Lithium iron manganese phosphate battery and formation process thereof

Abstract

The application provides a lithium manganese iron phosphate battery formation process, by setting a separate film forming and charging and discharging stage, the film forming effect of various additives in the electrolyte is improved; the formation process significantly improves the uniformity and compactness of the positive and negative solid electrolyte membranes, so that the lithium manganese iron phosphate battery after formation has lower impedance and better high-temperature cycle performance, and reduces the later gas generation of the battery; in addition, the battery is subjected to charging and discharging treatment at the film forming potential of the additives, the film forming additives can be fully reacted to form a film, and the consumption of active lithium during the film forming period is reduced, the high reactivity of active lithium and its film forming products on the negative side is effectively reduced, and the safety and stability of the battery are improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery formation, and more particularly to a lithium manganese iron phosphate battery and its formation process. Background Technology

[0002] Formation is a key process in battery manufacturing. The formation effect directly affects the battery's initial efficiency, cycle life, and safety. Battery formation mainly refers to the process of performing the first charge and discharge treatment on batteries (especially secondary batteries such as lithium-ion batteries and lead-acid batteries) after electrolyte filling and resting, in order to activate their internal active materials and form a stable solid electrolyte interphase (CEI / SEI) film.

[0003] Inside the battery, the core function of the CEI / SEI film is to prevent the dissolution of transition metals and isolate the electrodes from direct contact with the electrolyte. This film layer has electronic insulation but allows lithium ions to pass through, thereby blocking the subsequent continuous decomposition reaction of the electrolyte. This not only reduces the irreversible capacity loss of the battery (improving the initial coulombic efficiency to 80%-95%), but also avoids battery expansion and performance degradation caused by excessive electrolyte consumption. Therefore, controlling the formation of SEI and CEI films in lithium batteries through the formation process is an important way to improve battery performance.

[0004] Lithium manganese iron phosphate (LFP), as an upgraded material of lithium iron phosphate (LFP), boasts higher energy density (theoretically 15%-20% higher) and safety advantages. LFP is a novel olivine-structured cathode material formed by doping manganese into lithium iron phosphate (LiFeO4). Through the synergistic effect of iron (Fe) and manganese (Mn), its voltage platform is increased from 3.4V to 4.1V, significantly improving energy density while maintaining the stability and safety of the olivine structure. However, LFP lacks a continuous octahedral network, instead relying on tetrahedral links of PO4. This tetrahedral linking limits the LiFeO4 structure. + Movement within the one-dimensional channel results in poor conductivity and high-current discharge performance. As the proportion of manganese ions increases, numerous defects and voids appear in the material, potentially extending the Li... + Intercalation and extraction reduce lithium-ion mobility and can even lead to severe electrolyte side reactions. Dissolved transition metal ions migrate and deposit on the negative electrode surface, damaging the SEI (Sediment Injection Layer), causing increased electrode impedance and negative electrode gas generation problems. This also severely affects the Li-ion exchange rate. + Embedding and de-embedding.

[0005] In summary, existing formation methods for lithium iron phosphate batteries are not suitable for the formation of lithium manganese iron phosphate batteries. Therefore, there is an urgent need for a formation method for lithium manganese iron phosphate batteries to optimize the electrolyte membrane on the positive and negative electrode surfaces. Summary of the Invention

[0006] To solve the technical problems existing in the background art, the present invention proposes a formation process for lithium iron manganese phosphate batteries, and the formation process includes the following steps:

[0007] S1. Set the first-stage charging current, charge the lithium iron manganese phosphate battery in the first stage until the voltage reaches V1, then leave it on standby after charging. Perform cyclic operations on the lithium iron manganese phosphate battery until the voltage reaches V4, then charge it again with the first-stage charging current, and then leave it on standby after charging until the state of charge of the lithium iron manganese phosphate battery is Q1.

[0008] In step S1, before the first-stage charging of the lithium iron manganese phosphate battery, it further includes an initial standby. The cyclic operation includes discharging and standby after discharging. The specific steps of the cyclic operation are as follows:

[0009] Set the first-stage discharging current, perform the first discharge on the lithium iron manganese phosphate battery, and the voltage of the lithium iron manganese phosphate battery changes from V1 to V2. Then leave it on standby after the first discharge, and the voltage of the lithium iron manganese phosphate battery changes from V2 to V3. Perform the second discharge on the lithium iron manganese phosphate battery, and the voltage of the lithium iron manganese phosphate battery changes from V3 to V2. Then leave it on standby after the second discharge, and the voltage of the lithium iron manganese phosphate battery changes from V2 to V4;

[0010] During the formation of the battery, the first-stage charge and discharge operation is a specifically set charge and discharge stage for the reduction and film formation of the film-forming additive.

[0011] Among them, V1 is the highest reduction voltage of the film-forming additive, and V2 is the lowest film-forming potential of the film-forming additive.

[0012] In step S1, V2 < V3 < V1, and V2 < V4 < V1; V1 is 2.2 - 2.6V, and V2 is 1.6 - 1.8V.

[0013] In step S1, the standby time after charging is 5 - 10 min, and the initial standby time is 10 - 15 min; the standby time after the first discharge and the standby time after the second discharge are 30 - 45 min.

[0014] In the present invention, different from the prior art, during the formation of the battery, the first-stage charge and discharge operation is a specifically set charge and discharge stage for the reduction and film formation of the film-forming additive; among them, V1 is the highest reduction voltage of the film-forming additive, and V2 is the lowest film-forming potential of the film-forming additive; when the battery is charged and discharged at the corresponding film-forming potential of the additive, it can promote the full reaction and film formation of the negative electrode film-forming additive and reduce the consumption of active lithium during film formation, thereby forming a complete and dense CEI / SEI film, effectively reducing the high reactivity of active lithium and its film-forming products on the negative electrode side, and improving the safety stability and high-temperature long-term electrochemical performance of the battery.

[0015] The first stage uses the lowest charging current. This smaller current allows the additives to react fully, promoting the rapid formation of the organic components in the CEI / SEI film. The reactions occurring in this stage are primarily the reduction and film-forming reactions of the additives, specifically including the following:

[0016] LiBF₂C₂O₄ + 2Li + +2e - →2LiF + LiBO2 + 2CO2↑;

[0017] CH2(SO2O)2+4Li + +4e - →Li2SO3+Li2S+CH2O+SO2↑;

[0018] The temperature and environmental pressure settings during the initial resting process are consistent with the charging temperature and charging pressure during the full formation stage; the initial resting allows the cell temperature to adapt to facilitate the first charging temperature.

[0019] The post-discharge resting process of cyclic operation can continuously promote the diffusion of the internal adsorption layer, causing the voltage to gradually increase. Through cyclic operation, the additives can fully react to generate a uniform and dense protective film.

[0020] The formation process also includes the following steps:

[0021] S2. Set the second-stage charging current and perform the second-stage charging of the lithium manganese iron phosphate battery. The state of charge of the lithium manganese iron phosphate battery changes from Q1 to Q2.

[0022] S3. Set the third-stage charging current and perform the third-stage charging of the lithium manganese iron phosphate battery. The state of charge of the lithium manganese iron phosphate battery changes from Q2 to Q3.

[0023] S4. Set the fourth stage charging current to perform the fourth stage charging of the lithium manganese iron phosphate battery. The state of charge of the lithium manganese iron phosphate battery changes from Q3 to Q4.

[0024] S5. Set the fifth stage charging current to perform the fifth stage charging of the lithium manganese iron phosphate battery. The state of charge of the lithium manganese iron phosphate battery changes from Q4 to 100% SOC.

[0025] Q1 is 5-10% SOC, Q2 is 40-50% SOC, Q3 is 60-70% SOC, and Q4 is 80-90% SOC.

[0026] The first stage charging current and the first stage discharging current are 0.02-0.05C, the second stage charging current is 0.3-0.5C, the third stage charging current is 0.1-0.2C, the fourth stage charging current is 0.3-0.5C, and the fifth stage charging current is 0.1-0.2C.

[0027] The completion of any one of the second, third, fourth, and fifth stage charging, including post-charging rest;

[0028] The resting time after charging is 5-10 minutes.

[0029] In this invention, the second stage of charging corresponds to the iron plateau charging stage, the third stage of charging corresponds to the manganese-iron conversion region charging stage, the fourth stage of charging corresponds to the manganese plateau charging stage, and the fifth stage of charging corresponds to the high-potential charging stage; wherein:

[0030] The second stage charging current is larger. During the second stage charging process, the positive electrode material undergoes a reaction involving Fe. 2+ Oxidized to Fe 3+ ;

[0031] The third stage charging current is relatively small. During the third stage charging process, the positive electrode material undergoes a reaction involving Fe. 2+ Oxidized to Fe 3+ Gradually towards Mn 2+ Oxidized to Mn 3+ During this stage, a smaller current should be used to avoid distortion of the crystal structure caused by a large current. At the same time, it can also increase the gas production in the manganese-iron conversion zone and avoid gas production in the later stages of the cycle from affecting long-term performance.

[0032] The fourth stage charging current is relatively large, and during the fourth stage charging process, the reaction is completely Mn 2+ To Mn 3+ For oxidation, a larger current can be used;

[0033] The fifth stage charging current is relatively small. During the fifth stage charging process, the formation gas generation is more serious. Reducing the charging current in this stage can effectively increase the gas generation in the formation stage and reduce the gas generation throughout the entire life cycle. Selecting an appropriate charging current based on the stability of the oxidation reaction in different charging stages can improve the formation efficiency and formation effect, which helps to further improve the stability of the SEI film and CEI film, improve the cycle performance of lithium battery, and reduce the amount of gas generated by lithium battery in the later stage of cycle.

[0034] In this invention, a five-stage charging operation is adopted, and the charging and discharging process and cutoff charge state of each stage in the five-stage charging operation are adjusted according to different elements in the battery. With the control of the charging and discharging current of the corresponding charging stage, a more uniform and stable CEI / SEI film can be formed, thereby improving the stability of the lithium battery. In addition, the electrodes can achieve a close contact state, thereby appropriately balancing the polarization degree of each part of the electrode, which helps to improve the formation efficiency. According to the gas generation pattern of each platform, the gas generation efficiency of the formation stage is increased, thereby reducing gas generation during the later cycle process.

[0035] The lithium manganese iron phosphate battery is subjected to the same conditions in steps S1-S5: temperature of 45-60℃ and pressure of 0.4±0.1MPa.

[0036] In this invention, when the formation pressure is too high, the electrolyte on the electrode surface is squeezed out, the surface ion concentration decreases, which is not conducive to the formation of CEI / SEI film; when the formation pressure is too low, the electrode cannot make sufficient contact; when the formation temperature is too low, the ion movement slows down, and its activity speed cannot reach the speed of matching electrons; when the formation temperature is too high, the formed interface film will decompose. Therefore, this invention effectively improves the formation effect by selecting appropriate temperature and pressure.

[0037] The formation process also includes an aging operation, wherein the aging temperature is 45-60℃ and the aging time is 12-24h.

[0038] In this invention, the aging process can, on the one hand, promote the full wetting of the electrodes in the lithium battery by the electrolyte, and on the other hand, stabilize the electrochemical performance of the lithium battery, help form a stable electrolyte interface film, and help improve the cycle performance of the lithium battery.

[0039] This invention also proposes a lithium battery prepared by the above-mentioned lithium manganese iron phosphate battery formation process, wherein the positive electrode material of the lithium manganese iron phosphate battery includes lithium manganese iron phosphate, and the structural formula of the lithium manganese iron phosphate is LiFe. a Mn (1-a) PO4, 0 < a < 1.

[0040] The lithium manganese iron phosphate battery also includes an electrolyte, which contains film-forming additives;

[0041] The additive is one of LiODFB, MMDS or LiBOB;

[0042] The concentration of the additive in the electrolyte is 0.3-0.8 wt%.

[0043] Beneficial effects of this invention:

[0044] (1) The formation process of the present invention can effectively improve the film-forming effect of various additives in the electrolyte, especially the uniformity and density of the solid electrolyte film of the positive and negative electrodes.

[0045] (2) The formation process of the present invention improves the film formation effect, improves the impedance and high temperature cycle performance of the battery, reduces the gas production in the later stage of the battery, improves the stability of the SEI / CEI film, and improves the cycle performance of the lithium battery.

[0046] (3) Compared with the traditional formation process, the formation process of the present invention can reduce the formation time by about 40 to 90 minutes, which significantly improves the production efficiency. Attached Figure Description

[0047] Figure 1 The diagram shows the formation stages of lithium manganese iron phosphate batteries in Examples 1-5.

[0048] Figure 2 The graph shows a comparison of the gas production of lithium manganese iron phosphate batteries in Examples 1-5 and Comparative Examples 1-2 after formation, capacitation, and 15 days of rest at room temperature. Detailed Implementation

[0049] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0051] The technical solution of the present invention will now be described more clearly and completely with reference to specific embodiments and comparative examples.

[0052] Example 1

[0053] This embodiment presents a lithium-ion battery, which is prepared by the following formation method:

[0054] (1) Lithium manganese iron phosphate battery (LiFe) a Mn (1-a) PO4, a=0.2, and 0.3wt% LiODFB as the film-forming additive were used to heat the lithium manganese iron phosphate battery at 45℃. A pressure of 0.4MPa was applied to the battery using a clamp to perform the first stage of charge and discharge. The first stage charge and discharge current was 0.02C, where C is the battery's rated capacity.

[0055] First, let the lithium manganese iron phosphate battery rest for 10 minutes, then perform the first constant current charge to V1=2.4V (based on the highest film formation voltage of LiODFB, the charging limit voltage is 3.4V). After resting for 5 minutes, perform the first constant current discharge to V2=1.6V (based on the lowest film formation voltage of LiODFB, the discharge limit voltage is set to 1.2V). After resting for 30 minutes, the voltage of the lithium manganese iron phosphate battery rises to V3=2.0V. Then, perform a second constant current discharge until the voltage is the same as V2. After resting for another 30 minutes, the voltage of the lithium manganese iron phosphate battery rises to V4=1.8V. Finally, perform a constant current charge to V5=3.34V, and finally rest for 5 minutes to obtain the state of charge. The lithium-ion battery has a charging voltage limit of 3.6V;

[0056] (2) Perform a second-stage charging on the lithium-ion battery obtained in step (1). The second-stage charging current is I2 = 0.5C, and the charging time is t2 = 48min to obtain the state of charge. The lithium-ion battery has a charging voltage limit of 3.8V;

[0057] (3) Perform a third-stage charge on the lithium-ion battery obtained in step (2). The third-stage charging current is I3 = 0.1C, the charging time is t3 = 120 min, and finally let it rest for 5 min to obtain the state of charge. The lithium-ion battery has a charging voltage limit of 4.2V;

[0058] (4) Perform a fourth stage charge on the lithium-ion battery obtained in step (3). The fourth stage charging current is I4 = 0.5C, the charging time is t4 = 24min, and finally let it rest for 5min to obtain the state of charge. The lithium-ion battery has a charging voltage limit of 4.2V;

[0059] (5) Perform a fifth stage charge on the lithium-ion battery obtained in step (4). The fifth stage charging current is I5 = 0.1C. Finally, let it rest for 5 minutes to obtain the state of charge. The lithium-ion battery has a voltage of 4.25V and a charging limit voltage of 4.5V.

[0060] (6) The lithium battery obtained in step (5) is aged at 45°C for 12 hours.

[0061] Example 2

[0062] This embodiment presents a lithium-ion battery, which is prepared by the following formation method:

[0063] (1) Lithium manganese iron phosphate battery (LiFe) a Mn(1-a) PO4 (a=0.3, film-forming additive: 0.5wt% LiODFB) was heated to 45℃. A pressure of 0.4MPa was applied to the lithium manganese iron phosphate battery using a clamp to perform the first stage of charge and discharge. The first stage charge and discharge current was 0.03C, where C is the battery's rated capacity.

[0064] First, let the lithium manganese iron phosphate battery rest for 10 minutes, then perform the first constant current charge to V1=2.4V (based on the highest film formation voltage of LiODFB, the charging limit voltage is 3.4V). After resting for 5 minutes, perform the first constant current discharge to V2=1.6V (based on the lowest film formation voltage of LiODFB, the discharge limit voltage is set to 1.2V). After resting for 30 minutes, the voltage of the lithium manganese iron phosphate battery rises to V3=2.0V. Then, perform a second constant current discharge until the voltage is the same as V2. After resting for another 30 minutes, the voltage of the lithium manganese iron phosphate battery rises to V4=1.8V. Finally, perform a constant current charge to V5=3.34V, and finally rest for 5 minutes to obtain the state of charge. The lithium-ion battery has a charging voltage limit of 3.6V;

[0065] (2) Perform a second-stage charging on the lithium-ion battery obtained in step (1). The second-stage charging current is I2 = 0.5C, the charging time is t2 = 48min, and finally, let it rest for 5min to obtain the state of charge. The lithium-ion battery has a charging voltage limit of 3.8V;

[0066] (3) Perform a third-stage charge on the lithium-ion battery obtained in step (2). The third-stage charging current is I3 = 0.1C, the charging time is t3 = 120 min, and finally let it rest for 5 min to obtain the state of charge. The lithium-ion battery has a charging voltage limit of 4.2V;

[0067] (4) Perform a fourth stage charge on the lithium-ion battery obtained in step (3). The fourth stage charging current is I4 = 0.5C, the charging time is t4 = 24min, and finally let it rest for 5min to obtain the state of charge. The lithium-ion battery has a charging voltage limit of 4.2V;

[0068] (5) Perform a fifth stage charge on the lithium-ion battery obtained in step (4). The fifth stage charging current is I5 = 0.1C. Finally, let it rest for 5 minutes to obtain the state of charge. The lithium-ion battery has a voltage of 4.25V and a charging limit voltage of 4.5V.

[0069] (6) The lithium battery obtained in step (5) is aged at 55°C for 12 hours.

[0070] Example 3

[0071] This embodiment presents a lithium-ion battery, which is prepared by the following formation method:

[0072] (1) Lithium manganese iron phosphate battery (LiFe) a Mn (1-a) The lithium manganese iron phosphate battery (LiFePO4, a=0.6, film-forming additive: 0.3wt% LiODFB) was heated to 45℃. A pressure of 0.4MPa was applied to the battery using a clamp to perform the first stage of charge and discharge. The first stage charge and discharge current was 0.05C, where C is the battery's rated capacity.

[0073] First, let the lithium manganese iron phosphate battery rest for 10 minutes, then perform the first constant current charge to V1=2.4V (based on the highest film formation voltage of LiODFB, the charging limit voltage is 3.4V). After resting for 5 minutes, perform the first constant current discharge to V2=1.6V (based on the lowest film formation voltage of LiODFB, the discharge limit voltage is set to 1.2V). After resting for 30 minutes, the voltage of the lithium manganese iron phosphate battery rises to V3=2.0V. Then, perform a second constant current discharge until the voltage is the same as V2. After resting for another 30 minutes, the voltage of the lithium manganese iron phosphate battery rises to V4=1.8V. Finally, perform a constant current charge to V5=3.34V, and finally rest for 5 minutes to obtain the state of charge. The lithium-ion battery has a charging voltage limit of 3.6V;

[0074] (2) Perform a second-stage charging on the lithium-ion battery obtained in step (1). The second-stage charging current is I2 = 0.5C, the charging time is t2 = 48min, and finally, let it rest for 5min to obtain the state of charge. The lithium-ion battery has a charging voltage limit of 3.8V;

[0075] (3) Perform a third-stage charge on the lithium-ion battery obtained in step (2). The third-stage charging current is I3 = 0.1C, the charging time is t3 = 120 min, and finally let it rest for 5 min to obtain the state of charge. The lithium-ion battery has a charging voltage limit of 4.2V;

[0076] (4) Perform a fourth stage charge on the lithium-ion battery obtained in step (3). The fourth stage charging current is I4 = 0.5C, the charging time is t4 = 24min, and finally let it rest for 5min to obtain the state of charge. The lithium-ion battery has a charging voltage limit of 4.2V;

[0077] (5) Perform a fifth-stage charge on the lithium-ion battery obtained in step (4). The fifth-stage charging current is I5 = 0.1C. Finally, let it rest for 5 minutes to obtain the state of charge. The lithium-ion battery has a voltage of 4.25V and a charging limit voltage of 4.5V.

[0078] (6) The lithium battery obtained in step (5) is aged at 45°C for 12 hours.

[0079] Example 4

[0080] This embodiment presents a lithium-ion battery, which is prepared by the following formation method:

[0081] (1) Lithium manganese iron phosphate battery (LiFe) a Mn (1-a) PO4 (α=0.8, film-forming additive: 0.3wt% LiODFB) was heated to 45℃. A pressure of 0.4MPa was applied to the lithium manganese iron phosphate battery using a clamp to perform the first stage of charge and discharge. The first stage charge and discharge current was 0.02C, where C is the battery's rated capacity.

[0082] First, let the lithium manganese iron phosphate battery rest for 10 minutes, then perform the first constant current charge to V1=2.4V (based on the highest film formation voltage of LiODFB, the charging limit voltage is 3.4V). After resting for 5 minutes, perform the first constant current discharge to V2=1.6V (based on the lowest film formation voltage of LiODFB, the discharge limit voltage is set to 1.2V). After resting for 45 minutes, the voltage of the lithium manganese iron phosphate battery rises to V3=2.0V. Then, perform a second constant current discharge until the voltage is the same as V2. After resting for another 45 minutes, the voltage of the lithium manganese iron phosphate battery rises to V4=1.8V. Finally, perform a constant current charge to V5=3.34V, and finally rest for 5 minutes to obtain the state of charge. The lithium-ion battery has a charging voltage limit of 3.6V;

[0083] (2) Perform a second-stage charging on the lithium-ion battery obtained in step (1). The second-stage charging current is I2 = 0.5C, the charging time is t2 = 48min, and finally, let it rest for 5min to obtain the state of charge. The lithium-ion battery has a charging voltage limit of 3.8V;

[0084] (3) Perform a third-stage charge on the lithium-ion battery obtained in step (2). The third-stage charging current is I3 = 0.1C, the charging time is t3 = 120 min, and finally let it rest for 5 min to obtain the state of charge. The lithium-ion battery has a charging voltage limit of 4.2V;

[0085] (4) Perform a fourth stage charge on the lithium-ion battery obtained in step (3). The fourth stage charging current is I4 = 0.5C, the charging time is t4 = 24min, and finally let it rest for 5min to obtain the state of charge. The lithium-ion battery has a charging voltage limit of 4.2V;

[0086] (5) Perform a fifth stage charge on the lithium-ion battery obtained in step (4). The fifth stage charging current is I5 = 0.1C. Finally, let it rest for 5 minutes to obtain the state of charge. The lithium-ion battery has a voltage of 4.25V and a charging limit voltage of 4.5V.

[0087] (6) The lithium battery obtained in step (5) is aged at 45°C for 12 hours.

[0088] Example 5

[0089] This embodiment presents a lithium-ion battery, which is prepared by the following formation method:

[0090] (1) Lithium manganese iron phosphate battery (LiFe) a Mn (1-a) PO4, a=0.2, and 0.3wt% LiODFB as the film-forming additive were used to heat the lithium manganese iron phosphate battery at 60℃. A pressure of 0.4MPa was applied to the battery using a clamp to perform the first stage of charge and discharge. The first stage charge and discharge current was 0.02C, where C is the battery's rated capacity.

[0091] First, let the lithium manganese iron phosphate battery rest for 10 minutes, then perform the first constant current charge to V1=2.4V (based on the highest film formation voltage of LiODFB, the charging limit voltage is 3.4V). After resting for 5 minutes, perform the first constant current discharge to V2=1.6V (based on the lowest film formation voltage of LiODFB, the discharge limit voltage is set to 1.2V). After resting for 30 minutes, the voltage of the lithium manganese iron phosphate battery rises to V3=2.0V. Then, perform a second constant current discharge until the voltage is the same as V2. After resting for another 30 minutes, the voltage of the lithium manganese iron phosphate battery rises to V4=1.8V. Finally, perform a constant current charge to V5=3.34V, and finally rest for 5 minutes to obtain the state of charge. The lithium-ion battery has a charging voltage limit of 3.6V;

[0092] (2) Perform a second-stage charging on the lithium-ion battery obtained in step (1). The second-stage charging current is I2 = 0.5C, and the charging time is t2 = 48min to obtain the state of charge. The lithium-ion battery has a charging voltage limit of 3.8V;

[0093] (3) Perform a third-stage charge on the lithium-ion battery obtained in step (2). The third-stage charging current is I3 = 0.1C, the charging time is t3 = 120 min, and finally let it rest for 5 min to obtain the state of charge. The lithium-ion battery has a charging voltage limit of 4.2V;

[0094] (4) Perform a fourth stage charge on the lithium-ion battery obtained in step (3). The fourth stage charging current is I4 = 0.5C, the charging time is t4 = 24min, and finally let it rest for 5min to obtain the state of charge. The lithium-ion battery has a charging voltage limit of 4.2V;

[0095] (5) Perform a fifth stage charge on the lithium-ion battery obtained in step (4). The fifth stage charging current is I5 = 0.1C. Finally, let it rest for 5 minutes to obtain the state of charge. The lithium-ion battery has a voltage of 4.25V and a charging limit voltage of 4.5V.

[0096] (6) The lithium battery obtained in step (5) is aged at 45°C for 12 hours.

[0097] Comparative Example 1

[0098] This comparative example presents a lithium-ion battery, which is prepared by the following formation method:

[0099] (1) Cell formation environment setup: The cell is pressurized and heated; the heating temperature is 45℃ and the clamp pressure is 0.4 MPa;

[0100] (2) Charge the battery cell in the first stage with a charging current of 0.05C and a charging time of 240 min;

[0101] (3) Charge the battery cell in the second stage with a charging current of 0.33C and a charging time of 120 min;

[0102] (4) Charge the battery cell in the third stage with a charging current of 0.1C and a charging time of 60 min;

[0103] (5) Perform the fourth stage of charging on the battery cell, with a charging current of 0.2C, and charge to 4.25 V;

[0104] (6) Age at 60℃ for 12 hours.

[0105] Comparative Example 2

[0106] This comparative example presents a lithium-ion battery prepared by the following formation method: The formation method of Comparative Example 2 is the same as that of Example 1, except that the first stage of charging and discharging in step (1) is removed.

[0107] The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 does not have a first stage of charging and discharging operation, but directly enters the iron platform charging stage.

[0108] Comparative Example 3

[0109] This comparative example presents a lithium-ion battery, which is prepared by the following formation method: The formation method of Comparative Example 3 is the same as that of Example 1, except that the first stage of charging and discharging operation in step (1) is changed to "firstly, let the lithium manganese iron phosphate battery rest for 10 minutes, then perform constant current charging to V1=2.4V, the charging limit voltage is 3.4V, rest for 5 minutes, then perform the first constant current discharge to V2=1.6V, and finally perform constant current charging to V5=3.34V to obtain the state of charge". The lithium-ion battery has a charging voltage limit of 3.6V.

[0110] The difference between Comparative Example 3 and Example 1 is that the first stage of the charge and discharge operation lacks a second constant current discharge operation, and only the first constant current discharge operation is performed.

[0111] Comparative Example 4

[0112] This comparative example presents a lithium-ion battery, which is prepared by the following formation method: The formation method of Comparative Example 4 is the same as that of Example 1, except that step (4) "obtaining the state of charge" is changed. The phrase "lithium-ion battery" was changed to "obtaining state of charge". "Lithium-ion batteries".

[0113] The difference between Comparative Example 4 and Example 1 is that Comparative Example 4 does not have a high-potential charging stage, but directly charges the lithium-ion battery to full charge during the manganese platform charging stage.

[0114] After the lithium batteries of each embodiment and comparative example were formed and tested, the batteries of each embodiment and comparative example were subjected to performance tests.

[0115] Cyclic performance test: The test temperature was set to 45℃, the charge / discharge current was 1C / 1C, and the cutoff voltage was 2.5 / 4.2V. The initial discharge capacity was recorded as Q1. After 500 cycles, the discharge capacity was recorded as Q2. The capacity retention rate after 500 cycles was calculated as Q2 / Q1×100%. After the test, the cells of the example and comparative examples were disassembled, and the black spots on the interface were counted. The test results are shown in Table 1.

[0116] After formation, volume determination, and 15-day resting, the gas production of each embodiment and Comparative Examples 1-2 was tested using the water displacement method. The test results are shown in […]. Figure 2 .

[0117] Table 1 Test results for each embodiment and comparative example

[0118]

[0119] The experimental factors corresponding to Examples 1-5 are small current, medium current, large current, and long rest time, respectively. The experimental data show that the formation method of the present invention does not have much limitation on the size of the charging current. By extending the rest time, the capacity retention rate of the battery at high temperature can be further improved.

[0120] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A formation process for lithium iron phosphate batteries, characterized in that, The formation process includes the following steps: S1. Set the first-stage charging current, charge the lithium iron manganese phosphate battery in the first stage until the voltage reaches V1, then set it aside after charging. Perform cyclic operations on the lithium iron manganese phosphate battery until the voltage reaches V4, then charge it again with the first-stage charging current, and then set it aside after charging until the state of charge of the lithium iron manganese phosphate battery reaches Q1; In step S1, before the first-stage charging of the lithium iron manganese phosphate battery, there is also an initial set-aside. The cyclic operation includes discharging and setting aside after discharging. The specific steps of the cyclic operation are as follows: Set the first-stage discharging current, perform the first discharge on the lithium iron manganese phosphate battery. The voltage of the lithium iron manganese phosphate battery changes from V1 to V2, then set it aside after the first discharge. The voltage of the lithium iron manganese phosphate battery changes from V2 to V3, perform the second discharge on the lithium iron manganese phosphate battery. The voltage of the lithium iron manganese phosphate battery changes from V3 to V2, then set it aside after the second discharge. The voltage of the lithium iron manganese phosphate battery changes from V2 to V4; During the battery formation process, the first-stage charge-discharge operation is a specifically set charge-discharge stage for the reduction and film formation of the film-forming additive; Among them, V1 is the highest reduction voltage of the film-forming additive, and V2 is the lowest film-forming potential of the film-forming additive; In step S1, V2 < V3 < V1, and V2 < V4 < V1; V1 is 2.2 - 2.6V, and V2 is 1.6 - 1.8V.

2. The lithium iron phosphate battery formation process according to claim 1, characterized in that, In step S1, the set-aside time after charging is 5 - 10 min, and the initial set-aside time is 10 - 15 min; the set-aside time after the first discharge and the second discharge is 30 - 45 min.

3. The lithium manganese iron phosphate battery formation process according to claim 1 or 2, characterized in that, The formation process further includes the following steps: S2. Set the second-stage charging current, charge the lithium iron manganese phosphate battery in the second stage, and the state of charge of the lithium iron manganese phosphate battery changes from Q1 to Q2; S3. Set the third-stage charging current, charge the lithium iron manganese phosphate battery in the third stage, and the state of charge of the lithium iron manganese phosphate battery changes from Q2 to Q3; S4. Set the fourth-stage charging current, charge the lithium iron manganese phosphate battery in the fourth stage, and the state of charge of the lithium iron manganese phosphate battery changes from Q3 to Q4; S5. Set the fifth-stage charging current, charge the lithium iron manganese phosphate battery in the fifth stage, and the state of charge of the lithium iron manganese phosphate battery changes from Q4 to 100% SOC; Q1 is 5 - 10% SOC, Q2 is 40 - 50% SOC, Q3 is 60 - 70% SOC, and Q4 is 80 - 90% SOC.

4. The lithium iron phosphate battery formation process according to claim 3, characterized in that, The first-stage charging current and the first-stage discharging current are 0.02 - 0.05C, the second-stage charging current is 0.3 - 0.5C, the third-stage charging current is 0.1 - 0.2C, the fourth-stage charging current is 0.3 - 0.5C, and the fifth-stage charging current is 0.1 - 0.2C.

5. The lithium iron phosphate battery formation process according to claim 4, characterized in that, After any one of the second-stage charging, third-stage charging, fourth-stage charging, and fifth-stage charging is completed, it includes setting aside after charging; The set-aside time after charging is 5 - 10 min.

6. The lithium iron phosphate battery formation process according to claim 5, characterized in that, The lithium manganese iron phosphate battery is subjected to the same conditions in steps S1-S5: temperature of 45-60℃ and pressure of 0.4±0.1MPa.

7. The lithium iron phosphate battery formation process according to claim 6, characterized in that, The formation process also includes an aging operation, wherein the aging temperature is 45±3℃ and the aging time is 12-24h.

8. A lithium manganese iron phosphate battery prepared by the lithium manganese iron phosphate battery formation process according to any one of claims 1-7, characterized in that, The positive electrode material of the lithium manganese iron phosphate battery includes lithium manganese iron phosphate, and the structural formula of the lithium manganese iron phosphate is LiFe. a Mn (1-a) PO4, 0 < a < 1.

9. The lithium manganese iron phosphate battery according to claim 8, characterized in that, The lithium manganese iron phosphate battery also includes an electrolyte, which contains film-forming additives; The additive is one of LiODFB, MMDS or LiBOB; The concentration of the additive in the electrolyte is 0.3-0.8 wt%.

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