Repair methods for lithium iron phosphate materials used in lithium-ion batteries

Abstract

This invention relates to the field of batteries, specifically to a method for repairing lithium iron phosphate (LFP) materials used in lithium-ion batteries. The method includes: providing LFP powder material to be repaired; detecting the lithium content in the LFP powder material to be repaired and thereby determining the required amount of lithium replenishment; providing a lithium salt corresponding to the amount of lithium replenishment; mixing the LFP powder to be repaired, the lithium salt, polyethylene glycol, and chitosan with water to form a homogeneous paste mixture, wherein the mass ratio of polyethylene glycol, chitosan, and LFP powder to be repaired is (10~20):(5~15):100; and calcining the mixture under a protective atmosphere to obtain the repaired LFP powder material. This invention provides a mild and safe repair method, effectively improving the drawbacks of uneven repair. Batteries repaired and assembled according to this invention exhibit high specific capacity, good lithium-ion transport efficiency, and cycle stability.

Description

Technical Field

[0001] This invention relates to the repair or regeneration of lithium iron phosphate materials used in lithium-ion batteries. Background Technology

[0002] Currently, the main cathode materials used in lithium-ion batteries include LiCoO2 (LCO) and LiNi. x Co y Mn 1-x-y O2 (NCM) and LiFePO4 (LFP) are two main types of batteries. LFP batteries hold a major share of the power battery market due to their low cost, long cycle life, and high safety. However, LFP batteries degrade over time, primarily due to repeated lithium-ion insertion and extraction and related side reactions, leading to performance degradation. Therefore, the lifespan of LFP batteries is typically only 5-8 years. Forecasts indicate that a large number of LFP batteries will reach the end of their lifespan in the coming years. Proper management of end-of-life batteries and promoting their effective recycling and reuse present a significant challenge.

[0003] In industry, pyrometallurgical and hydrometallurgical processes are commonly used to recover metals from spent lithium-ion batteries. However, these methods often involve complex processes, high energy consumption, and serious environmental problems. Specifically, pyrometallurgical processes require high temperatures, consume large amounts of energy, and produce harmful gases, leading to air pollution. Hydrometallurgical processes, on the other hand, use large quantities of chemical reagents, resulting in difficult-to-treat acidic or alkaline waste liquids.

[0004] Studies have shown that the capacity decay of LFPs over long-term use is usually due to the irreversible consumption of lithium ions. The lack of lithium creates lithium vacancies, leading to the oxidation of Fe(II) to Fe(III) and the generation of Li-Fe "anti-site" defects, which block lithium-ion transport channels, limit electrochemical reaction kinetics, and further deteriorate the electrochemical performance of the cathode material. In addition, the degradation of the carbon coating during charge and discharge processes also contributes to the deterioration of LFPs.

[0005] Mixing supplementary Li source with waste cathode material and regenerating LFP through solid-state sintering is a direct remediation method that can repair LFP while preserving its original structure, thus simplifying the recycling process and reducing energy consumption and environmental pollution. However, in this remediation method, a uniform solid-solid interface cannot be formed between the lithium source and the waste LFP due to insufficient contact.

[0006] In addition, although hydrothermal treatment can overcome the shortcomings of this solid-state sintering method and has the advantages of fast lithium replenishment and uniform reaction interface, the hydrothermal method usually needs to be carried out under high temperature and high pressure conditions, and its safety and practicality are particularly difficult to guarantee. Summary of the Invention

[0007] The purpose of this invention is to provide a safe and effective repair treatment for lithium iron phosphate materials.

[0008] According to one aspect of the present invention, a method for repairing lithium iron phosphate material for lithium-ion batteries is provided, comprising: Provide lithium iron phosphate powder material to be repaired; The lithium content in the lithium iron phosphate powder material to be repaired is detected, and the required amount of lithium replenishment is determined accordingly. Provide a lithium salt corresponding to the amount of lithium replenishment; The lithium iron phosphate powder to be repaired, lithium salt, polyethylene glycol, and chitosan were mixed with water to form a homogeneous paste. The mass ratio of polyethylene glycol, chitosan, and lithium iron phosphate powder to be repaired was (10~20):(5~15):100, respectively. The mixture obtained by calcination under a protective atmosphere yields the repaired lithium iron phosphate powder material.

[0009] According to the repair treatment method of the present invention, the calcination temperature is preferably 630℃~670℃, more preferably about 650℃; the calcination time is preferably 4h~6h, more preferably about 5h.

[0010] According to the repair treatment method of the present invention, lithium hydroxide is preferably used as the lithium salt. In this case, the amount of lithium added (molar amount) can be 1 to 1.3 times the theoretical value.

[0011] According to another aspect of the present invention, a lithium iron phosphate material for lithium-ion batteries is provided, which is prepared according to the above-described repair treatment method.

[0012] According to another aspect of the present invention, a lithium-ion battery is also provided, comprising a positive electrode made of the aforementioned lithium iron phosphate material.

[0013] This invention utilizes the synergistic water-retention effect of chitin and polyethylene glycol to effectively adsorb onto the surface of lithium iron phosphate powder particles to be repaired. The steric hindrance effect prevents particle agglomeration, ensuring uniform distribution within the green body. This avoids localized over- or under-burning caused by uneven particle distribution during sintering or calcination, ultimately yielding a repaired product with uniform composition and performance. Furthermore, this invention achieves a 2-3 nm thick uniform nitrogen-doped carbon coating while simultaneously restoring and regenerating the structure, further enhancing the electrochemical performance of the lithium iron phosphate material on top of the repair process.

[0014] In summary, this invention provides a mild and safe repair method that effectively improves upon the drawbacks of uneven repair. The (half)cell assembled according to this invention exhibits high specific capacity, good lithium-ion transport efficiency, and cycle stability, increasing the battery's specific capacity at 1 C from 32 mAh g⁻¹. -1 Increased to 143 mAh g-1 It retains 94% of its capacity after 450 cycles at a 1 C rate. Attached Figure Description

[0015] Figure 1 The ICP test results of the lithium iron phosphate material to be repaired and the normal lithium iron phosphate material are shown respectively.

[0016] Figure 2 The XRD test results of the above-mentioned different powder materials are shown.

[0017] Figure 3 XPS test results of the repaired lithium iron phosphate material are shown.

[0018] Figure 4 The specific capacity and cycle stability of different batteries are shown.

[0019] Figure 5 Cyclic voltammetry test graphs for different batteries are shown.

[0020] Figure 6 The long-cycle performance graph of the corresponding battery is shown. Detailed Implementation

[0021] The present invention will be described in detail below with reference to embodiments and comparative examples. Those skilled in the art should understand that these embodiments and comparative examples are for explanation only and not for limiting the present invention.

[0022] Recycling lithium iron phosphate powder material from spent batteries (cathode or cathode material to be repaired) 1. First, discharge the used battery in a 10% NaCl solution for 24 hours, then manually disassemble it to separate the anode, cathode and diaphragm.

[0023] 2. The cathode electrode was calcined at 400℃ for 1 hour to remove some carbon, binder, and other impurities. After crushing and sieving, waste lithium iron phosphate powder (active material powder) was obtained, which was labeled as S-LFP.

[0024] Figure 1 The ICP test results for the obtained S-LFP and commercially available (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., CAS No.: 15365-14-7) normal lithium iron phosphate (labeled C-LFP) are shown respectively. Figure 1 It can be seen that the Li / Fe molar ratio in S-LFP is 0.3073, and the Li / P molar ratio is 0.2979; while the Li / Fe molar ratio in C-LFP is 1.104, and the Li / P molar ratio is 1.049. Therefore, compared with C-LFP, S-LFP is severely deficient in lithium and needs to be repaired and replenished.

[0025] Example

[0026] Take 1g of the above S-LFP, 0.15g of polyethylene glycol (PEG), 0.1g of chitin, and 0.12g of lithium hydroxide. At room temperature, directly mix the above polyethylene glycol, chitin, lithium hydroxide, and waste lithium iron phosphate powder with water to form a homogeneous paste. Sinter the resulting mixture in a tube furnace purged with argon at 650 °C for 5 h to obtain regenerated lithium iron phosphate powder, labeled as R-LFP (10% Chitin + 15% PEG).

[0027] Comparative Example 1 The rest is the same as in the example, except that polyethylene glycol is not added. The resulting recycled powder is labeled as 10% Chitin (or Chitin).

[0028] Comparative Example 2 The rest is the same as in the example, except that chitosan is not added. The resulting recycled powder is labeled as 15% PEG (or PEG).

[0029] Figure 2 The XRD test results for the aforementioned different powders are shown. From Figure 2 As can be seen, compared with S-LFP, the positions of several important peaks in the recycled powder materials of Examples and Comparative Examples 1-2 are shifted to the left, consistent with the standard peak positions of lithium iron phosphate. This indicates that the iron phosphate phase in the waste lithium iron phosphate powder was completely converted into the lithium iron phosphate phase, and the crystal structure of the material was restored. However, compared with Comparative Examples 1-2, the peak intensity of Examples is the highest, indicating that its crystallinity is the highest and its crystal structure is the most stable.

[0030] Figure 3 The XPS test results for the R-LFP are shown. Figure 3 As shown, the peak position in R-LFP is the same as that of ferrous iron, indicating that it does not contain ferric iron (no impurities such as ferric phosphate and ferric oxide), meaning that the oxidation state of iron has been reduced.

[0031] Assembled battery (R-LFP) The R-LFP, acetylene black, and PVDF binder were mixed in a mass ratio of 8:1:1. NMP (in a mass ratio of 20:1 to PVDE) was then added to form a homogeneous slurry, which was then coated onto aluminum foil and dried at 80°C for 12 h to obtain an active material loading of 2.5 mg / cm³. -2 The cathode plate.

[0032] The cathode plate was formed into a circular electrode with a diameter of 12 mm using a plate punch. The anode was a lithium metal sheet with a diameter of 15 mm and a thickness of 0.45 mm. Assembly of the CR2032 coin cell was carried out in a glove box, using lithium metal, Celgard 2400, and 1.0 M LiPF6 as the counter electrode, separator, and electrolyte, respectively, with a solution of ethylene carbonate / dimethyl carbonate / diethyl carbonate (EC:DMC:DEC = 1:1:1 by volume). Before testing, the battery was placed in a constant-temperature incubator at 30 °C for 6 hours to ensure complete electrolyte penetration.

[0033] Assembled batteries (S-LFP) / Chitin / PEG Other assembled batteries (R-LFP) differ only in that they are assembled by replacing R-LFP with S-LFP, 10% Chitin and 15% PEG respectively.

[0034] Battery performance test The NEWARE battery (CT4008T-5V50mA-164) testing system was used to test Li within a voltage range of 2.5~4.3 V. + / Li was used for charge / discharge performance testing. Figure 4 The specific capacity and cycle stability of half-cells assembled based on S-LFP and R-LFP lithium iron phosphate cathode powders are shown at 1C rate. Figure 4 It can be seen that the specific capacity of the battery (R-LFP) is 143 mAh g. -1 This is significantly higher than the 32 mAh g of the battery (S-LFP). -1 This indicates that the capacity of the repaired lithium iron phosphate battery has been significantly improved. Furthermore, the battery (R-LFP) retained 94% of its capacity after 450 charge-discharge cycles, demonstrating good cycle stability.

[0035] In addition, cyclic voltammetry (CV) performance tests were performed on a Corrtest electrochemical workstation. Figure 5 The cyclic voltammograms of each battery are shown. Figure 5 As shown, the battery (R-LFP) exhibits a more symmetrical redox peak and a higher peak current compared to the battery (S-LFP), indicating that the repaired material R-LFP has good charge-discharge reversibility. Furthermore, Comparative Examples 1 and 2 also show improved redox peaks, indicating that chitosan and PEG can also play a certain repair role when used alone, but the repair effect is limited and obviously not as good as the examples.

[0036] In addition, long-cycle performance tests were conducted on the aforementioned batteries. Figure 6 The long-cycle performance graphs for the corresponding batteries are shown. For example... Figure 6As shown, compared to the powder materials of the embodiments, the powder materials prepared according to Comparative Example 1 and Comparative Example 2 have lower specific capacity, faster capacity decay rate, and worse cycle stability. Specifically, after 400 cycles, the specific capacity of Comparative Example 1 and Comparative Example 2 decreased significantly, which also indicates that the repair degree of Comparative Example 1 and Comparative Example 2 is limited and cannot be fully repaired.

[0037] In summary, during the remediation process of this invention, PEG and Chitin exhibit a significant synergistic effect: while introducing carbon and nitrogen sources, they also synergistically promote the smooth progress of reduction and water retention processes. The remediation method of this invention simplifies the process flow, is environmentally friendly, and can be applied on a large scale industrial basis.

Claims

1. A method for repairing lithium iron phosphate material used in lithium-ion batteries, comprising: Provide lithium iron phosphate powder material to be repaired; The lithium content in the lithium iron phosphate powder material to be repaired is detected, and the required amount of lithium replenishment is determined accordingly. Provide a lithium salt corresponding to the amount of lithium replenishment; The lithium iron phosphate powder to be repaired, lithium salt, polyethylene glycol, and chitosan were mixed with water to form a homogeneous paste. The mass ratio of polyethylene glycol, chitosan, and lithium iron phosphate powder to be repaired was (10~20):(5~15):100, respectively. The mixture obtained by calcination under a protective atmosphere yields the repaired lithium iron phosphate powder material.

2. The repair treatment method according to claim 1, wherein the calcination temperature is 630℃~670℃ and the calcination time is 4h~6h.

3. The repair treatment method according to claim 1, wherein the lithium salt is lithium hydroxide.

4. The repair treatment method according to claim 3, wherein the amount of lithium replenishment is 1 to 1.3 times the theoretical value.

5. A lithium iron phosphate material for lithium-ion batteries, prepared by the repair treatment method according to any one of claims 1-4.

6. A lithium-ion battery comprising a positive electrode made of lithium iron phosphate material according to claim 5.

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