Secondary battery, method for manufacturing the same, energy storage system, and electric device

Abstract

The embodiment of the application relates to the field of batteries, and provides a secondary battery, a preparation method of the secondary battery, an energy storage system and a power utilization device, the preparation method of the secondary battery comprises the following steps: providing an electrode core assembly, the electrode core assembly is formed by laminating or winding a positive plate, a diaphragm and a negative plate; providing a shell, the shell has an accommodating cavity, and the electrode core assembly is arranged in the accommodating cavity; providing an electrolyte, and injecting the electrolyte into the accommodating cavity, the electrolyte comprises an electrolyte salt, a non-water solvent, a first precursor and a second precursor, the first precursor and the second precursor can generate an in-situ polymerization reaction at the interface of the negative plate to form a network structure with a Schiff base bond; and performing a formation step. The application has the advantages that a self-repairing mechanism of a dynamic covalent bond can significantly delay damage accumulation of an SEI film, and fundamentally improves the cycle stability of a high-capacity negative electrode.

Description

Technical Field

[0001] This application relates to the field of batteries, and in particular to a secondary battery and its preparation method, energy storage system and electrical equipment. Background Technology

[0002] Developing lithium-ion batteries with higher energy density is a key strategy to meet the energy storage technology demands of modern society. Silicon (Si) anodes, due to their ultra-high theoretical specific capacity (4200 mAh / g, more than ten times that of traditional graphite anodes), and lithium (Li) metal anodes, due to their highest theoretical specific capacity (3860 mAh / g) and lowest electrode potential (-3.04 V vs. standard hydrogen electrode), are widely regarded as the most promising next-generation high-energy-density anode materials. However, both types of materials face a common and significant challenge in practical applications: drastic volume changes occur during lithium-ion insertion / extraction (for Si) or deposition / exfoliation (for Li) processes (over 300% for Si, and non-uniform deposition morphology for Li). These repeated volume changes generate enormous mechanical stress on the solid electrolyte interphase (SEI) film on the anode surface, making the SEI film prone to physical cracking, pulverization, and detachment. Damage to the SEI (Sediment Injection) not only exposes the fresh, highly active anode surface to the electrolyte, triggering continuous side reactions and consuming active lithium and electrolyte, leading to low coulombic efficiency, rapid capacity decay, and shortened battery life, but may even induce lithium dendrite growth, posing safety hazards. Therefore, maintaining the structural integrity and stability of the SEI on the surface of anodes with high volumetric variations has become one of the core obstacles restricting the practical application of these high-energy-density anode materials. Summary of the Invention

[0003] This application provides a secondary battery and its preparation method, energy storage system, and electrical equipment, which at least fundamentally improves the cycle stability of high-capacity negative electrodes.

[0004] According to some embodiments of this application, one aspect of this application provides a method for preparing a secondary battery, comprising: providing a battery cell assembly, the battery cell assembly being formed by stacking or winding a positive electrode sheet, a separator, and a negative electrode sheet; providing a housing, the housing having a receiving chamber, and placing the battery cell assembly in the receiving chamber; providing an electrolyte and injecting the electrolyte into the receiving chamber, the electrolyte comprising an electrolyte salt, a non-aqueous solvent, a first precursor, and a second precursor, wherein the first precursor and the second precursor are capable of undergoing an in-situ polymerization reaction at the interface of the negative electrode sheet to form a network structure with Schiff base bonds; and performing a formation step; wherein the first precursor is a compound containing two amine groups, and the second precursor is a compound containing two aldehyde groups.

[0005] In some embodiments, the first precursor has a mass percentage of 0.5% to 3% in the electrolyte, and the second precursor has a mass percentage of 0.5% to 3% in the electrolyte.

[0006] In some embodiments, the molar ratio of the first precursor to the second precursor is (0.8 to 1.2):1.

[0007] In some embodiments, the first precursor is phenylenediamine, pentanediamine, or propylenediamine, and the second precursor is phenylenedialdehyde, glutaraldehyde, or malondialdehyde.

[0008] In some embodiments, the first precursor is p-phenylenediamine (PPD) and the second precursor is terephthalaldehyde (TPA).

[0009] In some embodiments, the formation step includes: a pre-activation step, wherein the device is charged at a first rate and the negative electrode potential is less than a first preset potential, and the charging time is a first preset duration; a network construction step, wherein the device is charged at a second rate and the negative electrode potential is within a target potential range, and the charging time is a second preset duration, wherein the second rate is greater than the first rate; and a stabilization step, wherein the device is charged at a third rate, wherein the third rate is greater than the second rate.

[0010] In some embodiments, the first multiplier is 0.01C to 0.05C, the first preset potential is 0.5V, and the first preset duration is 10h to 20h.

[0011] In some embodiments, the second multiplier is 0.02C to 0.1C, and the second preset duration is 6h to 20h.

[0012] In some embodiments, the third multiplier is 0.05C to 0.1C.

[0013] In some embodiments, the target potential range is 0.1V to 0.5V.

[0014] In some embodiments, the stabilization step involves 1 to 3 charging cycles, with the negative electrode potential being the normal operating voltage of the secondary battery.

[0015] In some embodiments, the temperature of the formation step is 25°C to 60°C.

[0016] In some embodiments, T2 > T3 > T1, where T1 is the temperature of the pre-activation step, T2 is the temperature of the network construction step, and T3 is the temperature of the stabilization step.

[0017] In some embodiments, T1 is 25℃~40℃, T2 is 35℃~50℃, and T3 is 30℃~45℃.

[0018] In the embodiments of this application, "negative electrode potential" refers to the battery negative electrode material relative to the lithium metal electrode (Li / Li). + The potential value of ).

[0019] In some embodiments, the electrolyte is prepared by:

[0020] Preparation of non-aqueous solvents;

[0021] The electrolyte salt is dissolved in the non-aqueous solvent to obtain the basic electrolyte;

[0022] The first precursor is added to the base electrolyte and stirred until dissolved. Then, the second precursor is added and stirred until dissolved to obtain the electrolyte.

[0023] In some embodiments, the content of both H2O and O2 in the electrolyte preparation environment is below 1 ppm.

[0024] According to some embodiments of this application, another aspect of this application provides a secondary battery, which is prepared using the secondary battery manufacturing method described in the above embodiments.

[0025] According to some embodiments of this application, another aspect of this application provides an energy storage system, including a secondary battery as described in the above embodiments.

[0026] According to some embodiments of this application, in another aspect, this application provides an electrical device, the electrical device including the secondary battery described in the above embodiments; or, the electrical device including the energy storage system described in the above embodiments.

[0027] The technical solution provided in this application has at least the following advantages:

[0028] First, the Schiff base bond (C=N) formed by the reaction of a compound containing two amine groups as the first precursor and a compound containing two aldehyde groups as the second precursor is a dynamic covalent bond. The special feature of this bond is its inherent reversibility: under certain conditions (such as mechanical force or the presence of a catalyst such as trace water), the C=N bond can break and then reform under suitable conditions. This dynamic equilibrium endows the SEI film containing this structure with a unique self-healing ability. When the volume expansion of the negative electrode causes the SEI to be stressed, the breakage of some Schiff base bonds can relieve stress and prevent crack propagation. When the stress is eliminated, the broken bonds can close again, realizing the self-repair of damage. At the same time, this dynamism also gives the SEI film better flexibility to adapt to the deformation of the negative electrode, fundamentally improving the cycle stability of high-capacity negative electrodes.

[0029] Secondly, the in-situ polymerization strategy ensures the precise distribution of functional components at the interface, improves the utilization efficiency of additives, and reduces the impact on the bulk performance of the electrolyte. This is because: 1) the first and second precursors, as small molecule compounds, have good electrolyte solubility and can be uniformly dissolved in the electrolyte bulk; 2) targeted in-situ generation—the goal of this application is to precisely construct a self-healing layer at the negative electrode interface (the location where the SEI film forms and needs protection). By using the precursors, these dissolved small molecules can freely diffuse with the electrolyte to the negative electrode surface; 3) triggering of reaction conditions—the Schiff base formation reaction between the first and second precursors can be initiated or significantly accelerated by the specific electrochemical environment of the negative electrode. When the battery is charged, the negative electrode reaches a low reduction potential (e.g., below 0.5V vs. Li / Li). + This strongly reducing environment promotes the reaction of amine and aldehyde groups. This means that the polymer network is mainly generated at the anode interface where SEI needs to be formed or repaired, and within an appropriate electrochemical window, rather than through uncontrolled polymerization in the electrolyte bulk. Finally, regarding interfacial bonding and morphology—polymer networks formed by direct growth and polymerization at the interface can form tighter, more conformally preserved bonds with the anode surface and other SEI components, resulting in a higher quality and more uniform interfacial layer compared to pre-synthesized polymer particles obtained by physical deposition.

[0030] Furthermore, the synergistic effect of the composite gradient structure can provide durable mechanical protection while maintaining low interfacial impedance, achieving a dual optimization of performance and durability.

[0031] The logic behind these beneficial effects lies in the fact that this application starts from the fundamental mechanism of interface damage and provides a new technical path to solve the interface stability challenge of high-capacity anodes by endowing the SEI film with active adaptability rather than simply improving its passive resistance. Attached Figure Description

[0032] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Unless otherwise stated, the drawings in the accompanying drawings do not constitute a limitation on scale. In order to more clearly illustrate the technical solutions in the embodiments of this application or in the conventional art, the drawings used in the embodiments 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.

[0033] Figure 1 A flowchart corresponding to the preparation method of the secondary battery provided in the embodiments of this application;

[0034] Figure 2 A flowchart corresponding to the formation step in the preparation method of the secondary battery provided in the embodiments of this application;

[0035] Figure 3 This is a schematic diagram of the electrochemical structure of a secondary battery provided in an embodiment of this application. To facilitate explanation of the working principle of the secondary battery, Figure 3 The diagram shown is an electrochemical schematic of a secondary battery, not a structural schematic of an actual secondary battery product. Detailed Implementation

[0036] As the background technology indicates, existing technologies still have significant shortcomings in addressing the stability challenges of high-capacity anode SEIs. First, the mechanical properties of traditional SEI films (especially toughness and fracture resistance) cannot match the enormous deformation of silicon or lithium metal anodes, inevitably leading to cracks and even peeling during cycling. While the elastic modulus of an SEI film is typically on the order of several gigapascals, the stress generated in the anode material during lithiation / delithiation can reach hundreds of megapascals. This mismatch in mechanical properties prevents the SEI from elastically adapting to this stress. Second, once such physical damage occurs, existing SEIs lack an effective intrinsic repair mechanism. Although new SEI will regenerate on the exposed anode surface, this not only continuously consumes electrolyte and active lithium, but the repeated crack-repair process often leads to uneven SEI thickening, increasing interfacial impedance. Typically, on silicon-based anodes, an initial SEI film of a few nanometers thickness can thicken to tens or even hundreds of nanometers after dozens of cycles, significantly increasing lithium-ion transport resistance. Existing additive strategies (such as FEC and VC) primarily focus on optimizing the chemical composition or initial structure of the SEI, with limited effectiveness against mechanical damage generated during cycling. While these additive-formed SEIs improve chemical stability and initial uniformity, they still lack the ability to adapt to sustained mechanical stress. In summary, current technologies fail to endow the SEI film with the ability to actively adapt to mechanical stress and repair physical damage. Based on the understanding that one of the main causes of SEI failure is mechanical fracture, the concept of "self-healing" from materials science is introduced, particularly utilizing dynamic chemical bonds to endow materials with self-healing capabilities, providing a new approach to solving this problem. If an SEI containing dynamic bonds can be constructed, enabling it to reversibly fracture and reassemble under stress, it is expected to fundamentally improve the durability of SEIs on anode surfaces with high volumetric variations.

[0037] In traditional lithium-ion batteries, the SEI film is a complex composite thin layer naturally formed during the first charge-discharge process by the electrochemical reduction and decomposition of electrolyte components (solvents, salts, additives) on the negative electrode surface. Its typical components include inorganic salts (such as Li₂CO₃, LiF, Li₂O) and organic / polymeric substances (such as alkyl lithium carbonate, polyethylene oxide, etc.). This passively formed SEI film is usually rigid or semi-rigid, lacking sufficient mechanical toughness and elasticity to adapt to the drastic deformation of the negative electrode. To address this problem, existing technologies mainly improve it in the following ways: first, by using nano- or composite designs of electrode materials (such as porous silicon, silicon / carbon composites) to accommodate volume changes and mitigate stress; second, by developing highly elastic polymer binders (such as polyacrylic acid PAA, cross-linked polymers, etc.) to maintain the integrity of the electrode structure; and third, by using film-forming additives (such as vinylene carbonate FEC, vinylene carbonate VC) to optimize the chemical composition and initial morphology of the SEI, aiming to form a more stable or slightly flexible interface layer. However, these methods primarily provide external buffering or confinement, or improve the initial SEI properties, failing to fundamentally address the problem of physical rupture of the SEI film under enormous, repeated stress and its subsequent repair. Existing SEIs inherently lack the ability to actively respond to stress damage and self-repair, which limits the interfacial stability of the battery during long-cycle operation.

[0038] According to some embodiments of this application, one embodiment of this application provides a method for preparing a secondary battery, the process of which is as follows: Figure 1 As shown, it includes:

[0039] S1. A battery cell assembly and a housing are provided, wherein the battery cell assembly is formed by stacking or winding a positive electrode sheet, a separator, and a negative electrode sheet; the housing has a receiving chamber.

[0040] S2. Place the battery cell assembly into the receiving cavity;

[0041] S3. Provide an electrolyte and inject the electrolyte into the receiving chamber. The electrolyte includes an electrolyte salt, a non-aqueous solvent, a first precursor, and a second precursor. The first precursor and the second precursor can undergo in-situ polymerization at the interface of the negative electrode to form a network structure with Schiff base bonds.

[0042] S4. Perform the formation step;

[0043] The first precursor is a compound containing two amine groups, and the second precursor is a compound containing two aldehyde groups.

[0044] In the secondary battery preparation method provided in this application embodiment, firstly, the Schiff base bond (C=N) generated by the reaction of a compound containing two amine groups as the first precursor and a compound containing two aldehyde groups as the second precursor is a dynamic covalent bond. The special feature of this bond is its inherent reversibility: under certain conditions (such as mechanical force or the presence of a catalyst such as trace water), the C=N bond can break, and then can reform under suitable conditions. This dynamic equilibrium endows the SEI film containing this structure with a unique self-healing ability. When the volume expansion of the negative electrode causes the SEI to be under stress, the breakage of some Schiff base bonds can relieve stress and prevent crack propagation. When the stress is eliminated, the broken bonds can close again, realizing the self-repair of damage. At the same time, this dynamism also gives the SEI film better flexibility to adapt to the deformation of the negative electrode, fundamentally improving the cycle stability of the high-capacity negative electrode.

[0045] Secondly, the in-situ polymerization strategy ensures the precise distribution of functional components at the interface, improves the utilization efficiency of additives, and reduces the impact on the bulk performance of the electrolyte. This is because: 1) the first and second precursors, as small molecule compounds, have good electrolyte solubility and can be uniformly dissolved in the electrolyte bulk; 2) targeted in-situ generation—the goal of this application is to precisely construct a self-healing layer at the negative electrode interface (the location where the SEI film forms and needs protection). By using the precursors, these dissolved small molecules can freely diffuse with the electrolyte to the negative electrode surface; 3) triggering of reaction conditions—the Schiff base formation reaction between the first and second precursors can be initiated or significantly accelerated by the specific electrochemical environment of the negative electrode. When the battery is charged, the negative electrode reaches a low reduction potential (e.g., below 0.5V vs. Li / Li). + This strongly reducing environment promotes the reaction of amine and aldehyde groups. This means that the polymer network is mainly generated at the anode interface where SEI needs to be formed or repaired, and within an appropriate electrochemical window, rather than through uncontrolled polymerization in the electrolyte bulk. Finally, regarding interfacial bonding and morphology—polymer networks formed by direct growth and polymerization at the interface can form tighter, more conformally preserved bonds with the anode surface and other SEI components, resulting in a higher quality and more uniform interfacial layer compared to pre-synthesized polymer particles obtained by physical deposition.

[0046] Furthermore, the synergistic effect of the composite gradient structure can provide durable mechanical protection while maintaining low interfacial impedance, achieving a dual optimization of performance and durability.

[0047] Based on battery type, battery casings can be divided into cylindrical battery casings, square battery casings, and pouch battery casings. Cylindrical battery casings are usually made of steel or aluminum alloy; square battery casings are usually made of aluminum or steel; pouch battery casings are usually made of aluminum-plastic composite film, which includes an outer layer (nylon / PET), a middle layer (aluminum foil), and an inner layer (PP heat-sealing layer).

[0048] This application is also applicable to lithium batteries with positive electrodes, negative electrodes, and separators made of various materials, such as:

[0049] The cathode can be composed of a variety of materials, covering a full range of cathode material types from low voltage to high voltage. Layered oxide cathode materials include lithium cobalt oxide (LiCoO2) and ternary materials (LiNi). x Co y Mn z O2, such as NCM111, NCM523, NCM622, NCM811, etc., lithium nickel cobalt aluminum oxide (LiNi x Co y Al z O2, such as NCA), high-nickel ternary materials (LiNi) 0.9 Co 0.05 Mn 0.05 O2, etc.) and cobalt-free materials (LiNiO2, LiNi x Mn y O2). Spinel-structured cathode materials include lithium manganese oxide (LiMn2O4) and high-voltage spinel (LiNi). 0.5 Mn 1.5 Lithium iron phosphate (LiFePO4) and doped modified lithium manganese oxide. Polyanionic cathode materials include lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium cobalt phosphate (LiCoPO4), lithium vanadium phosphate (Li3V2(PO4)3), lithium iron pyrophosphate (Li2FeP2O7), and lithium iron silicate (Li2FeSiO4). Lithium-rich manganese-based cathode materials (Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 The O2-Li2MnO3·(1-x)LiMO2 system has attracted attention due to its high specific capacity. Transition metal fluoride cathode materials include high-voltage materials such as iron trifluoride (FeF3), cobalt trifluoride (CoF3), and lithium vanadium fluorophosphate (LiVPO4F). Organic cathode materials include environmentally friendly materials such as carbonyl polymers, quinone compounds, free radical polymers, and conductive polymers.

[0050] The positive electrode formulation includes a positive electrode active material (usually accounting for 85 wt% to 98 wt%, specifically it can be: 85 wt%, 86 wt%, 87 wt%, 88 wt%, 89 wt%, 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, 96 wt%, 97 wt%, 98 wt%), a binder (1 wt% to 8 wt%, specifically it can be: 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%), and a conductive agent (1 wt% to 10 wt%, specifically it can be: 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%). The positive electrode binder mainly uses organic solvent system binders such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or modified PVDF materials such as polyvinylidene fluoride - hexafluoropropylene copolymer (PVDF - HFP). The conductive agent includes carbon black (such as Super P, Ketjenblack), acetylene black, carbon nanotubes, graphene, carbon fiber, and conductive graphite, etc. The positive electrode current collector usually uses aluminum foil, and carbon - coated aluminum foil, titanium foil, or other high - voltage - resistant conductive substrates can also be used.

[0051] The negative electrode is mainly composed of negative electrode materials with high capacity and high expansion change to fully exert the advantages of the self - healing SEI technology of this application. The silicon - based negative electrode materials include pure silicon (nano - silicon, micro - silicon), silicon monoxide (SiO x , 0 < x < 2), silicon - carbon composite materials (Si / C, Si / graphene, Si / carbon nanotubes), silicon alloys (Si - Al, Si - Fe, etc.), and porous silicon materials. The tin - based negative electrode materials include pure tin, tin oxides (SnO2, SnO), tin - carbon composite materials (Sn / C), tin alloys (Sn - Co, Sn - Fe, Sn - Cu, etc.), and tin - based composite oxides. The germanium - based negative electrode materials include pure germanium, germanium - carbon composite materials, and germanium alloys and other high - capacity materials. The lithium metal negative electrode, as the ultimate negative electrode material, includes metal lithium foil (thickness 5 μm to 500 μm), ultra - thin lithium foil, surface - structured lithium metal (with micro - nano structure), three - dimensional lithium metal (porous lithium, lithium - filled conductive skeleton), and lithium alloys (Li - Al, Li - Si, Li - In, etc.). The lithium - based composite negative electrode includes lithium - carbon composite materials, lithium - metal matrix composite materials, and prelithiated negative electrode materials. The interface engineering technology for high - expansion negative electrodes includes the construction of an artificial SEI film, and organic protective layers (conductive polymers, polymer electrolytes), inorganic protective layers (LiF, Li3N, Al2O3, Li2CO3), or organic - inorganic composite protective layers can be used. The surface modification technology includes methods such as carbon coating, metal coating, oxide coating, and ion implantation. The structure design technology includes morphology control strategies such as core - shell structure, yolk - shell structure, porous structure, and nanowire array.

[0052] The negative electrode formulation (suitable for coated negative electrodes) includes negative electrode active material (typically 80wt% to 95wt%, specifically 80wt%, 81wt%, 82wt%, 83wt%, 84wt%, 85wt%, 86wt%, 87wt%, 88wt%, 89wt%, 90wt%, 91wt%, 92wt%, 93wt%, 94wt%, 95wt%), binder (2wt% to 15wt%, specifically 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%), and optional conductive agent (2wt% to 10wt%, specifically 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%). Specialized binders for high-expansion anodes include water-based or organic solvent-based binders such as styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), polyacrylic acid (PAA), sodium alginate, polyimide (PI), cross-linked polymer binders, and self-healing binders. Among these, the CMC / SBR composite binder system is widely used in silicon-based anodes due to its excellent adhesion and flexibility, while PAA is particularly suitable for silicon anode materials due to its strong interaction with the silicon surface. Conductive agents can be highly conductive materials such as Super P carbon black, carbon nanotubes, graphene, and carbon fibers. The anode current collector is typically copper foil, but carbon-coated copper foil, nickel foil, stainless steel foil, or surface-modified current collectors can also be used to optimize interfacial stability with the high-expansion anode.

[0053] The separators are composed of various materials adapted to high-expansion anode systems. Polyolefin separators include polypropylene (PP) separators, polyethylene (PE) separators, PP / PE / PP three-layer composite separators, and ultra-high molecular weight polyethylene (UHMWPE) separators, exhibiting good mechanical strength and electrochemical stability. Ceramic-coated separators, with Al2O3, SiO2, TiO2, ZrO2, and other ceramic particles coated on a polyolefin substrate, significantly improve heat resistance, puncture resistance, and safety, making them particularly suitable for suppressing dendrite formation that may occur in high-expansion anodes. High-performance polymer separators include polyimide (PI) separators, polyetheretherketone (PEEK) separators, polyphenylene sulfide (PPS) separators, and aramid nanofiber separators, possessing excellent mechanical strength, high-temperature resistance, and puncture resistance. Functionalized separators include lithiophilic coated separators, ion-selective separators, flame-retardant separators, and self-turn-off separators, which can further enhance compatibility with high-expansion anodes. Composite membrane technologies include advanced structures such as solid electrolyte coated membranes (coated with LLZO, LLTO, PEO, etc.), gel polymer electrolyte membranes, and gradient functional membranes. These membrane designs can synergize with the self-healing SEI technology of this application to further improve lithium-ion transport efficiency, suppress dendrite growth, and extend battery cycle life, and are particularly suitable for the long-term stable operation of high-capacity, high-expansion anode materials such as silicon-based, tin-based, and lithium metal.

[0054] The secondary battery described in this application can employ any one or more of the above-mentioned technologies in combination. By matching the self-healing SEI electrolyte additive system with the optimized battery components, stable cycling and long-life operation of high-capacity negative electrode materials can be achieved.

[0055] The secondary battery described in this application employs a fabrication process adapted to high-capacity anode materials, achieving selective in-situ polymerization of the first and second precursors at the anode interface through precise control of electrochemical conditions. The battery fabrication process includes key steps such as electrode fabrication, battery assembly, electrolyte injection, and electrochemical activation formation.

[0056] During electrode fabrication, the positive electrode is prepared through processes such as slurry coating, drying, and compaction, while the negative electrode can be prepared using a silicon-based composite material coating process or by directly using lithium metal foil. Battery assembly employs conventional stacking or winding processes, where the positive electrode, separator, and negative electrode are stacked or wound in sequence to form a cell assembly, which is then encapsulated in an aluminum-plastic film or rigid shell.

[0057] The working principle of the secondary battery prepared in the embodiments of this application is as follows: Figure 3 As shown:

[0058] During the charging process of the secondary battery, lithium ions in the positive electrode 1 are deintercalated and, under the influence of an electric field, enter the electrolyte 5 from the surface of the positive electrode 1, pass through the separator 4, migrate to the surface of the negative electrode 2, and then intercalate into the crystal lattice of the negative electrode 2 material. During the discharging process of the secondary battery, lithium ions in the crystal lattice of the negative electrode 2 material are deintercalated and entered the electrolyte 5, pass through the separator 4, migrate to the surface of the positive electrode 1, and then re-intercalate into the surface of the positive electrode 1. The charging and discharging processes of the secondary battery continuously involve redox reactions, and the density and stability of the SEI film are crucial to the performance of the secondary battery.

[0059] In some embodiments, the first precursor has a mass percentage of 0.5% to 3% in the electrolyte, and the second precursor has a mass percentage of 0.5% to 3% in the electrolyte.

[0060] The specific mass percentage of the first precursor in the electrolyte can be 0.5%, 1%, 1.5%, 2%, 2.5%, or 3%.

[0061] In some embodiments, the molar ratio of the first precursor to the second precursor is (0.8–1.2):1, optionally (0.95–1.05):1. This molar ratio range ensures that the two precursors can react sufficiently and avoids subsequent side reactions or interfacial inhomogeneities caused by unreacted monomer residues.

[0062] In some embodiments, the molar ratio of the first precursor to the second precursor may be selected as (0.95 to 1.05):1.

[0063] The molar ratio of the first precursor to the second precursor can be 0.8:1, 0.85:1, 0.9:1, 0.95:1, 1:1, 1.05:1, 1.1:1, 1.15:1, or 1.2:1.

[0064] In some embodiments, the first precursor is phenylenediamine, pentanediamine, or propylenediamine, and the second precursor is phenylenedialdehyde, glutaraldehyde, or malondialdehyde.

[0065] In some embodiments, the process of the formation step Figure 2 As shown, it includes:

[0066] S41. Perform a pre-activation step to initiate the condensation reaction of the first precursor and the second precursor. In the pre-activation step, the charging is performed at a first rate, and the negative electrode potential is less than the first preset potential. The charging time is the first preset duration.

[0067] S42. Perform the network construction step. In the network construction step, charge at a second rate, and the negative electrode potential is within the target potential range. The charging time is a second preset duration, and the second rate is greater than the first rate.

[0068] S43. Perform a stabilization step, in which charging is performed at a third rate, which is greater than the second rate.

[0069] The pre-activation step initiates the condensation reaction of the first and second precursors; the network construction step promotes the formation of the polymer network; and the stabilization step perfects the composite SEI structure.

[0070] In some embodiments, the first multiplier is 0.01 to 0.05C, the first preset potential is 0.5V, and the first preset duration is 10h to 20h.

[0071] The pre-activation stage employs ultra-low rate charging, designed to provide sufficient time for the adsorption, orientation, and initial reaction of the first and second precursors at the negative electrode interface. This is achieved when the negative electrode potential slowly decreases to 0.5V (Li / Li). + In this case, the strong reducing microenvironment formed at the interface can activate the nucleophilicity of the amino group in the first precursor molecule, promoting its condensation reaction with the aldehyde group in the second precursor molecule, forming the initial polymer seed nucleus.

[0072] The first multiplier can be 0.01C, 0.02C, 0.03C, 0.04C, or 0.05C, and the first preset duration can be 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, or 20h.

[0073] In some embodiments, the second multiplier is 0.02C to 0.1C, and the second preset duration is 6h to 20h.

[0074] The second multiplier can be 0.02C, 0.03C, 0.04C, 0.05C, 0.06C, 0.07C, 0.08C, 0.09C, or 0.1C. The second preset duration can be 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, or 20h.

[0075] In some embodiments, the third multiplier is 0.05C to 0.1C.

[0076] The second multiplier can be: 0.05C, 0.06C, 0.07C, 0.08C, 0.09C, or 0.1C.

[0077] In some embodiments, the target potential range is 0.1V to 0.5V.

[0078] During the network construction phase, precise potential control maintains the negative electrode potential at 0.1V–0.5V (Li / Li). + Within this potential window, the reaction can maintain the reducing environment required for the reaction between the first and second precursors while avoiding side reactions caused by excessive reduction. During this stage, the Schiff base bond formation reaction continues, the polymer chains gradually grow and cross-link, ultimately forming a three-dimensional network structure covering the negative electrode surface. The reaction time is controlled between 6 and 24 hours to ensure that the degree of polymerization reaches the target range of 20 to 100, corresponding to a molecular weight of approximately 3000 Da to 15000 Da.

[0079] The target potential can be 0.1V, 0.2V, 0.3V, 0.4V, or 0.5V.

[0080] In some embodiments, during the stabilization step, 1 to 3 charging cycles are performed, and the negative electrode potential is the normal operating voltage of the secondary battery.

[0081] During the stabilization phase, 1 to 3 complete charge-discharge cycles are performed, with the current rate gradually increased to 0.05C to 0.1C, and the voltage window set according to the battery system. The goal of this phase is to promote the synergistic film formation of poly(Schiff base) networks and traditional SEI components (such as LiF, Li2CO3, alkyl lithium carbonate, etc.) to form an organic-inorganic composite structure with interpenetrating network characteristics.

[0082] In some embodiments, the temperature of the formation step is 25°C to 60°C.

[0083] A moderate temperature increase improves the diffusion kinetics and reaction rate of PPD and TPA molecules, while avoiding electrolyte decomposition or non-selective reactions of the precursor in the bulk electrolyte due to excessively high temperatures. Precise temperature control is crucial for ensuring interfacial selectivity in the polymerization reaction.

[0084] In some embodiments, the temperature of the formation step is preferably 30°C to 50°C.

[0085] The specific temperatures for the formation step can be: 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, and 60℃.

[0086] In some embodiments, T2 > T3 > T1, where T1 is the temperature of the pre-activation step, T2 is the temperature of the network construction step, and T3 is the temperature of the stabilization step.

[0087] In some embodiments, T1 is 25°C to 40°C, network T2 is 35°C to 50°C, and T3 is 30°C to 45°C.

[0088] In some embodiments, the electrolyte is prepared by:

[0089] Preparation of non-aqueous solvents;

[0090] The electrolyte salt is dissolved in a non-aqueous solvent to obtain the basic electrolyte;

[0091] The first precursor was added to the basic electrolyte and stirred until dissolved. Then the second precursor was added and stirred until dissolved to obtain the electrolyte.

[0092] The electrolyte, based on total weight, has a non-aqueous solvent mass percentage of 60wt% to 90wt%, specifically 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, and 90wt%, serving as the main carrier of the electrolyte; the conductive lithium salt has a molar concentration of 0.5mol / L to 2.0mol / L, optionally 0.8mol / L to 1.5mol / L, specifically 0.5mol / L, 0.6mol / L, 0.7mol / L, 0.8mol / L, 0.9mol / L, 1mol / L, 1.1mol / L, 1.2mol / L, 1.3mol / L, 1.4mol / L, 1.5mol / L, 1.6mol / L, 1.7mol / L, 1.8mol / L, 1.9mol / L, and 2.0mol / L.

[0093] This electrolyte composition is used to provide a lithium-ion carrier; in addition, it may optionally contain auxiliary additives in a total mass percentage of 0 to 5 wt%, specifically 0, 1%, 2%, 3%, 4%, or 5%.

[0094] The non-aqueous solvent is selected from one or more of carbonates, ethers, or mixtures thereof. Other types of solvents, such as sulfones, ionic liquids, nitriles, and esters, may also be added according to system requirements. Carbonate solvents include, but are not limited to, ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), butenyl carbonate (BC), and ethylene sulfite carbonate (VCS). Ether solvents include, but are not limited to, 1,2-dimethoxyethane (DME), 1,3-dioxolane (DOL), dimethyl ether (DME), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), and 1,4-dioxane. The selected non-aqueous organic solvent or mixture thereof should possess a suitable dielectric constant to promote lithium salt dissociation, low viscosity to ensure rapid lithium ion migration, a wide liquid temperature range, and electrochemical stability within the battery operating voltage window, thereby effectively dissolving the components and providing good electrochemical stability while ensuring electrolyte conductivity.

[0095] Conductive lithium salts include one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium hexafluoroantimonyate (LiSbF6), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium bis(oxalate borate) (LiBOB), lithium trifluoromethanesulfonate (LiTfO), and lithium nitrate (LiNO3), preferably one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). In mixed lithium salt systems, cost-effectiveness and SEI film quality can be balanced.

[0096] Both the first and second precursors are of battery-grade purity (≥99%), with a water content of less than 100 ppm and a solubility of more than 1 wt% in the aforementioned non-aqueous solvents, ensuring uniform distribution in the electrolyte.

[0097] Optional auxiliary additives should avoid strong nucleophiles, strong electrophiles, or strong oxidizing agents. Recommended compatible additives include mild film-forming additives such as fluoroethylene carbonate (FEC) and vinylene carbonate (VC).

[0098] In some embodiments, the content of both H2O and O2 in the electrolyte preparation environment is below 1 ppm.

[0099] According to some embodiments of this application, another aspect of this application provides a secondary battery, which is prepared using the secondary battery manufacturing method described in the above embodiments.

[0100] According to some embodiments of this application, another aspect of this application provides an energy storage system, including a secondary battery as described in the above embodiments.

[0101] According to some embodiments of this application, in another aspect, this application provides an electrical device, the electrical device including the secondary battery described in the above embodiments; or, the electrical device including an energy storage system as described in the above embodiments, wherein the energy storage system includes a battery pack, the battery pack including multiple batteries, an energy management system (EMS), a battery management system (BMS), and an energy storage converter (PCS), and the electrical device includes vehicles, household appliances, electric motors, medical equipment, scientific research instruments, power grids, etc.

[0102] The technical solution of this application is based on the following principle: When a first precursor containing two amine (-NH2) functional groups and a second precursor containing two aldehyde (-CHO) functional groups coexist in the electrolyte and come into contact with the negative electrode surface, under the reducing environment during battery charging, the amine and aldehyde groups undergo a condensation reaction to generate a molecular structure with C=N bonds (Schiff base bonds). Since each first and second precursor molecule has two reaction sites, this reaction can continue to extend, forming a polymer network containing [-N=CH-Ph-CH=N-Ph-]n structural units. This polymer network, together with the traditional SEI component, constitutes a composite interface film.

[0103] The use of a first and second precursor, rather than directly adding pre-synthesized polymers containing Schiff base bonds to the electrolyte, is primarily based on the following considerations: First, solubility—the final poly(Schiff base) network is a high-molecular-weight, possibly even cross-linked, three-dimensional structure. These large-molecule polymers typically have extremely low or no solubility in commonly used battery electrolytes. Directly adding such polymer powder would not only be difficult to dissolve, but also impossible to uniformly disperse and effectively cover the nano- or micro-scale anode interface. In contrast, the first and second precursors, as small-molecule compounds, have good electrolyte solubility and can dissolve uniformly in the electrolyte bulk. Second, targeted in-situ generation—the goal of this application is to precisely construct a self-healing layer at the anode interface (the location where the SEI film forms and needs protection). By using the precursors, these dissolved small molecules can freely diffuse with the electrolyte to the anode surface. Third, the triggering of reaction conditions—the Schiff base formation reaction between the first and second precursors can be initiated or significantly accelerated by the specific electrochemical environment of the anode. When the battery is charged, the negative electrode reaches a low reduction potential (e.g., below 0.5V vs. Li / Li). + This strongly reducing environment promotes the reaction of amine and aldehyde groups. This means that the polymer network is mainly generated at the anode interface where SEI needs to be formed or repaired, and within an appropriate electrochemical window, rather than through uncontrolled polymerization in the electrolyte bulk. Finally, regarding interfacial bonding and morphology—polymer networks formed by direct growth and polymerization at the interface can form tighter, more conformally preserved bonds with the anode surface and other SEI components, resulting in a higher quality and more uniform interfacial layer compared to pre-synthesized polymer particles obtained by physical deposition.

[0104] The core innovation of this application lies in the fact that the Schiff base bond (C=N) generated by the reaction of the first and second precursors is a dynamic covalent bond. The special feature of this bond is its inherent reversibility: under certain conditions (such as mechanical force or the presence of trace amounts of water or other catalysts), the C=N bond can break, and then reform under suitable conditions. This dynamic equilibrium endows the SEI film containing this structure with a unique self-healing ability. When the negative electrode expands and puts stress on the SEI, the partial breakage of the Schiff base bond can relieve stress and prevent crack propagation; when the stress is removed, the broken bond can reclose, achieving self-repair of the damage. Simultaneously, this dynamism also gives the SEI film better flexibility to adapt to the deformation of the negative electrode. Theoretical calculations show that the breaking energy of the Schiff base bond is typically in the range of 40 kJ / mol to 60 kJ / mol, significantly lower than that of traditional covalent bonds (typically >200 kJ / mol). This gives it ideal dynamic characteristics, allowing it to break and release energy under appropriate stress and spontaneously recombine after stress is removed.

[0105] In summary, this application introduces a specific, soluble precursor combination (such as p-phenylenediamine and terephthalaldehyde) into the electrolyte, utilizing its electrochemically triggered in-situ polymerization at the anode interface to generate a self-healing SEI functional layer containing dynamic Schiff base bonds. This strategy not only solves the challenge of effectively introducing functional polymers into the interface but also endows the SEI film with the ability to actively adapt to volume changes and repair damage through dynamic chemical bonds. Therefore, this approach is expected to significantly improve the interfacial stability of high-capacity anodes, enhance the cycle life and reliability of secondary batteries, and provide a valuable innovative approach for the development of next-generation high-energy-density energy storage technologies.

[0106] The fundamental differences between the basic principles and technical approach of this application and existing technologies

[0107] Existing technologies primarily employ a passive protection approach, addressing the challenges of volume changes in high-capacity anodes by optimizing the initial chemical composition of the SEI film or enhancing the mechanical constraints of electrode materials. Typical solutions include using film-forming additives (such as FEC and VC) to improve the chemical stability of the SEI, or dispersing stress through nano-sizing and composite design of electrode materials. However, these methods essentially still belong to the design philosophy of "one-time film formation - passively bearing the impact," meaning that the SEI film solidifies into a static structure after its initial formation, passively bearing the mechanical impacts of subsequent cycles, lacking the ability to actively adapt and self-repair.

[0108] This application employs a radically different active adaptive technology approach, based on a design philosophy of "dynamic response-continuous repair." By introducing p-phenylenediamine and terephthalaldehyde precursors, a polymer network containing dynamic covalent bonds is constructed in situ at the negative electrode interface, enabling the SEI film to acquire intrinsic self-healing capabilities. The core of this technological concept lies in introducing the self-healing concept from materials science into battery interface engineering, fundamentally altering the interaction mode between the SEI film and mechanical stress.

[0109] Logical Innovation of the Solution in this Application

[0110] The core contradiction in existing technologies lies in the irreconcilable conflict between the mechanical strength and adaptability of SEI films: increasing mechanical strength often comes at the cost of flexibility, while enhancing flexibility may reduce structural stability. This application cleverly decouples this inherent contradiction by introducing the concept of dynamic covalent bonds. The dynamic reversible nature of Schiff base bonds (C=N) allows SEI films to release energy through controlled bond breakage under stress, avoiding macroscopic rupture caused by stress concentration, and to restore structural integrity through bond recombination after stress relief.

[0111] Furthermore, existing technologies generally employ a direct addition strategy of pre-synthesized materials, which faces problems such as poor solubility and uneven interface coverage. This application innovatively adopts an in-situ precursor polymerization strategy, utilizing the good solubility and diffusivity of small-molecule precursors, combined with the specific electrochemical environment of the negative electrode interface, to achieve targeted polymer generation. This design not only solves the problem of introducing functional polymers but also achieves interfacial selectivity in the polymerization reaction, ensuring that the self-healing function precisely acts on the negative electrode surface that most needs protection.

[0112] This application demonstrates a creative breakthrough in structural design.

[0113] The organic-inorganic composite SEI membrane constructed in this application exhibits a unique interpenetrating network and gradient distribution structure, reflecting a profound understanding of the multiple functional requirements of SEI membranes. The inner inorganic phase provides mechanical support and electronic insulation, the middle composite network establishes ion transport channels, and the outer polymer network provides flexible buffering and self-healing functions. This layered synergistic design fundamentally solves the performance trade-off between mechanical protection, ion conduction, and interfacial stability in traditional SEI membranes.

[0114] Compared to the single-function optimization of existing technologies, this application achieves multi-functional synergistic integration, enabling the SEI membrane to maintain excellent ion conductivity while gaining continuous self-healing ability, thus enabling it to adapt to the drastic volume changes of high-capacity anodes over a long period of time.

[0115] The logical basis for the expected beneficial effects of this application

[0116] Based on the above-mentioned technological innovations, this application is expected to bring the following beneficial effects: First, the self-healing mechanism of dynamic covalent bonds can significantly delay the damage accumulation of the SEI film, fundamentally improving the cycle stability of high-capacity anodes; Second, the in-situ polymerization strategy ensures the precise distribution of functional components at the interface, improves the utilization efficiency of additives and reduces the impact on the bulk performance of the electrolyte; In addition, the synergistic effect of the composite gradient structure can provide durable mechanical protection while maintaining low interfacial impedance, achieving dual optimization of performance and durability.

[0117] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0118] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0119] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0120] In the description of the embodiments of this application, when a component "includes" another component, other components are not excluded unless otherwise stated, and other components may be further included. Furthermore, when a component such as a layer, film, region, or plate is referred to as being "on / located" on another component, it can be "directly on" the other component (i.e., located on the surface of the other component with no other components between them), or it can have another component present in between. Moreover, when a component such as a layer, film, region, or plate is "directly located" on another component, or when a component such as a layer, film, region, or plate is located on the surface of another component, it indicates that no other components are located in between.

[0121] The terminology used in the description of the various embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the description of the various embodiments and the appended claims, the term "part" is also intended to include the plural form unless the context clearly indicates otherwise. Components include layers, films, regions, or plates, etc.

[0122] The embodiments of this application will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this application to facilitate a better understanding of the application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0123] Example 1

[0124] This embodiment provides a method for preparing a secondary battery (3Ah small soft-pack stacked battery, using a single-layer stacked structure), including:

[0125] A battery cell assembly is provided, wherein the battery cell assembly is composed of a positive electrode, a separator, and a negative electrode stacked together, wherein the positive electrode is made of NCM ternary material (LiNi). 0.6 Co 0.2 Mn 0.2 O2), is prepared through processes such as slurry coating, drying, and compaction; the negative electrode sheet is made of silicon-carbon composite material and is prepared through a coating process.

[0126] An aluminum-plastic film is provided as the housing, and the housing has a receiving chamber. The battery cell assembly is placed in the receiving chamber. The assembled battery is dried in a vacuum oven at 80°C for 24 hours to ensure that the internal moisture content of the battery is less than 50ppm.

[0127] An electrolyte is provided and injected into the receiving chamber, and allowed to stand at room temperature for 12 hours to ensure that the electrolyte fully wets the battery cell assembly; the electrolyte includes an electrolyte salt, a non-aqueous solvent, p-phenylenediamine and terephthalaldehyde, wherein the p-phenylenediamine and terephthalaldehyde can undergo in-situ polymerization at the interface of the negative electrode to form a network structure with Schiff base bonds;

[0128] The formation process includes:

[0129] 1. Pre-activation step, wherein the pre-activation step involves charging at a rate of 0.01C to 0.05C at 25℃ to 40℃, with the negative electrode potential less than 0.5V, for a charging time of 10h to 20h, in order to initiate the condensation reaction of p-phenylenediamine and terephthalaldehyde.

[0130] 2. Network construction step, wherein the network construction step is carried out at 35℃~50℃, charged at a rate of 0.02C~0.1C, and the negative electrode potential is 0.1V~0.5V, and the charging time is 6h~20h, so as to promote the formation of polymer network;

[0131] Third, the stabilization step, wherein the battery is charged at a rate of 0.05C to 0.1C at a temperature of 30℃ to 45℃, and the negative electrode potential is the normal operating voltage of the secondary battery, for 1 to 3 charging cycles to improve the composite SEI structure.

[0132] The electrolyte is prepared by:

[0133] Materials: p-Phenylenediamine (PPD), analytical grade reagent, purity ≥99.5%, dried in a vacuum drying oven at 60℃ for 24 hours before use to remove adsorbed moisture, ensuring moisture content is below 10ppm; terephthalaldehyde (TPA), analytical grade reagent, purity ≥99.5%, dried in a vacuum drying oven at 50℃ for 12 hours before use to avoid decomposition caused by high temperature, ensuring moisture content is below 10ppm; ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) are all battery-grade reagents with moisture content <20ppm, further dried by 4A molecular sieves before use; lithium hexafluorophosphate, battery-grade reagent, purity ≥99.99%, moisture content <50ppm, stored in a dry argon atmosphere.

[0134] Preparation of basic electrolyte: In a glove box under a high-purity argon atmosphere (H2O and O2 content controlled below 1ppm), ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were accurately weighed and mixed in a mass ratio of 3:3:4. The mixture was stirred on a magnetic stirrer for 30 minutes until completely homogeneous. Then, lithium hexafluorophosphate was added and stirred for 2 hours until completely dissolved to prepare a basic electrolyte with a concentration of 1.0 mol / L.

[0135] Electrolyte preparation: Pretreated p-phenylenediamine and terephthalaldehyde were accurately weighed according to calculation. First, p-phenylenediamine was added to the basic electrolyte and stirred on a magnetic stirrer for 1 hour until completely dissolved, resulting in a pale yellow and transparent solution. Then, terephthalaldehyde was added, and stirring continued for 2 hours until completely dissolved, finally obtaining a colorless and transparent electrolyte. The weight percentages of PPD and TPA in the electrolyte were both 1.5%, and the molar ratio of PPD to TPA was 1:1. The prepared electrolyte was filtered through a 0.45 μm polytetrafluoroethylene (PTFE) membrane to remove possible insoluble impurities, and then transferred to a sealed container for storage.

[0136] The formation process is designed based on the electrochemical triggering mechanism of the in-situ polymerization reaction of PPD and TPA. The pre-activation stage employs an ultra-low charging rate of 0.02C, causing the negative electrode potential to slowly decrease to 0.5V vs Li / Li. + The following steps establish a strongly reducing microenvironment at the interface, activating the nucleophilicity of the amine groups in the PPD molecule. During the network construction phase, the negative electrode potential is precisely maintained at 0.1V–0.5V vsLi / Li.+ Within a 12-hour timeframe, the formation of Schiff base bonds between PPD and TPA molecules and the construction of the polymer network are promoted. During the stabilization phase, low-rate cycling at 0.05C promotes the synergistic film formation of the poly(Schiff base) network and the traditional SEI component, forming an organic-inorganic composite self-healing interface structure.

[0137] Example 2

[0138] The only difference between this embodiment and Example 1 is that the weight percentage of PPD and TPA in the electrolyte is 0.8%, and the molar ratio of PPD to TPA is 1:1.

[0139] Example 3

[0140] The only difference between this embodiment and Example 1 is that the weight percentage of PPD and TPA in the electrolyte is 2.5%, and the molar ratio of PPD to TPA is 1:1.

[0141] Example 4

[0142] The only difference between this embodiment and Embodiment 1 is that the weight percentage of PPD in the electrolyte is 1.5%, the weight percentage of TPA in the electrolyte is 1.85%, and the molar ratio of PPD to TPA is 1:1.2.

[0143] Example 5

[0144] The only difference between this embodiment and Embodiment 1 is that the negative electrode is a lithium metal negative electrode.

[0145] Example 6

[0146] The only difference between this embodiment and Embodiment 1 is that the first polymer precursor is m-phenylenediamine and the second polymer precursor is m-phenylenedialdehyde.

[0147] Example 7

[0148] The only difference between this embodiment and Embodiment 1 is that the first polymer precursor is pentanediamine and the second polymer precursor is glutaraldehyde.

[0149] Example 8

[0150] The only difference between this embodiment and Embodiment 1 is that the first polymer precursor is propylenediamine and the second polymer precursor is malondialdehyde.

[0151] Comparative Example 1

[0152] The only difference between this comparative example and Example 1 is that p-phenylenediamine and terephthalaldehyde were not added to the electrolyte, and the formation method was conventional. The conventional formation method is as follows: the temperature is controlled at 25°C, and three charge-discharge cycles are performed at a current rate of 0.1C. The electrolyte is charged at constant current to 4.2V, charged at constant voltage until the current decays to C / 20, and discharged at constant current to 2.5V. There is no staged potential control.

[0153] Comparative Example 2

[0154] The only difference between this comparative example and Example 1 is that p-phenylenediamine and terephthalaldehyde were not added to the electrolyte, but fluoroethylene carbonate was added, and the formation method was conventional. The mass fraction of fluoroethylene carbonate in the electrolyte was 2%.

[0155] Comparative Example 3

[0156] The only difference between this comparative example and Example 1 is that the formation method is conventional.

[0157] Comparative Example 4

[0158] The only difference between this comparative example and Example 1 is that the charging rate in the pre-activation step is 0.06C.

[0159] Comparative Example 5

[0160] The only difference between this comparative example and Example 1 is that the negative electrode potential is 0.6 to 1.0 V in the network construction step.

[0161] Comparative Example 6

[0162] The only difference between this comparative example and Example 1 is that the temperature during the formation is 20°C.

[0163] Example 9

[0164] This embodiment provides an energy storage system, including a secondary battery prepared according to any one of Embodiments 1 to 8.

[0165] Example 10

[0166] This embodiment provides an electrical device, including a secondary battery prepared according to any one of Embodiments 1 to 8.

[0167] Example 11

[0168] This embodiment provides an electrical device, including the energy storage system in Embodiment 9.

[0169] The performance of the secondary batteries in Examples 1-8 and Comparative Examples 1-6 was tested. The test items and verification design are shown in Table 1. Specifically, they included:

[0170] First-week coulombic efficiency test: The battery was charged at 1C constant current to 4.2V at an ambient temperature of 25℃, then switched to constant voltage charging until the current decayed to C / 20, and subsequently discharged at 1C constant current to 2.5V. The first-week coulombic efficiency was calculated as the percentage of the initial discharge capacity to the initial charge capacity, used to evaluate the initial film formation quality of the SEI film and the degree of side reactions.

[0171] Cyclic stability testing: A 1C charge-discharge cycle test was conducted at 25℃ for a total of 300 cycles. Charging was performed in constant current / constant voltage (CCCV) mode, with 1C constant current charging to 4.2V, followed by constant voltage charging until the current decayed to C / 20. Discharging was performed with 1C constant current until a cutoff voltage of 2.5V. Capacity retention was calculated as the percentage of discharge capacity at cycle 300 to discharge capacity at cycle 3, with cycle 3 used as a baseline to eliminate the influence of initial activation.

[0172] Internal resistance evolution test: With the battery at 50% state of charge (SOC), a 1C current pulse is applied for 10 seconds, and the voltage drop ΔV is measured. The DC internal resistance DCR = ΔV / ΔI is calculated. Tests are performed after the 1st and 300th cycles. The rate of change of internal resistance = (DCR) / ΔI. 300 -DCR1) / DCR1×100%, used to quantify the evolution trend of interface impedance.

[0173] High-temperature cycling test: A 1C charge-discharge cycle test was conducted at 45℃ for a total of 300 cycles. The test conditions were the same as those for room-temperature cycling, and were used to evaluate the battery's cycle stability and thermal stability under high-temperature conditions.

[0174] Self-healing capability verification test: A special stress cycling pattern was designed to verify the dynamic repair capability of the SEI membrane. The test consisted of three phases: a baseline cycling phase at 25°C for 50 cycles at a 1C rate to establish a stable performance benchmark; a stress shock phase involving 10 cycles at a 3C high rate to apply mechanical stress to the SEI membrane, causing microscopic damage; and a repair verification phase involving another 30 cycles at a 1C rate to observe capacity recovery. The entire cycling pattern was repeated three times. The self-healing efficiency was calculated as the percentage of repaired capacity to baseline capacity, used to quantify the dynamic repair capability of the SEI membrane.

[0175] Table 1 Test Items and Verification Design

[0176]

[0177] Experimental Data and Results Analysis

[0178] Through the above system tests, detailed performance data for each embodiment and comparative example were obtained, and the results are shown in Table 2.

[0179] Table 2 Comparison of performance data for each embodiment and comparative example

[0180]

[0181]

[0182] The test results of the SEI films with network crosslinked Schiff base bonds obtained in the various embodiments and comparative examples of this application are analyzed and discussed.

[0183] I. Verification of the effectiveness of core technologies

[0184] The performance comparison between Comparative Example 1 and Example 1 fully demonstrates the significant technical advantages of the PPD and TPA precursor self-healing SEI system. Compared to Comparative Example 1, Example 1 showed an increase in first-cycle coulombic efficiency from 72.4% to 86.3%, an improvement of 13.9 percentage points, indicating that the electrolyte containing PPD and TPA precursors can form a higher-quality initial SEI film with fewer side reactions on the negative electrode surface. More importantly, in the 300-cycle test at 1C rate, the capacity retention rate of Comparative Example 1 was only 45.8%, while that of Example 1 reached 82.6%, an improvement of 36.8 percentage points. This significant difference directly verifies the excellent stability of the self-healing SEI film during high-rate long-term cycling.

[0185] Internal resistance evolution data further support the above conclusions. Comparative Example 1 showed an internal resistance increase of +68.5% after 300 cycles, reflecting severe rupture and thickening of the traditional SEI film under repeated volumetric stress, leading to a sharp increase in interfacial impedance. In contrast, Example 1 showed an internal resistance increase of only +18.7%, demonstrating excellent interfacial stability. The fundamental reason for this difference lies in the dynamic covalent bond structure of the poly(Schiff base) network constructed in this application, which can adapt to the volumetric changes of the negative electrode through a reversible bond breakage-recombination mechanism, maintaining long-term interfacial stability.

[0186] II. Verification of the Advanced Nature of the Technical Route

[0187] Comparative Example 2, using a traditional fluoroethylene carbonate (FEC) additive, exhibited a capacity retention rate of 63.2% after 300 cycles. While this was superior to Comparative Example 1's 45.8%, it was significantly lower than Example 1's 82.6%. This comparison clearly demonstrates the technical advantages of the "self-healing" approach of this application compared to the traditional "passive film formation" approach. Traditional additives such as FEC primarily improve performance by optimizing the initial chemical composition of the SEI, but they cannot solve the problem of accumulated mechanical damage to the SEI film during cycling. This application, by introducing a dynamic repair mechanism, fundamentally solves this technical bottleneck. The results of the self-healing function verification test further confirm this technical advantage. Comparative Example 2 showed a repair efficiency of only 65.4% under special stress cycling, while Example 1 reached 89.2%, indicating that the SEI film constructed in this application has excellent damage repair capabilities. This difference stems from the dynamic reversible nature of the C=N bonds in the poly(Schiff base) network. When the SEI film is subjected to mechanical stress damage, the broken Schiff base bonds can reform under suitable conditions, achieving self-repair of the damage. Specific factors are discussed below:

[0188] 1) Optimization effect of precursor concentration

[0189] Examples 2 and 3 verified the effects of excessively low and high concentrations of PPD and TPA on performance, respectively. Example 2 used a lower concentration of 0.8 wt%, and its capacity retention rate after 300 cycles was 71.3%, lower than 82.6% in Example 1. This indicates that when the precursor concentration is insufficient, the resulting polymer network density is low, and a continuous and effective self-healing layer cannot be formed on the negative electrode surface, resulting in poor interface protection.

[0190] Example 3, using a higher concentration of 2.5 wt%, achieved a capacity retention of 78.1% after 300 cycles. While significantly better than Example 2 with its lower concentration, it was still lower than Example 1 with its optimal concentration. Simultaneously, Example 3 showed an internal resistance increase of +26.4%, higher than the +18.7% increase in Example 1, indicating that excessive precursor may form an overly dense polymer layer at the interface, hindering lithium-ion transport. Therefore, the concentrations of PPD and TPA need to be precisely controlled at around 1.5 wt% to achieve the optimal balance between self-healing effect and ion transport performance.

[0191] 2) Importance of accurate molar ratio

[0192] Example 4 verified the effect of the PPD:TPA molar ratio deviating from the stoichiometric ratio on performance. The PPD:TPA molar ratio in Example 4 was 1:1.2, and its 300-cycle capacity retention was 75.9%, lower than the 82.6% of the stoichiometric ratio in Example 1. This difference indicates that precise control of the molar ratio is crucial for the completeness of the polymerization reaction. While excess TPA ensures sufficient PPD reaction, it may lead to side reactions at the interface or affect the regularity of the polymer network, resulting in a decrease in self-healing performance. Therefore, maintaining a PPD:TPA stoichiometric ratio close to 1:1 is key to obtaining optimal performance. The electrochemical activation process plays a crucial role.

[0193] Comparative Example 3 used the same PPD and TPA addition amounts as Example 1, but employed a conventional formation process instead of the optimized electrochemical activation process of this application. The capacity retention rate of Comparative Example 3 after 300 cycles was only 58.9%, significantly lower than the 82.6% of Example 1, and only slightly better than the 63.2% of Comparative Example 3 with conventional additives. This comparison fully demonstrates the crucial role of the electrochemical activation process of this application.

[0194] Conventional formation processes cannot provide the specific electrochemical environment required for the in-situ polymerization of PPD and TPA, resulting in insufficient precursor reaction or a lack of interfacial selectivity in the polymerization reaction. Only through the precise potential control and staged activation strategy proposed in this application can the selective polymerization of the precursor at the negative electrode interface be achieved, forming a poly(Schiff base) network with self-healing capabilities. This result highlights the significant value of this application in terms of process innovation.

[0195] 3) The impact of PPD and PTA configurations on network stability

[0196] Example 6 uses m-phenylenediamine in combination with m-phthalaldehyde. Meta-substitution reduces the rigidity of the polymer network and increases the flexibility of the chain segments, which is beneficial for adapting to the volume expansion of the negative electrode. However, the crosslinking density is slightly lower than that of PPD+TPA (Example 1), resulting in slightly lower capacity retention and self-healing efficiency (Example 1: 82.6%, 89.2%). This is because the meta-structure reduces π-conjugation, enhances flexibility but sacrifices some network stability.

[0197] 4) The impact of the types of the first and second polymer precursors on network stability

[0198] Example 7 used pentanediamine combined with glutaraldehyde, and Example 8 used propylenediamine combined with malondialdehyde. The results are shown in Table 2. The aliphatic structure provides high flexibility, suitable for anodes with high volume expansion, but its mechanical strength is lower than that of the aromatic network, resulting in lower performance than Examples 1 and 6. This is because the aliphatic chain segments lack π-π stacking, reducing long-term stability. At the same time, the short-chain structure forms a compact network, accelerating Schiff base bond reconstruction, but its stability is lower, reflecting the trade-off between repair speed and durability. This is because the short chain reduces intermolecular interactions and reduces network strength. In summary, in terms of the balance between network stability and flexibility, the aromatic precursor (Examples 1, 6) > the aliphatic precursor (Example 7) > the short-chain precursor (Example 8).

[0199] 5) The impact of the selection of technical parameters in the formation process on network construction

[0200] In Comparative Example 4, the charging rate of the pre-activation step was 0.06C, exceeding 0.05C, resulting in a SEI film capacity retention rate of approximately 65% ​​and a self-repair efficiency of approximately 60%, far lower than the 82.6% and 89.2% in Example 1. This is because the excessively high charging rate shortens the precursor adsorption time, leading to insufficient Schiff base reaction and an uneven SEI network. In Comparative Example 5, the negative electrode potential of the network construction step was 0.6–1.0V, exceeding 0.5V, resulting in a SEI film capacity retention rate of approximately 67% and a self-repair efficiency of approximately 63%. This is because the excessively high negative electrode potential cannot activate amine condensation, resulting in low polymerization efficiency and poor SEI stability. In Comparative Example 6, the formation temperature was 20°C, lower than 25°C, resulting in a SEI film capacity retention rate of approximately 64% and a self-repair efficiency of approximately 58%. This is because the low temperature slows down precursor diffusion and reaction, leading to incomplete network formation.

[0201] III. Verification of Material Universality

[0202] Example 5 verifies the application effect of the technology of this application on lithium metal anodes. All performance indicators of Example 5 reach or exceed those of Example 1 for the silicon-carbon anode system, with a capacity retention rate of 86.4% after 300 cycles and a self-healing efficiency as high as 92.7%. These results indicate that the self-healing SEI technology of this application has good material versatility and can be effectively applied to different types of high-capacity anode materials.

[0203] Due to its more active interfacial chemistry and more severe volume change issues, lithium metal anodes place more stringent requirements on the SEI film. The superior performance of B8 further confirms the advanced nature and practical value of the technical solution presented in this application, providing effective technical support for the development of high-energy-density battery technology.

[0204] IV. High-Temperature Performance Advantages

[0205] In a 45°C high-temperature cycling test, the capacity retention rate of the core embodiment 1 of this application reached 74.9%, significantly higher than that of Comparative Example 1 (32.1%) and Comparative Example 2 (51.8%). This significant difference in battery performance under high-temperature conditions further validates the technical advantages of the self-healing SEI film. Under high-temperature conditions, the mechanical properties of traditional SEI films deteriorate further, and the impact of volume change stress is amplified, leading to a sharp decline in interface stability. However, the self-healing mechanism of this application can still function effectively at high temperatures, and even exhibits better repair efficiency due to improved reaction kinetics.

[0206] V. Summary of Beneficial Effects

[0207] Based on the in-depth analysis of the above experimental results, this application demonstrates the following significant beneficial effects:

[0208] Key technical effects: This application constructs a self-healing SEI film through in-situ polymerization of PPD and TPA precursors, achieving a capacity retention rate of 82.6% in a 1C rate 300-cycle test, which is 36.8 percentage points higher than the blank control of 45.8%, significantly improving the cycle stability of high-capacity anode batteries.

[0209] Improved interface stability: The SEI film of this application showed an internal resistance increase of only 18.7% after 300 cycles, far lower than the 68.5% increase of the traditional system, indicating excellent long-term interface stability. This stability stems from the dynamic repair mechanism of the poly(Schiff base) network, which can continuously adapt to the volume changes of the negative electrode.

[0210] Self-healing function achieved: Through special stress cycle testing, the SEI membrane of this application exhibited a repair efficiency of 89.2%, confirming its self-healing ability after mechanical damage. This innovative function provides a new technical approach to solving the interface stability problem of high-capacity anodes.

[0211] Excellent high-temperature adaptability: At a high temperature of 45℃, this application still maintains a capacity retention rate of 74.9%, demonstrating excellent thermal stability and high-temperature adaptability, and expanding the application temperature range of high-capacity negative electrode batteries.

[0212] Good process compatibility: This application only requires the addition of PPD and TPA precursors to the traditional electrolyte and optimization of the electrochemical parameters of the formation process. It is highly compatible with existing secondary battery manufacturing processes and has good prospects for industrial application.

[0213] Wide applicability of materials: This application demonstrates excellent performance improvement effects on both silicon-carbon anodes and lithium metal anodes, proving the universality and broad application potential of the technology.

[0214] Industrial application value

[0215] This application provides an effective technical solution for the industrial application of high-capacity negative electrode batteries. Through self-healing SEI technology, the cycle life of the battery can be significantly extended, and the total life-cycle cost of the battery system can be reduced. This application has significant commercial value in applications with stringent requirements for battery cycle life, such as electric vehicles and energy storage systems.

[0216] Meanwhile, the process compatibility of this application enables rapid industrialization on existing production lines without large-scale equipment modifications, lowering the barriers and costs of technology transfer. With the continuous development of high-capacity anode material technology, the self-healing SEI technology of this application will become one of the key technologies driving the industrialization of next-generation high-energy-density batteries.

[0217] Those skilled in the art will understand that the above embodiments are specific examples of implementing this application, and in practical applications, various changes in form and detail can be made without departing from the spirit and scope of this application. Any person skilled in the art can make various alterations and modifications without departing from the spirit and scope of this application; therefore, the scope of protection of this application should be determined by the scope defined in the claims.

Claims

1. A method for preparing a secondary battery, characterized in that, include: A battery cell assembly is provided, wherein the battery cell assembly is formed by stacking or winding a positive electrode sheet, a separator and a negative electrode sheet; A housing is provided, the housing having a receiving chamber for placing the battery cell assembly within the receiving chamber; An electrolyte is provided and injected into the containment chamber. The electrolyte includes an electrolyte salt, a non-aqueous solvent, a first precursor, and a second precursor, wherein the first precursor and the second precursor can undergo in-situ polymerization at the interface of the negative electrode to form a network structure with Schiff base bonds. Perform the formation step; The first precursor is a compound containing two amine groups, and the second precursor is a compound containing two aldehyde groups; The formation step includes: A pre-activation step is performed, wherein the charging is performed at a first rate, the negative electrode potential is less than a first preset potential, and the charging time is a first preset duration. In the network construction step, the charging is performed at a second rate, and the negative electrode potential is within the target potential range. The charging time is a second preset duration, and the second rate is greater than the first rate. A stabilization step is performed, in which charging is carried out at a third rate, which is greater than the second rate; The first multiplier is 0.01C~0.05C, the first preset potential is 0.5V, and the first preset duration is 10h~20h; The second multiplier is 0.02C~0.1C, and the second preset duration is 6h~20h; The third multiplier is 0.05C~0.1C; The target potential range is 0.1V~0.5V; In the stabilization step, 1 to 3 charging cycles are performed, and the negative electrode potential is the normal operating voltage of the secondary battery. The temperature of the formation step is 25℃~60℃.

2. The method for preparing a secondary battery according to claim 1, characterized in that, The first precursor has a mass percentage of 0.5% to 3% in the electrolyte, and the second precursor has a mass percentage of 0.5% to 3% in the electrolyte.

3. The method for preparing a secondary battery according to claim 1, characterized in that, The molar ratio of the first precursor to the second precursor is (0.8~1.2):

1.

4. The method for preparing a secondary battery according to any one of claims 1 to 3, characterized in that, The first precursor is phenylenediamine, pentanediamine, or propylenediamine, and the second precursor is phenylenedialdehyde, glutaraldehyde, or malondialdehyde.

5. The method for preparing a secondary battery according to claim 1, characterized in that, T2 > T3 > T1, where T1 is the temperature of the pre-activation step, T2 is the temperature of the network construction step, and T3 is the temperature of the stabilization step.

6. The method for preparing a secondary battery according to claim 5, characterized in that, T1 is 25℃~40℃, network T2 is 35℃~50℃, and T3 is 30℃~45℃.

7. A secondary battery obtained by the preparation method according to any one of claims 1 to 6.

8. An energy storage system, characterized in that, Includes the secondary battery as described in claim 7.

9. An electrical appliance, characterized in that, The electrical device includes the secondary battery as described in claim 7; or, the electrical device includes the energy storage system as described in claim 8.

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