Alkyl disulfonic acid electrode additive, preparation method thereof and lithium ion battery

Abstract

The invention belongs to the technical field of electrode additives, and discloses an alkyl disulfonic acid electrode additive, a preparation method thereof, a lithium ion battery and an alkyl disulfonic acid electrode additive, the alkyl disulfonic acid electrode additive has a structural general formula as shown in formula I, in the formula I, R is alkyl with the carbon atom number of 1-8 or alkyl substituted by one or more halogen atoms. The alkyl disulfonic acid electrode additive can be used as a positive electrode additive and a negative electrode additive at the same time, and has dual functions of lithium supplement and film formation improvement.

Description

Technical Field

[0001] This invention belongs to the field of electrode additive technology, specifically relating to an alkyl disulfonic acid electrode additive, its preparation method, and lithium-ion batteries. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] In the composition of lithium-ion batteries, besides the four main materials—positive electrode material, negative electrode material, electrolyte, and separator—additives, although present in small amounts, play a crucial role. The most common additives are primarily used in the electrolyte. Different additive structures have different mechanisms of action. For example, DTD (ethylene sulfate) can effectively reduce the SEI impedance of the negative electrode, improving battery durability; LiPO2F2 (lithium difluorophosphate) participates in positive electrode film formation, effectively improving battery cycle life and high-voltage resistance. These types of additives generally suffer from poor environmental (reactions with H2O, O2, etc.) and thermal stability, limiting their use to electrolytes. Their application is influenced by oxidation / reduction potentials, often involving reactions at the positive and negative electrode interfaces, making it difficult to maximize efficiency.

[0004] Aside from conductive agents and binders, the practical application of positive / negative electrode additives is relatively limited. Li5FeO4 and Li2NiO2, for example, can effectively improve the overall battery capacity, reduce DCR (DC internal resistance), and enhance battery kinetic performance and cycle life through lithium supplementation at the positive electrode, and have achieved mass application in recent years. However, after lithium removal, the residual metal oxides of these additives have high valence states of metal ions, leading to gas generation during high-temperature storage and cycling. Furthermore, the residual metal oxides have poor electron and lithium-ion conductivity, severely deteriorating the battery's DCR. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide an alkyl disulfonic acid electrode additive, its preparation method, and a lithium-ion battery.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides an alkyl disulfonic acid electrode additive, the general structural formula of which is shown in Formula I:

[0007] Formula I Wherein, R is an alkyl group having 1-8 carbon atoms, or an alkyl group substituted with one or more halogen atoms.

[0008] Secondly, the present invention provides a method for preparing the alkyl disulfonic acid electrode additive, comprising the following steps: The lithium reagent solution was slowly added to the alkyl disulfonic acid solution, and the reaction was stirred to obtain crude alkyl disulfonic acid lithium. The alkyl disulfonic acid contained alkyl groups with 1-8 carbon atoms. The crude alkyl disulfonate is obtained by purification.

[0009] Thirdly, the present invention provides a positive electrode material, including the alkyl disulfonic acid electrode additive, wherein the alkyl disulfonic acid electrode additive has a mass percentage of 0.01%-2%.

[0010] Fourthly, the present invention provides a negative electrode material, including the alkyl disulfonic acid electrode additive, wherein the alkyl disulfonic acid electrode additive has a mass percentage of 0.05%-0.2%.

[0011] Fifthly, the present invention provides a lithium-ion battery comprising the positive electrode material described in the third aspect and / or the negative electrode material described in the fourth aspect.

[0012] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows: The alkyl disulfonate lithium electrode additive of the present invention can be used as both a positive and negative electrode additive. When used as a positive electrode additive, it has the dual functions of lithium replenishment and positive electrode film formation improvement, effectively improving battery dynamics and enhancing fast charging, high and low temperature performance, and cycle performance. When used as a negative electrode additive, its main contribution is to participate in negative electrode film formation, reduce DCR and improve SEI thermal stability. At the same time, the presence of lithium in the compound also compensates for the loss of active lithium during long battery cycles. Attached Figure Description

[0013] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0014] Figure 1 These are the EIS spectra of the battery at 50% SOC in Examples 7-10 and Comparative Example 2 of the present invention; Figure 2 This is the XPS diagram of the negative electrode of the battery after three cycles in Embodiment 7 of the present invention. Detailed Implementation

[0015] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0016] To address the technical problems existing in the prior art mentioned in the background section, the present invention provides an alkyl disulfonic acid electrode additive, the general structural formula of which is shown in Formula I:

[0017] Formula I Wherein, R is an alkyl group having 1-8 carbon atoms, or an alkyl group substituted with one or more halogen atoms.

[0018] In some embodiments, R is an alkyl group having 1-3 carbon atoms.

[0019] Preferably, the alkyl disulfonic acid electrode additive is selected from compounds with the following structural formulas: ; ; or, .

[0020] Secondly, the present invention provides a method for preparing the alkyl disulfonic acid electrode additive, comprising the following steps: The lithium reagent solution was slowly added to the alkyl disulfonic acid solution, and the reaction was stirred to obtain crude alkyl disulfonic acid lithium. The alkyl disulfonic acid contained alkyl groups with 1-8 carbon atoms. The crude alkyl disulfonate is obtained by purification.

[0021] In some embodiments, the lithiation reagent is selected from lithium hydroxide, lithium hydroxide monohydrate, lithium carbonate, or lithium bicarbonate.

[0022] Thirdly, the present invention provides a positive electrode material, comprising the alkyl disulfonic acid electrode additive, wherein the mass percentage of the alkyl disulfonic acid electrode additive is 0.01%-2%. For example, it can be 0.01%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%.

[0023] In some embodiments, the mass percentage of alkyl disulfonic acid electrode additive in the cathode material is 0.05%-2%, preferably 0.5%-2%.

[0024] In some embodiments, the positive electrode active material in the positive electrode material is selected from at least one of nickel-cobalt-manganese ternary materials, lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium manganese oxide, nickel-cobalt-aluminum ternary materials, lithium nickel manganese oxide, and lithium-rich manganese materials.

[0025] Fourthly, the present invention provides a negative electrode material, comprising the alkyl disulfonic acid electrode additive, wherein the alkyl disulfonic acid electrode additive has a mass percentage of 0.01%-2%. For example, it can be 0.01%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%.

[0026] In some embodiments, the mass percentage of alkyl disulfonic acid electrode additive in the negative electrode material is 0.05%-2%, preferably 0.05%-0.2%.

[0027] In some embodiments, the negative electrode active material in the negative electrode material is selected from at least one of artificial graphite, natural graphite, and silicon-based materials.

[0028] In some embodiments, the particle size D50 of the alkyl disulfonic acid electrode additive is 20nm-1500nm, preferably 50nm-400nm.

[0029] Fifthly, the present invention provides a lithium-ion battery comprising the positive electrode material described in the third aspect and / or the negative electrode material described in the fourth aspect.

[0030] The present invention will be further described below with reference to the embodiments.

[0031] Example Taking lithium methanedisulfonate as an example, its preparation process is as follows: Step 1: Mix 185g (1.05M) methanedisulfonic acid with 500mL of deionized water to prepare aqueous solution A; dissolve 73.9g of lithium carbonate in 500mL of water to prepare solution B; Step 2: Slowly add solution B dropwise to solution A. After the addition is complete, neutralize the reaction under slow stirring for 3 hours. The temperature is controlled between 15℃ and 35℃ throughout the entire addition and reaction process. The solution after reaction is heated, concentrated, and filtered to obtain crude lithium methanedisulfonate with a yield of 92%. Step 3: Add crude lithium methyl disulfonate to an organic solvent and recrystallize three times to obtain refined lithium methyl disulfonate with a yield of 95% and a purity greater than 99.9%.

[0032] Examples 1-6 Lithium alkyl disulfonate was added to the positive electrode. The specific preparation process of the positive electrode, negative electrode, and battery in Example 1 (the preparation methods of Examples 2-6 and Comparative Examples 1-3 are the same as those in Example 1) is as follows: Preparation of the positive electrode: Polyvinylidene fluoride (PVDF), conductive agent (Super P), carbon nanotubes (CNT), positive electrode material (nickel-cobalt-manganese ternary material, NCM811), and lithium methanedisulfonate were added to N-methylpyrrolidone (NMP) in a mass ratio of 1.2%:0.5%:1%:96.5%:0.8% and mixed evenly to form a slurry. The slurry was then coated onto an aluminum foil current collector. The surface density of the positive electrode on one side was 200±3 g / m². 2 Cold-pressed to 3.05g / m³ 3 After punching, the positive electrode sheet is obtained.

[0033] Preparation of the negative electrode sheet: Sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber latex (SBR), conductive agent (SuperP), and artificial graphite were added to deionized water at a mass ratio of 1.2%:2%:1%:95.8%, and thoroughly mixed. The slurry was then coated onto a copper foil current collector. The negative electrode surface density was determined based on an N / P ratio of 1.10, and cold-pressed to 1.65 g / m³. 3 After punching, the negative electrode sheet is formed.

[0034] Preparation of the battery to be injected with electrolyte: The separator, negative electrode, and positive electrode are stacked in a "Z" shape to obtain the bare cell to be injected with electrolyte. The cell is then packaged in aluminum-plastic film and baked to obtain the battery to be injected with electrolyte. The designed capacity of the battery to be injected with electrolyte is 5Ah.

[0035] The electrolyte was prepared with a mass ratio of LiPF6:EMC:EC:1.3-PS:LiPO2F2:DTD of 14%:62.2%:21%:0.5%:0.8%:1.5%, and the electrolyte injection coefficient was calculated at 2.6g / Ah. After two sealing, formation and aging, the battery cell to be tested was obtained.

[0036] Compared with Example 1, Examples 2-5 only adjusted the amount of lithium methyl disulfonate added to the positive electrode and balanced it by adjusting the amount of positive electrode active material added. The corresponding mass percentages of lithium methyl disulfonate were 0.2%, 0.5%, 1.1% and 1.4%, respectively. Example 6 replaced lithium methyl disulfonate with lithium propyl disulfonate compared with Example 1, while keeping everything else the same. The specific implementation scheme is shown in Table 1.

[0037] Comparative Example 1 Compared with Example 1, lithium methyl disulfonate was not added to the positive electrode, while other aspects remained unchanged. The specific scheme is shown in Table 1.

[0038] Comparative Example 2 Compared to Example 1, in the positive electrode, lithium methyl disulfonate is replaced with the following lithium sulfonate compound A: Everything else is the same as in Example 1.

[0039] Comparative Example 3 Compared to Example 1, in the positive electrode, lithium methyl disulfonate is replaced with the following lithium sulfonate compound B: Everything else is the same as in Example 1.

[0040] Table 1

[0041] The performance test items of the lithium-ion batteries prepared in Examples 1-6 and Comparative Examples 1-3 are as follows, and the test results are shown in Table 2: First-time efficiency and specific capacity: Specific capacity = first discharge capacity / total weight of positive electrode active material; First-time efficiency = first discharge capacity / first charge capacity.

[0042] DCR (DC internal resistance) test: Charge the battery at 0.5C for 1 hour, i.e. the battery's state of charge is 50% SOC, and let it rest for ≥12 hours. After discharging at 2C for 30 seconds at 25℃, calculate the battery's discharge DCR through the voltage difference; calculate the DCR by discharging at 0.36C for 30 seconds at -20℃. Rate charging performance test: Charge the battery at 3C constant current and constant voltage to 4.2V, cutoff current is 0.05C, discharge at 1C to 2.75V, and calculate the constant current charging capacity ratio.

[0043] High-temperature cycling performance test: At 45℃, the capacity retention rate was tested at different cycles of 1C charge and discharge. The cutoff voltage for charge and discharge was 2.75V~4.2V, and the cutoff current for constant voltage charging was 0.05C. The negative electrode ICP was tested after 1000 cycles in the discharge state, and the Ni content was recorded.

[0044] Table 2

[0045] As shown in Table 2, compared with Comparative Examples 1-3, the specific capacity of the cathode materials in Examples 1-6 was improved, proving that the alkyl disulfonate lithium of the present invention can achieve effective lithium replenishment; at the same time, the battery's initial efficiency was reduced, and the amount of lithium depleted per unit mass during the first charge of alkyl disulfonate lithium was significantly higher than that of NCM811, which was due to the relatively lower reversible lithium content.

[0046] Compared with Comparative Example 1, the high-temperature cycling performance is significantly improved. Considering the reduction in DCR and the amount of Ni deposition on the negative electrode, the main reasons are: 1. Lithium replenishment on the positive electrode is beneficial to reducing the DCR of the negative electrode. This has been verified in the application of relatively mature positive electrode lithium replenishment agents such as Li5FeO4; 2. Lithium alkyl disulfonate participates in the formation of the positive electrode film, which reduces DCR and effectively inhibits the dissolution of Ni.

[0047] Examples 1-5 validated the amount of lithium methyl disulfonate in the NCM / Gr system. The system showed the best performance when the addition amount was 0.8%, mainly reflected in the best overall performance in terms of lithium replenishment efficiency, DCR improvement and high temperature cycling improvement.

[0048] Examples 1 and 6 mainly compared the performance differences between lithium methyl disulfonate and lithium propyl disulfonate. Overall, lithium methyl disulfonate was superior, mainly due to two reasons: first, lithium methyl disulfonate has a relatively smaller molecular weight, resulting in a higher molar content for the same mass fraction; second, a longer carbon-based main chain degrades lithium-ion conduction performance.

[0049] Compared to Example 1, Comparative Examples 2 and 3 used lithium sulfonate compounds A and B with the same mass fraction, respectively, to replace lithium methyl disulfonate. Battery performance results showed that, except for the DCR of the battery in Comparative Example 2, both were superior to Comparative Example 1, and the performance deteriorated significantly compared to Example 1. This suggests that the performance of such additives is related to their molecular structure (film-forming functional groups, lithium-ion conduction capacity of the product, etc.) and the molecular weight per molar lithium. The DCR of the battery in Comparative Example 2 at 25°C and -20°C was worse than that in Comparative Example 1, due to the higher activity of the isocyanate functional groups and the thicker film thickness. Lithium methyl disulfonate has a higher molecular weight per molar lithium than both, with a value of 94, while compounds A and B have values ​​of 159 and 109, respectively. This results in a higher theoretical lithium replenishment per unit mass fraction of lithium methyl disulfonate, thus providing a better improvement in specific capacity and cycle life.

[0050] Examples 7-10 Lithium alkyl disulfonate was added to the negative electrode material, and the positive electrode material was replaced with LFP (lithium iron phosphate). The preparation process of the positive electrode, negative electrode and battery in Example 7 (the preparation methods of Examples 8-10 and the comparative examples are the same as those in Example 7) is as follows: Preparation of the positive electrode: Polyvinylidene fluoride (PVDF), conductive agent (Super P), carbon nanotubes (CNT), and positive electrode material (lithium iron phosphate, LFP) are added to N-methylpyrrolidone (NMP) in a mass ratio of 2%:0.5%:1%:96.5% and mixed evenly to form a slurry. The slurry is then coated onto an aluminum foil current collector. The surface density of the positive electrode on one side is 200±3 g / m². 2 Cold-pressed to 2.6g / m³ 3 After punching, the positive electrode sheet is obtained.

[0051] Preparation of the negative electrode sheet: Sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber latex (SBR), conductive agent (SuperP), artificial graphite, and lithium methanedisulfonate were added to deionized water in a mass ratio of 1.2%:2%:1%:95.7%:0.1%, and thoroughly mixed. The slurry was then coated onto a copper foil current collector. The negative electrode surface density was determined according to an N / P ratio of 1.12, and cold-pressed to 1.65 g / m³. 3 After punching, the negative electrode sheet is formed.

[0052] Preparation of the battery to be injected with electrolyte: The separator, negative electrode, and positive electrode are stacked in a "Z" shape to obtain the bare cell to be injected with electrolyte. The cell is then packaged in aluminum-plastic film and baked to obtain the battery to be injected with electrolyte. The designed capacity of the battery to be injected with electrolyte is 5Ah.

[0053] The electrolyte was prepared with a mass ratio of LiPF6:EMC:EC:VC:FEC of 14%:61.2%:21%:3%:0.8%, and the electrolyte injection coefficient was calculated at 3.3g / Ah. After two sealing, formation and aging, the battery cell to be tested was obtained.

[0054] Compared with Example 7, Examples 8 and 9 only adjusted the amount of lithium methyl disulfonate added to the negative electrode and balanced it by adjusting the amount of active material added to the negative electrode. The corresponding lithium methyl disulfonate was 0.05% and 0.15%, respectively. In Example 10, lithium methyl disulfonate was replaced with lithium propyl disulfonate, while other aspects remained unchanged. The specific implementation scheme is shown in Table 3.

[0055] Comparative Example 4 Compared to Example 7, lithium alkyl disulfonate was not added to the negative electrode, while everything else remained the same.

[0056] Comparative Example 5 Compared to Example 7, in the negative electrode, lithium methyl disulfonate is replaced with the following lithium sulfonate compound A: Everything else is the same as in Example 7.

[0057] Comparative Example 6 Compared to Example 7, in the negative electrode, lithium methyl disulfonate is replaced with the following lithium sulfonate compound B: Everything else is the same as in Example 7.

[0058] Table 3

[0059] The performance test items of the lithium-ion batteries prepared in Examples 7-10 and Comparative Examples 4-6 are as follows, and the test results are shown in Table 4: First-time efficiency and specific capacity: Specific capacity = first discharge capacity / total weight of positive electrode active material; First-time efficiency = first discharge capacity / first charge capacity.

[0060] DCR (DC internal resistance) test: Charge the battery at 0.5C for 1 hour, i.e. the battery's state of charge is 50% SOC, and let it rest for ≥12 hours. After discharging at 2C for 30 seconds at 25℃, calculate the battery's discharge DCR through the voltage difference; calculate the DCR by discharging at 0.36C for 30 seconds at -20℃. Rate charging performance test: Charge the battery at 3C constant current and constant voltage to 3.65V, cut-off current is 0.05C, discharge at 1C to 2.0V, and calculate the constant current charging capacity ratio.

[0061] High-temperature cycling performance test: At 45℃, the capacity retention rate was tested at different cycles of 1C charge and discharge, with the cutoff voltage for charge and discharge being 2.0V~3.65V and the cutoff current for constant voltage charging being 0.05C; and the negative electrode ICP was tested after 1500 cycles in the discharge state, and the Fe content was recorded.

[0062] Other tests: EIS test of battery impedance at 50% SOC after 3 cycles, see [link to EIS test]. Figure 1 After the test, the battery was discharged to 2.0V, disassembled, and the XPS of the negative electrode in Example 7 was tested. See [link to relevant documentation]. Figure 2 .

[0063] Table 4

[0064] Compared with Comparative Example 4, Examples 7-10 showed little difference in initial efficiency and specific capacity. The slight improvement was mainly due to the participation of lithium alkyl disulfonate in film formation, which reduced the battery DCR, thereby improving kinetics and reducing battery polarization. This was also confirmed by the battery EIS test results. Figure 1 Adding lithium alkyl disulfonate to the negative electrode primarily contributes to a reduction in DCR and significantly improves the high-temperature cycling performance of the battery. This demonstrates that lithium alkyl disulfonate participates in negative electrode film formation, effectively reducing battery DCR while improving interfacial thermal stability. Compared with Comparative Example 4, Comparative Examples 5 and 6 show that lithium sulfonate compounds with similar structures all exhibit DCR reduction and cycle improvement effects. However, they are still affected by molecular structure and the molecular weight corresponding to one mole of lithium. The additive of this invention shows superior overall performance. In addition, the presence of lithium in the compound can participate in negative electrode film formation, providing more lithium-containing components, and can also effectively compensate for the loss of active lithium during cycling. Similar results have been verified in the practical application of lithium-containing binders such as PAA-Li and CMC-Li.

[0065] Figure 2XPS results for Example 7 showed that lithium methyl disulfonate participated in SEI formation, with higher levels of inorganic sulfides (160-162 eV) inside the SEI and increased sulfate content towards the outer edges (168-170 eV). In the LFP / Gr battery system, Examples 7-9 demonstrated that the optimal addition amount of methyl disulfonate was 0.1%. Compared to Example 10, Example 7 showed that methyl disulfonate was superior to propyl disulfonate, again due to the latter's larger molecular weight and longer carbon chain.

[0066] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An alkyl disulfonic acid electrode additive, characterized in that: Its general structural formula is shown in Formula I: Formula I Wherein, R is an alkyl group having 1-8 carbon atoms, or an alkyl group substituted with one or more halogen atoms.

2. The alkyl disulfonic acid electrode additive according to claim 1, characterized in that: R is an alkyl group having 1-3 carbon atoms; Preferably, the alkyl disulfonic acid electrode additive is selected from compounds with the following structural formulas: ； ； or, .

3. The method for preparing the alkyl disulfonic acid electrode additive according to claim 1 or 2, characterized in that: Includes the following steps: The lithium reagent solution was slowly added to the alkyl disulfonic acid solution, and the reaction was stirred to obtain crude alkyl disulfonic acid lithium. The alkyl disulfonic acid contained alkyl groups with 1-8 carbon atoms. The crude alkyl disulfonate is obtained by purification.

4. The method for preparing the alkyl disulfonic acid electrode additive according to claim 3, characterized in that: The lithium reagent is selected from lithium hydroxide, lithium hydroxide monohydrate, lithium carbonate, or lithium bicarbonate.

5. A cathode material, characterized in that: The electrode additive includes the alkyl disulfonic acid as described in claim 1 or 2, wherein the alkyl disulfonic acid electrode additive has a mass percentage of 0.01%-2%.

6. The cathode material according to claim 5, characterized in that: In the cathode material, the mass percentage of alkyl disulfonic acid electrode additive is 0.05%-2%, preferably 0.5%-2%.

7. A negative electrode material, characterized in that: The electrode additive includes the alkyl disulfonic acid as described in claim 1 or 2, wherein the alkyl disulfonic acid electrode additive has a mass percentage of 0.01%-2%.

8. The negative electrode material according to claim 7, characterized in that: In the negative electrode material, the mass percentage of alkyl disulfonic acid electrode additive is 0.05%-2%, preferably 0.05%-0.2%.

9. The positive electrode material according to claim 5 or 6, or the negative electrode material according to claim 7 or 8, characterized in that: The particle size D50 of the alkyl disulfonic acid electrode additive is 20nm-1500nm, preferably 50nm-400nm.

10. A lithium-ion battery, characterized in that: It includes the positive electrode material as described in claim 5 or 6 and / or the negative electrode material as described in claim 7 or 8.

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