A synergistic surface modification method of Li2niO2 and NCM cathode and cathode sheet and application thereof

Abstract

The application belongs to the technical field of lithium ion batteries, and discloses a synergistic surface modification method of Li2NiO2 and NCM positive electrodes, a positive electrode tab and application thereof. Specifically, fluoroborate is added into anhydrous ethanol to obtain a mixed solution; NCM and Li2NiO2 are added, filtered, and dried to obtain a composite lithium supplement positive electrode material; the composite lithium supplement positive electrode material, carbon nanotubes and polyvinylidene fluoride are uniformly dispersed in an N-methylpyrrolidone solution to obtain a positive electrode slurry; and the positive electrode slurry is coated on the surface of an aluminum foil to obtain a positive electrode tab. The synergistic surface modification strategy is adopted to simultaneously construct a LiF-NaF-LiBO2 multifunctional composite coating on the surfaces of Li2NiO2 and NCM, thereby improving the resistance of the two to CO2 and H2O, improving the air stability, improving the ionic conductivity, improving the interface contact of the two, and thereby improving the compatibility of the two.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically to a method for synergistic surface modification of lithium-ion additive Li2NiO2 and NCM cathode, and its application. Background Technology

[0002] Lithium-ion batteries have become the preferred power source for portable mobile devices and electric vehicles due to their advantages such as high energy density, environmental friendliness, long cycle life, and low self-discharge rate. As a key component of lithium-ion battery energy storage systems, the development of high-energy-density cathode materials has also attracted widespread attention, with LiNi being a prime example. x Co y Mn 1-x-y O2 (NCM) ternary cathode materials have become the preferred cathode material for lithium-ion batteries due to their advantages such as high discharge specific capacity, high energy density, and low cost. Based on the nickel content ratio in NCM, they are divided into low-nickel ternary (x < 0.6) and high-nickel ternary (x ≥ 0.6) cathode materials. For example, NCM111, NCM424, and NCM523 belong to low-nickel ternary cathode materials; NCM622, NCM721, and NCM811 belong to high-nickel ternary cathode materials. Increasing the nickel content significantly improves the specific capacity and energy density of the material, but it also causes side reactions on the material surface, leading to a sharp increase in residual alkalis such as LiOH and Li2CO3, which affects the slurry bonding process and causes slurry gelation. Furthermore, Li2CO3 decomposes during high-voltage charging, producing CO2 inside the battery, affecting the battery's cycle life and safety performance. Simultaneously, the high reactivity of Li2CO3 with the electrolyte leads to the formation of Li on the cathode. x POF y Organic and inorganic compounds such as ROCO2R and ROCO2Li significantly increase diffusion resistance and reduce the diffusion rate of lithium ions.

[0003] Meanwhile, developing high-capacity anode materials to replace graphite anodes has become an important direction, with silicon-based materials showing significant advantages as novel anode materials. However, during the first charge, the formation of the solid electrolyte interphase (SEI) film on the anode side consumes active lithium in the battery, resulting in irreversible capacity loss in the first cycle, thus reducing the battery's energy density and cycle life. To solve this problem, lithium replenishing agents can be introduced into lithium-ion batteries to replenish the lost active lithium ions. Positive electrode lithium replenishing agents have advantages such as low cost, simple operation, and high safety, making them the mainstream method of lithium replenishment technology. Among them, Li2NiO2 has received widespread attention. However, from the perspective of the positive electrode material itself, the NiO product generated after the first delithiation of Li2NiO2 (conductivity ~10) -11 S·cm -1 ) and NCM (conductivity ~10 -3S·cm -1 The difference in conductivity between the electrodes exacerbates the electrode polarization effect, thus affecting the Li. + The transport dynamics of Li2NiO2 are affected. Therefore, the introduction of Li2NiO2 will reduce the dynamic performance of the cathode, and its incompatibility with the cathode material system needs to be addressed.

[0004] High-nickel NCMs and cathode lithium supplements such as ternary lithium-containing compounds like Li₂NiO₂ suffer from high environmental sensitivity and poor air stability, severely restricting their production and application. Many solutions have been proposed to address these issues. Existing technologies often employ surface coating to improve air stability. CN 117577843 A uses Li₂Se as a coating layer for Li₂NiO₂, effectively improving its environmental stability, reducing side reactions with the electrolyte, and increasing battery energy density. CN 113178567 A uses zirconium dioxide as a coating layer on the surface of Li₂NiO₂. Zirconium dioxide, as an inactive material, has a porous structure that inhibits HF corrosion in the electrolyte to protect the Li₂NiO₂ core material, while allowing free insertion and extraction of lithium ions. In CN 115548274 A, Li2NiO2 is coated with alkyl phosphate ester, which has a certain degree of hydrophobicity and can effectively protect the main material from air corrosion when stored in an air environment. Furthermore, it forms lithium phosphate with good ion conduction, which greatly improves the electrochemical performance of the battery.

[0005] However, existing methods for improving air stability and resolving interfacial compatibility issues using high-nickel NCM and lithium-supplementing additives like Li2NiO2 often suffer from complex processes, high costs, and environmental pollution, hindering commercial application. Furthermore, current technologies struggle to simultaneously improve both air stability and kinetic performance. A single surface coating strategy cannot fully enhance air stability and reduce surface impedance, offering limited benefits for improving electrochemical performance and lithium-ion diffusion.

[0006] Therefore, developing a new strategy to optimize the kinetic performance of the lithium supplementation additive Li2NiO2 in high-nickel ternary cathodes is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0007] In view of this, to address the shortcomings and defects of the prior art, the first objective of this invention is to provide a synergistic surface modification strategy for the lithium-supplementing additive Li2NiO2 and the NCM cathode, aiming to ensure efficient lithium supplementation by Li2NiO2 while suppressing its negative impact on the kinetic performance of the cathode material. The second objective of this invention is to provide the application of the aforementioned lithium-supplementing additive Li2NiO2 and the NCM cathode in lithium-ion batteries, as well as the resulting cathode and battery.

[0008] One objective of this invention is to provide a method for synergistic surface modification of lithium-supplementing additive Li2NiO2 and NCM cathode, comprising the following steps:

[0009] (1) Add fluoroborate to anhydrous ethanol and stir to dissolve, to obtain a mixed solution;

[0010] (2) Add commercial high-nickel NCM and lithium supplementation additive Li2NiO2 to the mixed solution, stir evenly, separate solid and liquid, and vacuum dry to obtain composite lithium supplementation cathode material;

[0011] The purpose of the above technical solution is to utilize the hydrolysis products of fluoroborate to react directly with the residual alkali (Li2CO3) on the surfaces of Li2NiO2 and high-nickel NCM in situ, simultaneously constructing a LiF-NaF-LiBO2 multifunctional composite coating on the surfaces of Li2NiO2 and high-nickel NCM. This invention eliminates the need for a sintering process, thus obtaining a Li2NiO2 / NCM composite lithium-supplementing cathode material with high air stability and high ionic conductivity.

[0012] (3) The composite lithium-supplementing cathode material, carbon nanotubes (CNTs) and polyvinylidene fluoride (PVDF) are uniformly dispersed in N-methylpyrrolidone (NMP) solution. The stirring time is 4-8h and the stirring speed is 200-600r / min to obtain cathode slurry.

[0013] (4) The positive electrode slurry is coated on the surface of aluminum foil and dried in a vacuum oven to obtain a positive electrode sheet with synergistic surface modification.

[0014] Preferably, in step (1), the mass fraction of the fluoroborate in the anhydrous ethanol is 0.5-5%.

[0015] Preferably, the fluoroborate is selected from at least one of KBF4, NaBF4, and LiBF4.

[0016] Preferably, in step (2), the solid-liquid ratio of NCM, Li2NiO2 and the mixed solution is 1g:0.1g:10~50mL.

[0017] Preferably, the NCM is selected from at least one of NCM622, NCM721, and NCM811.

[0018] Preferably, in step (2), the stirring time is 15~45 min and the speed is 400~800 r / min; the vacuum drying temperature is 50~100℃ and the time is 5~10 h.

[0019] Preferably, in step (3), the mass ratio of the composite lithium-supplementing cathode material, carbon nanotubes, and polyvinylidene fluoride is 80:10:10; and the N-methylpyrrolidone accounts for 40-60% of the cathode slurry system.

[0020] Preferably, in step (4), the coating is performed with a scraper height of 200 μm; the vacuum drying temperature is 50~100℃ and the time is 6~12h.

[0021] This invention reveals that by employing a synergistic surface modification strategy, a multifunctional LiF-NaF-LiBO2 composite coating can be simultaneously constructed on the surfaces of Li2NiO2 and NCM. The presence of this coating not only effectively isolates the materials from direct contact with H2O and CO2 in the ambient air, improving their ability to resist CO2 and H2O and enhancing air stability, but also increases the ionic conductivity of the Li2NiO2 and NCM surfaces, improving their interfacial contact and thus enhancing the compatibility of Li2NiO2 in NCM.

[0022] The second objective of this invention is to provide a positive electrode sheet and a battery prepared by a synergistic surface modification method.

[0023] The third objective of this invention is to provide an application of synergistically surface-modified positive electrode sheets in lithium-ion batteries.

[0024] The technical concept of the fluoroborate and processing technology used in this invention is as follows: Since high-nickel NCM and lithium supplement Li2NiO2 inevitably react with air during storage, Li2CO3 is generated on their surfaces. By dissolving fluoroborates such as NaBF4 in anhydrous ethanol and then mixing them with high-nickel NCM and lithium supplement Li2NiO2, the hydrolysis products of NaBF4 directly react with the Li2CO3 on the surfaces of Li2NiO2 and NCM811 in situ, thus constructing a surface coating rich in LiF-NaF-LiBO2 on both surfaces in situ. This design is based on a triple mechanism optimization:

[0025] 1) By utilizing HBF4 generated from the hydrolysis of NaBF4 to react with Li2CO3 on the material surface, a LiF-NaF-LiBO2 composite coating is constructed on the LNO surface, blocking the H2O / CO2 erosion path; 2) LiF (conductivity ~10 -7 S·cm -1 NaF (conductivity ~10) -7 S cm -1 ) and LiBO2 (conductivity ~10) -6 S·cm -1The synergistic effect of NCM and LNO reconstructs the lithium-ion diffusion channel, which helps to further improve the kinetic properties; 3) By co-treating NCM and LNO in a "one-step" manner, a solid-like electrolyte interface layer is simultaneously formed on the surface of the cathode particles, which effectively buffers the conductivity mismatch between LNO decomposition products and NCM and reduces the interface impedance.

[0026] As can be seen from the above technical solution, compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0027] (1) The present invention uses a mixed washing solution containing anhydrous ethanol and fluoroborate to achieve synergistic surface modification of lithium supplementation additive Li2NiO2 and NCM cathode.

[0028] (2) The fluoroborates in this invention can react well with Li2CO3 generated on the material surface to form a surface coating containing LiF, NaF, and LiBO2. In the surface coating, LiF (with an electrical conductivity of ~10) -7 S·cm -1 NaF (conductivity ~10) -7 S cm -1 ) and LiBO2 (conductivity ~10) -6 S·cm -1 The synergistic effect of Li2NiO2 can reconstruct lithium-ion diffusion channels and suppress the negative impact of Li2NiO2 addition on the dynamic performance of cathode materials.

[0029] (3) This invention can obtain a Li2NiO2 and NCM composite lithium-supplementing cathode material with high air stability and high ionic conductivity without a secondary sintering process. It significantly reduces reaction energy consumption and is simple and inexpensive. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0031] Figure 1 EDS mapping images of Na, F, and B for LNO-NBF.

[0032] Figure 2 XRD images of LNO-NBF and LNO.

[0033] Figure 3 XPS spectra of (a) Na 1s, (b) F 1s and (c) B 1s for LNO-NBF.

[0034] Figure 4 (a) Charge-discharge capacity-voltage curves of LNO-NBF, (b) error bar plots and (c) cycle performance of LNO and LNO-NBF.

[0035] Figure 5 (a) CV curves and (b) impedance plots for LNO and LNO-NBF, with the inset showing the equivalent circuit model. (c) Z’- ω -1 / 2 (d) GITT curve, (e) Li under different charging states + Diffusion coefficient and (f) Li under different discharge states + Diffusion coefficient.

[0036] Figure 6 SEM images of (a) LNO-NBF, (b) 0.5D-LNO-NBF and (c) 1D-LNO-NBF.

[0037] Figure 7 XPS spectra of (a) C 1s and (b) Li 1s for LNO-NBF, 0.5D-LNO-NBF and 1D-LNO-NBF.

[0038] Figure 8 Images showing the contact angles of LNO and LNO-NBF electrodes with deionized water.

[0039] Figure 9 (a) Error bar plots and (b) Impedance plots for LNO-NBF, 0.5D-LNO-NBF, and 1D-LNO-NBF.

[0040] Figure 10 (a) Initial charge-discharge capacity-voltage curves, (b) rate performance, and (c) cycle performance of NCM811 cathode with 5 wt% LNO and LNO-NBF.

[0041] Figure 11 (a) Initial charge-discharge capacity-voltage curves, (b) rate performance, and (c) cycle performance of NCM811 cathode with 10 wt% LNO and LNO-NBF.

[0042] Figure 12 (a) Initial charge-discharge capacity-voltage curves, (b) rate performance, and (c) cycle performance of NCM811 cathode with 10 wt% LNO and LNO-NBF added and Ew-NCM811+LNO-NBF.

[0043] Figure 13(a) Initial charge-discharge capacity-voltage curves, (b) rate performance, and (c) cycle performance of NCM811||Si / C, NCM811+LNO||Si / C, and Ew-NCM811+LNO-NBF||Si / C full cells.

[0044] Figure 14 The first charge-discharge curves are for Example 1 and Comparative Examples 1 to 3.

[0045] Figure 15 The above are the rate performance diagrams for Example 1 and Comparative Examples 1 to 3.

[0046] Figure 16 The diagram shows the cyclic performance of Example 1 and Comparative Examples 1 to 3. Detailed Implementation

[0047] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] Example 1

[0049] A synergistic surface modification method for lithium supplementation additive Li2NiO2 and NCM cathode:

[0050] (1) Select Ni as the chemical composition 0.8 Co 0.1 Mn 0.1 Commercial high-nickel NCM (NCM811) and lithium-supplementing additive Li2NiO2 were used. Both were stirred with a mixed solution (3% by mass) containing anhydrous ethanol and NaBF4. The solid-liquid ratio of the anhydrous ethanol solution of NCM811:Li2NiO2:NaBF4 was 1 g:0.1 g:20 mL. The stirring time was 20 minutes at a speed of 800 r / min. After solid-liquid separation, the solid product was obtained by vacuum drying at 70 °C for 10 h. The resulting sample was designated Ew-NCM811+LNO-NBF.

[0051] (2) The Ew-NCM811+LNO-NBF, carbon nanotubes (CNTs), and polyvinylidene fluoride (PVDF) obtained above were uniformly dispersed in an N-methylpyrrolidone (NMP) solution at a mass ratio of 80:10:10 to prepare a positive electrode slurry (NMP accounted for 40-60% of the entire positive electrode slurry system). The stirring time was 4 h and the stirring speed was 500 r / min. The slurry was then coated on the surface of aluminum foil with a scraper height of 200 μm and placed in a vacuum oven for drying at a temperature of 70 °C for 8 h to obtain a modified NCM811 positive electrode sheet containing the modified lithium supplementing agent Li2NiO2.

[0052] Example 2

[0053] A synergistic surface modification method for lithium supplementation additive Li2NiO2 and NCM cathode:

[0054] (1) Select Ni as the chemical composition 0.8 Co 0.1 Mn 0.1 Commercial high-nickel NCM (NCM811) and lithium-supplementing additive Li2NiO2 were used. Both were stirred with a mixed solution (3% by mass) containing anhydrous ethanol and LiBF4. The solid-liquid ratio of the anhydrous ethanol solution of NCM811:Li2NiO2:LiBF4 was 1 g:0.1 g:20 mL. The stirring time was 20 minutes at a speed of 800 r / min. After solid-liquid separation, the solid product was obtained by vacuum drying at 70 °C for 10 h. The resulting sample was designated Ew-NCM811+LNO-LBF.

[0055] (2) The Ew-NCM811+LNO-LBF, carbon nanotubes (CNTs), and polyvinylidene fluoride (PVDF) obtained above were uniformly dispersed in an N-methylpyrrolidone (NMP) solution at a mass ratio of 80:10:10 to prepare a positive electrode slurry (NMP accounted for 40-60% of the entire positive electrode slurry system). The stirring time was 4 h and the stirring speed was 500 r / min. The slurry was then coated on the surface of aluminum foil with a scraper height of 200 μm and placed in a vacuum oven for drying at a temperature of 70 °C for 8 h to obtain a modified NCM811 positive electrode sheet containing the modified lithium supplementing agent Li2NiO2.

[0056] Example 3

[0057] A synergistic surface modification method for lithium supplementation additive Li2NiO2 and NCM cathode:

[0058] (1) Select Ni as the chemical composition 0.8 Co 0.1 Mn 0.1Commercial high-nickel NCM (NCM811) and lithium-supplementing additive Li2NiO2 were used. Both were stirred with a mixed solution (3% by mass) containing anhydrous ethanol and KBF4. The solid-liquid ratio of the anhydrous ethanol solution of NCM811:Li2NiO2:KBF4 was 1 g:0.1 g:20 mL. The stirring time was 20 minutes at a speed of 800 r / min. Solid-liquid separation was performed, and the solid product was obtained after vacuum drying at 70℃ for 10 hours. The resulting sample was designated Ew-NCM811+LNO-KBF.

[0059] (2) The Ew-NCM811+LNO-KBF, carbon nanotubes (CNTs), and polyvinylidene fluoride (PVDF) obtained above were uniformly dispersed in an N-methylpyrrolidone (NMP) solution at a mass ratio of 80:10:10 to prepare a positive electrode slurry (NMP accounted for 40-60% of the entire positive electrode slurry system). The stirring time was 4 h and the stirring speed was 500 r / min. The slurry was then coated on the surface of aluminum foil with a scraper height of 200 μm and placed in a vacuum oven for drying at a temperature of 70 °C for 8 h to obtain a modified NCM811 positive electrode sheet containing the modified lithium supplementing agent Li2NiO2.

[0060] Comparative Example 1

[0061] (1) Select Ni as the chemical composition 0.8 Co 0.1 Mn 0.1 Commercialization of O2 (NCM811) high-nickel NCM.

[0062] (2) The above-mentioned NCM811, carbon nanotubes (CNTs), and polyvinylidene fluoride (PVDF) were uniformly dispersed in an N-methylpyrrolidone (NMP) solution at a mass ratio of 80:10:10 to prepare a positive electrode slurry (NMP accounted for 40-60% of the entire positive electrode slurry system). The stirring time was 4 h and the stirring speed was 500 r / min. The slurry was then coated on the surface of aluminum foil with a scraper height of 200 μm and placed in a vacuum oven for drying at a temperature of 70 °C for 8 h to obtain an unmodified NCM811 positive electrode sheet without lithium supplementation agent Li2NiO2.

[0063] Comparative Example 2

[0064] (1) Select the lithium supplementation additive Li2NiO2 and stir a mixed solution containing anhydrous ethanol and NaBF4. The solid-liquid ratio of the anhydrous ethanol solution of Li2NiO2:NaBF4 is 0.1g:20mL. The stirring time is 20 minutes and the stirring speed is 800r / min. After solid-liquid separation, the solid product is obtained by vacuum drying at 70℃ for 10h. The obtained sample is denoted as LNO-NBF.

[0065] (2) Select Ni as the chemical composition 0.8 Co 0.1 Mn 0.1 Commercialization of O2 (NCM811) high-nickel NCM.

[0066] (3) NCM811, the LNO-NBF obtained above (mass ratio 10:1), carbon nanotubes (CNTs), and polyvinylidene fluoride (PVDF) were uniformly dispersed in an N-methylpyrrolidone (NMP) solution at a mass ratio of 80:10:10 to prepare a positive electrode slurry (NMP accounted for 40-60% of the entire positive electrode slurry system). The stirring time was 4 h and the stirring speed was 500 r / min. The slurry was then coated on the surface of aluminum foil with a scraper height of 200 μm and placed in a vacuum oven for drying at a temperature of 70 °C for 8 h to obtain an unmodified NCM811 positive electrode sheet containing the modified lithium supplementing agent Li2NiO2.

[0067] Comparative Example 3

[0068] (1) First, the chemical composition is selected as Ni. 0.8 Co 0.1 Mn 0.1 Commercialization of high-nickel NCM (NCM811) O2 and lithium supplementation additive Li2NiO2.

[0069] (2) The above-mentioned NCM811 and Li2NiO2 (mass ratio 10:1), carbon nanotubes (CNTs), and polyvinylidene fluoride (PVDF) were uniformly dispersed in an N-methylpyrrolidone (NMP) solution at a mass ratio of 80:10:10 to prepare a positive electrode slurry (NMP accounted for 40-60% of the entire positive electrode slurry system). The stirring time was 4 h and the stirring speed was 500 r / min. The slurry was then coated on the surface of aluminum foil with a scraper height of 200 μm and placed in a vacuum oven for drying at a temperature of 70 °C for 8 h to obtain an unmodified NCM811 positive electrode sheet containing unmodified lithium supplementer Li2NiO2.

[0070] In Embodiment 1 of the present invention, a LiF-NaF-LiBO2 (NBF) composite coating, denoted as LNO-NBF, is formed on the surface of Li2NiO2 (LNO).

[0071] Experiment 1 Material Characterization

[0072] like Figure 1 As shown, this indicates that the NBF composite coating has been uniformly formed on the surface of the LNO particles. Figure 2 As shown, the coating process does not significantly affect the main structure of the LNO material. Figure 3As shown in (ac), Na, F, and B elements exist on the surface of LNO-NBF in the forms of LiF, NaF, and LiBO2, respectively, which proves that there is an NBF composite coating on the LNO surface.

[0073] Experiment 2 Electrochemical Performance Testing

[0074] Figure 4 (a) shows the charge-discharge curves of the LNO-NBF electrode for the first three cycles at a current density of 0.1 C. It can be seen that the LNO-NBF exhibits a charge-discharge rate of 472.47 mAh g⁻¹. -1 and 171.17 mAh g -1 The first-cycle charge and discharge specific capacities were measured, and the first-cycle coulombic efficiency was 36.23%, indicating that more active Li was released from the positive electrode side during the initial charging process. + The specific capacity remained stable at 170 mAh g during the second and third charging cycles. -1 about. Figure 4 (b) A comparison of the first-cycle charging capacity of LNO and LNO-NBF showed that LNO-NBF can provide more Li + To compensate for the consumption on the negative electrode side. Figure 4 (c) shows the cycling performance of LNO and LNO-NBF in the voltage window of 2.5–4.25 V. At a current rate of 0.5 C, after 50 cycles, LNO-NBF still exhibits a 95.55 mAh g⁻¹ energy. -1 The discharge capacity of [the substance] is higher than that of LNO (82.04 mAh g) after the same number of cycles. -1 The capacity retention rates of LNO and LNO-NBF were 84.0% and 92.8%, respectively. This is because the composite coating on the NBF surface enhances the Li-terminal coupling between the electrolyte and the electrode material. + This process facilitates the transfer of electrolytes and avoids direct contact between the LNO-NBF surface and the electrolyte, thus improving the cycling stability of LNO-NBF.

[0075] To compare the differences in electrochemical behavior between the two electrode materials, LNO and LNO-NBF electrodes were subjected to voltages ranging from 2.5 to 4.25 V at 0.1 mV s⁻¹. -1 The CV curve of the sweep speed test is as follows Figure 5 As shown in (a), the oxidation peak of LNO-NBF shifted forward by 0.07 V compared to LNO, indicating that the NBF composite coating is beneficial for reducing polarization voltage and promoting electron migration. Subsequently, EIS was used to analyze the impedance changes of LNO and LNO-NBF, as shown in... Figure 5 As shown in (b), the R of the LNO-NBF electrode ct (101.3 Ω) is much smaller than the R of the LNO electrode. ct(132.79 Ω), indicating that NBF coating is beneficial to Li + Transport at the material interface enhances dynamic performance.

[0076] To further investigate the effect of NBF composite coating on Li + The effect of diffusion, Li + Diffusion coefficient (D) Li+ ) can be Z' and ω -1 / 2 The linear relationship was calculated to obtain, Figure 5 (c) This indicates that the NBF composite coating is beneficial to Li + Diffusion. The lithium-ion diffusion coefficients of LNO and LNO-NBF were determined using GITT, and the GITT curves are shown below. Figure 5 As shown in (d), the ionic conductivity during the charging and discharging processes was measured as follows: Figure 5 As shown in (e) and (f), LNO-NBF exhibits a larger lithium-ion diffusion coefficient during charge and discharge. This may be due to the introduction of LiF, NaF, and LiBO2 into the NBF composite coating, which can promote the diffusion of lithium ions. + Rapid migration.

[0077] Experiment 3 Air stability test

[0078] The micromorphological changes of LNO-NBF after half a day and one day of exposure to an environment with a relative humidity of 70% were studied using SEM, such as... Figure 6 As shown in (ac), under the protection of the NBF coating, the surface morphology of LNO-NBF particles did not change significantly after being exposed to the environment for half a day and one day. This indicates that the NBF coating can effectively isolate the material from direct contact with H2O and CO2 in the ambient air, thereby enhancing the air stability of LNO-NBF.

[0079] like Figure 7 XPS spectra of C 1s (Li₂CO₃, 289.7 eV) and Li 1s (Li₂CO₃, 55.3 eV) of LNO-NBF, 0.5D-LNO-NBF, and 1D-LNO-NBF were compared, confirming that the NBF composite coating can effectively suppress the increase of Li₂CO₃ on the material surface. Contact angle tests were also conducted on LNO and LNO-NBF electrodes with deionized water. Figure 8 As shown, this means that the NBF coating can enhance hydrophobic properties, thereby reducing its air sensitivity.

[0080] A half-cell was assembled using LNO-NBF, 0.5D-LNO-NBF, and 1D-LNO-NBF as positive electrodes and lithium metal as the negative electrode. Electrochemical tests were conducted at a current density of 0.1C within a voltage range of 2.5–4.25 V.

[0081] like Figure 9 As shown in (a), the first-cycle charging capacities of LNO-NBF, 0.5D-LNO-NBF, and 1D-LNO-NBF were tested, and were 472.47, 462.26, and 454.41 mAh g, respectively. -1 It exhibits good air stability. To explain the changes in reaction kinetics after half a day and one day in the LNO-NBF exposure environment, Figure 9 (b) The EIS spectrum shows that 0.5D-LNO-NBF has an impedance of 118.4 Ω and 1D-LNO-NBF has an impedance of 128.5 Ω. After exposure to ambient air, the impedance of both increased slightly, but the change was significantly less than that of LNO. This indicates that the LNO-NBF composite coating effectively inhibited the formation of Li2CO3 on the material surface, thereby slowing down the increase in charge transfer impedance of LNO-NBF during exposure to air.

[0082] Experiment 4: Synergistic Surface Modification of Li2NiO2 and NCM Cathode

[0083] To investigate the practical application effect of LNO-NBF as a positive electrode lithium supplement, it was added to NCM811 positive electrode material at different amounts to prepare electrode slurries, half-cells were assembled, and their electrochemical performance was tested.

[0084] First, 5 wt% LNO and LNO-NBF were added to the NCM811 cathode, respectively. Figure 10 (a) shows the initial charge-discharge curves. It can be seen that adding LNO or LNO-NBF to the NCM811 cathode effectively improves the initial charge specific capacity, and the improvement is more significant for the NCM811 cathode with added LNO-NBF. Figure 10 As shown in (b), when 5 wt% LNO or LNO-NBF was added, the discharge specific capacity of the half-cell at different rates was slightly lower than that of the original NCM811. Figure 10 As shown in (c), the discharge specific capacity of the NCM811 cathode with 5wt% LNO or LNO-NBF is slightly lower than that of the original NCM811. After 200 cycles, the discharge specific capacity of the NCM811 cathode with 5wt% LNO-NBF is close to that of the original NCM811.

[0085] Secondly, the addition amounts of LNO and LNO-NBF were increased; 10 wt% of LNO and LNO-NBF were added to the NCM811 cathode, respectively. Figure 11(a) shows that the initial charge specific capacity was further improved with the addition of 5 wt% lithium supplementer, among which the NCM811 cathode with 10 wt% LNO-NBF had the highest initial charge specific capacity (280.52 mAhg). -1 ).like Figure 11 As shown in (b), when 10 wt% LNO and LNO-NBF were added, the discharge specific capacity of the half-cell decreased more significantly at different discharge rates. Figure 11 As shown in (c), with the increase of LNO and LNO-NBF addition, the discharge specific capacity of NCM811 cathode shows a decreasing trend. The discharge specific capacity of NCM811 cathode with 10 wt% LNO and LNO-NBF addition is lower than that of the original NCM811.

[0086] Figure 12 (a) shows that the initial charge specific capacity of the Ew-NCM811+LNO-NBF cathode is 281.37 mAh g at a current density of 0.1C. -1 The initial discharge specific capacity is 215.34 mAh g. -1 It can be seen that the present invention effectively improves the initial charge and discharge capacity of NCM half-cells. Figure 12 (b) The discharge specific capacity of the NCM811+LNO-NBF cathode and the original NCM811 cathode at rates of 0.1 C, 0.2 C, 0.5 C, 1 C, 1.5 C, and 2 C is shown. Notably, the NCM811+LNO-NBF cathode exhibits better rate performance at low rates, effectively mitigating the rate performance reduction of the NCM cathode caused by the addition of LNO. Figure 12 As shown in (c), the discharge specific capacity of the NCM811+LNO-NBF cathode is very close to that of the original NCM cathode compared to the NCM811 cathode with 10 wt% LNO-NBF.

[0087] Finally, the NCM811 cathode with 10 wt% LNO and the Ew-NCM811+LNO-NBF cathode were matched with Si / C anodes to assemble full cells and perform electrochemical performance tests:

[0088] like Figure 13 As shown in (a), the first-cycle charging capacity of the Ew-NCM811+LNO-NBF||Si / C full cell is 257.18 mAhg. -1 The discharge capacity is 186.69 mAh g. -1 The ICE (Internal Capacity Efficiency) is 72.6%. However, the NCM811||Si / C full cell exhibits higher active lithium loss, with a first-cycle charging capacity of 231.65 mAh g⁻¹. -1The discharge capacity is 156.59 mAh g. -1 ICE was 67.6%. Figure 13 (b) It can be seen that the rate performance of the full cell has also been significantly improved. At current densities of 0.1 C, 0.2 C, 0.5 C, 1 C, 1.5 C, and 2 C, the capacity of Ew-NCM811+LNO-NBF||Si / C is higher than that of NCM811+LNO||Si / C and NCM811||Si / C. Figure 13 As shown in (c), after 100 cycles, the discharge specific capacity of the Ew-NCM811+LNO-NBF||Si / C full cell is 149.21 mAhg. -1 The capacity retention rate was 74.9%, and the discharge capacity was much higher than that of NCM811+LNO||Si / C (138.95 mAh g). -1 ) and NCM811||Si / C (124.92 mAh g) -1 This demonstrates promising application prospects.

[0089] In summary, this invention comprehensively investigated the microstructure and crystal structure of the coated material, confirming the formation of the LiF-NaF-LiBO2 composite coating with good coating effect. Simultaneously, the composite coating can inhibit the formation of residual alkali on the material surface, effectively reducing the air sensitivity of LNO-NBF (after one day of air exposure, the initial lithium replenishment capacity of LNO-NBF increased by 262.44 mAh g⁻¹ compared to unmodified LNO). -1 Meanwhile, the synergistic effect of the composite coating improved the ionic conductivity of the LNO and NCM811 surfaces, optimizing the kinetic performance of LNO added to the NCM811 cathode. The modified Ew-NCM811+LNO-NBF full cell matched with a Si / C anode showed a 30.1 mAh g⁻¹ increase in discharge capacity compared to the original NAC811||Si / C. -1 After 100 cycles at 0.5 C, the discharge capacity is 149.21 mAh g. -1 With a capacity retention rate of 74.9%, this chapter provides design references for achieving efficient lithium replenishment of LNO while suppressing its impact on the kinetic performance of NCM systems.

[0090] Experiment 5 Electrochemical Test

[0091] The positive electrode sheets from Examples 1, 1, 2, and 3 were cut into circular pieces with a diameter of 1.2 cm. A lithium metal sheet was used as the counter electrode, and a commercially available secondary lithium-ion electrolyte, LB-006 (1.0 M lithium hexafluorophosphate (LiPF6) dissolved in ethylene carbonate (EC), diethyl carbonate (DEC) (EC:DEC = 1:1 wt%), and a Celgard 2400 separator, was used. CR2025 coin cells were assembled in an argon-filled glove box. Constant current charge-discharge tests were performed on the cells in a battery testing cabinet, with a test range of 2.5–4.3 V (vs. Li / Li). + ).

[0092] The specific capacity and coulombic efficiency data for the first charge-discharge cycle of Examples 1-3 and Comparative Examples 1-3 are shown in Table 1:

[0093] Table 1

[0094]

[0095] Depend on Figures 14-16 It can be seen that directly adding Li2NiO2 to the NCM811 cathode leads to a decrease in the discharge capacity and rate performance of the half-cell. This is because the conductivity of NiO, the product of the first round of lithium delithiation of Li2NiO2, is low (10⁻⁶ Ω·cm). -11 S·cm -1 Less than NCM811 (10) -3 S·cm -1 The increased impedance intensifies the electrode polarization effect. Therefore, the introduction of Li2NiO2 has a significant impact on the discharge capacity and rate performance of the NCM811 cathode.

[0096] In Example 1, NCM811 cathode material, Li2NiO2 and NaBF4 were co-treated in one step. The hydrolysis products of NaBF4 reacted with Li2CO3 in situ, which effectively buffered the conductivity mismatch between the decomposition products of Li2NiO2 and NCM. The synergistic effect of LiF, NaF and LiBO2 in the coating reconstructed the lithium-ion diffusion channel, which helped to improve the kinetic properties.

[0097] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A synergistic surface modification method of lithium supplement additive Li2NiO2 and NCM cathode, characterized in that, The method comprises the following steps: (1) adding fluoroborate into anhydrous ethanol, stirring and dissolving to obtain a mixed solution; (2) adding NCM and Li2NiO2 into the mixed solution, stirring and filtering, and vacuum drying to obtain a composite lithium supplementing cathode material; (3) uniformly dispersing the composite lithium supplementing cathode material, carbon nanotubes and polyvinylidene fluoride in an N-methylpyrrolidone solution to obtain a cathode slurry; (4) coating the cathode slurry on the surface of an aluminum foil, vacuum drying to obtain a cathode sheet.

2. The synergistic surface modification method of lithium supplement additive Li2NiO2 and NCM cathode according to claim 1, characterized in that, In step (1), the mass fraction of the fluoroborate in the anhydrous ethanol is 0.5-5%.

3. The synergistic surface modification method of lithium supplement additive Li2NiO2 and NCM cathode according to claim 1, characterized in that, The fluoroborate is at least one selected from KBF4, NaBF4 and LiBF4.

4. The synergistic surface modification method of lithium supplement additive Li2NiO2 and NCM cathode according to claim 1, characterized in that, In step (2), the solid-liquid ratio of the NCM, Li2NiO2 and the mixed solution is 1g:0.1g:10-50mL.

5. The synergistic surface modification method of lithium supplement additive Li2NiO2 and NCM cathode according to claim 1, characterized in that, The NCM is at least one selected from NCM622, NCM721 and NCM811.

6. The synergistic surface modification method of lithium supplement additive Li2NiO2 and NCM cathode according to claim 1, characterized in that, In step (3), the mass ratio of the composite lithium supplementing cathode material, carbon nanotubes and polyvinylidene fluoride is 80:10:

10.

7. The synergistic surface modification method of lithium supplement additive Li2NiO2 and NCM cathode according to claim 1, characterized in that, In step (4), the height of the coating doctor blade is 200μm; the temperature of the vacuum drying is 50-100℃, and the time is 6-12h.

8. The cathode sheet prepared by the synergistic surface modification method according to any one of claims 1-7.

9. The cathode sheet according to claim 8 for use in a lithium ion battery.

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