Modified positive electrode material and preparation method and application thereof

Abstract

The present disclosure provides a modified positive electrode material and a preparation method and application thereof, the preparation method comprising the following steps: (1) mixing tungsten disulfide with a tannic acid solution, performing ultrasonic treatment, and then separating to obtain a TA-WS2 nanosheet solution; (2) mixing a positive electrode material with a solvent after performing corona discharge treatment, to obtain a positive electrode material solution, mixing the positive electrode material solution with the TA-WS2 nanosheet solution, and obtaining a mixed solution; (3) performing solid-liquid separation treatment on the mixed solution, and performing calcination treatment on the obtained solid material, to obtain the modified positive electrode material. The present disclosure prepares nanoparticles with strong electronegativity, simultaneously charges the positive electrode material particles, utilizes the interaction force between the strong electronegativity and electrons, makes the nanoparticles with strong electronegativity uniformly and spontaneously loaded on the charged particles, and finally forms a uniform coating layer on the surface of the positive electrode material through calcination.

Description

Technical Field

[0001] This disclosure belongs to the field of battery materials technology, and relates to a modified cathode material, its preparation method and application. Background Technology

[0002] As one of the most important products in the battery industry, lithium-ion batteries have experienced rapid development with the expansion of the new energy vehicle and energy storage markets, becoming a key product for the future development of the rechargeable battery industry. Lithium-ion rechargeable batteries have advantages such as high operating voltage, large capacity, small size, light weight, and long cycle life, and are widely used in portable electronic products, electric bicycles, electric vehicles, and energy storage. Meanwhile, cathode materials, as a key factor affecting the performance and application of lithium-ion batteries, have received considerable attention from researchers worldwide in recent years and have undergone rapid development.

[0003] Currently, lithium-ion battery cathode materials under development are mainly classified into three categories based on their structure: lithium cobalt oxide (LiCoO2), ternary lithium nickel cobalt manganese oxide (NCM), and lithium nickel cobalt aluminum oxide (NCA), which have hexagonal layered structures belonging to the R-3m space group; lithium manganese oxide (LiMn2O4), which have spinel structures with the Fd-3m space group; and lithium iron phosphate (LiFePO4), lithium iron silicate (Li2FeSiO4), and lithium vanadium phosphate (LiVPO4), which have polyanionic structures with olivine structures. Although cathode materials have been continuously developed, they still suffer from problems such as poor structural stability, cation mixing, transition metal dissolution, voltage decay, poor rate performance and high-temperature performance, and low initial coulombic efficiency.

[0004] CN110429275A discloses a method for preparing carbon-coated ternary cathode material and the carbon-coated ternary cathode material; the method for preparing the carbon-coated ternary cathode material includes placing a dry ternary cathode material, an organic carbon source and an organic solvent composite under heat treatment at a temperature of 240-350℃.

[0005] CN103474628A discloses a method for preparing carbon-coated ternary cathode material and the carbon-coated ternary cathode material. The preparation method includes the following steps: S1, preparing a ternary cathode material precursor using nickel salt, cobalt salt, and manganese salt as raw materials; S2, preparing a conductive carbon dispersion system: dispersing conductive carbon in water containing an organic carbon source; S3, adding the ternary cathode material precursor and a lithium compound to the conductive carbon dispersion system, mixing them evenly to obtain a mixture; S4, drying the mixture under vacuum conditions; S5, treating the dried mixture at high temperature under sealed conditions or in an inert gas protected atmosphere to obtain the carbon-coated ternary cathode material.

[0006] The above-mentioned method produces coated cathode materials, but the bonding effect between the coating layer and the cathode material is poor, and the coating layer is easy to fall off, which leads to a decrease in the material's cycle performance. Summary of the Invention

[0007] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0008] The purpose of this disclosure is to provide a modified cathode material, its preparation method and application. This disclosure involves preparing nanoparticles with strong electronegativity, while simultaneously charging the cathode material particles. By utilizing the interaction force between the strongly electronegative nanoparticles and electrons, the strongly electronegative nanoparticles are uniformly and spontaneously loaded onto the charged particles. Finally, a uniform coating layer is formed on the surface of the cathode material by calcination.

[0009] To achieve this objective, the present disclosure adopts the following technical solution:

[0010] In a first aspect, this disclosure provides a method for preparing a modified cathode material, the method comprising the following steps:

[0011] (1) Tungsten disulfide was mixed with tannic acid (TA) solution, and after ultrasonic treatment, TA-WS2 nanosheet solution was obtained by separation.

[0012] (2) After corona discharge treatment of the positive electrode material, it is mixed with a solvent to obtain a positive electrode material solution. The positive electrode material solution is then mixed with a TA-WS2 nanosheet solution to obtain a mixed solution.

[0013] (3) The mixed solution is subjected to solid-liquid separation treatment, and the obtained solid material is subjected to calcination treatment to obtain the modified cathode material.

[0014] This disclosure discloses the pre-preparation of highly electronegative TA-WS2 nanosheets. The unique layered structure of the two-dimensional TA-WS2 nanosheets allows for the free insertion and extraction of lithium ions due to their large interlayer spacing. WS2 also possesses advantages such as high conductivity, excellent high and low temperature resistance, and high capacity density, thus increasing the stability, capacity, and lifespan of lithium-ion batteries. Corona discharge technology is used to charge the cathode material particles. Based on the interaction between the highly electronegative nanoparticles and the negative charge, TA-WS2 nanosheets spontaneously and uniformly coat the surface of the ternary cathode material. Finally, by carbonizing TA, both the cathode material and WS2 are simultaneously carbon-coated. This addresses the expansion problem of tungsten disulfide during charge and discharge, while also buffering the volume expansion of the battery structure, improving cycle stability and high-rate performance. Furthermore, by coating the cathode material with a carbon layer, the conductivity of tungsten disulfide is increased, thereby improving the battery's charge and discharge efficiency, lifespan, performance, stability, and safety.

[0015] In one embodiment, the solvent in the tannic acid solution in step (1) includes any one or a combination of at least two of ultrapure water, ethanol, methanol, acetone or ethyl acetate.

[0016] In one embodiment, the concentration of the tannic acid solution is (0.2-10) g / L, for example: 0.2 g / L, 1 g / L, 2 g / L, 5 g / L or 10 g / L, etc.

[0017] In one embodiment, the mass ratio of tungsten disulfide to tannic acid in the tannic acid solution is (1-5):(1-5), for example: 1:5, 1:2, 1:1, 2:1 or 5:1, etc.

[0018] In one embodiment, the power of the ultrasonic treatment in step (1) is 200 to 600W, for example: 200W, 300W, 400W, 500W or 600W.

[0019] In one embodiment, the duration of the ultrasonic treatment is 1 to 5 hours, for example: 1 hour, 2 hours, 3 hours, 4 hours, or 5 hours.

[0020] In one embodiment, the separation method in step (1) includes centrifuging the ultrasonically treated suspension, taking the supernatant, and obtaining a TA-WS2 nanosheet solution.

[0021] In one embodiment, the solvent in step (2) includes any one or a combination of at least two of ultrapure water, ethanol, methanol, acetone or ethyl acetate.

[0022] In one embodiment, the mass ratio of the cathode material to the TA-WS2 nanosheet is 1:(0.1 to 1), for example: 1:0.1, 1:0.3, 1:0.5, 1:0.8 or 1:1, etc., preferably 1:(0.2 to 0.4).

[0023] In one embodiment, the mass concentration of the positive electrode material in the mixed solution is 20% to 50%, for example: 20%, 25%, 30%, 35%, or 50%.

[0024] In one embodiment, the mass concentration of TA-WS2 nanosheets in the mixed solution is 5% to 20%, for example: 5%, 8%, 10%, 15% or 20%, etc.

[0025] In one embodiment, the solid-liquid separation in step (3) includes filtration.

[0026] In one embodiment, the filtered material is then dried.

[0027] In one embodiment, the calcination temperature in step (3) is 300 to 500°C, for example: 300°C, 350°C, 400°C, 450°C or 500°C.

[0028] In one embodiment, the atmosphere of the calcination treatment includes nitrogen.

[0029] In one embodiment, the calcination treatment time is 15 to 60 minutes, for example: 15 minutes, 20 minutes, 30 minutes, 40 minutes or 60 minutes.

[0030] In a second aspect, this disclosure provides a modified cathode material, which is prepared by the method described in the first aspect.

[0031] Thirdly, this disclosure provides a positive electrode sheet comprising the modified positive electrode material as described in the second aspect.

[0032] Fourthly, this disclosure provides a lithium-ion battery comprising a positive electrode as described in the third aspect.

[0033] Compared with the prior art, this disclosure has the following beneficial effects:

[0034] (1) This disclosure pre-prepares TA-WS2 nanosheets with strong electronegativity. The unique layered structure of the two-dimensional TA-WS2 nanosheets allows for the free insertion and extraction of lithium ions due to the large interlayer spacing. WS2 also possesses advantages such as high conductivity, excellent resistance to high and low temperatures, and high capacity density, thereby increasing the stability, capacity, and lifespan of lithium-ion batteries. Corona discharge technology is used to charge the cathode material particles. Based on the interaction between the strongly electronegative nanoparticles and the negative charge, TA-WS2 nanosheets spontaneously and uniformly coat the surface of the ternary cathode material. Finally, by carbonizing TA, both the cathode material and WS2 are simultaneously carbon-coated. This solves the expansion problem of tungsten disulfide during charging and discharging, while also buffering the volume expansion of the battery structure, improving cycle stability and high-rate performance. Simultaneously, by coating the cathode material with a carbon layer, the conductivity of tungsten disulfide is increased, thereby improving the battery's charging and discharging efficiency, lifespan, and performance, while also enhancing the battery's stability and safety.

[0035] (2) The modification method described in this application can be used for various cathode materials, significantly improving their performance. The modified NCM811 cathode material obtained can maintain a capacity retention of over 97% after 100 cycles at a 0.1C charge / discharge rate. The modified lithium iron phosphate battery obtained can achieve a discharge specific capacity of over 149 mAh / g after 200 cycles at room temperature, and over 146 mAh / g after 100 cycles at 66℃. This significantly improves the cycling stability of the material.

[0036] After reading and understanding the accompanying diagrams and detailed descriptions, the other aspects can be understood. Attached Figure Description

[0037] The accompanying drawings are used to provide a further understanding of the technical solutions in this paper and form part of the specification. They are used together with the embodiments of this application to explain the technical solutions in this paper and do not constitute a limitation on the technical solutions in this paper.

[0038] Figure 1 This is a SEM image of the modified cathode material prepared in Example 1.

[0039] Figure 2 This is a SEM image of the modified cathode material prepared in Comparative Example 1.

[0040] Figure 3 This is a SEM image of the modified cathode material prepared in Comparative Example 2. Detailed Implementation

[0041] The technical solutions of this disclosure will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of this disclosure and should not be construed as specific limitations thereof.

[0042] Example 1

[0043] This embodiment provides a modified cathode material, and the preparation method of the modified cathode material is as follows:

[0044] (1) Tannic acid and ethanol were mixed in a mass-volume ratio of 1g:1L. WS2 was mixed in the mixture in a mass ratio of 2:1 between tungsten disulfide nanosheets and tannic acid. The mixed solution was then sonicated at 300W for 2h. The sonicated suspension was centrifuged for 30min and the supernatant was taken to obtain the TA-WS2 nanosheet solution.

[0045] (2) Select 3μm LiNi 0.8 Co 0.1 Mn 0.1 O2 cathode material particles are made to have a negatively charged surface through corona discharge technology. The cathode material particles are then mixed with ethanol until homogeneous. Then, TA-WS2 nanosheet solution is added at a mass ratio of cathode material to TA-WS2 of 1:0.2 to obtain a mixed solution. The mass concentration of cathode material in the mixed solution is 40%, and the mass concentration of TA-WS2 nanosheet is 8%.

[0046] (3) The mixed solution was filtered, vacuum dried, and then reacted at 400°C under a nitrogen atmosphere for 20 minutes to obtain the modified cathode material. The SEM image of the modified cathode material is shown below. Figure 1 As shown.

[0047] The obtained modified cathode material was used in LiNi 0.8 Co 0.1 Mn 0.1 The positive electrode material of the O2 battery, when assembled into a finished battery, exhibits an initial discharge capacity of 212 mAh / g and an initial coulombic efficiency of 86% at 0.1C within a voltage range of 2.75–4.3V. Under room temperature conditions and at 0.1C, the battery retains 97% of its capacity after 100 cycles at a 0.1C charge-discharge rate.

[0048] Example 2

[0049] This embodiment provides a modified cathode material, and the preparation method of the modified cathode material is as follows:

[0050] (1) Tannic acid and ethanol were mixed in a mass-volume ratio of 1g:1L. WS2 was mixed in the mixture in a mass ratio of 5:1 between tungsten disulfide nanosheets and tannic acid. The mixed solution was then sonicated at 200W for 5h. The sonicated suspension was centrifuged for 30min and the supernatant was taken to obtain the TA-WS2 nanosheet solution.

[0051] (2) Select 3μm lithium iron phosphate cathode material particles and make the particle surface negatively charged through corona discharge technology; then mix the obtained cathode material particles with ethanol evenly, and then add TA-WS2 nanosheet solution according to the mass ratio of cathode material to TA-WS2 of 1:0.3 to obtain a mixed solution. The mass concentration of cathode material in the mixed solution is 30% and the mass concentration of TA-WS2 nanosheet is 9%.

[0052] (3) The mixed solution was filtered, vacuum dried, and then the material was reacted at 300°C in a nitrogen atmosphere for 60 minutes to obtain the modified cathode material.

[0053] The modified cathode material obtained was used as the cathode material for lithium iron phosphate batteries. By assembling finished batteries, the discharge specific capacity reached 149 mAh / g after 200 cycles at 2.5-3.9V and a rate of 1C (1C = 170 mA / g) at room temperature. After electrochemical performance testing at 66℃, the discharge specific capacity reached 146 mAh / g after 100 cycles.

[0054] Example 3

[0055] This embodiment provides a modified cathode material, and the preparation method of the modified cathode material is as follows:

[0056] (1) Tannic acid and ethanol were mixed in a mass-volume ratio of 1g:1L. WS2 was mixed in the mixture in a mass ratio of 1:5 between tungsten disulfide nanosheets and tannic acid. The mixed solution was then sonicated at 600W for 1h. The sonicated suspension was centrifuged for 30min and the supernatant was taken to obtain the TA-WS2 nanosheet solution.

[0057] (2) Select 3μm LiNi 0.8 Co 0.1 Mn 0.1 O2 cathode material particles are made to have a negative charge on their surface through corona discharge technology. The cathode material particles are then mixed with ethanol until homogeneous. Then, TA-WS2 nanosheet solution is added at a mass ratio of cathode material to TA-WS2 of 1:0.4 to obtain a mixed solution. The mass concentration of cathode material in the mixed solution is 20%, and the mass concentration of TA-WS2 nanosheet is 8%.

[0058] (3) The mixed solution was filtered, vacuum dried, and then the material was reacted at 500°C in a nitrogen atmosphere for 15 minutes to obtain the modified cathode material.

[0059] The obtained modified cathode material was used in LiNi 0.8 Co 0.1 Mn 0.1 The positive electrode material of the O2 battery, when assembled into a finished battery, exhibits an initial discharge capacity of 214 mAh / g and an initial coulombic efficiency of 87% at 0.1C within a voltage range of 2.75–4.3V. Under room temperature conditions and at 0.1C, the battery retains 97% of its capacity after 100 cycles at a 0.1C charge-discharge rate.

[0060] Example 4

[0061] The only difference between this embodiment and Embodiment 1 is that the mass ratio of tungsten disulfide to tannic acid is 8:1; all other conditions and parameters are exactly the same as in Embodiment 1.

[0062] The obtained modified cathode material was used in LiNi 0.8 Co 0.1 Mn 0.1 The positive electrode material of the O2 battery, when assembled into a finished battery, exhibits an initial discharge capacity of 208 mAh / g and an initial coulombic efficiency of 84% at 0.1C within a voltage range of 2.75–4.3V. Under room temperature conditions and at 0.1C, the battery retains 87% of its capacity after 100 cycles at a 0.1C charge-discharge rate.

[0063] Example 5

[0064] The only difference between this embodiment and Embodiment 1 is that the mass ratio of tungsten disulfide to tannic acid is 1:8; all other conditions and parameters are exactly the same as in Embodiment 1.

[0065] The obtained modified cathode material was used in LiNi 0.8 Co 0.1 Mn 0.1 The positive electrode material of the O2 battery, when assembled into a finished battery, exhibits an initial discharge capacity of 204 mAh / g and an initial coulombic efficiency of 85% at 0.1C within a voltage range of 2.75–4.3V. Under room temperature conditions and at 0.1C, the battery retains 95% of its capacity after 100 cycles at a 0.1C charge-discharge rate.

[0066] Example 6

[0067] The only difference between this embodiment and Embodiment 1 is that the mass ratio of the cathode material to the TA-WS2 nanosheets is 1:0.1; all other conditions and parameters are exactly the same as in Embodiment 1.

[0068] The obtained modified cathode material was used in LiNi 0.8 Co 0.1 Mn 0.1 The positive electrode material of the O2 battery, when assembled into a finished battery, exhibits an initial discharge capacity of 210 mAh / g and an initial coulombic efficiency of 86% at 0.1C within a voltage range of 2.75–4.3V. Under room temperature conditions and at 0.1C, the battery retains 94% of its capacity after 100 cycles at a 0.1C charge-discharge rate.

[0069] Example 7

[0070] The only difference between this embodiment and Embodiment 1 is that the mass ratio of the cathode material to the TA-WS2 nanosheets is 1:0.5; all other conditions and parameters are exactly the same as in Embodiment 1.

[0071] The obtained modified cathode material was used in LiNi 0.8 Co 0.1 Mn 0.1 The positive electrode material of the O2 battery, when assembled into a finished battery, exhibits an initial discharge capacity of 213 mAh / g and an initial coulombic efficiency of 88% at 0.1C within a voltage range of 2.75–4.3V. Under room temperature conditions and at 0.1C, the battery retains 96% of its capacity after 100 cycles at a 0.1C charge-discharge rate.

[0072] Comparative Example 1

[0073] The only difference between this comparative example and Example 1 is that tannic acid was not added; all other conditions and parameters were exactly the same as in Example 1. The SEM image of the obtained modified cathode material is shown below. Figure 2 As shown.

[0074] The obtained modified cathode material was used in LiNi 0.8 Co 0.1 Mn 0.1 The positive electrode material of the O2 battery, when assembled into a finished battery, exhibits an initial discharge capacity of 190 mAh / g and an initial coulombic efficiency of 82% at 0.1C within a voltage range of 2.75–4.3V. Tested at 0.1C on a room-temperature battery, the capacity retention rate is 74% after 100 cycles at a 0.1C charge-discharge rate.

[0075] Comparative Example 2

[0076] The only difference between this comparative example and Example 1 is that the cathode material is not subjected to corona discharge treatment; all other conditions and parameters are exactly the same as in Example 1. The SEM image of the obtained modified cathode material is shown below. Figure 3 As shown.

[0077] The obtained modified cathode material was used in LiNi 0.8 Co 0.1 Mn 0.1 The positive electrode material of the O2 battery, when assembled into a finished battery, exhibits an initial discharge capacity of 208 mAh / g at 0.1C within a voltage range of 2.75–4.3V, with an initial coulombic efficiency of 84%. Tested at 1C under room temperature conditions, after 100 cycles at a 0.1C charge-discharge rate, the capacity retention rate is 79%.

[0078] As can be seen from the comparison of Examples 1-3, the modification method described in this application can be used for various cathode materials, significantly improving the performance of the cathode materials. The modified NCM811 cathode material obtained can maintain a capacity retention of over 97% after 100 cycles at a 0.1C charge-discharge rate. The modified lithium iron phosphate battery obtained can achieve a discharge specific capacity of over 149 mAh / g after 200 cycles at room temperature, and a discharge specific capacity of over 146 mAh / g after 100 cycles at 66℃. This significantly improves the cycle stability of the material.

[0079] A comparison of Examples 1 and 3-5 shows that the mass ratio of tungsten disulfide to tannic acid affects the performance of the modified cathode material described in this disclosure. Controlling the mass ratio of tungsten disulfide to tannic acid to 1:5 to 5:1 yields a cathode material with better performance. If the proportion of tannic acid is too high and the proportion of tungsten disulfide is too low, it will result in a waste of resources and will not actually improve the battery performance. If the proportion of tannic acid is too low and the proportion of tungsten disulfide is too high, it will cause the nanosheets to stack after exfoliation and will not achieve stable dispersion.

[0080] A comparison of Examples 1 and 6-7 shows that the mass ratio of the cathode material to TA-WS2 nanosheets affects the performance of the modified cathode material described in this disclosure. Controlling the mass ratio of the cathode material to TA-WS2 nanosheets to 1:0.2–0.4 yields a cathode material with better performance. If the amount of TA-WS2 nanosheets added is too high, it will cause stacking on the surface of the cathode material, preventing the formation of a thin and uniform coating layer. If the amount of TA-WS2 nanosheets added is too low, it cannot completely coat the cathode material, resulting in coating defects.

[0081] As can be seen from the comparison between Example 1 and Comparative Example 1, the addition of tannic acid to the surface carbon coating of WS2 and the cathode material in this disclosure can reduce the volume expansion problem of WS2 during charging and discharging, and at the same time, the conductivity of tungsten disulfide is significantly improved; after corona discharge treatment, TA-WS2 can spontaneously form a uniform coating around the cathode material.

[0082] As can be seen from the comparison between Example 1 and Comparative Example 2, without corona discharge treatment, the surface of the positive electrode material does not carry a negative charge, and TA-WS2 cannot spontaneously form around the positive electrode material, thus resulting in the inability to form a uniform coating layer, leading to defects on the surface of the positive electrode material. During long-term cycling, the effective coating rate is reduced, resulting in electrolyte corrosion.

Claims

1. A method for preparing a modified cathode material, the method comprising the following steps: (1) Tungsten disulfide was mixed with tannic acid solution, and after ultrasonic treatment, TA-WS2 nanosheet solution was obtained by separation; (2) After corona discharge treatment of the positive electrode material, it is mixed with a solvent to obtain a positive electrode material solution. The positive electrode material solution is then mixed with a TA-WS2 nanosheet solution to obtain a mixed solution. (3) The mixed solution is subjected to solid-liquid separation treatment, and the obtained solid material is subjected to calcination treatment to obtain the modified cathode material; The mass ratio of tungsten disulfide to tannic acid in the tannic acid solution is (1~5):(1~5); The mass ratio of the cathode material to TA-WS2 nanosheets is 1:(0.2~0.4); The separation method in step (1) includes centrifuging the ultrasonically treated suspension, taking the supernatant, and obtaining a TA-WS2 nanosheet solution; The calcination temperature in step (3) is 300~500℃; The atmosphere for the calcination treatment is nitrogen. The calcination treatment time is 15~60 minutes.

2. The preparation method according to claim 1, wherein, The solvent in the tannic acid solution in step (1) includes any one or a combination of at least two of ultrapure water, ethanol, methanol, acetone or ethyl acetate.

3. The preparation method according to claim 1, wherein, The concentration of the tannic acid solution is (0.2~10) g / L.

4. The preparation method according to claim 1, wherein, The power of the ultrasonic treatment in step (1) is 200~600W.

5. The preparation method according to claim 1, wherein, The ultrasonic treatment time is 1 to 5 hours.

6. The preparation method according to claim 1, wherein, The solvent in step (2) includes any one or a combination of at least two of ultrapure water, ethanol, methanol, acetone or ethyl acetate.

7. The preparation method according to claim 1, wherein, The mass concentration of the positive electrode material in the mixed solution is 20-50%.

8. The preparation method according to claim 1, wherein, The mass concentration of TA-WS2 nanosheets in the mixed solution is 5-20%.

9. The preparation method according to claim 1, wherein, The solid-liquid separation in step (3) includes filtration.

10. The preparation method according to claim 9, wherein, The filtered material is then dried.

11. A modified cathode material, said modified cathode material being prepared by the method described in any one of claims 1-10.

12. A positive electrode sheet, said positive electrode sheet comprising the modified positive electrode material as described in claim 11.

13. A lithium-ion battery, the lithium-ion battery comprising the positive electrode as described in claim 12.

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