A high-efficiency short-period lithium iron phosphate-graphite battery pulse formation method and a lithium iron phosphate-graphite battery prepared by using the method

Abstract

The application discloses a high-efficiency short-period lithium iron phosphate-graphite battery pulse formation method and a lithium iron phosphate-graphite battery prepared by using the method, and applies to the technical field of lithium battery manufacturing, and comprises the following steps: obtaining a lithium iron phosphate-graphite battery to be formed; wherein the battery is composed of a lithium iron phosphate positive electrode, a graphite negative electrode, an electrolyte and a diaphragm; pulse formation treatment is carried out by using the following three kinds of square wave pulse current regulation modes: scheme one: a pulse+rest mode of a charging pulse 1s+rest 1s; scheme two: a bidirectional pulse mode of a 1C charging pulse 1.5s+0.5C reverse discharging pulse 0.5s; scheme three: a bidirectional pulse charging+constant current discharging mode of a 1.5C charging pulse 1.5s+1C reverse discharging pulse 0.5s; when the charging and discharging voltage reaches a preset cut-off threshold value, the pulse formation is completed. The application realizes the simultaneous consideration of formation efficiency, initial efficiency and long cycle stability.

Description

Technical Field

[0001] This invention relates to the field of lithium battery manufacturing technology, and more specifically to a high-efficiency short-cycle lithium iron phosphate-graphite battery pulse formation method and a lithium iron phosphate-graphite battery prepared using this method. Background Technology

[0002] Lithium iron phosphate (LFP)-graphite batteries have become core energy storage devices for new energy vehicles and large-scale energy storage power stations due to their high safety, long cycle life, low cost, and environmental friendliness. The formation process is a crucial step in lithium battery manufacturing, with the core objective of constructing a stable, dense, and highly lithium-ion-conductive solid electrolyte interphase (SEI) film on the surface of the graphite anode. The quality of the SEI film directly determines the battery's initial coulombic efficiency (first efficiency), cycle stability, rate performance, and production cycle.

[0003] Traditional formation processes generally employ DC constant current (CC) or constant current constant voltage (CC-CV) modes, inducing SEI film formation through low-rate charging (0.05~0.15C). However, this process has significant drawbacks: First, the formation cycle is too long, with low-rate charging typically resulting in a single-cycle formation time exceeding 20 hours, severely limiting production efficiency. Second, ions easily form concentration polarization on the electrode surface, leading to uneven SEI film composition, high porosity, and easy breakage and recombination during cycling, causing continuous capacity decay. Third, the electrolyte decomposition is insufficient, resulting in a low proportion of highly stable inorganic phases (such as LiF) in the SEI film, high interfacial impedance, and low initial efficiency.

[0004] Existing pulsed formation technologies still have many limitations: for example, the pulsed formation method disclosed in patent CN113540573A uses a low-rate pulse of 0.05~0.15C, which can improve the density of the SEI film, but does not solve the problem of long formation cycle, and does not involve bidirectional pulse design; patent CN120767279A designs a pulse voltage scheme to address the volume expansion problem of silicon anodes, but its electrode system (silicon anode) is significantly different from the lithium iron phosphate-graphite system, and the pulse parameters (voltage regulation, millisecond-level high and low potentials) cannot be directly applied, and it does not focus on improving formation efficiency.

[0005] In summary, existing technologies lack high-rate, short-cycle pulsed formation solutions for lithium iron phosphate-graphite systems, making it difficult to simultaneously achieve formation efficiency, first-cycle efficiency, and long-cycle stability.

[0006] Therefore, how to provide a highly efficient short-cycle pulse formation method for lithium iron phosphate-graphite batteries that can significantly optimize the overall performance of the battery and promote the industrial upgrading of lithium iron phosphate-graphite batteries, as well as the lithium iron phosphate-graphite batteries prepared using this method, is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0007] In view of this, the present invention provides a high-efficiency, short-cycle pulse formation method for lithium iron phosphate-graphite batteries and a lithium iron phosphate-graphite battery prepared using this method. It aims to overcome the shortcomings of traditional DC formation and existing pulse formation technologies, achieving the triple goals of shortened formation cycle, improved first-cycle efficiency, and long-cycle stability.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A high-efficiency, short-cycle pulsed formation method for lithium iron phosphate-graphite batteries, comprising: Step 1: Obtain the lithium iron phosphate-graphite battery to be formed; wherein, the lithium iron phosphate-graphite battery is composed of a lithium iron phosphate positive electrode, a graphite negative electrode, an electrolyte and a separator; Step 2: The battery to be formed is subjected to pulse formation treatment using the following three square wave pulse current control methods for the charging and discharging stages: Option 1: Use a pulse + rest mode with a 1s charging pulse followed by a 1s rest period; Option 2: Use a bidirectional pulse mode of 1C charging pulse for 1.5s + 0.5C reverse discharge pulse for 0.5s; Option 3: Use a bidirectional pulse charging + constant current discharging mode with a 1.5C charging pulse of 1.5s + a 1C reverse discharging pulse of 0.5s; Step 3: When the charging and discharging voltage reaches the preset cutoff threshold, the pulse formation is completed.

[0009] Optionally, in step 1, the lithium iron phosphate-graphite battery is one of the following: a pouch battery, a cylindrical battery, or a square battery, with a rated capacity of 10mAh~200Ah, and after the lithium iron phosphate-graphite battery is assembled, it needs to be left to stand in an environment of 25℃ for 5 hours.

[0010] Optionally, in step 1, the cell manufacturing conditions for the lithium iron phosphate-graphite battery are as follows: The ambient temperature is 25±2℃, the relative humidity is ≤30%, the operating atmosphere is inert gas, and the oxygen content is ≤1ppm.

[0011] Optionally, in step 1, the electrolyte is 1.0~1.2 mol / L LiPF6 dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate, with a volume ratio of EC:DEC=1:2; where EC represents ethylene carbonate and DEC represents diethyl carbonate, and 10% of fluoroethylene carbonate relative to the total mass of the mixed solvent is added as a film-forming additive.

[0012] Optionally, in step 2, a pulse + rest mode of 1s charging pulse + 1s rest is adopted, specifically as follows: The 1C charging pulse lasts for 1 second, then rests for 1 second, and this process is repeated until the charging cutoff voltage is reached. Then the 1C discharging pulse lasts for 1 second, then rests for 1 second, and this process is repeated until the discharging cutoff voltage is reached.

[0013] Optionally, in step 2, a bidirectional pulse mode of 1C charging pulse for 1.5s + 0.5C reverse discharge pulse for 0.5s is adopted, specifically as follows: A 1C charging pulse is applied for 1.5 seconds, followed by a 0.5C reverse discharge pulse for 0.5 seconds. This process is repeated until the voltage reaches the charging cutoff voltage. Then, a 1C discharge pulse is applied for 1.5 seconds, followed by a 0.5C reverse charging pulse for 0.5 seconds. This process is repeated until the voltage reaches the discharge cutoff voltage.

[0014] Optionally, in step 2, a bidirectional pulse charging + constant current discharging mode of 1.5C charging pulse for 1.5s + 1C reverse discharging pulse for 0.5s is adopted, specifically as follows: A 1.5C charging pulse is applied for 1.5 seconds, followed by a 1C reverse discharge pulse for 0.5 seconds. This process is repeated to charge to the cutoff voltage, and then discharged at a constant current of 0.2C to the cutoff voltage.

[0015] Optionally, in step 2, the single pulse cycle period of schemes one, two, and three is 2s, and the number of cycles is adaptively adjusted according to the charge and discharge cutoff conditions.

[0016] Optionally, in step 3, the preset charging and discharging cutoff thresholds are 4V and 2V, respectively.

[0017] The present invention also provides a lithium iron phosphate-graphite battery prepared by a high-efficiency short-cycle lithium iron phosphate-graphite battery pulse formation method, wherein the battery has an initial coulombic efficiency ≥95%, a capacity retention rate ≥90% after 500 cycles under 1C charge-discharge test conditions, and a total formation time per cycle ≤6h.

[0018] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a high-efficiency short-cycle lithium iron phosphate-graphite battery pulse formation method and a lithium iron phosphate-graphite battery prepared by the method, achieving the following beneficial effects: (1) High-rate pulse design: adopts a high formation rate of 1~1.5C, which is different from the low formation rate of 0.05~0.15C in the existing technology, and significantly shortens the formation cycle (single cycle is shortened by more than 16 hours). (2) Bidirectional pulse control: Schemes 2 and 3 introduce reverse discharge pulses, which are different from the existing unidirectional pulse or voltage control. They can accurately control the SEI film composition and avoid the accumulation of unstable products. (3) System-specific adaptation: The parameters are designed for the electrochemical characteristics of the lithium iron phosphate-graphite system, which is different from the pulse scheme of special systems such as silicon anode. It has strong compatibility and significant effect. (4) Triple performance synergy: Simultaneously achieves shortened formation cycle, improved first-time efficiency, and stable long-term cycle, solving the core contradiction that existing technologies cannot achieve simultaneously. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the method flow provided by the present invention.

[0021] Figure 2 A schematic diagram of the square wave pulse current-time curve for Embodiment 2 of the present invention.

[0022] Figure 3 A schematic diagram showing the comparison curves of the battery 1C charge-discharge cycle capacity retention rate of Embodiments 2, 3, and 4 and the comparative examples provided by the present invention.

[0023] Figure 4 The diagram shows the X-ray diffraction (XRD) pattern and refinement results of the lithium iron phosphate cathode after formation in Example 2 of this invention.

[0024] Figure 5 The diagram shows the X-ray diffraction (XRD) pattern and refinement results of the lithium iron phosphate cathode after comparative formation, as provided by this invention.

[0025] Figure 6 Schematic diagrams of X-ray diffraction (XRD) patterns of graphite anodes after conversion in Examples 2, 3, and 4 and the comparative example provided by the present invention.

[0026] Figure 7 This is a schematic diagram of the electrochemical impedance spectroscopy (EIS) of the battery after formation in Example 2 of the present invention.

[0027] Figure 8 This is a schematic diagram of the electrochemical impedance spectroscopy (EIS) of the comparatively formed battery provided by the present invention.

[0028] Figure 9 A schematic diagram of the square wave pulse current-time curve for Embodiment 3 of the present invention.

[0029] Figure 10 The diagram shows the X-ray diffraction (XRD) pattern and refinement results of the lithium iron phosphate cathode after formation in Example 3 of this invention.

[0030] Figure 11The comparative example and Example 3 are schematic diagrams of in-situ XRD patterns and refinement results of graphite negative electrodes provided by the present invention.

[0031] Figure 12 This is a schematic diagram of the electrochemical impedance spectroscopy (EIS) of the battery after formation in Example 3 of the present invention.

[0032] Figure 13 A schematic diagram of the square wave pulse current-time curve of Embodiment 4 provided by the present invention.

[0033] Figure 14 The diagram shows the X-ray diffraction (XRD) pattern and refinement results of the lithium iron phosphate cathode after formation in Example 4 of this invention.

[0034] Figure 15 This is a schematic diagram of the electrochemical impedance spectroscopy (EIS) of the battery after formation in Example 4 of the present invention. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Example 1: Embodiment 1 of this invention discloses a high-efficiency short-cycle lithium iron phosphate-graphite battery pulse formation method, such as... Figure 1 As shown, it includes: Step 1: Obtain the lithium iron phosphate-graphite battery to be formed; wherein, the lithium iron phosphate-graphite battery is composed of a lithium iron phosphate positive electrode, a graphite negative electrode, an electrolyte and a separator.

[0037] Lithium iron phosphate-graphite batteries are one of the following types of batteries: pouch, cylindrical, and square. Their rated capacity is 10mAh~200Ah. After assembly, lithium iron phosphate-graphite batteries need to be left to stand at 25℃ for 5 hours.

[0038] The manufacturing conditions for lithium iron phosphate-graphite battery cells are as follows: The ambient temperature is 25±2℃ to avoid excessively high temperatures that could exacerbate side reactions, or excessively low temperatures that could prolong the formation time. The relative humidity is ≤30%, and the operating atmosphere is an inert gas with an oxygen content ≤1ppm.

[0039] The electrolyte is 1.0~1.2 mol / L LiPF6 dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC), with a volume ratio of EC:DEC = 1:2. Here, EC represents ethylene carbonate and DEC represents diethyl carbonate. Fluorinated ethylene carbonate (FEC) is added at 10% of the total mass of the mixed solvent as a film-forming additive, i.e., 1.0 M LiPF6 in EC:DEC = 1:2 Vol% with 10% FEC system. This system, in synergy with the pulsed formation process, can promote the formation of high-quality inorganic phases such as LiF and reduce interfacial impedance.

[0040] Step 2: Since the core of pulse formation is the pulse current regulation during the charge-discharge (CD) stage, the following three square wave pulse current regulation methods for the charge-discharge stage are used for pulse formation of the battery to be formed: Option 1 (CD) stage ): Employs a pulse + rest mode with a 1s charging pulse followed by a 1s rest period; Option 2 (CD) stage It adopts a bidirectional pulse mode of 1C charging pulse for 1.5s + 0.5C reverse discharge pulse for 0.5s; Option 3 (C) stage ): It adopts a bidirectional pulse charging + constant current discharging mode with a 1.5C charging pulse of 1.5s + a 1C reverse discharging pulse of 0.5s.

[0041] The pulse + rest mode, consisting of a 1s charging pulse followed by a 1s rest period, is adopted, specifically as follows: The 1C charging pulse lasts for 1 second, followed by a 1-second rest period. This process is repeated until the charging cutoff voltage is reached. Then, the 1C discharging pulse lasts for 1 second, followed by a 1-second rest period. This process is repeated until the discharging cutoff voltage is reached. The "charging-resting" mode alleviates concentration polarization, promotes uniform electrolyte decomposition, and induces dense growth of the SEI film.

[0042] It adopts a bidirectional pulse mode of 1C charging pulse for 1.5s + 0.5C reverse discharge pulse for 0.5s, specifically as follows: A 1C charging pulse is applied for 1.5s, followed by a 0.5C reverse discharge pulse for 0.5s. This process is repeated until the voltage reaches the charging cutoff voltage. Then, a 1C discharge pulse is applied for 1.5s, followed by a 0.5C reverse charging pulse for 0.5s. This process is repeated until the voltage reaches the discharge cutoff voltage. The reverse pulse can remove unstable organic intermediates adsorbed on the electrode surface and enhance the formation of inorganic phases such as LiF.

[0043] It adopts a bidirectional pulse charging + constant current discharging mode of 1.5C charging pulse for 1.5s + 1C reverse discharging pulse for 0.5s, specifically as follows: A 1.5C charging pulse is applied for 1.5 seconds, followed by a 1C reverse discharge pulse for 0.5 seconds. This process is repeated to charge to the cutoff voltage, followed by a 0.2C constant current discharge to the cutoff voltage. High-rate charging shortens the formation time, and the reverse pulse balances the interface charge distribution, avoiding over-polarization.

[0044] The single pulse cycle period for schemes one, two, and three is 2 seconds, and the number of cycles is adaptively adjusted according to the charge and discharge cutoff conditions.

[0045] Step 3: When the charging and discharging voltage reaches the preset cutoff threshold, the pulse formation is completed.

[0046] The preset charge and discharge cutoff thresholds are 4V and 2V, respectively, to ensure that the SEI film is fully formed and there is no risk of overcharging.

[0047] Example 2: Embodiment 2 of this invention discloses a specific implementation application of pulsed formation of high-efficiency short-cycle lithium iron phosphate-graphite batteries using Scheme 1 in Embodiment 1 (CD). stage :1Cpulse 1s -rest 1s ),as follows: (1) Battery to be formed: Square lithium iron phosphate-graphite battery with a rated capacity of 10.8mAh. The positive electrode active material is lithium iron phosphate with an areal density of 12.3mg / cm² and a compaction density of 1.9g / cm³. The negative electrode active material is natural graphite with an areal density of 5.8mg / cm² and a compaction density of 1.1g / cm³. The electrolyte is 1.0mol / L LiPF6 in EC:DEC=1:2 Vol% with 10%FEC. The electrolyte usage is 0.8mL / Ah. After assembly, the battery is placed in a test cabinet at 25℃ for 5h.

[0048] (2) Pulse formation parameters: The pulse current-time curve of Embodiment 2 of the present invention is shown in Figure 2. Figure 2 As shown in the figure, it can be clearly observed that Scheme 1 adopts a symmetrical square wave pulse + static formation mode. Both the charging and discharging stages adopt a symmetrical cycle of "1s pulse excitation + 1s relaxation". The formation charging cutoff voltage is 4V and the discharge cutoff voltage is 2V. The cycle period of a single pulse is 2s, and the number of cycles is adaptively adjusted according to the formation cutoff condition.

[0049] (3) Electrochemical performance testing: The formation processes and battery electrochemical performance of Examples 2, 3, and 4 are compared with those of the comparative examples, as shown in Table 1; the 1C charge-discharge cycle capacity retention rates of the batteries in Examples 2, 3, and 4 are compared with those of the comparative examples, as shown in Table 1. Figure 3 As shown; combined Figure 3As shown in Table 1, the total formation time for a single cycle in Example 2 of the present invention is 4.04 h, and the initial coulombic efficiency of the battery is 95.81%. After formation, after 500 cycles at 25°C and 1C charge-discharge, the battery discharge capacity retention rate is 91.58%.

[0050] Table 1. Comparison of formation processes and battery electrochemical performance between Examples 2, 3, and 4 and the comparative examples.

[0051] (4) Mechanism analysis and testing: The XRD pattern and Rietveld refinement results of the lithium iron phosphate cathode after formation in Example 2 of this invention are as follows: Figure 4 As shown, all diffraction peaks in the spectrum perfectly match the standard PDF card (PDF#40-1499) for olivine-type LiFePO4, with no extraneous peaks appearing. After precise calculation, the Fe antisite defect content of the lithium iron phosphate cathode in Example 2 of this invention is only 3.71%, far lower than... Figure 5 The comparative example shown is 10.02% of the XRD pattern of the lithium iron phosphate cathode after formation and the result refined by Rietveld, proving that the pulse formation scheme can effectively suppress the structural distortion and Fe dissolution of the lithium iron phosphate cathode and maintain the crystal structure stability of the cathode material.

[0052] The XRD patterns of the graphite anodes after formation in Examples 2, 3, and 4 of this invention are as follows: Figure 6 As shown in the spectrum, in Example 2 of the present invention, the characteristic peak of the graphite (002) crystal plane appears near 26.5°, and the characteristic peak of the copper foil current collector appears at 43.3° and 50.4°. Compared with the comparative example, the diffraction peak of the graphite (002) crystal plane is stronger, the peak shape is more symmetrical, and there is no obvious shift or broadening. Table 2 shows a comparison of the gas evolution amounts during the formation processes in Examples 2, 3, and 4 of this invention with those in the comparative examples. In Example 2 of this invention, the total H2 evolution amount was 6.87 × 10⁻⁶. -7 The total amount of O2 released was 2.66 × 10⁻⁶ mol. -8 The total amount of CO2 released was 5.38 × 10⁻⁶ mol. -8 The total amount of C2H4 precipitated was 1.02 × 10⁻⁶ mol. -7 The amount of four characteristic gases released was lower than that in the comparative example. Among them, H2 and C2H4 are characteristic products of the reduction decomposition of electrolyte solvent. The significant reduction in the amount of both gases released proves that the "pulse + standby" mode of Example 2 of this invention can effectively suppress the excessive reduction decomposition of EC and DEC solvents in the electrolyte. The significant decrease in CO2 release indicates that the pulse relaxation process reduces the oxidation side reaction of the electrolyte on the electrode surface, which is consistent with the result of improved cathode structural stability in XRD characterization. Table 2. Comparison of gas evolution amounts during the formation process in Examples 2, 3, and 4 of the present invention with those in comparative examples.

[0053] The electrochemical impedance spectroscopy (EIS) of the battery after formation in Example 2 of this invention is as follows: Figure 7 As shown, the membrane impedance Rf of Example 2 of the present invention is 0.27Ω and Rct is 2.58Ω, indicating that the "pulse + standby" mode can periodically alleviate interfacial concentration polarization, promote uniform electrolyte decomposition, and induce dense growth of the SEI membrane. Although... Figure 8 The comparative battery's electrochemical impedance spectroscopy (EIS) shows a slight increase in Rf but a decrease in Rct, resulting in a significant reduction in total interfacial impedance and a substantial improvement in battery kinetic performance and cycle stability.

[0054] Example 3: Embodiment 3 of this invention discloses a specific implementation application of pulsed formation of high-efficiency short-cycle lithium iron phosphate-graphite batteries using Scheme 2 in Embodiment 1 (#2: CD). stage :1Cpulse 1.5s -(-0.5C)pulse 0.5s ),as follows: (1) Battery to be formed: Same as in Example 2; (2) Pulse formation parameters: The pulse current-time curve of Embodiment 3 of the present invention, as shown in the figure. Figure 9 As shown in the figure, it can be clearly observed that this scheme adopts an asymmetric bidirectional square wave pulse mode. The charging stage (C stage) adopts a cycle mode of "1C charging pulse for 1.5s, 0.5C discharging pulse for 0.5s", and the discharging stage (D stage) adopts a cycle mode of "1C discharging pulse for 1.5s, 0.5C charging pulse for 0.5s". The formation discharge cutoff voltage is 2V; the formation charging cutoff voltage is 4V, and the discharge cutoff voltage is 2V. The cycle period of a single pulse is 2s, and the number of cycles is adaptively adjusted according to the formation cutoff conditions. (3) Performance testing: combined with Figure 3 As shown in Table 1, the formation time of Example 3 of the present invention is 4.27 hours, and the initial coulombic efficiency is 96.23%. After formation, after 500 cycles at 25°C and 1C charge-discharge, the capacity retention rate is 94.56%, which is the best level among the three examples. (4) Mechanism analysis and testing: The XRD pattern and refinement results of the lithium iron phosphate cathode after formation in Example 3 of this invention are as follows: Figure 10 As shown, the cathode has a complete crystal structure, sharp characteristic peaks, and no impurities. The Fe antisite defect content is 8.31%, which is lower than that shown in the figure. Figure 5The 10.02% comparative example shown demonstrates that this bidirectional pulsed formation scheme can effectively suppress structural distortion and Fe dissolution in the lithium iron phosphate cathode, and maintain the crystal structure stability of the cathode material. The XRD patterns of the graphite anodes after formation in Examples 2, 3, and 4 of this invention are as follows: Figure 6 As shown in the spectrum, the characteristic peak of the graphite (002) crystal plane appears near 26.5° in Example 3 of the present invention, and the characteristic peak of the copper foil current collector appears at 43.3° and 50.4°. Compared with the comparative example, the characteristic peak of the graphite (002) crystal plane is symmetrical and does not have obvious broadening, indicating that the bidirectional pulse did not destroy the layered structure of the graphite negative electrode, and the amount of by-products deposited at the negative electrode interface was less.

[0055] The in-situ XRD results of the graphite anode in Example 3 and the comparative example of the present invention are as follows: Figure 11 As shown, the changes in a-lattice and c-lattice can reflect the degree of lattice distortion and interlayer spacing changes in graphite. During the charge-discharge process of DC formation, the changes in a-lattice and c-lattice of the graphite anode are significant and irreversible; while during the charge-discharge process of pulse formation, the changes in a-lattice and c-lattice are small, indicating that pulse formation has little effect on the lattice distortion and interlayer spacing of graphite, which is consistent with the results of non-in-situ XRD tests.

[0056] Table 2 shows a comparison of the gas evolution amounts during the formation processes in Examples 2, 3, and 4 of this invention with those in the comparative examples. In Example 3 of this invention, the total H2 evolution amount was 5.95 × 10⁻⁶. -7 The total amount of O2 released was 1.38 × 10⁻⁶ mol. -8 The total amount of CO2 released was 4.80 × 10⁻⁶ mol. -7 The total amount of C2H4 precipitated was 3.55 × 10⁻⁶ mol. -7 The amount of four characteristic gases released was much lower than that in the comparative example; the reverse discharge pulse can remove unstable intermediates at the electrode interface and significantly suppress the side reactions of electrolyte solvent reduction and oxidation, which is the core reason for the battery’s first optimal coulombic efficiency. The electrochemical impedance spectroscopy (EIS) of the battery after formation in Example 3 of this invention is as follows: Figure 12 As shown, the membrane impedance Rf of Example 3 of the present invention is 0.15Ω, the charge transfer impedance Rct is 1.53Ω, and the total interface impedance is the lowest among the three examples; bidirectional pulses can induce the formation of a dense LiF-rich SEI film, which significantly reduces the interfacial ion transport resistance and charge exchange resistance, and improves the cycling performance and first coulombic efficiency.

[0057] Example 4: Embodiment 4 of this invention discloses a specific implementation application of pulsed formation of high-efficiency short-cycle lithium iron phosphate-graphite batteries using Scheme 3 in Embodiment 1 (#3: C).stage 1.5Cpulse 1.5s -(-1C)pulse 0.5s ),as follows: (1) Battery to be formed: Same as in Example 2; (2) Pulse formation parameters: The pulse current-time curve of the embodiment, such as Figure 13 As shown in the figure, it can be clearly observed that this scheme adopts a high-rate bidirectional square wave pulse mode. During the charging phase, a cycle of "1.5C charging pulse for 1.5s + 1C reverse discharge pulse for 0.5s" is used. During the discharging phase, a constant current discharge of 0.2C is used to discharge to the cutoff voltage. The formation charging cutoff voltage is 4V, and the discharge cutoff voltage is 2V. The cycle period of a single pulse is 2s, and the number of cycles is adaptively adjusted according to the formation cutoff conditions. (3) Performance testing: combined with Figure 3 As shown in Table 1, the formation time of Example 4 of the present invention is 5.8 hours, and the initial coulombic efficiency is 95.03%. After formation, after 500 cycles at 25°C and 1C charge-discharge, the capacity retention is 90.36%. (4) Mechanism analysis and testing: The XRD pattern and refinement results of the lithium iron phosphate cathode after formation in Example 4 of this invention are as follows: Figure 14 As shown, no obvious impurity phases were formed in the positive electrode, the diffraction peaks did not show abnormal broadening, and the Fe antisite defect content was 9.17%, which is much lower than that shown in the figure. Figure 5 The comparative examples shown demonstrate that even with a 1.5C high-rate pulse, this scheme can still suppress the degradation of the positive electrode structure and avoid electrode structure damage caused by high-rate formation. The XRD patterns of the graphite anodes after formation in Examples 2, 3, and 4 of this invention are as follows: Figure 6 As shown in the spectrum, in Example 4 of the present invention, a characteristic peak of the graphite (002) crystal plane appears near 26.5°. The peak shape is complete and without distortion, which is consistent with Examples 2 and 3. This indicates that the high-rate pulse did not damage the graphite anode structure and the interface stability is good. Table 2 shows a comparison of the gas evolution amounts during the formation processes in Examples 2, 3, and 4 of this invention with those in the comparative examples. In Example 4 of this invention, the total H2 evolution amount was 5.61 × 10⁻⁶. -7 The total amount of O2 released was 1.22 × 10⁻⁶ mol. -8 The total amount of CO2 released was 5.56 × 10⁻⁶ mol. -7 The total amount of C2H4 precipitated was 4.56 × 10⁻⁶ mol. -7 The amount of gas evolution was significantly lower than that of the comparative example; the 1C reverse discharge pulse can alleviate the interfacial polarization caused by high-rate charging, suppress the violent decomposition of electrolyte and gas production, and ensure the safety of battery formation. The electrochemical impedance spectroscopy (EIS) of the battery after formation in Example 4 of this invention is as follows: Figure 15 As shown, the membrane impedance Rf of Example 4 of the present invention is 0.311Ω and the charge transfer impedance Rct is 2.847Ω, which is slightly higher than that of Examples 2 and 3, but much lower than that of the comparative example; the reverse pulse under high-rate charging can still maintain a low interface impedance, achieving a balance between formation efficiency and battery performance.

[0058] Example 5: Example 5 of this invention discloses a lithium iron phosphate-graphite battery prepared using a high-efficiency short-cycle lithium iron phosphate-graphite battery pulse formation method. The battery has an initial coulombic efficiency ≥95%, a capacity retention rate ≥90% after 500 cycles under 1C charge-discharge test conditions, and a total formation time per cycle ≤6h.

[0059] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0060] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A high-efficiency, short-cycle pulsed formation method for lithium iron phosphate-graphite batteries, characterized in that, include: Step 1: Obtain the lithium iron phosphate-graphite battery to be formed; wherein the lithium iron phosphate-graphite battery is composed of a lithium iron phosphate positive electrode, a graphite negative electrode, an electrolyte, and a separator; Step 2: The battery to be formed is subjected to pulse formation treatment using the following three square wave pulse current control methods for the charging and discharging stages: Option 1: Use a pulse + rest mode with a 1s charging pulse followed by a 1s rest period; Option 2: Use a bidirectional pulse mode of 1C charging pulse for 1.5s + 0.5C reverse discharge pulse for 0.5s; Option 3: Use a bidirectional pulse charging + constant current discharging mode with a 1.5C charging pulse of 1.5s + a 1C reverse discharging pulse of 0.5s; Step 3: When the charging and discharging voltage reaches the preset cutoff threshold, the pulse formation is completed.

2. The method for pulse formation of a high-efficiency, short-cycle lithium iron phosphate-graphite battery according to claim 1, characterized in that, In step 1, the lithium iron phosphate-graphite battery is one of the following: a pouch battery, a cylindrical battery, or a square battery, with a rated capacity of 10mAh~200Ah. After the lithium iron phosphate-graphite battery is assembled, it needs to be left to stand in an environment of 25℃ for 5 hours.

3. The method for pulse formation of a high-efficiency, short-cycle lithium iron phosphate-graphite battery according to claim 1, characterized in that, In step 1, the cell manufacturing conditions for the lithium iron phosphate-graphite battery are as follows: The ambient temperature is 25±2℃, the relative humidity is ≤30%, the operating atmosphere is inert gas, and the oxygen content is ≤1ppm.

4. The method for pulse formation of a high-efficiency, short-cycle lithium iron phosphate-graphite battery according to claim 1, characterized in that, In step 1, the electrolyte is 1.0~1.2 mol / L LiPF6 dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate, wherein the volume ratio of the mixed solvent is EC:DEC=1:2; wherein EC represents ethylene carbonate and DEC represents diethyl carbonate, and 10% of fluoroethylene carbonate relative to the total mass of the mixed solvent is added as a film-forming additive.

5. The method for pulse formation of a high-efficiency, short-cycle lithium iron phosphate-graphite battery according to claim 1, characterized in that, In step 2, a pulse + rest mode of 1s charging pulse + 1s rest is adopted, specifically as follows: The 1C charging pulse lasts for 1 second, then rests for 1 second, and this process is repeated until the charging cutoff voltage is reached. Then the 1C discharging pulse lasts for 1 second, then rests for 1 second, and this process is repeated until the discharging cutoff voltage is reached.

6. The method for pulse formation of a high-efficiency, short-cycle lithium iron phosphate-graphite battery according to claim 1, characterized in that, In step 2, a bidirectional pulse mode of 1C charging pulse for 1.5s + 0.5C reverse discharge pulse for 0.5s is adopted, specifically as follows: A 1C charging pulse is applied for 1.5 seconds, followed by a 0.5C reverse discharge pulse for 0.5 seconds. This process is repeated until the voltage reaches the charging cutoff voltage. Then, a 1C discharge pulse is applied for 1.5 seconds, followed by a 0.5C reverse charging pulse for 0.5 seconds. This process is repeated until the voltage reaches the discharge cutoff voltage.

7. The method for pulse formation of a high-efficiency, short-cycle lithium iron phosphate-graphite battery according to claim 1, characterized in that, In step 2, a bidirectional pulse charging + constant current discharging mode of 1.5C charging pulse for 1.5s + 1C reverse discharging pulse for 0.5s is adopted, specifically as follows: A 1.5C charging pulse is applied for 1.5 seconds, followed by a 1C reverse discharge pulse for 0.5 seconds. This process is repeated to charge to the cutoff voltage, and then discharged at a constant current of 0.2C to the cutoff voltage.

8. The method for pulse formation of a high-efficiency, short-cycle lithium iron phosphate-graphite battery according to claim 1, characterized in that, In step 2, the single pulse cycle period of schemes 1, 2, and 3 is 2s, and the number of cycles is adaptively adjusted according to the charge and discharge cutoff conditions.

9. The method for pulse formation of a high-efficiency short-cycle lithium iron phosphate-graphite battery according to claim 1, characterized in that, In step 3, the preset charging and discharging cutoff thresholds are 4V and 2V, respectively.

10. A lithium iron phosphate-graphite battery prepared using the pulse formation method for a high-efficiency short-cycle lithium iron phosphate-graphite battery according to any one of claims 1-9, characterized in that, The battery's initial coulombic efficiency is ≥95%, its capacity retention rate after 500 cycles under 1C charge-discharge test conditions is ≥90%, and the total formation time per cycle is ≤6h.

Images