A low polarization formation method for lithium iron phosphate-triple material composite positive electrode battery

Abstract

The application discloses a low-polarization formation method of a lithium iron phosphate-ternary material composite positive electrode battery, and comprises the following steps: S01, performing primary formation on an activated battery cell to obtain a primary formation battery cell; the activation is realized by the following mode: placing the battery cell after liquid injection in an environment with a dew point of less than or equal to-40 DEG C and standing for 48-76 hours; S02, performing stage formation on the primary formation battery cell in step S01 in a vacuum degree of 25 DEG C plus or minus 5 DEG C, -75 Kpa to -90 Kpa, to obtain the lithium iron phosphate-ternary material composite positive electrode battery. Through the primary formation, a stable and dense SEI film can be formed to block the erosion of subsequent side reactions on the negative electrode. Through the secondary formation, the interval film formation of the lithium iron phosphate-ternary material can be effectively realized, the two film layers do not interfere with each other and are compatible, and the maximum synergistic release of the capacities of the two materials can be effectively realized.

Description

Technical Field

[0001] This invention belongs to the field of lithium iron phosphate battery technology, and particularly relates to a low-polarization formation method for a lithium iron phosphate-ternary material composite cathode battery. Background Technology

[0002] Lithium-ion batteries, with their advantages of high energy density and long cycle life, have been widely used in power batteries and energy storage systems. As application scenarios demand higher battery performance, single cathode material systems are increasingly unable to meet the requirement of "balancing high energy density and high safety." While ternary materials (such as NCM and NCA) offer outstanding energy density, they suffer from poor thermal stability and rapid capacity decay in the later stages of cycling. Lithium iron phosphate (LFP) materials, on the other hand, offer structural stability and excellent safety, but suffer from relatively low energy density. Therefore, LFP-ternary composite cathode batteries have become a research hotspot in the industry. Through the synergistic effect of these two materials, a performance balance can be achieved between "increasing capacity with ternary materials and ensuring safety with LFP." The cathode typically employs a particle-level mixing or gradient composite structure, demonstrating significant industrialization potential.

[0003] The formation process, a core step in lithium-ion battery manufacturing, involves the initial charge-discharge cycle to create stable positive electrolyte interphase (CEI) and negative solid electrolyte interphase (SEI) films on the positive and negative electrode surfaces, respectively. The quality of these two films directly determines the battery's polarization, cycle life, and safety performance. However, the differences in electrochemical characteristics between lithium iron phosphate-ternary composite cathodes render traditional single-material formation processes completely ineffective, becoming a key bottleneck restricting the performance of composite battery systems. Specific problems include:

[0004] (1) Voltage response mismatch leading to polarization imbalance: The voltage window of lithium iron phosphate is 2.5 to 3.65V, and lithium ion insertion and extraction are mainly concentrated at around 3.2V; the voltage window of ternary materials is 2.8 to 4.35V, and the core capacity contribution area is above 3.65V. Moreover, high-nickel ternary materials need to be at around 4.4V to fully activate the nickel redox reaction. When conventional single-rate formation is used, lithium iron phosphate reacts preferentially in the low voltage stage (2.5 to 3.65V), resulting in insufficient activation of the active material of ternary materials; in the high voltage stage (3.65 to 4.4V), when the ternary materials react rapidly, lithium iron phosphate has entered the end of the reaction, forming a phenomenon of "local reaction overload - overall uneven polarization", which ultimately leads to increased cell internal resistance and incomplete capacity utilization.

[0005] (2) Problem of performance degradation caused by disordered interfacial film formation: The formation of SEI / CEI film depends on the orderly decomposition of electrolyte at a specific potential, while the potential difference of composite cathode can lead to uncontrolled electrolyte decomposition reaction. Experiments show that when the charging rate exceeds 0.1C, the strong oxidizing property of the high voltage region of ternary material will accelerate electrolyte oxidation, forming a thick and loose CEI film on the cathode surface; at the same time, lithium salt byproducts produced by lithium iron phosphate reaction will migrate to the anode, interfering with the formation of inorganic LiF-rich layer of SEI film, resulting in a decrease of more than 30% in interfacial film ionic conductivity. This disordered interfacial structure not only aggravates polarization, but also reduces the capacity retention rate to below 80% after 100 cycles, which is far lower than the level of more than 90% of single material system.

[0006] (3) Production bottlenecks caused by poor adaptability of traditional processes: Existing formation processes are mostly designed for single cathode materials - ternary batteries focus on interface stability under high voltage, and lithium iron phosphate batteries focus on activity activation under low rate, neither of which considers the synergistic requirements of composite systems. If the high-voltage formation scheme of ternary batteries is directly adopted, lithium iron phosphate will cause lattice distortion due to overcharging; if the low-voltage scheme of lithium iron phosphate is adopted, the nickel capacity of ternary materials will be locked by 50% to 80%. In addition, the gas generation rate of composite cathodes is 1.5 to 2 times that of single materials. Improper degassing timing and pressure control in traditional formation will cause gas to stagnate in the electrode gap, further aggravating concentration polarization and causing cell consistency error to exceed ±5%, which cannot meet the requirements of large-scale production.

[0007] Therefore, developing a formation process that can precisely match the voltage response of the two materials, regulate the orderly growth of the interface film, and balance polarization control and production efficiency, based on the characteristics of lithium iron phosphate-ternary composite cathodes, is key to breaking through the performance bottleneck of composite battery systems and is of great significance to promoting the industrialization of high-safety, high-energy-density lithium-ion batteries. Summary of the Invention

[0008] This invention provides a low-polarity formation method for lithium iron phosphate-ternary material composite cathode batteries, aiming to solve the technical problem that existing formation processes cannot simultaneously adapt to the electrochemical characteristics of lithium iron phosphate and ternary materials, resulting in performance degradation of composite batteries.

[0009] The technical solution of this invention is implemented as follows: a low-polarity formation method for a lithium iron phosphate-ternary material composite cathode battery, comprising the following steps:

[0010] S01. The activated battery cell is subjected to a first formation to obtain a first-formed battery cell; the activation is achieved by placing the battery cell after liquid injection in an environment with a dew point ≤ -40℃ for 48 to 76 hours.

[0011] S02. At 25℃±5℃ and a vacuum of -75Kpa~-90Kpa, the primary formation cell in step S01 is subjected to staged formation (i.e., secondary formation) to obtain a lithium iron phosphate-ternary material composite cathode battery.

[0012] In a preferred embodiment, in step S01,

[0013] The battery cell is a composite positive electrode cell; the composite positive electrode is a positive electrode made of lithium iron phosphate and ternary particles.

[0014] The environment described is a dry environment.

[0015] In this embodiment, the composite cathode is composed of lithium iron phosphate and ternary particles, which have a complex pore structure. Conventional standing (typically 12–48 hours) easily leads to "surface wetting" of the electrolyte rather than "deep penetration," thus causing localized liquid shortage polarization. This application, through low dew point anti-water absorption and long-term penetration, ensures that the electrolyte uniformly covers the surfaces of both materials, laying the foundation for the subsequent orderly formation of the interface film.

[0016] The primary formation is carried out at 25±5℃ and a vacuum of -75Kpa to -90Kpa.

[0017] The primary conversion is performed in the following manner:

[0018] S011, Gradient pre-charge: The cell is pre-charged at a constant current of 0.02C to 0.05C in 2 to 3 steps to 10% ± 2% SOC, and then left to stand for 20 to 40 minutes;

[0019] S012, SEI complete film formation: The cell is continuously charged at a constant current of 0.03C to 0.05C to 10%±2% SOC, and then left to stand for 30 to 60 minutes; then continuously charged at a constant current of 0.02C to 0.04C to 10%±2% SOC, and then left to stand for a second time.

[0020] In a preferred embodiment, in step S012, the secondary settling is performed for 4 to 6 hours under normal temperature and negative pressure or for 12 to 24 hours under a dry environment of 45℃±3℃, 101Kpa±10Kpa, and dew point ≤-40℃.

[0021] In this application, 0% to 10% ± 2% SOC is the nucleation stage of the SEI film; the purpose of 2 to 3 steps of constant current pre-charging (for example, 2-step constant current pre-charging can be constant current charging at a rate of 0.02C to 0.03C for 100 min to 120 min, then constant current charging at a rate of 0.04C to 0.05C for 60 min to 100 min, and then resting for 20 to 40 min) is to efficiently construct a uniform, dense, and stable SEI film, while avoiding side reactions and structural damage caused by high current, laying the foundation for long cycle life, low internal resistance, and high safety performance of the cell; the purpose of resting for 20 to 40 min is to eliminate polarization and promote uniform repair of the film layer.

[0022] In this application, the 10%–20% ± 2% SOC stage represents the rapid growth stage of the SEI film. During this stage, the negative electrode potential continuously decreases (approximately 3.0V from 2.8V in the lithium iron phosphate system), and the electrolyte reduction and decomposition reaction enters an active phase. A small current of 0.03C–0.05C allows the electrolyte reduction reaction to occur uniformly, gradually reducing the SEI film porosity and forming a continuous and dense protective film. This is a core prerequisite for ensuring low internal resistance and long cycle life of the battery cell. A 30–60 minute resting period eliminates polarization and promotes the self-repair of the SEI film. The 20%–30% SOC stage represents the SEI film passivation and reinforcement stage. The formation with a small current of 0.02C to 0.04C allows the reduction and decomposition reaction of the electrolyte to be mild and controllable, which can fill the micropores of the membrane and promote the conversion of unstable organic components into more stable inorganic lithium salts (such as Li2CO3 and LiF), so that the density and chemical stability of the SEI membrane can reach the optimal state. The purpose of standing for 4 to 6 hours under negative pressure at room temperature and 12 to 24 hours under dry conditions of 45℃±3℃, 101Kpa±10Kpa and dew point ≤-40℃ is to further eliminate the concentration polarization inside the cell and lock the stability of the membrane, laying the foundation for subsequent high-voltage formation.

[0023] In a preferred embodiment, in step S02,

[0024] The phased transformation is performed in the following manner:

[0025] S021, Lithium iron phosphate activation stage: The primary formed cell in step S01 is continuously charged at a constant current rate of 0.08C to 0.1C to 3.6 to 3.7V, and then left to stand for 30 to 60 minutes;

[0026] S022, Ternary Material Synergistic Stage: The battery cell after being left to stand in step S021 is continuously charged at a constant current rate of 0.01 to 0.05C to 3.9 to 4.0V and then left to stand for 10 to 30 minutes; then it is continuously charged at a constant current rate of 0.01 to 0.05C to 4.1 to 4.2V and left to stand for 10 to 30 minutes; finally, it is charged at a constant current and constant voltage rate of 0.01 to 0.05C to 4.1 to 4.2V, with a cutoff current of 0.002 to 0.005C, and left to stand for 2 to 4 hours;

[0027] S023. Segmented discharge stage: Discharge at a constant current of 0.1 to 0.5C to 3.6 to 3.7V, then let stand for 60 to 120 minutes, and then discharge at a constant current of 0.05 to 0.15C to 2.5 to 2.8V.

[0028] In this application, charging at a rate of 0.08 to 0.1C ensures sufficient lithium-ion insertion and extraction; the purpose of standing for 30 to 60 minutes is to eliminate concentration polarization, which can effectively avoid overload caused by premature participation of ternary materials in the reaction.

[0029] In this embodiment, the core reaction region of the ternary material is above 3.65V, and the low-rate, staged formation can promote Ni² + →Ni³ + →Ni 4 The process involves: ⁺ Complete reaction; replenishing residual capacity under high voltage during the constant voltage stage; allowing the CEI film (mainly Li3PO4) on the surface of the ternary material to solidify during rest; during discharge, 3.6–3.7V is the reaction boundary between the two materials, and 60–120 minutes of rest allows lithium ions to redistribute; the low-voltage stage involves reduced-rate discharge to avoid lattice distortion caused by excessive lithium intercalation in lithium iron phosphate, while simultaneously stabilizing the SEI film structure. The maximum charging voltage is set to 4.1–4.2V to protect the lattice structure of lithium iron phosphate, as there is a significant risk of structural collapse above 4.2V.

[0030] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0031] (1) Through a single formation, a stable and dense SEI film can be effectively formed, blocking the subsequent side reactions from eroding the negative electrode. Through a two-stage formation, the lithium iron phosphate-ternary material can be effectively formed in separate sections, that is, the lithium iron phosphate segment forms a Li2CO3-phosphate composite CEI film, and the ternary segment forms a Li3PO4-fluoride composite CEI film. The two film layers do not interfere with each other and are synergistically compatible.

[0032] (2) The present application uses low-temperature formation at 25±5℃, which can effectively suppress oxygen evolution of high-nickel ternary materials and reduce the damage of electrolyte oxidation to the interface film.

[0033] (3) In this application, each stage of charging is appropriately extended and multiple rest periods are added: to eliminate concentration polarization generated inside the cell during the first charge.

[0034] (4) Through the embodiments of this application, the dual-material capacity can be fully utilized, and the first discharge specific capacity is increased by 10% to 15%; the staged voltage regulation strategy adopted in this application can effectively realize the maximum synergistic release of the capacity of the two materials. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of this application 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 some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a comparison diagram of the fully charged interface of the battery cell (sample A) formed in Example 1 of the present invention and the battery cell (sample B) formed in Comparative Example 1.

[0037] Figure 2 This is a comparison chart of the capacity discharge curves of the battery cell (sample A) formed in Example 1 of the present invention and the battery cell (sample B) formed in Comparative Example 1.

[0038] Figure 3 This is a comparison chart of the internal resistance data of the battery cell (sample A) formed in Example 1 of the present invention and the battery cell (sample B) formed in Comparative Example 1.

[0039] Figure 4 This is a comparison chart of the room temperature cycle life trends of the battery cell (sample A) formed in Example 1 of the present invention and the battery cell (sample B) formed in Comparative Example 1. Detailed Implementation

[0040] 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 a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0041] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, top, bottom, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0042] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0043] It should be noted that when a component is described as "fixed to" or "set on" another component, it can be directly on the other component or there may be an intervening component. When a component is described as "connected to" another component, it can be directly connected to the other component or there may be an intervening component.

[0044] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0045] Currently, existing technologies have not achieved precise voltage range matching between lithium iron phosphate and ternary materials, resulting in problems such as polarization imbalance, poor interface film quality, and insufficient capacity utilization. To address these technical issues, this invention proposes a low-polarization formation method for lithium iron phosphate-ternary material composite cathode batteries.

[0046] The embodiments of this application are designed with segmented formation parameters according to the voltage response range of the materials: exclusive reaction ranges for lithium iron phosphate (2.5~3.65V) and ternary materials (3.65~4.2V), with differentiated charge and discharge rates, constant voltage current and resting time, thereby effectively solving the polarization imbalance problem caused by the mismatch of the voltage responses of the two materials.

[0047] This application employs a gradient pre-charge-induced dense SEI film nucleation process strategy: pre-charged at an ultra-low rate of 0.02–0.05C to 10±2% SOC, followed by a 20–40 min settling period, to preferentially form a dense SEI film underlayer at the negative electrode and induce orderly CEI film nucleation at the positive electrode, thereby avoiding performance degradation caused by interfacial film disorder from the source.

[0048] In this application, a post-formation treatment combining segmented discharge and interface film stabilization is adopted: a segmented discharge strategy of "0.1-0.5C constant current discharge to 3.6-3.7V → standing for 60-120 minutes → 0.05-0.15C constant current discharge to 2.5-2.8V" is adopted to avoid lattice distortion caused by excessive lithium intercalation of lithium iron phosphate, while further stabilizing the interface film structure.

[0049] Example 1

[0050] A low-polarity formation method for a lithium iron phosphate-ternary material composite cathode battery includes the following steps:

[0051] S01, Primary Formation: After activation (i.e., cell pretreatment: the cell is left to stand in a dry environment with a dew point ≤ -40℃ for 76 hours after electrolyte injection), the cell undergoes the following staged formation at an ambient temperature of 25℃ and a vacuum of -80Kpa:

[0052] S011, Gradient pre-charge: Charge at a constant current rate of 0.03C for 100 minutes, then charge at a constant current rate of 0.05C for 60 minutes, and then let stand for 30 minutes;

[0053] S012 and SEI complete film formation: After charging with a constant current of 0.05C for 120 minutes and letting stand for 60 minutes, charge with a constant current of 0.03C for 200 minutes. Then transfer the cell to a dry environment of 45℃, 101±10Kpa and dew point ≤-40℃ and let stand for 24 hours.

[0054] S02, Secondary Formation: After primary formation, the battery cell undergoes the following staged formation at an ambient temperature of 25±5℃ and a vacuum of -70Kpa:

[0055] S021, Lithium iron phosphate exclusive activation stage: charge continuously at a rate of 0.08C to 3.65V, and then let stand for 60 minutes;

[0056] S022, Ternary Material Synergistic Section: Charged at a constant current rate of 0.02C to 3.95V and then left to stand for 30 minutes; then charged at a constant current rate of 0.02C to 4.2V and left to stand for 30 minutes; finally charged at a constant current and constant voltage rate of 0.02C to 4.2V, with a cutoff current of 0.005C, and left to stand for 4 hours;

[0057] S023, discharge at a constant current of 0.2C to 3.65V, let stand for 120 minutes, and then discharge at a constant current of 0.08C to 2.5V.

[0058] Example 2

[0059] A low-polarity formation method for a lithium iron phosphate-ternary material composite cathode battery includes the following steps:

[0060] S01, Primary Formation: After activation (the cell is left to stand in a dry environment with a dew point ≤ -40℃ for 76 hours after electrolyte injection), the cell undergoes the following staged formation at an ambient temperature of 25℃ and a vacuum of -80Kpa:

[0061] S011, Gradient pre-charge: Charge at a constant current rate of 0.02C for 120 minutes, then charge at a constant current rate of 0.05C for 80 minutes, and then let stand for 20 minutes;

[0062] S012 and SEI complete film formation: After charging with a constant current of 0.03C for 200 min and letting stand for 60 min, charge with a constant current of 0.05C for 120 min. Then transfer the cell to a dry environment with a high temperature of 45℃, 101±10Kpa and dew point ≤-40℃ and let stand for 24 h.

[0063] S02, Secondary Formation: After primary formation, the battery cell undergoes the following staged formation at an ambient temperature of 25±5℃ and a vacuum of -65Kpa:

[0064] S021, Lithium iron phosphate exclusive activation stage: charge continuously at a 0.1C rate to 3.65V, then let stand for 60 minutes;

[0065] S022, Ternary Material Synergistic Section: Charge at a constant current rate of 0.05C to 3.95V and let stand for 20 minutes; then charge at a constant current rate of 0.02C to 4.2V and let stand for 30 minutes; finally charge at a constant current and constant voltage rate of 0.02C to 4.2V, cut-off current 0.002C, and let stand for 4 hours;

[0066] S023. Discharge to 3.65V with a constant current of 0.1C, let stand for 120 minutes, and then discharge to 2.5V with a constant current of 0.08C.

[0067] Example 3

[0068] A low-polarity formation method for a lithium iron phosphate-ternary material composite cathode battery includes the following steps:

[0069] S01, Primary Formation: After activation (the cell is left to stand in a dry environment with a dew point ≤ -40℃ for 64 hours after electrolyte injection), the cell undergoes the following staged formation at an ambient temperature of 25℃ and a vacuum of -85Kpa:

[0070] S011, Gradient pre-charge: Charge at a constant current rate of 0.02C for 120 minutes, then charge at a constant current rate of 0.04C for 100 minutes, and let stand for 30 minutes;

[0071] S012 and SEI complete film formation: After charging with a constant current of 0.03C for 200 min and letting stand for 60 min, charge with a constant current of 0.05C for 120 min. Then transfer the cell to a dry environment with a high temperature of 45℃, 101±10Kpa and dew point ≤-40℃ and let stand for 24 h.

[0072] S02, Secondary Formation: After primary formation, the battery cell undergoes the following staged formation at an ambient temperature of 25±5℃ and a vacuum of -65Kpa:

[0073] S021, Lithium iron phosphate exclusive activation stage: charge continuously at a 0.1C rate to 3.65V, then let stand for 30 minutes;

[0074] S022, Ternary Material Synergistic Section: Charge at a constant current rate of 0.03C to 3.9V and let stand for 15 minutes; then charge at a constant current rate of 0.02C to 4.15V and let stand for 15 minutes; finally charge at a small constant current and constant voltage rate of 0.02C to 4.15V, cut-off current 0.005C, and let stand for 2 hours;

[0075] S023. Discharge to 3.65V with a constant current of 0.1C, let stand for 120 minutes, and then discharge to 2.5V with a constant current of 0.08C.

[0076] Comparative Example 1

[0077] The preparation of a lithium iron phosphate-ternary composite cathode battery using a conventional 60% SOC formation process includes the following steps: after electrolyte injection, the cell is left to stand in a dry environment with a dew point ≤ -40℃ for 48 hours, then charged at a constant current rate of 0.05C for 30 minutes and rested for 1 minute, then charged at a constant current rate of 0.1C for 90 minutes and rested for 1 minute, then charged at a constant current rate of 0.15C for 80 minutes and rested for 1 minute, and finally charged at a constant current rate of 0.2C for 60 minutes.

[0078] Effect Example

[0079] The effects of sample A prepared in Example 1 and sample B prepared in Comparative Example 1 were compared:

[0080] (1) After formation, both Sample A prepared in Example 1 and Sample B prepared in Comparative Example 1 were charged to 3.65V at a constant current and constant voltage of 0.5C, with a cutoff current of 0.05C. The comparison diagram of the fully charged interface is shown below. Figure 1 As shown: From Figure 1 It can be seen that the interface of sample A cell is uniformly golden yellow, while the interface of sample B cell electrode is mottled, with a large number of purple gas spots and lithium plating at the edges caused by gas not being discharged in time.

[0081] (2) The discharge curves of sample A prepared in Example 1 and sample B prepared in Comparative Example 1 were compared. The results are as follows: Figure 2 As shown. From Figure 2 As can be seen, the capacity of sample A cells is improved by 30% compared to sample B cells.

[0082] (3) The cell internal resistance data of sample A prepared in Example 1 and sample B prepared in Comparative Example 1 were compared. The results are as follows: Figure 3 As shown. From Figure 3 It can be seen that the internal resistance of sample A is 15% lower than that of sample B.

[0083] (4) The room temperature cycle life trend of sample A prepared in Example 1 and sample B prepared in Comparative Example 1 were compared. The results are as follows: Figure 4 As shown. From Figure 4 It can be seen that the cycle trend of sample A cells is significantly better than that of sample B cells.

[0084] This application employs a "phased adaptation, precise control, and interface synergy" approach. Specifically, based on the differences in voltage response ranges and reaction kinetics between lithium iron phosphate and ternary materials, a multi-stage formation strategy is designed to achieve the synergistic goals of "fully activated activity of both materials, orderly growth of the interface film, and precise polarization control."

[0085] Formation parameters are matched in segments according to voltage range: Different charge and discharge rates and constant voltage times are designed for the specific reaction ranges of lithium iron phosphate (2.5~3.65V) and ternary materials (3.65~4.4V) to avoid the "one-to-one" problem caused by a single parameter, and to ensure that both materials can be fully activated without the risk of overcharging / undercharging.

[0086] Gradient-controlled interfacial membrane formation process: The initial SEI / CEI membrane is induced to form dense nuclei by ultra-low rate pre-charging, and the electrolyte decomposition rate is controlled by segmented voltage / current increase to avoid interfacial membrane disorder caused by the difference in composite cathode potential and improve the ionic conductivity of the membrane layer.

[0087] Collaborative optimization of polarization and gas generation issues: Combining the high gas generation rate of composite cathodes, the settling time and degassing timing during the formation process are optimized to eliminate concentration polarization caused by gas trapped in the electrode gaps, while ensuring cell consistency.

[0088] This application solves the following technical problems:

[0089] To address the polarization imbalance caused by the voltage response mismatch between lithium iron phosphate and ternary materials: avoid preferential reaction of lithium iron phosphate in the low voltage stage and overload reaction of ternary materials in the high voltage stage, reduce the internal resistance of the cell, and ensure that the capacity of both materials is fully utilized;

[0090] To address the problem of disordered interface film formation caused by the potential difference of the composite cathode: suppress the excessive oxidation of the electrolyte under high voltage of ternary materials and the interference of lithium iron phosphate byproducts on the SEI film, form a dense interface film with high ionic conductivity, and improve the cycle stability of the battery;

[0091] Solve the performance and production contradiction caused by the poor adaptability of traditional single-material formation processes: avoid the lattice distortion of lithium iron phosphate or the capacity lock of nickel in ternary materials caused by using a single system process, while controlling the gas generation rate, improving cell consistency, and meeting the requirements of large-scale production.

[0092] Ultimately, the goal is to achieve the performance objectives of "low polarization, high capacity, long cycle life, and high consistency" in composite cathode batteries, breaking through the performance bottleneck of existing composite battery systems.

[0093] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-polarity formation method for a lithium iron phosphate-ternary material composite cathode battery, characterized in that, Includes the following steps: S01. The activated battery cell is subjected to a first formation to obtain a first-formed battery cell; the activation is achieved by placing the battery cell after liquid injection in an environment with a dew point ≤ -40℃ for 48 to 76 hours. S02. At 25℃±5℃ and a vacuum of -75Kpa~-90Kpa, the primary formation cell in step S01 is formed in stages to obtain a lithium iron phosphate-ternary material composite cathode battery.

2. The low-polarity formation method for the lithium iron phosphate-ternary composite cathode battery according to claim 1, characterized in that, In step S01, the battery cell is a composite positive electrode battery cell.

3. The low-polarity formation method for the lithium iron phosphate-ternary material composite cathode battery according to claim 2, characterized in that, The composite cathode is a cathode made of lithium iron phosphate and ternary particles.

4. The low-polarity formation method for the lithium iron phosphate-ternary composite cathode battery according to claim 1, characterized in that, In step S01, the environment is a dry environment.

5. The low-polarity formation method for the lithium iron phosphate-ternary composite cathode battery according to claim 1, characterized in that, In step S01, the primary formation is carried out at 25±5℃ and a vacuum of -75Kpa to -90Kpa.

6. The low-polarity formation method for the lithium iron phosphate-ternary composite cathode battery according to claim 1, characterized in that, In step S01, the primary transformation is performed in the following manner: S011, Gradient pre-charge: The cell is pre-charged at a constant current of 0.02C to 0.05C in 2 to 3 steps to 10% ± 2% SOC, and then left to stand for 20 to 40 minutes; S012, SEI complete film formation: The cell is continuously charged at a constant current of 0.03C to 0.05C to 10%±2% SOC, and then left to stand for 30 to 60 minutes; then continuously charged at a constant current of 0.02C to 0.04C to 10%±2% SOC, and then left to stand for a second time.

7. The low-polarity formation method for the lithium iron phosphate-ternary material composite cathode battery according to claim 6, characterized in that, In step S012, the second settling is to settling for 4 to 6 hours under normal temperature and negative pressure or to settling for 12 to 24 hours under a dry environment of 45℃±3℃, 101Kpa±10Kpa, and dew point ≤-40℃.

8. The low-polarity formation method for the lithium iron phosphate-ternary material composite cathode battery according to claim 1, characterized in that, In step S02, the phased transformation is performed in the following manner: S021, Lithium iron phosphate activation stage: The primary formed cell in step S01 is continuously charged at a constant current rate of 0.08C to 0.1C to 3.6 to 3.7V, and then left to stand for 30 to 60 minutes; S022, Ternary Material Synergistic Stage: The battery cell after being left to stand in step S021 is continuously charged at a constant current rate of 0.01 to 0.05C to 3.9 to 4.0V and then left to stand for 10 to 30 minutes; then it is continuously charged at a constant current rate of 0.01 to 0.05C to 4.1 to 4.2V and left to stand for 10 to 30 minutes; finally, it is charged at a constant current and constant voltage rate of 0.01 to 0.05C to 4.1 to 4.2V, with a cutoff current of 0.002 to 0.005C, and left to stand for 2 to 4 hours; S023. Segmented discharge stage: Discharge at a constant current of 0.1 to 0.5C to 3.6 to 3.7V, then let stand for 60 to 120 minutes, and then discharge at a constant current of 0.05 to 0.15C to 2.5 to 2.8V.

Images