Lithium ion battery monomer, lithium ion battery and power utilization device

Abstract

The invention relates to the technical field of batteries, and discloses a lithium ion battery monomer, a lithium ion battery and a power utilization device. The lithium ion battery monomer comprises an electrolyte and a positive pole piece, the positive pole piece comprises a positive active material, and the positive active material comprises a compound with a molecular formula of LicNixCoyMdNeOfAg; the electrolyte comprises additives, and the additives comprise lithium fluorosulfonate and lithium tetrafluoroborate. According to the present invention, the positive electrode material of the lithium ion battery monomer contains the Co element, and has good positive electrode dynamic performance, the lithium fluorosulfonate and the lithium tetrafluoroborate are further matched to be used as the electrolyte of the additive, and the use amounts of the lithium fluorosulfonate and the lithium tetrafluoroborate are optimized so as to improve the charge-discharge performance of the lithium ion battery at the low temperature.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a lithium-ion battery cell, a lithium-ion battery, and an electrical device. Background Art

[0002] As the popularity of electric vehicles increases, they are used in a wide range of areas, some of which have lower temperatures in winter, which affects the performance of electric vehicles. The main manifestation is that the discharge capacity decays at low temperatures, and charging is more difficult and slow.

[0003] The primary reason for the performance degradation of lithium-ion batteries at low temperatures is capacity decay due to irreversible losses caused by increased impedance. At low temperatures, the activity of positive and negative electrode materials decreases, and the electrolyte conductivity decreases. Consequently, during charging, lithium ions have difficulty embedding into the negative electrode and diffuse slowly, which can easily lead to lithium deposition. Similarly, the positive electrode faces the same challenges during discharge. Summary of the Invention

[0004] In view of the above problems, the embodiments of the present application provide a lithium-ion battery cell, a lithium-ion battery, and an electrical device, which aim to solve the problem of capacity attenuation of lithium-ion batteries due to increased impedance at low temperatures.

[0005] In a first aspect, the present invention provides a lithium-ion battery cell, comprising an electrolyte and a positive electrode plate, wherein the positive electrode plate comprises a positive electrode active material, wherein the positive electrode active material comprises a molecular formula of Li c Ni x Co y M d N e O f A g A compound, wherein M includes at least one of manganese and aluminum, N includes at least one of B, W, Si, Ti, Zr, Sr, Sn, Tb, Nb, Sb, Se, Ce or Te, A includes at least one of S, N, P, F, Cl, Br or I, 0.8≤c≤1.2, 0.5≤x≤0.8, 0.04≤y≤0.2, 0.01≤d≤0.5, 0≤e≤0.5, 0≤f≤2, and 0≤g≤2; the electrolyte includes an additive, the additive includes lithium fluorosulfonate and lithium tetrafluoroborate, and based on the total weight of the electrolyte as 100%, the mass percentage of the lithium fluorosulfonate is 0.005-0.1%, and the mass percentage of the lithium tetrafluoroborate is 0.001-0.2%.

[0006] The lithium-ion battery cell provided in the embodiment of the present application adopts a positive electrode active material containing the Co element, so its positive electrode has better kinetic performance and a stable structure, and is used in combination with an electrolyte containing lithium fluorosulfonate and lithium tetrafluorosulfonate as additives, and the amount of lithium fluorosulfonate and lithium tetrafluoroborate is optimized to improve the film formation impedance of the positive and negative electrodes, thereby improving the electrochemical performance of the lithium-ion battery at low temperatures. Among them, by using lithium fluorosulfonate as an additive and controlling the content of lithium fluorosulfonate in the electrolyte, the film formation impedance at the negative electrode is reduced, thereby improving the charging performance at low temperatures. By using lithium tetrafluoroborate as an additive and controlling the content of lithium tetrafluoroborate in the electrolyte, the film formation impedance at the positive electrode is reduced, thereby improving the charging performance at low temperatures.

[0007] In the positive electrode active material of the present application, the higher the Co content, the better the positive electrode kinetics. However, if the Co content is too high, it is easy to dissolve. Therefore, the Co content is limited, that is, 0.04≤y≤0.2.

[0008] In some embodiments, the mass percentage of the lithium tetrafluoroborate in the electrolyte is b%, where b=0.001-0.2; wherein y and b are inversely proportional, and the ratio of y to b is 0.2-200.

[0009] In order to better improve the low-temperature performance of the battery cell, in this application, the Co content of the positive electrode material is inversely proportional to lithium tetrafluoroborate, that is, when the Co content of the positive electrode material is low, more lithium tetrafluoroborate is required to form a film on the positive electrode to improve the positive electrode kinetic performance; when the Co content of the positive electrode material is high, the kinetic performance of the positive electrode itself is better, and less lithium tetrafluoroborate can be used.

[0010] In some embodiments, 0.05≤y≤0.12, 0.01≤b≤0.1, and the ratio of y to b is 0.5-12.

[0011] The Co content of the above-mentioned positive electrode material is matched with the mass percentage of lithium tetrafluoroborate to better improve the positive electrode kinetic performance.

[0012] In some embodiments, the mass percentage of the lithium fluorosulfonate is 0.01-0.08%.

[0013] The above-mentioned range of values ​​for the mass percentage content of lithium fluorosulfonate is combined with the range of values ​​for the mass percentage content of lithium tetrafluoroborate to better improve the positive and negative interface impedance, thereby better improving the low-temperature performance of the lithium-ion battery.

[0014] In some embodiments, the mass of the lithium fluorosulfonate is inversely proportional to the mass of the lithium tetrafluoroborate, and the mass ratio of the lithium fluorosulfonate to the lithium tetrafluoroborate is 0.025-100.

[0015] On the basis that the mass percentage of lithium fluorosulfonate and the mass percentage of lithium tetrafluoroborate meet the range defined in this application, and when a and b are inversely proportional, the matching of the positive and negative interface impedances can be better met, thereby meeting the matching of the positive and negative electrode kinetic properties, and better improving the low-temperature performance of the lithium-ion battery.

[0016] In some embodiments, the ratio of a to b is 0.1-8.

[0017] Within the above-mentioned ratio range of a to b, the matching of the positive and negative interface impedances can be better met, thereby meeting the matching of the positive and negative electrode kinetic properties, and better improving the low-temperature performance of the lithium-ion battery.

[0018] In some embodiments, the electrolyte further comprises Na + , the Na in the electrolyte + The mass concentration is 200-800ppm.

[0019] The ionic radius of sodium ion is larger than that of Li + The large ion radius can play a role in expanding the pores in the electrode, which is beneficial to accelerate the diffusion of lithium ions in the electrode and further improve the low-temperature charge and discharge performance of lithium-ion batteries.

[0020] The mass concentration of sodium ions within the above range can better accelerate the diffusion of lithium ions in the electrode.

[0021] In some embodiments, the lithium-ion battery cell further includes a negative electrode plate, the porosity of the negative electrode plate is 29-37%, and the porosity of the positive electrode plate is 20-25%.

[0022] The porosity of the positive electrode sheet and the porosity of the negative electrode sheet are matched, which is beneficial to the Li + The insertion and extraction of the positive and negative electrodes can achieve better electrochemical performance.

[0023] In a second aspect, an embodiment of the present application provides a lithium-ion battery comprising the above-mentioned lithium-ion battery cell.

[0024] By adopting the lithium-ion battery cells of the embodiments of the present application, the lithium-ion battery of the present application has good charge and discharge performance at low temperatures.

[0025] In a third aspect, an embodiment of the present application provides an electrical device comprising the above-mentioned lithium-ion battery cell and / or lithium-ion battery.

[0026] The electrical device of the present application includes the lithium-ion battery provided in the present application, and therefore has at least the same advantages as the lithium-ion battery, and can work better at low temperatures.

[0027] 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

[0028] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the optional embodiments below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference numerals are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0029] Figure 1 A schematic diagram of the exploded structure of a battery cell according to some embodiments of the present application;

[0030] Figure 2 This is a schematic structural diagram of an electrode assembly according to some embodiments of the present application;

[0031] Figure 3 Schematic diagram of the cross-sectional structure of the pole piece of some embodiments of the present application;

[0032] Figure 4 Schematic diagram of the exploded structure of a battery according to some embodiments of the present application;

[0033] Figure 5 This is a schematic structural diagram of a vehicle according to some embodiments of the present application.

[0034] The accompanying drawings in the specific implementation manner are as follows:

[0035] 10-pole piece; 1-current collector; 2-active material layer;

[0036] 20-electrode assembly; 101-negative electrode sheet; 102-positive electrode sheet; 201-negative electrode tab; 202-positive electrode tab; 203-diaphragm;

[0037] 30-battery cell; 301-housing; 302-end cover; 303-negative electrode adapter; 304-positive electrode adapter; 305-insulating member;

[0038] 40-battery; 401-box; 4011-box body; 4012-box cover;

[0039] 50-electrical device; 501-controller; 502-motor. DETAILED DESCRIPTION

[0040] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0042] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0043] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0044] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0045] 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).

[0046] 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., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0047] In the description of the embodiments of the present application, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0048] Lithium-ion batteries are widely used in various fields such as 3C electronics, electric vehicles, and energy storage power stations due to their advantages such as high energy density, good cycle performance, and environmental friendliness. Lithium-ion batteries generally include a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The positive electrode sheet includes a positive electrode active material layer containing a positive electrode active material. The positive electrode active material is the donor of lithium ions in the lithium-ion battery. The negative electrode sheet includes a negative electrode active material layer containing a negative electrode active material, and the negative electrode active material is the acceptor of lithium ions. The separator is a microporous membrane used to separate the positive and negative electrode sheets. Its main function is to prevent the positive and negative electrodes from contacting and causing a short circuit while allowing the electrolyte ions to pass through. The electrolyte generally includes components such as solvents, solutes, and additives. The positive and negative electrodes of the battery and the separator are all immersed in the electrolyte. During the charge and discharge process, the electrolyte acts as a transmission medium for lithium ions and, on the other hand, provides ion channels to help lithium ions move freely therein.

[0049] As the application areas of lithium-ion batteries continue to expand, their use areas and environments are also becoming more widespread. Some of these environments are relatively low in temperature, such as in some places where winter temperatures are low. This has led to problems with lithium-ion batteries when used at low temperatures, such as low capacity, severe degradation, poor cycle rate performance, and difficult and slow charging and discharging. Low temperature here generally refers to temperatures below 10°C.

[0050] Based on this, the embodiment of the present application provides a lithium-ion battery cell, whose positive electrode material contains cobalt and has better positive electrode kinetic performance. It is further used in conjunction with an electrolyte using lithium fluorosulfonate and lithium tetrafluorosulfonate as additives, and the dosage of lithium fluorosulfonate and lithium tetrafluoroborate is optimized, thereby improving the charge and discharge performance of the lithium-ion battery at low temperatures. Among them, by using lithium fluorosulfonate as an additive to reduce the film formation impedance at the negative electrode, the charging performance at low temperatures is improved; by using lithium tetrafluoroborate as an additive to reduce the film formation impedance at the positive electrode, the charging performance at low temperatures is improved. And by optimizing the dosage of lithium fluorosulfonate and lithium tetrafluoroborate, the interface kinetic performance of the positive and negative electrodes is matched, which can further improve the low-temperature cycle of the lithium-ion battery.

[0051] Lithium-ion battery cells:

[0052] In a first aspect, some embodiments of the present application provide a lithium-ion battery cell, comprising an electrolyte and a positive electrode plate, wherein the positive electrode plate comprises a positive electrode active material, wherein the positive electrode active material comprises a molecular formula of Li c Ni x Co y M d N e O f A g A compound, wherein M includes at least one of manganese and aluminum, N includes at least one of B, W, Si, Ti, Zr, Sr, Sn, Tb, Nb, Sb, Se, Ce or Te, A includes at least one of S, N, P, F, Cl, Br or I, 0.8≤c≤1.2, 0.5≤x≤0.8, 0.04≤y≤0.2, 0.01≤d≤0.5, 0≤e≤0.5, 0≤f≤2, and 0≤g≤2; the electrolyte includes an additive, the additive includes lithium fluorosulfonate and lithium tetrafluoroborate, and based on the total weight of the electrolyte as 100%, the mass percentage of lithium fluorosulfonate is a%, and the mass percentage of lithium tetrafluoroborate is b%; 0.005≤a≤0.1, and 0.001≤b≤0.2.

[0053] The positive electrode active material is a lithium ion donor for lithium-ion batteries. The performance and stability of the positive electrode material directly affect the performance and service life of the battery. Among them, the structure of the positive electrode material has an important influence on the low-temperature performance of the lithium-ion battery. Cobalt-containing positive electrode materials have the advantages of good cycle and rate performance, and the cobalt element can improve the structural stability of the positive electrode active material. Therefore, this application uses a positive electrode active material containing cobalt, so that the positive electrode material has better kinetic performance and a stable positive electrode material structure at low temperatures.

[0054] The electrolyte is a key component of lithium-ion batteries. It not only provides a channel for lithium ion transmission, enabling migration between the positive and negative electrodes, thereby enabling charge storage and release, but also stabilizes the battery's internal environment, reducing the occurrence of side reactions such as oxidation and reduction, thereby extending the battery's life and cycle performance. However, at low temperatures, the viscosity of general electrolytes increases, which tends to reduce conductivity and increase the film-forming resistance of the positive and negative electrodes, easily leading to battery capacity decay and poor charge and discharge performance.

[0055] By adding a small amount of additives to the electrolyte of lithium-ion batteries, certain battery properties can be effectively improved. The selection of additives usually needs to meet the following conditions: high solubility in the solvent; small amount of addition; few harmful side reactions; low toxicity.

[0056] According to the lithium-ion battery provided in the embodiment of the present application, it adopts a positive electrode active material containing the Co element, so its positive electrode has better kinetic performance and a stable positive electrode material structure. The specific type of the positive electrode active material containing the Co element here is not limited and can be selected according to actual needs. For example, the positive electrode active material may include but is not limited to lithium cobalt oxide materials, ternary positive electrode materials, etc. The positive electrode material is further used in combination with an electrolyte using lithium fluorosulfonate and lithium tetrafluorosulfonate as additives, which can reduce the film formation impedance of the positive and negative electrodes while having better positive electrode kinetic performance, thereby improving the charge and discharge performance at low temperatures. Among them, the electrolyte reduces the film formation impedance at the negative electrode by using lithium fluorosulfonate as an additive and controlling the content of lithium fluorosulfonate in the electrolyte, thereby improving the charging performance at low temperatures. The present application controls the value range of a to be 0.005≤a≤0.1 because if the content of lithium fluorosulfonate in the electrolyte is less than 0.005%, the film formation at the negative electrode interface is insufficient and the effect is not obvious. If the content of lithium fluorosulfonate is higher than 0.1%, the viscosity of the electrolyte will increase, which will worsen the performance of the electrolyte at low temperatures. Moreover, the electrolyte of the present application also uses lithium tetrafluoroborate as an additive and controls the content of lithium tetrafluoroborate in the electrolyte to reduce the film formation impedance at the positive electrode and improve the charging performance at low temperatures. The present application controls the value range of b to be 0.001≤b≤0.2 because if the content of lithium tetrafluoroborate in the electrolyte is less than 0.001%, the effect of improving the positive electrode interface impedance cannot be achieved because lithium tetrafluoroborate is difficult to dissociate. If the content of lithium tetrafluoroborate is higher than 0.2%, the electrolyte conductivity will be worsened, thereby worsening the low temperature performance.

[0057] The molecular formula of the positive electrode active material is Li c Ni x Co y M d N e O f A gIn the example, the subscript y of the Co element represents a molecule of Li c Ni x Co y M d N e O f A g In the cathode material, the number of Co atoms is y. In this application, the higher the Co content, the better the cathode kinetics. However, if the Co content is too high, it is easy to dissolve. Therefore, the Co content is limited to 0.04 ≤ y ≤ 0.2. For example, y can be any one of 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, or a range between any two of them.

[0058] As an example, the positive electrode active material may include LiNi 0.5 Co 0.2 Mn 0.3 O2、LiNi 0.6 Co 0.2 Mn 0.2 O2、LiNi 0.6 Co 0.15 Mn 0.25 O2、LiNi 0.7 Co 0.1 Mn 0.2 O2、LiNi 0.8 Co 0.1 Mn 0.1 O2、LiNi 0.8 Co 0.04 Mn 0.16 O2、LiNi 0.7 Co 0.15 Al 0.15 O2、LiNi 0.8 Co 0.05 Al 0.15 O2、LiNi 0.8 Co 0.04 Al 0.16 At least one of O2.

[0059] In some embodiments, y is inversely proportional to the mass percentage b% of lithium tetrafluoroborate, that is, 0.04≤y≤0.2 and 0.001≤b≤0.2, and 0.2≤y / b≤200.

[0060] In this application, to better improve the low-temperature performance of the battery cell, the Co content of the positive electrode material is inversely proportional to the lithium tetrafluoroborate. That is, when the Co content of the positive electrode material is low, more lithium tetrafluoroborate is required to form a film on the positive electrode to improve the positive electrode kinetic performance. When the Co content of the positive electrode material is high, the positive electrode's own kinetic performance is better, and less lithium tetrafluoroborate can be used. For example, y / b can be any one of 0.2, 1, 10, 20, 40, 60, 80, 100, 120, 140, 160, 180, 200, or any range therebetween.

[0061] For example, when the Co content in the positive electrode active material is low, that is, when y is 0.04, the amount of lithium tetrafluoroborate used is large, that is, its mass percentage b% in the electrolyte is preferably 0.2%, and y / b is 0.2. When the Co content in the positive electrode active material is high, that is, when y is 0.2, the amount of lithium tetrafluoroborate used is small, and its mass percentage b% in the electrolyte is preferably 0.001%, and y / b is 200.

[0062] In some embodiments, 0.05≤y≤0.12 and 0.01≤b≤0.1, that is, 0.5≤y / b≤12.

[0063] The Co content of the above-mentioned positive electrode material is matched with the mass percentage of lithium tetrafluoroborate to better improve the positive electrode kinetic performance.

[0064] In some embodiments, 0.01≤b≤0.1 and 0.01≤a≤0.08.

[0065] The combination of the mass percentage of lithium fluorosulfonate (b%) and the mass percentage of lithium tetrafluoroborate (a%) can better improve the positive and negative interface impedance, thereby better improving the low-temperature performance of the lithium-ion battery.

[0066] In some embodiments, 0.005≤a≤0.1, 0.001≤b≤0.2, and the mass percentage a% of lithium fluorosulfonate is inversely proportional to the mass percentage b% of lithium tetrafluoroborate, and the ratio of a to b is 0.025-100.

[0067] When designing lithium-ion batteries, it is necessary to consider the matching of the kinetic performance of the positive and negative electrodes. The interfacial impedance of the positive and negative electrodes is an important factor affecting the kinetics of the positive and negative electrodes. The interfacial impedance of the positive and negative electrodes can prevent lithium ions from being inserted or removed too quickly in one electrode and difficult to insert in the other electrode, thereby causing lithium loss and large battery polarization. Therefore, the matching of the interfacial impedance of the positive and negative electrodes is very important and can better improve the low-temperature performance of lithium-ion batteries.

[0068] When the mass percentage of lithium fluorosulfonate and lithium tetrafluoroborate falls within the ranges defined in this application, and a and b are inversely proportional, the impedance matching between the positive and negative interfaces can be improved, thereby matching the kinetic properties of the positive and negative electrodes and improving the low-temperature performance of the lithium-ion battery. For example, a / b can be any one of 0.025, 0.1, 1, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, or any range between any two of them.

[0069] For example, when the mass percentage of lithium fluorosulfonate is low, i.e., a is 0.005, the amount of lithium tetrafluoroborate used is higher, i.e., its mass percentage b% in the electrolyte is preferably 0.2%, and a / b is 0.025. When the mass percentage of lithium fluorosulfonate is high, i.e., a is 0.1, the amount of lithium tetrafluoroborate used is lower, and its mass percentage b% in the electrolyte is preferably 0.001%, and a / b is 100.

[0070] In some embodiments, the ratio of a to b is 0.1 to 8. For example, a / b can be any one of 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, or a range between any two thereof.

[0071] Within the above-mentioned ratio range of a to b, the matching of the positive and negative interface impedances can be better met, thereby meeting the matching of the positive and negative electrode kinetic properties, and better improving the low-temperature performance of the lithium-ion battery.

[0072] In some embodiments, the electrolyte further comprises Na + The mass concentration of the electrolyte is 10 to 1000 ppm. For example, the mass concentration may be any one of 10 ppm, 100 ppm, 200, 300, 400, 500, 600, 700, 800, 900, and 1000, or a value in the range between any two of the values.

[0073] metallic Na + The addition and regulation methods are as follows:

[0074] Na +The addition method includes but is not limited to adding one or more sodium salts such as NaPF6 (sodium hexafluorophosphate in Chinese), NaOTF (sodium trifluoromethanesulfonate in Chinese), NaFSI (sodium bis(trifluoromethylsulfonyl)imide in Chinese), NaBF4 (sodium tetrafluoroborate in Chinese), NaBOB (sodium bis(oxalatoborate) in Chinese), NaDFOB (sodium difluorooxalatoborate in Chinese), and NaFSO3 (sodium fluorosulfonate in Chinese) to the electrolyte, and the Na in the electrolyte is regulated by controlling the mass of the added sodium salt. + content.

[0075] In some embodiments, Na in the electrolyte + The mass concentration is 200-800ppm.

[0076] The electrolyte introduces ions with a larger radius than Li + Na with a large ionic radius + , which is beneficial to accelerate the diffusion of lithium ions in the electrode, because Na + The ionic radius of Na is larger than that of lithium ion, so + It can play the role of expanding the pores in the electrode, thereby improving the low-temperature charge and discharge performance of lithium-ion batteries.

[0077] [Electrolyte]

[0078] The electrolyte usually includes components such as solvents, solutes and additives. The positive and negative electrodes and the isolation membrane of the battery are immersed in the electrolyte. During the charging and discharging process, the electrolyte acts as a transmission medium for lithium ions and on the other hand provides ion channels to help lithium ions move freely in it.

[0079] In some embodiments, the electrolyte includes a solvent, and the solvent may include at least one of a carbonate ester and a carboxylic acid ester. The carbonate ester may include cyclic carbonates such as substituted and unsubstituted ethylene carbonate, propylene carbonate, butylene carbonate, and γ-butyrolactone. The carbonate ester may also include linear carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate, and ethyl propionate.

[0080] In some embodiments, the mass percentage of the cyclic carbonate in the solvent is less than or equal to 25 wt %.

[0081] In some embodiments, the electrolyte includes an electrolyte salt, the specific type of which is not limited and can be selected according to actual needs. For example, the electrolyte can be selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonylimide, lithium tetrafluoroborate, lithium trifluoromethylsulfonate, lithium hexafluoroarsenate, lithium bis(oxalatoborate), and lithium perchlorate.

[0082]

Positive electrode

[0083] The positive electrode sheet consists of a positive current collector and a positive active material layer, which is coated on the surface of the positive current collector. For lithium-ion batteries, for example, the positive current collector can be made of aluminum, and the positive active material layer includes the positive active material, which can be, but is not limited to, lithium cobalt oxide, lithium nickel cobalt oxide, lithium nickel cobalt manganese oxide, or lithium-rich manganese-based materials.

[0084]

Negative electrode

[0085] The negative electrode sheet consists of a negative electrode current collector and a negative electrode active material layer, which is coated on the surface of the negative electrode current collector. In lithium-ion batteries, for example, the negative electrode current collector can be made of copper, and the negative electrode active material layer includes the negative electrode active material, which can be silicon and / or silicon oxide compounds.

[0086] In some embodiments, the lithium-ion battery cell includes a positive electrode sheet and a negative electrode sheet, the porosity of the positive electrode sheet is 17-30%, and the porosity of the negative electrode sheet is 22-42%.

[0087] As an example, the porosity of the positive electrode sheet may be any one of 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, or a range between any two thereof. The porosity of the negative electrode sheet may be any one of 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, or 42%, or a range between any two thereof.

[0088] The porosity of the electrode is closely related to the compaction density of the electrode. When the porosity of the positive electrode is 17-30%, the battery cell has a better energy density and improves the ion migration rate and electrolyte infiltration effect. The porosity of the negative electrode affects the tortuosity of the negative electrode. By adjusting the porosity of the negative electrode, it is beneficial to improve the tortuosity of the negative electrode and reduce the lithium ion transmission path, thereby improving the fast charging performance of the battery. The combination of the porosity of the positive electrode and the porosity of the negative electrode is beneficial to Li + The insertion and extraction of lithium ions make the positive and negative electrodes have better electrochemical properties, further ensuring the charge and discharge performance of lithium ion points at low temperatures.

[0089] The porosity of the positive electrode sheet can be effectively controlled by the following methods:

[0090] The porosity of the positive electrode sheet can generally be controlled in two ways: one is to control the particle size of the positive electrode active material and the ratio of the amount of the positive electrode active material to the conductive agent and the binder; the other is to control the compaction of the positive electrode sheet; among them, the control of the compaction of the positive electrode sheet has a greater impact on the porosity of the positive electrode sheet. In this invention, the porosity of the positive electrode sheet is mainly controlled by adjusting the compaction of the positive electrode sheet.

[0091] The porosity of the negative electrode sheet can be effectively controlled by the following methods:

[0092] The porosity of the negative electrode sheet can generally be controlled in two ways: one is to control the particle size of the negative electrode active material and the ratio of the amount of the negative electrode active material to the conductive agent and the binder; the other is to control the compaction of the negative electrode sheet; among them, the control of the compaction of the negative electrode sheet has a greater impact on the porosity of the negative electrode sheet. In this invention, the porosity of the negative electrode sheet is mainly controlled by adjusting the compaction of the negative electrode sheet.

[0093] In some embodiments, the porosity of the positive electrode sheet is 20-25%, and the porosity of the negative electrode sheet is 22-42%.

[0094] The porosity of the positive electrode sheet and the porosity of the negative electrode sheet are matched, which is more conducive to the Li + Embedding and removal.

[0095] Please refer to Figure 1 , Figure 1 The exploded view of the lithium-ion battery cell 30 in some embodiments of the present application. The lithium-ion battery cell 30 refers to the basic unit that realizes the mutual conversion of chemical energy and electrical energy, and is also the smallest unit of the lithium-ion battery. Figure 1 The lithium-ion battery cell 30 includes a shell 301, an end cover 302, an electrode assembly 20, an electrolyte (not shown) and other functional components.

[0096] The shell 301 is a hollow structure with one end open. The shell 301 is used to cooperate with the end cap 302 to form an internal environment for accommodating the electrode assembly 20, the electrolyte and other functional components. The shell 301 can be of various shapes and sizes, such as a rectangular parallelepiped, a cylindrical shape, a hexagonal prism, etc. Specifically, the shape of the shell 301 can be determined according to the specific shape and size of the electrode assembly 20. The material of the shell 301 can be, but is not limited to, copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and is not limited here.

[0097] The end cap 302 is a component that covers the opening of the shell 301 to isolate the internal environment of the lithium-ion battery cell 30 from the external environment. Optionally, the shape of the end cap 302 can be adapted to the shape of the shell 301 to match the shell 301. Optionally, the end cap 302 can be made of a material with a certain hardness and strength (such as an aluminum alloy). In this way, the end cap 302 is less likely to deform when squeezed or collided, so that the lithium-ion battery cell 30 can have a higher structural strength and improved safety performance. The material of the end cap 302 can be, but is not limited to, copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and is not limited here.

[0098] In some embodiments, the lithium-ion battery cell 30 further includes functional components such as a negative electrode adapter 303 and a positive electrode adapter 304. The negative electrode adapter 303 is used to electrically connect to the negative electrode tab on the electrode assembly 20, and the positive electrode adapter 304 is used to electrically connect to the positive electrode tab on the electrode assembly 20, thereby outputting or inputting electrical energy into or out of the lithium-ion battery cell 30. It is understood that the negative electrode adapter 303 is made of a conductive material, and the material of the negative electrode adapter 303 can be, but is not limited to, copper, iron, aluminum, etc. The positive electrode adapter 304 is made of a conductive material, and the material of the positive electrode adapter 304 can be, but is not limited to, copper, iron, aluminum, etc.

[0099] In some embodiments, the lithium-ion battery cell 30 further includes an insulating member 305 located inside the housing 301 to isolate the housing 301 from the electrode assembly 20 and reduce the risk of short circuits. For example, the insulating member 305 may be made of plastic, rubber, or the like.

[0100] One or more electrode assemblies 20 may be contained within the housing 301 .

[0101] Please refer to Figure 2 , Figure 2 This is a schematic diagram of the structure of the electrode assembly 20 in some embodiments of the present application. The electrode assembly 20 is the component in the battery cell 30 where the electrochemical reaction occurs. The electrode assembly 20 is primarily formed by winding or stacking a negative electrode sheet 101 and a positive electrode sheet 102 into an integrated structure, and a separator 203 is typically provided between adjacent negative electrode sheets 101 and positive electrode sheets 102.

[0102] The negative electrode sheet 101 includes a negative electrode current collector and a negative electrode material layer, which is coated on the surface of the negative electrode current collector. Taking a lithium-ion battery as an example, the negative electrode current collector can be made of copper, and the negative electrode material layer includes a negative electrode material, which can be a silicon-based material.

[0103] The positive electrode sheet 102 includes a positive electrode current collector and a positive electrode material layer, which is coated on the surface of the positive electrode current collector. Taking a lithium-ion battery as an example, the positive electrode current collector can be made of aluminum, and the positive electrode material layer includes a positive electrode material, which can be lithium cobalt oxide, ternary lithium, etc.

[0104] The separator 203 is a porous plastic film that allows lithium ions in the electrolyte to pass freely, but separates the negative electrode 101 from the positive electrode 102, preventing electrons from freely passing through the battery. The separator 203 can be made of materials such as PP (polypropylene) or PE (polyethylene).

[0105] The negative electrode current collector and the positive electrode current collector also have portions that are not coated with the active material layer. These portions without the active material layer are provided with connecting tabs. Specifically, the negative electrode current collector is connected to the negative electrode tab 201, and the positive electrode current collector is connected to the positive electrode tab 202. During the charge and discharge process of the battery, the positive electrode material layer and the negative electrode material layer react with the electrolyte, the tab 201 is connected to the negative electrode adapter 303, and the positive electrode tab 202 is connected to the positive electrode adapter 304 to form a current loop. Of course, in some embodiments, the portions of the negative electrode current collector and the positive electrode current collector that are not coated with the active material layer each constitute a tab.

[0106] Please refer to Figure 3 , Figure 3 Schematic diagram of the structure of the pole piece 10 in some embodiments of the present application. The pole piece 10 includes a current collector 1 and an active material layer 2, wherein the active material layer 2 is disposed on at least one side of the current collector 1.

[0107] The current collector 1 refers to a component used to gather current. The current collector 1 can be a negative electrode current collector or a positive electrode current collector depending on the application. When the current collector 1 is a negative electrode current collector, the active material layer 2 correspondingly coated on the negative electrode current collector is a negative electrode active material layer, and the resulting electrode sheet 10 is a negative electrode electrode sheet; when the current collector 1 is a positive electrode current collector, the active material layer 2 correspondingly coated on the positive electrode current collector is a positive electrode active material layer, and the resulting electrode sheet 10 is a positive electrode electrode sheet. Taking lithium-ion batteries as an example, optionally, the negative electrode current collector is copper foil and the positive electrode current collector is aluminum foil. In addition, the current collector 1 can be in various shapes, such as strips or squares, which are not limited here.

[0108] Active material layer 2 includes active material, a conductive agent, and a binder. Active material refers to a material that participates in electrochemical oxidation / reduction reactions. Optionally, the active material is a powder. When active material layer 2 is a negative electrode material layer, the active material is a negative electrode active material. When active material layer 2 is a positive electrode material layer, the active material is a positive electrode active material. Taking lithium-ion batteries as an example, the negative electrode material can be silicon and / or silicon oxides; the positive electrode material can be, but is not limited to, lithium cobalt oxide, lithium nickel cobalt oxide, lithium nickel cobalt manganese oxide, or lithium-rich manganese-based materials. The conductive agent is a material that collects microcurrents between the active materials and between the active materials and the current collector 1. Examples of the conductive agent include, but are not limited to, conductive graphite, carbon nanotubes, and acetylene black. The binder binds the active materials to enhance electronic contact between the active material and the conductive agent, and between the active material and the current collector 1. Examples of the binder include, but are not limited to, styrene-butadiene rubber (SBR), acrylonitrile, acrylate, polyvinylidene fluoride (PVDF), and carboxymethyl cellulose (CMC).

[0109] The current collector 1 has a first surface and a second surface that are opposite to each other along the thickness direction of the current collector 1. At least one side of the current collector 1 includes the first surface and / or the second surface of the current collector 1. It is understood that the active material layer 2 can be provided on the first surface, the second surface, or both the first surface and the second surface.

[0110] Lithium-ion battery:

[0111] In a second aspect, some embodiments of the present application disclose a lithium-ion battery comprising the above-mentioned lithium-ion battery cell.

[0112] Please refer to Figure 4 , Figure 4 This is an exploded view of a lithium-ion battery 40 provided in some embodiments of the present application. The lithium-ion battery 40 includes a housing 401 and a lithium-ion battery cell 30, with the lithium-ion battery cell 30 contained within the housing 401. The housing 401 provides a space for the lithium-ion battery cell 30 and can have a variety of structures.

[0113] In some embodiments, the box body 401 may include a box body 4011 and a box cover 4012, which cover each other and together define a storage space for accommodating the lithium-ion battery cells 30. Alternatively, the box body 4011 may be a hollow structure with one end open, and the box cover 4012 may be a plate-like structure, covering the open side of the box body 4011.

[0114] In the lithium-ion battery 40, there can be multiple lithium-ion battery cells 30, and the multiple lithium-ion battery cells 30 can be connected in series, in parallel, or in a mixed connection. Mixed connection means that the multiple lithium-ion battery cells 30 are both connected in series and in parallel. The multiple lithium-ion battery cells 30 can be directly connected in series, in parallel, or in a mixed connection, and then the whole formed by the multiple lithium-ion battery cells 30 is accommodated in the box 401; of course, the battery 40 can also be a battery module formed by first connecting multiple lithium-ion battery cells 30 in series, in parallel, or in a mixed connection, and the multiple battery modules are then connected in series, in parallel, or in a mixed connection to form a whole, and accommodated in the box 401. The lithium-ion battery 40 may also include other structures, such as a busbar component (not shown), which is used to achieve electrical connection between the multiple battery cells 30.

[0115] The lithium-ion battery cell 30 may be cylindrical, flat, rectangular, or in other shapes.

[0116] Electrical devices:

[0117] In a third aspect, some embodiments of the present application disclose an electrical device comprising the above-mentioned lithium-ion battery cell and / or the above-mentioned lithium-ion battery.

[0118] The lithium-ion batteries disclosed in some embodiments of the present application may be used, but are not limited to, in electrical devices such as vehicles, ships, or aircraft. A power supply system comprising the batteries disclosed in the present application may be used to form the electrical device.

[0119] Some embodiments of the present application provide an electrical device using a lithium-ion battery as a power source. The electrical device may be, but is not limited to, a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, an electric tool, etc. Vehicles may be, but are not limited to, fuel-powered vehicles, gas-powered vehicles, or new energy vehicles. New energy vehicles may be, but are not limited to, pure electric vehicles, hybrid vehicles, or extended-range vehicles. Spacecraft include aircraft, rockets, space shuttles, and spacecraft. Electric toys include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys. Electric tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers.

[0120] For the convenience of description, the following embodiments are described by taking a vehicle 50 as an example of an electrical device according to an embodiment of the present application.

[0121] Please refer to Figure 5 , Figure 5This is a schematic diagram of the structure of a vehicle 50 provided in some embodiments of the present application. A lithium-ion battery 40 is provided within the vehicle 50, and the lithium-ion battery 40 can be located at the bottom, front, or rear of the vehicle 50. The lithium-ion battery 40 can be used to power the vehicle 50, for example, as an operating power source for the vehicle 50. The vehicle 50 may also include a controller 501 and a motor 502. The controller 501 is used to control the lithium-ion battery 40 to power the motor 502, for example, to meet the power requirements of the vehicle 50 during startup, navigation, and driving.

[0122] In some embodiments of the present application, the lithium-ion battery 40 can serve not only as an operating power source for the vehicle 50 , but also as a driving power source for the vehicle 50 , replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 50 .

[0123] In some embodiments of the present application, the lithium-ion battery 40 is a secondary battery. Secondary batteries come in many different forms, including but not limited to single cells, modules, and packs. A secondary battery is a battery that can be recharged after discharge to activate its active materials and continue to be used.

[0124] The following describes the details in conjunction with specific embodiments.

[0125] Example 1:

[0126] (1) Electrolyte

[0127] In an argon atmosphere glove box (H2O content <10ppm, O2 content <1ppm), ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a mass ratio of 25 / 70, and 1M LiPF6 lithium salt was dissolved. Then, lithium fluorosulfonate and lithium tetrafluoroborate additives were added and stirred uniformly to prepare an electrolyte. Based on the total mass of the electrolyte as 100%, the mass percentage of the lithium fluorosulfonate additive was 0.005%, and the mass percentage of the lithium tetrafluoroborate additive was 0.05%.

[0128] (2) Preparation of positive electrode sheet

[0129] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2, conductive agent and binder are fully stirred in an N-methylpyrrolidone solvent system at a mass ratio of 97:2:1. After being evenly mixed, they are coated on Al foil, dried and rolled to obtain a positive electrode sheet.

[0130] (3) Preparation of negative electrode sheet

[0131] The negative electrode active material graphite, conductive agent and binder are fully stirred in a water solvent system at a mass ratio of 97:2:1, mixed evenly, coated on Cu foil, dried and rolled to obtain a negative electrode sheet.

[0132] (4) Isolation film

[0133] The present application has no particular limitation on the type of isolation membrane. Any known porous isolation membrane with good chemical stability and mechanical stability can be selected. In this embodiment, a 12 μm polyethylene film is used as the isolation membrane.

[0134] (5) Preparation of lithium-ion batteries

[0135] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed in the middle of the positive and negative electrode sheets to isolate the positive and negative electrode sheets. The bare battery cell is wound and the tabs are welded. The bare battery cell is placed in the outer packaging and the electrolyte is injected. The lithium-ion battery cell is then produced through processes such as packaging, standing, formation, shaping, and capacity testing.

[0136] Example 2

[0137] The preparation method of the lithium-ion battery cell of this embodiment is substantially the same as that of embodiment 1, with the only difference being that the mass percentage a of lithium fluorosulfonate in the electrolyte is 0.05; correspondingly, a / b is 1.

[0138] Example 3

[0139] The preparation method of the lithium-ion battery cell of this embodiment is substantially the same as that of embodiment 1, with the only difference being that the mass percentage a of lithium fluorosulfonate in the electrolyte is 0.1; correspondingly, a / b is 2.

[0140] Example 4

[0141] The preparation method of the lithium-ion battery cell of this embodiment is basically the same as that of embodiment 2, except that the mass percentage b of lithium tetrafluoroborate in the electrolyte is 0.001; accordingly, y / b is 100 and a / b is 50.

[0142] Example 5

[0143] The preparation method of the lithium-ion battery cell of this embodiment is basically the same as that of embodiment 2, with the only difference being that the mass percentage b of lithium tetrafluoroborate in the electrolyte is 0.2; accordingly, y / b is 0.5 and a / b is 0.25.

[0144] Example 6

[0145] The preparation method of the lithium-ion battery cell of this embodiment is basically the same as that of embodiment 4, except that the positive electrode active material is LiNi 0.7 Co 0.2Mn 0.1 O2; correspondingly, y / b is 200 and a / b is 50.

[0146] Example 7

[0147] The preparation method of the lithium-ion battery cell of this embodiment is basically the same as that of embodiment 2, except that the positive electrode active material is LiNi 0.75 Co 0.15 Mn 0.1 O2; correspondingly, y / b is 3 and a / b is 1.

[0148] Example 8

[0149] The preparation method of the lithium-ion battery cell of this embodiment is basically the same as that of embodiment 5, except that the positive electrode active material is LiNi 0.8 Co 0.04 Mn 0.16 O2; correspondingly, y / b is 0.2 and a / b is 0.25.

[0150] Example 9

[0151] The preparation method of the lithium-ion battery cell of this embodiment is basically the same as that of embodiment 1, except that the mass percentage b of lithium tetrafluoroborate in the electrolyte is 0.2; accordingly, y / b is 0.5 and a / b is 0.025.

[0152] Example 10

[0153] The preparation method of the lithium-ion battery cell of this embodiment is basically the same as that of embodiment 3, except that the mass percentage b of lithium tetrafluoroborate in the electrolyte is 0.001; accordingly, y / b is 100 and a / b is 100.

[0154] Example 11

[0155] The preparation method of the lithium-ion battery cell of this embodiment is basically the same as that of embodiment 1, except that the mass percentage a of lithium fluorosulfonate in the electrolyte is 0.01, the mass percentage b of lithium tetrafluoroborate is 0.1; the positive electrode active material is LiNi 0.8 Co 0.05 Mn 0.15 O2; correspondingly, y / b is 0.5 and a / b is 0.1.

[0156] Example 12

[0157] The preparation method of the lithium-ion battery cell of this embodiment is basically the same as that of embodiment 1, except that: the mass percentage a of lithium fluorosulfonate in the electrolyte of this embodiment is 0.08, the mass percentage b of lithium tetrafluoroborate is 0.01; the positive electrode active material is LiNi 0.7 Co0.12 Mn 0.18 O2; correspondingly, y / b is 12 and a / b is 8.

[0158] Example 13

[0159] The preparation method of the lithium-ion battery cell of this embodiment is basically the same as that of embodiment 2, except that: + The mass concentration is 200ppm.

[0160] Example 14

[0161] The preparation method of the lithium-ion battery cell of this embodiment is basically the same as that of embodiment 2, except that: + The mass concentration is 800ppm.

[0162] Example 15

[0163] The preparation method of the lithium-ion battery cell of this embodiment is substantially the same as that of embodiment 2, with the only difference being that the porosity of the positive electrode sheet is 20% and the porosity of the negative electrode sheet is 29%.

[0164] Example 16

[0165] The preparation method of the lithium-ion battery cell of this embodiment is substantially the same as that of embodiment 2, with the only difference being that the porosity of the positive electrode sheet is 25% and the porosity of the negative electrode sheet is 37%.

[0166] Comparative Example 1

[0167] The preparation method of the lithium-ion battery cell of Comparative Example 1 is substantially the same as that of Example 1, with the only difference being that lithium fluorosulfonate and lithium tetrafluoroborate are not added to the electrolyte.

[0168] Comparative Example 2

[0169] The preparation method of the lithium-ion battery cell of Comparative Example 2 is basically the same as that of Example 1, except that the mass percentage a of lithium fluorosulfonate in the electrolyte is 0.003, the mass percentage b of lithium tetrafluoroborate is 0.3, and accordingly, y / b is 0.33 and a / b is 0.01.

[0170] Comparative Example 3

[0171] The preparation method of the lithium-ion battery cell of Comparative Example 3 is basically the same as that of Example 1, except that the mass percentage a of lithium fluorosulfonate in the electrolyte is 0.3, the mass percentage b of lithium tetrafluoroborate is 0.0003, and accordingly, y / b is 333.3 and a / b is 1000.

[0172] The details are shown in Table 1.

[0173] Table 1

[0174]

[0175] Performance Testing

[0176] In order to verify the progress of the embodiments of the present application, the performance of the electrolytes, positive and negative electrodes, and battery cells prepared in Examples 1 to 27 and Comparative Examples 1 to 3 was tested using the following characterization methods:

[0177] (1) Detection of additive composition and concentration in electrolyte

[0178] The concentrations of lithium fluorosulfonate and lithium tetrafluoroborate are tested using an ion chromatograph (IC), as per JY / T 0575-2020. The IC test can be performed by sampling the electrolyte from the battery cell. The electrolyte in the cell includes the free electrolyte, the electrolyte after centrifugation, and the supernatant from immersion of the positive and negative electrodes.

[0179] (2) Metal cation Na in the electrolyte + Detection of mass concentration

[0180] The electrolyte in the battery cell is tested by inductively coupled plasma emission spectrometry (ICP). The electrolyte in the battery cell includes the free electrolyte in the battery cell, the electrolyte after centrifugation, and the supernatant after the positive and negative electrodes are immersed.

[0181] (3) Detection of Co content in positive electrode active materials

[0182] The Co content in the positive electrode active material was detected by ICP testing.

[0183] (4) Detection of the porosity of positive and negative electrodes

[0184] The porosity of the positive and negative electrode plates can be calculated by model theory or tested by true density porosity analysis. For example, it can be obtained by referring to the national standard GB / T24586-2009 "Determination of apparent density, true density and porosity of iron ore". The specific test method is: the electrode is immersed in ethyl methyl carbonate (EMC) for cleaning; based on the gas displacement method, the negative electrode is placed in a true density tester, the test system is closed, helium is introduced according to the procedure, and the pressure of the gas in the sample chamber and the expansion chamber is detected. Among them, the percentage of the pore volume in the electrode to the total volume of the electrode is the electrode porosity, and the calculation formula is: Porosity = (V-V0) / V×100%, where V0 is the true volume and V is the apparent volume.

[0185] (5) Capacity retention measurement at 10°C

[0186] The lithium ion batteries prepared using all comparative examples and examples were repeatedly charged and discharged through the following steps, and the discharge capacity retention rate of the lithium ion batteries was calculated.

[0187] The lithium ion batteries prepared in all comparative examples and embodiments were allowed to stand at 25°C for 60 min, charged to 4.25V at a constant current of 0.5C, charged at a constant voltage of 4.25V, with a cut-off current of 0.05C (100% SOC), then allowed to stand for 10 min, discharged to 2.8V at 0.2C, and the discharge capacity of this step was recorded as C0, and allowed to stand for 10 min; the lithium ion batteries prepared above were allowed to stand at 10°C for 60 min, charged to 4.25V at a constant current of 0.5C, charged at a constant voltage of 4.25V, with a cut-off current of 0.05C (100% SOC), then allowed to stand for 10 min, discharged to 2.8V at 0.5C, and the discharge capacity of this step was recorded as C n , this is a charge and discharge cycle, the capacity retention rate of the battery cell = C n / C0*100%. Charge and discharge the battery cell in this manner until the cell capacity life decays to less than or equal to 80%. The cycle life at this point is the cycle life of the battery cell at 10°C.

[0188] (6) Capacity retention measurement at 25°C

[0189] The lithium ion batteries prepared using all comparative examples and examples were repeatedly charged and discharged through the following steps, and the discharge capacity retention rate of the lithium ion batteries was calculated.

[0190] The lithium ion batteries prepared in all comparative examples and embodiments were allowed to stand at 25°C for 60 min, charged to 4.25V at 0.5C constant current, charged at 4.25V constant voltage, with a cut-off current of 0.05C (100% SOC), then allowed to stand for 10 min, discharged to 2.8V at 0.2C, and the discharge capacity of this step was recorded as C0, and allowed to stand for 10 min; the lithium ion batteries prepared above were allowed to stand at 25°C for 60 min, charged to 4.25V at 1C constant current, charged at 4.25V constant voltage, with a cut-off current of 0.05C (100% SOC), then allowed to stand for 10 min, discharged to 2.8V at 1C, and the discharge capacity of this step was recorded as C n , this is a charge and discharge cycle, the capacity retention rate of the battery cell = C n / C0*100%. Charge and discharge the battery cell in this manner until the cell capacity life decays to less than or equal to 80%. The cycle life at this point is the cycle life of the battery cell at 25°C.

[0191] Table 2

[0192] Capacity retention rate 10℃ cycle @400cls Capacity retention rate 25℃ cycle @600cls Example 1 85.7％ 90.2％ Example 2 88.9％ 92.7％ Example 3 87.5％ 92.0％ Example 4 85.9％ 90.5％ Example 5 84.3％ 88.3％ Example 6 84.5％ 88.9％ Example 7 89.0％ 93.1％ Example 8 81.9％ 86.0％ Example 9 83.0％ 86.8％ Example 10 83.6％ 87.6％ Example 11 88.1％ 92.5％ Example 12 88.4％ 91.7％ Example 13 85.0％ 89.8％ Example 14 85.4％ 90.0％ Example 15 86.9％ 92.3％ Example 16 87.75 92.4％ Comparative Example 1 76.1％ 77.9％ Comparative Example 2 79.1％ 84.4％ Comparative Example 3 76.9％ 81.2％

[0193] As can be seen from Table 2, the batteries of Examples 1 to 16 have better cycle performance than those of Comparative Examples 1 to 3, which shows that the present application can effectively improve the low-temperature cycle performance of lithium-ion batteries.

[0194] 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 make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions 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 lithium-ion battery cell comprising an electrolyte and a positive electrode plate, characterized in that: The positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes a molecular formula of Li c Ni x Co y M d N e O f A g A compound, wherein M includes at least one of manganese and aluminum, N includes at least one of B, W, Si, Ti, Zr, Sr, Sn, Tb, Nb, Sb, Se, Ce, or Te, A includes at least one of S, N, P, F, Cl, Br, or I, 0.8≤c≤1.2, 0.5≤x≤0.8, 0.04≤y≤0.2, 0.01≤d≤0.5, 0≤e≤0.5, 0≤f≤2, and 0≤g≤2; The electrolyte includes additives, which include lithium fluorosulfonate and lithium tetrafluoroborate. Based on the total weight of the electrolyte being 100%, the mass percentage of the lithium fluorosulfonate is 0.005-0.1%, and the mass percentage of the lithium tetrafluoroborate is 0.001-0.2%.

2. The lithium-ion battery cell according to claim 1, characterized in that: The mass percentage of the lithium tetrafluoroborate in the electrolyte is b%, and b=0.001-0.2; wherein y and b are in inverse proportion, and the ratio of y to b is 0.2-200.

3. The lithium-ion battery cell according to claim 2, characterized in that: 0.05≤y≤0.12, 0.01≤b≤0.1, and the ratio of y to b is 0.5~12.

4. The lithium-ion battery cell according to any one of claims 1 to 3, characterized in that: The mass percentage of the lithium fluorosulfonate is 0.01-0.08%.

5. The lithium-ion battery cell according to any one of claims 1 to 4, characterized in that: The mass of the lithium fluorosulfonate is inversely proportional to the mass of the lithium tetrafluoroborate, and the mass ratio of the lithium fluorosulfonate to the lithium tetrafluoroborate is 0.025-100.

6. The lithium-ion battery cell according to any one of claims 1 to 5, characterized in that: The mass ratio of the lithium fluorosulfonate to the lithium tetrafluoroborate is 0.1-8.

7. The lithium-ion battery cell according to any one of claims 1 to 6, characterized in that: The electrolyte also contains Na + , the Na in the electrolyte + The mass concentration is 200-800ppm.

8. The lithium-ion battery cell according to any one of claims 1 to 7, characterized in that: The lithium-ion battery cell further includes a negative electrode plate, the porosity of the negative electrode plate is 29-37%, and the porosity of the positive electrode plate is 20-25%.

9. A lithium-ion battery, characterized in that: A lithium-ion battery cell comprising the lithium-ion battery cell according to any one of claims 1 to 8.

10. An electrical device, characterized in that: The invention comprises the lithium-ion battery cell according to any one of claims 1 to 8 and / or the lithium-ion battery according to claim 9.

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