Lithium ion battery and method for manufacturing the same, secondary battery, and energy storage device

Abstract

The application relates to the technical field of lithium ion batteries and the technical field of energy storage, further relates to a lithium ion battery and a preparation method thereof, a secondary battery and an energy storage device. The lithium ion battery comprises a positive electrode sheet and an electrolyte, the positive electrode sheet comprises a positive electrode active layer, the positive electrode active layer comprises a positive electrode active material, and the electrolyte comprises an electrolyte salt, a non-aqueous solvent and an additive; wherein the positive electrode active material comprises a lithium phosphate-based positive electrode material doped with an M element, the M element comprises any one or both of a Ti element and a V element; the additive comprises one or both of vinylene carbonate and lithium bisfluorosulfonylimide; and the non-aqueous solvent comprises a carbonate-based solvent, and the mass content of the carbonate-based solvent in the non-aqueous solvent is relatively high (such as greater than or equal to 80%). The lithium ion battery has a significantly improved RTE and simultaneously has a relatively long cycle life.

Description

[0001] Related applications

[0002] This application claims priority to international patent (PCT) application filed on December 5, 2025, with application number PCT / CN2025 / 140456, entitled "Lithium-ion battery and method of preparation thereof, secondary battery, energy storage device, energy storage system or charging network", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the fields of lithium-ion battery technology and energy storage technology, and further to lithium-ion batteries and their preparation methods, secondary batteries and energy storage devices. Background Technology

[0004] The statements herein are provided only as background information in connection with this application and do not necessarily constitute prior art.

[0005] In recent years, due to the high energy density and high efficiency of lithium-ion batteries, their applications have become increasingly widespread, and they are widely used in electric vehicles, energy storage systems, and portable electronic devices, including but not limited to energy storage power systems such as hydropower, thermal power, wind power, and solar power plants. For energy storage cells with large capacity designs, they typically have a higher volumetric energy density, thereby improving the overall efficiency and lifespan of the cells and cabinets. Among these, the battery's energy conversion efficiency (round-trip efficiency, RTE) and cycle life are usually interdependent.

[0006] Extending the RTE and / or cycle life of lithium-ion batteries is one of the important research directions. Summary of the Invention

[0007] According to various embodiments and examples of this application, this application provides at least a lithium-ion battery and a method for preparing the same, a secondary battery, and an energy storage device. This lithium-ion battery exhibits significantly improved real-time efficiency (RTE) while also possessing a long cycle life.

[0008] In some embodiments of the first aspect of the application, a lithium-ion battery is provided, comprising a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive active layer, the positive active layer includes a positive active material, and the electrolyte includes an electrolyte salt, a non-aqueous solvent, and additives. The positive active material comprises a lithium phosphate-based positive electrode material doped with element M, wherein element M includes one or both of titanium (Ti) and vanadium (V). The additives include one or both of vinylene carbonate (VC) and lithium bis(fluorosulfonyl)imide (LiFSI). The non-aqueous solvent comprises a carbonate solvent, wherein the carbonate solvent accounts for more than or equal to 80% by mass in the non-aqueous solvent.

[0009] This lithium-ion battery introduces a lithium phosphate-based cathode material doped with element M into the positive active layer of the positive electrode. The M element can include any one or both of Ti and V. The M element can be incorporated into the lattice of the lithium phosphate-based cathode material, for example, by replacing Fe sites. This improves the material's conductivity by introducing more electronic active sites or altering the Fermi level distribution. Furthermore, the valence stability of high-valence ions (e.g., ≥4+) of the M element can further enhance crystal structure stability. Lattice doping with the M element can also improve the lithium-ion diffusion rate. In addition, when the positive active material includes an M-doped lithium phosphate-based cathode material, a suitable potential window can be provided, allowing both VC and LiFSI to participate well in the cathode film formation. In this case, the introduction of ethylene carbonate into the electrolyte... One or both of the additives, namely olefin ester (VC) and lithium bis(fluorosulfonyl)imide (LiFSI), can participate in the formation of a stable solid electrolyte interphase (CEI) film on the surface of the positive electrode active material, improving the stability of the CEI film and providing better isolation, passivation, and protection. This can reduce the dissolution of macroelements (such as Ti) and the damage of acid byproducts in the electrolyte to the CEI film and the positive electrode active material, further reducing the possibility of macroelements (such as Ti) dissolution. It can also inhibit electrolyte decomposition and reduce side reactions between the electrolyte and the positive electrode active material. By controlling the non-aqueous solvent, including a higher content of carbonate solvents, it is beneficial to suppress gas generation and extend battery life. Therefore, it can reduce the battery's internal resistance, improve positive electrode stability and cycle stability, significantly delay battery capacity decay, improve the battery's round-trip efficiency (RTE), and also give lithium-ion batteries a longer cycle life. However, this is not limited to the aforementioned theories.

[0010] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0011] (a1) The mass fraction of element M in the positive electrode active material is 0.04%~0.16%, and can be selected as 0.06%~0.12%;

[0012] (a2) The element M is a metallic element with an ionic valence greater than or equal to 3;

[0013] (a3) The M element is a transition metal element;

[0014] (a4) In the lithium phosphate cathode material doped with element M, the sum of the atomic molar ratios of Ti and V in element M is 0.8 to 1, and can be selected as 0.9 to 1;

[0015] Optionally, the M element includes the Ti element;

[0016] (a5) The mass percentage of vinylene carbonate in the electrolyte is 0.7wt% to 6.5wt%, and optionally 1wt% to 4.5wt%;

[0017] (a6) The molar volume concentration of lithium difluorosulfonylimide in the electrolyte is 0.1 mol / L to 0.6 mol / L, and can be selected as 0.2 mol / L to 0.5 mol / L;

[0018] (a7) The carbonate solvents include at least one of cyclic carbonates and chain carbonates;

[0019] (a8) The carbonate solvent accounts for more than or equal to 90% of the mass of the non-aqueous solvent.

[0020] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0021] (t1) The mass fraction of element M in the positive electrode active material is 0.06%~0.12%;

[0022] (t2) In the lithium phosphate cathode material doped with element M, the sum of the atomic molar ratios of Ti and V in element M is 0.9~1;

[0023] (t3) The M element includes the Ti element;

[0024] (t4) The mass percentage of vinylene carbonate in the electrolyte is 1wt%~4.5wt%;

[0025] (t5) The molar volume concentration of lithium difluorosulfonylimide in the electrolyte is 0.2 mol / L to 0.5 mol / L;

[0026] (t6) The additives include vinylene carbonate and lithium difluorosulfonyl imide;

[0027] (t7) The carbonate solvent includes at least one of cyclic carbonates having 3 to 6 carbon atoms and chain carbonates having 3 to 9 carbon atoms;

[0028] (t8) The carbonate solvent includes cyclic carbonates and chain carbonates, wherein the mass ratio of the cyclic carbonates to the chain carbonates is (3~7):(7~3); the cyclic carbonates have 3~5 carbon atoms, and the chain carbonates have 4~7 carbon atoms.

[0029] When lithium phosphate cathode materials are doped with element M (e.g., Fe-site doping), if there is a difference in the ionic valence state or ionic size between element M and the doped element, for example, if the ionic valence state of element M is higher than that of the doped Fe, then...2+ When or when the ion size of element M is similar to that of the doped Fe 2+ When differences exist, there may be a risk of dissolution of element M. Taking Ti and V doping as an example, the dissolution of Ti and V elements leads to the destruction of the crystal lattice structure, which reduces the content of effective active materials that can participate in electrochemical reactions in the positive electrode, resulting in a decrease in battery specific capacity and potentially weakening the improvement effect of introducing element M on RTE. In addition, the dissolution of Ti and V elements may also lead to crystal structure collapse and the superposition of interfacial side reactions, thereby forming an unstable CEI film at the positive electrode / electrolyte interface, accelerating electrolyte decomposition, and further deteriorating battery cycle performance.

[0030] By controlling the doping amount of element M within the aforementioned range, the doping advantages of element M can be fully utilized, while also controlling the dissolution probability of element M, thus better controlling the overall impact of element M doping on battery RTE, improving battery RTE, and simultaneously achieving better cycle performance.

[0031] When element M is a metallic element with an ionic valence greater than or equal to 3, introducing more electronic active sites or changing the Fermi level distribution to optimize electronic conductivity can help improve the conductivity of the material itself.

[0032] When element M is a transition metal, the variable valence state of transition metals can be utilized to improve the charge matching between element M and the crystal structure of lithium phosphate-based cathode materials, which is beneficial for improving the stability of the crystal structure after element M doping. For example, high-valence ions of Ti and V elements can possess higher valence state stability, which is beneficial for further improving the stability of the doped crystal structure. Furthermore, the ion sizes of Ti and V elements are similar to those of Fe... 2+ A closer match is more beneficial to the stability of the doped crystal structure.

[0033] By controlling the atomic molar ratio of Ti and V elements in M ​​to be in a high range, it is beneficial to fully utilize the aforementioned doping advantages of M element, while also improving the stability of the doped crystal structure, which is conducive to improving the RTE of the battery; in addition, it is also conducive to achieving better battery cycle life.

[0034] Both VC and LiFSI can act as positive electrode film-forming additives and negative electrode film-forming additives. They can promote the formation of a stable and high-quality negative electrode solid electrolyte interphase (SEI) film, effectively suppress negative electrode interfacial side reactions, better delay battery capacity decay, and better extend battery cycle life.

[0035] VC can form carbonate, CO2, and C2O4-containing compounds on the surface of positive electrode active materials. 2-Components such as oxalate participate in the formation of a stable CEI interface film, reducing the dissolution of M element, reducing the direct contact between the electrolyte or acid by-products in the electrolyte and the positive electrode active material, and inhibiting the decomposition of the electrolyte and the structural damage of the positive electrode active material by acid by-products.

[0036] By controlling the content of VC in the electrolyte within the aforementioned range, it is beneficial to better leverage the aforementioned advantages of VC, and also to better control the increase in interfacial impedance, increase in battery internal resistance and gas generation that may be caused by VC. This not only helps to better improve the RTE of the battery after doping with M element, but also helps to improve the battery cycle performance.

[0037] LiFSI can not only promote the formation of a stable positive electrode CEI interface film, improve the stability of the positive electrode CEI film, and inhibit the dissolution of M element; LiFSI can also promote the rapid and uniform formation of the negative electrode SEI film, improve the ion conductivity of the SEI film, and inhibit the side reactions and lithium loss on the negative electrode surface; in addition, it has a good ability to dissociate lithium ions, which is beneficial to improve the liquid phase conductivity and reduce the battery internal resistance. By introducing LiFSI into the electrolyte, the battery RTE and cycle life can be better improved.

[0038] By controlling the content of LiFSI in the electrolyte within the aforementioned range, it is beneficial to better leverage the aforementioned advantages of LiFSI, significantly reduce the dissolution probability of element M, significantly improve the battery RTE and enhance the battery's long-term cycle performance; in addition, it is also beneficial to better control gas generation caused by LiFSI, such as gas generation caused by LiFSI contacting water or catalytic solvent decomposition.

[0039] By controlling the types and / or contents of carbonate solvents in the electrolyte, it is beneficial to better suppress gas production and / or extend battery life.

[0040] In some embodiments, the additive includes vinylene carbonate and lithium difluorosulfonylimide;

[0041] Optionally, the molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.2 mol / L to 0.5 mol / L; the mass percentage of vinylene carbonate in the electrolyte is 0.7 wt% to 5 wt%, optionally 1 wt% to 4 wt%.

[0042] Optionally, the molar volume concentration of the electrolyte salt in the electrolyte is 0.6 mol / L to 1.5 mol / L; further optionally, the electrolyte salt includes lithium hexafluorophosphate.

[0043] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0044] (x1) The mass percentage of vinylene carbonate in the electrolyte is 1wt%~4wt%;

[0045] (x2) The molar volume concentration of the electrolyte salt in the electrolyte is 0.6 mol / L to 1.5 mol / L;

[0046] (x3) The electrolyte salt includes lithium hexafluorophosphate.

[0047] When the electrolyte contains both VC and LiFSI, the potential difference between the two in film formation allows LiFSI to preferentially participate in the formation of CEI and SEI films, thereby reducing VC consumption and mitigating the increase in interfacial impedance and battery internal resistance that may result from VC participation in film formation. This can achieve excellent synergistic improvement in battery RTE and battery cycle performance.

[0048] By controlling the concentrations of VC and LiFSI within the aforementioned ranges, it is beneficial to better leverage their synergistic effect.

[0049] When the electrolyte also includes lithium hexafluorophosphate (LiPF6), compared to LiPF6 as an electrolyte salt of the same concentration, the combination of LiFSI and LiPF6 is beneficial to improving the battery RTE and cell cycle performance.

[0050] In some embodiments, the D of the positive electrode active material v 50 is 5μm~10μm, and can be selected as 6μm~8μm.

[0051] By using the D of the positive electrode active material v Controlling the specific surface area (D50) within the aforementioned relatively large range can provide a relatively low specific surface area, which is beneficial for suppressing side reactions between the electrolyte and the positive electrode active material, reducing lithium loss, improving battery RTE, and delaying capacity decay; at the same time, the D50 of this positive electrode active material... v The 50-degree gradient also allows for better control of lithium-ion diffusion paths, achieving a better balance between lower battery internal resistance and extended battery cycle life. Furthermore, it improves the stability of the cathode slurry, thereby enhancing the uniformity of the distribution of the cathode active material in the cathode active layer, which is more beneficial for constructing a superior conductive network.

[0052] In some embodiments, the D of the positive electrode active material n 10 has a thickness of 0.28μm to 0.45μm, and can be selected as 0.3μm to 0.4μm.

[0053] By using the D of the positive electrode active material nControlling 10 within the aforementioned range is beneficial for significantly reducing the content of extremely small particles with extremely small size and extremely large specific surface area, thereby significantly reducing the side reactions between the electrolyte and the positive electrode active material, which is conducive to better improving the battery RTE and extending the battery cycle life.

[0054] In some embodiments, the positive electrode sheet satisfies one or more of the following characteristics:

[0055] (y1) The D of the positive electrode active material v 50 has a thickness of 6μm to 8μm;

[0056] (y2) The D of the positive electrode active material n 10 is 0.3μm~0.4μm.

[0057] By using the D of the positive electrode active material v 50 or D n 10. Keeping it within the aforementioned range is beneficial for better control of D. v 50 or D n The aforementioned advantages of 10.

[0058] By using the D of the positive electrode active material v 50 and D n Controlling both of these factors within the aforementioned range is beneficial for better balancing a lower specific surface area and a suitable lithium-ion diffusion path, as well as better balancing lower battery internal resistance and extended battery cycle life.

[0059] In some embodiments, the negative electrode sheet includes a negative electrode active layer, the negative electrode active layer includes a negative electrode active material; the negative electrode active material includes secondary particles; optionally, the secondary particles account for 90% to 100% of the negative electrode active material, and optionally 95% to 100%.

[0060] By utilizing the agglomerated characteristics of secondary particles, improvements can be made in mechanical stability, ion / electron transport rate, structural buffering capacity, and cell heat dissipation. This is beneficial for improving battery RTE and better suppressing negative electrode volume expansion in the later stages of cycling, thereby extending battery cycle life.

[0061] In some embodiments, the D of the negative electrode active material v 50 is 10μm~15μm, and the average particle size of the primary particles in the negative electrode active material is 4μm~7μm; optionally, the D of the negative electrode active material is... vThe particle size of the primary particles in the negative electrode active material is 11 μm to 15 μm, and the average particle size is 4 μm to 6 μm. This allows for better control of the particle size of the negative electrode active material and the degree of aggregation of the primary particles in the secondary particles, which is beneficial for better balancing the lithium-ion diffusion rate and structural buffering capacity, and for better considering both battery RTE and cycle life.

[0062] In some embodiments, the negative electrode active material comprises a secondary particulate graphite-based material;

[0063] Optionally, the secondary particulate graphite-based material accounts for 90% to 100% of the total amount of the negative electrode active material, and can be 95% to 100%.

[0064] Graphite-based materials have relatively low volume expansion. Further use of secondary particulate graphite-based materials is beneficial to better suppress negative electrode expansion in the later stages of cycling and to better extend battery cycle life.

[0065] In some embodiments, the negative electrode sheet satisfies one or more of the following characteristics:

[0066] (z1) The secondary particles account for 95% to 100% of the negative electrode active material; at this time, it is beneficial to improve the battery RTE and better suppress the negative electrode volume expansion in the later stage of the cycle, thereby better extending the battery cycle life.

[0067] (z2) The D of the negative electrode active material v The particle size of 50 is 11μm~15μm, and the average particle size of the primary particles in the negative electrode active material is 4μm~6μm; at this time, it is beneficial to better balance the lithium-ion diffusion rate and structural buffering capacity, and better take into account the battery RTE and cycle life.

[0068] (z3) The negative electrode active material includes secondary particulate graphite-based material; the secondary particulate graphite-based material accounts for 95%~100% of the negative electrode active material; at this time, it is beneficial to better suppress the negative electrode expansion in the later stage of the cycle and to better extend the battery cycle life.

[0069] In some embodiments, the negative electrode sheet includes a negative electrode active layer, the negative electrode active layer includes a negative electrode active material; the negative electrode active material includes graphite, the graphitization degree of the graphite is 88%~95.5%, optionally 90%~95%, and further optionally 90%~93%;

[0070] Optionally, the graphite component accounts for 65% to 100% of the mass of the negative electrode active material, and more preferably 90% to 100%.

[0071] In some embodiments, the negative electrode sheet satisfies one or more of the following characteristics:

[0072] (h1) The graphitization degree of the graphite component is 90% - 95%;

[0073] (h2) The mass percentage of the graphite component in the negative electrode active material is 65% - 100%.

[0074] In some embodiments, the negative electrode sheet satisfies one or more of the following characteristics:

[0075] (h1’) The graphitization degree of the graphite component is 90% - 93%;

[0076] (h2’) The mass percentage of the graphite component in the negative electrode active material is 90% - 100%.

[0077] By controlling the graphitization degree of the graphite component in the negative electrode active material within the foregoing range, additional lithium-ion storage sites can be provided by using micropores, cracks or defects, thereby improving the specific capacity; it can also provide a larger interplanar spacing, which is beneficial to accelerating lithium-ion transport, can reduce the volume change during lithium-ion insertion / extraction, reduce cracks and pulverization of the electrode material, and is beneficial to improving the structural stability of the negative electrode active material; thus, it is more beneficial to improve the battery RTE, can also improve the battery cycle stability, and is more beneficial to extending the battery cycle life.

[0078] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics:

[0079] (b1) The lithium phosphate-based positive electrode material doped with M element includes an olivine crystal structure;

[0080] Optionally, the lithium phosphate-based positive electrode material doped with M element includes Fe element; further optionally, the atomic molar ratio of Fe element in the transition metal elements contained in the lithium phosphate-based positive electrode material doped with M element is denoted as q1, then q1 ≥ 0.8, optionally, 0.8 ≤ q1 ≤ 1;

[0081] (b2) The lithium phosphate-based positive electrode material doped with M element includes a composition with the chemical formula Li a Fe b M c PO d where 0.8 ≤ a ≤ 1.15, 0.9 ≤ b < 1, 0 < c ≤ 0.1 and b + c ≤ 1, 3.8 ≤ d ≤ 4; the Li a Fe b M c PO d satisfies the positive and negative charge balance;

[0082] Optionally, M includes one or more elements selected from Ti, V, and Mn;

[0083] Optionally, 0.8 ≤ a ≤ 1.

[0084] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics:

[0085] (b1') The atomic molar ratio of Fe element in the transition metal elements contained in the lithium phosphate cathode material doped with M element is denoted as q1, where 0.8≤q1≤1;

[0086] (b2') M includes one or more elements from Ti, V and Mn; 0.8 ≤ a ≤ 1.

[0087] In some embodiments, the positive electrode sheet satisfies one or more of the following characteristics:

[0088] (c1) The mass percentage of the lithium phosphate cathode material doped with element M in the cathode active material is 95%~100%;

[0089] (c2) The mass percentage of the lithium phosphate cathode material doped with element M in the cathode active layer is 90%~99%;

[0090] (c3) The positive electrode active material includes lithium iron phosphate doped with element M; optionally, the mass percentage of lithium iron phosphate doped with element M in the positive electrode active material is 95% to 100%.

[0091] When lithium phosphate cathode materials doped with element M include an olivine crystal structure and further include element Fe, it is beneficial to achieve better stability of the olivine crystal structure, better improve the structural stability of the cathode active material, and better reduce the dissolution of element M.

[0092] By controlling the types of positive electrode active materials mentioned above, it is beneficial to improve the battery RTE when the positive electrode sheet includes lithium phosphate-containing positive electrode materials and to better balance the battery cycle life.

[0093] In some embodiments, the lithium-ion battery includes a cell, the cell including the positive electrode, the separator and the negative electrode stacked together, and the separator is disposed between the positive electrode and the negative electrode;

[0094] The stacking direction of each electrode in the battery cell is denoted as the thickness direction of the battery cell, the direction of the lead-out tabs in the battery cell is denoted as the height direction of the battery cell, and the direction perpendicular to both the thickness direction and the height direction of the battery cell is denoted as the length direction of the battery cell.

[0095] The length of the battery cell is greater than or equal to 270 mm;

[0096] Optionally, the length of the battery cell is 280mm to 600mm;

[0097] Optionally, the length of the battery cell is greater than or equal to 500mm, and more preferably 500mm to 600mm.

[0098] The aforementioned design of lithium-ion batteries can also improve battery RTE and achieve longer cycle life in large-size cells, and the improvement effect is significant.

[0099] In some embodiments, the lithium-ion battery includes a cell, the cell including the positive electrode, the separator and the negative electrode stacked together, and the separator is disposed between the positive electrode and the negative electrode;

[0100] The battery cell includes multiple positive tabs extending from multiple positions on the positive electrode plate and multiple negative tabs extending from multiple positions on the negative electrode plate; the multiple positive tabs are combined to form a positive tab portion, and the combined area of ​​the multiple positive tabs is denoted as the solder area of ​​the positive tab portion; the multiple negative tabs are combined to form a negative tab portion, and the combined area of ​​the multiple negative tabs is denoted as the solder area of ​​the negative tab portion;

[0101] The stacking direction of each electrode in the battery cell is denoted as the Z direction, the direction of the lead-out tab in the battery cell is denoted as the Y direction, and the direction perpendicular to both the Z and Y directions is denoted as the X direction. The X direction is parallel to the width direction of the positive tab and the width direction of the negative tab.

[0102] The battery cell satisfies one or more of the following characteristics:

[0103] (d1) The area of ​​the solder mark on the positive electrode lug is 30 mm². 2 ~340mm 2 90mm is optional 2 ~180mm 2 The solder area of ​​the negative electrode ear is 20mm². 2 ~280mm 2 70mm is optional 2 ~150mm 2 ;

[0104] (d2) The width of the solder area of ​​the positive electrode tab in the X direction is 10% to 30% of the length of the cell in the X direction, and can be selected as 10% to 20%; the width of the solder area of ​​the negative electrode tab in the X direction is 10% to 30% of the length of the cell in the X direction, and can be selected as 10% to 20%.

[0105] By controlling one or more parameters, such as the area of ​​the soldering region on the positive and negative electrode tabs and the ratio of the width of the soldering region on the positive and negative electrode tabs to the length of the cell, it is beneficial to better optimize the cell's overcurrent capacity and improve the battery's RTE.

[0106] In some embodiments, the battery cell includes a positive electrode post located on the same side of the battery cell as the positive electrode tab and electrically connected to the positive electrode tab; the battery cell also includes a negative electrode post located on the same side of the battery cell as the negative electrode tab and electrically connected to the negative electrode tab; the axial directions of both the positive electrode post and the negative electrode post are parallel to the Y direction;

[0107] Along the positive electrode tab extension path, the distance between the center of the solder area of ​​the positive electrode tab in the Y direction and the center of the nearest end face of the positive electrode post (which can be denoted as "solder-post center distance" at the positive electrode, or Jc1) is 40mm~250mm, and can be selected as 50mm~200mm.

[0108] Along the negative electrode tab extension path, the distance between the center of the solder area of ​​the negative electrode tab in the Y direction and the center of the nearest end face of the negative electrode post (which can be denoted as "soldering-post center distance" at the negative electrode, or Jc2) is 40mm~250mm, and can be selected as 50mm~200mm.

[0109] By controlling one or both of the solder mark-terminal center distance parameters Jc1 and Jc2 within the aforementioned range, it is beneficial to better optimize the cell's overcurrent capability and improve the battery's RTE.

[0110] In some embodiments, the lithium-ion battery includes a square wound cell; the stacking direction of each electrode in the square wound cell is denoted as the thickness direction of the cell;

[0111] Along the thickness direction of the battery cell, the ratio of the number of positive electrode layers leading out to the total number of positive electrode layers is denoted as Rp. If Rp ≥ 50%, then Rp ≥ 50%.

[0112] Optionally, Rp is 90%~100%.

[0113] A tab structure design with Rp within the aforementioned range is more conducive to improving the cell's overcurrent capability and thus better improving the cell's RTE. Among them, a full tab structure (such as a full tab structure with Rp of 100%) is more conducive to improving the cell's overcurrent capability.

[0114] In some embodiments, the lithium-ion battery includes a battery casing and a cell and electrolyte disposed within the battery casing, and the lithium-ion battery satisfies one or more of the following characteristics:

[0115] (e1) The battery casing is square;

[0116] (e2) The battery casing is a rigid casing;

[0117] (e3) The lithium-ion battery is a secondary lithium-ion battery.

[0118] In some embodiments of the second aspect of the application, a method for preparing a lithium-ion battery is provided, which can be used to prepare the lithium-ion battery described in the first aspect of the application.

[0119] In some embodiments of the second aspect of the application, a method for preparing a lithium-ion battery is provided, which includes the following steps:

[0120] An electrode assembly is placed in a battery casing; wherein the electrode assembly includes a positive electrode, a separator, and a negative electrode, with the separator disposed between the positive electrode and the negative electrode; the positive electrode includes a positive active layer, the positive active layer including a positive active material; the positive active material includes a lithium phosphate-based positive electrode material doped with element M, wherein element M includes any one or both of elements Ti and V;

[0121] An electrolyte is injected into the battery casing, and the casing is allowed to stand to allow the electrolyte to wet the positive and negative electrode sheets, thereby forming a lithium-ion battery. The electrolyte comprises an electrolyte salt, a non-aqueous solvent, and additives. The additives include one or both of vinylene carbonate and lithium bis(fluorosulfonyl)imide. The non-aqueous solvent comprises a carbonate solvent, and the initial mass percentage of the carbonate solvent in the non-aqueous solvent is greater than or equal to 80%.

[0122] The lithium-ion battery described in the first aspect of this application can be prepared.

[0123] In some embodiments, the method for preparing the lithium-ion battery satisfies one or more of the following characteristics:

[0124] (f1) The initial mass percentage of vinylene carbonate in the electrolyte is 1.8 wt% to 7 wt%, optionally 2.5 wt% to 3.5 wt%;

[0125] (f2) The initial molar volume concentration of lithium difluorosulfonylimide in the electrolyte is 0.2 mol / L to 0.6 mol / L, and can be selected as 0.3 mol / L to 0.5 mol / L;

[0126] (f3) The carbonate solvents include at least one of cyclic carbonates and chain carbonates;

[0127] Optionally, the carbonate solvent includes at least one of cyclic carbonates having 3 to 6 carbon atoms and chain carbonates having 3 to 9 carbon atoms;

[0128] Alternatively, the carbonate solvent includes cyclic carbonates and chain carbonates, wherein the mass ratio of the cyclic carbonates to the chain carbonates is (3~7):(7~3); the cyclic carbonates have 3~5 carbon atoms, and the chain carbonates have 4~7 carbon atoms;

[0129] (f4) The initial mass percentage of the carbonate solvent in the non-aqueous solvent is greater than or equal to 90%.

[0130] By controlling the initial concentrations of VC and / or LiFSI in the electrolyte, it is beneficial to better control the concentrations of the two additives in the resulting lithium-ion battery, thereby improving the battery RTE and better balancing longer battery cycle performance.

[0131] By controlling the types and / or contents of carbonate solvents in the electrolyte, it is beneficial to better suppress gas production and / or extend battery life.

[0132] In some embodiments of the third aspect of the application, a secondary battery is provided, comprising at least one of the lithium-ion batteries described in the first aspect of the application and lithium-ion batteries prepared by the preparation method of the lithium-ion batteries described in the second aspect of the application.

[0133] In some embodiments of the fourth aspect of the application, an energy storage device is provided, which includes at least one of the lithium-ion battery described in the first aspect of the application, a lithium-ion battery prepared by the method for preparing a lithium-ion battery described in the second aspect of the application, and a secondary battery described in the third aspect of the application.

[0134] In some of these implementations, the energy storage device can be an energy storage unit, an energy storage system, or a charging network.

[0135] In some embodiments of the fourth aspect of the application, an energy storage device, energy storage system, or charging network is also provided, which includes at least one of the lithium-ion battery described in the first aspect of the application, a lithium-ion battery prepared by the method for preparing a lithium-ion battery described in the second aspect of the application, and a secondary battery described in the third aspect of the application.

[0136] The aforementioned secondary batteries, energy storage devices, energy storage systems, and charging networks can leverage the advantages of lithium-ion batteries to achieve significantly improved RTE, while also achieving a longer service life.

[0137] Details of one or more embodiments or examples of this application are set forth in the following drawings and description. Other features, objects, and advantages of this application will become apparent from the specification, drawings, and claims. Attached Figure Description

[0138] To better describe and illustrate the embodiments, examples, or models provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments, examples, or models, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0139] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0140] Figure 2 for Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0141] Figure 3 This is a schematic diagram of a battery device according to one embodiment of this application.

[0142] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0143] Figure 5 for Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0144] Figure 6 This is a schematic diagram of an energy storage system according to one embodiment of this application.

[0145] Explanation of reference numerals in the attached figures:

[0146] 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Battery assembly; 5. Individual battery cell; 51. Battery casing; 52. Electrode assembly; 53. Cover plate. Detailed Implementation

[0147] The following describes in detail, with appropriate reference to the accompanying drawings, some embodiments and examples of the lithium-ion battery, its preparation method, secondary battery, and energy storage device of this application. However, some unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0148] The "range" disclosed in this application can be defined in the form of 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. Any endpoint can be included or excluded independently and can be combined arbitrarily; 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 ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also 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" and "5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when describing a parameter as an integer ≥ 2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 for that parameter. For instance, when describing a parameter as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0149] In this application, the term "numerical value" includes the number itself and its reasonable approximations. The definition of "numerical value" can apply to discrete numerical points or to the endpoints of a numerical range. Unless otherwise specified, the term "approximation" covers a numerical interval based on a reasonable range of fluctuations of the number itself. This reasonable range of fluctuations can vary depending on the type and magnitude of the number. This reasonable range of fluctuations can be reasonably determined based on the accuracy of the testing or measurement method. Therefore, when referring to a numerical value or a numerical range, unless otherwise specified, it should be understood that the numerical value includes its reasonable approximation, and the numerical range includes reasonable approximations at both endpoints. Those skilled in the art will understand that acceptable fluctuation ranges of the relevant approximations can be included within the definition of the numerical value or the numerical range. In this application, unless otherwise specified, "N1" can be reasonably understood as "about N1," and "N1~N2" can be reasonably understood as "about N1 to about N2," where N1 and N2 are two unequal numerical values.

[0150] In this application, unless otherwise specified, "about" means within a reasonable range above and below the number, and the range of fluctuation may vary depending on the type and value of the number. For example, a range of ±10%, ±5%, ±2%, ±1% may be allowed.

[0151] In this application, the terms "multiple," "various," or "multiple items" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one item or two or more (greater than or equal to) items. It can be understood that when "any number of" items are involved, it refers to any suitable combination of multiple items, that is, a combination of "any number of" items in a manner that does not conflict and enables the implementation of this application.

[0152] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0153] 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 or implementation 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. The term "implementation" as used herein has a similar understanding.

[0154] Those skilled in the art will understand that, unless otherwise specified, the order in which the steps are written in the various embodiments or methods of this application does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, but are preferably performed sequentially. For example, if method M includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, method M may also include step (c), meaning that step (c) can be added to method M in any order. For example, method M may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0155] In this application, open-ended technical features or solutions described using terms such as "containing," "comprising," or "including" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, if 'a' includes a1, a2, and a3, it may also include other members or exclude additional members unless otherwise specified. This can be considered as providing both features or solutions where "a consists of a1, a2, and a3" or "a is selected from a1, a2, and a3," and features or solutions where "a includes not only a1, a2, and a3, but also other members."

[0156] In this application, unless otherwise specified, M (e.g., m1) means that m1 is a non-limiting example of M, and it is understood that M is not limited to m1.

[0157] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it is selected from either "with" or "without." If multiple "options" appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "option" is independent. Unless otherwise specified, the descriptions such as "optionally include" and "optionally contain" in this application, taking "optionally include" as an example, mean "may include or not include."

[0158] In this application, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. Any and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "M and / or N" represents the group consisting of M, N, and "a combination of M and N". "Containing M and / or N" can mean "containing M, containing N, and containing both M and N", or "containing M, containing N, or containing both M and N", and can be appropriately understood according to the context.

[0159] In this document, the word "appropriate" in phrases such as "combining in an appropriate manner" or "appropriate manner" refers to the technical solution that enables the implementation of this application.

[0160] In this document, "preferred" and "better" are merely descriptions of implementation methods or embodiments with better effects, and should be understood as not constituting a limitation on the scope of protection of this application. If multiple "preferred" terms appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "preferred" term shall be independent.

[0161] In this application, terms such as "further," "even more," "especially," "for example," "as," and "example" are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0162] In this application, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0163] In this application, unless otherwise expressly specified and limited, terms such as "connected" and "joined" in relation to mechanical structures should be interpreted broadly, for example, they can refer to a fixed connection, a detachable connection, or an integral part. Those skilled in the art can understand the meaning of the above terms in this application according to the circumstances.

[0164] In this application, unless otherwise expressly specified and limited, the phrase "above" or "below" the second feature can mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. In this application, unless otherwise expressly specified and limited, the phrase "above" or "below" the second feature can indicate a horizontal positional relationship, or it can simply indicate the existence of an attachment relationship without specifying a horizontal positional relationship.

[0165] In this application, the term "room temperature" generally refers to 4℃~35℃, and may refer to 20℃±5℃. In some embodiments or examples of this application, room temperature refers to 20℃~30℃.

[0166] In this application, when a unit is specified for a data range, if the unit is only followed by the right endpoint, it indicates that the units for the left and right endpoints are the same. For example, 3~5μm or 3-5μm both mean that the unit for the left endpoint "3" and the right endpoint "5" is μm (micrometer), and both have the same meaning as 3μm~5μm. Furthermore, similar descriptions of other parameters such as temperature and concentration are interpreted in the same way.

[0167] In this application, unless otherwise specified, wt% means weight percentage, which is numerically equal to mass percentage.

[0168] In the description of the embodiments or examples of this application, the terms "center", "length", "height", "width", "thickness", "upper", "lower", "horizontal", "top", "bottom", "inner", "outer", "axial", etc., indicating the orientation or positional relationship are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the embodiments of this application.

[0169] In this application, unless otherwise expressly specified and limited, in a device structure or mechanical structure, the first feature being "on" or "under" a second feature can mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. In this application, unless otherwise expressly specified and limited, the first feature being "on" or "under" a second feature can indicate a horizontal positional relationship, or it can simply indicate the existence of an attachment relationship without specifying a horizontal positional relationship.

[0170] In the description of the embodiments or examples of this application, unless otherwise explicitly specified and limited, the technical terms such as "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application according to the specific circumstances.

[0171] In this application, the exemplary descriptions such as "in some implementations (or embodiments)" and "in one implementation (or embodiment)" may cover, but are not limited to, the following meanings: these solutions can be combined with other solutions in a suitable manner to form new technical solutions.

[0172] Unless otherwise stated, the improvements described in this application are not intended to be limited to any theoretical constraints.

[0173] Large-capacity energy storage cells typically have a large length, which can significantly degrade the current flow path, reduce the battery's round-trip efficiency (RTE), and shorten its cycle life. Generally, the higher the capacity of the energy storage cell, the higher the ohmic polarization ratio and the lower the RTE. In addition, larger cell sizes are more prone to heat generation, poor heat dissipation, and greater expansion forces in the later stages of cycling, leading to a shorter cycle life.

[0174] Lithium phosphate cathode materials typically exhibit low electronic conductivity and poor intrinsic conductivity. When dopants are introduced into lithium phosphate cathode materials, if the ionic valence state or ionic size of the dopant differs from that of the doped element—for example, if the ionic valence state of the dopant is higher than that of the doped element, or if the ionic size of the dopant differs from that of the doped element—there may be a risk of dissolution of the dopant, leading to a reduction in specific capacity and a deterioration in battery cycle life.

[0175] According to various embodiments and examples of this application, this application provides at least a lithium-ion battery and a method for preparing the same, a secondary battery, and an energy storage device. This lithium-ion battery exhibits significantly improved real-time efficiency (RTE) while also possessing a long cycle life.

[0176] In some embodiments, a lithium-ion battery includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive active layer, which includes a positive active material. The electrolyte includes an electrolyte salt, a non-aqueous solvent, and additives.

[0177] In some embodiments, the positive electrode active material includes a lithium phosphate-based positive electrode material doped with element M, where element M includes any one or both of elements Ti and V; the additive includes one or more of vinylene carbonate and lithium bis(fluorosulfonyl)imide. In this case, doping with element M can improve the conductivity of the lithium phosphate-based positive electrode material, enhance crystal structure stability and lithium-ion diffusion rate, and provide a suitable potential window so that both vinylene carbonate (VC) and lithium bis(fluorosulfonyl)imide (LiFSI) can participate well in positive electrode film formation. It can also suppress the dissolution of element M, inhibit electrolyte decomposition, and reduce side reactions between the electrolyte and the positive electrode active material. Based on the aforementioned multiple effects, it can reduce battery internal resistance, improve positive electrode stability and cycle stability, significantly delay battery capacity decay, improve battery energy conversion efficiency (round-trip efficiency, RTE), and also give the lithium-ion battery a longer cycle life. However, this is not limited to the aforementioned theory.

[0178] In some embodiments, the non-aqueous solvent includes carbonate solvents; in some of these embodiments, the carbonate solvent accounts for more than 75% of the non-aqueous solvent by mass, and optionally, the carbonate solvent accounts for more than or equal to 80% of the non-aqueous solvent by mass. By controlling the non-aqueous solvent to include a higher content of carbonate solvents, it is beneficial to suppress gas generation and extend battery life.

[0179] In other embodiments, the lithium-ion battery includes a cell, which comprises a positive electrode, a negative electrode, and an electrolyte. The stacking direction of the electrodes in the cell is denoted as the thickness direction, the direction in which the tabs are led out of the cell is denoted as the height direction, and the direction perpendicular to both the thickness and height directions is denoted as the length direction. The length of the cell is greater than or equal to 270 mm. The aforementioned design of the lithium-ion battery can significantly improve the battery's real-time efficiency (RTE) and achieve a longer cycle life even in large-size cells. In this case, the larger cell size allows for the achievement of higher cell capacity (higher single-cell capacity) while simultaneously achieving significantly improved RTE and a longer cycle life.

[0180] In other embodiments, the additives include vinylene carbonate and lithium bis(fluorosulfonyl)imide. In this case, the synergistic effect of the two additives, VC and LiFSI, is advantageous, resulting in better suppression of element dissolution (M), better improvement of battery RTE, and better extension of battery cycle life.

[0181] In this application, unless otherwise specified, the term "lithium-ion battery" refers to a battery in which the active ions include lithium ions, and "lithium-ion battery cell" refers to a single battery cell in which the active ions include lithium ions. Typically, a lithium-ion battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. A separator is disposed between the positive and negative electrodes; the separator primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0182] In this application, unless otherwise specified, "electrode active layer" includes at least one of the positive active layer of the positive electrode sheet and the negative active layer of the negative electrode sheet. Depending on the specific circumstances, the electrode active layer may refer to either the positive active layer or the negative active layer. It is understood that the positive active layer contains positive active material, and the negative active layer contains negative active material.

[0183] In this application, the terms "electrode sheet" and "electrode plate" have the same meaning and can be used interchangeably. An electrode sheet can be a positive electrode sheet or a negative electrode sheet, and the "active material" or "active substance" in the electrode sheet has the ability to reversibly insert and extract active ions.

[0184] In this application, the term "positive electrode sheet" includes a positive electrode active layer, and the positive electrode active layer includes a positive electrode active material. The term "positive electrode active material" refers to a material used in a positive electrode sheet that is capable of reversibly extracting and inserting active ions.

[0185] In this application, unless otherwise specified, "positive electrode sheet" includes a positive current collector. A "positive current collector" refers to a structure responsible for collecting and conducting electrons at the positive electrode. In the positive electrode sheet, the positive active layer is located on at least one side of the positive current collector, and may be located on one or both sides of the positive current collector.

[0186] In this application, the term "negative electrode sheet" includes a negative electrode active layer, which includes a negative electrode active material. The term "negative electrode active material" refers to a material used in a negative electrode sheet that is capable of reversibly inserting and de-inserting active ions.

[0187] In this application, unless otherwise specified, "negative electrode sheet" includes a negative electrode current collector. A "negative electrode current collector" refers to a structure responsible for collecting and conducting electrons at the negative electrode. In the negative electrode sheet, the negative electrode active layer is located on at least one side of the negative electrode current collector, and may be located on one or both sides of the negative electrode current collector.

[0188] In this application, unless otherwise specified, "separation membrane" and "diaphragm" have the same meaning and can be used interchangeably.

[0189] In some embodiments of the first aspect of the application, a lithium-ion battery is provided, comprising a positive electrode and an electrolyte. The positive electrode includes a positive active layer, which includes a positive active material. The electrolyte includes an electrolyte salt, a non-aqueous solvent, and additives. The positive active material includes a lithium phosphate-based positive electrode material doped with element M, where element M includes one or both of titanium (Ti) and vanadium (V). The additives include one or both of vinylene carbonate and lithium bis(fluorosulfonyl)imide. Further, the non-aqueous solvent includes a carbonate solvent, wherein the carbonate solvent accounts for a relatively high mass percentage (e.g., greater than or equal to 80%) of the non-aqueous solvent.

[0190] In this application, unless otherwise specified, "lithium phosphate-containing cathode material" refers to a class of cathode active materials that include lithium phosphate components, and more specifically, materials that include lithium, transition metal elements, and phosphate (PO4). 3- The positive electrode active material is lithium phosphate. Unless otherwise specified, "lithium phosphate-containing positive electrode material" includes olivine crystal structure. The lithium phosphate component in lithium phosphate-containing positive electrode material may be the lithium phosphate itself, or it may be a composite material with other substances. For example, lithium phosphate-containing positive electrode material may be a composite material of lithium phosphate and carbon, or further, it may be a carbon-coated lithium phosphate.

[0191] One of the typical compounds with an olivine crystal structure is lithium iron phosphate (LiFePO4), in which the positions occupied by Li, Fe, P and O in the olivine crystal can be denoted as lithium (Li) sites, iron (Fe) sites, phosphorus (P) sites and oxygen (O) sites, respectively; vacancies may occur at the lithium and oxygen sites, and the iron sites may be doped by other types of metal elements.

[0192] In this application, unless otherwise specified, "M-doped lithium phosphate cathode material" includes lithium, a first transition metal element, M element, and phosphate ions. The first transition metal element can co-construct the basic crystal structure with Li and phosphate ions. The M element can act as a dopant element, replacing some of the positions of the first transition metal element to form the doped lithium phosphate cathode material. It is understood that the M element is different from the first transition metal element and can provide a positive valence. In some embodiments, the M element includes any one or both of Ti and V elements. Taking Fe as the first transition metal element as an example, Ti and V elements can be used to replace some Fe atoms at iron sites. For example, the atomic molar ratio of the first transition metal element in the transition metal element contained in the lithium phosphate cathode material doped with element M can be greater than or equal to 0.5, or greater than or equal to any of the following values, or greater than any of the following values, or be any of the following values, or be selected from the range of any of the following values ​​and the value "1": 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.92, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, etc.

[0193] In this application, unless otherwise specified, "lithium-containing phosphate" refers to a compound composed of lithium (Li), transition metal elements, and phosphate (PO4) ions. 3- Unless otherwise specified, "lithium phosphate" includes olivine crystal structures.

[0194] In this application, unless otherwise specified, "electrolyte" refers to a liquid electrolyte. Unless otherwise specified, electrolyte includes electrolyte salt and electrolyte solvent, and electrolyte solvent includes non-aqueous solvent; further, electrolyte solvent is a non-aqueous solvent.

[0195] Vinylene carbonate (VC), used in this article, is a cyclic carbonate compound containing unsaturated carbon-carbon bonds, with the following structure: Unless otherwise stated in this application, VC may be used as a film-forming additive in electrolytes.

[0196] Lithium bis(fluorosulfonyl)imide (LiFSI, with the chemical formula LiN(SO2F)2), used herein, is an example. Unless otherwise stated, LiFSI can be used as both a film-forming additive and an electrolyte salt in this application.

[0197] As used in this article, "carbonate solvents" refers to a class of non-aqueous solvents containing carbonate groups (-OC(=O)-O-). Carbonate solvents can have chain structures or contain cyclic structures. Compared to carboxylic acid ester solvents, carbonate solvents have several advantages, such as better electrochemical stability, which are more conducive to suppressing gas generation and extending battery life.

[0198] The aforementioned lithium-ion battery introduces lithium phosphate-based cathode materials doped with element M into the positive active layer of the positive electrode sheet. Element M can include any one or both of Ti and V. Element M can be incorporated into the lattice of the lithium phosphate-based cathode material, for example, replacing Fe sites. This improves the material's conductivity by introducing more electronic active sites or altering the Fermi level distribution. Furthermore, the valence stability of high-valence ions (e.g., ≥4+) of element M can further enhance crystal structure stability. Lattice doping with element M can also increase the lithium-ion diffusion rate. In addition, when the positive active material includes lithium phosphate-based cathode materials doped with element M, a suitable potential window can be provided, allowing both VC and LiFSI to participate well in the cathode film formation. In this case, introducing ethylene carbonate into the electrolyte... One or both of the additives, namely olefin ester (VC) and lithium bis(fluorosulfonyl)imide (LiFSI), can participate in the formation of a stable solid electrolyte interphase (CEI) film on the surface of the positive electrode active material, improving the stability of the CEI film and providing better isolation, passivation, and protection. This can reduce the dissolution of macroelements (such as Ti) and the damage of acid byproducts in the electrolyte to the CEI film and the positive electrode active material, further reducing the possibility of macroelements (such as Ti) dissolution. It can also inhibit electrolyte decomposition and reduce side reactions between the electrolyte and the positive electrode active material. By controlling the non-aqueous solvent, including a higher content of carbonate solvents, it is beneficial to suppress gas generation and extend battery life. Therefore, it can reduce the battery's internal resistance, improve positive electrode stability and cycle stability, significantly delay battery capacity decay, improve the battery's round-trip efficiency (RTE), and also give lithium-ion batteries a longer cycle life. However, this is not limited to the aforementioned theories.

[0199] The elemental composition of the positive electrode active material in the positive electrode active layer can be analyzed using methods known in the art, including but not limited to the following: inductively coupled plasma atomic emission spectrometry (ICP), X-ray diffraction (XRD), single-crystal X-ray diffraction (SCXRD), and energy dispersive spectroscopy (EDS). The sample preparation and testing methods for these methods are known to those skilled in the art, and the test parameters can be appropriately adjusted according to the sample characteristics. ICP can be used for quantitative analysis of the component content in the positive electrode active material.

[0200] The detection of positive electrode active material in the positive electrode active layer can be carried out by disassembling the battery after it is fully discharged, removing the positive electrode plate, scraping off the material of the positive electrode active layer, and using elemental analysis methods such as inductively coupled plasma (ICP) spectroscopy to test and analyze the types and proportions of elements, thereby confirming the elemental composition and chemical formula of the positive electrode active material.

[0201] The types and concentrations of inorganic components in the electrolyte (which may include electrolyte salts and inorganic additives, and further may include LiFSI) can be tested with reference to relevant standards such as GB / T 34672-2017 General Rules for Determination of Chemical Reagents by Ion Chromatography, JY / T020-1996 General Rules for Ion Chromatographic Analysis, and GB / T 6040-2019 General Rules for Infrared Spectroscopic Analysis, and the latest version of the standard method may be preferred. The types and contents of organic components in the electrolyte (including non-aqueous solvents and organic additives, and further may include VC) can be tested with reference to relevant standards such as GB / T 9722-2023 General Rules for Gas Chromatography of Chemical Reagents.

[0202] Those skilled in the art can also identify the components of the electrolyte in a lithium-ion battery using one or more of the following detection methods, including but not limited to: 1H NMR (1H NMR) spectroscopy (NMR) 1 Methods such as ¹H NMR, high-performance liquid chromatography (HPLC), matrix-assisted laser desorption / ionization mass spectrometry (MADI-TOF), Fourier transform infrared (FT-IR) spectroscopy, and ultraviolet spectroscopy are available. The sample preparation and testing methods for these methods are known to those skilled in the art, and the test parameters can be appropriately adjusted according to the structure of the material or substance and the characteristics of the sample. As a non-limiting example, FT-IR, ultraviolet spectroscopy, etc., can be used. 1 One or more of the following methods may be used to detect the types and contents of electrolyte components: ¹H NMR, mass spectrometry, MADI-TOF, etc., but not limited to these.

[0203] When lithium phosphate cathode materials are doped with element M (e.g., Fe-site doping), if there is a difference in the ionic valence state or ionic size between element M and the doped element, for example, if the ionic valence state of element M is higher than that of the doped Fe, then... 2+ When or when the ion size of element M is similar to that of the doped Fe 2+When differences exist, there may be a risk of dissolution of element M. Taking Ti and V doping as an example, the dissolution of Ti and V elements leads to the destruction of the crystal lattice structure, which reduces the content of effective active materials that can participate in electrochemical reactions in the positive electrode, resulting in a decrease in battery specific capacity and potentially weakening the improvement effect of introducing element M on RTE. In addition, the dissolution of Ti and V elements may also lead to crystal structure collapse and the superposition of interfacial side reactions, thereby forming an unstable CEI film at the positive electrode / electrolyte interface, accelerating electrolyte decomposition, and further deteriorating battery cycle performance.

[0204] In some implementations, element M is a metallic element, which may be a transition metal element.

[0205] In some implementations, element M includes transition metal elements.

[0206] In some embodiments, the mass fraction of element M in the element M-doped lithium phosphate cathode material is 0.04% to 0.16%, optionally 0.05% to 0.15%, further optionally 0.06% to 0.12%, and may also be any of the following percentages or a range selected from any two of the following percentages: 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, etc.

[0207] In some embodiments, the additives in the electrolyte include one or both of vinylene carbonate and lithium bis(fluorosulfonyl)imide; in some of these embodiments, the mass percentage of vinylene carbonate in the electrolyte is 0-6.5 wt%, and the molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 0-0.6 mol / L. The sum of the mass percentages of vinylene carbonate and lithium bis(fluorosulfonyl)imide in the electrolyte is greater than 0.

[0208] In some embodiments, the additives in the electrolyte include vinylene carbonate and lithium bis(fluorosulfonyl)imide; in some of these embodiments, the mass percentage of vinylene carbonate in the electrolyte is greater than 0 and less than or equal to 6.5 wt%, and the molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is greater than 0 and less than or equal to 0.6 mol / L.

[0209] In some implementations, the electrolyte satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0210] (a1) The mass fraction of element M in the positive electrode active material is 0.04%~0.16%, which can be selected as 0.05%~0.15%, and further selected as 0.06%~0.12%. It can also be any of the following percentages or a range selected from any two of the following percentages: 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, etc.

[0211] By controlling the doping amount of element M within the aforementioned range, we can fully leverage the aforementioned doping advantages of element M while also better controlling the dissolution probability of element M, better controlling the overall impact of element M doping on battery RTE, better improving battery RTE, and also better taking into account good cycle performance.

[0212] (a2) Element M is a metallic element with an ionic valence greater than or equal to 3; for example, the ionic valence of element M (in terms of positive valence) can be 3 to 6, and can be 3, 4, 5, 6 or a combination of the aforementioned valence states, but is not limited thereto;

[0213] When element M is a metallic element with an ionic valence greater than or equal to 3, introducing more electronic active sites or changing the Fermi level distribution to optimize electronic conductivity can help improve the conductivity of the material itself.

[0214] (a3) M is a transition metal element;

[0215] When element M is a transition metal, the variable valence state of transition metals can be utilized to improve the charge matching between element M and the crystal structure of lithium phosphate-containing cathode materials, which is beneficial to improving the stability of the crystal structure after element M doping. For example, high-valence ions of elements Ti and V can have higher valence state stability, which is beneficial to further improving the stability of the crystal structure after doping. In addition, the ion size of elements Ti and V is similar to that of Fe. 2+ The closer the doping structure is, the more beneficial it is to the stability of the doped crystal structure.

[0216] (a4) In lithium phosphate cathode materials doped with element M, the sum of the atomic molar ratios of Ti and V in element M is 0.8 to 1, which can be selected as 0.9 to 1, or any of the following values ​​or a range selected from any two of the following values: 0.8, 0.82, 0.84, 0.85, 0.86, 0.88, 0.9, 0.92, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, etc.

[0217] Optionally, the M element includes the Ti element;

[0218] By controlling the atomic molar ratio of Ti and V elements in M ​​to be in a high range, it is beneficial to fully utilize the aforementioned doping advantages of M element, while also improving the stability of the doped crystal structure, which is conducive to improving the RTE of the battery; in addition, it is also conducive to achieving better battery cycle life.

[0219] (a5) The mass percentage of vinylene carbonate in the electrolyte is 0.7wt% to 6.5wt%, optionally 1wt% to 4.5wt%, or any of the following percentages or a range of any two of the following percentages (unit: weight percentage): 0.7%, 0.8%, 1%, 1.2%, 1.5%, 1.6%, 1.8%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, etc.;

[0220] Both VC and LiFSI can act as positive electrode film-forming additives and negative electrode film-forming additives. They can promote the formation of a stable and high-quality negative electrode solid electrolyte interphase (SEI) film, better suppress negative electrode interfacial side reactions, better delay battery capacity decay, and better extend battery cycle life.

[0221] VC can form carbonate, CO2, and C2O4-containing compounds on the surface of positive electrode active materials. 2- Components such as oxalate participate in the formation of a stable CEI interface film, reduce the dissolution of M element, reduce the direct contact between the electrolyte or acid by-products in the electrolyte and the positive electrode active material, and inhibit the decomposition of the electrolyte and the structural damage of the positive electrode active material by acid by-products.

[0222] By controlling the content of VC in the electrolyte within the aforementioned range, it is beneficial to better leverage the aforementioned advantages of VC, and also to better control the increase in interfacial impedance, increase in battery internal resistance and gas generation that may be caused by VC. This not only helps to better improve the RTE of the battery after doping with M element, but also helps to better improve the battery cycle performance.

[0223] (a6) The molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.1 mol / L to 0.6 mol / L, which can be selected from 0.2 mol / L to 0.5 mol / L, or any of the following concentrations or a range selected from any two of the following concentrations: 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, etc.;

[0224] LiFSI can not only promote the formation of a stable positive electrode CEI interface film, improve the stability of the positive electrode CEI film, and inhibit the dissolution of M element; LiFSI can also promote the rapid and uniform formation of the negative electrode SEI film, improve the ion conductivity of the SEI film, and inhibit the side reactions and lithium loss on the negative electrode surface; in addition, it has a good ability to dissociate lithium ions, which is beneficial to improve the liquid phase conductivity and reduce the battery internal resistance; by introducing LiFSI into the electrolyte, the battery RTE and cycle life can be better improved.

[0225] By controlling the content of LiFSI in the electrolyte within the aforementioned range, it is beneficial to better leverage the aforementioned advantages of LiFSI, which can significantly reduce the dissolution probability of element M, significantly improve the battery RTE and enhance the battery's long-term cycle performance; in addition, it is also beneficial to better control gas generation caused by LiFSI, such as gas generation caused by LiFSI contacting water or catalytic solvent decomposition.

[0226] The inhomogeneity or instability of the negative electrode SEI film is the main reason for the low initial coulombic efficiency; introducing the aforementioned concentration of LiFSI can also help improve the initial coulombic efficiency of the battery.

[0227] (a7) The ester solvents include at least one of cyclic carbonates and chain carbonates; by controlling the ester solvents in the electrolyte to have the aforementioned types, it is beneficial to better suppress gas generation and / or extend battery life.

[0228] (a8) The mass percentage of carbonate solvents in non-aqueous solvents is greater than or equal to 90%; by controlling the carbonate solvent content in the electrolyte to the aforementioned level, it is beneficial to better suppress gas generation and / or extend battery life.

[0229] In some implementations, the electrolyte satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0230] (t1) The mass fraction of element M in the positive electrode active material is 0.06%~0.12%;

[0231] (t2) In lithium phosphate cathode materials doped with element M, the sum of the atomic molar ratios of Ti and V in element M is 0.9~1;

[0232] (t3) The M element includes the Ti element;

[0233] (t4) The mass percentage of vinylene carbonate in the electrolyte is 1wt%~4.5wt%;

[0234] (t5) The molar volume concentration of lithium difluorosulfonylimide in the electrolyte is 0.2 mol / L to 0.5 mol / L;

[0235] (t6) The additives in the electrolyte include vinylene carbonate and lithium difluorosulfonylimide;

[0236] (t7) Carbonate solvents include at least one of cyclic carbonates having 3 to 6 carbon atoms and chain carbonates having 3 to 9 carbon atoms; optionally, the cyclic carbonates have 3 to 5 carbon atoms and the chain carbonates have 4 to 7 carbon atoms; by controlling the carbonate solvents in the electrolyte to have the aforementioned types, it is beneficial to better suppress gas generation and / or extend battery life.

[0237] (t8) Carbonate solvents include cyclic carbonates and chain carbonates; optionally, the mass ratio of cyclic carbonates to chain carbonates is (3~7):(7~3); further optionally, the cyclic carbonates have 3~5 carbon atoms and the chain carbonates have 4~7 carbon atoms; by controlling the carbonate solvents in the electrolyte to have the aforementioned types and / or contents, it is beneficial to better suppress gas generation and / or extend battery life.

[0238] In this application, unless otherwise stated, "the ionic valence state of element M" refers to the numerical value of the positive valence of element M.

[0239] In some implementations, element M is a transition metal element with an ionic valence state greater than or equal to 3.

[0240] In some embodiments, element M includes element Ti. Non-limitingly, the mass fraction of element Ti in the positive electrode active material is 0.04% to 0.16%, optionally 0.05% to 0.15%, further optionally 0.06% to 0.12%, and may also be any of the following percentages or a range selected from any two of the following percentages: 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, etc.

[0241] In some embodiments, the atomic molar ratio of Ti to M is 0.8 to 1, optionally 0.9 to 1, and may also be any of the following values ​​or a range selected from any two of the following values: 0.8, 0.82, 0.84, 0.85, 0.86, 0.88, 0.9, 0.92, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, etc.

[0242] In some implementations, the gas generation problem can be mitigated by improving the height of the lower plastic layer and leaving sufficient top clearance.

[0243] In some embodiments, the electrolyte salt includes lithium hexafluorophosphate (LiPF6).

[0244] In some embodiments, the electrolyte salt includes lithium bis(fluorosulfonyl)imide (LiFSI) and lithium hexafluorophosphate (LiPF6), and in some embodiments, the molar volume concentration of LiFSI in the electrolyte is lower than that of LiPF6. This is beneficial for improving battery RTE and cycle performance, while also helping to better suppress gas generation problems caused by side reactions.

[0245] For example, the molar volume concentration of LiFSI in the electrolyte is 0.2 mol / L to 0.6 mol / L, and can also be selected from any suitable value or range in the context; the sum of the molar volume concentrations of LiFSI and LiPF6 in the electrolyte is 0.6 mol / L to 1.5 mol / L, and can also be any of the following concentrations or a range composed of any two of the following concentrations: 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, etc.

[0246] In some embodiments, the electrolyte includes a non-aqueous solvent. In some embodiments, the non-aqueous solvent in the electrolyte includes carbonate solvents. In some embodiments, the non-aqueous solvent in the electrolyte may include at least one of cyclic carbonates and chain carbonates, and further reference can be made to the context description of cyclic carbonates and chain carbonates. In some embodiments, the non-aqueous solvent in the electrolyte includes one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), etc. This is more beneficial for improving the cycle life and / or storage life of the battery.

[0247] In some embodiments, the non-aqueous solvent in the electrolyte includes carbonate solvents. Non-limitingly, the carbonate solvent may include at least one of cyclic carbonates and chain carbonates, in which case the non-aqueous solvent in the electrolyte may include at least one of cyclic carbonates and chain carbonates. The types of cyclic carbonates and chain carbonates can also be found in the context description. In some embodiments, the mass percentage of the carbonate solvent in the non-aqueous solvent in the electrolyte may be greater than 75%, greater than or equal to 80%, or greater than or equal to any of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 98%, etc. In some other embodiments, the mass percentage of carbonate solvent in the non-aqueous solvent in the electrolyte can be 80% to 100%, optionally 90% to 100%, or any of the following percentages or a range selected from any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 98%, 100%, etc.

[0248] In some embodiments, the non-aqueous solvent in the electrolyte includes cyclic carbonates and chain carbonates. Non-limitingly, the mass ratio of cyclic carbonates to chain carbonates can be (3~7):(7~3), and more preferably (5~7):(5~3).

[0249] For example, ethylene carbonate has 3 carbon atoms, and methyl ethyl carbonate has 4 carbon atoms.

[0250] Non-limiting, in the electrolyte, the mass percentage of cyclic carbonates in the carbonate solvent is less than or equal to 70%, optionally 30% to 70%, further optionally 50% to 70%, and may also be any of the following percentages or a range selected from any two of the following percentages: 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, etc.

[0251] Non-limitingly, in the electrolyte, the mass percentage of the chain carbonate in the carbonate solvent is less than or equal to 70%, optionally 30% to 70%, further optionally 30% to 50%, and may also be any of the following percentages or a range selected from any two of the following percentages: 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, etc.

[0252] In this application, unless otherwise specified, "cyclic carbonate" refers to a non-aqueous solvent having the following cyclic structure: containing a carbonate group (-OC(=O)-O-) and the two bonding sites of the carbonate group together with a divalent linker to form a cyclic structure.

[0253] In this application, unless otherwise specified, "chain carbonate" refers to a non-aqueous solvent having the following chain structure: containing a carbonate group (-OC(=O)-O-) and each of the two bonding sites of the carbonate group is connected to a monovalent group.

[0254] By controlling the non-aqueous solvents in the electrolyte, including the aforementioned types and / or amounts of carbonate solvents, it is more beneficial to the battery's cycle life and / or storage life.

[0255] In some embodiments, the additives in the electrolyte include vinylene carbonate and lithium bis(fluorosulfonyl)imide. The concentrations of vinylene carbonate and lithium bis(fluorosulfonyl)imide in the electrolyte can be selected from any suitable values ​​or ranges in the context. For example, the molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is greater than 0 and less than or equal to 0.6 mol / L, and can be selected from 0.1 mol / L to 0.6 mol / L, more preferably from 0.2 mol / L to 0.5 mol / L, or can be selected from any suitable value or range in the context. For example, it can be greater than 0 and less than or equal to any of the following concentrations, or can be any of the following concentrations or a range consisting of any two of the following concentrations: 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, etc. For example, the mass percentage of vinylene carbonate in the electrolyte is greater than 0 and less than or equal to 6.5%, optionally 0.7wt% to 6.5wt%, further optionally 0.7wt% to 5wt%, and even more preferably 1wt% to 4wt%. For example, it can be greater than 0 and less than or equal to any of the following percentages, or it can be any of the following percentages or a range selected from any two of the following percentages (in weight percentage): 0.7%, 0.8%, 1%, 1.2%, 1.5%, 1.6%, 1.8%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, etc.

[0256] In some embodiments, the molar volume concentration of the electrolyte salt in the electrolyte is 0.6 mol / L to 1.5 mol / L, and may also be any of the following concentrations or a range selected from any two of the following concentrations: 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, etc.; further optionally, the electrolyte salt includes lithium hexafluorophosphate.

[0257] In some implementations, the electrolyte satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0258] (x1) The mass percentage of vinylene carbonate in the electrolyte is 1wt%~4wt%;

[0259] (x2) The molar volume concentration of the electrolyte salt in the electrolyte solution is 0.6 mol / L to 1.5 mol / L;

[0260] (x3) Electrolyte salts include lithium hexafluorophosphate.

[0261] When the electrolyte contains both VC and LiFSI, the potential difference between the two in film formation allows LiFSI to preferentially participate in the formation of CEI and SEI films, thereby reducing VC consumption and mitigating the increase in interfacial impedance and battery internal resistance that may result from VC participation in film formation. This can achieve excellent synergistic improvement in battery RTE and battery cycle performance.

[0262] By controlling the concentrations of VC and LiFSI within the aforementioned ranges, it is beneficial to better leverage their synergistic effect.

[0263] When the electrolyte also includes lithium hexafluorophosphate (LiPF6), compared to when the electrolyte also includes lithium bisfluorosulfonyl imide (LiFSI) at the same concentration as LiPF6, the combination of LiFSI and LiPF6 is beneficial for improving battery RTE and cell cycle performance. In some embodiments, the D of the positive electrode active material... v 50 is 5μm~10μm, can be selected from 6μm~8μm, and can also be any of the following values ​​or a range composed of any two of the following values: 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, etc.

[0264] Unless otherwise stated in this application, D v 50 refers to the particle size corresponding to a cumulative volume distribution percentage of 50% in the material. This parameter indicates that the particle size of 50% of the material's volume is less than or equal to D. v 50, and particles accounting for 50% of the material volume have a particle size greater than D. v 50. D v 50 can be obtained from the volumetric cumulative distribution curve of the material particle size. Unless otherwise specified, the volumetric cumulative distribution curve is accumulated from zero on the smaller particle size side. Those skilled in the art will understand that D vThe meaning of 50 can be determined using instruments and methods known in the field. For example, it can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer or the LS-909 laser particle size analyzer from Malvern Instruments Ltd. (UK). Furthermore, for equipment models such as the Malvern 2000 laser particle size analyzer, the standard procedure GB / T19077-2016 / ISO 13320:2009 can be referenced for testing.

[0265] By using the D of the positive electrode active material v Controlling the specific surface area (D50) within the aforementioned relatively large range can provide a relatively low specific surface area, which is beneficial for suppressing side reactions between the electrolyte and the positive electrode active material, reducing lithium loss, improving battery RTE, and delaying capacity decay; at the same time, the D50 of this positive electrode active material... v The 50-degree gradient also allows for better control of lithium-ion diffusion paths, achieving a better balance between lower battery internal resistance and extended battery cycle life. Furthermore, it improves the stability of the cathode slurry, thereby enhancing the uniformity of the distribution of the cathode active material in the cathode active layer, which is more beneficial for constructing a superior conductive network.

[0266] In some embodiments, the D of the positive or negative electrode active material can be tested using the following methods. v Particle size parameters were measured using a Malvern 2000 (MasterSizer 2000) laser particle size analyzer, following the standard procedure GB / T19077-2016 / ISO 13320:2009. The detailed test procedure included: taking an appropriate amount of the sample, adding a solvent (deionized water is acceptable, sample concentration can be controlled at 8%~20% opacity, 15%~20% opacity is optional), and sonicating for 5 min (53 kHz / 120 W) to ensure thorough dispersion. The sample was then measured according to GB / T19077-2016 / ISO 13320:2009. Non-limiting examples of solvents include deionized water and anhydrous ethanol. After the sample was poured into the injection tower, it circulated with the solution to the test optical path system. Under laser beam irradiation, the particle size distribution characteristics were determined by receiving and measuring the energy distribution of the scattered light. Based on the test data, a particle size distribution map was plotted, and the Dsize was obtained from the distribution map. v Parameters such as 50 were used. To avoid agglomeration during the drying process affecting particle size testing, a dispersion test was performed on a washed and moistened sample.

[0267] In this application, the test sample of the "positive electrode active material" in the positive electrode sheet of a lithium-ion battery can be obtained by the following method: disassembling the battery, removing the positive electrode sheet, and extracting the positive electrode active material from the positive electrode active layer of the positive electrode sheet using methods such as solvent washing (e.g., soaking and cleaning with dimethyl carbonate), ultrasonic dispersion, centrifugation, and fractional sedimentation. The extracted powder sample is then dried to obtain a powder sample. The obtained powder sample can be used for laser particle size analysis or other tests, such as scanning electron microscopy (SEM) testing.

[0268] In some embodiments, the D of the positive electrode active material n 10 is 0.28μm~0.45μm, can be selected from 0.3μm~0.4μm, and can also be any of the following values ​​or a range composed of any two of the following values: 0.28μm, 0.3μm, 0.32μm, 0.34μm, 0.35μm, 0.36μm, 0.38μm, 0.4μm, 0.42μm, 0.44μm, 0.45μm, etc.

[0269] Unless otherwise stated in this application, D n 10 refers to the particle size corresponding to a cumulative percentage of 10% of the material. This parameter indicates that the particle size of 10% of the material is less than or equal to D. n 10, and 90% of the particles in the material have a particle size greater than D. n 10. D n 10 can be obtained from the cumulative number distribution curve of the material particle size, which, unless otherwise specified, accumulates from zero on the smaller particle size side. Those skilled in the art will understand that D... n The meaning of 10 can be determined using instruments and methods known in the art. Test D can be used. v The methods and instruments used at 50.

[0270] By using the D of the positive electrode active material n Controlling 10 within the aforementioned range is beneficial for significantly reducing the content of extremely small particles with extremely small size and extremely large specific surface area, thereby significantly reducing the side reactions between the electrolyte and the positive electrode active material, which is conducive to better improving the battery RTE and extending the battery cycle life.

[0271] In some implementations, the positive electrode sheet satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0272] (y1) D of the positive electrode active material v 50 has a thickness of 6μm to 8μm;

[0273] (y2) D of the positive electrode active materialn 10 is 0.3μm~0.4μm.

[0274] By using the D of the positive electrode active material v 50 or D n 10. Keeping it within the aforementioned range is beneficial for better control of D. v 50 or D n The aforementioned advantages of 10.

[0275] By using the D of the positive electrode active material v 50 and D n Controlling both of these factors within the aforementioned range is beneficial for better balancing a lower specific surface area and a suitable lithium-ion diffusion path, as well as better balancing lower battery internal resistance and extended battery cycle life.

[0276] In some embodiments, the negative electrode sheet includes a negative electrode active layer, which includes a negative electrode active material; the negative electrode active material includes secondary particles.

[0277] In this application, unless otherwise specified, "the negative electrode active material includes secondary particles" means that the negative electrode active material mainly comprises secondary particles. For example, the proportion of secondary particles in the negative electrode active material is greater than or equal to 80%, and may also be greater than or equal to any of the following percentages, or be any of the following percentages, or be selected from any of the following percentages and 100%: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 98%, 99%, etc. Non-limitingly, the proportion of secondary particles in the negative electrode active material may be 90% to 100%, optionally 95% to 100%, and may also be any of the following percentages or be selected from any two of the following percentages: 90%, 92%, 94%, 95%, 96%, 98%, 99%, 100%, etc.

[0278] In this application, unless otherwise specified, "primary particles" in the negative electrode active material refer to the basic particle unit in the negative electrode active material. It is understood that primary particles exist in the negative electrode active material. In the negative electrode active material, primary particles can be aggregates formed by multiple primary particles, but are not limited to this; for example, non-agglomerated states of primary particles may also exist. Agglomerated aggregates of multiple primary particles can be called "secondary particles," and non-agglomerated primary particles can be called "non-agglomerated primary particles."

[0279] By utilizing the agglomerated characteristics of secondary particles, improvements can be made in mechanical stability, ion / electron transport rate, structural buffering capacity, and cell heat dissipation. This is beneficial for improving battery RTE and better suppressing negative electrode volume expansion in the later stages of cycling, thereby extending battery cycle life.

[0280] In this application, unless otherwise stated, the percentage of secondary particles in the negative electrode active material can be statistically analyzed based on the results obtained from scanning electron microscopy (SEM) testing. N2 The sample to be tested can be obtained by laying the powder sample and sticking it onto conductive adhesive. SEM testing can be performed according to JY / T(001)-1996. One or more regions are randomly selected from the sample to be tested for scanning. Based on the SEM image at a certain magnification, the particle size of each primary particle in the scanned region and the frequency of occurrence of different particle sizes are statistically analyzed. The magnification of a single scanned region can be, for example, 500X, 1000X, or other magnifications, but is not limited to these. The total number of particles in each scanned region should not be less than 200. Based on the single SEM morphology image of the negative electrode active material, the aggregated secondary particles and non-agglomerated primary particles are counted separately, denoted as N2 and N1 respectively. The proportion of secondary particles in the negative electrode active material in the single SEM morphology image (F) can then be obtained. N ) = N2 / (N2+N1)×100%. To improve the accuracy of the statistical results, multiple regions can be randomly selected for scanning, for example, more than or equal to 5 regions, and the resulting F values ​​can be calculated. N The average value is used as the "proportion of secondary particles in the negative electrode active material (F)". N2 The test value is "). SEM instruments include ZEISS Sigma 300, JEOL scanning electron microscope, Axia Chemi SEM, etc.

[0281] In this application, the test sample of the "negative electrode active material" in the negative electrode sheet of a lithium-ion battery can be obtained by disassembling the battery, removing the negative electrode sheet, and extracting the negative electrode active material from the negative electrode active layer of the negative electrode sheet using methods such as solvent washing, ultrasonic dispersion, centrifugation, and fractional sedimentation. The extracted material is then dried to obtain a powder sample. The obtained powder sample can be used for laser particle size analysis or other tests, such as SEM testing.

[0282] In some embodiments, the D of the negative electrode active material v 50 represents 10μm to 15μm, and can be selected from 11μm to 15μm. It can also be any of the following values ​​or a range composed of any two of the following values: 10μm, 10.5μm, 11μm, 11.5μm, 12μm, 12.5μm, 13μm, 13.5μm, 14μm, 14.5μm, 15μm, etc.

[0283] In some embodiments, the average particle size of the primary particles in the negative electrode active material is 4μm to 7μm, optionally 4μm to 6μm, or any of the following values ​​or a range selected from any two of the following values: 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, etc.

[0284] In this application, unless otherwise specified, the "average particle size of primary particles" in the negative electrode active material refers to the average particle size of all primary particles in the negative electrode active material. The "particle size of primary particles" refers to the maximum diameter of the primary particles in each direction.

[0285] The particle morphology of the negative electrode active material can be used to statistically analyze the particle size and average value of the primary particles in the negative electrode active material. The particle morphology of the negative electrode active material can be obtained using scanning electron microscopy (SEM) results (e.g., ZEISS Sigma 300, JEOL SEM, Axia Chemi SEM, etc.). The sample to be tested can be obtained by laying a powder sample of the negative electrode active material on conductive adhesive. Non-limitingly, SEM testing can refer to JY / T(001)-1996. One or more regions are randomly selected from the sample to be tested for scanning. Based on the SEM image at a certain magnification, the particle size of each primary particle in the scanned region and the frequency of occurrence of different particle sizes are statistically analyzed, and the average particle size of the statistically analyzed primary particles can then be calculated. Non-limitingly, the magnification of a single scanned region can be, for example, 1000X, but is not limited to this. To improve the accuracy of the statistical results, multiple regions can be randomly selected for scanning.

[0286] In this application, unless otherwise specified, the maximum diameter of the primary particles in each direction in the SEM morphology image of the negative electrode active material is denoted as "the particle size of the primary particles in the negative electrode active material".

[0287] D of negative electrode active material v The average particle size of the primary particles in the 50 and negative electrode active materials can be combined in a suitable manner. Exemplarily, in some embodiments, the D of the negative electrode active material... v 50 is 10μm~15μm, and the average particle size of the primary particles in the negative electrode active material is 4μm~7μm; in some embodiments, the D of the negative electrode active material is... v The particle size of the primary particles in the negative electrode active material is 11μm~15μm, and the average particle size is 4μm~6μm. At this size, the particle size of the negative electrode active material and the degree of agglomeration of the primary particles in the secondary particles can be better controlled, which is beneficial to better balance the lithium-ion diffusion rate and structural buffering capacity, and better balance the battery RTE and cycle life.

[0288] In some embodiments, the negative electrode active material includes a graphite-based material. Non-limitingly, the amount of secondary particulate graphite-based material in the negative electrode active material is 90% to 100%, optionally 95% to 100%, and may also be any of the following percentages or a range selected from any two of the following percentages: 90%, 92%, 94%, 95%, 96%, 98%, 99%, 100%, etc.

[0289] In some embodiments, the negative electrode active material includes a secondary particulate graphite-based material. Non-limitingly, the secondary particulate graphite-based material may constitute 90% to 100% of the negative electrode active material, optionally 95% to 100%, or any of the following percentages or a range selected from any two of the following percentages: 90%, 92%, 94%, 95%, 96%, 98%, 99%, 100%, etc.

[0290] Unless otherwise stated in this application, "secondary particle type graphite-based material" is a type of graphite-based material and belongs to secondary particles.

[0291] In this application, unless otherwise specified, "graphite-based material" refers to a graphite-based material containing graphite components. In this application, the negative electrode active material containing graphite components in its particle bulk is referred to as "graphite-based material". Graphite components may include one or more of artificial graphite and natural graphite. Non-limitingly, the mass percentage of graphite components in the graphite-based material may be any of the following percentages or a range selected from any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 98%, 99%, 100%, etc.

[0292] In this application, unless otherwise specified, "the negative electrode active material includes secondary particulate graphite-based material" means that the negative electrode active material mainly includes secondary particulate graphite-based material. For example, the proportion of secondary particulate graphite-based material in the negative electrode active material is greater than or equal to 80%, and may also be greater than or equal to any of the following percentages, or be any of the following percentages, or be selected from the range of any of the following percentages and 100%: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 98%, 99%, etc.

[0293] Graphite-based materials have relatively low volume expansion. Further use of secondary particulate graphite-based materials is beneficial to better suppress negative electrode expansion in the later stages of cycling and to better extend battery cycle life.

[0294] In some implementations, the negative electrode sheet satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0295] (z1) The proportion of secondary particles in the negative electrode active material is 95%~100%; at this time, it is beneficial to improve the battery RTE and better suppress the negative electrode volume expansion in the later stage of the cycle, thereby better extending the battery cycle life.

[0296] (z2) D of the negative electrode active material v The particle size of 50 is 11μm~15μm, and the average particle size of the primary particles in the negative electrode active material is 4μm~6μm; at this point, it is beneficial to better balance the lithium-ion diffusion rate and structural buffering capacity, and better balance the battery RTE and cycle life.

[0297] (z3) The negative electrode active material includes secondary particulate graphite-based material; the proportion of secondary particulate graphite-based material in the negative electrode active material is 95%~100%; at this time, it is beneficial to better suppress the negative electrode expansion in the later stage of the cycle and to better extend the battery cycle life.

[0298] In some embodiments, the negative electrode sheet includes a negative electrode active layer, which includes a negative electrode active material; the negative electrode active material includes graphite components, that is, the negative electrode active material includes graphite-based materials. Exemplarily, the degree of graphitization of the graphite components in the negative electrode active material can be 88% to 95.5%, optionally 90% to 95%, further optionally 90% to 93%, and can also be any of the following percentages or a range selected from any two of the following percentages: 88%, 88.5%, 89%, 89.5%, 90%, 90.5%, 91%, 91.5%, 92%, 92.5%, 93%, 93.5%, 94%, 94.5%, 95%, 95.5%, etc.

[0299] In some embodiments, the graphitization degree of the graphite component in the negative electrode active material is 89%~93%, and can be selected as 90%~92.5%.

[0300] In some embodiments, the graphite component in the negative electrode active material may include one or more of artificial graphite and natural graphite.

[0301] In some embodiments, the graphite component in the negative electrode active material accounts for 65% to 100% by mass, and is further optionally 90% to 100%. It can also be any of the following percentages or a range selected from any two of the following percentages: 65%, 66%, 68%, 70%, 72%, 74%, 75%, 76%, 78%, 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0302] In some implementations, the negative electrode sheet satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0303] (h1) The graphitization degree of the graphite component is 90%~95%;

[0304] (h2) The graphite component accounts for 65%~100% of the mass of the negative electrode active material.

[0305] In some implementations, the negative electrode sheet satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0306] (h1') The graphitization degree of the graphite component is 90%~93%;

[0307] (h2') The graphite component accounts for 90%~100% of the mass of the negative electrode active material.

[0308] In this application, unless otherwise stated, "degree of graphitization" has a well-known meaning in the art and can be used to measure the degree to which the crystals of a carbon material approximate perfect graphite. The degree of graphitization can be tested using instruments and methods known in the art. As a non-limiting example, it can be tested using an X-ray diffractometer. X-ray diffractometers can be models such as the Bruker D8 Discover and Bruker D8 Advance, but are not limited to these. Testing can be performed in accordance with JIS K 0131-1996 and JB / T4220-2011. First, the interlayer spacing d of the (002) crystal plane of the carbon material is measured. 002 The interlayer spacing of the (002) crystal plane can be calculated using the Bragg equation; then, G = [1 - (0.344 - d] can be calculated using the Mering-Maire formula. 002 The graphitization degree is calculated by multiplying G by (0.344 - 0.3354) by 100%, where G is the graphitization degree (%), 0.3440 is the interlayer spacing of non-graphitized carbon (nm), 0.3354 is the interlayer spacing of ideal graphite crystals (half the c-axis lattice constant of hexagonal graphite, nm), and d.002 is the interlayer spacing of the (002) crystal plane of the carbon material, expressed in nanometers (nm). It should be noted that in order to obtain a more accurate d 002 value, silicon (Si) powder can be incorporated to correct the diffraction angle to reduce errors.

[0309] By controlling the graphitization degree of the graphite component in the negative electrode active material within the aforementioned range, additional lithium ion storage sites can be provided by micropores, cracks or defects, thereby improving the specific capacity; a larger interlayer spacing can also be provided, which is beneficial to accelerating lithium ion transmission, reducing the volume change during lithium ion insertion / extraction, reducing cracks and pulverization of the electrode material, and being beneficial to improving the structural stability of the negative electrode active material; thus, it is more beneficial to improve the battery RTE, and can also improve the battery cycle stability, and is more beneficial to extending the battery cycle life.

[0310] The graphitization degree of the graphite component can be controlled or adjusted by known methods in the art: for example, during carbonization treatment, the graphitization degree of the graphite component can be increased by increasing the pyrolysis temperature, extending the heat preservation time, reducing the heating rate, etc.

[0311] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable numerical value or range in the context):

[0312] (b1) The lithium phosphate-based positive electrode material doped with M element includes an olivine crystal structure, and further can be an olivine crystal structure;

[0313] Optionally, the lithium phosphate-based positive electrode material doped with M element includes Fe element; further optionally, the atomic molar ratio of Fe element in the transition metal elements of the lithium phosphate-based positive electrode material doped with M element is denoted as q1, then q1≥0.8, optionally, 0.8≤q1≤1; non-limitingly, q1 can also be greater than or equal to any one of the following numerical values, or greater than any one of the following numerical values, or greater than any one of the following numerical values and less than or equal to 1, or be any one of the following numerical values, or be selected from the ranges formed by any two of the following numerical values: 0.8, 0.82, 0.84, 0.85, 0.86, 0.88, 0.9, 0.92, 0.94, 0.95, 0.96, 0.98, 0.99, 1, etc.;

[0314] (b2) The lithium phosphate-based positive electrode material doped with M element includes a composition with the chemical formula Li a Fe b M c PO d , where 0.8≤a≤1.15, 0.9≤b<1, 0<c≤0.1 and b + c≤1, 3.8≤d≤4; Li aFe b M c PO d Satisfy the balance of positive and negative charges;

[0315] Optionally, M includes one or more elements selected from Ti, V, and Mn;

[0316] Optionally, 0.8 ≤ a ≤ 1.

[0317] In some implementations, 0.8 ≤ a < 1.15.

[0318] Without limitation, a can also be greater than or equal to any of the following values, or greater than any of the following values, or greater than any of the following values ​​and less than or equal to 1, or be any of the following values, or be selected from a range consisting of any two of the following values: 0.8, 0.82, 0.84, 0.85, 0.86, 0.88, 0.9, 0.92, 0.94, 0.95, 0.96, 0.98, 0.99, 1, etc.

[0319] In some embodiments, the positive electrode active material satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0320] (b1') The atomic molar ratio of Fe element in the transition metal elements contained in the lithium phosphate cathode material doped with M element is denoted as q1, where 0.8≤q1≤1;

[0321] (b2') M includes one or more elements from Ti, V and Mn; 0.8 ≤ a ≤ 1.

[0322] In some implementations, the positive electrode sheet satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0323] (c1) The mass percentage of the lithium phosphate-containing cathode material doped with element M in the cathode active material can be 95% to 100%, or it can be any of the following percentages or a range selected from any two of the following percentages: 90%, 91%, 92%, 93%, 94%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99%, 99.5%, 100%, etc.

[0324] (c2) The mass percentage of the lithium phosphate cathode material doped with element M in the cathode active layer can be 90% to 99%, or it can be any of the following percentages or a range selected from any two of the following percentages: 90%, 92%, 94%, 95%, 96%, 98%, 99%, 100%, etc.

[0325] (c3) The positive electrode active material includes lithium iron phosphate doped with element M; not limited thereto, the mass percentage of lithium iron phosphate doped with element M in the positive electrode active material can be 95% to 100%, or it can be any of the following percentages or a range selected from any two of the following percentages: 90%, 91%, 92%, 93%, 94%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99%, 99.5%, 100%, etc.

[0326] When lithium phosphate cathode materials doped with element M include an olivine crystal structure and further include element Fe, it is beneficial to achieve better stability of the olivine crystal structure, better improve the structural stability of the cathode active material, and better reduce the dissolution of element M.

[0327] By controlling the types of positive electrode active materials mentioned above, it is beneficial to improve the battery RTE when the positive electrode sheet includes lithium phosphate-containing positive electrode materials and to better balance the battery cycle life.

[0328] Those skilled in the art can identify the components in the positive and negative electrode active layers using one or more of the following detection methods known in the art, including but not limited to: Fourier transform infrared (FT-IR) spectroscopy, ultraviolet spectroscopy, 1H nuclear magnetic resonance (1H NMR) spectroscopy, gel permeation chromatography (GPC), high performance liquid chromatography (HPLC), mass spectrometry, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, single crystal X-ray diffraction (SCXRD), inductively coupled plasma optical emission spectrometry (ICP), energy dispersive spectroscopy (EDS), etc. The sample preparation and testing methods for these methods are known to those skilled in the art, and the test parameters can be appropriately adjusted according to the structure of the material or substance and the characteristics of the sample.

[0329] As a non-limiting example, EDS can be used to distinguish between carbon and silicon, and thus between carbon-based and silicon-based materials. Similarly, EDS can be used to detect the type and content of conductive agents, but is not limited to this.

[0330] Using natural graphite and artificial graphite as non-limiting examples, the negative electrode active materials can be distinguished by the appearance and morphology of the particles. Further X-ray diffraction (XRD) analysis can be performed. In the XRD pattern, if the 2θ characteristic peak near 26.5° is very sharp and has a high intensity, it is natural graphite; if the 2θ characteristic peak near 26.5° is relatively broad and has a weak intensity, it is artificial graphite.

[0331] Taking graphite and soft carbon as examples of negative electrode active materials, Raman spectroscopy can be used to distinguish between them. More specifically, the characteristic peak information of carbon components in the spectrum (such as the intensity ratio of the D peak to the G peak, I) can be used. D / G The analysis focused on soft carbon. Both the D and G peaks are Raman characteristic peaks of carbon atom crystals. The D peak represents defects in the carbon atom crystal; the more defects, the greater the intensity of the D peak. The intensity of the D peak reflects the content of amorphous (randomly stacked) regions. The G peak represents the sp(s) content of carbon atoms. 2 The in-plane stretching vibrations of hybridization, with the G peak intensity reflecting the content of graphitized (layered structure) regions; as the degree of carbon atom disorder increases, the intensity ratio of the D peak to the G peak also increases. This can also be compared with Raman spectra I. D / G Standard Raman spectrum of graphite I D / G The difference between the two peaks can be used to determine whether the material being tested contains soft carbon. Similarly, the difference between the D and G peaks in the Raman spectrum can be used to distinguish between graphite and hard carbon. Likewise, the difference between the D and G peaks in the Raman spectrum can be used to distinguish between natural graphite and synthetic graphite.

[0332] It is understandable that lithium-ion batteries include battery cells.

[0333] In some embodiments, a lithium-ion battery includes a cell, which includes a positive electrode and a negative electrode.

[0334] In some embodiments, a lithium-ion battery includes a cell, which includes a positive electrode, a separator, and a negative electrode stacked together, with the separator disposed between the positive electrode and the negative electrode.

[0335] In some implementations, the battery cell also includes an electrolyte.

[0336] In some embodiments, the length of the battery cell is greater than or equal to 270 mm, and may also be greater than or equal to any of the following values, or be any of the following values, or be selected from a range consisting of any two of the following values: 270 mm, 280 mm, 290 mm, 300 mm, 320 mm, 340 mm, 350 mm, 360 mm, 380 mm, 400 mm, 450 mm, 500 mm, 520 mm, 540 mm, 550 mm, 560 mm, 580 mm, 600 mm, etc.

[0337] In some embodiments, the lithium-ion battery includes a cell, which includes a positive electrode, a separator, and a negative electrode stacked together, with the separator disposed between the positive and negative electrode. In some embodiments, the length of the cell is greater than or equal to 270 mm, and may also be greater than or equal to any of the following values, or be any of the following values, or be selected from a range consisting of any two of the following values: 270 mm, 280 mm, 290 mm, 300 mm, 320 mm, 340 mm, 350 mm, 360 mm, 380 mm, 400 mm, 450 mm, 500 mm, 520 mm, 540 mm, 550 mm, 560 mm, 580 mm, 600 mm, etc.

[0338] In some implementations, the length of the battery cell is 280mm to 600mm.

[0339] In some implementations, the length of the battery cell is greater than or equal to 500 mm, and may be further selected as 500 mm to 600 mm.

[0340] In some embodiments, the height of the battery cell is greater than or equal to 100 mm, and can be selected from 100 mm to 250 mm. It can also be greater than or equal to any of the following values, or be any of the following values, or be selected from a range consisting of any two of the following values: 100 mm, 110 mm, 120 mm, 140 mm, 150 mm, 160 mm, 180 mm, 200 mm, 220 mm, 240 mm, 250 mm, etc.

[0341] In some embodiments, the thickness of the battery cell is greater than or equal to 50 mm, optionally greater than or equal to 60 mm, and further optionally greater than or equal to 70 mm. In some embodiments, the thickness of the battery cell is 50 mm to 100 mm, and may also be any of the following values, or a range selected from any two of the following values: 50 mm, 55 mm, 60 mm, 65 mm, 70 mm, 75 mm, 80 mm, 85 mm, 90 mm, 100 mm, etc.

[0342] The aforementioned design of lithium-ion batteries can also improve battery RTE and achieve longer cycle life in large-size cells, and the improvement effect is significant.

[0343] It is understandable that a battery cell includes a battery cell.

[0344] In this application, the cells in a lithium-ion battery or a single battery cell can be wound cells or stacked cells. In this application, unless otherwise specified, the electrode sheets used to assemble wound cells are referred to as "winding electrode sheets", and the electrode sheets used to assemble stacked cells are referred to as "stacking electrode sheets".

[0345] In this application, unless otherwise specified, the winding electrode sheet can be defined with a first direction, a second direction and a third direction that are perpendicular to each other; the extension direction of the electrode sheet can be referred to as the first direction, the thickness direction of the electrode sheet can be referred to as the second direction, and the third direction corresponds to the lead-out direction of the electrode tab.

[0346] In this application, unless otherwise specified, "tab" has the common meaning in the art, referring to a metallic conductor that connects the battery cell to an external circuit, used for electrically connecting the electrode terminals and the electrode active layer. The tab is connected to the current collector, thereby achieving electrical connection with the electrode active layer. The tab leading to the positive electrode in the electrode assembly can be called a "positive tab," which is the tab leading from the positive electrode plate. Further, the positive tab is led out from the positive current collector. The tab leading to the negative electrode can be called a "negative tab," which is the tab leading from the negative electrode plate. Further, the negative tab is led out from the negative current collector. The "tab portion" of the battery cell refers to the combination of similar tabs in the electrode plates. The tab portion of the battery cell can be divided into a positive tab portion and a negative tab portion. The positive electrode tab is a combination of positive electrodes, which can be obtained by soldering multiple positive electrodes led out from the positive electrode plate, allowing multiple positive electrodes to be electrically connected. Similarly, the negative electrode tab is a combination of negative electrodes, which can be obtained by soldering multiple negative electrodes led out from the negative electrode plate, allowing multiple negative electrodes to be electrically connected. The area where multiple electrodes are connected by soldering can be denoted as the "soldering area of ​​the electrode tab," where the soldering area of ​​the positive electrode tab corresponds to the area where multiple positive electrodes are connected at the positive electrode, and the soldering area of ​​the negative electrode tab corresponds to the area where multiple negative electrodes are connected at the negative electrode.

[0347] Those skilled in the art can choose a suitable soldering method to obtain the positive or negative electrode tab. For example, the soldering method can be ultrasonic soldering or laser soldering.

[0348] As used in this article, a "cell" can have multiple directions, including height, length, and thickness. The height, length, and thickness directions of a cell can be denoted as the Y direction, X direction, and Z direction, respectively.

[0349] Taking a wound cell as an example, after stacking the positive electrode, separator, and negative electrode in sequence and winding them around the winding axis to obtain a wound body, the wound body can be further pressed to form a multi-layered cell. This cell can be used to manufacture prismatic batteries. At this time, the tabs of the cell are led out along the winding axis; the thickness direction of the cell corresponds to the pressure direction of the pressing, which is also the stacking direction of the electrode in the cell; the height direction of the cell corresponds to the winding axis, the direction of the tabs, and also the third direction of the winding electrode; the length direction of the cell is perpendicular to both the thickness direction and the length direction of the cell.

[0350] Unless otherwise specified, "square battery" refers to a battery with a square-shaped casing.

[0351] In some implementations, the length direction of the battery cell may correspond to the direction of the line connecting the positive and negative terminals.

[0352] Taking a laminated battery cell as an example, the thickness direction of the battery cell corresponds to the stacking direction of the electrode sheets and is parallel to the thickness direction of the electrode sheets (that is, the fifth direction of the laminated electrode sheets); the height direction of the battery cell corresponds to the direction of the lead-out tabs in the battery cell, that is, it is parallel to the sixth direction of the laminated electrode sheets; the length direction of the battery cell is perpendicular to both the thickness direction and the height direction of the battery cell.

[0353] In this application, unless otherwise specified, "width of the tab" refers to the length of the tab along the length of the battery cell (i.e., along the X direction), the width of the positive tab refers to the length of the positive tab along the length of the battery cell, and the width of the negative tab refers to the length of the negative tab along the length of the battery cell. "Width of the solder area of ​​the tab" refers to the length of the solder area of ​​the tab along the length of the battery cell (i.e., along the X direction), the width of the solder area of ​​the positive tab refers to the length of the solder area of ​​the positive tab along the length of the battery cell, and the width of the solder area of ​​the negative tab refers to the length of the solder area of ​​the negative tab along the length of the battery cell.

[0354] For example, the tabs are at the same height throughout the entire length of the electrode sheet. After the electrode sheet of this structure is wound to form an electrode assembly, the tabs need to be shaped by mechanical flattening or direct extrusion flattening to form a relatively dense end face, so as to facilitate welding with other structures in subsequent processing.

[0355] The aforementioned tab structure design is beneficial for improving the cell's overcurrent capability and increasing the cell's real-time efficiency (RTE). Among them, the full tab structure is particularly beneficial for improving the cell's overcurrent capability.

[0356] In this application, unless otherwise specified, a "terminal post" is a structure in a battery cell used for connecting to other battery cells or for connecting to an external conductor, providing current to an external load. Exemplarily, a terminal post can be electrically connected to an electrode assembly, for example, via a tab. Depending on the difference between positive and negative electrodes, terminals can be classified as positive terminals and negative terminals. The surface in the cell where the terminal post is located is typically referred to as the "top surface." For example, the positive terminal post of one battery cell can be connected to the negative terminal post of another battery cell via a terminal post.

[0357] In some embodiments, a lithium-ion battery includes a cell, which includes a positive electrode, a separator, and a negative electrode stacked together, with a separator disposed between the positive electrode and the negative electrode.

[0358] The battery cell includes multiple positive tabs led out from multiple positions on the positive electrode plate and multiple negative tabs led out from multiple positions on the negative electrode plate; the multiple positive tabs are combined to form a positive tab section, and the combined area of ​​the multiple positive tabs is called the solder area of ​​the positive tab section; the multiple negative tabs are combined to form a negative tab section, and the combined area of ​​the multiple negative tabs is called the solder area of ​​the negative tab section.

[0359] The stacking direction of each electrode in the cell is denoted as the Z direction, the direction of the lead-out tab in the cell is denoted as the Y direction, and the direction perpendicular to both the Z and Y directions is denoted as the X direction. The X direction is parallel to the width direction of both the positive and negative tabs.

[0360] The battery cell satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0361] (d1) The solder area of ​​the positive electrode tab is 30mm². 2 ~340mm 2 90mm is optional 2 ~180mm 2 ;

[0362] The solder area of ​​the negative electrode ear is 20mm². 2 ~280mm 2 70mm is optional 2 ~150mm 2 ;

[0363] (d2) The width of the solder area of ​​the positive electrode tab in the X direction is 10% to 30% of the length of the cell in the X direction, and can be selected as 10% to 20%; the width of the solder area of ​​the negative electrode tab in the X direction is 10% to 30% of the length of the cell in the X direction, and can be selected as 10% to 20%.

[0364] In some embodiments, the solder area of ​​the positive electrode tab is 30 mm². 2 ~340mm 2 90mm is optional 2 ~180mm 2 It can also be any of the following values ​​or a range consisting of any two of the following values: 30mm 2 40 mm 2 50mm 2 60 mm 2 70 mm 2 80 mm 2 90 mm 2 100 mm 2 120 mm 2 150 mm2 160 mm 2 180 mm 2 200 mm 2 250 mm 2 260 mm 2 280 mm 2 300 mm 2 320 mm 2 340 mm 2 wait.

[0365] In some embodiments, the solder area of ​​the negative electrode lug is 20 mm². 2 ~280mm 2 70mm is optional 2 ~150mm 2 It can also be any of the following values ​​or a range consisting of any two of the following values: 20 mm 2 25 mm 2 430mm 2 40 mm 2 50 mm 2 60 mm 2 70 mm 2 80 mm 2 90 mm 2 100 mm 2 120 mm 2 150 mm 2 160 mm 2 180 mm 2 200 mm 2 250 mm 2 260 mm 2 280 mm 2 wait.

[0366] In some embodiments, the ratio of the solder area of ​​the positive electrode tab to the solder area of ​​the negative electrode tab (denoted as F) A The value should be controlled within a certain range, for example, within the range of 1.2 to 1.8. For instance, F... A The values ​​can be 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, etc., or can be selected from any two of the aforementioned values.

[0367] In some embodiments, the width of the solder area of ​​the positive electrode tab in the X direction is 10% to 30% of the length of the cell in the X direction, optionally 10% to 20%, or any of the following percentages or a range selected from any two of the following percentages: 10%, 12%, 14%, 15%, 16%, 18%, 20%, 22%, 24%, 25%, 26%, 28%, 30%, etc.

[0368] In some embodiments, the width of the solder area of ​​the negative electrode tab in the X direction is 10% to 30% of the length of the cell in the X direction, optionally 10% to 20%, or any of the following percentages or a range selected from any two of the following percentages: 10%, 12%, 14%, 15%, 16%, 18%, 20%, 22%, 24%, 25%, 26%, 28%, 30%, etc.

[0369] In some embodiments, the width of the solder area of ​​the positive electrode tab and the width of the solder area of ​​the negative electrode tab are each independently 20 mm to 68 mm, and can also be any of the following values, or a range composed of any two of the following values: 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, 55 mm, 60 mm, 65 mm, 68 mm, etc.

[0370] By controlling one or more parameters, such as the area of ​​the soldering region on the positive and negative electrode tabs and the ratio of the width of the soldering region on the positive and negative electrode tabs to the length of the cell, it is beneficial to better optimize the cell's overcurrent capacity and improve the battery's RTE.

[0371] In some embodiments, the battery cell includes a positive electrode post located on the same side of the battery cell as the positive electrode tab and electrically connected to the positive electrode tab, and the battery cell also includes a negative electrode post located on the same side of the battery cell as the negative electrode tab and electrically connected to the negative electrode tab; the axial directions of both the positive electrode post and the negative electrode post are parallel to the Y direction;

[0372] Along the positive electrode tab extension path, the distance between the center of the solder area of ​​the positive electrode tab in the Y direction and the center of the nearest end face of the positive electrode post (which can be denoted as "solder-post center distance" at the positive electrode, or Jc1) is 40mm~250mm, can be selected as 50mm~200mm, or can be any of the following values ​​or a range composed of any two of the following values: 40mm, 50mm, 60mm, 70mm, 80mm, 90mm, 100mm, 110mm, 120mm, 130mm, 140mm, 150mm, 160mm, 180mm, 200mm, 220mm, 240mm, 250mm, etc.

[0373] Along the negative electrode tab extension path, the distance between the center of the solder area of ​​the negative electrode tab in the Y direction and the center of the nearest end face of the negative electrode post (which can be denoted as "solder-post center distance" at the negative electrode, or Jc2) is 40mm~250mm, and can be selected as 50mm~200mm. It can also be any of the following values ​​or a range composed of any two of the following values: 40mm, 50mm, 60mm, 70mm, 80mm, 90mm, 100mm, 110mm, 120mm, 130mm, 140mm, 150mm, 160mm, 180mm, 200mm, 220mm, 240mm, 250mm, etc.

[0374] By controlling one or both of the solder mark-terminal center distance parameters Jc1 and Jc2 within the aforementioned range, it is beneficial to better optimize the cell's overcurrent capability and improve the battery's RTE.

[0375] In some embodiments, the lithium-ion battery includes a square wound cell; the stacking direction of each electrode in the cell is denoted as the thickness direction of the cell (in this case, the stacking direction of each electrode in the square wound cell is consistent with the "thickness direction of the cell").

[0376] Along the thickness direction of the battery cell, the ratio of the number of positive electrode layers leading out to the total number of positive electrode layers is denoted as Rp, and Rp≥50%.

[0377] In some implementations, Rp may be greater than or equal to any of the following percentages, or be any of the following percentages, or be selected from the range of any of the following percentages and 100%: 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, etc.

[0378] In some implementations, Rp is 90% to 100%. Electrode structures with Rp close to 100% (e.g., Rp is selected from 98% to 100%) can be included in the meaning of a full electrode structure.

[0379] A tab structure design with Rp within the aforementioned range is more conducive to improving the cell's overcurrent capability and thus better improving the cell's RTE. Among them, a full tab structure (such as a full tab structure with Rp of 100%) is more conducive to improving the cell's overcurrent capability.

[0380] In some embodiments, a lithium-ion battery includes a battery casing and a cell and electrolyte disposed within the battery casing. It is understood that the cell includes the aforementioned positive and negative electrode plates. In some embodiments, the cell includes a positive electrode plate, a negative electrode plate, and a separator, with the separator disposed between the positive and negative electrode plates.

[0381] In some embodiments, a lithium-ion battery includes a battery casing and a cell and electrolyte disposed within the battery casing, and the lithium-ion battery satisfies one or more of the following characteristics:

[0382] (d1) The battery casing is a rigid casing, which may be made of aluminum alloy, but is not limited thereto;

[0383] (d2) The battery casing has a square structure;

[0384] (d3) Lithium-ion batteries are secondary batteries.

[0385] In some embodiments, the rigid housing comprises an aluminum alloy material. Optionally, the rigid housing is made of aluminum alloy.

[0386] A lithium-ion battery includes at least one battery cell. A lithium-ion battery may include one or more battery cells.

[0387] In this application, unless otherwise specified, "cell battery" refers to the basic unit capable of converting chemical energy into electrical energy. Exemplarily, a cell battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator is disposed between the positive and negative electrodes, primarily preventing short circuits between the positive and negative electrodes while allowing ions to pass through.

[0388] In some implementations, the lithium-ion battery is an energy storage lithium-ion battery.

[0389] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 The example shown is a square-structured battery cell 5.

[0390] In some of these implementations, reference is made to... Figure 2The outer packaging may include a battery casing 51 and a cover plate 53. The battery casing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The battery casing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. The electrode assembly 52 is immersed in an electrolyte. The number of electrode assemblies 52 contained in a single battery cell 5 may be one or more, which can be selected by those skilled in the art according to actual needs.

[0391] The lithium-ion battery can be a battery device 4 or a battery pack 1.

[0392] The battery device includes at least one battery cell. The number of battery cells in the battery device can be one or more, and those skilled in the art can select an appropriate number according to the application and capacity of the battery device.

[0393] Figure 3 This is battery device 4, used as an example. (See reference...) Figure 3 In the battery assembly 4, multiple battery cells 5 can be arranged sequentially along the length of the battery assembly 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0394] Optionally, the battery device 4 may also include a housing with a receiving space in which multiple battery cells 5 are housed.

[0395] In some embodiments, the battery devices described above can also be assembled into a battery pack, and the number of battery devices contained in the battery pack can be one or more. Those skilled in the art can select an appropriate number according to the application and capacity of the battery pack.

[0396] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery devices 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery devices 4. The multiple battery devices 4 can be arranged in any manner within the battery box.

[0397] The following is a description of the positive electrode sheet.

[0398] The positive electrode includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector, the positive active layer including a positive active material.

[0399] Without limitation, the weight percentage of the positive electrode active material in the positive electrode active layer may be greater than or equal to 80 wt%, and may further be greater than or equal to 90 wt%.

[0400] As a non-limiting example, the positive current collector has two surfaces that are opposite to each other in its own thickness direction, and the positive active layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0401] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. In the positive electrode current collector, the composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. In the positive electrode current collector, the composite current collector may be obtained by forming a metal material on the polymer material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. Non-limitingly, in the positive electrode current collector, the polymer material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0402] The positive electrode active material may be any positive electrode active material known in the art for use in batteries. These positive electrode active materials may be used alone or in combination of two or more.

[0403] The types of positive electrode active materials in the positive electrode sheet can be found in the description in the context of this application. Without limitation, other types of positive electrode active materials may also be introduced into the positive electrode active material.

[0404] In some embodiments, the positive electrode active material includes a lithium phosphate-based positive electrode material with an olivine structure. Non-limiting examples of lithium phosphate-based positive electrode materials with an olivine structure include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites. Examples of lithium iron phosphate include LiFePO4. Examples of lithium manganese phosphate include LiMnPO4.

[0405] Non-limiting examples of lithium phosphate cathode materials include lithium iron phosphate cathode materials.

[0406] In this application, unless otherwise specified, "lithium iron phosphate cathode material" refers to a class of cathode active materials containing lithium iron phosphate components. Unless otherwise specified, "lithium iron phosphate cathode material" may have an olivine structure.

[0407] In some embodiments, the positive electrode active material includes lithium iron phosphate-based positive electrode materials. Further, the lithium iron phosphate-based positive electrode material may include at least one of lithium iron phosphate and a composite material of lithium iron phosphate and carbon.

[0408] In some embodiments, the composite material of lithium iron phosphate and carbon is carbon-coated lithium iron phosphate.

[0409] In some implementations, lithium iron phosphate cathode materials include carbon-coated lithium iron phosphate.

[0410] In this application, the term "carbon-coated lithium iron phosphate" includes a lithium iron phosphate body and a carbon coating layer located on at least a portion of the surface of the lithium iron phosphate body, wherein the lithium iron phosphate body comprises lithium iron phosphate. Non-limitingly, the carbon coating layer in the carbon-coated lithium iron phosphate may include one or more of soft carbon, hard carbon, and amorphous carbon. Non-limitingly, the mass percentage of the carbon coating layer in the lithium iron phosphate cathode material may be 1% to 1.5%.

[0411] In some embodiments, lithium iron phosphate cathode materials include lithium iron phosphate-based cathode materials. Lithium iron phosphate-based cathode materials refer to a class of cathode active materials containing lithium iron phosphate.

[0412] In some implementations, the lithium iron phosphate body includes lithium iron phosphate.

[0413] In some embodiments, the lithium iron phosphate-based cathode material includes carbon-coated lithium iron phosphate. In this case, the carbon-coated lithium iron phosphate comprises carbon-coated lithium iron phosphate.

[0414] In this application, the term "carbon-coated lithium iron phosphate" includes lithium iron phosphate and a carbon coating layer located on at least a portion of the surface of the lithium iron phosphate. Further, the carbon coating layer may include one or more of soft carbon, hard carbon, and amorphous carbon.

[0415] In some embodiments, the carbon coating layer in carbon-coated lithium iron phosphate includes soft carbon. In some embodiments, the carbon coating layer is a soft carbon coating layer, and in this case, the carbon-coated lithium iron phosphate can be referred to as soft carbon-coated lithium iron phosphate. "Soft carbon coating layer" refers to a coating layer mainly composed of soft carbon, and the mass percentage of soft carbon in the coating layer can be close to 100%. The mass percentage of soft carbon in the soft carbon coating layer in the carbon-coated lithium iron phosphate can be 1% to 1.5%, optionally 1.4% to 1.5%, but is not limited to this.

[0416] Understandably, lithium (Li) is intercalated and deintercalated during the charging and discharging process of a battery, and the Li content in the positive electrode varies depending on the state of discharge. In the exemplary description of the positive electrode active material in this application, unless otherwise specified, the Li content can be the initial state of the material or a non-initial state after charge-discharge cycles. When the positive electrode active material is applied to the positive electrode in a battery system, the Li content in the positive electrode active material at the positive electrode will usually change after charge-discharge cycles. The Li content can be measured in atomic molar content, but is not limited to this. Regarding "Li content is the initial state of the material," the initial state of the material refers to the state before it is formed into the positive electrode active layer. It is understood that new materials or substances obtained by appropriately modifying the listed positive electrode active materials are also within the scope of positive electrode active materials. The aforementioned appropriate modification refers to an acceptable modification method for the positive electrode active material, and non-limiting examples include one or more of coating modification and doping modification.

[0417] In the exemplary description of the positive electrode active material in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause changes in the atomic molar content of oxygen, and the actual O content will fluctuate. The O content can be measured in atomic molar content, but is not limited to this.

[0418] In some embodiments, the positive electrode active layer optionally includes a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. Typically, the binder may constitute 0-10 wt% of the weight of the positive electrode active layer, more commonly 0-8 wt%, and even more commonly 1 wt%-5 wt%, based on the total weight of the positive electrode active layer.

[0419] In some embodiments, the positive electrode active layer optionally includes a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Typically, the weight percentage of the conductive agent in the positive electrode active layer can be 0-10 wt%, more commonly 0-8 wt%, and even more commonly 0-5 wt%, based on the total weight of the positive electrode active layer.

[0420] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry. Further, the positive electrode slurry is coated onto at least one surface of the positive current collector, and after drying, cold pressing, and other processes, the positive electrode sheet is obtained. Cold pressing can be performed using a cold rolling mill. The solvent in the positive electrode slurry can be, but is not limited to, any of the solvents described in the foregoing embodiments, for example, it can include N-methylpyrrolidone (NMP), and more specifically, NMP. The surface of the positive current collector coated with the positive electrode slurry can be a single surface of the positive current collector or both surfaces of the positive current collector. The solid content of the positive electrode slurry can be 40wt% to 80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 mPa·s to 25000 mPa·s. When coating the positive electrode slurry, the coating areal density (based on dry weight, minus solvent) can also be (0.1~0.5) g / 1540.25 mm. 2 The optional value is (0.2~0.4) g / 1540.25 mm. 2 However, this is not the only possibility. The compaction density of the positive electrode sheet can be 2.0 g / cm³. 3 ~2.8g / cm 3 2.3g / cm³ is an option. 3 ~2.7g / cm 3 .

[0421] The term "compacted density" as used in this application has a meaning known in the art and is one of the reference indicators for the energy density of materials. In this application, unless otherwise specified, the compacted density of the positive electrode refers to the ratio of the mass of the positive electrode active layer to its volume, and the compacted density of the negative electrode refers to the ratio of the mass of the negative electrode active layer to its volume.

[0422] The following are some other descriptions of the negative electrode plate.

[0423] The negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector, the negative active layer including a negative active material.

[0424] Without limitation, the weight percentage of the negative electrode active material in the negative electrode active layer may be greater than or equal to 80 wt%, and may further be greater than or equal to 90 wt%.

[0425] As a non-limiting example, the negative electrode current collector has two surfaces that are opposite to each other in its own thickness direction, and the negative electrode active layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0426] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. In the negative electrode current collector, the composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. In the negative electrode current collector, the composite current collector may be formed by forming a metal material on the polymer material substrate. Non-limiting examples of the metal material in the negative electrode current collector may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limitingly, in the negative electrode current collector, the polymer material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0427] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As a non-limiting example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon-oxygen materials, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials or substances, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0428] In some embodiments, the negative electrode active material includes a carbon-based material. The carbon-based material may include, but is not limited to, one or more of graphite-based materials, soft carbon, hard carbon, etc. The graphite-based material may include graphite. The graphite material may include one or more of artificial graphite and natural graphite. Non-limitingly, the mass percentage of the carbon-based material in the negative electrode active material may be ≥80%, optionally ≥90%, further optionally ≥95%, even more optionally ≥96%, and even more optionally 100%. Non-limitingly, the mass percentage of the carbon-based material in the negative electrode active material may also be any of the following percentages, or greater than or equal to any of the following percentages and less than or equal to 100%, or selected from any two of the following percentage ranges: 80%, 82%, 83%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 98%, etc. For example, the carbon-based material may be a graphite-based material, and more specifically, graphite.

[0429] In some embodiments, the negative electrode active layer optionally includes a binder. Non-limitingly, the binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). Non-limitingly, the weight percentage of the binder in the negative electrode active layer may be 0 wt% to 20 wt%, more further 0 wt% to 10 wt%, even further 0 to 5 wt%, even further 1 wt% to 5 wt%, and even more preferably 1 wt% to 3 wt%.

[0430] For further information on the types of negative electrode active materials, please refer to the context of this application.

[0431] In some embodiments, the negative electrode active layer optionally includes a conductive agent. Non-limitingly, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Non-limitingly, the weight percentage of the conductive agent in the negative electrode active layer may be 0 wt% to 15 wt%, more preferably 0 wt% to 10 wt%, and even more preferably 0 wt% to 5 wt%.

[0432] In some embodiments, the negative electrode active layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)). Without limitation, the weight percentage of other additives in the negative electrode active layer may be 0 wt% to 15 wt%, more preferably 0 wt% to 10 wt%, even more preferably 0 wt% to 5 wt%, even more preferably 0 wt% to 3 wt%, and even more preferably 0 wt% to 2 wt%.

[0433] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and optional other components, in a solvent (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry. Further, the negative electrode slurry is coated onto at least one surface of the negative electrode current collector, and after drying, cold pressing, and other processes, the negative electrode sheet is obtained. Cold pressing can be performed using a cold rolling mill. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 30wt% to 70wt%, optionally 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 mPa·s to 10000 mPa·s, optionally 3000 mPa·s to 10000 mPa·s. When coating the negative electrode slurry, the surface density of the coating on one side of the negative electrode current collector, based on dry weight (excluding solvent), can be (0.12~0.2) g / 1540.25 mm. 2 The compaction density of the negative electrode sheet can be 1.0 g / cm³. 3 ~2.0g / cm 3 1.0g / cm can be selected. 3 ~1.8g / cm 3 .

[0434] The electrolyte is described below as an example.

[0435] Electrolytes function to conduct ions between the positive and negative electrodes. The electrolyte used in this application includes, and more specifically, an electrolyte solution. An electrolyte solution includes an electrolyte salt and a solvent.

[0436] In some embodiments, the electrolyte is a non-aqueous electrolyte. A non-aqueous electrolyte may include an electrolyte salt and a non-aqueous solvent.

[0437] The concentration of electrolyte salts in the electrolyte solution is typically 0.5 mol / L to 5 mol / L.

[0438] In some embodiments, the electrolyte salt includes an electrolyte lithium salt. Non-limitingly, the electrolyte lithium salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0439] Non-limitingly, the non-aqueous solvent in the electrolyte may include one or more of carbonate solvents, carboxylic acid ester solvents, and sulfone solvents. Carbonate solvents may include one or more of cyclic carbonates and chain carbonates. Cyclic carbonates may include, but are not limited to, ethylene carbonate (EC). Also known as ethylene carbonate, propylene carbonate (PC), Also known as propylene carbonate (BC), butene carbonate (BC). The cyclic carbonate may include, but is not limited to, one or more of ethylene carbonate, propylene carbonate, and butene carbonate. Non-limitingly, the cyclic carbonate may have 3 to 6 carbon atoms, optionally 3 to 5, or 3, 4, 5, or 6, or selected from any range of the foregoing values. The chain carbonate may include, but is not limited to, one or more of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC). Non-limitingly, the chain carbonate may have 3 to 9 carbon atoms, optionally 3 to 7, further optionally 4 to 7, or 3, 4, 5, 6, 7, 8, or 9, or selected from any range of the foregoing values. Carboxylic acid ester solvents may include one or more of chain carboxylic acid esters and cyclic carboxylic acid esters. Chain carboxylic acid esters may include, but are not limited to, one or more of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate. Non-limitingly, the number of carbon atoms in the chain carboxylic acid ester may be 2 to 8, optionally 3 to 8, or may be 2, 3, 4, 5, 6, 7, or 8, or selected from any range of two of the aforementioned numbers. Cyclic carboxylic acid esters may include, but are not limited to, 1,4-butyrolactone. Sulfone solvents may include, but are not limited to, one or more of sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0440] In some embodiments, the carboxylic acid ester solvent accounts for less than 25% by mass in the non-aqueous solvent, optionally less than or equal to 20%, and may also be less than or equal to any of the following percentages, or may be selected from a range consisting of 0 and any of the following percentages, or may be any of the following percentages or a range consisting of any two of the following percentages: 0.1%, 0.2%, 0.4%, 0.5%, 1%, 1.5%, 2%, 3%, 4%, 5%, 6%, 8%, 10%, 12%, 15%, 20%, etc. In some embodiments, the carboxylic acid ester solvent accounts for 0% by mass in the non-aqueous solvent.

[0441] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve the battery's high-temperature or low-temperature performance.

[0442] The following is an exemplary description of the separator membrane.

[0443] In some embodiments, the lithium-ion battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0444] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0445] In some embodiments, the thickness of the separator is 6 μm to 40 μm, optionally 7 μm to 20 μm.

[0446] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0447] In some embodiments of the second aspect of this application, a method for preparing a lithium-ion battery is provided, which can be used to prepare the lithium-ion battery described in the first aspect of this application.

[0448] In some embodiments of the second aspect of this application, a method for preparing a lithium-ion battery is provided, comprising the following steps:

[0449] The electrode assembly is placed in the battery casing; wherein the electrode assembly includes a positive electrode sheet, a separator, and a negative electrode sheet, and a separator is disposed between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet includes a positive active layer, and the positive active layer includes a positive active material; the positive active material includes a lithium phosphate positive electrode material doped with element M, and element M includes any one or two of elements Ti and V.

[0450] An electrolyte is injected into a battery casing, and the casing is left to stand to allow the electrolyte to wet the positive and negative electrode sheets, thereby forming a lithium-ion battery. The electrolyte includes additives, which include one or both of vinylene carbonate and lithium bis(fluorosulfonyl)imide. In some embodiments, the electrolyte includes an electrolyte salt, a non-aqueous solvent, and additives. The non-aqueous solvent includes carbonate solvents, and the initial mass percentage of the carbonate solvent in the non-aqueous solvent is relatively high (e.g., greater than or equal to 80%).

[0451] In some embodiments of the second aspect of this application, a method for preparing a lithium-ion battery is provided, comprising the following steps:

[0452] The electrode assembly is placed in the battery casing; wherein the electrode assembly includes a positive electrode sheet, a separator, and a negative electrode sheet, and a separator is disposed between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet includes a positive active layer, and the positive active layer includes a positive active material; the positive active material includes a doping element, and the doping element includes Ti.

[0453] An electrolyte is injected into a battery casing, and the casing is left to stand to allow the electrolyte to wet the positive and negative electrode sheets, thereby forming a lithium-ion battery. The electrolyte comprises an electrolyte salt, a non-aqueous solvent, and additives, wherein the additives include one or both of vinylene carbonate and lithium bis(fluorosulfonyl)imide. In some embodiments, the electrolyte comprises an electrolyte salt, a non-aqueous solvent, and additives, wherein the non-aqueous solvent comprises a carbonate solvent, and the initial mass percentage of the carbonate solvent in the non-aqueous solvent is relatively high (e.g., greater than or equal to 80%).

[0454] The lithium-ion battery described in the first aspect of this application can be prepared.

[0455] In some embodiments, the formation includes the following steps performed sequentially: charging to 6% SOC at 0.05C and letting stand for 5 minutes; charging to 20% SOC at 0.1C and letting stand for 5 minutes; charging to 70% SOC at 0.2C; and the formation is complete.

[0456] SOC (State of Charge) indicates the state of charge. When "SOC=0", it means that the battery is fully discharged, and when "SOC=100%", it means that the battery is fully charged.

[0457] In some embodiments, the method for preparing a lithium-ion battery satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0458] (f1) The initial mass percentage of vinylene carbonate in the electrolyte is 1.8wt% to 7wt%, optionally 2.5wt% to 3.5wt%, or any of the following percentages or a range of any two of the following percentages (unit: weight percentage): 1.8%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, etc.

[0459] (f2) The initial molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.2 mol / L to 0.6 mol / L, which can be selected from 0.3 mol / L to 0.5 mol / L, or any of the following concentrations or a range selected from any two of the following concentrations: 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, etc.;

[0460] (f3) Carbonate solvents include at least one of cyclic carbonates and chain carbonates;

[0461] Optionally, the carbonate solvent includes at least one of cyclic carbonates having 3 to 6 carbon atoms and chain carbonates having 3 to 9 carbon atoms;

[0462] Alternatively, the carbonate solvent includes cyclic carbonates and chain carbonates, and in some embodiments therein the mass ratio of cyclic carbonates to chain carbonates is (3~7):(7~3); the cyclic carbonates have 3~5 carbon atoms and the chain carbonates have 4~7 carbon atoms;

[0463] The number of carbon atoms in cyclic carbonates and the number of carbon atoms in chain carbonates can each be independently selected from any suitable value or range in the context.

[0464] (f4) The initial mass percentage of carbonate solvent in the non-aqueous solvent is greater than or equal to 80%, and optionally, the initial mass percentage of carbonate solvent in the non-aqueous solvent is greater than or equal to 90%. Non-limitingly, the initial mass percentage of carbonate solvent in the non-aqueous solvent may also be greater than or equal to any of the following percentages: 82%, 84%, 85%, 86%, 88%, 92%, 94%, 95%, 96%, 98%, etc. In the electrolyte, the initial mass percentage of carbonate solvent in the non-aqueous solvent may also be 80% to 100%, optionally 90% to 100%, and may also be any of the following percentages or a range selected from any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 98%, 100%, etc.

[0465] By controlling the initial concentrations of VC and / or LiFSI in the electrolyte, it is beneficial to better control the concentrations of the two additives in the resulting lithium-ion battery, thereby improving the battery RTE and better balancing longer battery cycle performance.

[0466] By controlling the types and / or initial content of carbonate solvents in the electrolyte, it is beneficial to better suppress gas production and / or extend battery life.

[0467] Those skilled in the art will understand that the content of some additive components in the electrolyte may change after formation treatment. As a non-limiting example, for instance, the content of some film-forming additive components may decrease due to their participation in the formation of the solid electrolyte interface film of the positive and / or negative electrodes. As a non-limiting example, the content of additives in the electrolyte is generally reduced after formation treatment compared to the electrolyte before formation treatment.

[0468] In some embodiments of the third aspect of the application, a secondary battery is provided, comprising at least one of the lithium-ion batteries described in the first aspect of the application and lithium-ion batteries prepared by the preparation method of the lithium-ion batteries described in the second aspect of the application.

[0469] In some embodiments of the fourth aspect of the application, an energy storage device is provided, which includes at least one of the lithium-ion battery described in the first aspect of the application, a lithium-ion battery prepared by the method for preparing a lithium-ion battery described in the second aspect of the application, and a secondary battery described in the third aspect of the application.

[0470] Without limitation, energy storage devices may include at least one of energy storage devices, energy storage systems, charging networks, etc.

[0471] In some implementations, the energy storage device can be an energy storage unit, an energy storage system, or a charging network.

[0472] In some embodiments of the fourth aspect of the application, an energy storage device, energy storage system, or charging network is provided, which includes at least one of the lithium-ion battery described in the first aspect of the application, a lithium-ion battery prepared by the method for preparing a lithium-ion battery described in the second aspect of the application, and a secondary battery described in the third aspect of the application.

[0473] The aforementioned secondary batteries, energy storage devices, energy storage systems, and charging networks can leverage the advantages of lithium-ion batteries to achieve significantly improved RTE, while also achieving a longer service life.

[0474] Typically, a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. A separator is placed between the positive and negative electrodes; its primary function is to prevent short circuits between the positive and negative electrodes while allowing ions to pass through. Active ions can include lithium ions; more specifically, the active ions can be lithium ions. The term "lithium-ion secondary battery" refers to a secondary battery in which the active ions include lithium ions.

[0475] Unless otherwise specified, an "energy storage device" is a device that integrates a battery unit and a control cabinet. The control cabinet and battery unit are coupled together to manage the battery unit and utilize the conversion between electrical energy and chemical energy to store and output electrical energy. The battery unit can serve as a backup power source, perform peak shaving and valley filling when the power system supply is uneven, regulate frequency when the power system load or power generation is high, or be applied in a photovoltaic-storage power generation system.

[0476] Energy storage devices may include one or more battery clusters to increase the voltage and capacity of the energy storage device. A battery cluster may include multiple battery units, which are connected in series via a busbar to increase the voltage of the energy storage device. When an energy storage device includes multiple battery clusters, the battery clusters are connected in parallel to increase the capacity of the energy storage device.

[0477] For example, energy storage devices can be used in energy storage power stations, wind power generation systems, solar power generation systems, mobile power systems, or temporary power supply systems. Energy storage devices can store electrical energy as needed and output it when appropriate. For instance, an energy storage device can store electrical energy during off-peak hours and provide power to relevant users or electrical equipment during peak hours. The energy storage system provided in this application embodiment can be any power system that requires energy storage devices.

[0478] In some embodiments, the energy storage device is an energy storage container or an energy storage cabinet.

[0479] In some embodiments, the energy storage device may include a cabinet and one or more battery clusters housed within the cabinet.

[0480] In some embodiments, the energy storage device may include modules such as a thermal management module, a main control module, a central control module, a power distribution module, and a fire protection module.

[0481] In some embodiments, a "battery device" is a device in an energy storage system used to store and release electrical energy. The number of battery devices can be one, two, or more. A battery device may include one or more individual battery cells, which can be connected in series, parallel, or a combination thereof. A combination thereof means that multiple battery cells are connected in both series and parallel connections. Multiple battery cells can be directly connected in series, parallel, or a combination thereof, and then the entire assembly of the multiple battery cells is housed within a casing. Alternatively, a battery device can be formed by first connecting multiple battery cells in series, parallel, or a combination thereof to form a battery module, and then connecting multiple battery modules in series, parallel, or a combination thereof to form a whole. The battery device may also include other structures; for example, it may include a busbar component for electrical connection between multiple battery cells.

[0482] In some embodiments of this application, the energy storage system includes an energy storage device; the energy storage system also includes a power conversion device for electrically connecting the power generation device and the energy storage device.

[0483] For example, an energy storage system may include one or more energy storage devices and a power conversion system (PCS), with the power conversion system connecting the power generation device and the energy storage device. The power generation device generates electrical energy, which can be stored in the energy storage device through the power conversion system. As examples, the power generation device may specifically be a solar panel, hydroelectric power generation equipment, thermal power generation equipment, wind power generation equipment, etc. The specific type of power generation device is not particularly limited in this application.

[0484] Figure 6 This is an example of an energy storage system where each PCS can connect to one or more battery packs. Multiple battery packs are connected in parallel to the power grid via the PCS, enabling charging and discharging with the grid. Battery packs can be, for example, battery cabinets or containers. A cabinet can be considered a battery product formed from battery clusters; therefore, the cabinet in this embodiment can also be called a battery cluster. Multiple cabinets can be assembled to form battery products such as containers. Each battery cluster includes multiple enclosures connected in series and / or parallel, and each enclosure includes multiple individual battery cells connected in series and / or parallel.

[0485] In some embodiments of this application, the charging network includes at least one of an energy storage device and an energy storage system; the charging network also includes a charging pile, and the energy storage device provides electrical energy to the charging pile. The charging pile is electrically connected to the energy storage device, which provides electrical energy to the charging pile. The charging pile is electrically connected to a battery device in the energy storage device via a cable, and the battery device can provide its stored electrical energy to the charging pile. The charging pile has one or more connectors for connecting to electrical equipment (such as a vehicle), thereby enabling the charging equipment to be recharged.

[0486] Energy storage devices can be located inside the charging pile (e.g., an integrated energy storage and charging unit) or outside the charging pile.

[0487] The following describes some embodiments of this application. The described embodiments are only a part of the embodiments of this application, and not all of them. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application and its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0488] Unless otherwise specified in the examples, the procedures described above, or those described in the literature in this field, or those described in the product instructions, shall be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products, or products that can be synthesized using conventional methods from commercially available products.

[0489] In the following examples, room temperature refers to 20°C to 30°C.

[0490] In the following examples, unless otherwise specified, the parameters involved can be confirmed by referring to the test methods described above. For example, but not limited to, those involving the D of the positive electrode active material... v 50 and D n 10. D of negative electrode active material v 50. The average particle size of primary particles in the negative electrode active material, the degree of graphitization of the graphite component, etc.

[0491] Unless otherwise specified, in the following embodiments, the thickness of the positive electrode active layer in the step of preparing the positive electrode sheet is in the range of 100μm~300μm.

[0492] Unless otherwise stated, in the following embodiments, the negative electrode active material is mainly secondary particles, and the number of secondary particles accounts for nearly 100%.

[0493] Unless otherwise stated, in the following embodiments, the areal capacity ratio of the negative electrode to the positive electrode in the prepared lithium-ion battery is in the range of 1.05 to 1.15.

[0494] Unless otherwise stated, in the following embodiments, the height of the lithium-ion battery cells is in the range of 100mm to 250mm, and the width of the solder area of ​​the positive electrode tab and the width of the solder area of ​​the negative electrode tab are each independently in the range of 20mm to 68mm. Taking Embodiment 1 as an example, the width of the solder area (X direction) of the positive electrode tab and the width of the solder area (X direction) of the negative electrode tab are both 45mm.

[0495] Unless otherwise stated, in the following embodiments, the number of positive electrode layers in the lithium-ion battery, in the cell thickness direction, is in the range of 10 to 70 layers, and further in the range of 30 to 70 layers.

[0496] In the following embodiments, element M is Ti, and the lithium iron phosphate cathode material doped with element M is Ti-doped lithium iron phosphate. It is understood that other types of element M with similar functions can be substituted. For example, element M can also be element V, or a combination of Ti and V. Ti-doped lithium iron phosphate can also be replaced with other types of "lithium phosphate cathode materials doped with element M".

[0497] I. Preparation of Lithium-ion Secondary Batteries (using lithium-ion secondary batteries as an example)

[0498] Example 1.

[0499] (1) Positive electrode plate

[0500] Ti-doped lithium iron phosphate (hereinafter referred to as "Ti-doped LFP"), conductive agent carbon black (SuperP), and binder polyvinylidene fluoride (PVDF) were mixed uniformly in N-methylpyrrolidone (NMP) at a mass ratio of 96.2:2.7:1.1 to obtain a positive electrode slurry with a solid content of 68 wt%. The positive electrode slurry was coated on both sides of the positive electrode current collector aluminum foil, and the positive electrode sheet was obtained through processes such as drying, cold pressing, slitting, and cutting. The compacted density of the positive electrode sheet was 2.65 g / cm³. 3 .

[0501] In this example, the mass fraction of Ti in the positive electrode active material (i.e., the Ti doping amount) is 0.05%, and the D of the positive electrode active material is... v 50 is 7μm, D n 10 is 0.35μm.

[0502] (2) Negative electrode plate

[0503] Artificial graphite (anode active material), carbon black (Super P) (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC-Na) were mixed evenly in deionized water at a mass ratio of 96.4:0.7:1.8:1.1 to obtain a negative electrode slurry with a solid content of 55 wt%. The negative electrode slurry was coated onto both sides of a copper foil current collector. Through drying, cold pressing, slitting, and cutting, the negative electrode sheet was obtained. The compacted density of the negative electrode sheet was 1.5 g / cm³. 3 .

[0504] In this example, the negative electrode active material is artificial graphite with a graphitization degree of 91.7%, and the D of the negative electrode active material is... v The diameter of 50 is approximately 12 μm, while the average particle size of primary particles in the negative electrode active material is approximately 5 μm.

[0505] (3) Electrolyte

[0506] Ethyl carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 30:70 to obtain a non-aqueous organic solvent. The thoroughly dried electrolyte salt was dissolved in the above non-aqueous organic solvent and mixed evenly to obtain an electrolyte solution. The initial total concentration of the electrolyte salt was 1.0 mol / L. The electrolyte salt was a combination of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI), and the molar volume concentration of LiFSI was 0.4 mol / L (that is, the initial concentration of LiFSI in the electrolyte solution was 0.4 mol / L).

[0507] In this example, the non-aqueous solvent in the electrolyte has a high content of carbonate solvents, and further, the carbonate solvents are a combination of EC and EMC.

[0508] (4) Separating membrane

[0509] A porous PE base membrane is used, with an inorganic ceramic coating on the base membrane. The thickness of the separator is 7μm.

[0510] (5) Assemble lithium-ion secondary batteries

[0511] Following the sequence of "separator-negative electrode sheet-separator-positive electrode sheet", the above-mentioned positive electrode sheet, separator, and negative electrode sheet are stacked, wound, and hot-pressed to obtain a bare cell (electrode assembly); tabs are welded to the bare cell, and then it is placed in an outer packaging (square aluminum alloy hard shell), baked at 80°C to remove water, injected with the electrolyte prepared above, and then subjected to vacuum sealing, standing, formation, aging and other processes to obtain a lithium-ion battery.

[0512] The formation process includes the following steps performed sequentially: charging at 0.05C to 6% SOC and letting stand for 5 minutes; charging at 0.1C to 20% SOC and letting stand for 5 minutes; charging at 0.2C to 70% SOC; formation complete.

[0513] In this example, a full-tab structure design is adopted. The cell length (X direction) is 280mm, the cell height (Y direction) is 215mm, and the cell thickness (Z direction) is 71.5mm. Multiple positive tabs from the positive current collector and multiple negative tabs from the negative current collector are soldered using ultrasonic soldering. The width of both the positive and negative tabs is 120mm. The soldering area (A1) of the positive tab is 136 mm². 2 The solder area (A2) of the negative electrode lug is 102 mm. 2 The ratio A1 / A2 is approximately 1.33; the solder mark-terminal center distance (Jc1) at the positive electrode and the solder mark-terminal center distance (Jc2) at the negative electrode are both 55 mm.

[0514] Examples 2-4 were prepared using essentially the same method as Example 1, with the difference being the use of different positive electrode active materials, primarily in the amount of Ti doping. In Examples 2-4, the mass fraction of Ti in the positive electrode active material (i.e., the Ti doping amount) was 0.1%, 0.15%, and 0.2%, respectively. See Table 1 for details.

[0515] Examples 5-7 used essentially the same method as Example 1 to prepare lithium-ion batteries, the difference being that the initial concentration of LiFSI in the electrolyte was different, while the initial total concentration of the electrolyte salt (a combination of LiPF6 and LiFSI) was 1.0 mol / L. See Table 1 for details.

[0516] Examples 8-10 used essentially the same method as Example 1 to prepare lithium-ion batteries, the difference being that the additives were different, LiFSI was replaced with different initial concentrations of VC, and lithium hexafluorophosphate was used as the electrolyte salt with an initial concentration of 1 mol / L. See Table 1 for details.

[0517] Example 11 prepared a lithium-ion battery using essentially the same method as Example 1, the difference being that the additives were different; a combination of VC and LiFSI was used. See Table 1 for details.

[0518] Comparative Example 1 used essentially the same method as Example 1 to prepare a lithium-ion battery, except that a different positive electrode active material was used and additives were omitted. Undoped lithium iron phosphate (referred to as "undoped LFP") was used, and the electrolyte salt was lithium hexafluorophosphate (LiPF6) with an initial concentration of 1 mol / L. See Table 1 for details.

[0519] Comparative Example 2 used essentially the same method as Example 1 to prepare a lithium-ion battery, the difference being that a different positive electrode active material was used: undoped LFP was employed; in this example, the electrolyte contained LiFSI at an initial concentration of 0.4 mol / L. See Table 1 for details. Compared to Example 1, the M element doping was omitted from the positive electrode active material. In this example, the electrolyte composition was the same as in Example 1.

[0520] Comparative Example 3 used essentially the same method as Example 1 to prepare a lithium-ion battery, the difference being that a different electrolyte was used, additives were omitted, and the electrolyte salt was lithium hexafluorophosphate (LiPF6) with an initial concentration of 1 mol / L; in this example, the positive electrode active material was LFP with a Ti doping content of 0.05%. See Table 1 for details.

[0521] Examples 12-14 were prepared using the same method as in Example 11, employing the same non-aqueous organic solvent. The differences were: the composition of the additives and the composition of the electrolyte salts were different. The additives were a combination of VC and LiFSI, and the initial molar concentration of VC in the electrolyte was 3%. The types and initial concentrations of the electrolyte salts can be found in Table 2.

[0522] Comparative Example 4 used essentially the same method as Example 13 to prepare a lithium-ion battery, the difference being the type of electrolyte salt. See Table 2 for details.

[0523] Examples 15-17 were prepared using essentially the same method as in Example 2, the difference being: different positive electrode active materials; and different D-type positive electrode active materials were used. v 50, Controlling the D of the positive electrode active material n Example 10 is basically the same as Example 2. See Table 3 for details.

[0524] Comparative Example 5 used essentially the same method as Example 17 to prepare a lithium-ion battery, the difference being that different positive electrode active materials and electrolytes were used. The positive electrode active material and electrolyte in Example 17 were the same as those in Comparative Example 1 (the positive electrode active material used was undoped LFP, and the electrolyte was based on Example 1, omitting LiFSI). See Table 3 for details.

[0525] Examples 18-22 were prepared using essentially the same method as Example 2, with the differences being: different negative electrode active materials and different degrees of graphitization of the negative electrode active materials. See Table 4 for details. The negative electrode active materials in Examples 18-22 were primarily secondary particles, and the D0 of the negative electrode active materials was... v The average particle size of the primary particles in 50 and the negative electrode active material is similar to that in Example 2.

[0526] Examples 23-25 ​​used essentially the same method as Example 2 to prepare lithium-ion batteries, the difference being: different negative electrode active materials; the negative electrode active materials used particles with different agglomeration morphologies, and the D of the negative electrode active materials... v The average particle size distribution of 50 is different from that of the primary particles in the negative electrode active material. See Table 5 for details.

[0527] Examples 26-31 use the same method as Example 2 to prepare lithium-ion batteries, except that at least one of the tab structure parameters (including Rp) and tab soldering parameters (including the soldering area of ​​the positive tab, the soldering area of ​​the negative tab, and the center distance between the soldering and the terminal post) is different, as can be seen in Table 6.

[0528] Examples 32-34 use the same method as Example 2 to prepare lithium-ion batteries, the difference being that negative electrode active materials with different degrees of graphitization (graphitization of about 92.7%) and positive electrode active materials with different Ti doping amounts are used, as shown in Table 7.

[0529] Examples 35-37 use the same method as Example 2 to prepare lithium-ion batteries, the difference being that different graphitization degrees of negative electrode active materials (graphitization degree of approximately 94.5%) are used, and different tab structures (different Rp) are used, as shown in Table 8.

[0530] As mentioned earlier, along the thickness direction of the battery cell, the ratio of the number of positive electrode layers leading to the positive electrode tab to the total number of positive electrode layers is denoted as Rp.

[0531] II. Testing Methods

[0532] 1. Ti dissolution test of positive electrode active material

[0533] Take a certain amount of positive electrode active material, grind it into a uniform powder, and accurately weigh an appropriate amount of sample (e.g., 0.1g~1g). Mix the weighed sample with the test electrolyte in a certain proportion, soak it under the set conditions, and take samples periodically (including samples taken at 0 h, 12 h, 24 h, 48 h, and 72 h). After sampling, centrifuge the soaking solution to remove particulate matter, and send it for ICP-MS (inductively coupled plasma mass spectrometry). Each group of experiments should be tested in parallel at least 3 times, and the average value and standard deviation should be calculated. The average value is used as the test value of Ti dissolution, and the Ti dissolution rate can be calculated.

[0534] The composition of the test electrolyte was the same as in Example 1.

[0535] 2. Electrode resistance test: using the four-probe method.

[0536] Sample preparation: Prepare electrode sheets with a diameter of 1 cm to 3 cm. Ensure the surface is flat and free of cracks or pores (this can be checked by scanning electron microscopy (SEM)).

[0537] Instrument calibration: Calibrate the four-probe instrument using standard reference materials (such as copper sheets).

[0538] Test procedure: Place the four probes on the electrode surface at equal intervals (probe spacing d). Apply a constant current (typically within the range of 10μA to 100μA, 10μA is selected) and measure the voltage drop (V).

[0539] Data calculation:

[0540] Formula for calculating bulk resistivity (ρ):

[0541] Where t is the electrode thickness, V is the voltage drop, and I is the current.

[0542] Bulk resistance (Rb) = ρ × L / A (L is the length, A is the cross-sectional area). Where L is the path length through which the current flows; A is the cross-sectional area through which the current flows perpendicularly.

[0543] 3. Ohmic impedance and ion transport impedance (using electrochemical impedance spectroscopy (EIS) method)

[0544] EIS test:

[0545] Based on the design of confined symmetric cells, the activated electrode plates are assembled into symmetric cells for EIS, which can separate the impedance of the anode and cathode.

[0546] Frequency points: 73

[0547] Number of single-frequency point tests: 2

[0548] Test frequency range: 500kHz-30mHz

[0549] The curves were fitted with equivalent circuits to obtain the ohmic impedance (electron transport impedance) and ion diffusion impedance, in units of Ω·cm. 2 .

[0550] 4. Battery energy conversion efficiency (RTE) and cycle performance testing

[0551] At 25℃, the battery was charged at a constant current rate of 0.5P to 3.65V, then charged at a constant voltage rate until the current ≤0.05C, allowed to rest for 5 minutes, and then discharged at a constant current rate of 0.5P to 2.5V, allowed to rest for 5 minutes. The battery capacity C0 at this point was recorded. The battery was cycled using this method, and the battery capacity after the nth cycle was recorded as Cn. The cycle capacity retention rate P of the battery after n cycles at 25℃ is also recorded. n =Cn / C0×100%. This gives the number of cycles required to reduce capacity to 80%, which can be denoted as "the number of cycles required to reduce capacity to 80% at 25℃".

[0552] RTE = First discharge energy / First charge capacity × 100%.

[0553] By changing the test temperature, you can also obtain the number of cycles at which the capacity decays to 80% at the corresponding temperature, such as the number of cycles at which the capacity decays to 80% at a test temperature of 60℃.

[0554] By changing the test temperature and / or the number of cycles, the cycle capacity retention rate at a specific number of cycles at the corresponding temperature can also be obtained, such as the cycle capacity retention rate after 2000 cycles at 60℃.

[0555] III. Test Result Analysis

[0556] The positive electrode active materials used in each embodiment were tested, and the Ti dissolution rate gradually increased with the increase of Ti doping amount (mass fraction of Ti element in positive electrode active material).

[0557] The positive electrode active layer of the lithium-ion batteries prepared in Examples 1-37 all includes a lithium phosphate-based positive electrode material doped with element M. The electrolyte includes additives, specifically one or both of vinylene carbonate and lithium bis(fluorosulfonyl)imide. The resulting lithium-ion batteries all exhibit significantly improved RTE and long cycle life. As can be seen, the lithium-ion batteries of these examples demonstrate excellent cycle life, capable of nearly 10,000 cycles or more at 25°C. The lithium-ion batteries of Examples 1-37 can perform excellently as energy storage batteries. See Tables 1-8 for further details.

[0558] In Comparative Example 1, the positive electrode active material was not doped with element M, and the electrolyte did not include either vinylene carbonate or lithium bis(fluorosulfonyl)imide. As a result, the RTE and cycle life of the lithium-ion battery were severely degraded.

[0559] Compared to Example 1, Comparative Example 2 omitted M element doping, and Comparative Example 3 omitted LiFSI. The RTE and cycle life of the lithium-ion batteries in Comparative Examples 2 and 3 were significantly worse.

[0560] For example, in the lithium-ion batteries prepared in each of Examples 8-10, after formation, the mass percentage of vinylene carbonate (VC) in the electrolyte is in the range of 0.7wt% to 6.5wt%, and in Example 9 it is in the range of 1wt% to 4.5wt%.

[0561] For example, in the lithium-ion batteries prepared in each of Examples 1-7, after formation, the molar volume concentration of lithium bisfluorosulfonylimide (LiFSI) in the electrolyte is in the range of 0.1 mol / L to 0.6 mol / L, and in Examples 1-4 and 6 it is in the range of 0.2 mol / L to 0.5 mol / L.

[0562] For example, by simultaneously incorporating VC and LiFSI into the electrolyte (see Example 11), the synergistic effect of VC and LiFSI can be utilized to better improve battery RTE and extend battery cycle life.

[0563] Table 1.

[0564]

[0565] In Table 1, "Ti doping amount" refers to the mass fraction of Ti doping element in the positive electrode active material.

[0566] Table 2.

[0567]

[0568] In Table 2, the electrolyte salt in the electrolyte is lithium electrolyte salt.

[0569] According to Table 2, the high-temperature cycle performance of lithium-ion batteries can also be improved by adding LiFSI to the electrolyte.

[0570] For example, the lithium-ion batteries of Examples 12-14 exhibited more than 3000 cycles with capacity decay to 80% at 60°C, and all exceeded 3500 cycles. The lithium-ion batteries of Examples 12-14 can perform excellently as energy storage batteries.

[0571] Table 3.

[0572]

[0573] In Table 3, the positive electrode active materials in Examples 15-17 are all Ti-doped LFP (Ti doping amount is 0.1%, that is, the mass fraction of Ti in the positive electrode active material is 0.1%). The additives are all LiFSI with an initial concentration of 0.4 mol / L (also used as electrolyte salt). The electrolyte salts are LiFSI and lithium hexafluorophosphate (LiPF6) with an initial total concentration of 1 mol / L.

[0574] According to Table 3, the D of the positive electrode active material in Example 15 v The value of 50 is lower than that of Example 16. The cathode active material of Example 15 has a relatively small size and a larger specific surface area for side reactions. However, Example 15 has a better battery cycle life. This is a result of the synergistic effect of Ti doping.

[0575] Table 4.

[0576]

[0577] According to Table 4, a relatively high degree of graphitization is more conducive to improving the RTE and cycle life of the battery. However, the manufacturing process of the negative electrode active material in Example 22 is more difficult.

[0578] Table 5.

[0579]

[0580] According to Table 5, the D of the negative electrode active material in Example 2 is... v The 50 has a better match with the average particle size of the primary particles in the negative electrode active material, resulting in better overall performance in terms of RTE and battery cycle performance.

[0581] Table 6.

[0582]

[0583] In Table 6, the cell length of each of Examples 26-31 is 550mm, and the ratio of the solder area of ​​the positive electrode tab to the solder area of ​​the negative electrode tab remains basically unchanged.

[0584] The definition of Rp in Table 6 can be found in the previous text.

[0585] In Table 6, in each of the embodiments 26-31, the solder mark-terminal center distance (Jc) refers to the fact that the solder mark-terminal center distances Jc1 and Jc2 at the positive and negative terminals are equal, and both are numerically Jc; Jc1 refers to the solder mark-terminal center distance at the positive terminal, and more specifically, it refers to the distance in the Y direction of the center of the solder mark area of ​​the positive terminal along the extension path of the positive terminal, relative to the center of the nearest end face of the positive terminal; unless otherwise specified, the solder mark-terminal center distance (Jc2) at the negative terminal is equal to Jc1.

[0586] According to Examples 26-28 in Table 6, as Rp increases, the cell's overcurrent capability improves, and the battery's RTE is also higher, which correspondingly affects the cycle life. According to Examples 29-30 in Table 6, increasing the solder area of ​​the positive and negative electrode tabs improves the battery's RTE and also significantly increases the theoretical battery cycle life.

[0587] According to Examples 29-31 in Table 6, the adjustment of the solder mark-terminal center distance (Jc) can also be used to adjust the battery RTE and cycle life.

[0588] According to Table 7, with a slight increase in Ti doping concentration, both electron transport impedance and ion transport impedance are significantly reduced.

[0589] According to Table 8, as the number of tabs increases, both electron transport impedance and ion transport impedance decrease significantly.

[0590] Table 7.

[0591]

[0592] Table 8.

[0593]

[0594] In Table 8, the cell length of each of the embodiments 35-37 is 550mm, the center distance between the solder mark and the terminal post at the positive and negative terminals is 55mm, and the area of ​​the solder mark area at the positive terminal lug is 150mm². 2 The ratio of the solder area of ​​the positive electrode tab to the solder area of ​​the negative electrode tab remains basically unchanged.

[0595] In all of the above embodiments 1-37, the cells have a large size, which can achieve a high cell capacity (high single cell capacity) while also achieving a significantly improved RTE and a long cycle life, making them high-performance, long-life energy storage cells; while for traditional lithium-ion batteries, the cycle life of energy storage cells deteriorates severely when the size is large.

[0596] In some embodiments, Ti-doped LFP is used as the positive electrode active material, with a Ti mass fraction of 0.05%~0.15%. Compared to undoped LFP as the positive electrode active material, this significantly improves the cell's RTE performance by 1.8%~2.3%. Further, in these embodiments, the D of the positive electrode active material... v 50 is 6μm~8μm.

[0597] In some embodiments, a full-tab design is employed to further improve overcurrent capability. Compared to tab structures with approximately 50% Rp, the full-tab design in these embodiments shortens the current path by 60% to 80%, reduces electron transport impedance by 60% to 85%, reduces ion transport impedance by 45% to 60%, and improves RTE by 1% to 2.5%.

[0598] In some embodiments, the addition of 0.2 mol / L to 0.6 mol / L LiFSI to the electrolyte significantly improves the long-term cycle performance of the battery. Furthermore, the electrolyte salt is a combination of LiFSI and lithium hexafluorophosphate (LiPF6), with a total electrolyte salt concentration of 0.6 mol / L to 1.5 mol / L in the electrolyte. Compared to LiPF6 as an electrolyte salt of the same concentration, the combination of LiFSI and LiPF6 improves the battery's RTE and cell cycle performance, increasing the number of cycles before capacity decay to 80% at 60°C by 1.2% and the number of cycles before capacity decay to 80% at 25°C by 1.1%.

[0599] In some embodiments, the negative electrode active material includes graphite material (using artificial graphite), wherein the graphite material is secondary particles, and the D of the negative electrode active material... v The particle size of the primary particles in the negative electrode active material is 10μm~15μm, and the average particle size is 4μm~7μm, which improves the negative electrode expansion in the later stage of the battery. Among them, the graphitization degree of the graphite material is 89%~93%, and the graphitization degree of one embodiment is 91.7%.

[0600] In some embodiments, by optimizing the ultrasonic soldering area, the battery RTE is improved as the soldering area increases.

[0601] The descriptions of the various implementation methods and embodiments above tend to emphasize the differences between them. Similarities or resemblances can be referenced interchangeably, and for the sake of brevity, they will not be repeated here. The technical features of the implementation methods and embodiments described above can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combinations of these technical features do not contradict each other, they should be considered within the scope of this specification.

[0602] It should be noted that this application is not limited to the above-described embodiments and examples. The above-described embodiments and examples are merely examples, and any embodiments and examples that have the same structure and achieve the same effect as the technical concept within the scope of this application are included in the technical scope of this application. The embodiments and examples described above only illustrate several embodiments and examples of this application, and although the descriptions are relatively detailed, they should not be construed as limiting the scope of the patent. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments or examples, and other ways of constructing embodiments or examples by combining some of the constituent elements of the embodiments or examples, are also included in the scope of this application without departing from the spirit of this application.

Claims

1. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive active layer, the positive active layer includes a positive active material, and the electrolyte includes an electrolyte salt, a non-aqueous solvent, and additives. The lithium-ion battery includes a cell, which is a wound cell. The cell includes a positive electrode, a separator, and a negative electrode stacked together, with the separator disposed between the positive and negative electrode. The stacking direction of each electrode in the cell is denoted as the thickness direction of the cell, the direction in which the tabs are led out of the cell is denoted as the height direction of the cell, and the direction perpendicular to both the thickness and height directions of the cell is denoted as the length direction of the cell. The length of the cell is greater than or equal to 270 mm. The positive electrode active material includes a lithium phosphate positive electrode material doped with element M, wherein element M includes any one or both of elements Ti and V; the additive includes one or both of elements vinylene carbonate and lithium bis(fluorosulfonyl)imide. The mass fraction of element M in the positive electrode active material is 0.04% to 0.16%; the electrolyte meets one or two of the following characteristics: (i) the mass percentage of vinylene carbonate in the electrolyte is 0.7wt% to 6.5wt%; (ii) the molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.1mol / L to 0.6mol / L; The non-aqueous solvent includes carbonate solvents, and the carbonate solvent accounts for more than or equal to 80% of the mass of the non-aqueous solvent.

2. The lithium-ion battery according to claim 1, characterized in that, The electrolyte satisfies one or more of the following characteristics: (a1) The mass fraction of element M in the positive electrode active material is 0.05%~0.15%; (a2) The element M is a metallic element with an ionic valence greater than or equal to 3; (a3) The M element is a transition metal element; (a4) In the lithium phosphate cathode material doped with element M, the sum of the atomic molar ratios of Ti and V in element M is 0.8 to 1; (a5) The mass percentage of vinylene carbonate in the electrolyte is 0.7 wt% to 5 wt%; (a6) The molar volume concentration of lithium difluorosulfonylimide in the electrolyte is 0.2 mol / L to 0.6 mol / L; (a7) The carbonate solvents include at least one of cyclic carbonates and chain carbonates; (a8) The carbonate solvent accounts for more than or equal to 90% of the mass of the non-aqueous solvent.

3. The lithium-ion battery according to claim 2, characterized in that, The electrolyte satisfies one or more of the following characteristics: (t1) The mass fraction of element M in the positive electrode active material is 0.06%~0.12%; (t2) In the lithium phosphate cathode material doped with element M, the sum of the atomic molar ratios of Ti and V in element M is 0.9~1; (t3) The M element includes the Ti element; (t4) The mass percentage of vinylene carbonate in the electrolyte is 1wt%~4.5wt%; (t5) The molar volume concentration of lithium difluorosulfonylimide in the electrolyte is 0.2 mol / L to 0.5 mol / L; (t6) The additives include vinylene carbonate and lithium difluorosulfonyl imide; (t7) The carbonate solvent includes at least one of cyclic carbonates having 3 to 6 carbon atoms and chain carbonates having 3 to 9 carbon atoms; (t8) The carbonate solvent includes cyclic carbonates and chain carbonates, wherein the mass ratio of the cyclic carbonates to the chain carbonates is (3~7):(7~3); the cyclic carbonates have 3~5 carbon atoms, and the chain carbonates have 4~7 carbon atoms.

4. The lithium-ion battery according to claim 1, characterized in that, The additives include vinylene carbonate and lithium difluorosulfonylimide; The molar volume concentration of lithium difluorosulfonylimide in the electrolyte is 0.2 mol / L to 0.5 mol / L; the mass percentage of vinylene carbonate in the electrolyte is 0.7 wt% to 5 wt%.

5. The lithium-ion battery according to claim 4, characterized in that, The electrolyte satisfies one or more of the following characteristics: (x1) The mass percentage of vinylene carbonate in the electrolyte is 1wt%~4wt%; (x2) The molar volume concentration of the electrolyte salt in the electrolyte is 0.6 mol / L to 1.5 mol / L; (x3) The electrolyte salt includes lithium hexafluorophosphate.

6. The lithium-ion battery according to any one of claims 1 to 5, characterized in that, The positive electrode active material D v 50 represents 5μm to 10μm.

7. The lithium-ion battery according to any one of claims 1 to 5, characterized in that, The positive electrode active material D n 10 has a thickness of 0.28μm to 0.45μm.

8. The lithium-ion battery according to any one of claims 1 to 5, characterized in that, The positive electrode sheet satisfies one or more of the following characteristics: (y1) The D of the positive electrode active material v 50 has a thickness of 6μm to 8μm; (y2) The D of the positive electrode active material n 10 is 0.3μm~0.4μm.

9. The lithium-ion battery according to any one of claims 1 to 5, characterized in that, The negative electrode sheet includes a negative electrode active layer, and the negative electrode active layer includes a negative electrode active material; the negative electrode active material includes secondary particles; The secondary particles account for 90% to 100% of the total amount in the negative electrode active material.

10. The lithium-ion battery according to claim 9, characterized in that, The negative electrode active material D v 50 is 10μm~15μm, and the average particle size of the primary particles in the negative electrode active material is 4μm~7μm.

11. The lithium-ion battery according to claim 9, characterized in that, The negative electrode active material includes a secondary particulate graphite-based material; The secondary particulate graphite-based material accounts for 90% to 100% of the total amount of the negative electrode active material.

12. The lithium-ion battery according to claim 9, characterized in that, The negative electrode sheet satisfies one or more of the following characteristics: (z1) The secondary particles account for 95% to 100% of the total amount in the negative electrode active material; (z2) The D of the negative electrode active material v 50 is 11μm~15μm, and the average particle size of the primary particles in the negative electrode active material is 4μm~6μm; (z3) The negative electrode active material includes secondary particulate graphite-based material; the secondary particulate graphite-based material accounts for 95% to 100% of the negative electrode active material.

13. The lithium-ion battery according to any one of claims 1 to 5, characterized in that, The negative electrode sheet includes a negative electrode active layer, which includes a negative electrode active material; the negative electrode active material includes graphite, and the degree of graphitization of the graphite is 88%~95.5%.

14. The lithium-ion battery according to claim 13, characterized in that, The negative electrode sheet satisfies one or more of the following characteristics: (h1) The graphitization degree of the graphite component is 90%~95%; (h2) The graphite component accounts for 65% to 100% of the mass of the negative electrode active material.

15. The lithium-ion battery according to claim 13, characterized in that, The negative electrode sheet satisfies one or more of the following characteristics: (h1') The graphitization degree of the graphite component is 90%~93%; (h2') The graphite component accounts for 90% to 100% of the mass of the negative electrode active material.

16. The lithium-ion battery according to any one of claims 1 to 5, characterized in that, The positive electrode active material satisfies one or more of the following characteristics: (b1) The lithium phosphate cathode material doped with element M includes an olivine crystal structure; The lithium phosphate cathode material doped with element M includes element Fe; (b2)The lithium phosphate-based cathode material doped with the M element includes a composition with the chemical formula Li a Fe b M c PO d , where 0.8 ≤ a ≤ 1.15, 0.9 ≤ b < 1, 0 < c ≤ 0.1 and b + c ≤ 1, 3.8 ≤ d ≤ 4; the Li a Fe b M c PO d satisfies the positive and negative charge balance.

17. The lithium-ion battery according to claim 16, characterized in that, The positive electrode active material satisfies one or more of the following characteristics: (b1') The atomic molar ratio of Fe element in the transition metal elements contained in the lithium phosphate cathode material doped with M element is denoted as q1, where 0.8≤q1≤1; (b2') M includes one or more elements from Ti, V and Mn; 0.8 ≤ a ≤ 1.

18. The lithium-ion battery according to any one of claims 1 to 5, characterized in that, The positive electrode sheet satisfies one or more of the following characteristics: (c1) The mass percentage of the lithium phosphate cathode material doped with element M in the cathode active material is 95%~100%; (c2) The mass percentage of the lithium phosphate cathode material doped with element M in the cathode active layer is 90%~99%; (c3) The positive electrode active material includes lithium iron phosphate doped with element M; the mass percentage of lithium iron phosphate doped with element M in the positive electrode active material is 95%~100%.

19. The lithium-ion battery according to any one of claims 1 to 5, characterized in that, The length of the battery cell is 270mm~600mm.

20. The lithium-ion battery according to claim 19, characterized in that, The length of the battery cell is 280mm~600mm.

21. The lithium-ion battery according to claim 19, characterized in that, The length of the battery cell is 500mm~600mm.

22. The lithium-ion battery according to any one of claims 1 to 5, characterized in that, The battery cell includes multiple positive tabs extending from multiple positions on the positive electrode plate and multiple negative tabs extending from multiple positions on the negative electrode plate; the multiple positive tabs are combined to form a positive tab portion, and the combined area of ​​the multiple positive tabs is denoted as the solder area of ​​the positive tab portion; the multiple negative tabs are combined to form a negative tab portion, and the combined area of ​​the multiple negative tabs is denoted as the solder area of ​​the negative tab portion; The stacking direction of each electrode in the battery cell is denoted as the Z direction, the direction of the lead-out tab in the battery cell is denoted as the Y direction, and the direction perpendicular to both the Z and Y directions is denoted as the X direction. The X direction is parallel to the width direction of the positive tab and the width direction of the negative tab. The battery cell satisfies one or more of the following characteristics: (d1) The area of ​​the solder mark on the positive electrode lug is 30 mm². 2 ~340mm 2 The solder area of ​​the negative electrode ear is 20mm². 2 ~280mm 2 ; (d2) The width of the solder area of ​​the positive electrode tab in the X direction is 10% to 30% of the length of the cell in the X direction; the width of the solder area of ​​the negative electrode tab in the X direction is 10% to 30% of the length of the cell in the X direction.

23. The lithium-ion battery according to claim 22, characterized in that, The battery cell satisfies one or more of the following characteristics: (d1') The solder area of ​​the positive electrode lug is 90 mm². 2 ~180mm 2 The solder area of ​​the negative electrode ear is 70mm². 2 ~150mm 2 ; (d2') The width of the solder area of ​​the positive electrode tab in the X direction is 10% to 20% of the length of the cell in the X direction; the width of the solder area of ​​the negative electrode tab in the X direction is 10% to 20% of the length of the cell in the X direction.

24. The lithium-ion battery according to claim 22, characterized in that, The battery cell includes a positive electrode post located on the same side of the battery cell as the positive electrode lug and electrically connected to the positive electrode lug; the battery cell also includes a negative electrode post located on the same side of the battery cell as the negative electrode lug and electrically connected to the negative electrode lug; the axial directions of both the positive electrode post and the negative electrode post are parallel to the Y direction; Along the positive electrode extension path of the positive electrode tab, the distance between the center of the solder area of ​​the positive electrode tab in the Y direction and the center of the nearest end face of the positive electrode post is 40mm~250mm; Along the negative electrode tab extension path, the distance between the center of the solder area of ​​the negative electrode tab in the Y direction and the center of the nearest end face of the negative electrode post is 40mm~250mm.

25. The lithium-ion battery according to claim 24, characterized in that, Along the positive electrode extension path of the positive electrode tab, the distance between the center of the solder area of ​​the positive electrode tab in the Y direction and the center of the nearest end face of the positive electrode post is 50mm~200mm; Along the negative electrode tab extension path, the distance between the center of the solder area of ​​the negative electrode tab in the Y direction and the center of the nearest end face of the negative electrode post is 50mm~200mm.

26. The lithium-ion battery according to any one of claims 1 to 5, characterized in that, Includes a square wound battery cell; the stacking direction of each electrode sheet in the square wound battery cell is denoted as the thickness direction of the battery cell; Along the thickness direction of the battery cell, the ratio of the number of positive electrode layers leading out to the total number of positive electrode layers is denoted as Rp, and Rp≥50%.

27. The lithium-ion battery according to any one of claims 1 to 5, characterized in that, Rp is 90%~100%.

28. The lithium-ion battery according to any one of claims 1 to 5, characterized in that, The lithium-ion battery includes a battery casing and a cell and electrolyte disposed within the battery casing, and the lithium-ion battery satisfies one or more of the following characteristics: (e1) The battery casing is square; (e2) The battery casing is a rigid casing; (e3) The lithium-ion battery is a secondary lithium-ion battery.

29. A method for preparing a lithium-ion battery, characterized in that, Includes the following steps: An electrode assembly is placed in a battery casing; wherein the electrode assembly includes a positive electrode, a separator, and a negative electrode, with the separator disposed between the positive and negative electrode; the positive electrode includes a positive active layer, which includes a positive active material; the positive active material includes a lithium phosphate-based positive electrode material doped with element M, wherein element M includes any one or both of elements Ti and V; the mass fraction of element M in the positive active material is 0.04% to 0.16%; An electrolyte is injected into the battery casing, and the mixture is allowed to stand to allow the electrolyte to wet the positive and negative electrode plates, thus forming a lithium-ion battery. The lithium-ion battery includes a cell, which is a wound cell. The cell includes the stacked positive electrode plate, a separator, and a negative electrode plate, with the separator between the positive and negative electrode plates. The stacking direction of each electrode plate in the cell is denoted as the thickness direction of the cell, the direction of the tabs leading out of the cell is denoted as the height direction of the cell, and the direction perpendicular to both the thickness and height directions of the cell is denoted as the length direction of the cell. The length of the cell is greater than... The electrolyte is 270 mm or more; the electrolyte includes an electrolyte salt, a non-aqueous solvent, and additives, the additives including one or two of vinylene carbonate and lithium bis(fluorosulfonyl)imide; the non-aqueous solvent includes carbonate solvents, the initial mass percentage of the carbonate solvent in the non-aqueous solvent is greater than or equal to 80%; in the prepared lithium-ion battery, the electrolyte satisfies one or two of the following characteristics: (i) the mass percentage of vinylene carbonate in the electrolyte is 0.7 wt% to 6.5 wt%; (ii) the molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.1 mol / L to 0.6 mol / L.

30. The method for preparing a lithium-ion battery according to claim 29, characterized in that, The electrolyte satisfies one or more of the following characteristics: (f1) The initial mass percentage of vinylene carbonate in the electrolyte is 1.8 wt% to 7 wt%; (f2) The initial molar volume concentration of lithium difluorosulfonylimide in the electrolyte is 0.2 mol / L to 0.6 mol / L; (f3) The carbonate solvents include at least one of cyclic carbonates and chain carbonates; (f4) The initial mass percentage of the carbonate solvent in the non-aqueous solvent is greater than or equal to 90%.

31. The method for preparing a lithium-ion battery according to claim 30, characterized in that, The electrolyte satisfies one or more of the following characteristics: (f1') The initial mass percentage of vinylene carbonate in the electrolyte is 2.5 wt% to 4.5 wt%; (f2') The initial molar volume concentration of lithium difluorosulfonylimide in the electrolyte is 0.3 mol / L to 0.5 mol / L; (f3') The carbonate solvents include at least one of cyclic carbonates having 3 to 6 carbon atoms and chain carbonates having 3 to 9 carbon atoms; (f4') The carbonate solvent includes cyclic carbonates and chain carbonates, wherein the mass ratio of the cyclic carbonates to the chain carbonates is (3~7):(7~3); the cyclic carbonates have 3~5 carbon atoms, and the chain carbonates have 4~7 carbon atoms.

32. A secondary battery, characterized in that, The lithium-ion battery includes at least one of the lithium-ion batteries according to any one of claims 1 to 28 and the lithium-ion battery prepared by any one of claims 29 to 31.

33. An energy storage device, characterized in that, It includes at least one of the lithium-ion batteries according to any one of claims 1 to 28, lithium-ion batteries prepared by the method of preparing lithium-ion batteries according to any one of claims 29 to 31, and secondary batteries according to claim 32.

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