Battery monomer, preparation method and application thereof, and low-temperature charging method of battery

Abstract

The invention discloses a battery monomer and a preparation method thereof, a battery module, a battery pack, a power utilization device and a low-temperature charging method of a battery. The battery monomer provided by the embodiment of the invention comprises an electrolyte and an electrode assembly infiltrated in the electrolyte, and the viscosity of the electrolyte is 5-10mPa. S at 0 DEG C; and / or the electrode assembly comprises a sodium ion layered oxide in which the stoichiometric ratio of manganese element to oxygen element is (0.1-0.4): 2. The low-temperature impedance of the battery cell of the single battery is improved, polarization heat is generated during charging under the low-temperature condition, and the charging time of the single battery under the low-temperature condition can be obviously shortened. The battery module, the battery pack and the power utilization device all contain the single battery.

Description

Technical Field

[0001] The present application belongs to the field of battery technology, and specifically relates to a battery cell and a preparation method and application thereof, and a low-temperature charging method for a battery. Background Art

[0002] Ion batteries store and discharge energy through the migration of ions between the positive and negative electrodes. However, the migration of metal ions (such as sodium ions, lithium ions, etc.) between the positive and negative electrodes is greatly affected by temperature. For example, in a low-temperature environment, due to factors such as increased electrolyte viscosity and decreased conductivity, the internal resistance of the ion battery will increase significantly, and the performance will drop sharply, resulting in the inability of the ion battery to discharge at low temperatures. At the same time, the ion battery will charge slowly and for too long in a low-temperature environment. Even worse, it will cause side reactions such as metal ion precipitation at the negative electrode, which will lead to safety issues. Summary of the invention

[0003] In view of the above problems, the present application provides a battery cell and a preparation method and application thereof, and a method for low-temperature charging of the battery cell, so as to solve the technical problems of long charging time and potential safety risks of existing batteries at low temperatures.

[0004] In a first aspect, an embodiment of the present application provides a battery cell. The battery cell of the embodiment of the present application includes an electrolyte and an electrode assembly immersed in the electrolyte, and at 0° C., the viscosity of the electrolyte is 5 to 10 mPa·S.

[0005] The viscosity of the electrolyte in the battery cell of the embodiment of the present application is controlled within the above range under the low temperature condition of 0°C, which can increase the low temperature impedance of the battery cell, so that polarization heat will be generated when the battery cell is charged under low temperature conditions, and the temperature of the single cell can be quickly and evenly increased in a short time to reach the temperature range of conventional charging. This can significantly shorten the charging time of the battery cell under low temperature conditions. At the same time, the amount of crystallization of the negative electrode caused by low temperature charging of the battery cell is reduced, the attenuation of the reversible capacity of the battery cell is alleviated, and the safety performance of the battery cell is improved. Moreover, the battery cell of the embodiment of the present application has good cycle performance during conventional charging and discharging, and can maintain a normal cell temperature.

[0006] In some embodiments, at 0° C., the viscosity of the electrolyte is 5-8 mPa·S.

[0007] In some embodiments, the positive electrode material contained in the positive electrode sheet in the electrode assembly includes a sodium ion layered oxide, and the layered oxide contains a manganese element. In the sodium ion layered oxide, the stoichiometric ratio of the manganese element to the oxygen element is (0.1 to 0.4):2, and can be optionally (0.2 to 0.3):2.

[0008] Further controlling the viscosity of the electrode liquid at 0°C to 5-8mPa·S, or further controlling the stoichiometric ratio of the manganese element in the positive electrode material contained in the positive electrode sheet to be within the range based on the above-mentioned low-temperature viscosity of the electrolyte, can further adjust, for example, increase the low-temperature impedance of the battery cell, thereby further appropriately increasing the polarization heat generated by the battery cell when charging under low temperature conditions, further shortening the charging time of the battery cell under low temperature conditions, and at the same time improving the cycle performance of the battery cell in the conventional charging and discharging process and the temperature stability of the cell of the embodiment of the present application.

[0009] In some embodiments, the non-aqueous organic solvent contained in the electrolyte includes at least one of a linear carbonate and a cyclic carbonate.

[0010] In an exemplary embodiment, the linear carbonate includes at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0011] In an exemplary embodiment, the cyclic carbonate includes at least one of ethylene carbonate (EC) and propylene carbonate (PC).

[0012] The selection of these non-aqueous organic solvents can further adjust the viscosity of the electrolyte under low temperature conditions (0°C) to the above 5-10mPa·S, which can be selected to be in the range of 5-8mPa·S, and further appropriately improve the low temperature impedance of the battery cell, shortening the charging time of the battery cell at low temperatures. At the same time, it can also further reduce the crystallization phenomenon during low temperature charging, thereby further improving the safety performance of the battery cell. At the same time, it improves the cycle performance and cell temperature stability of the battery cell in the conventional charging and discharging process of the embodiment of the present application.

[0013] In some embodiments, the non-aqueous organic solvent comprises a mixed organic solvent of any one of the following (1) to (3):

[0014] (1) ethylene carbonate (EC) and dimethyl carbonate (DMC), wherein the volume ratio of ethylene carbonate to dimethyl carbonate is 10:(5-10), or alternatively 10:(5-8);

[0015] (2) propylene carbonate (PC) and ethyl methyl carbonate (EMC), wherein the volume ratio of propylene carbonate to ethyl methyl carbonate is 10:(5-10), or alternatively 10:(5-8);

[0016] (3) Ethylene carbonate (EC) and propylene carbonate (PC), wherein the volume ratio of ethylene carbonate to propylene carbonate is 10:(10-15), and optionally 10:(10-12).

[0017] In each embodiment, the non-aqueous organic solvent is compounded with two or more components, which can further adjust the viscosity of the electrolyte under low temperature conditions, such as 0°C, to 5-10 mPa·S, which can be optionally 5-8 mPa·S, and more effectively adjust and appropriately improve the low temperature impedance of the battery cell, further shortening the charging time at low temperature. When the temperature of the battery cell gradually increases during low temperature charging, the viscosity of the electrode liquid can be reduced to reduce the impedance of the battery cell during conventional charging and discharging, improve the electrochemical performance of the battery cell in the embodiment of the present application during conventional charging and discharging, and enable the cell to maintain a normal cell temperature.

[0018] In some embodiments, the concentration of the electrolyte contained in the electrolyte is 0.7-1.3 mol / L, and optionally 0.8-1.2 mol / L. Setting the concentration of the electrolyte in the electrolyte within this range can adjust the viscosity of the electrolyte under low temperature conditions, such as below 0°C, in conjunction with components such as solvents, more effectively adjust and appropriately improve the low temperature impedance of the battery cell, and further shorten the charging time at low temperatures. At the same time, the electrochemical performance of the battery cell during conventional charging and discharging is improved.

[0019] In some embodiments, the sodium ion layered oxide comprises Na x Mn y M z O2, wherein 0.8≤x≤1, optionally 0.85≤x≤1; 0.1≤y≤0.4, optionally 0.2≤y≤0.3; 0.9≤y+z≤1, optionally 0.95≤y+z≤1; M is at least one of an active metal element and an inert metal element. x Mn y M z The sodium ion layered oxide shown in O2 can further improve the low-temperature impedance of the battery cell under low-temperature conditions, further increase the polarization heat generated by the battery cell during low-temperature charging, accelerate the heating rate of the battery cell during low-temperature charging, and reach the temperature range of conventional charging in a short time. Since the low-temperature charging time can be further shortened, the amount of negative electrode crystallization caused by low-temperature charging is further reduced, and the battery safety performance and cycle performance are improved.

[0020] In an embodiment, M includes at least one of Fe, Ni, Co, Cr, Sc, Ti, V, Cr, Cu, Zn, and Al.

[0021] When the M includes active metal elements among the metal elements, the active metal elements represented by the M can increase the Na x Mn y M zO2 gram capacity; when the M includes inert metal elements in these metal elements, the inert metal elements shown in these M can increase Na x Mn y M z The structural stability of O2 increases the Na x Mn y M z O2 cycle performance and gram capacity play.

[0022] In some embodiments, the sodium ion layered oxide includes at least one of the oxides represented by the following chemical formula:

[0023] Na 0.94 Mn 0.36 Fe 0.3 Ni 0.3 O2、Na 0.94 Mn 0.26 Fe 0.35 Ni 0.35 O2、Na 0.94 Mn 0.36 Fe 0.3 Ni 0.24 Zn 0.08 O2、Na 0.94 Mn 0.36 Fe 0.3 Ni 0.24 Cu 0.08 O2、Na 0.92 Mn 0.3 Fe 0.3 Ni 0.36 O2、Na 0.92 Mn0.1Fe 0.3 Ni 0.56 O2、Na 0.92 Mn 0.2 Fe 0.3 Ni 0.4 6O2、Na 0.92 Mn 0.4 Fe 0.3 Ni 0.26 O2.

[0024] The sodium ion layered oxides shown in these chemical formulas have a specific stoichiometric ratio of manganese elements to other metal elements, which can further improve the low-temperature impedance of the battery cell under low-temperature conditions, thereby further accelerating the heating rate of the battery cell during low-temperature charging, so as to quickly heat up to the temperature range of conventional charging, thereby further shortening the low-temperature charging time of the battery cell. At the same time, it can also reduce the amount of crystallization of the negative electrode caused by low-temperature charging, thereby improving the safety performance and cycle performance of the battery.

[0025] In some embodiments, the battery cells include sodium ion battery cells.

[0026] In a second aspect, the present invention provides a method for preparing a battery cell. The method for preparing a battery cell in the present invention comprises the following steps:

[0027] Prepare electrolyte and provide electrode assembly;

[0028] The electrode assembly is installed in the containing cavity of the battery shell, the electrolyte is injected into the containing cavity, and the battery cell packaging process is performed to obtain the battery cell.

[0029] Wherein, when the electrolyte is at 0°C, the viscosity of the electrolyte is 5-10 mPa·S.

[0030] The battery cell prepared by the battery cell preparation method of the embodiment of the present application has a higher low-temperature impedance than the existing conventional battery cell, so that the battery cell can generate polarization heat when charged at low temperature, so that it can quickly heat up in a short time, thereby significantly shortening the charging time of the battery cell under low temperature conditions. At the same time, the prepared battery cell can effectively volatilize its electrochemical properties during the conventional charging and discharging process, such as having good cycle performance and being able to maintain normal battery cell temperature.

[0031] In some embodiments, the positive electrode material contained in the positive electrode sheet of the electrode assembly includes a sodium ion layered oxide, and the layered oxide contains a manganese element. In the sodium ion layered oxide, the stoichiometric ratio of the manganese element to the oxygen element is (0.1-0.4):2, and can be optionally (0.2-0.3):2. Further controlling the manganese-oxygen ratio of the sodium ion layered oxide within this range can assist the electrolyte in further adjusting the low-temperature impedance of the battery cell, thereby further appropriately increasing the polarization heat generated by the battery cell when charging under low temperature conditions, further shortening the charging time of the battery cell under low temperature conditions, and at the same time improving the volatilization of the electrochemical performance of the battery cell of the embodiment of the present application during conventional charging and discharging.

[0032] In a third aspect, the embodiments of the present application provide a battery module. The battery module of the embodiments of the present application includes a battery cell of the embodiments of the present application or a battery cell prepared by a battery cell preparation method of the embodiments of the present application.

[0033] Since the battery module of the embodiment of the present application contains the battery cells of the embodiment of the present application, the battery module of the embodiment of the present application has a higher low-temperature impedance than the conventional battery module. When charging under low temperature conditions, it can increase its own temperature in a short time, such as reaching the temperature range of conventional charging, shortening the charging time at low temperature, and the temperature of each battery cell contained therein after heating is uniform. On this basis, the amount of crystallization of the negative electrode caused by low-temperature charging of the battery cells of the embodiment of the present application contained in the battery module can be significantly reduced, thereby improving the safety performance of the battery module. At the same time, the battery module of the embodiment of the present application has good cycle performance during conventional charging and discharging, and the battery cell temperature is stable.

[0034] In a fourth aspect, an embodiment of the present application provides a battery pack. The battery pack of the embodiment of the present application includes a battery module of the embodiment of the present application.

[0035] Since the battery pack of the embodiment of the present application also contains the battery cells of the embodiment of the text application, the battery pack of the embodiment of the present application has a higher low-temperature impedance than the conventional battery pack. When charging under low temperature conditions, it can increase its own temperature in a short time to reach the temperature range of conventional charging, shortening the charging time at low temperatures, and the temperature of each battery cell contained therein after heating is uniform. On this basis, the amount of crystallization of the negative electrode caused by low-temperature charging of the battery cells of the embodiment of the text application contained in the battery pack can be significantly reduced, thereby improving the safety performance and cycle performance of the battery pack. At the same time, the battery pack of the embodiment of the present application has good cycle performance during conventional charging and discharging, and the battery cell temperature is stable.

[0036] In a fifth aspect, the present application provides an electric device. The electric device of the present application includes at least one of the battery cell of the present application, the battery module of the present application, and the battery pack of the present application.

[0037] Since the electrical device of the embodiment of the present application contains at least one of the battery cells, battery modules or battery packs of the embodiment of the present application, the power supply unit or energy storage unit of the electrical device of the embodiment of the present application can be quickly charged at low temperatures, and has relatively high safety performance at low temperatures, and the power supply unit or energy storage unit contained therein has relatively high cycle performance.

[0038] In a fifth aspect, an embodiment of the present application provides a low-temperature charging method for a battery. The low-temperature charging method for a battery in an embodiment of the present application comprises the following steps:

[0039] When it is detected that the initial temperature of the battery is lower than or equal to a threshold value, pulse charging is performed on the battery;

[0040] When the temperature of the battery rises to a predetermined temperature, the pulse charging process for the battery is stopped, and a conventional charging process is performed on the battery;

[0041] Among them, the battery includes at least one of the battery cell of the embodiment of the present application, the battery module of the embodiment of the present application, and the battery pack of the embodiment of the present application, and the charging rate of the pulse charging process is higher than the charging rate of the conventional charging process.

[0042] The low-temperature charging method of the battery in the embodiment of the present application can generate polarization heat in the battery cell during high-rate pulse charging, so that the temperature of the battery itself can rise rapidly in a short time, thereby heating up to a predetermined temperature in a relatively short time, effectively shortening the charging time of the battery under low-temperature conditions. It can also improve the uniformity of the temperature of each battery cell, reduce the amount of crystallization of the negative electrode caused by low-temperature charging, thereby significantly alleviating the attenuation of the battery's reversible capacity and improving the battery's safety performance and cycle performance.

[0043] In some embodiments, the pulse charging process includes the following conditions:

[0044] 1.5~5C charging 0.01~0.1S, optional 2~3C charging 0.05~0.1S;

[0045] 1.5~5C discharge for 0.01~1S, optionally 3~5C discharge for 0.01~0.05S.

[0046] The pulse charging process is set to the high rate condition to pulse charge the battery, increase the polarization heat generated by the battery in a short time, further increase the temperature rise rate of the battery during the pulse charging process, shorten the pulse charging process time, and thus further shorten the overall charging time of the battery under low temperature conditions. At the same time, the amount of negative electrode crystallization occurring during the pulse charging process is further reduced to further alleviate the attenuation of the battery's reversible capacity.

[0047] In some embodiments, the threshold value is -40 to 5°C, and may be -40 to 0°C.

[0048] In some embodiments, before the pulse charging process is performed on the battery, a state of charge detection process is further performed on the battery, and when the state of charge is ≤50%, the pulse charging process is performed on the battery.

[0049] On the basis of detecting the initial temperature of the battery, the state of charge of the battery is further detected. Specifically, the pulse charging of the battery is started when the state of charge of the battery is ≤50%. This can increase the heating rate of the battery cell under pulse charging at low temperature and high rate.

[0050] In some embodiments, the predetermined temperature is 0-10°C.

[0051] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0053] Figure 1 This is a schematic structural diagram of an implementation of a battery cell according to an embodiment of the present application;

[0054] Figure 2 for Figure 1 An exploded schematic diagram of the battery cell shown;

[0055] Figure 3 This is a schematic structural diagram of an implementation scheme of a battery module according to an embodiment of the present application;

[0056] Figure 4 A schematic diagram of the exploded structure of a battery pack according to an embodiment of the application;

[0057] Figure 5 It is a schematic diagram of an implementation of an electrical device including the battery of an embodiment of the present application as a power source.

[0058] The reference numerals in the specific implementation manner are as follows:

[0059] 10-battery cell, 11-housing, 12-electrode assembly, 13-cover plate;

[0060] 20-battery module;

[0061] 30-battery pack, 31-upper box, 32-lower box. DETAILED DESCRIPTION

[0062] The following embodiments of the technical solution of the present application are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0063] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field 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" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0064] In the description of the embodiments of the present application, the technical terms "first", "second", etc. 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. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0065] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0066] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0067] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0068] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, which 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 referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the embodiments of the present application.

[0069] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0070] With the continuous development of the application of batteries as power batteries and energy storage batteries, higher requirements are put forward for the application environment of batteries, especially low-temperature applications and safety performance. Ion batteries store and discharge energy through the migration of metal ions such as lithium ions or sodium ions between the positive and negative electrodes. However, the migration of metal ions such as lithium ions or sodium ions between the positive and negative electrodes is greatly affected by temperature, especially at low temperatures, the kinetic conditions of the positive and negative electrodes deteriorate and the battery performance drops sharply.

[0071] If ion batteries are charged directly at low temperatures, the amount of electricity that can be charged into the ion batteries will be significantly lower than that at normal temperature, and the charging time will be significantly extended, or even impossible to charge; at the same time, low-temperature charging can easily lead to crystallization of the negative electrode, which will not only cause the battery's reversible capacity to rapidly decay, but may also cause serious safety hazards.

[0072] At present, the common solutions to solve the problem of low-temperature charging of ion batteries are: first, to establish an additional external heating system, use the external heating system to heat the ion battery to the optimal working temperature or room temperature of the ion battery, and then charge the ion battery; second, to add insulation and heat preservation materials to the periphery of the ion battery to ensure that the temperature of the ion battery does not drop too low, so as to make the temperature of the ion battery at or close to the optimal working temperature or room temperature as much as possible. However, each of these methods has certain shortcomings. For example, when an external heating system is used for heating, due to the poor heat transfer performance of the battery, especially the battery module or battery pack itself, the scheme has the defects of low efficiency and easy to cause uneven temperature of the ion battery, which is not ideal for improving the low-temperature charging and discharging of the battery, and the uneven working temperature of the battery, especially the battery module or battery pack, will have an adverse effect on the battery life, safety and other aspects. When adding heat preservation and heat insulation materials, the volume energy density of the battery will be reduced, and it will not be able to keep warm for a long time. In addition, the above two common methods will also increase the cost of the battery.

[0073] In order to effectively alleviate the problem of low-temperature charging of ion batteries, an ion battery monomer is proposed through research. By selecting the positive electrode material contained in the ion battery monomer and controlling the viscosity of the electrolyte at low temperature, the ion battery monomer can generate polarization heat when charging at low temperature, and can increase the temperature of the ion battery monomer in a short time and relatively evenly, thereby improving the electrochemical performance of the ion battery monomer in a low-temperature environment, shortening the charging time of the battery, and improving the safety performance. At the same time, the ion battery monomer can give full play to its electrochemical performance during the conventional charging and discharging process, such as having good cycle performance, and can maintain a normal battery cell temperature.

[0074] Based on the above research, the embodiments of the present application propose the following technical solutions.

[0075] [Battery Cell]

[0076] In a first aspect, the embodiments of the present application provide a battery cell. In some embodiments, the battery cell of the embodiments of the present application includes an electrode assembly and an electrolyte, wherein the electrode assembly is immersed in the electrolyte. Wherein, at 0°C, the viscosity of the electrolyte is 5 to 10 mPa·S.

[0077] The battery cell of the embodiment of the present application is also called a battery cell, which refers to a battery outer package and the electrode assembly and the electrolyte encapsulated in the battery outer package. The number of the electrode assemblies contained in the battery cell can be one or more, which can be adjusted according to actual needs; the electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator, and the positive electrode sheet and the negative electrode sheet are alternately stacked, and the separator is stacked between the positive electrode sheet and the negative electrode sheet to play an isolation role, separating the positive electrode sheet from the negative electrode sheet. The electrolyte is a carrier that conducts ions between the positive and negative electrodes. The stoichiometric ratio of manganese element to oxygen element can be the mole of manganese element to oxygen element, or it can be a mass ratio based on molar conversion.

[0078] The viscosity of the electrolyte in the battery cell of the embodiment of the present application at 0°C is 5-10 mPa·S, which does not mean that the viscosity is the same when the temperature rises to the normal operating temperature of the battery cell. For example, as the temperature gradually rises, the viscosity of the electrolyte in the battery cell of the embodiment of the present application will gradually decrease and reach the viscosity range of the normal operation of the battery cell. Similarly, the viscosity range of 5-10 mPa·S of the electrolyte refers to the viscosity at 0°C. When the temperature continues to decrease, the temperature of the electrolyte will also decrease. Therefore, even if the electrolyte is not 5-10 mPa·S when it is below 0°C, as long as the viscosity of the electrolyte is 5-10 mPa·S when the temperature is raised to 0°C, it is also within the scope disclosed and defined in the embodiments of the present application.

[0079] The viscosity of the electrolyte in the battery cell of the embodiment of the present application at 0°C is controlled within the above range, which can increase the low-temperature impedance of the battery cell, so that polarization heat will be generated when the battery cell is charged under low-temperature conditions, and the temperature of the single cell can be quickly and evenly increased in a short time to reach the temperature range of conventional charging. This can significantly shorten the charging time of the battery cell under low-temperature conditions.

[0080] Further research found that, because the charging time of battery cells under low temperature conditions can be shortened, the amount of negative electrode crystallization caused by low temperature charging of battery cells is significantly reduced, thereby alleviating the attenuation of the reversible capacity of the battery cells and improving the safety performance of the battery cells. At the same time, after testing, in addition to having relatively high low-temperature impedance at low temperatures, the battery cells of the embodiments of the present application also have good cycle performance during conventional charging and discharging processes, and can maintain normal battery cell temperatures, such as the battery cells can be maintained within a safe operating temperature range.

[0081] Electrolyte of battery cells:

[0082] The electrolyte contained in the battery cell of the embodiment of the present application refers to a solution capable of conducting electric current, which contains a solvent, an electrolyte dissolved in the solvent, and may further contain an electrolyte additive dispersed in the solvent. Among them, the solvent serves as a solvent carrier of the electrolyte; the electrolyte is an inorganic salt or organic salt that plays a role in transferring ions and maintaining ion balance in the electrolyte; the additive is a component other than the organic solvent and the electrolyte component used to improve the relevant properties of the battery cell, such as improving film formation, conductivity, etc., and the additive dispersed in the solvent can at least be understood as dissolved in the organic solvent.

[0083] In some embodiments, the viscosity of the electrolyte at 0°C is 5 to 10 mPa·S, optionally 5 to 8 mPa·S. In the exemplary embodiment, the viscosity at 0°C can be 5 mPa·S, 6 mPa·S, 7 mPa·S, 8 mPa·S, 9 mPa·S, 10 mPa·S, or other typical but non-limiting viscosities or a range between any two viscosity values. These viscosities are all viscosities at 0°C. When the temperature continues to decrease, such as below 0°C, the viscosity of the electrolyte will decrease, that is, the viscosity value will be lower than 5 to 10 mPa·S. However, as long as the temperature of the electrolyte is raised to 0°C, its viscosity is in the range of 5 to 10 mPa·S, which is within the scope disclosed in the embodiments of the present application. In the demonstration example, it was tested that when the viscosity of the electrolyte at a low temperature of 0°C was 6mPa·S, 7mPa·S, 8mPa·S, etc., the viscosity at a low temperature of -40°C was reduced to 22mPa·S, 26mPa·S, 30mPa·S, respectively.

[0084] Under low temperature conditions, controlling the viscosity of the electrolyte within the above range can effectively increase the low temperature impedance of the battery cell. When charging under low temperature conditions, the battery cell will increase its own temperature in a short period of time to reach the temperature range of conventional charging, shortening the charging time at low temperatures. On this basis, the amount of crystallization of the negative electrode caused by low temperature charging of the battery cell can be significantly reduced, thereby improving the safety performance of the battery. At the same time, when the battery cell of the embodiment of the present application can give full play to the electrochemical properties of the cell during conventional charging and discharging, such as having good cycle performance, and can maintain a normal cell temperature.

[0085] In some embodiments, the solvent contained in the electrolyte includes a non-aqueous organic solvent, and the non-aqueous organic solvent may include at least one of a linear carbonate and a cyclic carbonate.

[0086] In an exemplary embodiment, the cyclic carbonate may include at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and γ-butyrolactone (GBL).

[0087] In an exemplary embodiment, the linear carbonate may include at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate, methyl formate (MF), ethyl formate, methyl acetate, ethyl acetate (EA), propyl formate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate.

[0088] The above-mentioned non-aqueous organic solvents can adjust the viscosity of the above-mentioned electrolyte to 5-10mPa·S, and can be selected as 5-8mPa·S under low temperature conditions such as 0°C, so as to adjust, specifically, appropriately increase the low-temperature impedance of the battery cell, and further shorten the charging time at low temperature. Moreover, as the temperature of the battery cell of the embodiment of the present application increases, the viscosity of the electrolyte can be adjusted to decrease as the temperature gradually increases. For example, when the temperature rises to the normal operating temperature range of the battery cell, the viscosity of the electrolyte can be reduced to the viscosity range of the normal operation of the battery cell. In addition, these non-aqueous organic solvents can also effectively improve the stability of the electrolyte during the charging and discharging process, further reduce the crystallization phenomenon and the amount of crystallization during the low-temperature charging process, and improve the safety performance of the battery cell. At the same time, the electrochemical performance of the battery cell of the embodiment of the present application in the normal charging and discharging process is improved, such as having good cycle performance and maintaining a normal cell temperature.

[0089] In some embodiments, the non-aqueous organic solvent may include at least one of EC, PC, DMC, and EC. The selection of these non-aqueous organic solvents can further adjust the viscosity of the electrolyte under low temperature conditions within the above range of 5 to 10 mPa·S, and further adjust and appropriately improve the low temperature impedance of the battery cell, shortening the charging time of the battery cell at low temperatures. At the same time, it can also further reduce the crystallization phenomenon during low temperature charging, thereby further improving the safety performance of the battery cell and the electrochemical performance during conventional charging and discharging, as well as maintaining normal cell temperature.

[0090] In some embodiments, the non-aqueous organic solvent contained in the electrolyte in the above embodiments includes any one of the following mixed organic solvents (1) to (3):

[0091] (1) Composition A1: ethylene carbonate (EC) and dimethyl carbonate (DMC), the volume ratio of ethylene carbonate (EC) to dimethyl carbonate (DMC) is 10:(5-10), optionally 10:(5-8);

[0092] (2) Composition A2: propylene carbonate (PC) and ethyl methyl carbonate (EMC), wherein the volume ratio of PC to EMC is 10:(5-10), optionally 10:(5-8);

[0093] (3) Composition A3: ethylene carbonate (EC) and propylene carbonate (PC), wherein the volume ratio of EC to PC is 10:(10-15), and optionally 10:(10-12).

[0094] In the above embodiments, the non-aqueous organic solvent is compounded with two or more components, which can further adjust the viscosity of the electrolyte under low temperature conditions, such as at 0°C, to 5-10 mPa·S, more effectively adjust and appropriately improve the low temperature impedance of the battery cell, and further shorten the charging time at low temperature. When the temperature of the battery cell gradually increases during low temperature charging, it can be further adjusted to specifically reduce the viscosity of the electrode liquid to reduce the impedance of the battery cell during conventional charging and discharging. At the same time, it can further reduce the crystallization phenomenon of the battery cell during low temperature charging, improve the safety performance of the battery cell and the electrochemical performance during conventional charging and discharging, and maintain normal cell temperature.

[0095] In some embodiments, the concentration of the electrolyte contained in the electrolyte of the embodiment of the present application in the electrolyte of the embodiment of the present application is 0.7 to 1.3 mol / L, optionally 0.8 to 1.2 mol / L. In the exemplary embodiment, it can be 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, etc. Typical but non-limiting viscosities or a range between any two viscosity values. Setting the concentration of the electrolyte in the electrolyte within this range can adjust the viscosity of the electrolyte under low temperature conditions such as below 0°C in conjunction with components such as solvents, more effectively adjust and appropriately increase the low temperature impedance of the battery cell, and further shorten the charging time at low temperatures. The concentration of the electrolyte can be achieved by adjusting the units of the above-mentioned solvent and electrolyte, such as mass or molar ratio.

[0096] In some embodiments, the electrolyte contained in the electrolyte may include sodium salt or lithium salt. When the electrolyte contains sodium salt, the battery cell of the embodiment of the present application may be a sodium battery cell; when the electrolyte contains lithium salt, the battery cell of the embodiment of the present application may be a lithium battery cell.

[0097] In an embodiment, when the electrolyte contains a sodium salt, the sodium salt may include at least one of a fluorine-containing sodium salt, a boron-containing sodium salt, and other sodium salts. In an exemplary embodiment, the fluorine-containing sodium salt may include at least one of sodium hexafluorophosphate (NaPF6), sodium trifluoromethanesulfonate (NaOTF), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), etc. In an exemplary embodiment, the boron-containing sodium salt may include at least one of sodium tetrafluoroborate (NaBF4), sodium bis(oxalatoborate) (NaBOB), sodium difluorooxalatoborate (NaDFOB), sodium trifluoromethanesulfonylimide, sodium metaborate (NaBO2), sodium borate (Na2B4O7), etc. In the exemplary embodiment, other sodium salts may include but are not limited to at least one of sodium perchlorate (NaClO4), sodium sulfide, sodium chloride, sodium fluoride, sodium sulfate, sodium carbonate, sodium phosphate, sodium nitrate, sodium pyrophosphate, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, trisodium citrate, sodium molybdate, sodium tungstate, sodium bromide, sodium nitrite, sodium iodate, sodium iodide, sodium silicate, sodium lignin sulfonate, sodium oxalate, sodium aluminate, sodium methane sulfonate, sodium acetate, sodium dichromate, and sodium hexafluoroarsenate.

[0098] The above-mentioned sodium salt electrolyte has good stability and has good functions of transferring ions, maintaining ion balance and electrochemical stability in the electrolyte. When under low temperature conditions, its solubility in solvents such as the non-aqueous organic solvents mentioned above is reduced, so that the viscosity of the electrolyte at low temperature is adjusted with solvents such as the non-aqueous organic solvents mentioned above, such as adjusting to 5-10 mPa·S (0°C), which can more effectively adjust and appropriately improve the low-temperature impedance of the battery cell, and further shorten the charging time of the battery cell at low temperature. Moreover, as the temperature of the battery cell of the embodiment of the present application increases, the solubility of these electrolytes in solvents such as the non-aqueous organic solvents mentioned above can gradually increase, so that the viscosity of the electrolyte will decrease with the increase in temperature, such as when the temperature rises to the normal operating temperature range of the battery cell, the viscosity of the electrolyte can be reduced to the normal working viscosity range of the battery cell.

[0099] In addition, when the electrolyte contains a lithium salt, the lithium salt can also be a composite of two or more lithium salts to more effectively adjust the viscosity of the electrolyte under low temperature conditions, specifically appropriately increase the viscosity of the electrolyte under low temperature conditions, further shorten the charging time of the battery cell under low temperature, and at the same time improve the stability of the electrolyte charge and discharge.

[0100] In some embodiments, the electrolyte may further contain additives, such as vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), succinonitrile (SN), adiponitrile (ADN), glutaronitrile (GLN), hexanetrinitrile (HTN), 1,3-propane sultone (1,3-PS), vinyl sulfate (DTD), methylene disulfonate (MMDS), 1-propylene-1,3-sulfonic acid The invention can include one or more of tris(trimethylsilyl) phosphate (TMSP) and tris(trimethylsilyl) borate (TMSB), but is not limited thereto.

[0101] These additives can improve the performance of the electrolyte, such as film-forming property, low temperature resistance and high temperature resistance, etc., depending on the specific type of the additive. The presence of the additive can also appropriately increase the viscosity of the electrolyte under low temperature conditions together with the electrolyte and other components, and adjust the low temperature impedance of the battery cell, thereby shortening the charging time of the battery cell under low temperature.

[0102] Electrode assembly of battery cell:

[0103] The electrode assembly contained in the battery cell of the embodiment of the present application generally includes a positive electrode sheet, a negative electrode sheet and a separator. The positive electrode sheet and the negative electrode sheet are alternately stacked, and the separator is stacked between the positive electrode sheet and the negative electrode sheet to play an isolation role, separating the positive electrode from the negative electrode. The positive electrode sheet, the separator layer and the negative electrode sheet can form an electrode assembly of a laminated structure through a lamination process, or can form an electrode assembly of a roll core structure through a winding process.

[0104] Positive electrode of the electrode assembly:

[0105] In the embodiment, the positive electrode sheet contained in the electrode assembly includes a positive electrode current collector and a positive electrode active material layer bonded to at least one surface of the positive electrode current collector.

[0106] In the embodiment, the positive electrode current collector contained in the positive electrode sheet may include but is not limited to a metal current collector, a carbon current collector, a conductive resin current collector, a composite current collector of metal and resin, and more specifically aluminum, copper, nickel, titanium, iron and their respective alloys, stainless steel, carbon fiber, carbon nanotube (CNT), graphite, etc. In the embodiment, the current collector may also be a dense film layer or a film layer with a porous structure. In the embodiment, the current collector may be but is not limited to aluminum foil or porous aluminum foil, etc.

[0107] In the embodiment, the positive electrode active material layer contained in the positive electrode sheet may be combined with one surface of the positive electrode current collector, or may be combined with two surfaces of the positive electrode current collector that are arranged opposite to each other. When the surface layer of the positive electrode current collector contains a porous structure or the positive electrode current collector itself is a porous structure, the positive electrode active material layer may be at least partially embedded in the current collector.

[0108] In some embodiments, in the battery cell of the embodiment of the present application, the positive electrode active material in the positive electrode active material layer contained in the positive electrode sheet includes a sodium ion layered oxide, and the layered oxide contains a manganese element. In the sodium ion layered oxide, the stoichiometric ratio of the manganese element to the oxygen element is (0.1-0.4):2. Optionally, the stoichiometric ratio of the manganese element to the oxygen element is (0.2-0.3):2. In the exemplary embodiment, the stoichiometric ratio of the manganese element to the oxygen element can be a typical but non-limiting stoichiometric ratio such as 0.1:2, 0.2:2, 0.3:2, 0.4:2, or a range between any two stoichiometric ratios.

[0109] Under low temperature conditions, the manganese element contained in the layered oxide is controlled within the above-mentioned stoichiometric ratio range, which can be matched with the low temperature viscosity range of the electrolyte contained in the battery body of the above-mentioned application embodiment, and further adjusted, such as increasing the low temperature impedance of the battery cell, appropriately increasing the polarization heat generated when the battery cell is charged under low temperature conditions, and further shortening the charging time at low temperature. At the same time, it can also improve the cycle performance of the battery cell in the conventional charging and discharging process and the temperature stability of the cell of the present application embodiment.

[0110] In an embodiment, the sodium ion layered oxide comprises Na x Mn y M z O2, wherein 0.8≤x≤1, optionally 0.85≤x≤1; 0.1≤y≤0.4, optionally 0.2≤y≤0.3; 0.9≤y+z≤1, optionally 0.95≤y+z≤1; M is at least one of an active metal element and an inert metal element. The active metal element refers to a metal element that can react with Na x Mn y M z O2 gram capacity, inert metal elements are those that can x Mn y M z A class of metal elements that contribute to the stability of O2 structure. x Mn y M z The stoichiometry of the sodium ion layered oxide manganese element shown in O2 is controlled at 0.1 to 0.4, and can further be 0.2 to 0.3, which can further improve the low-temperature impedance of the battery cell under low-temperature conditions. When the battery cell is charged under low-temperature conditions, the polarization heat generated by the battery cell can be further increased to accelerate the heating rate of the battery cell during low-temperature charging, so as to reach the temperature range of conventional charging in a short time. Since the low-temperature charging time can be further shortened, the amount of negative electrode crystallization caused by low-temperature charging is further reduced, and the battery safety performance and cycle performance are improved.

[0111] Further research has shown that when the battery monomer of the present embodiment contains the above-mentioned sodium ion layered oxide such as the above-mentioned Na x Mn y M z When the temperature is lower than O2, the low temperature impedance of the battery cell will increase appropriately as the content of the Mn element increases; of course, conversely, the low temperature impedance of the battery cell will decrease appropriately as the content of the Mn element decreases.

[0112] In the embodiment, the above Na x Mn y M z M in O2 includes at least one of Fe, Ni, Co, Cr, Sc, Ti, V, Cr, Cu, Zn, and Al. When M includes active metal elements among these metal elements, the active metal elements shown in these M can increase the Na x Mn y M z O2 gram capacity; when the M includes inert metal elements in these metal elements, the inert metal elements shown in these M can increase Na x Mny M z The structural stability of O2 increases the Na x Mn y M z O2 cycle performance and gram capacity play.

[0113] In the example, the above Na x Mn y M z The sodium ion layered oxide may include at least one of the oxides shown in the following chemical formula:

[0114] Na 0.94 Mn 0.36 Fe 0.3 Ni 0.3 O2、Na 0.94 Mn 0.26 Fe 0.35 Ni 0.35 O2、Na 0.94 Mn 0.36 Fe 0.3 Ni 0.24 Zn 0.08 O2、Na 0.94 Mn 0.36 Fe 0.3 Ni 0.24 Cu 0.08 O2、Na 0.92 Mn 0.3 Fe 0.3 Ni 0.36 O2、Na 0.92 Mn0.1Fe 0.3 Ni 0.56 O2、Na 0.92 Mn 0.2 Fe 0.3 Ni 0.4 6O2、Na 0.92 Mn 0.4 Fe 0.3 Ni 0.26 O2.

[0115] The manganese element and other metal elements in the sodium ion layered oxides shown in these chemical formulas have a specific stoichiometric ratio, which can further improve the low-temperature impedance of the battery cell under low-temperature conditions, thereby further accelerating the heating rate of the battery cell during low-temperature charging, so as to quickly heat up to the temperature range of conventional charging, thereby further shortening the low-temperature charging time of the battery cell. Since the low-temperature charging time can be further shortened, the amount of negative electrode crystallization caused by low-temperature charging is further reduced, and the battery safety and cycle performance are improved. The content of iron and manganese elements in these sodium ion layered oxides also has relatively high gram capacity and structural stability.

[0116] In the embodiment, the mass content of the positive electrode active material in the positive electrode active material layer contained in the positive electrode sheet can be 90% to 98%, optionally 92% to 96%. In the exemplary embodiment, it can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% and other typical but non-limiting contents or the range between any two content values. When the positive electrode active material is all sodium ion layered oxides with a stoichiometric ratio of manganese element to oxygen element of (0.1 to 0.4):2 as mentioned above, the mass content of the sodium ion layered oxide in the positive electrode active material layer is 90% to 98%. The positive electrode active material in this content range can effectively improve the energy density of the positive electrode sheet. When containing the sodium ion layered oxide with a stoichiometric ratio of manganese element to oxygen element of (0.1 to 0.4):2 as mentioned above, it can improve the low temperature impedance of the battery cell under low temperature conditions and shorten its low temperature charging time.

[0117] In the embodiment, when the positive active material in the positive active material layer contained in the positive electrode sheet is all or mainly the above sodium ion layered oxide, the battery cell of the embodiment of the present application includes a sodium battery cell. Therefore, the sodium battery cell has a relatively high low temperature impedance, and the charging time can be significantly shortened under low temperature conditions.

[0118] In the embodiment, the positive electrode active material layer contained in the positive electrode sheet generally includes components such as a binder and a conductive agent in addition to the positive electrode active material components mentioned above. The binder can enhance the mechanical properties between the positive electrode active material layer itself and the current collector. The conductive agent can effectively improve the conductivity of the positive electrode, such as reducing the resistance of the positive electrode.

[0119] In an embodiment, the mass content of the binder contained in the above-mentioned positive electrode active material layer can be 0.5% to 5%, optionally 1% to 3%. In a demonstration example, it can be 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, 3% and other typical but non-limiting contents or a range between any two content values.

[0120] In an embodiment, the binder may include one or more of an oil-soluble binder, a water-soluble binder, an emulsion-type binder, etc. In an exemplary example, the oil-soluble binder may include one or more of polyvinylidene fluoride, polyimide, polytetrafluoroethylene, polybutyl acrylate, polyacrylonitrile, etc.; in an exemplary example, the water-soluble binder may include one or more of carboxymethyl cellulose, carboxymethyl cellulose salt, polyacrylic acid, polyacrylic acid salt, polyvinyl alcohol, sodium alginate, cyclodextrin, etc.; in an exemplary example, the emulsion-type binder may include one or more of styrene-butadiene rubber, vinyl acetate resin, acrylic resin, and chlorinated rubber.

[0121] The content within this range and the above-mentioned types of binders can effectively enhance the mechanical properties of the positive electrode active material layer and the bonding strength between the positive electrode and the current collector, and can effectively improve the cycle performance of the positive electrode.

[0122] In the embodiment, the mass content of the conductive agent contained in the positive electrode active material layer can be 0.5% to 5%, optionally 1% to 3%. In the exemplary embodiment, it can be 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, 3% and other typical but non-limiting contents or the range between any two content values. In the embodiment, the conductive agent can include one or more of acetylene black (SP), conductive carbon black (super-P), Ketjen black, graphene, etc. This range of content and the above-mentioned types of conductive agents can effectively improve the conductivity of the positive electrode active material layer.

[0123] Negative electrode sheet of electrode assembly:

[0124] In the embodiment, the negative electrode sheet contained in the electrode assembly may include a negative electrode current collector, and may optionally include a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer contains a negative electrode active material. In the embodiment, the negative electrode current collector may include, but is not limited to, a metal or a composite current collector. For example, as a metal, sodium, sodium alloy, lithium, lithium alloy, copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc. may be used. In the case of using sodium or sodium alloy as the negative electrode current collector, since sodium or sodium alloy itself can also be used as a negative electrode active material; similarly, in the case of using lithium or lithium alloy as the negative electrode current collector, since lithium or lithium alloy itself can also be used as a negative electrode active material; therefore, the negative electrode sheet may not contain a negative electrode active material layer, and sodium, sodium alloy or lithium, lithium alloy is both a current collector and a negative electrode active material.

[0125] The composite current collector may include a composite material of a polymer material and a metal, wherein the polymer material may include but is not limited to polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc., and the metal may include but is not limited to sodium, lithium, copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. The composite current collector may be obtained by mixing a polymer material and a metal, or may be coated on at least one side of the polymer material by electroplating, coating, or other methods.

[0126] When the negative electrode includes a negative electrode active material layer, the negative electrode active material in the negative electrode active material layer may include but is not limited to a mixture or composite material formed by any one or more of carbon-based materials, alloy materials, titanium-based materials, sodium metal, and lithium metal. Among them, the carbon-based material includes but is not limited to one or more of graphite, soft carbon, hard carbon, carbon microspheres, and carbon fibers; the alloy material includes but is not limited to one or more of sodium-tin alloy, sodium-germanium alloy, and sodium-antimony alloy, or the alloy material includes but is not limited to one or more of lithium-tin alloy, lithium-germanium alloy, and lithium-antimony alloy; the titanium-based material includes but is not limited to one or more of titanium dioxide, titanate, and titanium phosphate.

[0127] The mass content of the negative electrode active material in the negative electrode active material layer can be 85% to 98%, and can be optionally 95% to 98%. In the exemplary embodiment, it can be 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% and other typical but non-limiting contents or the range between any two content values.

[0128] The negative electrode active material layer may also include at least one of a conductive agent and a binder. The conductive agent is used to collect current between the negative electrode active materials and between the active materials and the current collector to improve the electronic conductivity. At the same time, the conductive agent can also promote the infiltration of the electrolyte into the negative electrode sheet. The binder can improve the bonding strength between the various substances in the negative electrode active material layer and between the negative electrode active material layer and the current collector.

[0129] In the embodiment, the mass content of the conductive agent in the negative electrode active material layer can be 0.5% to 10%. In the exemplary embodiment, it can be 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% and other typical but non-limiting contents or a range between any two content values, and can also be set to other contents as needed. In the exemplary embodiment, the conductive agent includes one or more of acetylene black (SP), carbon nanotubes, conductive carbon black (super-P), Ketjen black, carbon fiber, and graphene.

[0130] In the embodiment, the mass content of the binder in the negative electrode active material layer can be 0.5% to 10%. In the exemplary embodiment, it can be 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% and other typical but non-limiting contents or a range between any two content values, and can also be set to other contents as needed. In the exemplary embodiment, the binder includes but is not limited to polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, polyimide, polytetrafluoroethylene, polybutyl acrylate, polyacrylonitrile, carboxymethyl cellulose, carboxymethyl cellulose salt, polyacrylic acid, polyacrylate, polyvinyl alcohol, sodium alginate, cyclodextrin, styrene-butadiene rubber, vinyl acetate resin, acrylic resin, chlorinated rubber and one or more thereof.

[0131] In the embodiment, the negative electrode active material layer may also optionally include a thickener, such as but not limited to carboxymethyl cellulose (CMC). The mass content of the thickener in the negative electrode active material layer may be set to 0.5% to 5%. In the exemplary embodiment, it may be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc., which are typical but non-limiting contents, or a range between any two content values.

[0132] Separator membrane of electrode assembly:

[0133] In the embodiment, the separator is arranged between the positive electrode sheet and the negative electrode sheet as described above, separating the positive electrode sheet from the negative electrode sheet. The separator can prevent the electrons in the battery cell from passing freely, preventing the electrodes from short-circuiting, but can allow cations such as sodium ions or lithium ions in the electrolyte to pass freely between the positive electrode sheet and the negative electrode sheet. The separator can be any known porous structure separator with electrochemical stability and mechanical stability. In the embodiment, the separator includes a single-layer or multi-layer film of at least one of glass fiber, non-woven fabric, polyethylene (PE), polypropylene (PP) and polyvinylidene fluoride (PVDF).

[0134] Outer packaging of battery cells:

[0135] In the embodiment, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.; or it may be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate, etc. The outer packaging shape may be cylindrical, square, or any other shape. The outer packaging shape gives the battery cell a shape, so the shape of the battery cell may also be cylindrical, square, or any other shape corresponding to the shape of the outer packaging. In the exemplary embodiment, the battery cell may be as follows: Figure 1 The battery cell 10 shown has a square structure.

[0136] In some embodiments, Figure 2 As shown, the outer packaging of the battery cell 10 may include a shell 11 and a cover plate 13. The shell 11 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 11 has an opening connected to the receiving cavity, and the cover plate 13 is used to cover the opening to close the receiving cavity. One or more upper electrode assemblies 12 and the upper electrolyte are encapsulated in the receiving cavity.

[0137] [Method for preparing battery cell]

[0138] In a second aspect, the present application also provides a method for preparing the above battery cell. The method for preparing the battery cell in the present application comprises the following steps:

[0139] S10: preparing electrolyte and providing electrode assembly;

[0140] S20: installing the electrode assembly into the containing cavity of the battery shell, injecting electrolyte into the containing cavity, and performing battery cell packaging processing to obtain a battery cell.

[0141] In the method for preparing a battery cell in the embodiment of the present application, the electrolyte prepared in step S10 may be the electrolyte of a conventional ion battery cell. In the embodiment, it may be the electrolyte contained in the battery cell in the embodiment of the above text application, such as having a viscosity of 5 to 10 mPa·S at 0°C, which may be 5 to 8 mPa·S. When the electrolyte prepared in step S10 is the electrolyte contained in the battery cell in the embodiment of the above text application, the components and component contents contained in the prepared electrolyte are the same as the components and component contents contained in the electrolyte in the battery cell in the embodiment of the above text application, and are not described here in order to save space in this specification.

[0142] The electrode assembly provided in step S10 may be an electrode assembly contained in a conventional liquid ion battery. In an embodiment, it may be an electrode assembly contained in a battery cell of the above-mentioned application embodiment, such as a positive electrode material contained in the positive electrode sheet of the electrode assembly includes a sodium ion layered oxide with a stoichiometric ratio of manganese element to oxygen element of (0.1-0.4):2. When the electrode assembly provided in step S10 is further an electrode assembly contained in a battery cell of the above-mentioned application embodiment, that is, the positive electrode material includes a sodium ion layered oxide with a stoichiometric ratio of manganese element to oxygen element of (0.1-0.4):2, then the electrode assembly may be an electrode assembly in which the positive electrode sheet, negative electrode sheet and separator contained in the electrode assembly in the battery cell of the above-mentioned application embodiment can be formed into a laminated structure by a lamination process, or an electrode assembly in a coiled core structure by a winding process. In addition, there is no particular order in which the electrolyte is prepared and the electrode assembly is provided in the above-mentioned step S10.

[0143] The battery cell packaging process in S20 may be performed according to a conventional battery cell packaging process, or may be performed using an improved packaging process based on an existing battery cell packaging process, as long as the packaging of the battery cell is completed.

[0144] Since the electrolyte contained in the battery cell prepared by the battery cell preparation method of the embodiment of the present application has a viscosity of 5 to 10 mPa·S at a low temperature of 0°C, it can be selected as 5 to 8 mPa·S, or in a further embodiment. The electrode assembly contains a sodium ion layered oxide with a stoichiometric ratio of manganese element to oxygen element of 0.1 to 0.4:2. Therefore, the prepared battery cell has a higher low-temperature impedance than the existing conventional battery cell, so that the battery cell can generate polarization heat when charged at a low temperature, so that it can heat up quickly in a short time, thereby significantly shortening the charging time of the battery cell under low temperature conditions, and can effectively reduce the amount of negative electrode crystallization caused by low-temperature charging of the battery cell, thereby improving the safety performance of the battery. At the same time, the prepared battery cell can effectively volatilize the electrochemical properties during conventional charging and discharging, such as having good cycle performance and being able to maintain normal battery cell temperature.

[0145] [Battery module]

[0146] In a third aspect, the present application also provides a battery module. The battery module of the present application includes the battery cell of the above application or includes the battery cell prepared by the preparation method of the above application.

[0147] The battery module is assembled from battery cells, that is, it can contain a plurality of the above-mentioned battery cells, and the specific number can be adjusted according to the application and capacity of the battery module.

[0148] Since the battery module of the embodiment of the present application contains the battery cells of the embodiment of the present application, the battery module of the embodiment of the present application has a higher low-temperature impedance than the conventional battery module. When charging under low temperature conditions, it can increase its own temperature in a short time, such as reaching the temperature range of conventional charging, shortening the charging time at low temperature, and the temperature of each battery cell contained therein after heating is uniform. On this basis, the amount of crystallization of the negative electrode caused by low-temperature charging of the battery cells of the embodiment of the present application contained in the battery module can be significantly reduced, thereby improving the safety performance and cycle performance of the battery module. At the same time, the battery module of the embodiment of the present application has good cycle performance during conventional charging and discharging, and the battery cell temperature is stable.

[0149] In some embodiments, Figure 3 2 is a schematic diagram of a battery module 20 as an example. Figure 3 As shown, in the battery module 20, the plurality of battery cells 10 may be arranged in sequence along the length direction of the battery module 20. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 10 may be fixed by fasteners.

[0150] Optionally, the battery module 20 may further include a housing having an accommodation space, and the plurality of sodium battery cells 10 are accommodated in the accommodation space.

[0151] [Battery Pack]

[0152] Fourthly, the embodiments of the present application also provide a battery pack. The battery pack of the embodiments of the present application refers to a battery pack assembled from the battery cells of the embodiments of the present application, that is, it may contain multiple battery cells of the embodiments of the present application, and multiple battery cells are assembled into a battery module of the embodiments of the present application. The specific number of the battery cells or battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0153] Since the battery pack of the embodiment of the present application also contains the battery cells of the embodiment of the text application, the battery pack of the embodiment of the present application has a higher low-temperature impedance than the conventional battery pack. When charging under low temperature conditions, it can increase its own temperature in a short time to reach the temperature range of conventional charging, shortening the charging time at low temperatures, and the temperature of each battery cell contained therein after heating is uniform. On this basis, the amount of crystallization of the negative electrode caused by low-temperature charging of the battery cells of the embodiment of the text application contained in the battery pack can be significantly reduced, thereby improving the safety performance and cycle performance of the battery pack. At the same time, the battery pack of the embodiment of the present application has good cycle performance during conventional charging and discharging, and the battery cell temperature is stable.

[0154] In some embodiments, Figure 4 3 is a schematic diagram of an exemplary battery pack 30. The battery pack 30 may include a battery box and a plurality of battery modules 20 disposed in the battery box. The battery box includes an upper box body 31 and a lower box body 32, wherein the upper box body 31 is used to cover the lower box body 32 and form a closed space for accommodating the battery module 20. The plurality of battery modules 20 may be arranged in the battery box in any manner.

[0155] [Electrical devices]

[0156] In the fifth aspect, the embodiments of the present application also provide an electric device. The electric device of the embodiments of the present application includes a power supply unit or an energy storage unit, and of course may also include other auxiliary components or necessary components. Among them, the power supply unit or energy storage unit contains at least one of the battery cells, battery modules or battery packs of the embodiments of the present application.

[0157] Since the electrical device of the embodiment of the present application contains at least one of the battery cells, battery modules or battery packs of the above-mentioned embodiments of the present application, the power supply unit or energy storage unit of the electrical device of the embodiment of the present application can be quickly charged at low temperatures, and has relatively high safety performance at low temperatures, and the power supply unit or energy storage unit contained therein has relatively high cycle performance.

[0158] In the embodiment, the electric device may include but is not limited to a mobile phone, a tablet, a laptop computer, an electric toy, an electric tool, a battery car, an electric car, a ship, a spacecraft, etc. Among them, the electric toy may include a fixed or mobile electric toy, for example, a game console, an electric car toy, an electric ship toy, and an electric airplane toy, etc., and the spacecraft may include an airplane, a rocket, a space shuttle, and a spacecraft, etc. As an electric device, a battery cell, a battery module, or a battery pack in a battery may be selected according to its use requirements.

[0159] Figure 5 Schematic diagram of an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirements of the electric device for high power and high energy density, a battery pack or a battery module can be used.

[0160] In the embodiment, when the electric device contains an energy storage unit, the electric device can be an energy storage device, which includes an energy storage unit and may also include other auxiliary components or necessary components. The energy storage unit contains at least one of the battery cells, battery modules, or battery packs in the above-mentioned embodiments of the application. Since the electric device in the embodiment of the present application contains at least one of the battery cells, battery modules, or battery packs in the above-mentioned embodiments of the application, the energy storage device in the embodiment of the present application can quickly charge and store energy at low temperatures, and also has relatively high safety performance at low temperatures.

[0161] [How to charge the battery at low temperature]

[0162] In a sixth aspect, the present application also provides a method for charging a battery at low temperature. The method for charging a battery at low temperature in the present application comprises the following steps:

[0163] S30: When it is detected that the initial temperature of the battery is lower than or equal to a threshold, pulse charging is performed on the battery;

[0164] S40: When the temperature of the battery rises to a predetermined temperature, the pulse charging process for the battery is stopped, and the battery is subjected to a conventional charging process.

[0165] In the low-temperature charging method of the battery of the embodiment of the present application, the threshold value in step S30 should refer to the battery temperature being reduced to a preset temperature point value or a temperature range, such as being equal to or lower than the lower limit of the temperature of the battery's conventional charging and discharging; pulse charging processing refers to charging the battery with a pulse current, then discharging the battery, and repeatedly charging in a cycle, and the charging rate of the pulse charging processing is higher than the charging rate of the conventional charging processing; the battery includes at least one of the battery cells of the above-mentioned embodiment of the present application, the battery module of the embodiment of the present application, and the battery pack of the embodiment of the present application.

[0166] The predetermined temperature in step S40 is the temperature after the threshold is raised, so it is higher than the temperature of the threshold in step S30, such as any temperature value or a certain temperature range within the normal charging and discharging temperature range of the battery; conventional charging processing refers to the charging method of the battery within the normal operating temperature range, such as conventional constant current charging or step charging.

[0167] The low-temperature charging method of the battery of the embodiment of the present application first adopts a high-rate pulse charging method under low-temperature conditions to pulse charge the battery containing the battery monomer of the embodiment of the present application at low temperatures. Since the battery monomer of the embodiment of the present application has a relatively high low-temperature impedance relative to the existing conventional battery monomer, the battery cell of the battery can generate polarization heat during the low-temperature high-rate pulse charging process, so that the temperature of the battery itself can rise rapidly in a short time, thereby heating up to a predetermined temperature in a relatively short time, and performing conventional charging treatment, thereby effectively shortening the charging time of the battery under low-temperature conditions. Moreover, since the battery monomer of the embodiment of the present application contained in the battery itself generates polarization heat, when the battery contains multiple battery monomers of the embodiment of the present application, the uniformity of the temperature of each battery monomer can be improved. At the same time, since the charging time under low-temperature conditions is shortened, the amount of negative electrode crystallization caused by low-temperature charging is effectively reduced, thereby significantly alleviating the attenuation of the reversible capacity of the battery and improving the battery safety performance and cycle performance.

[0168] Step S30:

[0169] In the exemplary embodiment, the initial temperature of the battery may be detected by using a temperature detection system or a temperature sensor.

[0170] In some embodiments, the threshold value may be -40°C to 5°C, optionally -40°C to 0°C, and further -40°C to -10°C. In the exemplary embodiment, it may be 5°C, 4°C, 3°C, 2°C, 1°C, 0°C, -10°C, -20°C, -30°C, -40°C, and other typical but non-limiting temperatures or a range between any two temperature values. At this time, the initial temperature of the battery itself may be lower than or equal to the threshold value. If the initial temperature of the battery is below the threshold temperature (including being equal to the threshold temperature), the battery is directly subjected to conventional charging treatment, which will result in a long charging time, and may even fail to charge. At the same time, the risk of a large amount of crystallization at the negative electrode due to long-term charging will increase the safety risk of the battery and reduce the cycle performance. Therefore, when the initial temperature of the battery is lower than the threshold, a high-rate pulse charging treatment is first performed on it. In combination with conventional charging, the charging time of the battery under low temperature conditions can be effectively shortened, and the safety and cycle performance of the battery can be improved.

[0171] In some embodiments, the pulse charging process in step S30 may include the following conditions:

[0172] 1.5~5C charging 0.01~0.1S, optional 2~3C charging 0.05~0.1S;

[0173] 1.5~5C discharge for 0.01~1S, optionally 3~5C discharge for 0.01~0.05S.

[0174] The pulse charging process is set to the high rate condition to pulse charge the battery, increase the polarization heat generated by the battery in a short time, further increase the temperature rise rate of the battery during the pulse charging process, shorten the pulse charging process time, and thus further shorten the overall charging time of the battery under low temperature conditions. At the same time, the amount of negative electrode crystallization occurring during the pulse charging process is further reduced, further easing the attenuation of the reversible capacity of the battery, and further improving the safety performance and cycle performance of the battery.

[0175] In some embodiments, before the pulse charging treatment is performed on the battery, the state of charge detection treatment is also included for the battery, and when the state of charge is ≤50%, the above-mentioned pulse charging treatment is performed on the battery. The state of charge is the ratio of the remaining capacity of the battery after it has been used for a period of time or has been shelved for a long time to the capacity of its fully charged state, and is usually expressed as a percentage. Its value range is 0-100%. When SOC=0, it means that the battery is fully discharged, and when SOC=100%, it means that the battery is fully charged. The state of charge of the battery can be detected by the static voltage method. The static voltage method is based on an initial static OCV, that is, the SOC state corresponding to different voltages, to determine its SOC state. The test method is: charge 5% of the rated capacity each time, and then record its voltage after standing for more than 3 hours, then the voltage corresponding to each 5% SOC is obtained, and the full SOC can be fitted. On the basis of detecting the initial temperature of the battery, the battery's state of charge is further detected. Specifically, the pulse charging of the battery is started when the battery's state of charge is ≤50%. This can achieve rapid temperature rise and effectively alleviate the low-temperature charging window when the battery cell's state of charge is above 50%, and the phenomenon of sodium precipitation that is prone to occur when pulse charging is used.

[0176] Step S40:

[0177] In some embodiments, the predetermined temperature is 0-10°C, optionally 5-10°C. In exemplary embodiments, it can be typical but non-limiting temperatures such as 10°C, 8°C, 5°C, 3°C, 0°C, or a range between any two temperature values.

[0178] Setting the predetermined temperature within this range can effectively reduce the pulse charging time and reduce the side effects of long-term high-rate charging on the battery, such as reducing the occurrence of negative electrode crystallization or other adverse phenomena, thereby improving the safety and cycle performance of the battery.

[0179] [Example]

[0180] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0181] Example 1

[0182] The present embodiment provides a sodium ion battery cell. The sodium ion battery cell of the present embodiment includes an outer package and an electrode assembly encapsulated in the outer package, the electrode assembly includes a positive electrode sheet, a separator and a negative electrode sheet stacked, and the separator is stacked between the positive electrode sheet and the negative electrode sheet. Among them, the positive electrode sheet includes a 13μm positive electrode current collector aluminum foil and a positive electrode active material layer combined on two opposite surfaces of the aluminum foil, and the positive electrode material in the positive electrode active material layer is a sodium ion layered oxide as shown in Table 1, and the viscosity of the electrolyte is as shown in Table 1.

[0183] The sodium ion battery monomer of this embodiment is assembled as follows:

[0184] Positive electrode sheet: Sodium ion positive electrode active material, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in an appropriate amount of solvent NMP at a weight ratio of 95:2.5:2.5 to form a uniform positive electrode slurry; the positive electrode slurry is evenly coated on the surface of 13μm positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet is obtained; wherein the sodium ion positive electrode active material is Na 0.92 Mn 0.3 Fe 0.3 Ni 0.36 O2.

[0185] Negative electrode sheet: Add hard carbon, conductive agent SP, and CMC binder into deionized water in a weight ratio of 8:1:1, stir and mix thoroughly to form a uniform negative electrode slurry; evenly coat the negative electrode slurry on the surface of a 6μm copper foil, and obtain a negative electrode sheet after drying and cold pressing.

[0186] Electrolyte: In an environment with a water content of less than 10 ppm, non-aqueous organic solvents ethylene carbonate and propylene carbonate are mixed in a volume ratio of 10:15 to obtain an electrolyte solvent, and then sodium hexafluorophosphate sodium salt and the mixed solvent are mixed to prepare an electrolyte with a sodium salt concentration of 1 mol / L.

[0187] Isolation film: A 12μm thick porous polyethylene (PE) isolation film is selected.

[0188] Battery assembly: The above-mentioned positive electrode sheets, separators and negative electrode sheets are stacked in order, so that the separator is placed between the positive electrode sheets and the negative electrode sheets to play an isolating role, and the electrode assembly is obtained through the lamination process. Each electrode assembly is placed in an outer package, and after drying, the electrolyte is injected, and after vacuum packaging, standing, forming, shaping and other processes, a sodium ion battery monomer is obtained.

[0189] Example 2 to Example 8

[0190] Embodiments 2 to 8 provide a sodium ion battery monomer, respectively. The sodium ion battery monomers in each embodiment are different from the sodium ion battery monomer in Embodiment 1 in that the electrolyte formula and viscosity are different or the molar ratio of manganese element to oxygen element in the positive electrode material is different, as shown in Embodiments 2 to 8 in Table 1 below.

[0191] The sodium ion battery cells in each of Examples 2 to 8 are assembled with reference to the sodium ion battery cell assembly method in Example 1.

[0192] Comparative Example 1 to Comparative Example 2

[0193] Comparative Examples 1 and 2 provide a sodium ion battery monomer, respectively. The sodium ion battery monomer in each comparative example is different from the sodium ion battery monomer in Example 1 in that the electrolyte formula is different, the viscosity is different, or the molar ratio of manganese element to oxygen element in the positive electrode material is different, as shown in Comparative Examples 1 and 2 in Table 1 below.

[0194] The sodium ion battery monomers in each of Comparative Examples 1 to Comparative Example 2 were assembled according to the sodium ion battery monomer assembly method in Example 1.

[0195] Viscosity test of the electrolyte contained in the sodium ion battery monomer at relevant temperatures in each embodiment:

[0196] The electrolytes prepared in the above-mentioned Examples 1 to 8 and Comparative Examples 1 to 2 were respectively subjected to viscosity tests at the corresponding temperatures in Table 1 below according to the following methods:

[0197] Viscosity test method: The kinematic viscosity test is specifically measured according to the Stabinger viscometer method. The results of the viscosity test are shown in Table 1.

[0198] Table 1

[0199]

[0200]

[0201] Electrochemical performance test of sodium ion battery monomer in each embodiment:

[0202] The sodium ion battery monomers provided in the above-mentioned Examples 1 to 8 and Comparative Examples 1 to 2 were respectively subjected to the relevant electrochemical performance tests in Table 2 below according to the following methods, and the test results are shown in Table 2. Among them, the relevant electrochemical performance test methods of the sodium ion battery monomers in Table 2 are as follows:

[0203] Battery cell (cell) cycle capacity retention rate (%): At 25°C, charge the secondary battery to 3.85V at a constant current of 0.33C, then charge at a constant voltage of 3.85V to a current of 0.05C, and then discharge at a constant current of 1C to 1.5V. This is one charge and discharge cycle. Taking the capacity of the first discharge as 100%, calculate the capacity retention rate of the battery after 1000 cycles. Capacity retention rate (%) after 1000 cycles of the battery = discharge capacity of the 1000th cycle / capacity of the first discharge × 100%.

[0204] Temperature detection of battery cells: The sodium ion battery cells provided in Examples 1 to 8 and Comparative Examples 1 to 2 are respectively discharged at 1C at room temperature and constant current to measure the temperature of the battery cells. The battery cell temperature test method: Use an infrared thermal imager to perform non-contact temperature measurement on the tested battery cells.

[0205] The sodium ion battery cells (cells) in each embodiment are subjected to low temperature pulse charging test:

[0206] The sodium ion battery cells provided in the above-mentioned Examples 1 to 8 and Comparative Examples 1 to 2 were respectively subjected to low temperature charging tests according to the following methods:

[0207] The initial temperature of each battery cell was cooled to -20°C, the state of charge (SOC) of each battery cell was 10%, and a low-temperature (-20°C) high-rate pulse charging treatment of 2C charging for 0.05s and 3C discharging for 0.02s was adopted. Each battery cell was quickly heated using a rapid heating strategy, and the time for each battery cell to rise from -20°C to 0°C was recorded.

[0208] Among them, after the initial temperature of the battery cell in Example 1 is cooled to -20°C, the battery cell is directly charged using an equivalent 0.2C rate until it is charged to 50% SOC, and the total equivalent 0.2C rate charging time is recorded, which is recorded as Comparative Example 3.

[0209] Take another sodium ion battery cell in Comparative Example 2, and set its state of charge (SOC) to 10%. Use a low-temperature (-20°C) rate pulse charging treatment of 1.5C charging for 0.02s and 1.5C discharging for 0.01s to quickly heat the battery cell using a rapid heating strategy, and record the time it takes for the battery cell to heat up from -20°C to 0°C.

[0210] The results of the sodium ion battery cell charging test in each embodiment are shown in Table 2.

[0211] Table 2

[0212]

[0213] Combining Table 1 and Table 2 above, it can be seen from the comparison of Examples 1 to 3 that as the viscosity of the electrolyte increases at low temperatures, the time it takes for the battery cell to heat up to 0°C is shortened under the same low-temperature high-rate pulse charging, indicating that the low-temperature viscosity of the electrolyte increases, and the low-temperature impedance of the battery cell increases accordingly, so that during low-temperature pulse charging, relatively large polarization heat can be generated, thereby shortening the low-temperature pulse charging time of the battery cell, thereby shortening the total charging time of the battery cell at low temperatures. At the same time, during the conventional charging and discharging process of the battery cell, the cell temperature of the battery cell is lower than 25°C, which can keep the cell temperature stable and has good cycle performance.

[0214] By comparing Example 3 and Comparative Example 1, it can be seen that when the viscosity of the electrolyte continues to decrease to 4mPa·S (0°C) at low temperature, although the battery cell can have good cycle performance and maintain a relatively stable cell temperature during conventional charge and discharge; however, under the same low-temperature high-rate pulse charging, the time for the cell to heat up to 0°C is significantly increased, extending to 25 minutes. Therefore, when the low-temperature viscosity of the electrolyte is as low as 4mPa·S (0°C), the low-temperature impedance of the battery cell is too small, the polarization heat generated during low-temperature pulse charging is small, and the temperature of the battery cell rises slowly.

[0215] By comparing Example 1 and Comparative Example 2, it can be seen that when the viscosity of the electrolyte continues to increase to 11mPa·S at low temperature (0°C), under the same low-temperature high-rate pulse charging, the battery cell cannot be charged at a high rate (charging: 2C, 0.05S, discharging: 3C, 0.02S). When pulse charging is performed at a relatively small rate (charging: 1.5C, 0.02S, discharging: 1.5C, 0.01S), the time to heat up to 0°C is significantly increased, extending to 30 minutes. Therefore, when the low-temperature viscosity of the electrolyte increases to 11mPa·S (0°C), the low-temperature impedance of the battery cell is too large, and low-temperature high-rate charging cannot be achieved. Moreover, the cell temperature of the battery cell discharged at room temperature exceeds 25°C, resulting in a decrease in the safety performance of the battery cell, and the cycle performance of the battery cell is also significantly reduced.

[0216] Therefore, by comparing Examples 1 to 3 with Comparative Examples 1 to 2, it can be seen that the electrolyte contained in the battery cell of the present application is controlled within the range of 5-10 mPa·S at 0°C, which effectively increases the low-temperature impedance of the battery cell and enables the battery cell to fully exert its electrochemical properties during conventional charge and discharge, has good cycle performance, and can maintain the normal cell temperature of the battery cell.

[0217] By comparing Examples 2, 4 to 8, it can be seen that by keeping the low-temperature viscosity of the electrode liquid unchanged and increasing the manganese-oxygen ratio (that is, increasing the content of manganese), the time it takes for the battery cell to heat up to 0°C is correspondingly shortened under the same low-temperature pulse charging. This shows that increasing the manganese content contained in the sodium ion layered oxide can increase the low-temperature impedance of the battery cell, and correspondingly increase the polarization heat generated by the low-temperature pulse, thereby shortening the total charging time of the battery cell at low temperature. At the same time, during the conventional charging and discharging process of the battery cell, the cell temperature is lower than 25°C, which can keep the cell temperature stable and has good cycle performance. At the same time, during the conventional charging and discharging process of the battery cell, the manganese-oxygen ratio is increased, and the cell temperature is appropriately increased. Further comparison of Examples 2, 4 to 6 shows that when the manganese-oxygen ratio is 0.2 to 0.3:2, the battery cell is relatively excellent. Further comparison of Example 4 with Example 7 shows that when the manganese-oxygen ratio is 0.08:2, the impedance of the battery cell is low, which makes the time for the battery cell to heat up to 0°C relatively prolonged; further comparison of Example 6 with Example 8 shows that when the manganese-oxygen ratio is 0.5:2, the impedance of the battery cell increases greatly, which makes the time for the battery cell to heat up to 0°C relatively shortened, and at the same time, the battery cell temperature rises during conventional charge and discharge, and the cycle performance decreases.

[0218] By comparing Example 1 and Comparative Example 3, it can be seen that when the battery cell provided in Example 1 is charged conventionally at 0.2C in Comparative Example 3 (non-low-temperature high-rate pulse charging), it takes about 2 hours to charge from 10% SOC to 50% because the rate is very small and the temperature remains basically unchanged.

[0219] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A battery cell, comprising an electrolyte and an electrode assembly immersed in the electrolyte, characterized in that: At 0°C, the viscosity of the electrolyte is 5-10 mPa·S.

2. The battery cell according to claim 1, characterized in that: The positive electrode material contained in the positive electrode sheet in the electrode assembly includes a sodium ion layered oxide, and the sodium ion layered oxide contains a manganese element, and in the sodium ion layered oxide, the stoichiometric ratio of the manganese element to the oxygen element is (0.1-0.4):2, and can be optionally (0.2-0.3):2; and / or At 0°C, the viscosity of the electrolyte is 5-8 mPa·S.

3. The battery cell according to claim 1 or 2, characterized in that: The non-aqueous organic solvent contained in the electrolyte includes at least one of a chain carbonate and a cyclic carbonate.

4. The battery cell according to claim 3, characterized in that: The linear carbonate comprises at least one of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; and / or The cyclic carbonate includes at least one of ethylene carbonate and propylene carbonate.

5. The battery cell according to claim 4, characterized in that: The non-aqueous organic solvent includes a mixed organic solvent of any one of the following (1) to (3): (1) ethylene carbonate and dimethyl carbonate, wherein the volume ratio of ethylene carbonate to dimethyl carbonate is 10:(5-10), or alternatively 10:(5-8); (2) propylene carbonate and ethyl methyl carbonate, wherein the volume ratio of propylene carbonate to ethyl methyl carbonate is 10:(5-10), or alternatively 10:(5-8); (3) Ethylene carbonate and propylene carbonate, wherein the volume ratio of ethylene carbonate to propylene carbonate is 10:(10-15), and optionally 10:(10-12).

6. The battery cell according to any one of claims 1 to 5, characterized in that: The concentration of the electrolyte contained in the electrolyte solution is 0.7 to 1.3 mol / L, and optionally 0.8 to 1.2 mol / L.

7. The battery cell according to any one of claims 1 to 6, characterized in that: The sodium ion layered oxide includes Na x Mn y M z O2, wherein 0.8≤x≤1, optionally 0.85≤x≤1; 0.1≤y≤0.4, optionally 0.2≤y≤0.3; 0.9≤y+z≤1, optionally 0.95≤y+z≤1; M is at least one of an active metal element and an inert metal element.

8. The battery cell according to claim 7, characterized in that: The M includes at least one of Fe, Ni, Co, Cr, Sc, Ti, V, Cr, Cu, Zn, and Al.

9. The battery cell according to any one of claims 1 to 8, characterized in that: The sodium ion layered oxide includes at least one of the oxides shown in the following chemical formula: So 0.94 Mr 0.36 Feb 0.3 Ni 0.3 O2、Na 0.94 Mr 0.26 Feb 0.35 Ni 0.35 O2、Na 0.94 Mr 0.36 Feb 0.3 Ni 0.24 Zn 0.08 O2、Na 0.94 Mr 0.36 Feb 0.3 Ni 0.24 Cu 0.08 O2、Na 0.92 Mr 0.3 Feb 0.3 Ni 0.36 O2、Na 0.92 Mn0.1Fe 0.3 Ni 0.56 O2、Na 0.92 Mr 0.2 Feb 0.3 Ni 0.4 6O2、Na 0.92 Mr 0.4 Feb 0.3 Ni 0.26 O2。 10. The battery cell according to any one of claims 1 to 9, characterized in that: The battery cells include sodium ion battery cells.

11. A method for preparing a battery monomer, characterized in that: The steps include: Prepare electrolyte and provide electrode assembly; Installing the electrode assembly into the containing cavity of the battery shell, injecting the electrolyte into the containing cavity, and performing battery cell packaging to obtain a battery cell; Wherein, when the electrolyte is at 0°C, the viscosity of the electrolyte is 5-10 mPa·S.

12. The preparation method according to claim 11, characterized in that: The positive electrode material contained in the positive electrode sheet in the electrode assembly includes a sodium ion layered oxide, and the layered oxide contains a manganese element. In the sodium ion layered oxide, the stoichiometric ratio of the manganese element to the oxygen element is (0.1-0.4):2, and can be optionally (0.2-0.3):

2.

13. A battery module, characterized in that: A battery cell comprising the battery cell according to any one of claims 1 to 10 or a battery cell prepared by the preparation method according to claim 11 or 12.

14. A battery pack, characterized in that: Comprising the battery module as claimed in claim 13.

15. An electrical device, characterized in that: The invention comprises at least one of the battery cell according to any one of claims 1 to 10, the battery module according to claim 13, and the battery pack according to claim 14.

16. A low temperature charging method for a battery, comprising the following steps: When it is detected that the initial temperature of the battery is lower than or equal to a threshold value, pulse charging is performed on the battery; When the temperature of the battery rises to a predetermined temperature, the pulse charging process for the battery is stopped, and a conventional charging process is performed on the battery; in, The battery comprises at least one of the battery cell according to any one of claims 1 to 10, the battery module according to claim 13, and the battery pack according to claim 14, and the charging rate of the pulse charging process is higher than the charging rate of the conventional charging process.

17. The battery cell according to claim 16, characterized in that: The pulse charging process includes the following conditions: 1.5~5C charging 0.01~0.1S, optional 2~3C charging 0.05~0.1S; 1.5~5C discharge for 0.01~1S, optionally 3~5C discharge for 0.01~0.05S.

18. The battery cell according to claim 16 or 17, characterized in that: The threshold value is -40 to 5°C, and may be -40 to 0°C; and / or Before the pulse charging process is performed on the battery, the method further includes performing a state of charge detection process on the battery, and when the state of charge is ≤50%, the pulse charging process is performed on the battery.

19. The battery cell according to any one of claims 16 to 18, characterized in that: The predetermined temperature is 0-10°C.

Images