Secondary battery and power-consuming device

Abstract

Secondary battery, characterized in that it comprises an electrolyte solution and a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode active material, wherein the positive electrode active material comprises a core of lithium iron phosphate-based material and a carbon shell layer with which at least partially the outer surface of the core is coated, wherein in the Raman spectrum of the positive electrode active material the peak intensity at the wavenumber of 1360 ± 50 cm⁻¹ -1 as I d and the peak intensity at a wavenumber of 1580 ± 50 cm -1 as I g is, where the I d / I g The positive electrode active material has a value of 0.2 to 1.5, wherein the electrolyte solution comprises cyclic ester compounds that do not exceed 25% of the total mass of the solvent in the electrolyte solution.

Description

Cross-references

[0001] The present application refers to Chinese patent application No. 202411310454.9, entitled “Secondary battery and power-consuming device”, filed on Thursday, September 19, 2024, which is hereby incorporated by reference in its entirety. Technical field

[0002] The present disclosure relates to the technical field of secondary batteries and in particular to a secondary battery and a power-consuming device. State of the art

[0003] In recent years, secondary batteries have been increasingly used in energy storage systems such as hydroelectric, coal-fired, wind, and solar power plants, as well as in many different sectors including power tools, e-bikes, e-motorcycles, electric vehicles, military equipment, aerospace, and more. The market is also placing higher demands on the capacity of secondary batteries. Therefore, increasing the size of battery components is now the trend in the battery industry.

[0004] Increasing the size of battery components increases the distance between the electrode plates and the electrode tabs, thus lengthening the electron transfer path during the cycle. Simultaneously, the cell height also increases, which impairs the wetting effect of the electrolyte solution on the electrode plates. This leads to an increase in the cell's DC resistance (DCR), negatively impacting the energy efficiency and cycle life of the secondary batteries. The larger the battery components, the more pronounced this problem becomes. Disclosure of the invention

[0005] Based on the above prior art, the present application provides a secondary battery comprising an electrolyte solution and a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode active material, the positive electrode active material comprising a core of lithium iron phosphate-based material and a carbon shell layer with which at least partially coats the outer surface of the core, wherein in the Raman spectrum of the positive electrode active material the peak intensity at the wavenumber of 1360 ± 50 cm⁻¹ -1 as I d and the peak intensity at a wavenumber of 1580 ± 50 cm -1 as I g is, where the I d / I g The positive electrode active material has a value of 0.2 to 1.5, wherein the electrolyte solution comprises cyclic ester compounds that do not exceed 25% of the total mass of the solvent in the electrolyte solution.

[0006] The I d / I g The Ig value in the Raman spectrum of the positive electrode active material can characterize the degree of graphitization of the positive electrode active material; the lower the value, the closer the material is to the ideal graphite structure, and the more favored the formation of a continuous conductive network is. d / I gThe Ip value of the positive electrode active material is within a suitable range, which helps to improve the material's electronic conductivity, reduce the cell's internal resistance, minimize energy loss during charging, and improve the battery's energy efficiency. Due to their high dielectric constant, cyclic ester compounds can effectively improve the conductivity of the electrolyte solution, but they can also increase its viscosity. Reducing the amount of cyclic ester compounds in the electrolyte solution can decrease its viscosity, improve the cell's fluid absorption capacity and internal wettability, provide more ion conduction pathways, and increase the desolvation capability of the active ions. This leads to a reduction in the migration resistance of the active ions and thus to improved battery cycle performance. By adjusting the Ip value, the electrolyte viscosity can be reduced, the cell's fluid absorption capacity and internal wettability can be improved, and more ion conduction pathways can be provided.d / I g By adjusting the pH value of the positive electrode active material and the amount of cyclic ester compounds in the electrolyte solution, sufficient wetting of the positive electrode active material with the electrolyte solution can be achieved, the polarization of the positive electrode active material reduced, and the electron conductivity of the positive electrode active material improved. This enables an increased cyclic capacity retention rate of the battery while simultaneously maintaining good conductivity of the electrolyte solution and charging performance of the battery.

[0007] In any embodiment, the I d / I g The value of the positive electrode active material is 0.6 to 1.5. In any embodiment, the I d / I gThe p-value of the positive electrode active material should be between 0.6 and 1.2. This improves the electron conductivity of the lithium iron phosphate-based material, reduces electron transfer resistance, and minimizes energy loss during charging. Furthermore, it promotes contact between the positive electrode active materials, ensuring sufficient contact points and thus leading to an overall increase in the energy efficiency of the secondary battery.

[0008] In various embodiments, the mass fraction of the cyclic ester compounds ranges from 5% to 25%, based on the total mass of the electrolyte solution. In other embodiments, the mass fraction of the cyclic ester compounds ranges from 5% to 20%, based on the total mass of the electrolyte solution. This further reduces the viscosity of the electrolyte solution, improves the liquid absorption capacity and internal wettability of the cell in the electrolyte solution, provides more ion conduction pathways, and increases the dessolvation capability of the active ions. This reduces the migration resistance of the active ions, resulting in an increased cyclic capacity retention rate of the battery.

[0009] In any embodiment, the cyclic carbonate compounds comprise one or more of ethylene carbonate, fluoroethylene carbonate, propylene carbonate, and γ-butyrolactone. The cyclic ester compounds exhibit good stability and a low tendency to decompose, readily dissociate the electrolyte salt in the electrolyte solution, and also contribute to reducing the polarization of the positive electrode active material and improving its electron conductivity.

[0010] The cyclic ester compounds include cyclic carbonate compounds. The cyclic carbonate compounds include one or more of ethylene carbonate, fluoroethylene carbonate, and propylene carbonate.

[0011] In any embodiment, the cyclic carbonate compounds comprise ethylene carbonate and propylene carbonate in a mass ratio of (1-7) : 1 and exhibit good compounding properties.

[0012] In any embodiment, the conductivity of the electrolyte solution is 9 mS / cm to 11 mS / cm, which promotes the migration of the active ions in the electrolyte solution.

[0013] In any embodiment, the lithium iron phosphate-based material comprises the structural formula shown in Formula I, Li x Fe y M z PO4 Form I where 0.95 < x < 1.05, 0.96 < y ≤ 1, 0 ≤ z < 0.04, M comprises one or more of Nb, Ti, V, W and Mn, and the molar content of element M in the positive electrode active material is 0.01% to 0.2%.

[0014] The positive electrode active material is characterized by high specific capacity, high safety, and a long cycle life. Doping the positive electrode active material with the element M in a suitable molar proportion can effectively reduce the transfer barrier for lithium ions, increase the lithium ion diffusion rate, and improve lithium ion migration.

[0015] In any embodiment, the length L, the height H, and the thickness T of the secondary battery are such that 200 mm ≤ L ≤ 550 mm, 150 mm ≤ H ≤ 250 mm, 60 mm ≤ T ≤ 80 mm, and 1 ≤ L / H ≤ 4 and 2 ≤ H / T ≤ 4. This not only enables the industrial manufacturability of the secondary battery but also, while simultaneously increasing battery capacity, shortens the electron transfer path, improves the current density uniformity, reduces the internal resistance of the secondary battery, and improves the energy efficiency and the cyclic capacity retention rate of the battery.

[0016] In any embodiment, the capacity of a single cell of the secondary battery is greater than or equal to 300 Ah and less than or equal to 1300 Ah, which helps to store more electrical energy and provide a longer cycle life of the secondary battery.

[0017] A second aspect of the present disclosure provides a power-consuming device comprising a secondary battery according to the first aspect. Brief description of the drawings Fig. Figure 1 is a schematic representation of a secondary battery of an embodiment of the present disclosure. Fig. 2 is an exploded view of the in Fig. 1 Secondary battery of the embodiment of the present disclosure shown. Fig. Figure 3 is a schematic representation of a battery module of an embodiment of the present disclosure. Fig.Figure 4 is a schematic representation of a battery pack of an embodiment of the present disclosure. Fig. 5 is an exploded view of the in Fig. 4 battery packs shown in an embodiment of the present disclosure. Fig. Figure 6 is a schematic representation of a power-consuming device that uses a secondary battery as a power source in an embodiment of the present disclosure. Reference symbol list:

[0018] 1. Battery pack; 2. Upper housing body; 3. Lower housing body; 4. Battery module; 5. Secondary battery; 51. Housing body; 52. Electrode assembly; 53. Cover plate. Detailed descriptions

[0019] The following describes in detail embodiments of a positive electrode active material and its manufacturing process, a positive electrode sheet, a secondary battery, a battery module, a battery pack, and a current-consuming device, which are specifically disclosed in the present disclosure, optionally with reference to the drawings. However, an unnecessarily detailed description can be omitted. For example, a detailed description of known facts and a repeated description of essentially the same structure can be omitted. This is to prevent the following description from becoming unnecessarily lengthy, thus facilitating understanding by those skilled in the art. Furthermore, the drawings and the following description serve to provide those skilled in the art with a complete understanding of the present disclosure and are not intended to limit the subject matter described in the claims.

[0020] The “range” disclosed in this disclosure is defined in terms of a lower bound and an upper bound. A given range is defined by selecting a lower bound and an upper bound. The selected lower bound and upper bound define the limits of the specific range. The ranges thus defined may or may not include the end values ​​and may be specified in any combination; that is, any lower bound can be combined with any upper bound to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, then ranges of 60 to 110 and 80 to 120 are also conceivable. Furthermore, if minimum range values ​​of 1 and 2 and maximum range values ​​of 3, 4, and 5 are listed, then all of the following ranges are conceivable: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5.In this disclosure, unless otherwise specified, a range of numbers "a to b" represents an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the range "0 to 5" means that all real numbers between "0 to 5" have been listed herein, and "0 to 5" is simply an abbreviation for these number combinations. Furthermore, when a particular parameter is specified as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0021] Unless otherwise stated, all embodiments and optional embodiments of the present disclosure can be combined to form a new technical solution.

[0022] Unless otherwise stated, all technical features and optional technical features of this disclosure can be combined to form a new technical solution.

[0023] Unless otherwise stated, all steps of this disclosure may be carried out sequentially or in any order, but preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) carried out sequentially, or that it may include steps (b) and (a) carried out sequentially. For example, when it is mentioned that the method may further include step (c), this means that step (c) may be added in any order. For example, the method may include steps (a), (b), and (c), or steps (a), (c), and (b), or steps (c), (a), and (b), etc.

[0024] Unless otherwise stated, the terms “comprise” and “contain” used in this disclosure may be interpreted as either open or closed. For example, the terms “comprise” and “contain” may mean that they may also include or contain other, unlisted components, or that they may only include or contain the listed components.

[0025] Unless otherwise specified, the term "or" in this disclosure means an inclusive "or". For example, the expression "A or B" means "A, B, or both A and B". More precisely, the condition "A or B" is satisfied if any of the following is true: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0026] With the steadily growing market demand for higher-capacity secondary batteries, the cell is evolving towards larger size and higher capacity. As the battery components become larger, the distance between the electrode plates and electrode tabs increases. This forces the electrons to travel a longer path to reach the external circuit. Consequently, the battery's DC resistance increases, and the current distribution becomes uneven. This negatively impacts the energy efficiency of secondary batteries, thereby affecting their overall performance and lifespan.

[0027] At the same time, the increased size of the battery components leads to a greater cell height. The electrolyte solution's ability to permeate upwards via capillary action is insufficient. Therefore, the electrolyte solution does not distribute evenly across the entire electrode sheet, particularly in the upper part of the cell. Consequently, the resistance during the intercalation and deintercalation process of the electrolyte's active ions increases, or lithium ion transfer ceases entirely. This significantly reduces the battery's energy efficiency, accelerates its capacity degradation, and shortens its cycle life. [Lithium secondary battery]

[0028] A first aspect of the present application proposes a secondary battery comprising, in particular, a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator arranged between the positive and negative electrode sheets. During the charging and discharging process of the battery, the active ions migrate between the positive and negative electrode sheets for intercalation and deintercalation, the electrolyte serving to conduct the ions between the positive and negative electrode sheets. The separator is arranged between the positive and negative electrode sheets and serves primarily to prevent a short circuit between the electrodes while simultaneously allowing ion permeability. In some embodiments, the secondary battery is a lithium secondary battery.

[0029] The present application does not impose any specific restrictions regarding the type of electrolyte, and the type can be selected according to the requirements. For example, the electrolyte can be liquid, gel-like, or completely solid. In some embodiments, the electrolyte is in the form of an electrolyte solution. The electrolyte solution comprises an electrolyte salt and a solvent.

[0030] In some embodiments, the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises a positive electrode active material. For example, the positive electrode current collector has two opposing surfaces in its own thickness direction, with the positive electrode film layer arranged on one or both of the two opposing surfaces of the positive electrode current collector.

[0031] In some embodiments, the positive electrode active material comprises a core of lithium iron phosphate-based material and a carbon shell layer with which at least partially coats the outer surface of the core, wherein the I d / I gThe positive electrode active material has a value of 0.2 to 1.5. The electrolyte solution contains cyclic ester compounds that do not exceed 25% of the total mass of the solvent in the electrolyte solution.

[0032] In this document, the term “I” refers to d “on the peak intensity of the D-peak.”

[0033] In this document, the term "D-peak" refers to the peak at 1360 ± 50 centimeters. -1 (cm -1 ) in the Raman spectrum analysis, which corresponds to a peak characteristic of lattice defects and disordered structures in the carbon shell layer with which the surface of the positive electrode active material is coated.

[0034] In this document, the term “I” refers to g “on the peak intensity of the G-peak.”

[0035] In this document, the term "G-peak" refers to the peak at 1580 ± 50 cm. -1in the Raman spectrum analysis, which corresponds to a peak characteristic of graphite and graphite-like structures in the carbon shell layer with which the surface of the positive electrode active material is coated.

[0036] In this document, the term “I” refers to d / I g “ on the ratio of the intensity of the D-peak to the intensity of the G-peak and is used to quantify the degree of graphitization of the positive electrode active material.

[0037] In the present document, the term “degree of graphitization” refers to the degree of graphitization of the carbon component, which reflects the degree of integrity of the graphite crystal structure, i.e., the degree of regularity of the arrangement of the carbon atoms in the graphite structure, in the carbon-coated lithium iron phosphate, in particular in the carbon coating layer of the present disclosure.

[0038] Graphite crystals exhibit a layered structure in which electrons can move freely between the layers, resulting in the high conductivity of graphite. The higher the degree of graphitization of the positive electrode active material, the closer the arrangement of carbon atoms on the material's surface is to the ideal graphite crystal structure, the more complete the layered structure within the material, the shorter the electron transfer path, and the higher the electron mobility and conductivity of the material. This contributes to improving the electron conductivity of the positive electrode active material and reducing electron transfer resistance and energy loss. The setting of the I d / I gMaintaining a suitable pH value for the positive electrode active material helps improve its electronic conductivity and provides sufficient contact points between the particles of the positive electrode active material. Uniform distribution of the positive electrode active material across the positive electrode sheet creates a continuous conductive network within the positive electrode sheet, which reduces powder film resistance and interfacial impedance, lowers the cell's DC resistance, reduces energy loss during charging, and consequently improves the battery's energy efficiency.

[0039] In this document, the term “cyclic ester compounds” refers to organic compounds containing an ester group (-C(=O)O-) that is involved in the formation of a ring.

[0040] The cyclic ester compounds exhibit a relatively high dielectric constant and can therefore increase the solubility of the electrolyte salt and effectively stabilize and solvate the electrolyte salt ions. It is generally assumed that a high proportion of cyclic ester compounds in the electrolyte solution can lead to increased conductivity of the electrolyte solution, which improves the liquid-phase transfer capability and charging performance of the secondary battery. However, the cyclic ester compounds exhibit poor performance at low temperatures. In the present application, it was found that by controlling the degree of graphitization of the positive electrode active material in combination with reducing the mass ratio of the cyclic ester compounds in the electrolyte solution to a maximum of 25%, the secondary battery still exhibits excellent liquid-phase transfer capability and charging performance.Regardless of theoretical limitations, this could be due to the high viscosity of cyclic ester compounds: A high concentration of these compounds can impair the wetting of the electrode sheet by the electrolyte solution, deteriorate liquid-phase transfer, and reduce charging performance. Furthermore, the dessolvation capacity of the electrolyte salt ions is reduced, which adversely affects the charging and cycle life of the battery. Reducing the proportion of cyclic ester compounds in the electrolyte solution enables sufficient wetting of the cell by the electrolyte solution, reduces the polarization of the positive electrode active material, and improves the electron conductivity of the positive electrode active material.At the same time, this contributes to providing more ion pathways for the cell, improving the dessolvation capacity of the electrolyte salt ions, and reducing the migration resistance of the active ions. Through the synergistic adaptation of the I. d / I g By increasing the value of the positive electrode active material, the electron conductivity can be further improved, which improves the liquid phase transfer capability and the overall charging performance of the secondary battery, while also contributing to the improvement of the low-temperature charging performance of the secondary battery.

[0041] For the measurement of I d / I gAny method known in engineering can be used to determine the value. As an example, and with reference to GB / T 40219-2021, the powder of the positive electrode active material is pressed into a tablet. The tablet is then measured using a LabRAM HR Evolution laser micro-Raman spectrometer, with measurements taken at three randomly selected points on the tablet and the mean of the three measurements calculated. A solid-state laser with a wavelength of 523 nanometers (nm), a beam diameter of 1.2 micrometers (µm), and a power of 1 milliwatt (mW) is used as the light source. The measurement is performed in macro-Raman mode using a CCD detector.

[0042] In some embodiments, the I d / I g The value of the positive electrode active material is 0.6 to 1.5. In some embodiments, the I d / I gThe value of the positive electrode active material is 0.6 to 1.2. In some embodiments, the I d / I g The value of the positive electrode active material is 0.9 to 1.2. In some embodiments, the I d / I g -Value of the positive electrode active material 0.2 to 1.4, 0.2 to 1.2, 0.2 to 1.0, 0.2 to 0.8, 0.2 to 0.6, 0.2 to 0.4, 0.4 to 1.5, 0.6 to 1.5, 0.8 to 1.5, 1.0 to 1.5, 0.9 to 1.0, 1.0 to 1.1, 1.1 to 1.2.

[0043] In some embodiments, the I d / I g -Value of the positive electrode active material 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, or lies in a range between any two of the above values ​​or is any value within these ranges.

[0044] The I d / I gThe value is within a suitable range, which helps to obtain a positive electrode active material with a high degree of graphitization, further improving the electronic conductivity of the positive electrode active material, reducing the internal resistance of the battery, decreasing energy loss during charging, and providing sufficient contact points between the particles of the positive electrode active material, thereby building a good conductive network and improving the energy efficiency of the secondary battery.

[0045] In some embodiments, the lithium iron phosphate-based material comprises the structural formula shown in Formula I, Li x Fe y M z PO4 Form I where 0.95 < x < 1.05, 0.96 < y ≤ 1, 0 ≤ z < 0.04,

[0046] In some embodiments, M comprises one or more of Nb, Ti, V, W, Mn.

[0047] In some embodiments, the element M is selected from Nb, Ti, V or W.

[0048] In some embodiments, the molar content of element M in the positive electrode active material is 0.01% to 0.2%.

[0049] Lithium iron phosphate-based materials are characterized by high specific capacity, high safety, and a long cycle life, but exhibit relatively low intrinsic conductivity. Doping with the element M in a suitable molar proportion can increase the concentration of free electrons in the lithium iron phosphate crystal lattice, reduce the transfer barrier for lithium ions, increase the migration rate of lithium ions, and consequently improve lithium ion conductivity.

[0050] The positive electrode active material can be produced using conventional techniques. In some embodiments, the process for producing the positive electrode active material comprises the following steps: providing a lithium iron phosphate substrate, mixing a lithium source, an iron source, a phosphorus source, a magnesium source, and a carbon source in a specific ratio, ball milling, drying the ball-milled powder, and sintering, thereby producing a carbon-coated lithium iron phosphate positive electrode active material.

[0051] In some embodiments, the lithium source comprises one or more of Li2CO3, LiH2PO4, Li3PO4.

[0052] In some embodiments, the iron source comprises one or more of FeSO4, FePO4, FeCl2, FeC2O4, Fe2O3.

[0053] In some embodiments, the phosphorus source comprises one or more of NH4H2PO4, H3PO4.

[0054] In some embodiments, the M source comprises one or more of metal salts, metal oxides and organometallic compounds containing the elements Nb, Ti, V, W or Mn.

[0055] In some embodiments, the carbon source comprises one or more of glucose, sucrose, starch, polyethylene glycol, phenolic resin, carbon black, graphite, carbon nanotube, graphene, tannic acid, sodium dodecylbenzenesulfonate.

[0056] In some embodiments, the sintering temperature is 500 degrees Celsius (°C) to 900 °C and the sintering time is 8 hours to 20 hours.

[0057] In some embodiments, the sintering temperature is 500 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, 900 °C, or lies in a range between any two of the above values ​​or is any value within these ranges.

[0058] In some embodiments, the sintering time is 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, or lies in a range between any two of the above values ​​or is any value within these ranges.

[0059] In some embodiments, the Dv50 value of the positive electrode active material is 300 µm to 3570 µm.

[0060] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used as the metal foil. The composite current collector can comprise a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on the polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0061] In some embodiments, the positive electrode film layer optionally comprises a binder. For example, the binder may comprise at least one of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin.

[0062] In some embodiments, the positive electrode film layer optionally further comprises a conductive material. For example, the conductive material may comprise at least one of superconducting carbon, carbon black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0063] In some embodiments, the positive electrode sheet can be produced as follows: The above-mentioned components for producing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, are dispersed in a solvent (such as N-methyl-2-pyrrolidone) to form a positive electrode paste; the positive electrode current collector is coated with the positive electrode paste, and after drying, cold pressing, and other processes, the positive electrode sheet can be obtained.

[0064] In some embodiments, the mass fraction of the cyclic ester compounds is 5% to 25%, based on the total mass of the electrolyte solution. In some embodiments, the mass fraction of the cyclic ester compounds is 5% to 20%, based on the total mass of the electrolyte solution. In some embodiments, the mass fraction of the cyclic ester compounds is 8% to 20%, 10% to 20%, 12% to 20%, 14% to 20%, 16% to 20%, or 18% to 20%, based on the total mass of the electrolyte solution.

[0065] In some embodiments, the mass fraction of the cyclic ester compounds is 5%, 8%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, based on the total mass of the electrolyte solution, or lies in a range between any two of the above values ​​or is any value within these ranges.

[0066] The proportion of cyclic ester compounds in the specified range promotes a reduction in the viscosity of the electrolyte solution and an increase in the cell's fluid absorption capacity. This ensures sufficient wetting of the cell with the electrolyte solution, reduces the polarization of the lithium iron phosphate-based active material, and improves the ion conduction pathways. Simultaneously, sufficient dissociation of the electrolyte salt in the electrolyte solution is promoted, resulting in reduced migration resistance of the active ions while maintaining good conductivity. The secondary battery thus exhibits not only good charging performance but also a further improved cyclic capacity retention rate and enhanced low-temperature charging performance.

[0067] In some embodiments, the cyclic ester compounds comprise one or more of ethylene carbonate, fluoroethylene carbonate, propylene carbonate and γ-butyrolactone.

[0068] The cyclic ester compounds include cyclic carbonate compounds. The cyclic carbonate compounds include one or more of ethylene carbonate, fluoroethylene carbonate, and propylene carbonate.

[0069] The cyclic ester compounds exhibit good chemical stability within the battery's operating voltage range and do not tend to decompose at the electrode surface. This contributes to maintaining the stability of the electrolyte solution and to the battery's long cycle life. Furthermore, the cyclic ester compounds have a high dielectric constant and can therefore readily dissociate the electrolyte salt in the electrolyte solution. Simultaneously, they reduce the polarization of the positive electrode active material and improve its electron conductivity as well as the transfer of active ions.

[0070] In some embodiments, the cyclic ester compounds comprise ethylene carbonate and propylene carbonate in a volume ratio of (1-7) : 1. In some embodiments, the cyclic ester compounds comprise ethylene carbonate and propylene carbonate in a volume ratio of (0.5-2) : 1. For example, the mass ratio of ethylene carbonate and propylene carbonate in the electrolyte solution may be 0.5 : 1, 0.8 : 1, 1 : 1, 1.5 : 1, 2 : 1, 3 : 1, 4 : 1, 5 : 1, 6 : 1, 7 : 1.

[0071] In some embodiments, the electrolyte solution also comprises an electrolyte salt. In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluorobisoxalatophosphate, and lithium tetrafluoro(oxalato)phosphate.

[0072] In some embodiments, the electrolyte solution comprises, in addition to the cyclic ester compounds, a solvent which may be selected, for example, from at least one of ethylene dicarbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0073] In some embodiments, the electrolyte solution optionally includes an additive. For example, the additive may include an additive for film formation on the negative electrode, an additive for film formation on the positive electrode, and an additive that can improve certain battery performance characteristics, such as an additive that improves the battery's overcharge behavior, an additive that improves the battery's high-temperature performance, and an additive that improves the battery's low-temperature performance.

[0074] In some embodiments, the conductivity of the electrolyte solution is 9 millisiemens per centimeter (mS / cm) to 11 mS / cm, e.g. 9 mS / cm, 9.5 mS / cm, 10 mS / cm, 10.5 mS / cm, 11 mS / cm, which promotes the migration of active ions in the electrolyte solution.

[0075] In some embodiments, the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material.

[0076] As an example, the negative electrode current collector has two opposing surfaces in its own thickness direction, with the negative electrode film layer being arranged on one or both of these opposing surfaces of the negative electrode current collector.

[0077] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, copper foil can be used as the metal foil. The composite current collector can comprise a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on the polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0078] In some embodiments, the negative electrode active material comprises, but is not limited to, one or more of conventional natural graphite, other synthetic graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate. The silicon-based material may comprise one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material. The tin-based material may comprise one or more of elemental tin, tin oxide, and tin alloy. However, the present disclosure is not limited to these materials, and other conventional materials suitable for use as a negative electrode active material for a battery may also be used. This negative electrode active material may be used alone or in combination with two or more.

[0079] In some embodiments, the negative electrode film layer optionally comprises a binder. The binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0080] In some embodiments, the negative electrode film layer optionally further comprises a conductive material. The conductive material can be selected from at least one of superconducting carbon, carbon black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0081] In some embodiments, the negative electrode film layer may optionally also include other excipients, such as a thickening agent (such as sodium carboxymethylcellulose (CMC-Na)).

[0082] In some embodiments, the negative electrode sheet can be produced as follows: The above-mentioned components for producing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode paste; the negative electrode current collector is coated with the negative electrode paste, and after drying, cold pressing, and other processes, the negative electrode sheet, comprising a negative electrode film layer, can be obtained.

[0083] In some embodiments, the secondary battery also includes a separator. The present disclosure does not impose any particular restrictions on the type of separator, and any known separator with good chemical and mechanical stability and a porous structure may be used.

[0084] In some embodiments, the separator material can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film without any particular restriction. If the separator is a multi-layer composite film, the materials of each layer can be the same or different without any particular restriction.

[0085] In some embodiments, the positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode arrangement by a winding or stacking process.

[0086] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the aforementioned electrode arrangement and the electrolyte solution.

[0087] In some embodiments, the outer packaging of the secondary battery can be a rigid casing, such as a hard plastic casing, an aluminum casing, a steel casing, etc. The outer packaging of the secondary battery can also be a soft casing, such as a bag-like soft casing. The material of the soft casing can be plastic. Examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0088] The present disclosure does not impose any particular restrictions regarding the shape of the secondary battery; it may be cylindrical, rectangular, or have any other shape. In some embodiments, the secondary battery is square. For example, shows Fig. 1 as an example a secondary battery 5 with a square structure, where the length of the secondary battery is L, the height is H and the thickness is T.

[0089] In some embodiments, 200 millimeters (mm) ≤ L ≤ 550 mm, 150 mm ≤ H ≤ 250 mm, 60 mm ≤ T ≤ 80 mm, as well as 1 ≤ L / H ≤ 4 and 2 ≤ H / T ≤ 4.

[0090] In some embodiments, the length L of the secondary battery is 200 mm, 300 mm, 350 mm, 400 mm, 450 mm, 500 mm, 550 mm, or lies in a range between any two of the above values ​​or is any value within these ranges.

[0091] In some embodiments, the height H of the secondary battery is 150 mm, 200 mm, 205 mm, 210 mm, 215 mm, 220 mm, 225 mm, 230 mm, 235 mm, 240 mm, 245 mm, 250 mm, or lies in a range between any two of the above values ​​or is any value within these ranges.

[0092] In some embodiments, the thickness T of the secondary battery is 60 mm, 65 mm, 70 mm, 75 mm, 80 mm, or lies in a range between any two of the above values ​​or is any value within these ranges.

[0093] In some embodiments, the L / H ratio of the secondary battery is 1, 1.5, 2, 2.5, 3, 3.5, 4, or lies in a range between any two of the above values, or is any value within these ranges.

[0094] In some embodiments, the H / T ratio of the secondary battery is 2, 2.5, 3, 3.5, 4, or lies in a range between any two of the above values, or is any value within these ranges.

[0095] Increasing the size of the battery components leads to a longer electron transfer path in the electrode sheet to the electrode tab, further exacerbating the current density inconsistency. By controlling the size of the secondary battery cell components within a specific range, the electron transfer path can be shortened and the wettability of the electrolyte solution in the upper region of the electrode sheet can be improved. This reduces the current density inconsistency, lowers the battery's internal resistance, and contributes to increased energy efficiency, higher battery capacity, and extended cycle life. Simultaneously, the industrial manufacturability of the secondary battery with the described dimensions is ensured.

[0096] In some embodiments, the outer packaging of the battery, referring to Fig.2, comprising a housing body 51 and a cover plate 53. The housing body 51 may comprise a base plate and a side plate connected to the base plate, the base plate and the side plate forming a receiving chamber. The housing body 51 has an opening that communicates with the receiving chamber, and the cover plate 53 may cover the opening to close the receiving chamber. The positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly 52 by a winding or stacking process. The electrode assembly 52 is encapsulated in the receiving chamber. The electrolyte solution is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 may be one or more; the person skilled in the art may choose according to specific actual requirements.

[0097] In some embodiments, the capacity of a single cell of the secondary battery is greater than or equal to 300 ampere-hours (Ah) and less than or equal to 1300 Ah.

[0098] In some embodiments, the capacity of a single cell of the secondary battery is 300 Ah, 400 Ah, 450 Ah, 500 Ah, 550 Ah, 600 Ah, 650 Ah, 700 Ah, 750 Ah, 800 Ah, 850 Ah, 900 Ah, 950 Ah, 1000 Ah, 1050 Ah, 1100 Ah, 1150 Ah, 1200 Ah, 1250 Ah, 1300 Ah, or lies in a range between any two of the above values ​​or is any value within these ranges.

[0099] In this document, the term "capacity of a single cell" refers to the maximum amount of charge that can be stored in a single battery unit (cell).

[0100] The capacity of a single cell can be tested using devices and methods known in engineering. For example, the manufactured secondary battery is charged at 25 °C with a cycle rate of 0.5 P (i.e., the charge rate and discharge rate are each 0.5 P) and a charging voltage of 2.5 volts (V) to 3.65 V. This process constitutes a charge and discharge cycle. The discharge capacity value recorded during the cycle corresponds to the capacity of a single cell of the secondary battery.

[0101] A secondary battery with a high-capacity single cell can store more electrical energy and offer a longer lifespan. Setting the capacity of a single cell in the secondary battery within a suitable range helps optimize the charge and discharge rate, reduce chemical reaction losses within the battery, and extend the battery's cycle life.

[0102] The secondary battery provided by this application can be used for grid-side energy storage (e.g., large energy storage devices) and for user-side energy storage (e.g., commercial and industrial energy storage devices, energy storage devices for private households). For example, the secondary battery can be used as a photovoltaic charging station, as a microgrid, or as an emergency power generator for factories, shopping centers, hospitals, or schools. A secondary battery with a high capacity per cell can store more electrical energy, which helps to improve the cycle performance and service life of the secondary battery and reduce power plant costs, thus taking into account the capacity, performance, manufacturing, and operating costs of the secondary battery.

[0103] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The exact number can be selected by a person skilled in the art depending on the application and capacity of the battery module.

[0104] Fig. Figure 3 shows an example of a battery module 4. Referring to Fig. 3. Several secondary batteries 5 can be arranged one after the other in the battery module 4 along its length. Of course, other arrangements are also possible. Furthermore, the multiple secondary batteries 5 can be secured by fastening elements.

[0105] Optionally, the battery module 4 can also include a housing with a receiving space, in which the multiple secondary batteries 5 are received.

[0106] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, wherein the number of battery modules contained in the battery pack can be one or more; the person skilled in the art can select a specific number depending on the application and capacity of the battery pack.

[0107] The Fig. 4 and Fig. Figure 5 shows, as an example, a battery pack 1. Referring to the Fig. 4 and Fig. 5. The battery pack 1 can comprise a battery box and several battery modules 4 arranged therein. The battery box comprises an upper box body 2 and a lower box body 3; the upper box body 2 can cover the lower box body 3 and form an enclosed space for receiving the battery modules 4. The multiple battery modules 4 can be arranged in any way within the battery box.

[0108] Furthermore, the present disclosure provides a power-consuming device comprising at least one of the secondary batteries, battery modules, or battery packs provided by the present disclosure. The secondary battery, battery module, or battery pack can be used as a power source for the power-consuming device or as an energy storage device for the power-consuming device. The power-consuming devices may include, but are not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0109] The secondary battery, battery module or battery pack can be selected as needed for the power-consuming device.

[0110] Fig. Figure 6 shows an example of a power-consuming device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the power-consuming device's requirements for high power and high energy density of the secondary battery, a battery pack or battery module can be used.

[0111] As another example, the device could be a mobile phone, a tablet, a laptop, etc. The device typically needs to be lightweight and thin and can use a secondary battery as a power source. Examples of implementation

[0112] The following are exemplary embodiments of the present disclosure. These embodiments are for illustrative purposes only and should not be construed as limiting the present disclosure. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the technical literature or product instructions must be followed. All reagents and instruments used without manufacturer information are commercially available products. I. Performance Test Method 1. Test of the Degree of Graphitization I d / I g of the positive electrode active material

[0113] Following GB / T 40219-2021, the powder of the positive electrode active material was pressed into a tablet. The tablet was then measured using a LabRAM HR Evolution laser micro-Raman spectrometer. Measurements were taken at three randomly selected points on the tablet, and the mean of the three measurements was calculated. A solid-state laser with a wavelength of 523 nm, a beam diameter of 1.2 µm, and a power of 1 mW was used as the light source. The measurement was performed in macro-Raman mode using a CCD detector. 2. Capacity of a cell

[0114] At 25 °C, the manufactured secondary battery was charged with a cycle rate of 0.5 P (i.e., the charge rate and discharge rate were each 0.5 P) and a charging voltage of 2.5 V to 3.65 V. This process constituted a charge and discharge cycle. The discharge capacity value recorded during the cycle corresponded to the capacity of one cell of the secondary battery. 3. Conductivity test of the electrolyte solution

[0115] Referring to the conductivity test method specified in HG / T 4067-2015: Approximately 100 mL of the electrolyte solution was taken using a dry, clean, corrosion-resistant sample bottle, sealed, placed in a thermostatic bath at 25 °C ± 0.5 °C, and shaken occasionally. Once the sample temperature had stabilized, the bottle cap was replaced with a stopper into which the electrode of the conductivity meter was inserted. As soon as the temperature remained within the range of 25 °C ± 0.5 °C, the conductivity meter readings were taken, representing the conductivity of the sample. 4. Battery energy efficiency test at a rate of 0.5 P

[0116] At 25 °C and atmospheric pressure, the manufactured secondary battery was discharged to 2.5 V at a constant power of 0.5 P and left to rest for 30 minutes. It was then charged to 3.65 V at a constant power of 0.5 P, with the energy absorbed (E1) recorded, and left to rest again for 30 minutes. Finally, it was discharged to 2.5 V at a constant power of 0.5 P, with the energy released (E2) recorded. The energy efficiency of the cell at a rate of 0.5 P is then calculated as E2 / E1 × 100%. 5. Testing the battery's cyclic capacity retention rate

[0117] At 25°C, the manufactured secondary battery was charged with a cycle rate of 0.5 P (i.e., the charge and discharge rates were each 0.5 P) and a charging voltage of 2.5 V to 3.65 V. This process constituted a charge and discharge cycle. The discharge capacity C1 during the first cycle was recorded. This charge-discharge cycle was repeated 1000 times, after which the test was terminated and the capacity retention rate after the cycles was calculated. The capacity retention rate for 1000 cycles at 25°C is: Capacity retention rate after the 1000th cycle = (Discharge capacity after the 1000th cycle / Discharge capacity at the first cycle) × 100%. 6. Charging time test

[0118] The test battery underwent an initial charge and discharge cycle at a current of 1C (i.e., the current rate at which the theoretical capacity was completely discharged within 1 hour). Specifically, this involved: at 35°C, the battery was charged at a constant current of 1C to a voltage of 3.65V, then continued charging at a constant voltage until the current dropped to ≤ 0.05C, left to rest for 5 minutes, and finally discharged at a constant current of 0.33C to a voltage of 2.5V. Its actual capacity was recorded as C0. Subsequently, each battery was successively charged with a constant current of 0.5 C0-, 1.0 C0-, 1.3 C0-, 1.5 C0-, 1.8 C0-, 2.0 C0-, 2.3 C0-, 2.5 C0-, 3.0 C0-, 3.5 C0-, 4 C0-, 4.5 C0- and 5 C0-rate until the final charging voltage of 3.65 V of the full cell system or a negative electrode final potential of 0 V (whichever was reached first).After each charging cycle, the battery had to be discharged at 1 C0 to the discharge cut-off voltage of 2.5 V for the full-cell system. The negative electrode potentials that occurred when reaching 10%, 20%, 30%, ... up to 80% SOC (state of charge) were recorded at the various charging rates. Charging rate-negative potential curves were plotted for different SOC states. After linear fitting, the charging rates at which the negative electrode potential was 0 V for the various SOC states were determined. These charging rates represented the charging window for the respective SOC state and were designated C(10% SOC), C(20% SOC), C(30% SOC), C(40% SOC), C(50% SOC), C(60% SOC), C(70% SOC), and C(80% SOC). The charging time T (in minutes) of the battery from 0 to 80% SOC was calculated according to the formula (60 / C(10% SOC) + 60 / C(20% SOC) + 60 / C(30% SOC) + 60 / C(40% SOC) + 60 / C(50% SOC) + 60 / C(60% SOC) + 60 / C(70% SOC) + 60 / C(80% SOC)) × 10%.The shorter the charging time, the higher the charging power. II. Production of the positive electrode active material

[0119] Sucrose and polyethylene glycol (PEG) with a molecular weight of 3000 were used as carbon sources, and the mass ratio of sucrose to PEG was adjusted according to Table 1. Iron phosphate was used as the iron and phosphorus source, monoammonium phosphate as the phosphorus source, and lithium carbonate as the lithium source. These were mixed in a molar ratio of Li:Fe:P = 1.01 : 1 : 1.04 and with a carbon content in the final product of 1.20% until a homogeneous mixture was obtained. The starting materials were finely milled in a sand mill until the particle size Dv50 of the suspension was 0.38 ± 0.01 µm and then spray-dried. The spray-dried material was sintered for 12 hours at 800 °C under a nitrogen atmosphere. After natural cooling, it was ground into a powder with a Dv50 of 1.4 ± 0.2 µm by jet milling, yielding lithium iron phosphate materials with different Id / Ig values. III. Production of the secondary battery (Example 11) Production of the positive electrode sheet

[0120] The prepared positive electrode active material, with an Id / Ig ratio of 1.01, the conductive agent Super P, and the binder polyvinylidene fluoride were mixed in a mass ratio of 96.5:1.5:2. The solvent N-methyl-2-pyrrolidone was then added and stirred uniformly to obtain the positive electrode paste. The aluminum foil of the positive electrode current collector was uniformly coated with this positive electrode paste. After drying, cold pressing, and cutting, the positive electrode sheet was obtained. The one-sided coating weight of the positive electrode film layer was 21.7 mg / cm². 2 . 2) Production of the negative electrode sheet

[0121] The negative electrode active material graphite, the conductive agent Super P, the dispersant sodium carboxymethylcellulose, and the binder styrene-butadiene rubber were mixed in a mass ratio of 96:0.7:1.0:2.3. Deionized water was then added as a solvent and stirred thoroughly to obtain a negative electrode paste. This paste was applied evenly to the copper foil of the negative electrode current collector. After drying, cold pressing, and cutting, the negative electrode sheet was obtained. The single-sided coating weight of the negative electrode film layer was 9.7 mg / cm². 2 . 3) Preparation of the electrolyte solution

[0122] In a glovebox with an argon atmosphere and a water content of < 10 ppm, ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and ethylene dicarbonate (VC) were mixed in a ratio of 15 : 53 : 30 : 2 to obtain an organic solvent, and then LiPF6 was dissolved in the above organic solvent at a concentration of 1.1 mol / L to obtain an electrolyte solution with a conductivity of 10.2 mS / cm. 4) Separator

[0123] A polypropylene film was selected as the separator. 5) Production of the secondary battery

[0124] The aforementioned positive electrode sheet, the separator, and the negative electrode sheet were stacked sequentially. The separator was positioned between the positive and negative electrode sheets to provide insulation, and an electrode assembly was formed by winding. The electrode assembly was placed in an outer packaging shell (length × height × thickness: 350 mm × 210 mm × 70 mm). After drying, the electrolyte solution was injected, and a lithium-ion battery with a capacity of 587 Ah was obtained through vacuum sealing, standing, formation, calibration, etc. Examples 2 to 13

[0125] Exemplary embodiments 2 to 5 had a manufacturing process similar to that of exemplary embodiment 1, but differed in the use of positive electrode active material with different Id / Ig values.

[0126] Exemplary embodiments 6 to 11 featured a manufacturing process similar to that of exemplary embodiment 1, but differed in the type or proportion of solvents in the electrolyte solution. The amount of DMC in the electrolyte solution was also adjusted accordingly.

[0127] Exemplary embodiments 12 to 13 had a manufacturing process similar to that of exemplary embodiment 1, but differed in the adjustment of the cell capacity and the battery dimensions. Comparative examples 1 to 2

[0128] Comparative example 1 had a manufacturing process similar to that of embodiment 1, but differed in the use of positive electrode active material with different Id / Ig values.

[0129] Comparative example 2 had a manufacturing process similar to that of embodiment 1, but differed in that the proportion of ethylene carbonate in the electrolyte solution was adjusted to 40%. The amount of DMC in the electrolyte solution was adjusted accordingly.

[0130] The specific manufacturing parameters for embodiments 1 to 13 and for comparison examples 1 to 2 can be found in Table 2. Table 2 Serial number material electrolyte solution Battery dimensions ID / Ig Carbonate solvents Mass fraction in the solvent Conductivity (in mS / cm) Length (L) (in mm) Height (H) (in mm) Thickness (T) (in mm) L / H H / T Example 1 1,01 EC 15 % 10,2 350 210 70 1,7 3,0 Example 2 0,68 EC 15 % 10,2 350 210 70 1,7 3,0 Example 3 0,91 EC 15 % 10,2 350 210 70 1,7 3,0 Example 4 1,15 EC 15 % 10,2 350 210 70 1,7 3,0 Example 5 1,45 EC 15 % 10,2 350 210 70 1,7 3,0 Example 6 1,01 EC 25 % 10,2 350 210 70 1,7 3,0 Example 7 1,01 EC 20 % 10,8 350 210 70 1,7 3,0 Example 8 1,01 EC 10 % 9,7 350 210 70 1,7 3,0 Example 9 1,01 EC 5 % 9,3 350 210 70 1,7 3,0 Example 10 1,01 PC 15 % 10,0 350 210 70 1,7 3,0 Example 11 1,01 EC + PC 10%+10% 10,7 350 210 70 1,7 3,0 Example 12 1,01 EC 15 % 10,2 550 240 75 2,3 3,2 Example 13 1,01 EC 15 % 10,2 203 173 70 1,2 2,5 Comparative example 1 1,7 EC 15 % 10,2 350 210 70 1,7 3,0 Comparative example 2 1,01 EC 40 % 11,6 350 210 70 1,7 3,0 EC: ethylene carbonate; PC: propylene carbonate

[0131] The performance of the secondary batteries in embodiments 1 to 13 and comparison examples 1 to 2 was tested using the method described under "Performance Test Method". The results are shown in Table 3. Table 3 Serial number Cell capacity (in Ah) Loading time (in minutes) Energy efficiency of the cell at a rate of 0.5 P Capacity retention rate after 1000 cycles at 25 °C Example 1 587 20,9 93,9 % 95,1 % Example 2 587 20,7 94,3 % 95,2 % Example 3 587 20,8 94,1 % 95,2 % Example 4 587 21,5 92,6 % 94,9 % Example 5 587 21,7 92,2 % 94,5 % Example 6 587 21,5 93,6 % 93,7 % Example 7 587 21,1 93,4 % 94,7 % Example 8 587 20,9 93,9 % 95,7 % Example 9 587 21,1 93,9 % 95,8 % Example 10 587 20,9 93,8 % 95,0 % Example 11 587 21,2 93,9 % 94,4 % Example 12 1132 21,2 93,4 % 94,4 % Example 13 314 21,2 94,9 % 95,3 % Comparative example 1 587 21,9 91,8 % 93,5 % Comparative example 2 314 22,0 93,4 % 92,7 %

[0132] By comparing embodiments 1 to 13 with comparative example 1, it can be determined that in the case of an I d / I g With a positive electrode active material value in the range of 0.2 to 1.5 and a mass fraction of cyclic ester compounds in the electrolyte solution between 5% and 25%, the charging time of the secondary batteries is significantly reduced, and energy efficiency and the cyclic capacity retention rate after 1000 cycles are significantly improved. This demonstrates that the secondary battery exhibits good charging performance and cycle stability, which improves the battery's lifespan.

[0133] By comparing embodiments 1 to 5 with comparative example 1, it can be determined that in the case of an I d / I gWith a value of 0.6 to 1.5 for the positive electrode active material, the electron conductivity of the positive electrode active material is improved and the internal resistance of the battery is reduced. The secondary battery not only exhibits good charging performance but also significantly higher energy efficiency and, consequently, an improved cyclic capacity retention rate after 1000 cycles. At an I d / I g With a positive electrode active material value of 0.6 to 1.2, the secondary battery combines excellent charging performance, high energy efficiency and an excellent cyclic retention rate.

[0134] By comparing embodiments 6 to 9 with comparative example 2, it can be seen that when the electrolyte solution contains cyclic ester compounds comprising 5% to 25% of the total mass of the solvent in the electrolyte solution, the charging time of the secondary battery is significantly reduced, the capacity retention rate is considerably increased, and the energy efficiency is noticeably improved. This demonstrates that the secondary battery exhibits good charging performance and a high cyclic capacity retention rate. A mass fraction of cyclic ester compounds in the electrolyte solution of 5% to 20% can further increase the charging performance and the cyclic capacity retention rate of the battery.

[0135] Examples 10 and 11 show that the use of propylene carbonate in the electrolyte solution or the combination of ethylene carbonate with propylene carbonate ensures excellent charging performance, high energy efficiency and excellent cyclic capacity retention rate.

[0136] Examples 12 and 13 show that even after adjusting its capacity to 314 Ah to 1132 Ah, the secondary battery continues to have excellent charging performance, high energy efficiency and excellent cyclic capacity retention rate.

[0137] It should be noted that the present disclosure is not limited to the embodiments mentioned above. The above embodiments are merely examples, and all embodiments that exhibit essentially the same structure and effect as the technical idea within the technical solution of the present disclosure are all included within the technical scope of the present disclosure. Furthermore, other possibilities in which various modifications conceivable to a person skilled in the art are added to the embodiments, and some components of the embodiments are combined to form other embodiments, are also included within the scope of the present disclosure without departing from the core of the present disclosure. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] CN 202411310454.9

[0001]

Claims

[1] Secondary battery, characterized by , that it comprises an electrolyte solution and a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode active material, the positive electrode active material comprising a core of lithium iron phosphate-based material and a carbon shell layer with which at least partially coats the outer surface of the core, wherein in the Raman spectrum of the positive electrode active material the peak intensity at the wavenumber of 1360 ± 50 cm⁻¹ -1 as I d and the peak intensity at a wavenumber of 1580 ± 50 cm -1 as I g is, where the I d / I g The positive electrode active material has a value of 0.2 to 1.5, wherein the electrolyte solution comprises cyclic ester compounds that do not exceed 25% of the total mass of the solvent in the electrolyte solution. [2] Secondary battery according to claim 1, characterized by , that the Id / I g The value of the positive electrode active material is 0.6 to 1.

5. [3] Secondary battery according to claim 1 or 2, characterized by , that the I d / I g The value of the positive electrode active material is 0.6 to 1.

2. [4] Secondary battery according to any one of claims 1 to 3, characterized by , that the mass fraction of the cyclic ester compounds is 5% to 25%, based on the total mass of the electrolyte solution. [5] Secondary battery according to any one of claims 1 to 4, characterized by , that the mass fraction of the cyclic ester compounds is 5% to 20%, based on the total mass of the electrolyte solution. [6] Secondary battery according to any one of claims 1 to 5, characterized by , that the cyclic ester compounds comprise one or more of ethylene carbonate, fluoroethylene carbonate, propylene carbonate and γ-butyrolactone. [7] Secondary battery according to any one of claims 1 to 6, characterized by, that the cyclic ester compounds comprise cyclic carbonate compounds, wherein the cyclic carbonate compounds comprise one or more of ethylene carbonate, fluoroethylene carbonate and propylene carbonate. [8] Secondary battery according to any one of claims 1 to 7, characterized by , that the cyclic ester compounds comprise ethylene carbonate and propylene carbonate in a mass ratio of (1-7) :

1. [9] Secondary battery according to any one of claims 1 to 8, characterized by , that the conductivity of the electrolyte solution is 9 mS / cm to 11 mS / cm. [10] Secondary battery according to any one of claims 1 to 9, characterized by , that the lithium iron phosphate-based material comprises the structural formula shown in Formula I, Li x Fe y M z PO4 Form I where 0.95 < x < 1.05, 0.96 < y ≤ 1.0 ≤ z < 0.04, M comprises one or more of Nb, Ti, V, W and Mn and the molar content of element M in the positive electrode active material is 0.01% to 0.2%. [11] Secondary battery according to any one of claims 1 to 10, characterized by , that the length of the secondary battery is L, the height is H and the thickness is T, where 200 mm ≤ L ≤ 550 mm, 150 mm ≤ H ≤ 250 mm, 60 mm ≤ T ≤ 80 mm, and 1 ≤ L / H ≤ 3 and 2 ≤ H / T ≤ 4. [12] Secondary battery according to any one of claims 1 to 11, characterized by that the capacity of a single cell of the secondary battery is greater than or equal to 300 Ah and less than or equal to 1300 Ah. [13] Power-consuming device, characterized by that it comprises a secondary battery according to any one of claims 1 to 12.

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