Electrode structure, battery cell and battery
By using a stacked design of heterogeneous positive and negative electrodes and a "Z"-shaped separator, the contradiction between energy density, safety and cycle life in lithium-ion batteries is resolved, achieving battery performance with high energy density, high safety and long cycle life.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-31
- Publication Date
- 2026-04-07
AI Technical Summary
Existing lithium-ion batteries struggle to simultaneously achieve high energy density, safety, and long cycle life. In particular, wound structures have high internal resistance and slow heat dissipation, while homogeneous stacked structures cannot simultaneously achieve both high energy density and safety.
The design employs a stacked design of heterogeneous positive and negative electrodes. The positive electrode is alternately composed of nickel-containing ternary materials and lithium iron phosphate materials, while the negative electrode is alternately composed of silicon-carbon composite materials and graphite. Combined with a "Z"-shaped folded separator, the ion transport path and mechanical stress distribution are optimized.
The battery achieves a balance of high energy density, high safety, and long cycle life. By matching heterogeneous active layers and designing a separator, the battery's energy density, safety, and cycle stability are improved.
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Figure CN121812698A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of battery technology, specifically to electrode structures, battery cells, and batteries. Background Technology
[0002] In lithium-ion batteries, a variety of different positive and negative electrode active materials can be selected, each with different performance characteristics. For example, high-nickel ternary materials (such as NCM811) have high energy density (≥200 mAh / g), but poor thermal stability and easy oxygen evolution at high temperatures, leading to safety hazards; lithium iron phosphate (LFP) materials have good thermal stability and long cycle life, but lower energy density (~150 mAh / g); silicon-carbon anode materials (such as Si@C) have high specific capacity (approximately 2000 mAh / g), but large volume expansion rate (>50%), which easily leads to electrode pulverization during cycling and poor cycle life. Currently, lithium-ion batteries mainly adopt two structures: wound structure: with high internal resistance and slow heat dissipation during high-rate charging and discharging, it is not suitable for continuous high-current discharge; homogeneous stacked structure: using a single positive electrode material and a single negative electrode material in a Z-shaped stack, although with lower internal resistance than the wound structure, it still cannot simultaneously achieve high energy density and safety. Summary of the Invention
[0003] This invention aims to at least partially address one of the technical problems in the related art. To this end, one object of this invention is to provide an electrode structure that can simultaneously improve the energy density, safety, and cycle life of a battery.
[0004] In one aspect of the invention, an electrode structure is provided. According to an embodiment of the invention, the electrode structure includes alternately arranged positive electrode sheets, a separator, and a negative electrode sheet. The positive electrode sheet includes a positive current collector and a first positive active layer and a second positive active layer disposed on two surfaces of the positive current collector. The first positive active layer includes a nickel-containing ternary material, and the second positive active layer includes a lithium iron phosphate material. The negative electrode sheet includes a negative current collector and a first negative active layer and a second negative active layer disposed on two surfaces of the negative current collector. The first negative active layer includes a silicon-carbon composite material and graphite, and the second negative active layer is graphite. The first positive active layer is disposed close to the first negative active layer, and the second positive active layer is disposed close to the second negative active layer. Therefore, this invention employs a stacked electrode structure with heterogeneous positive and negative electrode sheets. The nickel-containing ternary material in the first positive active layer enhances the battery's energy density, while the lithium iron phosphate material in the second positive active layer ensures thermal safety, serving as a thermal stability foundation and overcharge protection layer. The first negative active layer is adjacent to the first positive active layer. The carbon composite material and graphite in the first negative active layer match the high capacity of the nickel-containing ternary material, and the high capacity of the silicon-carbon material compensates for its volume expansion defects. The second negative active layer is adjacent to the second positive active layer. The graphite in the second negative active layer matches the lithium iron phosphate material, providing structural support and ensuring cycle stability. Thus, the electrode structure of this invention forms a "high capacity-high stability" pairing structure, while optimizing ion transport paths and mechanical stress distribution, enabling batteries using this electrode structure to simultaneously achieve high energy density, high safety, and long cycle life.
[0005] According to an embodiment of the present invention, the electrode structure further includes a first capping electrode and a second capping electrode located at both ends, wherein one of the following conditions is met: the first capping electrode and the second capping electrode are both positive capping electrodes, the first capping electrode includes the positive current collector and a first positive active layer disposed on one surface of the positive current collector, and the second capping electrode includes the positive current collector and a second positive active layer disposed on one surface of the positive current collector; or the first capping electrode and the second capping electrode are both negative capping electrodes, the first capping electrode includes the negative current collector and a first negative active layer disposed on one surface of the negative current collector, and the second capping electrode includes the negative current collector and a second negative active layer disposed on one surface of the negative current collector.
[0006] According to an embodiment of the present invention, the nickel-containing ternary material is LiNi. x Co y Mn z M 1-x-y-zThe layered oxide material of O2, wherein M is a dopant element selected from at least one of Al, Mg, Ti, Zr, Y, and W, with 0.5 ≤ x < 1.0, y > 0, z > 0, and x + y + z ≤ 1; the lithium iron phosphate material is LiFe 1-a M' a PO4 or LiFe 1-a M' a PO4 / C, where M' is a doping element selected from at least one of Mn, Co, Ni, Mg, Zn, Ti, V, and Zr, 0 ≤ a < 0.2, and C represents carbon coating.
[0007] According to an embodiment of the present invention, the ratio of the areal density of the first positive electrode active layer to the areal density of the first negative electrode active layer is 1.5 to 3, and the ratio of the areal density of the second positive electrode active layer to the areal density of the second negative electrode active layer is 1.5 to 3.
[0008] According to an embodiment of the present invention, the areal density of the first positive electrode active layer is 100~300 g / m². 2 The areal density of the second positive electrode active layer is 100~300 g / m². 2 And / or, the areal density of the first negative electrode active layer is 30~140 g / m². 2 The areal density of the second negative electrode active layer is 50~140 g / m². 2 .
[0009] According to an embodiment of the present invention, based on the total mass of the negative electrode active material in the first negative electrode active layer, the negative electrode active material comprises 5-30 wt% of the silicon-carbon composite material and 70-95 wt% of graphite.
[0010] According to an embodiment of the present invention, the compaction density of the first positive electrode active layer is 3.2~3.8 g / cm³. 3 The compaction density of the second positive electrode active layer is 2.4~2.8 g / cm³. 3 The compaction density of the first negative electrode active layer is 1.5~1.9 g / cm³. 3 The compaction density of the second negative electrode active layer is 1.6~2.0 g / cm³. 3 .
[0011] According to an embodiment of the present invention, the diaphragm is folded in a "Z" shape to separate the positive electrode and the negative electrode.
[0012] In another aspect, the present invention provides a battery cell. According to an embodiment of the present invention, the battery cell includes the electrode structure and electrolyte described above. Thus, the electrode structure of the battery cell forms a "high capacity-high stability" paired structure, while optimizing the ion transport path and mechanical stress distribution, enabling batteries using this cell to simultaneously achieve high energy density, high safety, and long cycle life.
[0013] According to an embodiment of the present invention, the electrolyte comprises a lithium salt, a solvent, and additives, wherein the additives include fluoroethylene carbonate (FEC) and lithium difluorooxalate borate (LiDFOB).
[0014] According to an embodiment of the present invention, the fluoroethylene carbonate has a mass percentage of 1-5% in the electrolyte, and the lithium difluorooxalate borate has a mass percentage of 0.5-2% in the electrolyte.
[0015] In another aspect, the present invention provides a battery. According to embodiments of the invention, the battery includes the electrode structure described above, or includes the battery cell described above. Thus, the battery can simultaneously achieve high energy density, high safety, and long cycle life. Those skilled in the art will understand that the battery possesses all the features and advantages of the electrode structure and battery cell described above, and will not be elaborated further here.
[0016] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description
[0017] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a schematic diagram of the electrode structure in one embodiment of the present invention; Figure 2 This is a schematic diagram of the electrode structure in another embodiment of the present invention. Detailed Implementation
[0018] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.
[0019] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values of 1 and 2 are listed, and if maximum range values of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.
[0020] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.
[0021] The terms "first" and "second" used in this document are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature marked "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.
[0022] In one aspect, the present invention provides an electrode structure. According to an embodiment of the present invention, referring to... Figure 1The electrode structure includes alternating positive electrode plates 10, separators 30, and negative electrode plates 20. The positive electrode plate 10 includes a positive current collector 13 and a first positive active layer 11 and a second positive active layer 12 disposed on two surfaces of the positive current collector 13. The first positive active layer 11 comprises a nickel-containing ternary material, and the second positive active layer 12 comprises lithium iron phosphate material. The negative electrode plate 20 includes a negative current collector 23 and a first negative active layer 21 and a second negative active layer 22 disposed on two surfaces of the negative current collector 23. The first negative active layer 21 comprises silicon-carbon composite material and graphite, and the second negative active layer 22 is graphite. 11 is positioned close to the first negative electrode active layer 21, and the second positive electrode active layer 12 is positioned close to the second negative electrode active layer 22. That is, the stacking order of the first positive electrode active layer 11, the positive electrode current collector 13, the second positive electrode active layer 12, the first negative electrode active layer 21, the negative electrode current collector 23, and the second negative electrode active layer 22 is: first positive electrode active layer 11, first negative electrode active layer 21, negative electrode current collector 23, second negative electrode active layer 22, second positive electrode active layer 12, positive electrode current collector 13, first positive electrode active layer 11, first negative electrode active layer 21, negative electrode current collector 23, second negative electrode active layer 22, second positive electrode active layer 12, positive electrode current collector 13...
[0023] According to embodiments of the present invention, the present invention employs an electrode structure with a stacked design of heterogeneous positive and negative electrode sheets. The nickel-containing ternary material in the first positive active layer can improve the energy density of the battery, while the lithium iron phosphate material in the second positive active layer can ensure the thermal safety of the battery, serving as a thermal stability foundation and overcharge protection layer. The first negative active layer is arranged adjacent to the first positive active layer. The carbon composite material and graphite in the first negative active layer can match the high capacity of the nickel-containing ternary material, and the high capacity of the silicon-carbon material compensates for its volume expansion defects. The second negative active layer is arranged adjacent to the second positive active layer. The graphite in the second negative active layer matches the lithium iron phosphate material, providing structural support and ensuring cycle stability. Therefore, the electrode structure of the present invention forms a "high capacity-high stability" paired structure, while optimizing the ion transport path and mechanical stress distribution, enabling the battery using this electrode structure to simultaneously achieve high energy density, high safety, and long cycle life.
[0024] According to some embodiments of the present invention, with reference to Figure 1 and Figure 2The separator 30 is folded in a "Z" shape to separate the positive electrode 10 and the negative electrode 20. Thus, the "Z"-shaped folded separator acts as a continuous "isolation barrier," completely separating each positive and negative electrode, effectively preventing contact between them and eliminating the risk of short circuits in the edge decoupling strands. This folding method allows for a more compact separator arrangement with no redundant gaps, reducing ineffective gap volume and enabling the stacking of more electrode layers per unit volume, directly increasing the battery's volumetric energy density. The "Z"-shaped folded structure of the separator significantly optimizes electrolyte adsorption and ion conduction; it also helps enhance mechanical stability and improves the battery's resistance to shock and vibration.
[0025] According to some embodiments of the present invention, with reference to Figure 1 and Figure 2 The electrode structure also includes a first end cap 41 and a second end cap 42 located at both ends of the electrode structure.
[0026] In some embodiments, refer to Figure 1 Both the first capping electrode 41 and the second capping electrode 42 are positive electrode capping electrodes. The first capping electrode 41 includes a positive current collector 13 and a first positive active layer 11 disposed on one surface of the positive current collector. The second capping electrode 42 includes a positive current collector 13 and a second positive active layer 12 disposed on one surface of the positive current collector 13. The first positive active layer 11 in the first capping electrode faces inwards towards the electrode structure, and the second positive active layer 12 in the second capping electrode faces inwards towards the electrode structure, while the positive current collector is disposed on the outside. This better ensures the structural stability, electrical safety, and consistency of electrochemical performance of the battery. Furthermore, the lithium iron phosphate (LFP) in the second positive active layer has extremely high thermal stability (decomposition temperature > 200℃). As the capping electrode faces inwards towards the electrode, it forms a "lithium iron phosphate +" structure at both ends of the battery (the areas where heat is most easily accumulated). The separator provides a double thermal stability barrier, while the active layer (graphite / silicon-carbon-graphite) of the negative electrode capping has a much lower thermal stability than LFP. The positive electrode current collector is aluminum foil, which has much better welding compatibility with the battery tabs (usually made of aluminum) than the negative electrode current collector (copper foil) and aluminum tabs. The contact resistance of aluminum-aluminum welding is smaller (≤5mΩ), and it is less prone to poor welding or desoldering during cycling (copper-aluminum welding is prone to cracking due to the difference in thermal expansion coefficients). The mechanical strength (tensile strength ≥150MPa) and folding resistance of aluminum foil are better than those of copper foil (tensile strength ≤120MPa). When used as a capping electrode, it is less prone to wrinkles, damage or edge warping during the continuous folding and stacking of Z-shaped sheets.
[0027] In other embodiments, reference is made to Figure 2Both the first capping electrode 41 and the second capping electrode 42 are negative electrode capping electrodes. The first capping electrode 41 includes a negative electrode current collector 23 and a first negative electrode active layer 21 disposed on one surface of the negative electrode current collector 23. The second capping electrode 42 includes a negative electrode current collector 23 and a second negative electrode active layer 22 disposed on one surface of the negative electrode current collector 23. The first negative electrode active layer 21 in the first capping electrode is positioned facing inwards towards the electrode structure, and the second negative electrode active layer 22 in the second capping electrode is positioned facing inwards towards the electrode structure. The positive electrode current collector is positioned on the outside. This design better ensures the structural stability, electrical safety, and consistency of electrochemical performance of the battery. Furthermore, it eliminates the risk of lithium plating, resulting in high safety. It also offers high capacity utilization, good internal resistance stability, and helps improve the battery's rate performance and cycle life. Finally, it helps reduce the risk of thermal runaway and improves battery reliability.
[0028] According to some embodiments of the present invention, there is no limitation on the number of positive and negative electrode plates in the electrode structure, and those skilled in the art can flexibly select them according to the actual needs of the battery.
[0029] According to some embodiments of the present invention, the nickel-containing ternary material is LiNi. x Co y Mn z M 1-x-y-z The O2-containing layered oxide material, wherein M is a dopant element selected from at least one of Al, Mg, Ti, Zr, Y, and W, with 0.5 ≤ x < 1.0, y > 0, z > 0, and x + y + z ≤ 1. Therefore, the nickel-containing ternary material is a high-nickel ternary material with a high energy density.
[0030] According to some embodiments of the present invention, the lithium iron phosphate material is LiFe. 1-a M' a PO4 (without a carbon coating) or LiFe 1-a M' a PO4 / C (i.e., lithium iron phosphate with a carbon coating layer), where M' is a doping element selected from at least one of Mn, Co, Ni, Mg, Zn, Ti, V, and Zr, 0 ≤ a < 0.2, and C represents the carbon coating. The above-mentioned lithium iron phosphate material exhibits good thermal stability, thereby effectively improving the thermal safety performance of the battery. In some specific embodiments, the lithium iron phosphate material is LiFePO4 (LFP).
[0031] According to some embodiments of the present invention, in addition to the nickel-containing ternary material described above, the first positive electrode active layer 11 may further include a conductive agent and a binder. Similarly, in addition to the lithium iron phosphate material described above, the second positive electrode active layer 12 may further include a conductive agent and a binder. The binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene ternary copolymer, PVDF-hexafluoropropylene-tetrafluoroethylene ternary copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin. The conductive junction may include at least one of conductive carbon black (Super-P, SP), acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
[0032] According to some embodiments of the present invention, the ratio of the areal density of the first positive electrode active layer to the areal density of the first negative electrode active layer is 1.5 to 3, for example, ratios of 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, etc. Thus, the areal densities of the first positive electrode active layer and the first negative electrode active layer are synergistically coupled. The first positive electrode active layer provides a higher energy density, while the relatively lower areal density of the first negative electrode active layer effectively limits the absolute volume change of the silicon-carbon composite material of the active material in the first negative electrode active layer, thereby reducing the destructive force on the electrode structure. The matching of their areal densities can better simultaneously and improve the battery's energy density, safety, and cycle life.
[0033] According to some embodiments of the present invention, the ratio of the areal density of the second positive electrode active layer to the areal density of the second negative electrode active layer is 1.5 to 3, for example, a ratio of 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, etc. Thus, the areal densities of the second positive electrode active layer and the second negative electrode active layer are synergistically coupled. The second positive electrode active layer can not only provide higher energy density but also good thermal stability, while the second negative electrode active layer provides solid mechanical support for the entire negative electrode sheet and simultaneously constrains the expansion of the first negative electrode active layer. The matching of their areal densities can better balance and improve the battery's energy density, safety, and cycle life.
[0034] According to some embodiments of the present invention, the areal density of the first positive electrode active layer is 100~300 g / m². 2 (For example, 100g / m 2 120g / m 2 150g / m 2 180g / m 2 200g / m 2 220g / m2 250g / m 2 280g / m 2 300g / m 2 (etc.), the areal density of the second positive electrode active layer is 100~300 g / m2 (e.g., 100 g / m2). 2 120g / m 2 150g / m 2 180g / m 2 200g / m 2 220g / m 2 250g / m 2 280g / m 2 300g / m 2 (etc.). Therefore, the areal density of the first positive electrode active layer can provide the battery with a high energy density. If the areal density of the first positive electrode active layer is too low, the energy density will decrease significantly, which is detrimental to improving the overall battery capacity. If the areal density of the first positive electrode active layer is too high, ion diffusion will be difficult, internal resistance will increase, rate performance and low-temperature performance will deteriorate, lithium plating will be more likely during charging, and safety hazards will increase. The areal density of the second positive electrode active layer can provide the battery with good thermal stability. If the areal density of the second positive electrode active layer is too low, it is relatively easy to result in insufficient mass as a "thermal stability barrier," reduced thermal safety protection effect, and insufficient capacity contribution. If the areal density of the second positive electrode active layer is too high, it will not contribute much to the overall energy density but will increase weight, and a thick electrode will also deteriorate its own rate performance.
[0035] According to some embodiments of the present invention, the areal density of the first negative electrode active layer is 30~140 g / m². 2 (For example, 30g / m 2 40g / m 2 50g / m 2 60g / m 2 70g / m 2 80g / m 2 90g / m 2 100g / m 2 110g / m 2 120g / m 2 130g / m 2 140g / m 2 (etc.), the areal density of the second negative electrode active layer is 50~140 g / m². 2 (For example, 50g / m 2 60g / m 2 70g / m 2 80g / m 2 90g / m 2 100g / m 2 110g / m2 120g / m 2 130g / m 2 140g / m 2 (etc.). Therefore, the lower areal density of the first negative electrode active layer can effectively limit the absolute volume change of the silicon-carbon composite material in the first negative electrode active layer, thereby reducing the destructive force on the electrode structure. If the areal density of the first negative electrode active layer is too low, its high capacity advantage cannot be fully utilized, and its contribution to improving energy density will be weakened. If the areal density of the first negative electrode active layer is too high, the local volume expansion stress will be huge, the electrode structure will be easily damaged, the cycle life will be drastically shortened, and the side reactions with the electrolyte will be aggravated. At the same time, the areal density of the second negative electrode active layer can provide a solid mechanical support "skeleton" for the entire negative electrode sheet, jointly constraining the expansion of the first negative electrode active layer. If the areal density of the second negative electrode active layer is too low, the mechanical support will be weakened, and the expansion of the first negative electrode active layer will not be effectively constrained, affecting the overall stability. If the areal density of the second negative electrode active layer is too high, the kinetic performance will deteriorate, affecting the rate performance of the second positive electrode active layer, and the compaction in the process will be difficult, which will easily lead to a decrease in electrode flexibility.
[0036] According to some embodiments of the present invention, the areal density of the first positive electrode active layer and the second positive electrode active layer needs to be designed in conjunction with the areal density of the first negative electrode active layer and the second negative electrode active layer, so as to better balance and improve the energy density, safety and cycle life of the battery.
[0037] According to some embodiments of the present invention, the graphite in the first negative electrode active layer and the second negative electrode active layer can be natural graphite or artificial graphite.
[0038] According to some embodiments of the present invention, based on the total mass of the negative electrode active material (i.e., silicon-carbon composite material and graphite) in the first negative electrode active layer, the negative electrode active material includes 5-30 wt% (e.g., 5 wt%, 8 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, 20 wt%, 22 wt%, 25 wt%, 28 wt%, 30 wt%, etc.) of silicon-carbon composite material and 70-95 wt% (e.g., 70 wt%, 72 wt%, 75 wt%, 78 wt%, 80 wt%, 82 wt%, 85 wt%, 88 wt%, 90 wt%, 92 wt%, 95 wt%, etc.) of graphite. Therefore, the silicon-carbon composite material with the above-mentioned content can effectively achieve both high battery capacity and cycle life. Specifically, the addition of the above-mentioned nickel-content silicon-carbon composite material (~2000 mAh / g) can greatly improve the reversible capacity of the negative electrode surface, while controlling the volume expansion of silicon material within an acceptable range. Dispersing the above-mentioned silicon-carbon composite material in 70%-95% graphite, and with the pure graphite in the second negative electrode active layer and the lithium iron phosphate material in the second positive electrode active layer providing overall structural support, can control the relative volume expansion rate of the entire electrode sheet at a level that does not damage the electrode structure or cause severe pulverization. Moreover, it can effectively ensure the stability of the SEI film. Further, combined with additives in the electrolyte (such as FEC), it can better form a relatively stable SEI film. The capacity of the first negative electrode active layer and the first positive electrode active layer are matched by the above-mentioned content ratio. The first negative electrode active layer has a sufficiently high areal capacity, which can achieve good capacity matching (NP≈1.1) with the high-capacity first positive electrode active layer (NCM811, etc.), avoiding lithium deposition due to insufficient negative electrode capacity, while maximizing energy density.
[0039] Among them, NP (Negative to Positive ratio) is the ratio of the reversible capacity of the negative electrode to the reversible capacity of the positive electrode in the battery. NP = Reversible capacity of negative electrode surface / Reversible capacity of positive electrode surface. It can be expanded into an operable engineering calculation formula: NP = (Area density of negative electrode active material × Reversible specific capacity of negative electrode active material) / (Area density of positive electrode active material × Reversible specific capacity of positive electrode active material).
[0040] According to some embodiments of the present invention, the compaction density of the first positive electrode active layer is 3.2~3.8 g / cm³. 3 Thus, for high-nickel ternary materials (nickel-containing ternary materials with 0.5 ≤ x < 1.0), both energy density and thermal stability degradation caused by material crystal structure destruction can be guaranteed; the compaction density of the second positive electrode active layer is 2.4~2.8 g / cm³. 3 This effectively balances the structural support of the second positive electrode active layer with the ion diffusion efficiency; the compaction density of the first negative electrode active layer is 1.5~1.9 g / cm³.3 This effectively avoids the risk of electrode pulverization caused by the volume expansion of silicon-carbon composite materials; the compaction density of the second negative electrode active layer is 1.6~2.0 g / cm³. 3 This effectively provides mechanical support for the entire electrode structure while constraining the expansion of the first negative electrode active layer, ensuring cycle stability. The aforementioned compaction density range, in conjunction with the heterogeneous active layer pairing structure and areal density design of this invention, can better achieve the technical effects of high energy density, high safety, and long cycle life in the battery.
[0041] According to some embodiments of the present invention, the first negative electrode active layer 21, in addition to including active materials such as silicon-carbon composite material and graphite, may further include conductive agents and / or binders. Similarly, the second negative electrode active layer 22, in addition to including the active material graphite, may further include conductive agents and / or binders. The binder may include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), sodium carboxymethyl cellulose (CMC), and carboxymethyl chitosan (CMCS). The conductive junction may include at least one of conductive carbon black (SP), acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
[0042] According to some embodiments of the present invention, the positive current collector can be aluminum foil, and the negative current collector can be copper foil.
[0043] According to some embodiments of the present invention, the diaphragm can be at least one of glass fiber, nonwoven fabric, polyethylene (PE), polypropylene (PP), and polyvinylidene fluoride (PVDF). In some embodiments, the diaphragm includes a base membrane and adhesive layers disposed on both sides of the base membrane, wherein the base membrane is at least one of polyethylene (PE), polypropylene (PP), and polyvinylidene fluoride (PVDF).
[0044] In another aspect, the present invention provides a battery cell. According to an embodiment of the present invention, the battery cell includes the electrode structure and electrolyte described above. Thus, the electrode structure of the battery cell forms a "high capacity-high stability" paired structure, while optimizing the ion transport path and mechanical stress distribution, enabling batteries using this cell to simultaneously achieve high energy density, high safety, and long cycle life.
[0045] According to some embodiments of the present invention, the electrolyte comprises a lithium salt, a solvent, and additives, wherein the additives include at least one of fluoroethylene carbonate (FEC), lithium difluorooxalate borate (LiDFOB), and vinylene carbonate (VC). Thus, the addition of fluoroethylene carbonate (FEC) can help construct a high-performance negative electrode SEI film, improve the compatibility between the electrolyte and the negative electrode, and assist in improving the stability of the positive electrode interface; the addition of lithium difluorooxalate borate (LiDFOB) can help construct both the negative electrode interface film SEI and the positive electrode interface film CEI, achieving simultaneous protection of both the positive and negative electrodes, and can also optimize the ion conductivity of the electrolyte, inhibiting electrolyte hydrolysis and corrosion of the current collector; vinylene carbonate (VC) can help form a dense, stable, thin, and uniform SEI film.
[0046] In some specific embodiments, the additives include fluoroethylene carbonate (FEC) and lithium difluorooxalate borate (LiDFOB). The electrolyte of this invention simultaneously employs fluoroethylene carbonate (FEC) and lithium difluorooxalate borate (LiDFOB), and matches the electrode structure described above, which can better achieve functional complementarity. For example, it can synergistically strengthen the interface film (FEC provides a lithium fluoride-based SEI film with high ionic conductivity, and LiDFOB enhances the mechanical strength of the film through BO bond crosslinking, forming a "dense + tough" composite interface film that covers both the positive and negative electrodes, achieving full battery interface protection), synergistically improve electrolyte stability (LiDFOB inhibits electrolyte hydrolysis and HF generation, and FEC reduces the decomposition of the main solvent, jointly reducing the side reaction rate of the electrolyte and extending the battery cycle life), and synergistically optimize performance (FEC improves the cycle stability of the negative electrode, and LiDFOB improves the rate and low-temperature performance; the combination of the two can achieve a comprehensive improvement in battery cycle life, rate performance, and high and low temperature adaptability).
[0047] According to some embodiments of the present invention, the mass percentage of fluoroethylene carbonate (FEC) in the electrolyte is 1-5%, and the mass percentage of lithium difluorooxalate borate (LiDFOB) in the electrolyte is 0.5-2%. Thus, the amounts of FEC and LiDFOB can be flexibly adjusted according to the content of the silicon-carbon composite material in the first negative electrode active layer to form a more stable SEI film. In some embodiments, as the silicon content and / or the areal density of silicon-carbon in the first negative electrode active layer increases, the amount of film-forming additive (FEC) added can be increased, and the synergistic additive (LiDFOB) can be introduced, thereby further improving the stability of the SEI film and the cycle life of the battery.
[0048] According to some embodiments of the present invention, the lithium salt in the electrolyte may be at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.
[0049] According to some embodiments of the present invention, the solvent in the electrolyte may be at least one selected from ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.
[0050] In some embodiments of the present invention, there are no specific requirements for the concentration of lithium salt and the mass ratio of solvent in the electrolyte. Those skilled in the art can make flexible choices according to actual needs, and no limitation is imposed here.
[0051] In another aspect, the present invention provides a battery. According to embodiments of the invention, the battery includes the electrode structure described above, or includes the battery cell described above. Thus, the battery can simultaneously achieve high energy density, high safety, and long cycle life. Those skilled in the art will understand that the battery possesses all the features and advantages of the electrode structure and battery cell described above, and will not be elaborated further here.
[0052] According to some embodiments of the present invention, the battery is a lithium-ion battery.
[0053] According to some embodiments of the present invention, the battery can be a single-junction battery, or a battery pack or battery stack formed by connecting multiple single-junction batteries in series.
[0054] Example Example 1 (1) Preparation of positive electrode sheet The slurry for the first positive electrode active layer (defined as surface A) consists of 97.2 wt% NCM811, 1.8 wt% PVDF, and 1.0 wt% Super-P. This slurry is coated onto a 9 μm aluminum foil to form an areal density of 200 g / m². 2 The first positive electrode active layer (i.e., the A side of the positive electrode).
[0055] The slurry for the second positive electrode active layer (defined as the B-side) consists of 97.2 wt% LFP, 1.8 wt% PVDF, and 1.0 wt% Super-P. This slurry is coated onto the other side of the same aluminum foil to form an areal density of 200 g / m². 2The second positive electrode active layer (i.e., the B side of the positive electrode).
[0056] The compaction density of the first positive electrode active layer is 3.5 g / cm³. 3 The compaction density of the second positive electrode active layer is 2.6 g / cm³. 3 .
[0057] (2) Preparation of negative electrode sheet The slurry for the first negative electrode active layer (defined as the C-side) consists of 86.4 wt% artificial graphite, 9.6 wt% CVD silicon-carbon composite material (the mass ratio of artificial graphite to CVD silicon-carbon composite material is 90%:10%), 1.2 wt% CMC, 1.8 wt% SBR, and 1.0 wt% Super-P. This slurry is coated onto a 6 μm copper foil to form an areal density of 80 g / m². 2 The first negative electrode active layer (i.e., the C-side of the negative electrode sheet).
[0058] The slurry for the second negative electrode active layer (defined as the D-side) consists of 96.0 wt% artificial graphite, 1.2 wt% CMC, 1.8 wt% SBR, and 1.0 wt% Super-P. This slurry is coated onto the other side of the same copper foil to form an areal density of 90 g / m². 2 The second negative electrode active layer (i.e., the D side of the negative electrode sheet).
[0059] The compaction density of the first negative electrode active layer is 1.7 g / cm³. 3 The compaction density of the second negative electrode active layer is 1.7 g / cm³. 3 .
[0060] (3) Cell assembly The positive and negative electrode plates are cut into 200×150mm rectangles, and the electrode tabs are ultrasonically welded.
[0061] Separator: A 6μm thick PE porous separator (using a 4μm thick PE base film, with a 1μm thick adhesive layer coated on both sides of the PE base film) is folded in a Z-shape.
[0062] The positive and negative electrode sheets, a total of 15 layers, are stacked in the separator in the following sequence: (A-side-C-side-D-side-B-side)-(A-side-C-side-D-side-B-side)-(A-side-C-side-D-side-B-side)... (the end-capping electrodes on both sides are positive end-capping electrodes, the top positive end-capping electrode sheet is coated only with the A-side coating, the middle positive electrode sheets are coated with the A / B sides respectively, the bottom positive end-capping electrode sheet is coated only with the B-side coating, and each negative electrode sheet is coated with the C / D sides respectively). In this way, the high-nickel ternary active layer on the A-side of the positive electrode matches the silicon-carbon-graphite active layer on the C-side of the negative electrode, and the pure graphite active layer on the D-side of the negative electrode matches the lithium iron phosphate active layer on the B-side of the positive electrode.
[0063] Electrolyte: A solution of ethylene carbonate EC / ethyl methyl carbonate EMC / diethyl carbonate DEC (3:5:2) containing 1.0 mol / L LiPF6, with 2 wt% FEC and 1 wt% LiDFOB additives.
[0064] The battery cell is obtained by inserting an aluminum-plastic film shell, injecting electrolyte, and then encapsulating it. The process involves aging, formation, high-temperature aging, capacity testing, and OCV (Optical Characteristic Cell) steps.
[0065] Examples 2 to 16 The steps for preparing the battery cell are basically the same as in Example 1. The difference lies in the proportion of silicon-carbon composite material and graphite in the first positive electrode active layer, the second positive electrode active layer, the first negative electrode active layer, the second negative electrode active layer, the first negative electrode active layer, the first negative electrode active layer, the first negative electrode active layer, the proportion of graphite in the first negative electrode active layer, and the materials and proportions of additives in the electrolyte. For details, please refer to Table 1.
[0066] Comparative Example 1 The steps for preparing the battery cell are basically the same as in Example 1, except for the following steps: (1) In the preparation of the positive electrode, a high-nickel ternary material slurry is coated on both surfaces of the aluminum foil, namely: 97.2wt% NCM811, 1.8wt% PVDF, and 1.0wt% Super-P, forming a single-sided density of 200g / m². 2 The positive electrode active layer (i.e., both sides of the positive electrode sheet are A-side).
[0067] (2) In the preparation of the negative electrode, a slurry containing silicon-carbon composite material-graphite is coated on both surfaces of the copper foil. The slurry consists of 86.4 wt% artificial graphite, 9.6 wt% CVD silicon-carbon composite material (the mass ratio of artificial graphite to CVD silicon-carbon composite material is 90%:10%), 1.2 wt% CMC, 1.8 wt% SBR and 1.0 wt% Super-P, forming a single-sided density of 85 g / m². 2 The negative electrode active layer (i.e., both sides of the negative electrode sheet are C-surfaces).
[0068] The subsequent electrode stacking sequence is: (A-side-C-side-A-side-C-side)-(A-side-C-side-A-side-C-side)-(A-side-C-side-A-side-C-side)... sequence stacked in the separator (the end caps on both sides are positive end caps, the positive end caps only have the A-side coating on one side of the aluminum foil, the positive end caps only have the A-side coating on both sides, and each negative end cap has the C-side coating on both sides).
[0069] Comparative Example 2 The steps for preparing the battery cell are basically the same as in Example 1, except for the following steps: (1) In the preparation of the positive electrode, a slurry containing lithium iron phosphate material is coated on both surfaces of the aluminum foil, namely: 97.2 wt% LFP, 1.8 wt% PVDF, and 1.0 wt% Super-P, forming a single-sided density of 200 g / m². 2 The positive electrode active layer (i.e., both sides of the positive electrode sheet are B-sides).
[0070] (2) In the preparation of the negative electrode sheet, a graphite-containing slurry is coated on both surfaces of the copper foil. The slurry consists of 96.0 wt% artificial graphite, 1.2 wt% CMC, 1.8 wt% SBR and 1.0 wt% Super-P, forming a single-sided density of 85 g / m². 2 The negative electrode active layer (i.e., both sides of the negative electrode sheet are D-surfaces).
[0071] The subsequent electrode stacking sequence is: (B-side-D-side-D-side-B-side)-(B-side-D-side-D-side-B-side)-(B-side-D-side-D-side-B-side)... sequence stacked in the separator (the end caps on both sides are positive end caps, the positive end caps on both ends are coated with B-side coating only on one side of the aluminum foil, the positive end caps in the middle are coated with B-side on both sides, and each negative end cap is coated with D-side on both sides).
[0072] Comparative Example 3 The steps for preparing the battery cell are basically the same as in Example 1, except for the following steps: (2) In the preparation of the negative electrode, a slurry containing silicon-carbon composite material-graphite is coated on both surfaces of the copper foil. The slurry consists of 86.4 wt% artificial graphite, 9.6 wt% CVD silicon-carbon composite material (the mass ratio of artificial graphite to CVD silicon-carbon composite material is 90%:10%), 1.2 wt% CMC, 1.8 wt% SBR and 1.0 wt% Super-P, forming a single-sided density of 85 g / m². 2 The negative electrode active layer (i.e., both sides of the negative electrode sheet are C-surfaces).
[0073] The subsequent electrode stacking sequence is: (A-side-C-side-C-side-B-side)-(A-side-C-side-C-side-B-side)-(A-side-C-side-C-side-B-side)... stacked in the separator (both sides of the end capping electrode are positive end capping electrodes, the top positive end capping electrode is coated with the A-side coating only on one side of the aluminum foil, the middle positive electrode is coated with the A / B sides respectively, the bottom positive end capping electrode is coated with the B-side coating only on one side of the aluminum foil, and each negative electrode is coated with the C-side on both sides).
[0074] Comparative Example 4 The steps for preparing the battery cell are basically the same as in Example 1, except for the following steps: (2) In the preparation of the negative electrode sheet, a graphite-containing slurry is coated on both surfaces of the copper foil. The slurry consists of 96.0 wt% artificial graphite, 1.2 wt% CMC, 1.8 wt% SBR and 1.0 wt% Super-P, forming a single-sided density of 85 g / m². 2 The negative electrode active layer (i.e., both sides of the negative electrode sheet are D-surfaces).
[0075] The subsequent electrode stacking sequence is: (A-side-D-side-D-side-B-side)-(A-side-D-side-D-side-B-side)-(A-side-D-side-D-side-B-side)... stacked in the separator (both sides of the end capping electrode are positive end capping electrodes, the top positive end capping electrode is coated with the A-side coating only on one side of the aluminum foil, the middle positive electrode is coated with the A / B sides respectively, the bottom positive end capping electrode is coated with the B-side coating only on one side of the aluminum foil, and each negative electrode is coated with the D side on both sides).
[0076] Comparative Example 5 The steps for preparing the battery cell are basically the same as in Example 1, except for the following steps: (1) In the preparation of the positive electrode, a high-nickel ternary material slurry is coated on both surfaces of the aluminum foil, namely: 97.2wt% NCM811, 1.8wt% PVDF, and 1.0wt% Super-P, forming a single-sided density of 200g / m². 2 The positive electrode active layer (i.e., both sides of the positive electrode sheet are A-side).
[0077] The subsequent electrode stacking sequence is: (A-side-C-side-D-side-A-side)-(A-side-C-side-D-side-A-side)-(A-side-C-side-D-side-A-side)... sequence stacked in the separator (the end caps on both sides are positive end caps, the top and bottom positive end caps only have the A-side coating on one side of the aluminum foil, the middle positive end caps are coated on both sides, and each negative end cap is coated with the C / D side respectively).
[0078] Comparative Example 6 The steps for preparing the battery cell are basically the same as in Example 1, except for the following steps: (1) In the preparation of the positive electrode, a slurry containing lithium iron phosphate material is coated on both surfaces of the aluminum foil, namely: 97.2 wt% LFP, 1.8 wt% PVDF, and 1.0 wt% Super-P, forming a single-sided density of 200 g / m². 2 The positive electrode active layer (i.e., both sides of the positive electrode sheet are B-sides).
[0079] The subsequent electrode stacking sequence is: (B-side-C-side-D-side-B-side)-(B-side-C-side-D-side-B-side)-(B-side-C-side-D-side-B-side)... The electrodes are stacked in sequence in the separator (both sides of the end capping electrode are positive end capping electrode, the top positive end capping electrode is coated with B-side coating only on one side of the aluminum foil, the middle positive electrode is coated with B-side coating on both sides, the bottom positive end capping electrode is coated with B-side coating only on one side of the aluminum foil, and each negative electrode is coated with C / D side respectively).
[0080] Comparative Example 7 The steps for preparing the battery cell are basically the same as in Example 1, except for the following steps: The positive and negative electrode sheets, a total of 15 layers, are stacked in the separator in the following sequence: (A-side-D-side-C-side-B-side)-(A-side-D-side-C-side-B-side)-(A-side-D-C-B-side)... (the end capping sheets on both sides are positive end capping sheets, the top positive end capping sheet is coated only with the A-side coating, the middle positive electrode sheets are coated with the A / B sides respectively, the bottom positive end capping sheet is coated only with the B-side coating, and each negative electrode sheet is coated with the C / D sides respectively).
[0081] The relevant parameters for Comparative Examples 1 to 7 can be found in Table 1.
[0082] The performance of the batteries obtained in each embodiment and comparative example was tested, and the test results are shown in Table 2.
[0083] The testing methods for the relevant parameters are as follows: Cycle life (cycles @ 80% capacity) test method: 1) Ambient temperature: 25℃±2℃; 2) Charge / discharge regime: Constant current constant voltage (CC-CV) mode, charge with 1C current to the battery rated voltage of 4.2V, cut-off current 0.05C; Constant current (CC) mode, discharge with 1C current to the battery lower limit voltage of 2.5V; 3) Cycle interval: let stand for 30 minutes after each charge / discharge cycle to avoid temperature accumulation affecting test accuracy; Test equipment: 4) High-precision battery cycle tester (such as Landian, Xinwei, etc.). 5) Test steps: ① Pretreatment: let the test cell stand for 24 hours in an environment of 25℃±2℃, perform 3 standard charge / discharge cycles (same as the above charge / discharge regime), and record the discharge capacity of the 3rd cycle as the initial capacity (C0); ② Cycle test: continue to cycle according to the above charge / discharge regime, and record the discharge capacity (Ci) once for each cycle; ③ Termination condition: when the discharge capacity Ci≤0.8×C0, stop the cycle and record the cumulative number of cycles.
[0084] Test method for thermal runaway temperature (°C): 1) Environment: Adiabatic environment (using an adiabatic accelerated calorimeter (ARC) to avoid heat loss); 2) Heating rate: 5°C / min (after heating from room temperature to 100°C, change to 2°C / min to accurately capture the thermal runaway critical point); 3) Sample state: Fully charged (charged to rated voltage using the above 1C CC-CV method, left to stand for 2 hours before testing to simulate the most dangerous fully charged thermal runaway scenario); 4) Test steps: ① Place the fully charged battery cell into the adiabatic accelerated calorimeter, fix the sample and seal the test chamber; ② Start the heating program and monitor the battery cell temperature, voltage and gas production rate in real time; ③ Thermal runaway determination: When the battery cell temperature "suddenly rises" (heating rate ≥ 20°C / min) and is accompanied by a sudden drop in voltage and a surge in gas production, record the temperature at this time as the thermal runaway temperature.
[0085] Test method for low-temperature performance (-20℃, %): 1) Ambient temperature: -20℃±2℃ (low-temperature simulation scenario); 2) Charge and discharge regime: First, let the cell stand at -20℃ for 12 hours, then charge it to the rated voltage using a 0.3C current CC-CV, with a cutoff current of 0.05C (reduce the charging current at low temperatures to avoid lithium deposition); after charging, keep it at -20℃ for 2 hours, then discharge it to the cutoff voltage using a 0.3C current CC; 3) Comparison benchmark: Discharge capacity at room temperature (25℃). 4) Test steps: ① Room temperature capacity test: According to the charge and discharge regime in "Cycle Life Test", test the discharge capacity (C) at 25℃. 25℃ ) as a benchmark; ② Low-temperature pretreatment: Place the battery cell in a -20℃ low-temperature chamber for 12 hours to ensure uniform temperature; ③ Low-temperature charge and discharge: Test the discharge capacity (C) according to the above low-temperature charge and discharge regime. -20℃ ); ④ Calculate low-temperature performance: Low-temperature performance = (C -20℃ / C 25℃ ) × 100%.
[0086] Test conditions and methods for rate performance (3C / 1C, %): 1) Ambient temperature: 25℃±2℃; 2) Charge and discharge regime: uniformly use 1C CC-CV charging to rated voltage, cut-off current 0.05C (ensuring full and consistent charging each time); 1C discharge: CC mode 1C current discharge to cut-off voltage, record discharge capacity (C). 1C ); 3C discharge: CC mode 3C current discharge to the cutoff voltage, record the discharge capacity (C). 3C); Resting time: 60 minutes after each charge and discharge cycle to eliminate the temperature effect caused by the rate effect. 3) Test steps: ① Pretreatment: The cell is placed in a 25℃ environment for 24 hours, and then subjected to one 1C standard charge and discharge cycle to ensure that the active materials are fully activated; ② 1C capacity test: After charging according to the above charging regime, discharge at 1C to the cutoff voltage and record the C value. 1C ③ 3C Capacity Test: After charging again according to the above charging procedure, discharge to the cutoff voltage using 3C and record the C value. 3C ④ Calculate the rate performance: Rate performance = (C 3C / C 1C )×100%; ④ Parallel test: Repeat 3 times and take the average value as the final result.
[0087] Test conditions and methods for first-time efficiency (%): 1) Ambient temperature: 25℃±2℃; 2) Charge-discharge regime: Charge to rated voltage using 1C CC-CV, cut-off current 0.05C, record the first charge capacity (Charge); After charging, let stand for 30 minutes, then discharge to cut-off voltage using 1C CC, record the first discharge capacity (Discharge); 3) Sample state: Brand new battery cell that has not undergone any charge-discharge process (to avoid pretreatment affecting the first interface reaction). 4) Test steps: ① Sample preparation: Let the brand new battery cell stand at 25℃ for 24 hours to ensure consistent initial state; ② First charge: Charge according to the above regime, record Charge; ③ First discharge: Discharge according to the above regime, record Discharge; ④ Calculate first-time efficiency: First-time efficiency = (Discharge / Charge) × 100%.
[0088] Test conditions and methods for capacity retention (%) after 500 and 1000 cycles: 1) The test conditions are completely consistent with those for "cycle life (cycles @ 80% capacity)" (ambient temperature, charge / discharge regime, equipment) to ensure data consistency. 2) Test steps: ① Initial capacity recording: Record the initial capacity C0 using the same pre-processing steps as the cycle life test; ② Cycle test: Continuously cycle according to the charge / discharge regime of the cycle life; ③ Capacity recording: After the 500th and 1000th cycles, test the discharge capacity C according to the standard charge / discharge regime (1C CC-CV charge, 1C CC discharge). 500 C 1000 ④ Calculate capacity retention rate: Capacity retention rate after 500 cycles = (C 500 / C0) × 100%; Capacity retention rate after 1000 cycles = (C 1000 / C0)×100%.
[0089] Test conditions and methods for DCR growth (after 1000 cycles): 1) Ambient temperature: 25℃±2℃; 2) Test state: 3) Test nodes: before cycling (initial state) and after 1000 cycles; 4) State of charge (SOC): 50% SOC (to avoid the influence of SOC on internal resistance, take the middle value); 5) Test equipment: DC internal resistance tester (accuracy ≥0.01mΩ) or battery comprehensive tester. 6) Test Procedure: ① Initial DCR Test: After pretreatment of the new cell, charge it to 50% SOC according to the standard charge-discharge regime (charge capacity = 0.5 × C0), and let it rest for 2 hours; use the "current pulse method": apply a 1C current pulse (lasting 10 seconds), record the voltage change ΔV0 before and after the pulse, and calculate the initial internal resistance DCR0 = ΔV0 / 1C current according to Ohm's law; ② Post-Cycle DCR Test: After completing 1000 cycles, charge the cell to 50% SOC and let it rest for 2 hours; test the voltage change ΔV0 using the same current pulse method. 1000 Calculate the internal resistance DCR after the cycle. 1000 =ΔV 1000 / 1C current; ③ Calculate DCR growth: DCR growth rate = ((DCR) / (C ... 1000 - DCR0) / DCR0) × 100%; if DCR 1000 <DCR0, record as 0% (considered as fluctuation due to test error).
[0090] Table 1
[0091] In Table 1, the silicon-carbon content and graphite content of the negative electrode C-side refer to the total mass of the negative electrode active material in the first negative electrode active layer (i.e., the total mass of silicon-carbon composite material and graphite), the content of silicon-carbon composite material, and the content of graphite.
[0092] Table 2
[0093] As can be seen from Tables 1 and 2, compared to Comparative Examples 1-7, the batteries corresponding to Examples 1-16 can better simultaneously meet the multiple performance requirements of high energy density, high safety (the higher the thermal runaway temperature, the better the safety), and long cycle life. They also exhibit better low-temperature performance, first-efficiency performance, capacity retention, and relatively low internal resistance. In other words, the batteries in the embodiments of this invention have superior electrochemical performance. Furthermore, compared to Examples 9-16, the batteries in Examples 1-8 can have superior energy density, safety, and cycle life, and better electrochemical performance.
[0094] As can be seen from Examples 1, 3-6, 9, and 10, when the ratio of the areal density of the first positive electrode active layer to the areal density of the first negative electrode active layer is 1.5 to 3, the matching and synergistic effect of the first positive electrode active layer and the first negative electrode active layer is better. If the ratio of the areal density of the first positive electrode active layer to the areal density of the first negative electrode active layer is too low (as in Example 10) or too high (as in Example 9), it is relatively unfavorable to the overall improvement of the battery's energy density, safety, and cycle life performance. The cycle life is seriously affected, and the battery's internal resistance is relatively increased.
[0095] As can be seen from Examples 1, 7, 8, 11, and 12, when the ratio of the areal density of the second positive electrode active layer to the areal density of the second negative electrode active layer is 1.5 to 3, the matching and synergistic effect of the second positive electrode active layer and the second negative electrode active layer is better. If the ratio of the areal density of the second positive electrode active layer to the areal density of the second negative electrode active layer is too low (as in Example 12) or too high (as in Example 11), it is relatively unfavorable to the overall improvement of the battery's energy density, safety, and cycle life. The cycle life is seriously affected, the energy density is relatively reduced, and the battery's internal resistance is relatively increased.
[0096] As can be seen from the comparison of Examples 1, 2 and 13-16, when additives such as FEC, LiDFOB, and VC (ethylene carbonate) are added to the electrolyte, it is more beneficial to improve the overall performance of the battery. In particular, when the electrolyte contains both fluoroethylene carbonate (FEC) and lithium difluorooxalate borate (LiDFOB), the electrode structure matched with the above structure can achieve complementary functions, such as synergistic enhancement of the interface film, synergistic improvement of electrolyte stability, and synergistic optimization of performance, thereby achieving a comprehensive improvement in battery cycle life, rate performance, and high and low temperature adaptability.
[0097] As can be seen from the comparison between Example 1 and Comparative Example 7, only when the first positive electrode active layer and the first negative electrode active layer are arranged opposite each other, and the second positive electrode active layer and the second negative electrode active layer are arranged opposite each other, can the technical goal of the battery simultaneously achieve high energy density, high safety and long cycle life be effectively achieved. If the opposite is true, that is, the first positive electrode active layer and the second negative electrode active layer are arranged opposite each other, and the second positive electrode active layer and the first negative electrode active layer are arranged opposite each other, the cycle life and safety of the battery will be seriously affected, and the low temperature performance, rate capability, first efficiency, capacity retention rate and internal resistance of the battery will be severely affected, which will seriously reduce the quality and performance of the battery.
[0098] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.
[0099] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.
Claims
1. An electrode structure, characterized in that, The device includes alternating positive electrode sheets, a separator, and a negative electrode sheet. The positive electrode sheet comprises a positive current collector and a first positive active layer and a second positive active layer disposed on two surfaces of the current collector. The first positive active layer comprises a nickel-containing ternary material, and the second positive active layer comprises lithium iron phosphate material. The negative electrode sheet includes a negative current collector and a first negative active layer and a second negative active layer disposed on two surfaces of the current collector. The first negative active layer comprises a silicon-carbon composite material and graphite, and the second negative active layer is graphite. The first positive electrode active layer is disposed close to the first negative electrode active layer, and the second positive electrode active layer is disposed close to the second negative electrode active layer.
2. The electrode structure according to claim 1, characterized in that, It also includes a first end-capping electrode and a second end-capping electrode located at both ends of the electrode structure, wherein one of the following conditions is met: Both the first and second end-capped electrode sheets are positive end-capped electrode sheets. The first end-capped electrode sheet includes the positive current collector and a first positive active layer disposed on one surface of the positive current collector. The second end-capped electrode sheet includes the positive current collector and a second positive active layer disposed on one surface of the positive current collector. Both the first and second end-capped electrode sheets are negative end-capped electrode sheets. The first end-capped electrode sheet includes the negative current collector and a first negative active layer disposed on one surface of the negative current collector. The second end-capped electrode sheet includes the negative current collector and a second negative active layer disposed on one surface of the negative current collector.
3. The electrode structure according to claim 1 or 2, characterized in that, The nickel-containing ternary material is LiNi. x Co y Mn z M 1-x-y-z O2 layered oxide material, wherein M is a dopant element selected from at least one of Al, Mg, Ti, Zr, Y, W, 0.5≤x<1.0, y>0, z>0, x+y+z≤1; The lithium iron phosphate material is LiFe 1-a M' a PO4 or LiFe 1-a M' a PO4 / C, where M' is a doping element selected from at least one of Mn, Co, Ni, Mg, Zn, Ti, V, and Zr, 0 ≤ a < 0.2, and C represents carbon coating.
4. The electrode structure according to claim 1 or 2, characterized in that, The ratio of the areal density of the first positive electrode active layer to the areal density of the first negative electrode active layer is 1.5 to 3, and the ratio of the areal density of the second positive electrode active layer to the areal density of the second negative electrode active layer is 1.5 to 3.
5. The electrode structure according to claim 4, characterized in that, The areal density of the first positive electrode active layer is 100~300 g / m³ 2 The areal density of the second positive electrode active layer is 100~300 g / m². 2 , And / or, the areal density of the first negative electrode active layer is 30~140 g / m². 2 The areal density of the second negative electrode active layer is 50~140 g / m². 2 .
6. The electrode structure according to claim 1 or 2, characterized in that, Based on the total mass of the negative electrode active material in the first negative electrode active layer, the negative electrode active material comprises 5-30 wt% of the silicon-carbon composite material and 70-95 wt% of graphite.
7. The electrode structure according to claim 1 or 2, characterized in that, The compaction density of the first positive electrode active layer is 3.2~3.8 g / cm³. 3 The compaction density of the second positive electrode active layer is 2.4~2.8 g / cm³. 3 The compaction density of the first negative electrode active layer is 1.5~1.9 g / cm³. 3 The compaction density of the second negative electrode active layer is 1.6~2.0 g / cm³. 3 .
8. The electrode structure according to claim 1 or 2, characterized in that, The diaphragm is folded in a "Z" shape to separate the positive electrode and the negative electrode.
9. A battery cell, characterized in that, The electrode structure and electrolyte are included in any one of claims 1 to 8.
10. The battery cell according to claim 9, characterized in that, The electrolyte comprises lithium salt, solvent, and additives, the additives including fluoroethylene carbonate and lithium difluorooxalate borate.
11. The battery cell according to claim 10, characterized in that, The fluoroethylene carbonate has a mass percentage of 1-5% in the electrolyte, and the lithium difluorooxalate borate has a mass percentage of 0.5-2% in the electrolyte.
12. A battery, characterized in that, It includes the electrode structure of any one of claims 1 to 8, or the battery cell of any one of claims 9 to 11.