmosphere of the first roasting is 60 - 100 vt% oxygen atmosphere; the loading amount of the first roasting is 4 - 8 kg.

[0013] Preferably, the temperature of the secondary calcination is 500 - 700 °C, the time of the secondary calcination is 6 - 12 h, the atmosphere of the secondary calcination is air or compressed air; the loading amount of the secondary calcination is 8 - 12 kg.

[0014] Preferably, the molar ratio of nickel cobalt manganese hydroxide to lithium source is 1:(1.0 - 1.2).

[0015] In a third aspect, the present application provides a positive electrode sheet, which includes a quasi-single crystal ternary positive electrode material. The beneficial effects of the present application are as follows: The present application modifies the positive electrode material through specific coating agents and doping agents, improves the stability of the positive electrode material, simultaneously increases the diffusion radius of Li ions in the positive electrode material and enhances the diffusion rate of Li ions, reduces the impedance of the positive electrode material, and improves the electrical properties; through secondary sintering, the present application obtains a positive electrode material with a quasi-single crystal morphology, ensuring the capacity and cycle performance of the positive electrode material. Description of the Drawings

[0016] Figure 1 SEM image of the quasi-single crystal positive electrode material obtained in Example 1; Figure 2 XRD patterns of the quasi-single crystal positive electrode material obtained in Example 1 before and after 50 cycles; Figure 3 Cross-sectional view of the quasi-single crystal positive electrode material obtained in Example 1 after 50 cycles. Detailed Embodiments

[0017] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0018] The present application provides a quasi-single crystal ternary positive electrode material, including a matrix material and a coating layer coated on the matrix material; the chemical formula of the matrix material is Li 1+a Ni x Co y Mn z HbO 2 ; wherein, 0 < a ≤ 0.2, 0 < x ≤ 0.8, 0 ≤ y ≤ 0.4, 0 ≤ z ≤ 0.4, 0 < b ≤ 0.01, a + x + y + z + b = 1; H contains Na and K elements, and contains at least one of Zr, Y, W, Al, Co, Ti, Sr elements; the chemical composition of the coating layer contains Rb and Cs elements, and contains at least one of Zr, Y, W, Al, Co, Ti, Sr elements.

[0019] In this application, Zr, Y, W, Al, Co, Ti, Sr, etc. are used to modify the bulk structure of the NCM cathode-like single crystal material for core doping and coating of the positive electrode material, so as to obtain the effect of ensuring the cycling performance of the material without changing the capacity, and at the same time, the thermal stability of the material can be improved, thereby improving the overall electrochemical performance of the LMRO cathode; in addition, when doping the core, Na and K elements are added at the same time, and when coating, Rb and Cs elements are added for modification to expand the Li ion channel radius, and the ionic radius is Li + <Na + <K + <Rb + <Cs + , by doping, Na and K elements are burned into the inner layer of the single crystal, and by coating, Rb and Cs elements are burned into the outer layer of the single crystal, forming a gradient Li ion diffusion radius, reducing the internal resistance of the material, greatly enhancing the migration speed of Li ions, and enhancing the electrochemical performance of the single crystal-like ternary positive electrode material at high voltage.

[0020] In some embodiments, the mass of the coating layer is 0.001-0.5% of the matrix material.

[0021] In this embodiment, if the amount of the coating layer is too much, it will affect the lithium ion transmission and diffusion; if the amount of the coating layer is too little, side reactions will occur between the material surface and the electrolyte.

[0022] 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.

[0023] In this embodiment, for the single crystal-like ternary positive electrode material within the limited D50 and specific surface area, the smaller the particle size, the higher the capacity, but the lower the cycling retention rate; the larger the particle size, the lower the capacity, but the higher the cycling retention rate. In order to balance the capacity and cycling, it is appropriate to select a particle size of 2.0-6.0 μm; the smaller the BET, the lower the capacity, but the higher the cycling retention rate; the larger the BET, the higher the capacity, but the lower the cycling retention rate. In order to balance the capacity and cycling, it is appropriate to select a BET of 0.5-1.5 m 2 / g is appropriate.

[0024] This application provides a method for preparing a single crystal-like ternary positive electrode material, including the following steps: Mix nickel cobalt manganese hydroxide, lithium source, and dopant and perform a first calcination to obtain the matrix material Li 1+ a Ni 0.6 Co 0.3 Mn 0.1 H b O2; mix the matrix material with the coating agent and perform a second calcination to obtain the single crystal-like ternary positive electrode material.

[0025] In this application, a doped matrix material is prepared by one-time roasting, and then the matrix material is coated by secondary roasting to finally obtain a ternary cathode material in the form of quasi-single crystals. The secondary sintering process improves the capacity and cycling performance of the cathode material on the premise of forming quasi-single crystals, while the dopants and coating agents used improve the stability of the cathode material, increase the diffusion radius of Li ions in the cathode material, and enhance the diffusion rate of Li ions.

[0026] In some embodiments, among the dopants, the proportion of Na is 0.01 - 0.5 wt%, and the proportion of K is 0.01 - 0.5 wt%.

[0027] In this embodiment, if the amount of Na used is too large, the material capacity is low and the internal resistance becomes large; if the amount of Na used is too small, there is no obvious improvement effect; if the amount of K used is too large, the capacity is low and the internal resistance becomes large; if the amount of K used is too small, there is no obvious improvement effect.

[0028] In some embodiments, among the coating agents, the proportion of Rb is 0.001 - 0.5 wt%, and the proportion of Cs is 0.001 - 0.5 wt%.

[0029] In this embodiment, if the amount of Rb used is too large, the capacity is low and the internal resistance becomes large; if the amount of Rb used is too small, there is no obvious improvement effect; if the amount of Cs used is too large, the capacity is low and the internal resistance becomes large; if the amount of Cs used is too small, there is no obvious improvement effect.

[0030] In some embodiments, the temperature of the one-time roasting is 800 - 1000 °C, the time of the one-time roasting is 6 - 12 h, the atmosphere of the one-time roasting is 60 - 100 vt% oxygen atmosphere; the loading amount of the one-time roasting is 4 - 8 kg.

[0031] In some embodiments, the temperature of the secondary roasting is 500 - 700 °C, the time of the secondary roasting is 6 - 12 h, the atmosphere of the secondary roasting is air or compressed air; the loading amount of the secondary roasting is 8 - 12 kg.

[0032] In this application, by adjusting the process conditions of the one-time roasting and the secondary roasting, a cathode material in the form of quasi-single crystals and within the target range of D50 and specific surface area can be finally obtained. If the temperature of the one-time roasting is too high, the primary grains become larger and the capacity becomes lower; if the temperature of the one-time roasting is too low, the crystallinity of the material is insufficient and the cycling stability is poor; if the temperature of the secondary roasting is too high, the primary grains become larger and the capacity becomes lower; if the temperature of the secondary roasting is too low, the coating agent cannot be effectively coated.

[0033] In some embodiments, the molar ratio of nickel-cobalt-manganese hydroxide to the lithium source is 1:(1.0 - 1.2).

[0034] This application provides a positive electrode sheet, which includes a quasi-single crystal ternary positive electrode material.

[0035] The following further illustrates this solution through specific embodiments.

[0036] Example 1 A preparation method of a quasi-single crystal ternary positive electrode material includes the following steps: Weigh Ni 0.6 Co 0.1 Mn 0.3 (OH) 2 (purchased from GEM (Jingmen) New Materials Co., Ltd.), Li 2 CO 3 Weigh according to the molar ratio of lithium metal Li / Me (Me is the total molar amount of Ni, Co, and Mn) of 1:1, and then add Ni 0.6 Co 0.1 Mn 0.3 (OH) 2 and 0.1% of the total mass of Li 2 CO 3 The dopant, where the dopant includes zirconia, yttria, tungsten oxide with a mass ratio of 1:1:1, and a mixture of sodium carbonate and potassium carbonate. Among them, the proportion of Na in the dopant is 0.3 wt%, and the proportion of K in the dopant is 0.2 wt%. After mixing the mixture in a high-speed mixer, put it into a crucible, with a loading amount of 4 kg, and then place the crucible in a muffle furnace. Under an air atmosphere containing 60 vt% oxygen, perform a first calcination at 1000 °C for 8 h. After natural cooling, crush and sieve to obtain a matrix material with a D50 of 3.5 μm; Mix the matrix material with the coating agent. Among them, the mass of the coating layer is 0.1% of the matrix material. The coating agent contains tungsten oxide, alumina, and cobalt oxide with a mass ratio of 1:1:1, with a content of 0.1 wt%. Among them, Rb (accounting for 0.2% of the mass of the coating agent) and Cs (accounting for 0.1% of the mass of the coating agent) are added in the form of carbonates. Put the mixture into a crucible, with a loading amount of 12 kg, and then place it in a muffle furnace. Under an air atmosphere, perform a second calcination at 500 °C for 6 h. After cooling, a quasi-single crystal ternary positive electrode material with a D50 of 3.0 μm and a specific surface area of 1.0 m2 / g is obtained.

[0037] Example 2 A preparation method of a quasi-single crystal ternary positive electrode material is the same as that in Example 1 for other contents. The difference is that in the dopant, the proportion of Na is 0.5 wt%, and the proportion of K is 0.5 wt%.

[0038] Example 3 A preparation method of a quasi-single crystal ternary cathode material, the other contents are the same as those in Example 1, the difference is that in the dopant, the proportion of Na is 0.01 wt%, and the proportion of K is 0.01 wt%.

[0039] Example 4 A preparation method of a quasi-single crystal ternary cathode material, the other contents are the same as those in Example 1, the difference is that in the coating agent, the proportion of Rb is 0.5 wt%, and the proportion of Cs is 0.5 wt%.

[0040] Example 5 A preparation method of a quasi-single crystal ternary cathode material, the other contents are the same as those in Example 1, the difference is that in the coating agent, the proportion of Rb is 0.001 wt%, and the proportion of Cs is 0.001 wt%.

[0041] Comparative Example 1 A preparation method of a cathode material, the other contents are the same as those in Example 1, the difference is that in the dopant, the proportion of Na is 0.

[0042] Comparative Example 2 A preparation method of a cathode material, the other contents are the same as those in Example 1, the difference is that in the dopant, the proportion of K is 0.

[0043] Comparative Example 3 A preparation method of a cathode material, the other contents are the same as those in Example 1, the difference is that in the coating agent, the proportion of Rb is 0.

[0044] Comparative Example 4 A preparation method of a cathode material, the other contents are the same as those in Example 1, the difference is that in the coating agent, the proportion of Cs is 0.

[0045] Comparative Example 5 A preparation method of a cathode material, the other contents are the same as those in Example 1, the difference is that in the coating agent, the proportion of Rb is 0 and the proportion of Cs is 0.

[0046] Testing and Evaluation The quasi-single crystal cathode material obtained in Example 1 was tested by SEM images, and the results are as Figure 1 shown in the final product. It can be seen that the particle size D50 of the quasi-single crystal cathode material obtained in the example is 4.2 μm, and the specific surface area is 1.0 m 2 / g; The XRD patterns of the quasi-single crystal cathode material obtained in Example 1 before and after 50 cycles were tested, and the results are as Figure 2 shown. It can be seen that there is no difference in the quasi-single crystal cathode material obtained in Example 1 before and after cycling, and the stability of the material is good; Figure 3The cross-sectional view of the single-crystal-like cathode material obtained in Example 1 after 50 cycles can be seen that after cycling, the single-crystal-like cathode material obtained in Example 1 has no cracks, indicating its good stability.

[0047] The cathode materials obtained in the above examples and comparative examples were assembled into batteries and subjected to coin cell testing. The specific method is as follows: The cathode 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, respectively, added with NMP (N-methylpyrrolidone), and mixed at high speed for 15 min by a degassing machine to form a slurry, which was then evenly coated on aluminum foil with a doctor blade scale of 100 μm to form a pole piece; then the pole piece was placed in a vacuum drying oven at 80 °C for baking, and after drying, it was pressed, punched, and cut into a positive electrode sheet with a diameter of 14 mm; according to the order of negative electrode shell, lithium sheet, dropping 3 drops of DEC / EC (volume ratio 1:1) electrolyte with a syringe, celgard2500 separator, dropping 3 drops of DEC / EC (volume ratio 1:1) electrolyte with a syringe, positive electrode sheet, and positive electrode shell, coin cells were assembled in a glove box filled with argon to make lithium-ion batteries respectively. The prepared lithium-ion batteries were respectively subjected to specific capacity testing, cycling performance testing, and impedance testing. The above tests are briefly described as follows: Specific capacity testing: At 25 °C, the charge-discharge performance of the material was studied by constant current charge-discharge (0.1C), and the voltage range was 3.0V - 4.55V. The first charge-discharge efficiency was calculated based on the specific charge and discharge capacity.

[0048] Cycling performance testing: At 25 °C, the battery was charged at a constant current of 0.1C and a constant voltage of 4.50V until the cut-off current of 0.05C, and then discharged at a constant current of 0.1C to 3.0V. This cycle was repeated, and the capacity retention rate at the 50th cycle was calculated after 50 charge-discharge cycles.

[0049] The calculation formula is: Capacity retention rate at the 50th cycle (%) = (Discharge capacity at the 50th cycle / Discharge capacity at the first cycle) × 100%.

[0050] Impedance testing (DCR): EIS data was collected at room temperature using an IVIUMSTAT impedance analyzer with an amplitude of 5 mA and a frequency range of 102 - 105 Hz, and the impedance data was obtained by fitting with Zview software.

[0051] Thermal stability testing (TR): Differential scanning calorimetry (DSC) analysis was carried out under the condition that the SOC of the material was 80%. The highest temperature at which the material underwent thermal decomposition was TR, and the higher TR was, the better the thermal stability of the material.

[0052] The test results of specific capacity testing, cycling performance testing, and impedance testing are shown in Table 1.

[0053] Table 1 Test Results

[0054] It can be seen from the above results that the cathode material prepared by this application has a large specific capacity, low impedance, good cycle stability, and strong thermal stability; while in the comparative example, the types of elements of the dopant or coating agent are changed, and it is difficult to achieve a balanced development of its specific capacity, impedance, cycle stability, and thermal stability, resulting in poor electrical and thermal performance of the obtained battery.

[0055] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention.

Claims

1. A single crystal ternary cathode material, characterized in that: It comprises a base material and a coating layer coated on the base material; The chemical formula of the matrix material is Li 1+a Ni x Co y Mn z H b O2; wherein, 0 < a ≤ 0.2, 0 < x ≤ 0.8, 0 ≤ y ≤ 0.4, 0 ≤ z ≤ 0.4, 0 < b ≤ 0.01, a + x + y + z + b = 1; H contains Na and K elements, and contains 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 includes at least one of Zr, Y, W, Al, Co, Ti, and Sr elements.

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

3. The single-crystal-like ternary cathode material according to claim 1, characterized in that: 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 m 2 / g.

4. A method for preparing the single-crystal-like ternary cathode material according to any one of claims 1 to 3, characterized in that: The following steps are involved: Mixing nickel-cobalt-manganese hydroxide, a lithium source and a dopant and then calcining the mixture to obtain a matrix material; The matrix material and the coating agent are mixed and then calcined twice to obtain the single crystal ternary positive electrode material.

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

6. The method for preparing a quasi-single-crystal ternary cathode material according to claim 4, characterized in that: In the coating agent, the proportion of Rb is 0.001-0.5wt%, and the proportion of Cs is 0.001-0.5wt%.

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

8. The method for preparing a quasi-single-crystal ternary cathode material according to claim 4, characterized in that: The temperature of the secondary roasting is 500-700° C., the time of the secondary roasting is 6-12 hours, the atmosphere of the secondary roasting is air or compressed air; and the potting capacity of the secondary roasting is 8-12 kg.

9. The method for preparing a 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).

10. A positive electrode sheet, characterized in that: The invention comprises a single-crystal-like ternary positive electrode material obtained by the preparation method as described in any one of claims 4 to 9.

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