An electrolyte for use in high cutoff voltage environments and its preparation method

Abstract

This invention discloses an electrolyte for use under high cutoff voltage conditions and its preparation method, relating to the field of battery electrolyte materials technology. This electrolyte, through extraction using a reference electrolyte solution, can specifically extract electrochemically active molecular components from anthocyanins, allowing them to preferentially adsorb onto the negatively charged positive electrode surface under high cutoff voltage conditions via electrostatic interactions. This not only interrupts the chain reaction but also directly anchors lattice oxygen, inhibiting lattice oxygen release at its source. It achieves a synergistic effect of a dual protection mechanism of "dynamic removal and static anchoring." Furthermore, high-speed centrifugation avoids increased ion transport impedance. This electrolyte significantly inhibits chain reactions under high cutoff voltage conditions, effectively preventing the formation of excessively thick or high-impedance interface layers, ensuring the battery's capacity and cycle capacity retention under high cutoff voltage conditions, making it suitable for large-scale application in lithium batteries under high cutoff voltage conditions.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, mainly to the field of lithium battery electrolyte materials technology, and specifically to an electrolyte for use in high cutoff voltage environments and its preparation method. Background Technology

[0002] With the increasing demand for higher energy density in lithium-ion batteries, high-nickel ternary cathode materials (such as NCM811) have become a research focus due to their high specific capacity. To fully utilize their capacity advantage, batteries typically need to be charged to a high cutoff voltage of 4.5V or higher. However, under this high cutoff voltage condition, the interfacial stability between the cathode material and the electrolyte faces severe challenges. On the one hand, the cathode material itself undergoes irreversible lattice oxygen release, triggering a transformation of the material structure from a layered structure to an electrochemically inert rock salt phase, leading to capacity decay and transition metal dissolution. On the other hand, the released highly reactive oxygen species violently oxidize carbonate electrolytes, causing continuous electrolyte decomposition and gas production, and forming a thick and unstable cathode-electrolyte interfacial film, resulting in increased battery internal resistance and shortened cycle life.

[0003] To address the aforementioned issues, existing technologies typically employ a strategy of adding functional additives to high-cutoff-voltage electrolytes to formulate composite electrolytes. However, the mechanisms of action of mainstream additives such as vinylene carbonate (VC) and fluorovinylene carbonate (FEC) are relatively simple, primarily relying on preferential oxidation on the cathode surface to form a polymer protective film. This singular "film-forming" mechanism has significant limitations: firstly, they cannot fundamentally suppress the source problem of lattice oxygen release from the cathode material under high cutoff voltages; secondly, at extremely high cutoff voltages >4.5 V, these traditional additives themselves may be over-oxidized, forming excessively thick or highly impedance interface layers, which are detrimental to ion conduction; furthermore, they generally lack the ability to actively scavenge highly reactive free radicals, making it difficult to effectively inhibit the chain decomposition reactions initiated by already generated oxygen free radicals. Due to the aforementioned shortcomings of existing functional additives, the composite electrolytes formulated using them still exhibit low scavenging rates of highly reactive free radicals and are prone to excessive oxidation, resulting in overly thick or highly impedance interface layers. These defects severely impact battery capacity and cycle capacity retention, making them unsuitable for large-scale application. Therefore, there is an urgent need in this field to develop a novel, high-efficiency electrolyte suitable for use in high-cutoff-voltage environments. Summary of the Invention

[0004] The purpose of this invention is to overcome the defects of existing composite electrolytes, such as low scavenging rate of highly active free radicals and easy over-oxidation to form an interface layer that is too thick or has too high impedance. This invention proposes an electrolyte for use in high cutoff voltage environments and its preparation method.

[0005] To achieve the above-mentioned objectives, this invention proposes an electrolyte for use in high cutoff voltage environments, which is mainly prepared from a reference electrolyte solution and anthocyanins by the following preparation method;

[0006] The preparation method includes the following steps:

[0007] (1) Prepare a reference electrolyte solution; the reference electrolyte solution is mainly composed of lithium hexafluorophosphate, ethylene carbonate and diethyl carbonate;

[0008] (2) Add 0.2-1.0% anthocyanin by mass fraction of the reference electrolyte solution to the reference electrolyte solution, stir to dissolve and obtain an electrolyte suspension;

[0009] (3) Centrifuge the electrolyte suspension and take the supernatant, which is the electrolyte for use in high cutoff voltage environments.

[0010] This invention discloses an electrolyte for use in high cutoff voltage environments. It not only utilizes the extraction effect of a reference electrolyte solution to specifically extract electrochemically active molecular components (catechol structures) from anthocyanins, but also allows these components to preferentially adsorb onto the negatively charged high cutoff voltage cathode surface via electrostatic interactions (unique positive charge properties). This enables efficient scavenging of superoxide radicals at the interface using the phenolic hydroxyl groups, interrupting chain decomposition reactions; it also utilizes the hydrogen bonds formed by the catechol groups to directly anchor lattice oxygen, significantly increasing the oxygen vacancy formation energy and inhibiting lattice oxygen release at the source; thus achieving "dynamic cleaning." The synergistic effect of the dual protection mechanism of "static anchoring" can form a thin and stable CEI layer on the positive electrode surface, effectively inhibiting the decomposition of the electrolyte and the degradation of the positive electrode material structure. Moreover, high-speed centrifugation is used to remove the residual components after anthocyanin extraction in the electrolyte solution, thereby avoiding the increase of ion transport impedance. This electrolyte can significantly inhibit the chain decomposition reaction under high cutoff voltage conditions, effectively avoiding the formation of excessively thick or high-impedance interface layers, ensuring the battery capacity and cycle capacity retention rate under high cutoff voltage conditions, and is suitable for large-scale application in lithium batteries under high cutoff voltage conditions.

[0011] In step (1), preferably, the concentration of lithium hexafluorophosphate in the reference electrolyte solution is 1-1.2 mol / L; the volume ratio of ethylene carbonate to diethyl carbonate is 1:0.8-1.2; the preferred composition of the reference electrolyte solution can better achieve the extraction of electrochemically active molecular components in anthocyanins.

[0012] In step (2), preferably, the amount of anthocyanin added is 0.2-0.4% of the mass fraction of the reference electrolyte solution; more preferably, the amount of anthocyanin added is 0.4% of the mass fraction of the reference electrolyte solution. Although the added anthocyanin can significantly inhibit the chain decomposition reaction under high cutoff voltage conditions and effectively avoid the formation of an interface layer that is too thick or has too high impedance, it is still essentially a large molecular organic matter. If too much is attached to the positive electrode surface, it will greatly affect the transport of ions. Therefore, only a reasonable amount of anthocyanin electrochemically active molecular component can achieve better electrical performance enhancement.

[0013] Preferably, during the stirring and dissolving process, the stirring speed is 500-700 r / min; this allows for better dissolution and extraction of electrochemically active molecular components in anthocyanins.

[0014] Preferably, during the stirring and dissolving process, the temperature is 20-30℃ and the time is not less than 2 hours; this can better dissolve and extract the electrochemically active molecular components in anthocyanins.

[0015] In step (3), preferably, the centrifugation speed is 6000-10000 r / s and the time is 5-10 min; the preferred centrifugation speed and time can more thoroughly remove the remaining components after the anthocyanins are extracted from the reference electrolyte solution and improve the electrolyte performance.

[0016] To achieve the above-mentioned objectives, the present invention further proposes a lithium battery containing the aforementioned electrolyte; the lithium battery containing the electrolyte of the present invention has significantly improved capacity and cycle capacity retention.

[0017] Preferably, the positive electrode material of the lithium battery is NCM811 material; the chemical composition of the NCM811 material is LiNi. 0.8 Co 0.1 Mn 0.1 O2 contains nickel, cobalt, and manganese in a molar ratio of 8:1:1.

[0018] The beneficial effects of the technical solution of this invention are as follows:

[0019] 1. The electrolyte of this invention, through the extraction effect of a reference electrolyte solution, can specifically extract the electrochemically active molecular components (catechol structure) from anthocyanins, and enable them to preferentially adsorb onto the negatively charged high-cutoff-voltage positive electrode surface through electrostatic interaction (unique positive charge characteristics). This allows for both efficient scavenging of superoxide radicals at the interface using the phenolic hydroxyl groups, interrupting the chain decomposition reaction, and direct anchoring of lattice oxygen using hydrogen bonds formed by the catechol groups, significantly increasing the oxygen vacancy formation energy and inhibiting lattice oxygen release from the source. This achieves a synergistic effect of a dual protection mechanism of "dynamic scavenging - static anchoring," forming a thin and stable CEI layer on the positive electrode surface, effectively inhibiting electrolyte decomposition and positive electrode material structure degradation.

[0020] 2. The electrolyte of this invention utilizes high-speed centrifugation to remove the remaining components after anthocyanin extraction from the electrolyte solution, thereby avoiding an increase in ion transport impedance.

[0021] 3. The electrolyte of this invention can significantly suppress chain decomposition reactions under high cutoff voltage conditions, effectively avoid the formation of excessively thick or high-resistivity interface layers, and ensure the capacity and cycle capacity retention rate of the battery under high cutoff voltage conditions. It is suitable for large-scale application in lithium batteries under high cutoff voltage conditions. Attached Figure Description

[0022] Figure 1 The Fourier transform infrared spectra of the electrolyte samples in Example 2 and the blank example of this invention are shown.

[0023] Figure 2 The graph shows the electrical performance test results of the electrolyte samples in Example 2 and the blank example of the present invention.

[0024] Figure 3 The graph shows the test results of the electrolyte samples' ability to absorb superoxide radicals in Example 2 and the blank example of this invention.

[0025] Figure 4 The images show the surface morphology of NCM811 particles after cycling in a high cutoff voltage environment using full cells assembled with electrolyte samples from Example 2 and the blank example (a is Example 2, b is the blank example).

[0026] Figure 5 The graph shows the cycle count test results of the full cells assembled using the electrolyte samples in Example 2 and the blank example of this invention at different rates.

[0027] Figure 6 The graph shows the thickness and uniformity of the CEI of NCM811 particle powder after the full cells assembled using electrolyte samples from Example 2 and the blank example were cycled for the same number of times at a high cutoff voltage (a is the blank example, b is Example 2).

[0028] Figure 7 The graph shows the cycle performance test results of the full cells assembled using the electrolyte samples in Example 2 and the blank example of this invention under 4.3V conditions.

[0029] Figure 8 The graph shows the cycle performance test results of the full cells assembled using the electrolyte samples in Example 2 and the blank example of this invention under 4.5V conditions. Detailed Implementation

[0030] The specific embodiments of the present invention will be further described below with reference to examples, but the present invention is not limited to the scope of the embodiments described herein.

[0031] Examples 1-5

[0032] An electrolyte for use in high cutoff voltage environments is prepared by the following method, with the specific steps as follows:

[0033] (1) Prepare a reference electrolyte solution; the reference electrolyte solution is mainly composed of lithium hexafluorophosphate, ethylene carbonate and diethyl carbonate; wherein, the concentration of lithium hexafluorophosphate is 1 mol / L; the volume ratio of ethylene carbonate to diethyl carbonate is 1:1;

[0034] (2) Add different weights (see Table 1 for specific weights, expressed as a percentage of the mass of the reference electrolyte solution) of anthocyanins to the reference electrolyte solution, stir to dissolve (stirring speed is 600 r / min, temperature is 25℃, time is 2h) to obtain an electrolyte suspension;

[0035] (3) Centrifuge the electrolyte suspension (centrifugation speed is 8000 r / s, time is 10 min), and take the supernatant, which is the electrolyte for use in high cutoff voltage environments.

[0036] Table 1. Amount of anthocyanins added in Examples 1-5

[0037]

[0038] Example 6

[0039] An electrolyte for use in high cutoff voltage environments is prepared by the following method, with the specific steps as follows:

[0040] (1) Prepare a reference electrolyte solution; the reference electrolyte solution is mainly composed of lithium hexafluorophosphate, ethylene carbonate and diethyl carbonate; wherein, the concentration of lithium hexafluorophosphate is 1 mol / L; the volume ratio of ethylene carbonate to diethyl carbonate is 1:1;

[0041] (2) Add 0.4% anthocyanin by mass to the reference electrolyte solution and stir to dissolve (stirring speed 700 r / min, temperature 30℃, time 2 h) to obtain an electrolyte suspension;

[0042] (3) Centrifuge the electrolyte suspension (centrifugation speed is 6000 r / s, time is 10 min), and take the supernatant, which is the electrolyte for use in high cutoff voltage environments.

[0043] Example 7

[0044] An electrolyte for use in high cutoff voltage environments is prepared by the following method, with the specific steps as follows:

[0045] (1) Prepare a reference electrolyte solution; the reference electrolyte solution is mainly composed of lithium hexafluorophosphate, ethylene carbonate and diethyl carbonate; wherein, the concentration of lithium hexafluorophosphate is 1.1 mol / L; the volume ratio of ethylene carbonate to diethyl carbonate is 1:1;

[0046] (2) Add 0.4% anthocyanin by mass to the reference electrolyte solution and stir to dissolve (stirring speed is 650 r / min, temperature is 25℃, time is 2.5 h) to obtain an electrolyte suspension;

[0047] (3) Centrifuge the electrolyte suspension (centrifugation speed is 9000 r / s, time is 8 min), and take the supernatant, which is the electrolyte for use in high cutoff voltage environments.

[0048] Comparative Example 1

[0049] An electrolyte for a high cutoff voltage environment was prepared according to the steps of Example 2, except that "adding 0.4 wt% anthocyanin" in step 2 was changed to "adding 0.1 wt% anthocyanin".

[0050] Comparative Example 2

[0051] An electrolyte for a high cutoff voltage environment was prepared according to the steps of Example 2, except that "adding 0.4 wt% anthocyanin" in step 2 was changed to "adding 1.2 wt% anthocyanin".

[0052] Comparative Example 3

[0053] The electrolyte for high cutoff voltage environments was prepared according to the steps of Example 2, except that the electrolyte suspension was not centrifuged.

[0054] Comparative Example 4

[0055] The electrolyte for high cutoff voltage environments was prepared according to the steps of Example 2, with the only difference being that the centrifugation speed of the electrolyte suspension was only 5000 r / min.

[0056] Blank example:

[0057] The reference electrolyte solution is mainly composed of lithium hexafluorophosphate, ethylene carbonate, and diethyl carbonate; the concentration of lithium hexafluorophosphate is 1 mol / L; and the volume ratio of ethylene carbonate to diethyl carbonate is 1:1.

[0058] Experimental example:

[0059] 1. Fourier transform infrared spectroscopy was used to detect the samples of Example 2 and the blank example. The results are as follows: Figure 1 As shown.

[0060] analyze Figure 1 It can be seen that, due to the addition of anthocyanins, the electrolyte in Example 2 successfully introduced phenolic hydroxyl groups with strong antioxidant properties.

[0061] 2. The electrical properties of the electrolyte samples from Example 2 and the blank example were tested using linear sweep voltammetry (LSV), and the results are as follows: Figure 2 As shown.

[0062] analyze Figure 2 It can be seen that the oxidation window of the electrolyte in the high cutoff voltage environment in Example 2 is 5.0V, while the reference electrolyte begins to undergo significant oxidation decomposition at 4.3V, indicating that the electrolyte used in the high cutoff voltage environment has significantly stronger antioxidant properties than the reference electrolyte.

[0063] 3. The absorption capacity of the electrolytes in Example 2 and the blank example for superoxide radicals was tested, and the results are as follows: Figure 3 As shown.

[0064] analyze Figure 3 The results clearly show that, with the same amount of superoxide added, the superoxide radical content of the electrolyte used in the high cutoff voltage environment (Example 2) is significantly lower than that of the reference electrolyte (blank example). This indicates that the electrolyte used in the high cutoff voltage environment has a significantly stronger ability to absorb superoxide radicals than the reference electrolyte, and that the electrolyte used in the high cutoff voltage environment has significantly stronger antioxidant properties.

[0065] 4. Using the electrolyte samples from Example 2 and the blank example, full cells (Li || NCM811) were assembled respectively. The surface morphology of the NCM811 particles was observed after the cells were cycled the same number of times under a high cutoff voltage of 4.5V. Figure 4 As shown.

[0066] analyze Figure 4It can be clearly seen that the NCM811 particles used in the high cutoff voltage environment (Example 2) showed only slight cracking after cycling, while the NCM811 particles of the reference electrolyte (blank example) showed obvious cracking and structural collapse on the surface after cycling.

[0067] 5. The full cells assembled using the electrolyte samples from Example 2 and the blank example were subjected to cycle number tests at different rates, and cycle curves were plotted. Figure 5 As shown.

[0068] analyze Figure 5 It can be clearly seen that the capacity of the electrolyte remains more stable when used in high cutoff voltage environments, and it has higher capacity at any rate.

[0069] 6. After cycling the full cells assembled using the electrolyte samples from Example 2 and the blank example for the same number of cycles at a high cutoff voltage of 4.5V, the thickness and uniformity of the CEI of the NCM811 particle powder were measured. The results are as follows: Figure 6 As shown.

[0070] analyze Figure 6 It can be seen that the CEI thickness on the surface of NCM811 particles after cycling in a high cutoff voltage environment is significantly thinner and more uniform than that of the reference electrolyte.

[0071] 7. The full cells assembled using the electrolyte samples from Example 2 and the blank example were subjected to cycle performance testing at 4.3V. The results are as follows: Figure 7 As shown.

[0072] analyze Figure 7 It can be seen that the full cell assembled using the electrolyte for high cutoff voltage environment (Example 2) has a capacity retention of 80% after 504 cycles, while the reference electrolyte (blank example) has a capacity retention of only 80% after only 226 cycles.

[0073] 8. The full cells assembled using electrolyte samples from Examples 1-7, Comparative Examples 1-4, and the blank example were subjected to cycle performance testing at 4.5V (cycling was stopped when the capacity retention rate was below 80%). The results are shown in Table 2; and the battery performance of Example 2 and the blank example is plotted as follows (e.g., Figure 8 (As shown)

[0074] Table 2. Experimental results of Examples 1-7, Comparative Examples 1-4, and Blank Examples

[0075]

[0076] Analysis Table 2 and Figure 8It can be seen that the full cell assembled with the electrolyte for a high cutoff voltage environment (Example 2) of this invention achieved a capacity retention of 80% in 219 cycles, compared to only 157 cycles with the reference electrolyte (blank example) achieving the same capacity retention. In other embodiments of this invention, the full cell assembled with the electrolyte for a high cutoff voltage environment achieved a capacity retention of 80% in more than 177 cycles, significantly better than Comparative Examples 1-4 and the blank example. In Comparative Example 1, the amount of anthocyanin added was too low, failing to effectively form the synergistic effect of the "dynamic scavenging-static anchoring" dual protection mechanism, resulting in a significantly lower cycle count than the examples. In Comparative Example 2, the amount of anthocyanin added was too high, resulting in too many electrochemically active molecular components attached to the positive electrode surface, greatly affecting ion transport, thus leading to a significantly lower cycle count than the examples. In Comparative Examples 3 and 4, the failure to effectively remove impurities after anthocyanin extraction significantly increased the impedance of ion transport, resulting in a significantly lower cycle count than the examples. It is evident that the amount of anthocyanins added, the preparation process (centrifugation), and the speed and time of centrifugation all have a significant impact on the electrical properties of the electrolyte.

[0077] The above description is merely a specific embodiment of the present invention and the technical principles used, and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An electrolyte for use in high cutoff voltage environments, characterized in that, It is mainly prepared from a reference electrolyte solution and anthocyanins through the following preparation method; The preparation method includes the following steps: (1) Prepare a reference electrolyte solution; the reference electrolyte solution is mainly composed of lithium hexafluorophosphate, ethylene carbonate and diethyl carbonate; (2) Add 0.2-1.0% anthocyanin by mass fraction of the reference electrolyte solution to the reference electrolyte solution, stir to dissolve and obtain an electrolyte suspension; (3) Centrifuge the electrolyte suspension and take the supernatant, which is the electrolyte for use in high cutoff voltage environments.

2. The electrolyte according to claim 1, characterized in that, In step (1), the concentration of lithium hexafluorophosphate in the reference electrolyte solution is 1-1.2 mol / L.

3. The electrolyte according to claim 1, characterized in that, In step (1), the volume ratio of ethylene carbonate to diethyl carbonate is 1:0.8-1.

2.

4. The electrolyte according to claim 1, characterized in that, In step (2), the amount of anthocyanin added is 0.2-0.4% of the mass fraction of the reference electrolyte solution.

5. The electrolyte according to claim 4, characterized in that, The amount of anthocyanin added is 0.4% of the mass fraction of the reference electrolyte solution.

6. The electrolyte according to claim 1, characterized in that, In step (2), the stirring speed during the stirring and dissolving process is 500-700 r / min.

7. The electrolyte according to claim 1, characterized in that, In step (2), the temperature during the stirring and dissolving process is 20-30℃ and the time is not less than 2 hours.

8. The electrolyte according to claim 1, characterized in that, In step (3), the centrifugation speed is 6000-10000 r / s and the time is 5-10 min.

9. A lithium battery, characterized in that, The lithium battery contains the electrolyte according to any one of claims 1-8.

10. The lithium battery according to claim 9, characterized in that, The positive electrode material of the lithium battery is NCM811.

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