Method for purifying benzene tetracarboxylic acid lithium

Abstract

The invention discloses a purification method of lithium benzenetetracarboxylic acid, and relates to the technical field of lithium ion batteries. The method comprises the following steps: reacting pyromellitic acid with a methanol solution of lithium methoxide to obtain a crude product of benzenetetracarboxylic acid, and purifying the crude product of benzenetetracarboxylic acid, namely dissolving the crude product of benzenetetracarboxylic acid into a mixed solution of water and ethanol under a heating condition, slowly cooling the solution, separating out a solid, filtering, and carrying out vacuum drying on the obtained solid to obtain a lithium benzenetetracarboxylic acid crystal. The purity of the purified lithium benzenetetracarboxylic acid is high; the purified lithium benzenetetracarboxylic acid is used as a lithium battery additive, has more excellent performance than unpurified lithium benzenetetracarboxylic acid and a common lithium battery additive, and has a wide industrialization prospect.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and specifically to a method for purifying lithium phenyltetracarboxylate. Background Technology

[0002] The article “Enhanced Lithium Storage Capacity of a Tetralithium 1,2,4,5-Benzenetetracarboxylate (Li4C10H2O8) Salt Through Crystal Structure Transformation”, Handi Setiadi Cahyadi, et al., ACS Applied Materials & Interfaces, Vol. 10, No. 20, pp. 17183–17194, 2018-04-30 (hereinafter referred to as the background article) reports a method for preparing lithium benzoate. Pyromellitic acid and lithium methoxide solids are dissolved separately in methanol. The lithium methoxide solution is added dropwise to the pyromellitic acid methanol solution at room temperature. After the reaction is complete, the mixture is filtered, and the solid is dried to obtain lithium benzoate. However, this background article does not describe the purification steps, nor does it introduce the yield and purity of lithium benzoate. The cycling performance and rate performance of the prepared unpurified lithium benzoate also need to be improved. We found that the reaction of pyromellitic acid with lithium methoxide inevitably produces a small amount of incompletely reacted byproducts, which need to be purified to obtain high-purity lithium pyromellitic acid. Summary of the Invention

[0003] The purpose of this invention is to provide a method for purifying lithium phenyltetracarboxylate.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A method for purifying lithium phenyltetracarboxylate includes the following steps: Under heating conditions, crude lithium phenyltetracarboxylate was dissolved in a mixed solution of water and ethanol. The solution was slowly cooled, and a solid precipitated. The solid was filtered and dried under vacuum to obtain lithium phenyltetracarboxylate crystals.

[0005] Preferably, in step (1), the volume ratio of water to ethanol in the water and ethanol mixture is 2:1, the ratio of crude lithium benzoate to the mixture is 1g:3-6ml, the heating temperature is 70-90℃, the solution is slowly cooled at a rate of 0.5-1℃ / min, the slow cooling temperature is 30-50℃, the vacuum drying temperature is 60-100℃, and the vacuum drying time is 24-30h.

[0006] The beneficial effects of this invention are: The inventors discovered that in the process of preparing lithium phenyltetracarboxylate by reacting pyromellitic acid with a methanol solution of lithium methoxide, the main impurities are lithium methoxide, lithium diphthalate, and lithium triphthalate. Traditional recrystallization purification processes are insufficient to remove these impurities, necessitating more targeted purification techniques. This invention dissolves crude lithium phenyltetracarboxylate in a water-ethanol mixed solution. Utilizing the different solubilities of lithium phenyltetracarboxylate and impurities in the water-ethanol mixture, a cooling crystallization method is employed. By selecting the appropriate solvent (a 2:1 water-ethanol mixture) and controlling the cooling rate and temperature, high-purity lithium phenyltetracarboxylate crystals are precipitated. This invention employs a specific mixed solvent cooling crystallization purification method, which demonstrates excellent purification effects for impurities such as lithium methoxide, lithium diphthalate, and lithium triphthalate, yielding high-purity lithium phenyltetracarboxylate crystals.

[0007] The purified lithium phenyltetracarboxylate of this invention has high purity (>99.99%) and low impurity content (free acid <10ppm, moisture <10ppm, chloride ion <3ppm, sulfate ion <3ppm). As a lithium battery additive, the purified lithium phenyltetracarboxylate exhibits superior performance compared to unpurified lithium phenyltetracarboxylate and commonly used lithium battery additives. Its high-temperature performance, room-temperature performance, rate performance, and low-temperature performance are significantly better than VC and VC compound systems. A battery with 1.5% of the lithium phenyltetracarboxylate of this invention shows a capacity retention of 86.5%-91.6% after 300 cycles at 50℃, a reversible capacity of 840-920mAh / g after 100 cycles at room temperature, a reversible capacity of 80-102mAh / g at a current density of 4A / g, and a discharge capacity retention of 86.2%-88.6% from 0.5C to 20℃, demonstrating broad industrialization prospects.

[0008] Using the higher-purity lithium phenylenetetracarboxylate obtained by the method of this invention as an additive in lithium batteries can reduce side reactions in the electrolyte, thereby further improving battery performance. The reversible capacity after 100 cycles at room temperature increases from 700 mAh / g in the previous article to 840-920 mAh / g, and the reversible capacity at a current density of 4 A / g increases from 50 mAh / g in the previous article to 80-102 mAh / g. Attached Figure Description

[0009] Figure 1 This is the H-NMR spectrum of lithium phenyltetracarboxylate purified in Example 4 of the present invention. Detailed Implementation

[0010] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. However, those skilled in the art will understand that the embodiments described below are only some embodiments of the present invention, not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. 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.

[0011] In this embodiment of the invention, crude lithium phenylenetetracarboxylate was obtained by the following preparation method: Pyromellitic acid was dissolved in methanol to prepare a 0.2 mol / L methanol solution of pyromellitic acid. A 10% methanol solution of lithium methoxide was added dropwise to the methanol solution of pyromellitic acid (the molar ratio of pyromellitic acid to lithium methoxide was 1:4.0). The reaction was carried out at 1500 rpm for 12 hours at room temperature. The resulting solid was filtered and dried to obtain crude lithium pyromellitic acid. Example 1

[0012] 100g of crude lithium phenyltetracarboxylate was dissolved in a mixed solution of 200ml + 100ml water + ethanol under heating at 70℃. The solution was slowly cooled to 30℃ at a rate of 0.5℃ / min, and the precipitated solid was vacuum dried at 60℃ for 24h to obtain lithium phenyltetracarboxylate crystals. The purity was 99.992%. The high-temperature performance, room-temperature performance, rate performance, and low-temperature performance of lithium phenyltetracarboxylate were tested in a 4.5V NCM811 / graphite pouch battery system. The lithium-ion battery electrolyte solvent was 30wt% DMC + 25wt% DEC, the electrolyte was lithium hexafluorophosphate with a content of 30wt%-40wt%, and the additive lithium phenyltetracarboxylate content was 1.5%. The results were compared with commercially available additives (1.5% VC, 1.5% VC + 1.5% FEC, 1.5% VC + 2% 1,3PS) and the lithium phenyltetracarboxylate described in the background article. In Example 1, the battery with added lithium benzoate achieved a capacity retention of 86.5% after 300 cycles at 50°C, while Comparative Examples 1, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), and 11 (1.5% VC + 2% 1,3PS) only retained 83.2%, 73.4%, 78.5%, and 79.2%, respectively. The battery with added lithium benzoate in Example 1 had a reversible capacity of 840 mAh / g after 100 cycles at room temperature, while Comparative Examples 1, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3PS), and 12 (background article: lithium benzoate) only retained 790 mAh / g. Ah / g, 650mAh / g, 670mAh / g, 680mAh / g, 700mAh / g; In Example 1, the battery with added lithium benzoate achieved a discharge capacity retention rate of 86.2% at 0.5C-20℃, while Comparative Examples 1, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), and 11 (1.5% VC + 2% 1,3PS) only achieved 82.5%, 65.2%, and 700mAh / g, respectively. 71.4%, 71.7%; In Example 1, the reversible capacity of the battery with added lithium benzoate at a current density of 4A / g was 80mAh / g, while that of Comparative Examples 1, 9 (1.5%VC), 10 (1.5%VC+1.5%FEC), 11 (1.5%VC+2%1,3PS), and 12 (Lithium benzoate in the background article) was only 70mAh / g, 44mAh / g, 48mAh / g, 55mAh / g, and 50mAh / g, respectively. Example 2

[0013] 100g of crude lithium phenyltetracarboxylate was dissolved in a mixed solution of 400ml + 200ml water + ethanol under heating at 90℃. The solution was slowly cooled to 50℃ at a rate of 1℃ / min. The precipitated solid was dried under vacuum at 100℃ for 30h to obtain lithium phenyltetracarboxylate crystals. The purity was 99.993%.

[0014] Lithium phenylenetetroxide (PPTO) was tested for high-temperature performance, room-temperature performance, rate performance, and low-temperature performance in a 4.5V NCM811 / graphite pouch cell system. The lithium-ion battery electrolyte solvent was 30wt% DMC + 25wt% DEC, the electrolyte was lithium hexafluorophosphate (LiPF6) at a content of 30wt%-40wt%, and the additive PTO was 1.5%. The results were compared with commercially available additives (1.5% VC, 1.5% VC + 1.5% FEC, 1.5% VC + 2% 1,3PS) and the PTO mentioned in the background article. In Example 2, the battery with added PTO achieved a capacity retention of 87.5% after 300 cycles at 50°C, while Comparative Examples 2, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), and 11 (1.5% VC + 2%) showed significantly better performance. The 1,3PS batteries in Example 2 had reversible capacities of only 83.7%, 73.4%, 78.5%, and 79.2% respectively after 100 cycles at room temperature. In Comparative Examples 2 (1,3PS), the reversible capacity of the battery with added lithium benzoate was 850 mAh / g, while Comparative Examples 2, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3PS), and 12 (Lithium benzoate) had only 810 mAh / g, 650 mAh / g, 670 mAh / g, 680 mAh / g, and 700 mAh / g respectively. The battery with added lithium benzoate in Example 2 achieved a discharge capacity retention rate of 86.5% at 0.5C-20℃, while Comparative Examples 2... Comparative Example 9 (1.5% VC), Comparative Example 10 (1.5% VC + 1.5% FEC), and Comparative Example 11 (1.5% VC + 2% 1,3PS) had reversible capacities of only 82.7%, 65.2%, 71.4%, and 71.7%, respectively. In Example 2, the battery with added lithium benzoate had a reversible capacity of 85 mAh / g at a current density of 4 A / g, while Comparative Example 2, Comparative Example 9 (1.5% VC), Comparative Example 10 (1.5% VC + 1.5% FEC), Comparative Example 11 (1.5% VC + 2% 1,3PS), and Comparative Example 12 (background article: lithium benzoate) had reversible capacities of only 78 mAh / g, 44 mAh / g, 48 mAh / g, 55 mAh / g, and 50 mAh / g, respectively. Example 3

[0015] 100g of crude lithium phenyltetracarboxylate was dissolved in a mixed solution of 260ml + 130ml water + ethanol under heating at 75℃. The solution was slowly cooled to 35℃ at a rate of 0.7℃ / min. The precipitated solid was dried under vacuum at 70℃ for 26h to obtain lithium phenyltetracarboxylate crystals. The purity was 99.996%.

[0016] Lithium phenylenetetroxide (PPTO) was tested for high-temperature performance, room-temperature performance, rate performance, and low-temperature performance in a 4.5V NCM811 / graphite pouch cell system. The lithium-ion battery electrolyte solvent was 30wt% DMC + 25wt% DEC, the electrolyte was lithium hexafluorophosphate (30wt%-40wt%), and the additive PPTO content was 1.5%. The results were compared with commercially available additives (1.5% VC, 1.5% VC + 1.5% FEC, 1.5% VC + 2% 1,3PS) and the PPTO described in the background article. In Example 3, the battery with added PPTO achieved a capacity retention of 90.3% after 300 cycles at 50°C, while Comparative Examples 3, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), and 11 (1.5% VC + 2%) showed significantly better performance. The 1,3PS batteries in Example 3 had reversible capacities of only 82.1%, 73.4%, 78.5%, and 79.2% respectively; the battery with added lithium benzoate in Example 3 had a reversible capacity of 880 mAh / g after 100 cycles at room temperature, while the comparative examples 3, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3PS), and 12 (background article: lithium benzoate) had only 770 mAh / g, 650 mAh / g, 670 mAh / g, 680 mAh / g, and 700 mAh / g respectively; the battery with added lithium benzoate in Example 3 achieved a discharge capacity retention rate of 87.6% at 0.5C-20℃, while the comparative examples 3, Comparative Examples 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), and 11 (1.5% VC + 2% 1,3PS) had reversible capacities of only 81.2%, 65.2%, 71.4%, and 71.7%, respectively. In Example 3, the battery with added lithium benzoate had a reversible capacity of 88 mAh / g at a current density of 4 A / g, while Comparative Examples 3, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3PS), and 12 (background article: lithium benzoate) had reversible capacities of only 70 mAh / g, 44 mAh / g, 48 mAh / g, 55 mAh / g, and 50 mAh / g, respectively. Example 4

[0017] 100g of crude lithium phenyltetracarboxylate was dissolved in a mixed solution of 300ml + 150ml water + ethanol under heating at 80℃. The solution was slowly cooled to 40℃ at a rate of 0.7℃ / min. The precipitated solid was dried under vacuum at 80℃ for 27h to obtain lithium phenyltetracarboxylate crystals. The purity was 99.997%.

[0018] Lithium phenylenetetroxide (PPD) was tested for high-temperature performance, room-temperature performance, rate performance, and low-temperature performance in a 4.5V NCM811 / graphite pouch cell system. The lithium-ion battery electrolyte solvent was 30wt% DMC + 25wt% DEC, the electrolyte was lithium hexafluorophosphate (LiPF6) at a content of 30wt%-40wt%, and the additive PPD was 1.5%. The results were compared with commercially available additives (1.5% VC, 1.5% VC + 1.5% FEC, 1.5% VC + 2% 1,3PS) and the PPD described in the background article. In Example 4, the battery with added PPD achieved a capacity retention of 91.6% after 300 cycles at 50°C, while Comparative Examples 4, 5, 6, 7, 8, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), and 11 (1.5% VC + 2%) showed significantly better performance. The 1,3PS batteries had reversible capacities of only 83.5%, 81.6%, 81.7%, 82.2%, 83.6%, 73.4%, 78.5%, and 79.2%, respectively. In Example 4, the battery with added lithium benzoate had a reversible capacity of 920 mAh / g after 100 cycles at room temperature, while Comparative Examples 4, 5, 6, 7, 8, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3PS), and 12 (background article: lithium benzoate) had capacities of only 820 mAh / g, 780 mAh / g, 790 mAh / g, 810 mAh / g, and 830 mAh / g, respectively. 650mAh / g, 670mAh / g, 680mAh / g, 700mAh / g; In Example 4, the battery with added lithium benzoate achieved a discharge capacity retention rate of 88.6% at 0.5C-20℃, while Comparative Examples 4, 5, 6, 7, 8, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), and 11 (1.5% VC + 2% 1,3PS) only achieved 82.1%, 81.1%, 81.3%, 82.0%, 82.2%, and 65.2%, respectively. 71.4%, 71.7%; In Example 4, the reversible capacity of the battery with added lithium benzoate at a current density of 4 A / g was 102 mAh / g, while the comparative examples 4, 5, 6, 7, 8, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3 PS), and 12 (background article: lithium benzoate) had only 74 mAh / g, 65 mAh / g, 67 mAh / g, 71 mAh / g, 75 mAh / g, 44 mAh / g, 48 mAh / g, 55 mAh / g, and 50 mAh / g, respectively. Example 5

[0019] 100g of crude lithium phenyltetracarboxylate was dissolved in a mixed solution of 320ml + 160ml water + ethanol under heating at 85℃. The solution was slowly cooled to 45℃ at a rate of 0.9℃ / min. The precipitated solid was dried under vacuum at 85℃ for 28h to obtain lithium phenyltetracarboxylate crystals. The purity was 99.994%.

[0020] Lithium phenylenetetroxide (PPTO) was tested for high-temperature performance, room-temperature performance, rate performance, and low-temperature performance in a 4.5V NCM811 / graphite pouch cell system. The lithium-ion battery electrolyte solvent was 30wt% DMC + 25wt% DEC, the electrolyte was lithium hexafluorophosphate (LiPF6) at a content of 30wt%-40wt%, and the additive PTO was 1.5%. The results were compared with commercially available additives (1.5% VC, 1.5% VC + 1.5% FEC, 1.5% VC + 2% 1,3PS) and the PTO mentioned in the background article. In Example 5, the battery with added PTO achieved a capacity retention of 87.2% after 300 cycles at 50°C, while Comparative Examples 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), and 11 (1.5% VC + 2%) showed significantly better performance. The capacity retention rates of the batteries with added lithium benzoate in Example 5 were only 73.4%, 78.5%, and 79.2% respectively; the reversible capacity of the battery with added lithium benzoate in Example 5 after 100 cycles at room temperature was 870 mAh / g, while that of Comparative Examples 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3PS), and 12 (Lithium benzoate in the background article) were only 650 mAh / g, 670 mAh / g, 680 mAh / g, and 700 mAh / g respectively; the capacity retention rate of the battery with added lithium benzoate in Example 5 reached 86.3% during discharge at 0.5C-20℃, while that of Comparative Examples 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), and 11 (1.5% VC + 2% 1,3PS) were only 82.1%, 65.2%, and 12.3%, respectively. 71.4%, 71.7%; In Example 5, the reversible capacity of the battery with added lithium benzoate at a current density of 4A / g was 83mAh / g, while that of Comparative Example 9 (1.5%VC), Comparative Example 10 (1.5%VC+1.5%FEC), Comparative Example 11 (1.5%VC+2%1,3PS), and Comparative Example 12 (background article: lithium benzoate) was only 44mAh / g, 48mAh / g, 55mAh / g, and 50mAh / g, respectively. Example 6

[0021] 100g of crude lithium phenyltetracarboxylate was dissolved in a mixed solution of 360ml + 180ml water + ethanol under heating at 90℃. The solution was slowly cooled to 40℃ at a rate of 1℃ / min. The precipitated solid was dried under vacuum at 95℃ for 29h to obtain lithium phenyltetracarboxylate crystals. The purity was 99.993%.

[0022] Lithium phenylenetetroxide (PPTO) was tested for high-temperature performance, room-temperature performance, rate performance, and low-temperature performance in a 4.5V NCM811 / graphite pouch cell system. The lithium-ion battery electrolyte solvent was 30wt% DMC + 25wt% DEC, the electrolyte was lithium hexafluorophosphate (LiPF6) at a content of 30wt%-40wt%, and the additive PTO content was 1.5%. The results were compared with commercially available additives (1.5% VC, 1.5% VC + 1.5% FEC, 1.5% VC + 2% 1,3PS) and the PTO mentioned in the background article. In Example 6, the battery with added PTO achieved a capacity retention of 88.1% after 300 cycles at 50°C, while Comparative Examples 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), and 11 (1.5% VC + 2%) showed significantly lower retention. The capacity retention rates of the batteries with added lithium benzoate in Example 6 were only 73.4%, 78.5%, and 79.2% respectively; the reversible capacity of the battery with added lithium benzoate in Example 6 after 100 cycles at room temperature was 890 mAh / g, while that of Comparative Examples 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3PS), and 12 (Lithium benzoate in the background article) were only 650 mAh / g, 670 mAh / g, 680 mAh / g, and 700 mAh / g respectively; the capacity retention rate of the battery with added lithium benzoate in Example 6 at 0.5C-20℃ reached 87.1%, while that of Comparative Examples 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), and 11 (1.5% VC + 2% 1,3PS) were only 82.1%, 65.2% respectively. 71.4%, 71.7%; In Example 6, the reversible capacity of the battery with added lithium benzoate at a current density of 4A / g was 92mAh / g, while that of Comparative Example 9 (1.5%VC), Comparative Example 10 (1.5%VC+1.5%FEC), Comparative Example 11 (1.5%VC+2%1,3PS), and Comparative Example 12 (background article: lithium benzoate) was only 44mAh / g, 48mAh / g, 55mAh / g, and 50mAh / g, respectively. Comparative Example 1 (Low Cooling Temperature)

[0023] 100g of crude lithium phenyltetracarboxylate was dissolved in a mixed solution of 200ml + 100ml water + ethanol under heating at 70℃. The solution was slowly cooled to 20℃ at a rate of 0.5℃ / min. The precipitated solid was dried under vacuum at 60℃ for 24h to obtain lithium phenyltetracarboxylate crystals. The purity was 99.926%.

[0024] Lithium phenylenetetroxide (PPTO) was tested for high-temperature performance, room-temperature performance, rate performance, and low-temperature performance in a 4.5V NCM811 / graphite pouch cell system. The lithium-ion battery electrolyte solvent was 30wt% DMC + 25wt% DEC, the electrolyte was lithium hexafluorophosphate (30wt%-40wt%), and the additive PPTO content was 1.5%. The results were compared with commercially available additives (1.5% VC, 1.5% VC + 1.5% FEC, 1.5% VC + 2% 1,3PS) and the PPTO described in the background article. In Example 1, the battery with added PPTO achieved a capacity retention of 86.5% after 300 cycles at 50°C, while Comparative Examples 1, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), and 11 (1.5% VC + 2%) showed significantly better performance. The 1,3PS batteries in Example 1 had reversible capacities of only 83.2%, 73.4%, 78.5%, and 79.2% respectively. The battery with added lithium benzoate in Example 1 had a reversible capacity of 840 mAh / g after 100 cycles at room temperature, while Comparative Examples 1, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3PS), and 12 (Lithium benzoate) had only 790 mAh / g, 650 mAh / g, 670 mAh / g, 680 mAh / g, and 700 mAh / g respectively. The battery with added lithium benzoate in Example 1 achieved a discharge capacity retention rate of 86.2% at 0.5C-20℃, while Comparative Examples 1, Comparative Examples 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), and 11 (1.5% VC + 2% 1,3PS) had reversible capacities of only 82.5%, 65.2%, 71.4%, and 71.7%, respectively. In Example 1, the battery with added lithium benzoate had a reversible capacity of 80 mAh / g at a current density of 4 A / g, while Comparative Examples 1, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3PS), and 12 (background article: lithium benzoate) had reversible capacities of only 70 mAh / g, 44 mAh / g, 48 mAh / g, 55 mAh / g, and 50 mAh / g, respectively. Comparative Example 2 (High Cooling Temperature)

[0025] 100g of crude lithium phenyltetracarboxylate was dissolved in a mixed solution of 400ml + 200ml water + ethanol under heating at 90℃. The solution was slowly cooled to 60℃ at a rate of 1℃ / min. The precipitated solid was dried under vacuum at 100℃ for 30h to obtain lithium phenyltetracarboxylate crystals. The purity was 99.932%.

[0026] Lithium phenylenetetroxide (PPTO) was tested for high-temperature performance, room-temperature performance, rate performance, and low-temperature performance in a 4.5V NCM811 / graphite pouch cell system. The lithium-ion battery electrolyte solvent was 30wt% DMC + 25wt% DEC, the electrolyte was lithium hexafluorophosphate (LiPF6) at a content of 30wt%-40wt%, and the additive PTO was 1.5%. The results were compared with commercially available additives (1.5% VC, 1.5% VC + 1.5% FEC, 1.5% VC + 2% 1,3PS) and the PTO mentioned in the background article. In Example 2, the battery with added PTO achieved a capacity retention of 87.5% after 300 cycles at 50°C, while Comparative Examples 2, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), and 11 (1.5% VC + 2%) showed significantly better performance. The 1,3PS batteries in Example 2 had reversible capacities of only 83.7%, 73.4%, 78.5%, and 79.2% respectively after 100 cycles at room temperature. In Comparative Examples 2 (1,3PS), the reversible capacity of the battery with added lithium benzoate was 850 mAh / g, while Comparative Examples 2, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3PS), and 12 (Lithium benzoate) had only 810 mAh / g, 650 mAh / g, 670 mAh / g, 680 mAh / g, and 700 mAh / g respectively. The battery with added lithium benzoate in Example 2 achieved a discharge capacity retention rate of 86.5% at 0.5C-20℃, while Comparative Examples 2... Comparative Example 9 (1.5% VC), Comparative Example 10 (1.5% VC + 1.5% FEC), and Comparative Example 11 (1.5% VC + 2% 1,3PS) had reversible capacities of only 82.7%, 65.2%, 71.4%, and 71.7%, respectively. In Example 2, the battery with added lithium benzoate had a reversible capacity of 85 mAh / g at a current density of 4 A / g, while Comparative Example 2, Comparative Example 9 (1.5% VC), Comparative Example 10 (1.5% VC + 1.5% FEC), Comparative Example 11 (1.5% VC + 2% 1,3PS), and Comparative Example 12 (background article: lithium benzoate) had reversible capacities of only 78 mAh / g, 44 mAh / g, 48 mAh / g, 55 mAh / g, and 50 mAh / g, respectively. Comparative Example 3 (Slow Cooling Rate)

[0027] 100g of crude lithium phenyltetracarboxylate was dissolved in a mixed solution of 260ml + 130ml water + ethanol under heating at 75℃. The solution was slowly cooled to 35℃ at a rate of 0.3℃ / min. The precipitated solid was dried under vacuum at 70℃ for 26h to obtain lithium phenyltetracarboxylate crystals. The purity was 99.917%.

[0028] Lithium phenylenetetroxide (PPTO) was tested for high-temperature performance, room-temperature performance, rate performance, and low-temperature performance in a 4.5V NCM811 / graphite pouch cell system. The lithium-ion battery electrolyte solvent was 30wt% DMC + 25wt% DEC, the electrolyte was lithium hexafluorophosphate (30wt%-40wt%), and the additive PPTO content was 1.5%. The results were compared with commercially available additives (1.5% VC, 1.5% VC + 1.5% FEC, 1.5% VC + 2% 1,3PS) and the PPTO described in the background article. In Example 3, the battery with added PPTO achieved a capacity retention of 90.3% after 300 cycles at 50°C, while Comparative Examples 3, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), and 11 (1.5% VC + 2%) showed significantly better performance. The 1,3PS batteries in Example 3 had reversible capacities of only 82.1%, 73.4%, 78.5%, and 79.2% respectively; the battery with added lithium benzoate in Example 3 had a reversible capacity of 880 mAh / g after 100 cycles at room temperature, while the comparative examples 3, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3PS), and 12 (background article: lithium benzoate) had only 770 mAh / g, 650 mAh / g, 670 mAh / g, 680 mAh / g, and 700 mAh / g respectively; the battery with added lithium benzoate in Example 3 achieved a discharge capacity retention rate of 87.6% at 0.5C-20℃, while the comparative examples 3, Comparative Examples 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), and 11 (1.5% VC + 2% 1,3PS) had reversible capacities of only 81.2%, 65.2%, 71.4%, and 71.7%, respectively. In Example 3, the battery with added lithium benzoate had a reversible capacity of 88 mAh / g at a current density of 4 A / g, while Comparative Examples 3, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3PS), and 12 (background article: lithium benzoate) had reversible capacities of only 70 mAh / g, 44 mAh / g, 48 mAh / g, 55 mAh / g, and 50 mAh / g, respectively. Comparative Example 4 (Fast Cooling Rate)

[0029] 100g of crude lithium phenyltetracarboxylate was dissolved in a mixed solution of 300ml + 150ml water + ethanol under heating at 80℃. The solution was slowly cooled to 40℃ at a rate of 1.2℃ / min. The precipitated solid was dried under vacuum at 80℃ for 27h to obtain lithium phenyltetracarboxylate crystals. The purity was 99.934%.

[0030] Lithium phenylenetetroxide (PPTO) was tested for high-temperature performance, room-temperature performance, rate performance, and low-temperature performance in a 4.5V NCM811 / graphite pouch cell system. The lithium-ion battery electrolyte solvent was 30wt% DMC + 25wt% DEC, the electrolyte was lithium hexafluorophosphate (LiPF6) at a content of 30wt%-40wt%, and the additive PTO was 1.5%. The results were compared with commercially available additives (1.5% VC, 1.5% VC + 1.5% FEC, 1.5% VC + 2% 1,3PS) and the PTO mentioned in the background article. In Example 4, the battery with added PTO achieved a capacity retention of 91.6% after 300 cycles at 50°C, while Comparative Examples 4, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), and 11 (1.5% VC + 2%) showed significantly higher retention. The 1,3PS batteries in Example 4 had reversible capacities of only 83.5%, 73.4%, 78.5%, and 79.2% respectively; the battery with added lithium benzoate in Example 4 had a reversible capacity of 920 mAh / g after 100 cycles at room temperature, while the comparative examples 4, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3PS), and 12 (background article: lithium benzoate) had only 820 mAh / g, 650 mAh / g, 670 mAh / g, 680 mAh / g, and 700 mAh / g respectively; the battery with added lithium benzoate in Example 4 achieved a discharge capacity retention rate of 88.6% at 0.5C-20℃ ... + 1.5% FEC), 11 (1.5% VC + 2% 1,3PS), and 12 (background article: lithium benzoate) had only 820 mAh / g, 650 mAh / g, 670 mAh / g, 680 mAh / g, and 700 mAh / g respectively; the battery with added lithium benzoate in Comparative Example 9 (1.5% VC), Comparative Example 10 (1.5% VC + 1.5% FEC), and Comparative Example 11 (1.5% VC + 2% 1,3PS) had reversible capacities of only 82.1%, 65.2%, 71.4%, and 71.7%, respectively. In Example 4, the battery with added lithium benzoate had a reversible capacity of 102 mAh / g at a current density of 4 A / g, while Comparative Examples 4, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3PS), and 12 (background article: lithium benzoate) had reversible capacities of only 74 mAh / g, 44 mAh / g, 48 mAh / g, 55 mAh / g, and 50 mAh / g, respectively. Comparative Example 5 (Water was used as the purification solvent)

[0031] 100g of crude lithium phenyltetracarboxylate was dissolved in 450ml of water under heating at 80℃. The solution was slowly cooled to 40℃ at a rate of 0.8℃ / min. The precipitated solid was dried under vacuum at 80℃ for 27h to obtain lithium phenyltetracarboxylate crystals. The purity was 99.921%.

[0032] Lithium phenylenetetroxide (PPTO) was tested for high-temperature performance, room-temperature performance, rate performance, and low-temperature performance in a 4.5V NCM811 / graphite pouch cell system. The lithium-ion battery electrolyte solvent was 30wt% DMC + 25wt% DEC, the electrolyte was lithium hexafluorophosphate (30wt%-40wt%), and the additive PPTO content was 1.5%. The results were compared with commercially available additives (1.5% VC, 1.5% VC + 1.5% FEC, 1.5% VC + 2% 1,3PS) and the PPTO described in the background article. In Example 4, the battery with added PPTO achieved a capacity retention of 91.6% after 300 cycles at 50°C, while Comparative Examples 5, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), and 11 (1.5% VC + 2%) showed significantly higher retention. The 1,3PS batteries in Example 4 had reversible capacities of only 81.6%, 73.4%, 78.5%, and 79.2% respectively after 100 cycles at room temperature. The batteries with added lithium benzoate in Example 4 had a reversible capacity of 920 mAh / g after 100 cycles at room temperature, while Comparative Examples 5, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3PS), and 12 (Lithium benzoate) had only 780 mAh / g, 650 mAh / g, 670 mAh / g, 680 mAh / g, and 700 mAh / g respectively. The battery with added lithium benzoate in Example 4 achieved a discharge capacity retention rate of 88.6% at 0.5C-20℃, while Comparative Examples 5, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3PS), and 12 (Lithium benzoate) had a reversible capacity of only 780 mAh / g, 650 mAh / g, 670 mAh / g, 680 mAh / g, and 700 mAh / g respectively. Comparative Example 9 (1.5% VC), Comparative Example 10 (1.5% VC + 1.5% FEC), and Comparative Example 11 (1.5% VC + 2% 1,3PS) had reversible capacities of only 81.1%, 65.2%, 71.4%, and 71.7%, respectively. In Example 4, the battery with added lithium benzoate had a reversible capacity of 102 mAh / g at a current density of 4 A / g, while Comparative Examples 5, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3PS), and 12 (background article: lithium benzoate) had reversible capacities of only 65 mAh / g, 44 mAh / g, 48 mAh / g, 55 mAh / g, and 50 mAh / g, respectively. Comparative Example 6 (Ethanol was used as the purification solvent)

[0033] 100g of crude lithium phenyltetracarboxylate was dissolved in 450ml of ethanol under heating at 80℃. The solution was slowly cooled to 40℃ at a rate of 0.8℃ / min. The precipitated solid was dried under vacuum at 80℃ for 27h to obtain lithium phenyltetracarboxylate crystals. The purity was 99.922%.

[0034] Lithium phenylenetetroxide (PPTO) was tested for high-temperature performance, room-temperature performance, rate performance, and low-temperature performance in a 4.5V NCM811 / graphite pouch cell system. The lithium-ion battery electrolyte solvent was 30wt% DMC + 25wt% DEC, the electrolyte was lithium hexafluorophosphate (30wt%-40wt%), and the additive PPTO content was 1.5%. The results were compared with commercially available additives (1.5% VC, 1.5% VC + 1.5% FEC, 1.5% VC + 2% 1,3PS) and the PPTO described in the background article. In Example 4, the battery with added PPTO achieved a capacity retention of 91.6% after 300 cycles at 50°C, while Comparative Examples 6, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), and 11 (1.5% VC + 2%) showed significantly better performance. The reversible capacity of the battery with added lithium phenylene oxide in Example 4 was only 81.7%, 73.4%, 78.5%, and 79.2% respectively after 100 cycles at room temperature. In contrast, the reversible capacity of the batteries with added lithium phenylene oxide in Example 4 was 920 mAh / g after 100 cycles at room temperature, while that of Comparative Examples 6, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1.3PS), and 12 (Lithium phenylene oxide) was only 790 mAh / g, 650 mAh / g, 670 mAh / g, 680 mAh / g, and 700 mAh / g respectively. The battery with added lithium phenylene oxide in Example 4 achieved a discharge capacity retention rate of 88.6% at 0.5C-20℃, while that of Comparative Examples 6, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1.3PS), and 12 (Lithium phenylene oxide) was only 790 mAh / g, 650 mAh / g, 670 mAh / g, 680 mAh / g, and 700 mAh / g respectively. Comparative Example 9 (1.5% VC), Comparative Example 10 (1.5% VC + 1.5% FEC), and Comparative Example 11 (1.5% VC + 2% 1,3PS) had reversible capacities of only 81.3%, 65.2%, 71.4%, and 71.7%, respectively. In Example 4, the battery with added lithium benzoate had a reversible capacity of 102 mAh / g at a current density of 4 A / g, while Comparative Examples 6, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3PS), and 12 (background article: lithium benzoate) had reversible capacities of only 67 mAh / g, 44 mAh / g, 48 mAh / g, 55 mAh / g, and 50 mAh / g, respectively. Comparative Example 7 (purification solvent: water: ethanol = 1:1)

[0035] 100g of crude lithium phenyltetracarboxylate was dissolved in a mixed solution of 225ml water and 225ml ethanol under heating at 80℃. The solution was slowly cooled to 40℃ at a rate of 0.8℃ / min. The precipitated solid was dried under vacuum at 80℃ for 27h to obtain lithium phenyltetracarboxylate crystals. The purity was 99.933%.

[0036] Lithium phenylenetetroxide (PPTO) was tested for high-temperature performance, room-temperature performance, rate performance, and low-temperature performance in a 4.5V NCM811 / graphite pouch cell system. The lithium-ion battery electrolyte solvent was 30wt% DMC + 25wt% DEC, the electrolyte was lithium hexafluorophosphate (30wt%-40wt%), and the additive PPTO content was 1.5%. The results were compared with commercially available additives (1.5% VC, 1.5% VC + 1.5% FEC, 1.5% VC + 2% 1,3PS) and the PPTO described in the background article. In Example 4, the battery with added PPTO achieved a capacity retention of 91.6% after 300 cycles at 50°C, while Comparative Examples 7, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), and 11 (1.5% VC + 2%) showed significantly lower performance. The 1,3PS batteries in Example 4 had reversible capacities of only 82.2%, 73.4%, 78.5%, and 79.2% respectively after 100 cycles at room temperature. The batteries with added lithium benzoate in Example 4 had a reversible capacity of 920 mAh / g after 100 cycles at room temperature, while Comparative Examples 7, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3PS), and 12 (Lithium benzoate) had only 810 mAh / g, 650 mAh / g, 670 mAh / g, 680 mAh / g, and 700 mAh / g respectively. The battery with added lithium benzoate in Example 4 achieved a discharge capacity retention rate of 88.6% at 0.5C-20℃, while Comparative Examples 7, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3PS), and 12 (Lithium benzoate) had only 82.2%, 73.4%, 78.5%, and 79.2% respectively. Comparative Example 9 (1.5% VC), Comparative Example 10 (1.5% VC + 1.5% FEC), and Comparative Example 11 (1.5% VC + 2% 1,3PS) had reversible capacities of only 82.0%, 65.2%, 71.4%, and 71.7%, respectively. In Example 4, the battery with added lithium benzoate had a reversible capacity of 102 mAh / g at a current density of 4 A / g, while Comparative Examples 7, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3PS), and 12 (Lithium benzoate from the background article) had reversible capacities of only 71 mAh / g, 44 mAh / g, 48 mAh / g, 55 mAh / g, and 50 mAh / g, respectively. Comparative Example 8 (purification solvent: water: ethanol = 3:1)

[0037] 100g of crude lithium phenyltetracarboxylate was dissolved in a mixed solution of 336ml water and 112ml ethanol under heating at 80℃. The solution was slowly cooled to 40℃ at a rate of 0.8℃ / min. The precipitated solid was dried under vacuum at 80℃ for 27h to obtain lithium phenyltetracarboxylate crystals. The purity was 99.942%.

[0038] Lithium phenylenetetroxide (PPD) was tested for high-temperature performance, room-temperature performance, rate performance, and low-temperature performance in a 4.5V NCM811 / graphite pouch cell system. The lithium-ion battery electrolyte solvent was 30wt% DMC + 25wt% DEC, the electrolyte was lithium hexafluorophosphate (30wt%-40wt%), and the additive PPD was 1.5%. The results were compared with commercially available additives (1.5% VC, 1.5% VC + 1.5% FEC, 1.5% VC + 2% 1,3PS) and the PPD described in the background article. In Example 4, the battery with added PPD achieved a capacity retention of 91.6% after 300 cycles at 50°C, while Comparative Examples 8, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), and 11 (1.5% VC + 2%) showed significantly better performance. The 1,3PS batteries in Example 4 had reversible capacities of only 83.6%, 73.4%, 78.5%, and 79.2% respectively; the battery with added lithium benzoate in Example 4 had a reversible capacity of 920 mAh / g after 100 cycles at room temperature, while Comparative Examples 8, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3PS), and 12 (Lithium benzoate) had only 830 mAh / g, 650 mAh / g, 670 mAh / g, 680 mAh / g, and 700 mAh / g respectively; the battery with added lithium benzoate in Example 4 achieved a discharge capacity retention rate of 88.6% at 0.5C-20℃, while Comparative Examples 8, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3PS), and 12 (Lithium benzoate) had only 83.6%, 73.4%, 78.5%, and 79.2% respectively. Comparative Examples 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), and 11 (1.5% VC + 2% 1,3PS) had reversible capacities of only 82.2%, 65.2%, 71.4%, and 71.7%, respectively. In Example 4, the battery with added lithium benzoate had a reversible capacity of 102 mAh / g at a current density of 4 A / g, while Comparative Examples 8, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3PS), and 12 (background article: lithium benzoate) had reversible capacities of only 75 mAh / g, 44 mAh / g, 48 mAh / g, 55 mAh / g, and 50 mAh / g, respectively. Comparative Example 9

[0039] The VC used in this comparative example was purchased commercially from McLean, with a purity of 98% and a grade of CAS872-36-6. Similarly, high-temperature cycle stability, room-temperature cycle performance, and low-temperature performance were tested in a 4.5V NCM811 / graphite pouch battery system. The lithium-ion battery electrolyte solvent was 30wt% DMC + 25wt% DEC, the electrolyte was lithium hexafluorophosphate with a content of 30wt%-40wt%, and the VC additive content was 1.5%. Comparative Example 10

[0040] This comparative example uses a combination of 1.5% VC + 1.5% FEC. The FEC was purchased commercially from Shanghai Fluorine Technology Co., Ltd., with a purity of 99% and a grade of 114435-02-8. Similarly, high-temperature cycle stability, room-temperature cycle performance, and low-temperature performance were tested in a 4.5V NCM811 / graphite pouch battery system. The lithium-ion battery electrolyte solvent was 30wt% DMC + 25wt% DEC, the electrolyte was lithium hexafluorophosphate with a content of 30wt%-40wt%, and the additive content was 1.5% VC + 1.5% FEC. Comparative Example 11

[0041] This comparative example uses a combination of 1.5% VC + 2% 1,3PS. The 1,3PS was purchased commercially from Jihechang, with a purity of 99.9% and a grade of 1120-71-4. Similarly, high-temperature cycle stability, room-temperature cycle performance, and low-temperature performance were tested in a 4.5V NCM811 / graphite pouch battery system. The lithium-ion battery electrolyte solvent was 30wt% DMC + 25wt% DEC, the electrolyte was lithium hexafluorophosphate with a content of 30wt%-40wt%, and the additive content was 1.5% VC + 2% 1,3PS. Comparative Example 12

[0042] The background article describes lithium phenyltetracarboxylate prepared at room temperature without purification.

[0043]

[0044] Table 1 shows that the lithium phenyltetracarboxylate obtained in each embodiment has high purity (>99.99%) and low impurity content (free acid <10ppm, water <10ppm, chloride ion <3ppm, sulfate ion <3ppm). In contrast, the comparative example (with a different purification solvent, cooling rate, and cooling temperature than the embodiments) has higher impurity content and significantly lower purity, indicating that the purification solvent, cooling rate, and cooling temperature used in the embodiments of this invention are more effective.

[0045] The purity of lithium phenylenetetracarboxylate was determined using the internal standard method with tetramethylsilane as the internal standard and deuterated water as the solvent. A small amount of lithium phenylenetetracarboxylate and tetramethylsilane were dissolved in deuterated water to prepare the test solution. Then, the 1H NMR spectrum was obtained. Formula for calculation using the internal standard method: Purity % = (A x ·M i ·W i ·P i ) / (A i ·M x ·W x )×100% in: A x / A i =Integral value of peak area of ​​analyte / internal standard M x / M i =Number of analyte / number of internal standard particles W x / W i =Analyte / Internal Standard (sample weight in mg) P i =Purity of internal standard (%).

[0046] The purity of lithium phenyltetracarboxylate was obtained.

[0047]

[0048] As shown in Table 2, the high-temperature performance, room-temperature performance, rate performance, and low-temperature performance of the lithium phenylene oxide obtained in the examples are significantly higher than those of the comparative examples. In Example 4, the battery with added lithium phenylene oxide achieved a capacity retention rate of 91.6% after 300 cycles at 50°C, while the comparative examples 4, 5, 6, 7, 8, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), and 11 (1.5% VC + 2%) showed significantly lower performance. The 1,3PS batteries had reversible capacities of only 83.5%, 81.6%, 81.7%, 82.2%, 83.6%, 73.4%, 78.5%, and 79.2%, respectively. In Example 4, the battery with added lithium benzoate had a reversible capacity of 920 mAh / g after 100 cycles at room temperature, while Comparative Examples 4, 5, 6, 7, 8, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3PS), and 12 (background article: lithium benzoate) had capacities of only 820 mAh / g, 780 mAh / g, 790 mAh / g, 810 mAh / g, and 830 mAh / g, respectively. 650mAh / g, 670mAh / g, 680mAh / g, 700mAh / g; In Example 4, the battery with added lithium benzoate achieved a discharge capacity retention rate of 88.6% at 0.5C-20℃, while Comparative Examples 4, 5, 6, 7, 8, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), and 11 (1.5% VC + 2% 1,3PS) only achieved 82.1%, 81.1%, 81.3%, 82.0%, 82.2%, and 65.2%, respectively. 71.4%, 71.7%; In Example 4, the reversible capacity of the battery with added lithium benzoate at a current density of 4 A / g was 102 mAh / g, while the comparative examples 4, 5, 6, 7, 8, 9 (1.5% VC), 10 (1.5% VC + 1.5% FEC), 11 (1.5% VC + 2% 1,3 PS), and 12 (background article: lithium benzoate) had only 74 mAh / g, 65 mAh / g, 67 mAh / g, 71 mAh / g, 75 mAh / g, 44 mAh / g, 48 mAh / g, 55 mAh / g, and 50 mAh / g, respectively.

[0049] This demonstrates that the mixed solvent in the embodiments of the present invention exhibits superior cooling rate and temperature control. Furthermore, the lithium phenylenetetroxide of the present invention, as a lithium battery additive, demonstrates better performance than commonly used additives on the market and the unpurified lithium phenylenetroxide described in the background article.

[0050] Figure 1 This is the H NMR spectrum of lithium phenylenetetracarboxylate from Example 4. From... Figure 1 The 1H NMR spectrum showed two absorption peaks at 4.71 ppm and 7.37 ppm. The 4.71 ppm peak was attributed to the deuterated solvent heavy water, and the 7.37 ppm peak was attributed to lithium phenyltetracarboxylate. The presence of only one lithium phenyltetracarboxylate signal in the 1H NMR spectrum indicates that the product is very pure and free of other organic impurities.

Claims

1. A method for purifying lithium phenylenetetracarboxylate, characterized in that, Includes the following steps: Under heating conditions, crude lithium benzoate was dissolved in a mixed solution of water and ethanol. The solution was slowly cooled, and a solid precipitated. The solid was filtered and dried under vacuum to obtain lithium benzoate crystals.

2. The purification method for lithium phenylenetetracarboxylate according to claim 1, characterized in that, In step (1), the volume ratio of water to ethanol in the mixed solution is 2:1, the ratio of crude lithium benzoate to the mixed solution is 1g:3-6ml, the heating temperature is 70-90℃, the solution is slowly cooled at a rate of 0.5-1℃ / minute, the slow cooling temperature is 30-50℃, the vacuum drying temperature is 60-100℃, and the vacuum drying time is 24-30h.

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