Secondary battery and electric device

Abstract

The invention relates to a secondary battery and an electric device. The embodiment of the invention provides a secondary battery. The secondary battery comprises an electrolyte. And the phase change temperature of the solid-liquid phase change reaction of the electrolyte is 15-40 DEG C. The electrolyte of the secondary battery is the phase-change electrolyte with the phase-change temperature of 15-40 DEG C, so that the electrolyte is kept in a liquid state, low in viscosity and high in conductivity in the charging and discharging process of the secondary battery; when the battery is stored, the electrolyte is kept in a solid state, the viscosity is improved, free solvent molecules are reduced, and side reactions are inhibited; therefore, the storage performance of the lithium iron phosphate battery can be effectively improved.

Description

Technical Field

[0001] The present application relates to a secondary battery and an electrical device. Background Art

[0002] In recent years, with the development of lithium-ion secondary battery technology, lithium-ion secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. As lithium-ion secondary batteries have achieved great development, higher requirements have been placed on their storage performance and cycle performance. Summary of the Invention

[0003] The purpose of this application is to provide a secondary battery and an electrical device.

[0004] The embodiment of the present application is implemented as follows:

[0005] In a first aspect, an embodiment of the present application provides a secondary battery, the secondary battery comprising:

[0006] Electrolyte; the phase transition temperature of the solid-liquid phase transition reaction of the electrolyte is 15°C-40°C.

[0007] In the above technical solution, the electrolyte of the secondary battery is set to a phase change electrolyte with a phase change temperature of 15°C-40°C; when the secondary battery generates heat during the charging and discharging process, the electrolyte can undergo a solid-liquid phase change reaction, maintaining a liquid state (low viscosity), thereby exhibiting a high conductivity effect; when the battery is stored (no heat is generated), the electrolyte remains in a solid state (high viscosity), reducing free solvent molecules and inhibiting the occurrence of side reactions; thereby effectively improving the storage performance of the lithium iron phosphate battery.

[0008] In some optional embodiments, the secondary battery includes: a positive electrode sheet, wherein the porosity of the positive electrode sheet is 0.2-0.45.

[0009] By setting the porosity of the positive electrode of the secondary battery to 0.2-0.45; it can be coordinated with a phase change electrolyte with a phase change temperature of 15℃-40℃, which can further effectively improve the problem of poor wettability caused by high viscosity of the electrolyte; and when the secondary battery generates heat during the charging and discharging process, the electrolyte can undergo a solid-liquid phase change reaction, maintaining a liquid state (low viscosity), thereby showing a high conductivity effect; when the battery is stored (no heat is generated), the electrolyte remains in a solid state (high viscosity), reducing free solvent molecules and inhibiting the occurrence of side reactions; thereby effectively improving the storage performance of the lithium iron phosphate battery.

[0010] In some optional embodiments, the porosity of the positive electrode sheet is 0.28-0.45; alternatively, the porosity of the positive electrode sheet is 0.35-0.4. In the above technical solution, by further limiting the porosity of the positive electrode sheet to the above range, it is beneficial to further improve the electrolyte infiltration effect, increase the ion migration rate, and thus improve the battery capacity.

[0011] In some optional embodiments, the secondary battery includes: a negative electrode plate; the porosity of the negative electrode plate is 0.25-0.45. By setting the porosity of the negative electrode plate of the secondary battery to 0.25-0.45, it can be used in conjunction with a phase change electrolyte with a phase change temperature of 15°C-40°C, which can further effectively improve the problem of poor wettability caused by high electrolyte viscosity. Moreover, when the secondary battery generates heat during the charging and discharging process, the electrolyte can undergo a solid-liquid phase change reaction, maintaining a liquid state (low viscosity), thereby exhibiting a high conductivity effect. When the battery is stored (no heat is generated), the electrolyte remains in a solid state (high viscosity), reducing free solvent molecules and suppressing the occurrence of side reactions. This can effectively improve the storage performance of the lithium iron phosphate battery.

[0012] In some optional embodiments, the porosity of the negative electrode sheet is 0.31-0.45; optionally, the porosity of the negative electrode sheet is 0.35-0.4.

[0013] In the above technical solution, by further limiting the porosity of the negative electrode sheet to the above range, it is beneficial to further improve the electrolyte infiltration effect, to increase the ion migration rate, and thus to maximize the battery capacity.

[0014] In some optional embodiments, the phase transition temperature of the solid-liquid phase transition reaction of the electrolyte is 19°C-28°C.

[0015] In some optional embodiments, the electrolyte includes: a phase change host material and a phase change initiator.

[0016] In the above technical solution, the phase change main material can undergo a solid-liquid phase change reaction under the action of a phase change initiator; thereby, the electrolyte can be transformed from a solid phase to a liquid phase; or the electrolyte can be transformed from a liquid phase to a solid phase; and thus the electrolyte can exist in different phases during the charge and discharge and storage states. When the electrolyte remains in a liquid phase during the battery charge and discharge process, the conductivity can be effectively improved; when the electrolyte remains in a solid phase in the battery storage state, the free solvent molecules can be effectively reduced and the occurrence of side reactions can be inhibited; thereby, the storage performance of the lithium iron phosphate battery can be effectively improved.

[0017] In some optional embodiments, the phase-change host material includes: an organic compound having a five-membered oxygen ring structure.

[0018] Organic compounds with a five-membered oxygen ring structure can undergo ring-opening polymerization under the action of a phase change initiator, causing the electrolyte to undergo a solid-liquid phase change reaction. During the battery's charge and discharge process, the electrolyte exists in a liquid state, effectively improving conductivity. During battery storage, the electrolyte remains in a solid phase, effectively reducing free solvent molecules and inhibiting side reactions, thereby effectively improving the storage performance of lithium iron phosphate batteries.

[0019] In some optional embodiments, the phase change host material includes: 1,3-dioxolane.

[0020] In the above technical solution, 1,3-dioxolane can undergo a ring-opening reaction under the action of a phase change initiator and further polymerize to form poly-1,3-dioxolane. After the ring-opening polymerization of 1,3-dioxolane, it changes from a liquid to a solid state. The electrolyte undergoes a solid-liquid phase change reaction. When the battery is charging and discharging, 1,3-dioxolane exists in a liquid state, which can effectively improve the conductivity. When the battery is in storage, 1,3-dioxolane undergoes ring-opening polymerization, and the electrolyte remains in a solid phase, which can effectively reduce free solvent molecules and inhibit the occurrence of side reactions. This can effectively improve the storage performance of lithium iron phosphate batteries.

[0021] In some optional embodiments, the phase change initiator includes: a lithium salt.

[0022] In the above technical solution, lithium salts act as phase change initiators, triggering a solid-liquid phase transition reaction in the phase change host material, thereby maintaining different phases during the battery's charge, discharge, and storage states. During the battery's charge and discharge processes, 1,3-dioxolane exists in a liquid state, effectively improving electrical conductivity. During storage, 1,3-dioxolane undergoes ring-opening polymerization, and the electrolyte remains in a solid phase, effectively reducing free solvent molecules and inhibiting the occurrence of side reactions. This effectively improves the storage performance of lithium iron phosphate batteries.

[0023] In some optional embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl imide), lithium tetrafluoroborate, or lithium bis(oxalatoborate).

[0024] In some optional embodiments, the electrolyte includes: 1,3-dioxolane and lithium hexafluorophosphate.

[0025] In the above technical solution, lithium hexafluorophosphate (LiPF6) can induce a ring-opening reaction of 1,3-dioxolane, which further polymerizes to form poly-1,3-dioxolane. During this process, LiPF6 loses a fluoride ion and becomes LiPF5 with Lewis acid properties, thereby inducing the ring-opening polymerization of 1,3-dioxolane. This causes the electrolyte to undergo a solid-liquid phase transition reaction. When the battery is charging and discharging, 1,3-dioxolane exists in a liquid state, which can effectively improve the conductivity. When the battery is in storage, 1,3-dioxolane undergoes ring-opening polymerization, and the electrolyte remains in a solid phase, which can effectively reduce free solvent molecules and inhibit the occurrence of side reactions. This can effectively improve the storage performance of lithium iron phosphate batteries.

[0026] In some optional embodiments, the electrolyte includes one or more of esters, ethers, or thioethers.

[0027] In some optional embodiments, the mass ratio of the phase change initiator to the phase change host material is (0.02-0.3): 1. Alternatively, the mass ratio of the phase change initiator to the phase change host material is (0.05-0.25):1.

[0028] In some optional embodiments, the positive electrode sheet includes: the positive electrode sheet includes: a positive electrode active material;

[0029] Optionally, the positive electrode active material includes at least one of lithium iron phosphate, lithium manganese iron phosphate, and modified and doped lithium manganese iron phosphate;

[0030] Optionally, the chemical formula of the modified doped lithium manganese iron phosphate includes: LiMFePO4, where M includes Mn and non-Mn elements;

[0031] Optionally, the non-Mn element includes one or both of a first doping element and a second doping element, the first doping element is a manganese doping element, and the second doping element is a phosphorus doping element;

[0032] Optionally, the first doping element includes one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge.

[0033] Further optionally, the first doping element includes at least two of Ti, V, Ni, Co or Mg;

[0034] Optionally, the second doping element includes one or more elements selected from B, S, Si or N;

[0035] Optionally, the positive electrode active material includes: Li 1+x Mn 1-y A y P 1-z Rz O4, wherein x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, or Ge, and R includes one or more elements selected from B, S, Si, or N;

[0036] Optionally, the positive electrode active material includes: Li a A e Mn 1-f B f P 1-g C g O 4-n D n ;

[0037] wherein A comprises one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Nb, Mo, and W;

[0038] B includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, or Ge;

[0039] C includes one or more elements selected from B, S, Si, or N;

[0040] D includes one or more elements selected from the group consisting of S, F, Cl, and Br;

[0041] a is selected from the range of 0.9 to 1.1, e is selected from the range of 0.001 to 0.1, f is selected from the range of 0.001 to 0.5, g is selected from the range of 0.001 to 0.1, n is selected from the range of 0.001 to 0.1, and the positive electrode active material is electrically neutral.

[0042] In some optional embodiments, the negative electrode sheet includes: a negative electrode active material;

[0043] The negative electrode active material includes at least one of graphite, soft carbon or hard carbon material.

[0044] In a second aspect, an embodiment of the present application provides an electrical device, which includes the secondary battery provided in the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0046] Figure 1 A schematic structural diagram of a vehicle provided in some embodiments of the present application;

[0047] Figure 2 An exploded view of a battery provided in accordance with some embodiments of the present application;

[0048] Figure 3 for Figure 2 An exploded view of a battery cell is shown;

[0049] Figure 4 A schematic diagram of a partial structure of an electrode assembly provided in some embodiments of the present application;

[0050] Figure 5 Schematic diagram of the partial structure of the positive electrode plate provided in some embodiments of the present application.

[0051] icon:

[0052] Vehicles 1000;

[0053] Secondary battery 100; controller 200; motor 300;

[0054] Box body 10; first part 11; second part 12; accommodating space 13;

[0055] Battery cell 20; housing 21; electrode assembly 22; electrode terminal 23; pressure relief structure 24;

[0056] Housing 211; cover 212; positive electrode sheet 221; negative electrode sheet 222; separator 223;

[0057] Positive electrode current collector 2211; positive electrode active material layer 2212;

[0058] Negative electrode current collector 2221 ; negative electrode active material layer 2222 . DETAILED DESCRIPTION

[0059] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0060] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0061] In the description of the embodiments of the present application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0062] In the description of the embodiments of the present application, the orientations or positional relationships indicated by technical terms such as "inside" and "outside" are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the embodiments of the present application.

[0063] In the description of the embodiments of this application, unless otherwise specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; they can refer to direct connections or indirect connections through an intermediate medium. Those skilled in the art will understand the specific meanings of the above terms in the embodiments of this application based on specific circumstances.

[0064] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0065] In the embodiments of this application, the same reference numerals represent the same components, and for the sake of brevity, detailed descriptions of the same components in different embodiments are omitted. It should be understood that the heights, lengths, widths, and other dimensions of the various components in the embodiments of this application, as well as the overall heights, lengths, widths, and other dimensions of the integrated device shown in the drawings are merely illustrative and do not constitute any limitation on this application.

[0066] Lithium iron phosphate (LiFePO4) is used as the active cathode material in lithium-ion batteries due to its excellent structural stability. Consequently, LiFePO4 batteries offer excellent structural stability and cycling performance. However, under high-temperature conditions, LiFePO4 batteries are prone to significantly accelerated performance degradation during cycling and storage. Dissolved oxygen and regeneration of the SEI film on the negative electrode during cycling and storage lead to the depletion of active lithium, ultimately manifesting as accelerated capacity degradation.

[0067] Research has found that regulating the electrolyte's solid-liquid state transition by changing the temperature can effectively improve this problem. When the battery generates heat during charging and discharging, the electrolyte remains in a liquid state (low viscosity), resulting in high conductivity. When the battery is stored (no heat is generated), the electrolyte remains in a solid state (high viscosity), reducing the number of free solvent molecules and inhibiting side reactions. This effectively improves the problem of lithium iron phosphate batteries that often experience significantly accelerated performance degradation during cycling and storage.

[0068] Further research has found that when secondary batteries use a phase-change electrolyte that can undergo solid-liquid state conversion, there is a problem of high viscosity of the phase-change electrolyte, which leads to poor wettability.

[0069] Further research found that designing the porosity of the positive and negative electrodes of secondary batteries can work synergistically with the phase-change electrolyte to effectively improve the problem of poor wettability caused by high electrolyte viscosity; thereby effectively improving the electrochemical performance of the battery.

[0070] In view of this, an embodiment of the present application provides a secondary battery, the battery comprising:

[0071] Electrolyte; the phase transition temperature of the solid-liquid phase transition reaction of the electrolyte is 15°C-40°C.

[0072] In the above technical solution, the electrolyte of the secondary battery is set so that the electrolyte remains in liquid state (low viscosity) during the charging and discharging process of the secondary battery, thereby exhibiting a high conductivity effect; when the battery is stored (no heat is generated), the electrolyte remains in solid state (high viscosity), reducing the free solvent molecules and inhibiting the occurrence of side reactions; thereby effectively improving the storage performance of the lithium iron phosphate battery.

[0073] The present application provides an electrical device including the aforementioned secondary battery.

[0074] The electrical equipment has improved comprehensive performance by being provided with the secondary battery provided in the aforementioned embodiment.

[0075] See also Figure 1 , Figure 1A schematic structural diagram of a vehicle 1000 provided for some embodiments of the present application. The vehicle 1000 may be a fuel vehicle, a gas vehicle or a new energy vehicle. The new energy vehicle may be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A battery 100 is provided inside the vehicle 1000. The battery 100 may be provided at the bottom, head or tail of the vehicle 1000. The battery 100 may be used to power the vehicle 1000. For example, the battery 100 may serve as an operating power source for the vehicle 1000. The vehicle 1000 may further include a controller 200 and a motor 300. The controller 200 is used to control the battery 100 to power the motor 300, for example, to meet the power requirements for starting, navigating and driving the vehicle 1000.

[0076] In some embodiments of the present application, the battery 100 can not only serve as the operating power source of the vehicle 1000, but also serve as the driving power source of the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0077] In this application, a secondary battery 100 refers to a single physical module that includes one or more battery cells 20 to provide voltage and capacity. The battery 100 generally includes a housing 10 for enclosing one or more battery cells 20. The housing 10 prevents liquids or other foreign matter from affecting the charging or discharging of the battery cells 20.

[0078] See also Figure 2 , Figure 2 This is an exploded view of a battery 100 provided in some embodiments of the present application. The battery 100 may include a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10. The housing 10 is used to house the battery cell 20 and may have various structures. In some embodiments, the housing 10 may include a first portion 11 and a second portion 12, which overlap each other and together define a storage space 13 for accommodating the battery cell 20. The second portion 12 may be a hollow structure with one end open, and the first portion 11 may be a plate-like structure. The first portion 11 overlaps the open side of the second portion 12 to form the housing 10 with the storage space 13. The first portion 11 and the second portion 12 may also be hollow structures with one end open, with the open side of the first portion 11 overlapping the open side of the second portion 12 to form the housing 10 with the storage space 13. Of course, the first portion 11 and the second portion 12 may have various shapes, such as a cylinder, a rectangular parallelepiped, etc.

[0079] In the battery 100, there can be one or more battery cells 20. If there are multiple battery cells 20, the multiple battery cells 20 can be connected in series, in parallel, or in a mixed connection. Mixed connection means that the multiple battery cells 20 are connected in series and in parallel. The multiple battery cells 20 can be directly connected in series, in parallel, or in a mixed connection, and then the whole formed by the multiple battery cells 20 is accommodated in the case 10. Alternatively, multiple battery cells 20 can be first connected in series, in parallel, or in a mixed connection to form a module, and the multiple modules are then connected in series, in parallel, or in a mixed connection to form a whole, and accommodated in the case 10. The battery 100 can also include other structures. For example, the multiple battery cells 20 can be electrically connected through a busbar component to achieve parallel, series, or mixed connection of the multiple battery cells 20.

[0080] See also Figure 3 , Figure 3 for Figure 2 The exploded view of the battery cell 20 is shown. The battery cell 20 is the smallest unit constituting the battery 100. The battery cell 20 may include a housing 21, an electrode assembly 22, and an electrolyte, wherein the electrode assembly 22 and the electrolyte are both contained in the housing 21.

[0081] The outer shell 21 may include a shell 211 and a cover 212. The shell 211 is a component used to cooperate with the cover 212 to form an internal sealed space of the battery cell 20, wherein the formed sealed space can be used to accommodate the electrode assembly 22, electrolyte and other components. The cover 212 refers to a component that covers the opening of the shell 211 to isolate the internal environment of the battery cell 20 from the external environment. The shape of the cover 212 can be adapted to the shape of the shell 211 to cooperate with the shell 211. Functional components such as electrode terminals 23 and pressure relief structures 24 can also be provided on the cover 212. A sealing ring can be configured between the opening of the shell 211 and the cover 212 to achieve sealing between the shell 211 and the cover 212.

[0082] The shell 211 and the cover 212 can be of various shapes and sizes, such as a rectangular parallelepiped, a cylindrical shape, a hexagonal prism, etc. Specifically, the shapes of the shell 211 and the cover 212 can be determined according to the specific shape and size of the electrode assembly 22. The material of the shell 211 and the cover 212 can be various, such as but not limited to metals such as copper, iron, aluminum, stainless steel, and aluminum alloy. The material of the sealing ring can be various, such as but not limited to PP (polypropylene), PC (polycarbonate), PET (polyethylene terephthalate) and other materials that are resistant to electrolyte corrosion, high toughness and fatigue resistance. A coating can be formed on the outer surface of the shell 211, and the material of the coating can be various, such as but not limited to corrosion-resistant materials such as Ni and Cr.

[0083] See also Figure 4The electrode assembly 22 may be composed of a positive electrode sheet 221, a negative electrode sheet 222, and a separator 223. The separator 223 is located between the positive electrode sheet 221 and the negative electrode sheet 222 to provide isolation. The electrode assembly 22 may be a wound structure or a laminated structure, but the present invention is not limited thereto.

[0084] See also Figure 5 The negative electrode sheet 222 includes a negative electrode current collector 2221 and a negative electrode active material layer 2222 . The negative electrode current collector 2221 may be made of copper.

[0085] Please continue to see Figure 5 The positive electrode sheet 221 includes a positive electrode current collector 2211 and a positive electrode active material layer 2212. Taking a lithium-ion battery cell as an example, the material of the positive electrode current collector 2211 can be aluminum.

[0086] In some embodiments of the present application, the secondary battery includes: an electrolyte; and a phase transition temperature of a solid-liquid phase transition reaction of the electrolyte is 15°C-40°C.

[0087] In the above technical solution, by setting the electrolyte of the secondary battery to a phase change electrolyte with a phase change temperature of 15°C-40°C, the heat generated by the secondary battery during the charging and discharging process can keep the electrolyte in a liquid state (low viscosity), thereby showing a high conductivity effect; when the secondary battery is stored (no heat is generated), the electrolyte remains in a solid state (high viscosity), reducing the free solvent molecules and inhibiting the occurrence of side reactions; thereby, the storage performance of the lithium iron phosphate battery can be effectively improved.

[0088] Furthermore, in some embodiments of the present application, a solid-liquid phase change reaction refers to a process in which an electrolyte changes from one phase to another, including a process in which an electrolyte changes from a solid phase to a liquid phase; and a process in which an electrolyte changes from a liquid phase to a solid phase.

[0089] Further optionally, in some embodiments of the present application, the phase transition temperature of the solid-liquid phase transition reaction of the electrolyte is 16° C. to 38° C. Further optionally, in some embodiments of the present application, the phase transition temperature of the solid-liquid phase transition reaction of the electrolyte is 17° C. to 35° C.

[0090] Illustratively, in some embodiments of the present application, the phase change temperature of the electrolyte is 15°C, 16°C, 17°C, 18°C, 19°C, 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 30°C, 35°C, 38°C, 40°C or a range between any two of the foregoing values.

[0091] It should be noted that the above-mentioned phase transition temperature refers to the critical temperature at which the electrolyte undergoes phase transition, and the critical temperature is within the range of 15°C-40°C.

[0092] Further optionally, in some embodiments of the present application, the phase change temperature of the solid-liquid phase change reaction of the electrolyte is 19°C-28°C.

[0093] The phase change temperature of the solid-liquid phase change reaction of the electrolyte is within the above range, which is more conducive to the storage performance of the battery.

[0094] Furthermore, in some embodiments of the present application, the secondary battery includes: a positive electrode plate 221 , and the porosity of the positive electrode plate 221 is 0.2-0.45.

[0095] By setting the porosity of the positive electrode of the secondary battery to 0.2-0.45; it can be coordinated with a phase change electrolyte with a phase change temperature of 15℃-40℃, which can further effectively improve the problem of poor wettability caused by high viscosity of the electrolyte; and when the secondary battery generates heat during the charging and discharging process, the electrolyte can undergo a solid-liquid phase change reaction, maintaining a liquid state (low viscosity), thereby showing a high conductivity effect; when the battery is stored (no heat is generated), the electrolyte remains in a solid state (high viscosity), reducing free solvent molecules and inhibiting the occurrence of side reactions; thereby effectively improving the storage performance of the lithium iron phosphate battery.

[0096] Further optionally, in some embodiments of the present application, the porosity of the positive electrode sheet is 0.21-0.44.

[0097] Illustratively, in some embodiments of the present application, the porosity of the positive electrode sheet is 0.21, 0.22, 0.25, 0.28, 0.30, 0.35, 0.38, 0.40, 0.41, 0.42, 0.43, 0.44, or a range between any two of the foregoing values.

[0098] Furthermore, in some embodiments of the present application, the secondary battery includes: a negative electrode plate 222; the porosity of the negative electrode plate 222 is 0.25-0.45. By setting the porosity of the negative electrode plate of the secondary battery to 0.25-0.45, it can be used in conjunction with a phase change electrolyte with a phase change temperature of 15°C-40°C, which can further effectively improve the problem of poor wettability caused by high electrolyte viscosity. Moreover, when the secondary battery generates heat during the charging and discharging process, the electrolyte can undergo a solid-liquid phase change reaction, maintaining a liquid state (low viscosity), thereby exhibiting a high conductivity effect. When the battery is stored (no heat is generated), the electrolyte remains in a solid state (high viscosity), reducing free solvent molecules and suppressing the occurrence of side reactions. This can effectively improve the storage performance of the lithium iron phosphate battery.

[0099] Further optionally, in some embodiments of the present application, the porosity of the negative electrode sheet is 0.26, 0.27, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.41, 0.42, 0.43, 0.44 or a range between any two of the foregoing values.

[0100] Further optionally, in some embodiments of the present application, the porosity of the positive electrode sheet is 0.28-0.45; further optionally, in some embodiments of the present application, the porosity of the positive electrode sheet is 0.35-0.4.

[0101] In the above technical solution, by further limiting the porosity of the positive electrode sheet to the above range, it is beneficial to further improve the electrolyte infiltration effect, to increase the ion migration rate, and thus to maximize the battery capacity.

[0102] Furthermore, in some embodiments of the present application, the porosity of the negative electrode sheet is 0.31-0.45; optionally, the porosity of the negative electrode sheet is 0.35-0.4.

[0103] In the above technical solution, by further limiting the porosity of the negative electrode sheet to the above range, it is beneficial to further improve the electrolyte infiltration effect, to increase the ion migration rate, and thus to maximize the battery capacity.

[0104] Furthermore, in some embodiments of the present application, the electrolyte includes: a phase change host material and a phase change initiator.

[0105] In the above technical solution, the phase change main material can undergo a solid-liquid phase change reaction under the action of a phase change initiator; thereby, the electrolyte can be transformed from a solid phase to a liquid phase; or the electrolyte can be transformed from a liquid phase to a solid phase; and thus the electrolyte can exist in different phases during the charge and discharge and storage states. When the electrolyte remains in a liquid phase during the battery charge and discharge process, the conductivity can be effectively improved; when the electrolyte remains in a solid phase in the battery storage state, the free solvent molecules can be effectively reduced and the occurrence of side reactions can be inhibited; thereby, the storage performance of the lithium iron phosphate battery can be effectively improved.

[0106] In some optional embodiments, the phase-change host material includes: an organic compound having a five-membered oxygen ring structure.

[0107] Organic compounds with a five-membered oxygen ring structure can undergo ring-opening polymerization under the action of a phase change initiator, causing the electrolyte to undergo a solid-liquid phase change reaction. During the battery's charge and discharge process, the electrolyte exists in a liquid state, effectively improving conductivity. During battery storage, the electrolyte remains in a solid phase, effectively reducing free solvent molecules and inhibiting side reactions, thereby effectively improving the storage performance of lithium iron phosphate batteries.

[0108] Furthermore, in some embodiments of the present application, the phase change host material includes: 1,3-dioxolane.

[0109] In the above technical solution, the phase change main material includes: 1,3-dioxolane. 1,3-dioxolane can undergo a ring-opening reaction under the action of a phase change initiator and further polymerize to form poly-1,3-dioxolane. After the ring-opening polymerization of 1,3-dioxolane, it changes from a liquid to a solid. The electrolyte undergoes a solid-liquid phase change reaction. When the battery is charged and discharged, 1,3-dioxolane exists in a liquid state, which can effectively improve the conductivity; when the battery is in the storage state, 1,3-dioxolane undergoes ring-opening polymerization, and the electrolyte remains in a solid phase, which can effectively reduce free solvent molecules and inhibit the occurrence of side reactions; thereby effectively improving the storage performance of lithium iron phosphate batteries.

[0110] Furthermore, in some embodiments of the present application, the phase change initiator includes: a lithium salt.

[0111] In the above technical solution, lithium salts act as phase change initiators, triggering a solid-liquid phase transition reaction in the phase change host material, thereby maintaining different phases during the battery's charge, discharge, and storage states. During the battery's charge and discharge processes, 1,3-dioxolane exists in a liquid state, effectively improving conductivity. During storage, 1,3-dioxolane undergoes ring-opening polymerization, and the electrolyte remains in a solid phase, effectively reducing free solvent molecules and inhibiting side reactions. This effectively improves the storage performance of lithium iron phosphate batteries.

[0112] Furthermore, in some embodiments of the present application, the lithium salt includes at least one of lithium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl imide), lithium tetrafluoroborate, or lithium bis(oxalatoborate).

[0113] In the above technical solution, lithium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl imide), lithium tetrafluoroborate, or lithium bis(oxalatoborate) can serve as phase change initiators, causing 1,3-dioxolane to undergo a ring-opening reaction and further polymerization to form poly-1,3-dioxolane. After the ring-opening polymerization of 1,3-dioxolane, it transforms from a liquid to a solid state, and the electrolyte undergoes a solid-liquid phase change reaction. During the battery's charge and discharge processes, 1,3-dioxolane exists in a liquid state, effectively improving conductivity. During battery storage, 1,3-dioxolane undergoes ring-opening polymerization, while the electrolyte remains in a solid phase, effectively reducing free solvent molecules and suppressing side reactions. This effectively improves the storage performance of lithium iron phosphate batteries.

[0114] Further optionally, illustratively, in some embodiments of the present application, the lithium salt is selected from any one of lithium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl imide), lithium tetrafluoroborate or lithium bis(oxalatoborate).

[0115] Further optionally, illustratively, in some embodiments of the present application, the lithium salt is selected from a mixture of lithium hexafluorophosphate and lithium trifluoromethanesulfonate; the two can be mixed in any mass ratio.

[0116] Further optionally, illustratively, in some embodiments of the present application, the lithium salt is selected from a mixture of lithium bis(trifluoromethanesulfonyl)imide and lithium tetrafluoroborate; the two can be mixed in any mass ratio.

[0117] Further optionally, illustratively, in some embodiments of the present application, the lithium salt is selected from a mixture of lithium tetrafluoroborate and lithium bis(oxalatoborate); the two can be mixed in any mass ratio.

[0118] Further optionally, illustratively, in some embodiments of the present application, the lithium salt is selected from a mixture of lithium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonylimide), lithium tetrafluoroborate and lithium bis(oxalatoborate); the five can be mixed in any mass ratio.

[0119] Furthermore, in some embodiments of the present application, the electrolyte includes: 1,3-dioxolane and lithium hexafluorophosphate.

[0120] In the above technical solution, lithium hexafluorophosphate (LiPF6) can induce 1,3-dioxolane to undergo a ring-opening reaction, which is then further polymerized to form poly-1,3-dioxolane. During the polymerization process, LiPF6 loses a fluoride ion and becomes LiPF5 with Lewis acid properties, thereby inducing 1,3-dioxolane to undergo ring-opening polymerization. This causes the electrolyte to undergo a solid-liquid phase transition reaction. During the battery charging and discharging process, the heat generated by charging and discharging causes 1,3-dioxolane to exist in a liquid state, which can effectively improve the electrical conductivity. In the battery storage state, the temperature is low, 1,3-dioxolane undergoes ring-opening polymerization to form poly-1,3-dioxolane, and the electrolyte remains in a solid phase, which can effectively reduce free solvent molecules and inhibit the occurrence of side reactions; thus, the storage performance of lithium iron phosphate batteries can be effectively improved.

[0121] Furthermore, in some embodiments of the present application, the electrolyte includes: one or more of esters, ethers or thioethers.

[0122] Further optionally, in some embodiments of the present application, the esters include: fluoroethylene carbonate, ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, ethylene carbonate, or at least one of 1,4-butyrolactone.

[0123] Further optionally, in some embodiments of the present application, the ethers include: one or more of chain ether organic solvents and cyclic ether organic solvents.

[0124] Further optionally, in some embodiments of the present application, the chain ether organic solvent includes one or more of ethylene glycol dimethyl ether, triethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether, and the cyclic ether organic solvent includes one or more of 1,3-dioxolane or tetrahydrofuran.

[0125] Further optionally, in some embodiments of the present application, the sulfide includes: methyl sulfide, dimethyl sulfide or methyl ethyl sulfide.

[0126] Furthermore, in some embodiments of the present application, the mass ratio of the phase change initiator to the phase change host material is: (0.02-0.3):1.

[0127] Illustratively, in some embodiments of the present application, the mass ratio of the phase change initiator to the phase change host material is: 0.02:1, 0.03:1, 0.05:1, 0.08:1, 0.1:1, 0.2:1, 0.3:1 or a range between any two of the foregoing values.

[0128] Further optionally, in some embodiments of the present application, the mass ratio of the phase change initiator to the phase change host material is: (0.05-0.25):1.

[0129] The mass ratio of the phase change initiator to the phase change main material being within the above range is more conducive to improving the storage performance of the lithium iron phosphate battery.

[0130] Furthermore, in some embodiments of the present application, the positive electrode plate includes: a positive electrode active material; the positive electrode active material includes: at least one of lithium iron phosphate, lithium manganese iron phosphate, and modified doped lithium manganese iron phosphate.

[0131] Furthermore, in some embodiments of the present application, the chemical formula of the modified doped lithium manganese iron phosphate includes: LiMFePO4, where M includes Mn and non-Mn elements.

[0132] The above-mentioned LiMFePO4 is not a specific molecular structure formula, but a general expression of lithium manganese phosphate.

[0133] Furthermore, in some embodiments of the present application, the non-Mn element includes one or both of a first doping element and a second doping element, the first doping element is a manganese doping element, and the second doping element is a phosphorus doping element.

[0134] Furthermore, in some embodiments of the present application, the first doping element includes one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge.

[0135] Furthermore, in some embodiments of the present application, the first doping element includes at least two of Ti, V, Ni, Co or Mg.

[0136] Furthermore, in some embodiments of the present application, the second doping element includes one or more elements selected from B, S, Si, or N.

[0137] Furthermore, in some embodiments of the present application, the positive electrode active material includes: Li 1+x Mn 1-y A y P 1-z R z O4, wherein x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A includes one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, and R includes one or more elements selected from the group consisting of B, S, Si, and N.

[0138] Furthermore, in some embodiments of the present application, the positive electrode active material includes: Li a A e Mn 1-f B f P 1-g C g O 4-n D n ;

[0139] wherein A comprises one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Nb, Mo, and W;

[0140] B includes one or more elements selected from the group consisting of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge;

[0141] C includes one or more elements selected from B, S, Si, or N;

[0142] D includes one or more elements selected from S, F, Cl, or Br;

[0143] a is selected from the range of 0.9 to 1.1, e is selected from the range of 0.001 to 0.1, f is selected from the range of 0.001 to 0.5, g is selected from the range of 0.001 to 0.1, n is selected from the range of 0.001 to 0.1, and the positive electrode active material is electrically neutral.

[0144] In some embodiments, the compound Li a A e Mn 1-f B f P 1-g C g O 4-n D n The preparation method may include the following steps:

[0145] (1) dissolving a manganese source, a source of element A to be doped at the manganese position, and an acid in a solvent and stirring to generate a suspension of a manganese salt doped with element A, filtering the suspension and drying the filter cake to obtain a manganese salt doped with element A;

[0146] (2) adding a lithium source, a phosphorus source, an element R source, a solvent, and the manganese salt doped with element A obtained in step (1) into a reaction vessel, grinding and mixing to obtain a slurry;

[0147] (3) transferring the slurry obtained in step (2) to a spray drying device for spray drying and granulation to obtain granules;

[0148] (4) Sintering the particles obtained in step (3) to obtain a positive electrode active material.

[0149] In any embodiment, the manganese source may be a manganese-containing substance known in the art that can be used to prepare lithium manganese phosphate. For example, the manganese source may be selected from elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, manganese carbonate, or a combination thereof.

[0150] The acid is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and organic acids such as oxalic acid, and may be, for example, oxalic acid. The source of element R is selected from at least one of sulfates, borates, nitrates, and silicates of element R. The source of element A is selected from at least one of a simple substance, oxide, phosphate, oxalate, carbonate, and sulfate of A.

[0151] In some embodiments, the positive electrode active material includes Li a A e Mn 1-f B f P 1-g C g O 4-n D n, wherein A includes one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Nb, Mo, and W, B includes one or more elements selected from the group consisting of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge, C includes one or more elements selected from the group consisting of B, S, Si, and N, D includes one or more elements selected from the group consisting of S, F, Cl, and Br, a is selected from the range of 0.9 to 1.1, e is selected from the range of 0.001 to 0.1, f is selected from the range of 0.001 to 0.5, g is selected from the range of 0.001 to 0.1, n is selected from the range of 0.001 to 0.1, and the positive electrode active material is electrically neutral.

[0152] It should be noted that Li a A e Mn 1-f B f P 1-g C g O 4-n D n The compound is actually a specific LiMPO4 material. Its preparation method can refer to Li a A e Mn 1-f B f P 1-g C g O 4-n D n , no limitation is made here.

[0153] In some embodiments, the positive electrode active material further has a coating layer comprising carbon.

[0154] The introduction of a carbon-containing coating layer improves the conductivity of the positive electrode active material. At this time, the structure of the positive electrode active material is actually a core-shell structure with LiMPO4 as the core and the surface of the core covered with the coating layer.

[0155] The battery is accompanied by Li deintercalation and consumption during the charging and discharging process, and the molar content of Li is different when the battery is discharged to different states.

[0156] In the list of positive electrode active materials in this application, the molar content of Li is the initial state of the material, that is, the state before adding the material. When the positive electrode active material is used in a battery system, the molar content of Li will change after charge and discharge cycles.

[0157] In the list of positive electrode active materials in this application, the molar content of O is only a theoretical value. Oxygen release from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate. For example, Li 1+x Mn 1-y A y P 1-z R zThe molar content of the O element in O4 is not strictly 4.

[0158] Furthermore, in some embodiments of the present application, the negative electrode plate includes: a negative electrode active material; the negative electrode active material includes: at least one of graphite, soft carbon or hard carbon material.

[0159] For example, in some embodiments of the present application, the negative electrode active material is selected from: any one of graphite, soft carbon or hard carbon material; or in some embodiments of the present application, the negative electrode active material is selected from: a mixture of graphite and soft carbon, and the two can be mixed in any proportion; or in some embodiments of the present application, the negative electrode active material is selected from: a mixture of graphite, soft carbon and hard carbon material, and the three can be mixed in any proportion.

[0160] Some specific embodiments are listed below to better illustrate the present application.

[0161] Example 1

[0162] A battery is provided, which is prepared according to the following steps:

[0163]

Preparation of positive electrode sheet

[0164] By mass percentage, 97.2% lithium iron phosphate powder (the positive electrode active material), 2% polyvinylidene fluoride (PVDF) binder, and 0.8% conductive carbon black (Super P) were mixed. An appropriate amount of N-methylpyrrolidone (NMP) solvent was added and stirred thoroughly to obtain a positive electrode slurry. The slurry was then coated onto aluminum foil, dried, and cold-pressed. The porosity of the positive electrode sheet was controlled to 0.28 by controlling the cold-pressing pressure.

[0165]

Preparation of negative electrode sheet

[0166] By mass percentage, 96% graphite, 0.5% binder (styrene-butadiene rubber (SBR), 1.5% conductive carbon, and 2% thickener (sodium carboxymethyl cellulose (CMC)) were mixed. An appropriate amount of water was added and stirred evenly to obtain a negative electrode slurry. The slurry was then coated onto copper foil, dried, and cold-pressed. The porosity of the negative electrode sheet was controlled to 0.31 by controlling the cold-pressing pressure.

[0167] Preparation of electrolyte

[0168] The electrolyte includes: a phase change main material, a phase change initiator and a solvent.

[0169] Phase change host material: 1,3-dioxolane;

[0170] Phase change initiator: LiPF6; electrolyte phase temperature 25℃;

[0171] The phase change initiator and the phase change main material are mixed in a mass ratio of 0.15:1.

[0172] Solvent: ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) are mixed in a volume ratio of 1:1:1.

[0173] The phase change main material and the phase change initiator are dissolved in the above-mentioned mixed solvent to prepare an electrolyte solution with a concentration of 1 mol / L.

[0174]

Battery preparation

[0175] A polypropylene film (Φ16mm) with a thickness of 12μm was used as an isolating membrane. The positive electrode sheet, isolating membrane, and negative electrode sheet prepared above were placed in order, so that the isolating membrane was placed between the positive and negative electrode sheets to play an isolating role. The film was dried in an oven at 100°C for 12h and cooled to room temperature. The above-mentioned electrolyte was then injected and subjected to formation and aging.

[0176] Example 2-16

[0177] The difference from Example 1 is that the parameters related to the positive electrode sheet, negative electrode sheet or electrolyte are detailed in Table 1.

[0178] Comparative Example 1

[0179] The difference from Example 1 is that [Preparation of electrolyte]:

[0180] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 1:1:1. Lithium salt LiPF6 was then dissolved in the mixed solvent to prepare an electrolyte solution with a concentration of 1 mol / L. See Table 1 for details.

[0181]

Performance test method

[0182] 1. Pole piece porosity

[0183] The test is conducted in accordance with the standard GB / T 24586-2009. The specific process involves using tweezers to select >20 discs with good appearance and no powdering on the edges and place them into a sample cup. The number of discs is recorded and the apparent volume is calculated. The sample cup containing the sample is then placed in a true density tester. The test system is sealed, and helium is introduced according to the program. The pressure of the gas in the sample chamber and expansion chamber is measured, and the true volume is calculated according to Bohr's law (PV = nRT), thereby determining the porosity of the sample. The porosity output for the electrode sample does not deduct the substrate.

[0184] 2. Phase transition temperature

[0185] The test method is as follows: the electrolyte prepared in each embodiment or comparative example is placed in a constant temperature box, starting from 25°C, and the temperature is maintained at a constant temperature for 30 minutes after each increase of 1°C, and the physical state of the phase change product is observed. The temperature is increased and maintained in sequence. When the electrolyte changes from a solid phase to a liquid phase at a certain temperature value, the temperature value is the phase change temperature of the electrolyte.

[0186] 3. Battery storage performance

[0187] The batteries prepared in each embodiment or comparative example were used as test objects. At a charge and discharge temperature of 45°C, the battery was charged at a constant current of 0.33C to a voltage of 3.6V, then charged at a constant voltage of 3.6V to a current of 0.05C. After standing for 5 minutes, the battery was discharged at a constant current of 0.1C to a voltage of 2.5V. This constituted one charge and discharge cycle, and the initial charge and discharge capacity in grams was obtained (which can be directly read on a blue light test device).

[0188] Then, the battery was stored at a storage temperature of 15°C for 100 days, and then the battery was taken out and allowed to stand at the aforementioned A1 temperature for 24 hours. The battery was then charged at a constant current of 0.33C to a voltage of 3.6V, and then charged at a constant voltage of 3.6V to a current of 0.05C. After standing for 5 minutes, the battery was discharged at a constant current of 0.33C to a voltage of 2.5V, and the 100-day storage capacity was obtained (which can be directly read on the blue electric test equipment).

[0189] Calculate the 100-day storage capacity retention rate based on the initial charge and discharge capacity and the 100-day storage capacity:

[0190] 100-day storage capacity retention rate = 100-day storage capacity / first charge and discharge capacity in grams.

[0191] The test results are shown in Table 2.

[0192] Table 1

[0193]

[0194] Table 2

[0195]

[0196]

[0197] From the above table data we can see that:

[0198] After 100 days of storage at 15°C, the battery of the comparative example had a 100-day capacity retention rate of 83.4%. In contrast, after 100 days of storage at 15°C, the battery of the embodiment had a 100-day capacity retention rate of 84.2% to 93.5%. It can be seen that the 100-day capacity retention rate of the battery of the embodiment is significantly better than that of the comparative example.

[0199] This shows that the embodiment of the present application can significantly improve the storage performance of the battery.

[0200] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

Claims

1. A secondary battery, characterized in that: The secondary battery includes: Electrolyte; the phase transition temperature of the solid-liquid phase transition reaction of the electrolyte is 15°C-40°C.

2. The secondary battery according to claim 1, wherein The secondary battery includes: The positive electrode sheet has a porosity of 0.2-0.

45.

3. The secondary battery according to claim 2, wherein The porosity of the positive electrode sheet is 0.28-0.

45.

4. The secondary battery according to any one of claims 1 to 3, characterized in that: The secondary battery includes: Negative electrode sheet; the porosity of the negative electrode sheet is 0.25-0.

45.

5. The secondary battery according to claim 4, wherein The porosity of the negative electrode plate is 0.31-0.

45.

6. The secondary battery according to any one of claims 1 to 5, characterized in that: The phase transition temperature of the solid-liquid phase transition reaction of the electrolyte is 19°C-28°C.

7. The secondary battery according to any one of claims 1 to 6, characterized in that: The electrolyte includes: a phase change main material and a phase change initiator.

8. The secondary battery according to claim 7, wherein: The mass ratio of the phase change initiator to the phase change main material is: (0.02-0.3):

1.

9. The secondary battery according to claim 7 or 8, characterized in that: The phase change main material includes: an organic compound with a five-membered oxygen ring structure.

10. The secondary battery according to any one of claims 7 to 9, characterized in that: The phase change main material includes: 1,3-dioxolane.

11. The secondary battery according to any one of claims 7 to 10, characterized in that: The phase change initiator includes: lithium salt.

12. The secondary battery according to claim 11, wherein The lithium salt includes at least one of lithium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl imide), lithium tetrafluoroborate, or lithium bis(oxalatoborate).

13. The secondary battery according to claim 1, wherein The electrolyte includes 1,3-dioxolane and lithium hexafluorophosphate.

14. The secondary battery according to any one of claims 1 to 13, characterized in that: The electrolyte comprises: One or more of esters, ethers or thioethers.

15. The secondary battery according to any one of claims 2 to 3, characterized in that: The positive electrode plate includes: a positive electrode active material; The positive electrode active material includes at least one of lithium iron phosphate, lithium manganese iron phosphate, or modified and doped lithium manganese iron phosphate.

16. The secondary battery according to claim 15, characterized in that The chemical formula of the modified and doped lithium manganese iron phosphate includes: LiMFePO4, where M includes Mn and non-Mn elements; The non-Mn element includes one or both of a first doping element and a second doping element, wherein the first doping element is a manganese doping element and the second doping element is a phosphorus doping element; The first doping element includes one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge; and / or the second doping element includes one or more elements selected from the group consisting of B, S, Si, and N.

17. The secondary battery according to claim 15, characterized in that The positive electrode active material includes: Li 1+x Mn 1-y A y P 1-z R z O4, wherein x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, and z is any value in the range of 0.001 to 0.100, said A comprises one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, or Ge, and said R comprises one or more elements selected from B, S, Si, or N; or The positive electrode active material includes: Li a A e Mn 1-f B f P 1-g C g O 4-n D n ; wherein, A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo or W; B includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb or Ge; C includes one or more elements selected from B, S, Si or N; D includes one or more elements selected from S, F, Cl or Br; a is selected from the range of 0.9 to 1.1, e is selected from the range of 0.001 to 0.1, f is selected from the range of 0.001 to 0.5, g is selected from the range of 0.001 to 0.1, n is selected from the range of 0.001 to 0.1, and the positive electrode active material is electrically neutral.

18. The secondary battery according to any one of claims 4 to 5, characterized in that: The negative electrode plate includes: a negative electrode active material; The negative electrode active material includes at least one of graphite, soft carbon or hard carbon material.

19. An electrical device, characterized in that: The electrical device comprises the secondary battery according to any one of claims 1 to 18.

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