Secondary battery and electric device including the same

Abstract

The application provides a secondary battery and a power utilization device comprising the same, the secondary battery comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte, the porosity of the positive electrode sheet being A, the porosity of the negative electrode sheet being B, the electrolyte comprising a first component, the first component comprising one or more of compounds represented by formula 1, the weight percentage content of the first component in the electrolyte being D1, the secondary battery satisfying 0.80≤A / B≤1.20 and 0.14≤100D1 / B≤1.50. The secondary battery of the application can balance high energy density and good cycle performance and power performance.

Description

[0001] This application is a divisional application of patent application 202280012822.4 entitled “Secondary Battery and Electrical Device Including the Same”, filed on October 17, 2022. Technical Field

[0002] This application belongs to the field of battery technology, specifically relating to a secondary battery and an electrical device containing the same. Background Technology

[0003] In recent years, rechargeable batteries have been widely used in energy storage systems for hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. With the increasing application and promotion of rechargeable batteries, their comprehensive performance has received growing attention. For example, rechargeable batteries need to simultaneously meet requirements such as high energy density, long cycle life, and good power performance. Therefore, how to provide a rechargeable battery with excellent overall performance is a pressing technical problem that needs to be solved. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery and an electrical device comprising the same, wherein the secondary battery can achieve both high energy density and good cycle performance and power performance.

[0005] This application provides a secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte, wherein the porosity of the positive electrode is A, the porosity of the negative electrode is B, and the electrolyte comprises a first component, the first component comprising one or more compounds of Formula 1, wherein R1 and R2 each independently represent a fluorine atom, or at least one of the following groups that are partially or fully fluorinated: C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C6-C8 aryl, C1-C10 alkoxy, C2-C10 alkenyloxy, C2-C10 alkynyloxy, C6-C8 aryloxy, and Me comprises one or more alkali metals and alkaline earth metals, and the weight percentage of the first component in the electrolyte is D1.

[0006]

[0007] The secondary battery satisfies the following conditions: 0.80≤A / B≤1.20 and 0.14≤100D1 / B≤1.50.

[0008] During the research process, the inventors of this application discovered that when the porosity A of the positive electrode, the porosity B of the negative electrode, and the content D1 of the first component in the electrolyte are adjusted to satisfy 0.80≤A / B≤1.20 and 0.14≤100D1 / B≤1.50, the matching between the extraction / intercalation of ions in the positive electrode and the intercalation / extraction in the negative electrode is better. This ensures that the compound shown in Formula 1 is as evenly wetted as possible in the positive and negative electrode sheets, and that the compound shown in Formula 1 effectively participates in film formation on the negative and positive electrode surfaces to form a low-resistance interface film. At this time, the battery polarization and internal resistance are both small, the capacity decay rate and heat generation are reduced during battery charging and discharging, and thus the secondary battery can have good power performance and long cycle life while having high energy density. In addition, the secondary battery can also have good low-temperature discharge performance.

[0009] In any embodiment of this application, 0.85 ≤ A / B ≤ 1.15, and optionally, 0.90 ≤ A / B ≤ 1.15. This helps to further improve the matching between the positive and negative electrode sheets, helps to form a low-resistance interface film on both the positive and negative electrode surfaces, and also helps to reduce battery polarization and internal resistance.

[0010] In any embodiment of this application, 0.16 ≤ 100D1 / B ≤ 1.40, and optionally, 0.20 ≤ 100D1 / B ≤ 1.20. This ensures that the compound shown in Formula 1 effectively participates in film formation on both the negative and positive electrode surfaces, forming an interface film with lower impedance, thereby enabling the secondary battery to better balance high energy density, good power performance, and low-temperature discharge performance.

[0011] In any embodiment of this application, the secondary battery further satisfies: 0.16 ≤ 100D1 / A ≤ 1.20, and optionally, 0.20 ≤ 100D1 / A ≤ 1.10. When the secondary battery further satisfies the above parameter range, it can better ensure that the compound shown in Formula 1 effectively participates in film formation on the positive electrode surface, further improving the film formation quality and forming a lower impedance interface film. This allows the secondary battery to better balance high energy density and good power performance, while also having a long cycle life.

[0012] In any embodiment of this application, 18% ≤ A ≤ 32%.

[0013] In any embodiment of this application, 20% ≤ B ≤ 35%.

[0014] When the porosity A of the positive electrode and / or the porosity B of the negative electrode further meet the above-mentioned specific ranges, it helps the positive electrode and / or negative electrode to also have the best electron transport network and the best ion conduction channel, thereby further improving the electrochemical performance of the secondary battery.

[0015] In any embodiment of this application, 0.05% ≤ D1 ≤ 0.3%. When the content of the first component D1 in the electrolyte is within a suitable range, it helps to form a low-resistivity interface film on both the positive and negative electrode surfaces, thereby enabling the secondary battery to have good power performance and long cycle life.

[0016] In any embodiment of this application, the compaction density of the positive electrode sheet is P1 g / cm³. 3 The compaction density of the negative electrode sheet is P2 g / cm³. 3 Furthermore, the secondary battery also satisfies the following relationship: 1.75 ≤ P1 / P2 ≤ 2.50, optionally, 2.00 ≤ P1 / P2 ≤ 2.40. By adjusting the ratio of the compaction density of the positive electrode to that of the negative electrode within the above range, it is helpful to form a low-resistance interface film on both the positive and negative electrode surfaces. It also helps the positive and negative electrode plates to have optimal electron transport networks and optimal ion conduction channels, thereby further improving the electrochemical performance of the secondary battery.

[0017] In any embodiment of this application, the compaction density of the positive electrode sheet is P1 g / cm³. 3 Furthermore, the secondary battery also satisfies the following conditions: 1.43 ≤ 10000D1 / P1 ≤ 9.34, and optionally, 2.00 ≤ 10000D1 / P1 ≤ 8.00. This ensures that the compound shown in Formula 1 effectively participates in film formation on the positive electrode surface, further improving film quality and forming a lower impedance interface film. In addition, it helps to avoid deterioration in the power performance of the secondary battery due to excessively high or low compaction density of the positive electrode sheet.

[0018] In any embodiment of this application, the compaction density of the negative electrode sheet is P2 g / cm³. 3 Furthermore, the secondary battery also satisfies the following conditions: 2.78 ≤ 10000D1 / P2 ≤ 21.40, optionally, 5.00 ≤ 10000D1 / P2 ≤ 15.00. This ensures that the compound shown in Formula 1 effectively participates in film formation on the negative electrode surface, further improving film quality and forming a lower impedance interface film. In addition, it helps to avoid deterioration in the power performance and / or low-temperature discharge performance of the secondary battery due to excessively high or low compaction density of the negative electrode sheet.

[0019] In any embodiment of this application, 2.8 ≤ P1 ≤ 3.65, and optionally, 3.2 ≤ P1 ≤ 3.5.

[0020] In any embodiment of this application, 1.2≤P2≤1.85, and optionally, 1.4≤P2≤1.8.

[0021] When the compaction density P1 of the positive electrode and / or the compaction density P2 of the negative electrode further meet the above-mentioned specific ranges, it helps the positive electrode and / or negative electrode to have suitable porosity, as well as optimal electron transport network and optimal ion conduction channel, thereby further improving the electrochemical performance of the secondary battery.

[0022] In any embodiment of this application, Me represents Li.

[0023] In any embodiment of this application, the compound represented by Formula 1 includes one or more of the following compounds:

[0024]

[0025] In any embodiment of this application, the electrolyte further includes a second component, the second component including lithium hexafluorophosphate.

[0026] In any embodiment of this application, the weight percentage D2 of the second component in the electrolyte is 5% or more, and optionally 8% or more.

[0027] Lithium hexafluorophosphate has high ionic conductivity, so when its content is within a suitable range, it helps to improve the overall ionic conductivity of the electrolyte, accelerate ion transport, and improve the capacity of the secondary battery.

[0028] In any embodiment of this application, the electrolyte further includes a third component, which includes one or more of lithium tetrafluoroborate, lithium difluorophosphate, lithium perchlorate, lithium hexafluoroarsenate, lithium difluorodioxarate phosphate, and lithium tetrafluorooxarate phosphate, and may optionally include lithium tetrafluoroborate, lithium difluorophosphate, or a combination thereof.

[0029] In any embodiment of this application, the weight percentage D3 of the third component in the electrolyte is 0.5% or less, and optionally 0.25% or less.

[0030] The third component can serve as an auxiliary lithium salt, further improving the interfacial properties of the positive and / or negative electrodes, or improving the ionic conductivity or thermal stability of the electrolyte.

[0031] In any embodiment of this application, the weight ratio D3 / D1 of the third component to the first component is 0.5 to 2. This helps to fully utilize the synergistic effect between the third component and the first component, and also contributes to the good low-temperature discharge performance of the secondary battery.

[0032] In any embodiment of this application, the electrolyte further includes a fourth component, which includes fluoroethylene carbonate.

[0033] In any embodiment of this application, the weight percentage D4 of the fourth component in the electrolyte is 5% or less, and optionally 2.5% or less.

[0034] When the electrolyte contains fluoroethylene carbonate, it can effectively improve the cycle performance of the secondary battery.

[0035] In any embodiment of this application, the weight ratio D4 / D1 of the fourth component to the first component is 5 to 100. When the weight ratio of the fourth component to the first component is within a suitable range, the synergistic effect between the fourth component and the first component can be fully utilized. In this case, not only will the gas production of the secondary battery not be significantly increased, but the cycle performance of the secondary battery will also be further improved.

[0036] In any embodiment of this application, the electrolyte further includes a fifth component, which includes one or more of cyclic carbonate compounds, chain carbonate compounds, carboxylic acid ester compounds, sulfone compounds and ether compounds, and optionally includes cyclic carbonate compounds and chain carbonate compounds.

[0037] In any embodiment of this application, the weight percentage D5 of the fifth component in the electrolyte is 60% or more, and optionally 75% or more.

[0038] In any embodiment of this application, the positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector and including a positive electrode active material. Optionally, the positive electrode active material includes one or more of layered lithium transition metal oxides, lithium phosphates and their respective modified compounds, or may include one or more of layered lithium transition metal oxides and their modified compounds, or a mixture of layered lithium transition metal oxides and their modified compounds and lithium phosphates and their modified compounds.

[0039] In any embodiment of this application, the morphology of the positive electrode active material includes one or more of spherical and near-spherical shapes.

[0040] In any embodiment of this application, the positive electrode active material includes primary particles, secondary particles, or a combination thereof, and may be selected to include secondary particles or a combination of primary and secondary particles.

[0041] In any embodiment of this application, the proportion of secondary particles in the positive electrode active material is more than 50%.

[0042] In any embodiment of this application, the volume average particle size of the positive electrode active material satisfies 2.5μm≤Dv50≤30μm, and optionally, 2.5μm≤Dv50≤25μm.

[0043] In any embodiment of this application, the radial distance of the positive electrode active material satisfies 1≤(Dv90-Dv10) / Dv50≤5, and optionally, 1≤(Dv90-Dv10) / Dv50≤2.

[0044] By adjusting one or more of the following parameters of the positive electrode active material: particle morphology, volume average particle size Dv50, and diameter (Dv90-Dv10) / Dv50, to meet the above range, it is helpful for the positive electrode sheet to have suitable porosity and / or compaction density, and also helps the secondary battery to better balance high energy density, high power density, and high capacity.

[0045] In any embodiment of this application, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and comprising a negative electrode active material. Optionally, the negative electrode active material includes one or more of carbon-based materials, silicon-based materials, tin-based materials, lithium titanate, and composite materials obtained by coating modification of the above materials. More preferably, it includes one or more of carbon-based materials and composite materials obtained by coating modification of the above materials. Optionally, the carbon-based material includes one or more of graphite, soft carbon, hard carbon, and composite materials obtained by coating modification of the above materials.

[0046] In any embodiment of this application, the morphology of the negative electrode active material includes one or more of the following: spherical, near-spherical, blocky, and sheet-like.

[0047] In any embodiment of this application, the negative electrode active material includes primary particles, secondary particles, or a combination thereof, and may be selected to include secondary particles or a combination of primary and secondary particles.

[0048] In any embodiment of this application, the proportion of secondary particles in the negative electrode active material is more than 50%.

[0049] In any embodiment of this application, the volume average particle size of the negative electrode active material satisfies 8μm≤Dv50≤22μm, and optionally, 10μm≤Dv50≤16μm.

[0050] In any embodiment of this application, the diameter of the negative electrode active material satisfies 0.5≤(Dv90-Dv10) / Dv50≤5, and optionally, 0.5≤(Dv90-Dv10) / Dv50≤1.5.

[0051] By adjusting one or more parameters of the negative electrode active material, such as particle morphology, volume average particle size Dv50, and diameter (Dv90-Dv10) / Dv50, to meet the above range, it is helpful for the negative electrode sheet to have suitable porosity and / or compaction density, and also helps the secondary battery to better balance high energy density, high power density, and high capacity.

[0052] The second aspect of this application provides an electrical device, including the secondary battery of the first aspect of this application.

[0053] The inventors of this application discovered during their research that when the porosity A of the positive electrode, the porosity B of the negative electrode, and the content D1 of the first component in the electrolyte are adjusted to satisfy 0.80≤A / B≤1.20 and 0.14≤100D1 / B≤1.50, the secondary battery can achieve good power performance and long cycle life while maintaining high energy density. Furthermore, the secondary battery can also exhibit good low-temperature discharge performance. The electrical device of this application includes the secondary battery provided in this application and therefore possesses at least the same advantages as the described secondary battery. Attached Figure Description

[0054] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0055] Figure 1 This is a schematic diagram of one embodiment of the battery cell of this application.

[0056] Figure 2 This is an exploded view of one embodiment of the battery cell of this application.

[0057] Figure 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0058] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0059] Figure 5 yes Figure 4 An exploded view of an embodiment of the battery pack shown.

[0060] Figure 6 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in this application.

[0061] The accompanying drawings are not necessarily drawn to scale. The reference numerals are explained as follows: 1 Battery pack, 2 Upper casing, 3 Lower casing, 4 Battery module, 5 Individual battery cell, 51 Housing, 52 Electrode assembly, 53 Cover plate. Detailed Implementation

[0062] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the secondary battery and an electrical device incorporating the same. However, unnecessary details may be omitted. For example, detailed descriptions of well-known facts and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0063] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0064] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0065] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0066] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0067] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0068] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0069] Throughout this specification, substituents of compounds are disclosed by groups or ranges. It is expressly intended that such description include each individual sub-combination of members of these groups and ranges. For example, it is expressly intended that the term "C1-C6 alkyl" individually discloses alkyl groups of C1, C2, C3, C4, C5, C6, C1-C6, C1-C5, C1-C4, C1-C3, C1-C2, C2-C6, C2-C5, C2-C4, C2-C3, C3-C6, C3-C5, C3-C4, C4-C6, C4-C5, and C5-C6.

[0070] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0071] In this application, the porosity of the electrode sheet has a meaning known in the art, referring to the percentage of the internal pore volume of the rolled electrode sheet to the total volume of the rolled electrode sheet. It can be tested using methods known in the art, such as referring to GB / T 24586-2009. The testing instrument can be a Micromeritics AccuPyc II1340 fully automatic true density meter. An exemplary testing method may include the following steps: The fully dried electrode sheet is punched into small round pieces of a certain diameter (e.g., 14 mm) using a punching machine. The small round pieces should have intact edges and be free of powder. The true volume V1 of the electrode sheet sample is accurately measured using a small-molecule diameter inert gas (e.g., helium) displacement method, combined with Archimedes' principle and Bohr's law. The porosity of the electrode sheet is calculated as [(V2-V1) / V2]×100%, where V2 is the apparent volume of the electrode sheet, and V2 = S×H×A, where S represents the area of ​​the electrode sheet sample, H represents the thickness of the electrode sheet sample, and A represents the number of electrode sheet samples.

[0072] In this application, the compaction density of the electrode sheet has a meaning known in the art and can be tested using methods known in the art. The compaction density of the electrode sheet = the areal density of the electrode sheet / the thickness of the electrode film. The areal density of the electrode sheet has a meaning known in the art and can be tested using methods known in the art. For example, take an electrode sheet that is coated on one side and cold-pressed (if it is a double-sided coated electrode sheet, the electrode film on one side can be wiped off first), cut it into small circular pieces with an area of ​​S0, weigh it, and record its weight as M1; then wipe off the electrode film on the weighed electrode sheet, weigh the current collector, and record it as M0. The areal density of the electrode sheet = (M1-M0) / S0. The thickness of the electrode film has a meaning known in the art and can be tested using methods known in the art, such as using a micrometer.

[0073] In this application, the volumetric particle sizes Dv90, Dv50, and Dv10 of the electrode active material have meanings known in the art, representing the particle sizes corresponding to a cumulative volume distribution percentage of 90%, 50%, and 10%, respectively, and can be determined using instruments and methods known in the art. For example, they can be determined using a laser particle size analyzer according to GB / T 19077-2016. The testing instrument can be a Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK.

[0074] In this application, the relevant parameters of the electrode sheet (e.g., areal density, compaction density, porosity) can be tested by sampling during the secondary battery preparation process or by sampling from the prepared secondary battery. An exemplary method for sampling from the prepared secondary battery may include the following steps: placing the secondary battery at 25°C for 30 minutes, discharging it at a constant current of 0.33C to the discharge cutoff voltage; after placing it at 25°C for another 30 minutes, disassembling the secondary battery, removing the electrode sheet, and soaking it in a solvent for a period of time (e.g., dimethyl carbonate, soaking for 20 hours), and then thoroughly drying the electrode sheet in a drying room (e.g., drying for more than 2 hours) to obtain the test sample.

[0075] The secondary battery mentioned in the embodiments or implementations of this application refers to a single physical module comprising one or more battery cells to provide higher voltage and capacity. For example, the secondary battery mentioned in this application may include battery cells, battery modules, or battery packs. A battery cell is the smallest unit constituting a secondary battery, capable of charging and discharging independently. This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. Figure 1 The example shown is a square-structured battery cell 5.

[0076] In some embodiments, a single battery cell includes an electrode assembly, and the single battery cell may also include an outer packaging. The electrode assembly is made from a positive electrode sheet, a negative electrode sheet, and a separator, etc., through a winding process and / or a stacking process, and the outer packaging is used to encapsulate the aforementioned electrode assembly. The outer packaging can be a rigid shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging can also be a flexible package, such as a pouch-type flexible package. The material of the flexible package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0077] In some embodiments, such as Figure 2 As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. Electrode assemblies 52 are encapsulated in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, and can be adjusted as needed.

[0078] In some embodiments of this application, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module. Figure 3 This is a schematic diagram of battery module 4 as an example. Figure 3As shown, in battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0079] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0080] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack. Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5 As shown, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0081] The secondary battery of this application includes a positive electrode, a negative electrode, and an electrolyte. The porosity of the positive electrode is A, the porosity of the negative electrode is B, and the electrolyte includes a first component. The first component includes one or more compounds shown in Formula 1, where R1 and R2 each independently represent a fluorine atom, or at least one of the following groups that are partially or fully fluorinated: C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C6-C8 aryl, C1-C10 alkoxy, C2-C10 alkenyloxy, C2-C10 alkynyloxy, C6-C8 aryloxy, and Me includes one or more alkali metals and alkaline earth metals. The weight percentage of the first component in the electrolyte is D1, and the secondary battery satisfies: 0.80 ≤ A / B ≤ 1.20 and 0.14 ≤ 100D1 / B ≤ 1.50.

[0082]

[0083] The operation of a secondary battery involves a series of mass transfer and reaction processes, including electron conduction, ion conduction, and electrochemical reactions. The structure and parameter design of its electrode plates are crucial to the battery's performance. For secondary batteries, the two most important indicators are energy density and power density. Energy density refers to the energy stored per unit volume or weight of the secondary battery, while power density refers to the power output per unit weight or volume of the secondary battery.

[0084] The smaller the porosity of the electrode sheets, the more electrode sheets can be packed into the limited battery casing, and the higher the weight ratio of the electrode active material. This not only improves the volumetric energy density but also the gravimetric energy density of the secondary battery. However, smaller porosity is not always better. Smaller porosity leads to greater compression between the electrode active material particles, making it difficult for the electrolyte to fully wet the electrode sheets, resulting in poorer capacity utilization. Furthermore, smaller porosity reduces the secondary battery's ability to absorb and retain electrolyte, leading to a significant increase in internal resistance and polarization during cycling, resulting in faster capacity decay.

[0085] Furthermore, high energy density and high power density are contradictory in the design and manufacturing of secondary batteries. To improve the energy density of a secondary battery, it is necessary to increase the weight ratio of the electrode active material and reduce the porosity of the electrode sheets. However, for high-power batteries, a larger discharge current is required to provide sufficient power output during use, resulting in higher heat generation during discharge. This leads to more electrolyte decomposition reactions at the electrode interface, which in turn increases the electrode interface impedance and affects the performance of the secondary battery. Therefore, to improve the power performance of a secondary battery, it is necessary to increase the porosity of the electrode sheets, reduce the heat generation during discharge, and reduce the electrode interface impedance.

[0086] Therefore, balancing the energy density and power density of secondary batteries has become very difficult, and currently it is also difficult for secondary batteries to achieve good power performance and long cycle life while having high energy density.

[0087] During the research process, the inventors of this application discovered that when the porosity A of the positive electrode, the porosity B of the negative electrode, and the content D1 of the first component in the electrolyte are adjusted to satisfy: 0.80≤A / B≤1.20 and 0.14≤100D1 / B≤1.50, a secondary battery that balances high energy density with good cycle performance and power performance can be obtained.

[0088] The first component of the electrolyte includes one or more compounds shown in Formula 1. The compounds shown in Formula 1 have fluorine atoms in their molecular structure, which are preferentially reduced at the negative electrode compared to organic solvents, and their reduction products exhibit low impedance characteristics, thereby contributing to the formation of a low-impedance negative electrode interface film. The compounds shown in Formula 1 contain oxalate groups in their molecular structure, which are preferentially oxidized at the positive electrode compared to organic solvents, and their oxidation products also exhibit low impedance characteristics, thereby contributing to the formation of a low-impedance positive electrode interface film. Furthermore, the oxalate atoms in the molecular structure of the compounds shown in Formula 1 readily and firmly bind to inorganic components such as LiF in the positive and / or negative electrode interface films, thereby accelerating ion transport and significantly reducing battery polarization.

[0089] The compound shown in Formula 1 exhibits high thermal stability, superior to common LiPF6, thus contributing to improved overall heat resistance of the electrolyte. Simultaneously, the compound in Formula 1 is less sensitive to moisture than LiPF6, further enhancing the electrolyte's water resistance, reducing HF formation, and lowering electrolyte acidity. Therefore, when the electrolyte contains the compound shown in Formula 1, it possesses high thermal and electrochemical stability, thereby reducing electrolyte decomposition reactions at high temperatures and lowering battery internal resistance. According to Joule's law, the heat generation of a secondary battery is directly related to its internal resistance; therefore, reducing internal resistance lowers heat generation, enabling the secondary battery to achieve both high energy density and good power performance.

[0090] Therefore, the compound shown in Formula 1 helps to form a low-resistivity interfacial film on the surface of the positive and / or negative electrodes, improving the performance of the secondary battery. However, the inventors of this application found in further research that the content of the compound shown in Formula 1 also needs to be reasonably matched with the porosity of the positive and negative electrode sheets to achieve an ideal match between the extraction / intercalation of ions in the positive electrode and the intercalation / extraction in the negative electrode.

[0091] In this application, the porosity A of the positive electrode and the porosity B of the negative electrode need to satisfy 0.80 ≤ A / B ≤ 1.20. Further research by the inventors of this application revealed that, at this point, the matching between the positive and negative electrodes is better. In particular, the matching between ion extraction / intercalation at the positive electrode and intercalation / extraction at the negative electrode is better, thereby ensuring that the compound shown in Formula 1 is as evenly wetted as possible in both the positive and negative electrodes. This facilitates subsequent formation and film formation, and helps to form a low-resistance interface film on both the positive and negative electrode surfaces. Furthermore, it also helps to reduce battery polarization and internal resistance. When A / B is greater than 1.20, the porosity of the positive electrode is high while that of the negative electrode is low. This results in poor electrolyte wettability of the negative electrode, poor film quality, and poor capacity utilization. Furthermore, ions that successfully migrate from the positive electrode to the negative electrode may not be able to embed into the negative electrode active material in time, and some ions may even be directly reduced and deposited on the negative electrode surface, forming dendrites. In addition, the low porosity of the negative electrode also results in poor liquid absorption and retention, leading to a significant increase in polarization and a significantly faster capacity decay during battery cycling. When A / B is less than 0.80, the porosity of the positive electrode is low while that of the negative electrode is high. In this case, the electrolyte wettability of the positive electrode is poor, resulting in poor film quality and poor capacity utilization, making it difficult to achieve both high energy density and good power performance in the secondary battery. In some embodiments, A / B can be a range consisting of any value greater than or equal to 0.80, 0.85, 0.90, 0.95, 1.00, 1.05, 1.10, 1.15, or 1.20. Optionally, 0.85 ≤ A / B ≤ 1.15, and 0.90 ≤ A / B ≤ 1.15. This helps to further improve the matching between the positive and negative electrode sheets, helps to form a low-resistance interface film on both the positive and negative electrode surfaces, and also helps to reduce battery polarization and internal resistance.

[0092] In this application, the porosity B of the negative electrode sheet and the content D1 of the first component in the electrolyte also need to satisfy: 0.14 ≤ 100D1 / B ≤ 1.50. The inventors of this application further discovered that, at this point, the compound shown in Formula 1 can effectively participate in film formation on both the negative and positive electrode surfaces, forming a low-resistance interfacial film. This allows the secondary battery to achieve both high energy density and good power performance. Furthermore, the impedance growth rate of the negative electrode is much higher than that of the positive electrode at low temperatures. Therefore, when the negative electrode surface has a low-resistance interfacial film, it also contributes to the secondary battery's good low-temperature discharge performance. When 100D1 / B is greater than 1.50, the content of the first component in the electrolyte is high while the porosity of the negative electrode sheet is small. Since the compound shown in Formula 1 preferentially participates in film formation on the negative electrode surface, the film formed by the compound shown in Formula 1 on the negative electrode becomes too thick, resulting in high negative electrode interfacial impedance. Consequently, it becomes difficult for the secondary battery to achieve both high energy density and good power performance, and the low-temperature discharge performance of the secondary battery also deteriorates. When 100D1 / B is less than 0.14, the content of the first component in the electrolyte is low while the porosity of the negative electrode is high. The compound shown in Formula 1 cannot effectively participate in film formation on either the negative or positive electrode surface, resulting in high interfacial impedance at both the negative and positive electrodes. Consequently, the power performance and cycle performance of the secondary battery deteriorate significantly. In some embodiments, 100D1 / B can be a range consisting of 0.16, 0.18, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, 0.90, 1.00, 1.10, 1.20, 1.30, 1.40, 1.50, or any of the above values. Optionally, 0.16 ≤ 100D1 / B ≤ 1.40, 0.20 ≤ 100D1 / B ≤ 1.20. This ensures that the compound shown in Formula 1 can effectively participate in film formation on both the negative and positive electrode surfaces and form an interface film with lower impedance, thereby enabling the secondary battery to better balance high energy density, good power performance, and low-temperature discharge performance.

[0093] Therefore, when the secondary battery satisfies 0.80≤A / B≤1.20 and 0.14≤100D1 / B≤1.50, the matching between ion extraction / intercalation at the positive electrode and intercalation / extraction at the negative electrode is good. This ensures that the compound shown in Formula 1 is as evenly wetted as possible on the positive and negative electrode plates, and that the compound shown in Formula 1 effectively participates in film formation on the negative and positive electrode surfaces to form a low-resistance interface film. At this time, the battery polarization and internal resistance are both small, the capacity decay rate and heat generation are reduced during battery charging and discharging, and thus the secondary battery can have good power performance and long cycle life while having high energy density. In addition, the secondary battery can also have good low-temperature discharge performance.

[0094] In some embodiments, the secondary battery further satisfies 0.16 ≤ 100D1 / A ≤ 1.20. The inventors of this application further discovered that when the secondary battery further satisfies the above parameter range, it can better ensure that the compound shown in Formula 1 effectively participates in film formation on the positive electrode surface, further improving the film formation quality and forming a lower impedance interface film. This allows the secondary battery to better balance high energy density and good power performance, while also exhibiting a long cycle life. Furthermore, it effectively avoids the following situations: when 100D1 / A is greater than 1.20, the compound shown in Formula 1 may form a thicker film on the positive electrode, resulting in potentially higher positive electrode interface impedance, which may further deteriorate the improvement in cycle performance of the secondary battery's power performance; when 100D1 / A is less than 0.16, since the compound shown in Formula 1 preferentially participates in film formation on the negative electrode surface, the compound shown in Formula 1 may form a smaller film on the positive electrode, resulting in a poorer reduction in positive electrode interface impedance, which may further deteriorate the improvement in the power performance of the secondary battery. In some embodiments, 100D1 / A can be a range consisting of any of the following values: 0.18, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, 0.90, 1.00, 1.10, 1.20, or higher. Optionally, 0.20 ≤ 100D1 / A ≤ 1.10, 0.30 ≤ 100D1 / A ≤ 1.10.

[0095] In some embodiments, the porosity A of the positive electrode sheet satisfies 18% ≤ A ≤ 32%, for example, A can be any range of values ​​consisting of 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, or higher. Optionally, 24% ≤ A ≤ 32%.

[0096] In some embodiments, the porosity B of the negative electrode sheet satisfies 20% ≤ B ≤ 35%, for example, B can be any range of values ​​consisting of 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35% or more.

[0097] The principle of a secondary battery's charge-discharge reaction involves the combination of electrons and ions. To ensure good power performance and long cycle life, the migration rates of ions and electrons need to be matched to achieve an optimal electron transport network and ion conduction pathway. When the porosity A of the positive electrode and / or the porosity B of the negative electrode further meet the aforementioned specific ranges, it helps the positive and / or negative electrodes to possess an optimal electron transport network and ion conduction pathway, thereby further improving the electrochemical performance of the secondary battery. While high porosity of the electrode sheets contributes to good ion conduction pathways, it also reduces the electronic contact between the active material particles. This leads to increased contact electronic impedance between active material particles and between the active material particles and the current collector, resulting in increased internal resistance and hindering further improvement in the electrochemical performance of the secondary battery. When the electrode sheet has low porosity, it helps to have a well-developed electron transport network. However, the conduction of ions in the electrode sheet becomes difficult, thereby increasing the ion conduction impedance. At the same time, the contact area between the electrode active material particles and the electrolyte increases, which also increases the charge exchange impedance. All of these factors lead to an increase in the internal resistance of the battery, which is not conducive to further improving the electrochemical performance of the secondary battery.

[0098] In some embodiments, 0.05% ≤ D1 ≤ 0.3%, for example, D1 can be any range of values ​​including 0.05%, 0.08%, 0.10%, 0.12%, 0.14%, 0.16%, 0.18%, 0.20%, 0.22%, 0.24%, 0.26%, 0.28%, 0.3%, or more. When the content of the first component D1 in the electrolyte is within a suitable range, it helps to form a low-resistance interfacial film on both the positive and negative electrode surfaces, thereby enabling the secondary battery to have good power performance and long cycle life. It can effectively avoid the following situations: when the content of the first component D1 in the electrolyte is greater than 0.3%, the film thickness formed on the positive electrode surface and / or negative electrode surface increases, which may lead to an increase in battery internal resistance, a deterioration in power performance and cycle performance, and a deterioration in capacity utilization; when the content of the first component D1 in the electrolyte is less than 0.05%, the effect of the first component in reducing battery internal resistance is not obvious, which may also lead to an insignificant improvement in the power performance and cycle performance of the secondary battery.

[0099] In some embodiments, the compaction density of the positive electrode sheet is P1 g / cm³. 3 The compaction density of the negative electrode sheet is P2 g / cm³. 3Furthermore, the secondary battery also satisfies the relationship: 1.75 ≤ P1 / P2 ≤ 2.50. For example, P1 / P2 can be a range consisting of any of the following values: 1.80, 1.85, 1.90, 1.95, 2.00, 2.05, 2.10, 2.15, 2.20, 2.25, 2.30, 2.35, 2.40, 2.45, 2.50, or above. Optionally, 2.00 ≤ P1 / P2 ≤ 2.40.

[0100] The compaction density of electrode sheets is an important indicator in the electrode sheet production process. Adjusting the compaction density helps to obtain electrode sheets with suitable porosity. Furthermore, by adjusting the ratio of the compaction density of the positive electrode sheet to that of the negative electrode sheet within the aforementioned range, it helps the compound shown in Formula 1 to be more evenly wetted into both the positive and negative electrode sheets, thus facilitating subsequent formation and film formation. This also helps to form low-resistance interfacial films on both the positive and negative electrode surfaces. Additionally, it helps the positive and negative electrode sheets to have optimal electron transport networks and ion conduction channels, thereby further improving the electrochemical performance of the secondary battery.

[0101] In some embodiments, the secondary battery further satisfies: 1.43 ≤ 10000D1 / P1 ≤ 9.34. For example, 10000D1 / P1 can be a range consisting of any of the following values: 1.45, 1.50, 2.00, 2.50, 3.00, 3.50, 4.00, 4.50, 5.00, 5.50, 6.00, 6.50, 7.00, 7.50, 8.00, 8.50, 9.00, or above. Optionally, 2.00 ≤ 10000D1 / P1 ≤ 8.00. The inventors of this application further discovered that, in this case, the compound shown in Formula 1 can effectively participate in film formation on the positive electrode surface, further improving the film quality and forming a lower impedance interface film; in addition, it helps to avoid a deterioration in the power performance of the secondary battery due to excessively high or low compaction density of the positive electrode sheet.

[0102] In some embodiments, the secondary battery further satisfies: 2.78 ≤ 10000D1 / P2 ≤ 21.40. For example, 10000D1 / P2 can be a range consisting of any of the following values: 2.80, 3.00, 4.00, 5.00, 6.00, 7.00, 8.00, 9.00, 10.00, 11.00, 12.00, 13.00, 14.00, 15.00, 16.00, 17.00, 18.00, 19.00, 20.00, 21.00, or more. Optionally, 5.00 ≤ 10000D1 / P2 ≤ 15.00. The inventors of this application discovered in further research that, at this time, it can be ensured that the compound shown in Formula 1 can effectively participate in film formation on the negative electrode surface, further improving the film formation quality and forming an interface film with lower impedance; in addition, it also helps to avoid the deterioration of the power performance and / or low-temperature discharge performance of the secondary battery due to the excessive or insufficient compaction density of the negative electrode sheet.

[0103] In some embodiments, the secondary battery also simultaneously satisfies: 1.75≤P1 / P2≤2.50, 1.43≤10000D1 / P1≤9.34, and 2.78≤10000D1 / P2≤21.40. This helps to further optimize the performance of the secondary battery.

[0104] In some embodiments, the compaction density P1 of the positive electrode sheet is... 3 The condition 2.8 ≤ P1 ≤ 3.65 is satisfied. For example, P1 is a range consisting of any of the following values: 2.8, 2.85, 2.9, 2.95, 3.0, 3.05, 3.1, 3.15, 3.2, 3.25, 3.3, 3.35, 3.4, 3.45, 3.5, 3.55, 3.6, 3.65, or above. Optionally, 3.2 ≤ P1 ≤ 3.5.

[0105] In some embodiments, the compaction density P2 of the negative electrode sheet is... 3 The condition 1.2 ≤ P2 ≤ 1.85 is satisfied. For example, P2 is a range consisting of any of the following values: 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, 1.85, or above. Optionally, 1.4 ≤ P2 ≤ 1.8.

[0106] When the compaction density P1 of the positive electrode and / or the compaction density P2 of the negative electrode further meet the above-mentioned specific ranges, it helps the positive electrode and / or negative electrode to have suitable porosity, as well as optimal electron transport network and optimal ion conduction channel, thereby further improving the electrochemical performance of the secondary battery.

[0107] In this application, the cold pressing process parameters of the electrode sheet, such as cold pressing rate, cold pressing temperature, cold pressing pressure, and number of cold pressing cycles, affect the porosity and / or compaction density of the electrode sheet. The parameters of the electrode active material itself, such as particle size, particle size distribution, and particle morphology, also affect the porosity and / or compaction density of the electrode sheet. The composition of the electrode film or electrode slurry, such as the types and contents of each component, also affects the porosity and / or compaction density of the electrode sheet. Therefore, the porosity and / or compaction density of the electrode sheet can be adjusted by regulating one or more of the parameters of the electrode active material itself, the composition of the electrode film or electrode slurry, and the cold pressing process parameters of the electrode sheet.

[0108] In some embodiments, the morphology of the positive electrode active material includes one or more of spherical and near-spherical shapes.

[0109] In some embodiments, the positive electrode active material includes primary particles, secondary particles, or a combination thereof, optionally including secondary particles or a combination of primary and secondary particles. When positive electrode active materials with primary particle morphology are combined with positive electrode active materials with secondary particle morphology, it is beneficial to increase the compaction density of the positive electrode sheet, thereby increasing the energy density of the secondary battery. In some embodiments, optionally, the proportion of secondary particles is 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more.

[0110] In some embodiments, the positive electrode sheet includes a positive electrode active material, wherein the volume average particle size of the positive electrode active material satisfies 2.5μm≤Dv50≤30μm, and optionally, 2.5μm≤Dv50≤25μm.

[0111] Optionally, when the positive electrode active material has a primary particle morphology, the volume average particle size of the primary particle morphology positive electrode active material satisfies 2.5μm≤Dv50≤7μm, and more preferably satisfies 2.5μm≤Dv50≤5.5μm.

[0112] Optionally, when the positive electrode active material has a secondary particle morphology, the volume average particle size of the positive electrode active material with the secondary particle morphology satisfies 6μm≤Dv50≤30μm, and more preferably satisfies 6μm≤Dv50≤25μm.

[0113] Different volume average particle sizes (Dv50) of the positive electrode active material particles result in different compressibility, which in turn affects the porosity and / or compaction density of the positive electrode sheet. When the volume average particle size (Dv50) of the positive electrode active material is within a suitable range, it helps the positive electrode sheet to have appropriate porosity and / or compaction density, and also contributes to high conductivity of both ions and electrons.

[0114] In some embodiments, the pitch of the positive electrode active material satisfies 1 ≤ (Dv90 - Dv10) / Dv50 ≤ 5, and optionally, 1 ≤ (Dv90 - Dv10) / Dv50 ≤ 2. The pitch (Dv90 - Dv10) / Dv50 of the positive electrode active material can reflect the dispersion of the particle size distribution of the positive electrode active material, and the dispersion of the particle size distribution will affect the porosity and / or compaction density of the positive electrode sheet. When the pitch (Dv90 - Dv10) / Dv50 of the positive electrode active material is within a suitable range, it helps the positive electrode sheet to have a suitable porosity and / or compaction density, and at the same time, it can make the pore size distribution of the positive electrode sheet more uniform, thereby helping the secondary battery to better achieve high energy density, high power density and high capacity.

[0115] Therefore, by adjusting one or more parameters of the positive electrode active material, such as particle morphology, volume average particle size Dv50, and diameter (Dv90-Dv10) / Dv50, to meet the above range, it is helpful for the positive electrode sheet to have suitable porosity and / or compaction density, and also helps the secondary battery to better balance high energy density, high power density, and high capacity.

[0116] In some embodiments, the morphology of the negative electrode active material includes one or more of the following: spherical, near-spherical, blocky, and sheet-like.

[0117] In some embodiments, the negative electrode active material includes primary particles, secondary particles, or a combination thereof, optionally including secondary particles or a combination of primary and secondary particles. When negative electrode active materials with primary particle morphology are combined with negative electrode active materials with secondary particle morphology, it is beneficial to increase the compaction density of the negative electrode sheet, thereby increasing the energy density of the secondary battery. In some embodiments, optionally, the proportion of secondary particles is 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more.

[0118] In some embodiments, the negative electrode sheet is provided with a negative electrode active material, the volume average particle size of which satisfies 8 μm ≤ Dv50 ≤ 22 μm, optionally 10 μm ≤ Dv50 ≤ 16 μm. Different volume average particle sizes (Dv50) of the negative electrode active material result in different compressibility of the particles, thereby affecting the porosity and / or compaction density of the negative electrode sheet. When the volume average particle size (Dv50) of the negative electrode active material is within a suitable range, it helps the negative electrode sheet to have appropriate porosity and / or compaction density, and also contributes to high conductivity for both ions and electrons.

[0119] In some embodiments, the pitch of the negative electrode active material satisfies 0.5 ≤ (Dv90 - Dv10) / Dv50 ≤ 5, and optionally, 0.5 ≤ (Dv90 - Dv10) / Dv50 ≤ 1.5. The pitch (Dv90 - Dv10) / Dv50 of the negative electrode active material can reflect the dispersion of the particle size distribution of the negative electrode active material, and the dispersion of the particle size distribution affects the porosity and / or compaction density of the negative electrode sheet. When the pitch (Dv90 - Dv10) / Dv50 of the negative electrode active material is within a suitable range, it helps the negative electrode sheet to have a suitable porosity and / or compaction density, and at the same time, it can make the pore size distribution of the negative electrode sheet more uniform, thereby also helping the secondary battery to better achieve high energy density, high power density and high capacity.

[0120] Therefore, by adjusting one or more parameters of the negative electrode active material, such as particle morphology, volume average particle size Dv50, and diameter (Dv90-Dv10) / Dv50, to meet the above range, it is helpful for the negative electrode sheet to have suitable porosity and / or compaction density, and also helps the secondary battery to better balance high energy density, high power density, and high capacity.

[0121] The proportion of secondary particles in the electrode sheet can be obtained as follows: Select multiple test areas in the electrode film layer, acquire images of multiple test areas using a scanning electron microscope, and count the proportion of the number of particles with secondary particle morphology in each image to the total number of particles in the electrode active material. The average value of the statistical results of multiple test areas is the proportion of secondary particles.

[0122] Electrolyte

[0123] In this application, R1 and R2 represent fluorine atoms or fluorine-containing groups (e.g., partially or fully fluorinated organic groups). The presence of fluorine atoms helps to form thinner and denser positive and / or negative electrode interface films, thereby facilitating uniform ion transport and effectively suppressing dendrite formation.

[0124] In some embodiments, one of R1 and R2 represents a fluorine atom, and the other represents at least one of the following groups that are partially or fully fluorinated: C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C6-C8 aryl, C1-C10 alkoxy, C2-C10 alkenyloxy, C2-C10 alkynyloxy, and C6-C8 aryloxy.

[0125] In some embodiments, one of R1 and R2 represents a fluorine atom, and the other represents at least one of the following groups that are partially or fully fluorinated: methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, vinyl, propenyl, allyl, butadienyl, ethynyl, propynyl, phenyl, methoxy, ethoxy, propoxy, ethyleneoxy, propenyloxy, ethynyloxy, propynyloxy, and phenoxy.

[0126] In some embodiments, R1 and R2 both represent fluorine atoms.

[0127] In this application, Me includes one or more of alkali metals and alkaline earth metals. Optionally, the alkali metal includes one or more of Li, Na, and K. Optionally, the alkaline earth metal includes Ca, Mg, or a combination thereof.

[0128] In some embodiments, Me represents Li.

[0129] In some embodiments, the compound represented by Formula 1 includes one or more of the following compounds:

[0130]

[0131] In some embodiments, the electrolyte further includes a second component, the second component comprising lithium hexafluorophosphate (LiPF6).

[0132] Lithium hexafluorophosphate (LiPF6) possesses high ionic conductivity, which, when its content is within a suitable range, helps improve the overall ionic conductivity of the electrolyte, accelerates ion transport, and enhances the capacity of the secondary battery. However, LiPF6 exhibits poor thermal stability at high temperatures, decomposing to form PF5. PF5 reacts with water to form HF, which easily corrodes the positive electrode active material and increases battery gas expansion. When the electrolyte contains both the compound shown in Formula 1 and LiPF6, the compound shown in Formula 1 can also react with LiPF6 to form the compound LiPF4C2O4, thereby reducing some of the decomposition of LiPF6 and the formation of HF, resulting in better cycle performance of the secondary battery.

[0133] In some embodiments, the second component in the electrolyte may optionally have a weight percentage D2 of 5% or more, more preferably 8% or more, for example, 8% to 30%, 10% to 25%, or 10% to 20%.

[0134] In some embodiments, the electrolyte further includes a third component, which comprises one or more of lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium difluorodioxanol phosphate (LiDFOP), and lithium tetrafluorooxanol phosphate (LiTFOP). The third component can serve as an auxiliary lithium salt, further improving the interfacial properties of the positive and / or negative electrodes, or improving the ionic conductivity or thermal stability of the electrolyte.

[0135] In some embodiments, the third component optionally includes lithium tetrafluoroborate, lithium difluorophosphate, or a combination thereof. Lithium tetrafluoroborate exhibits high thermal stability, thereby improving the high-temperature stability of the secondary battery; it also has low charge transfer resistance, thereby improving the low-temperature discharge performance of the secondary battery and broadening the electrochemical window of the electrolyte. Lithium difluorophosphate exhibits high electrochemical stability, improving the ionic conductivity of the electrolyte, enhancing the properties of the positive and / or negative electrode interfacial films, and contributing to the construction of stable and low-impedance positive and / or negative electrode interfacial films, thereby effectively reducing electrolyte decomposition and further improving the power and safety performance of the secondary battery.

[0136] In some embodiments, the third component in the electrolyte, D3, is optionally less than 0.5% by weight, and more preferably less than 0.25%.

[0137] In some embodiments, the weight ratio D3 / D1 of the third component to the first component is optionally 0.5 to 2. This helps to fully utilize the synergistic effect between the third component and the first component, and also contributes to good low-temperature discharge performance of the secondary battery.

[0138] In some embodiments, optionally, the weight percentage D3 of the third component in the electrolyte satisfies that D3 is less than 0.5% and D3 / D1 is 0.5 to 2. This is beneficial for further enhancing the synergistic effect between the third component and the first component.

[0139] In some embodiments, the electrolyte further includes a fourth component, which comprises fluoroethylene carbonate (FEC). FEC can undergo a reductive decomposition reaction at a higher potential, forming a flexible interfacial film on the surface of the negative electrode active material. It also inhibits the reductive decomposition of organic solvents at lower potentials and suppresses the intercalation of organic solvents into the negative electrode active material. Therefore, when the electrolyte contains FEC, it can effectively improve the cycle performance of the secondary battery. However, FEC easily decomposes to form HF, which can damage the positive electrode interfacial film, corrode the positive electrode active material, and increase the heat and gas generation of the secondary battery. The compound shown in Formula 1 can act as a stabilizer for the positive electrode active material. The B atoms in its structure have the function of interacting with the O atoms on the surface of the positive electrode active material, thereby stabilizing the crystal structure of the positive electrode active material and reducing the damage to the crystal structure of the positive electrode active material caused by HF. Therefore, using the compound shown in Formula 1 in combination with FEC is beneficial to fully utilize the further improvement effect of FEC on the cycle performance of the secondary battery. In addition, FEC has a high dielectric constant, which helps the anions of the compound shown in Formula 1 to become free ions and reduces the association between anions and cations, thereby fully leveraging the effect of the compound shown in Formula 1 on improving the power performance and cycle performance of secondary batteries.

[0140] In some embodiments, the fourth component D4 in the electrolyte may optionally be less than 5% by weight, and more preferably less than 2.5%.

[0141] In some embodiments, optionally, the weight ratio D4 / D1 of the fourth component to the first component is 5 to 100, more preferably 5 to 75, 5 to 50, or 5 to 40. The inventors further discovered that when the weight ratio of the fourth component to the first component is within a suitable range, the synergistic effect between the fourth component and the first component can be fully utilized. In this case, not only is the gas production of the secondary battery not significantly increased, but the cycle performance of the secondary battery is further improved.

[0142] In some embodiments, optionally, the weight percentage D4 of the fourth component in the electrolyte satisfies that D4 is less than 5% and D4 / D1 is 5 to 100. This is beneficial for further enhancing the synergistic effect between the fourth component and the first component.

[0143] In some embodiments, the electrolyte further includes a fifth component, which comprises one or more of cyclic carbonate compounds, chain carbonate compounds, carboxylic acid ester compounds, sulfone compounds, and ether compounds. In this application, the fifth component primarily functions as an organic solvent to dissolve the other components in the electrolyte.

[0144] As an example, the cyclic carbonate compound may include one or more of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). As an example, the chain carbonate compound may include one or more of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC). As an example, the carboxylic acid ester compound may include one or more of methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), and 1,4-butyrolactone (GBL). As an example, the sulfone compound may include one or more of sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE). As an example, the ether compounds include one or more of tetrahydrofuran (THF), 2-methyltetrahydrofuran, 1,3-dioxolane (DOL), ethylene glycol monomethyl ether, ethylene glycol dimethyl ether (DME), tetraethylene glycol dimethyl ether, dimethoxymethane (DMM), and diethylene glycol dimethyl ether (DG).

[0145] In some embodiments, the fifth component in the electrolyte may optionally have a weight percentage D5 of 60% or more, optionally 65% ​​or more, 70% or more, 75% or more, or 80% or more.

[0146] In some embodiments, the fifth component optionally includes at least cyclic carbonate compounds and chain carbonate compounds. When the content of lithium salts such as lithium hexafluorophosphate is high, the viscosity of the electrolyte increases and the ionic conductivity decreases, which is detrimental to ion transport. Cyclic carbonate compounds, due to their higher dielectric constant, can increase the ionic conductivity of the electrolyte, while chain carbonate compounds, due to their lower viscosity, can reduce the viscosity of the electrolyte. Therefore, when the fifth component includes both cyclic and chain carbonate compounds, it helps to achieve suitable viscosity and ionic conductivity in the electrolyte, thereby facilitating ion transport.

[0147] Cyclic carbonate compounds have a high dielectric constant, which helps to increase the ionic conductivity of the electrolyte. However, they are prone to decomposition reactions, which affect the storage performance of secondary batteries. Therefore, their content needs to be controlled within an appropriate range.

[0148] In some embodiments, the weight percentage of the cyclic carbonate compound in the electrolyte may be greater than 0 and less than or equal to 40%, and may be 5% to 40%, 8% to 35%, or 10% to 30%.

[0149] In some embodiments, the weight percentage of the chain carbonate compound in the electrolyte may be 40% to 85%, optionally 50% to 80%, 55% to 80%, or 60% to 80%.

[0150] In some embodiments, the electrolyte may further include other components besides those described above, such as one or more of halogen-substituted cyclic carbonate compounds, nitrile compounds, phosphazene compounds, aromatic hydrocarbons and halogenated aromatic hydrocarbons, isocyanate compounds, acid anhydride compounds, sulfate compounds, sulfite compounds, sulfonate compounds, and disulfonate compounds. This application does not impose any particular limitation on the types of other components in the electrolyte, as long as it does not impair the spirit of this application. For example, it may include one or more of 1,3-propanesulfonate lactone (PS), vinylene carbonate (VC), and vinyl sulfate (DTD).

[0151] In some embodiments, optionally, the total weight percentage of these other components is less than 5%, more preferably less than 2.5%, based on the total weight of the electrolyte.

[0152] In this application, the components and their contents in the electrolyte can be determined according to methods known in the art. For example, they can be determined by gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), or inductively coupled plasma optical emission spectrometry (ICP-OES).

[0153] It should be noted that during the electrolyte testing of this application, freshly prepared electrolyte can be used directly, or electrolyte can be obtained from a secondary battery. An exemplary method for obtaining electrolyte from a secondary battery includes the following steps: discharging the secondary battery to the discharge cutoff voltage (for safety, the battery is generally left fully discharged), followed by centrifugation. A suitable amount of the centrifuged liquid is then taken as the electrolyte. Alternatively, electrolyte can be obtained directly from the secondary battery's filling port.

[0154] [Positive electrode plate]

[0155] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector and comprising a positive active material. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0156] The positive electrode active material can be any positive electrode active material known in the art for secondary batteries. For example, the positive electrode active material includes one or more of layered lithium transition metal oxides, lithium-containing phosphates, and their respective modified compounds. It can be optionally composed of one or more of layered lithium transition metal oxides and their modified compounds, or a mixture of layered lithium transition metal oxides and their modified compounds with lithium-containing phosphates and their modified compounds. Optionally, the layered lithium transition metal oxide includes one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Optionally, the lithium-containing phosphate includes one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds. In this application, the modified compounds of the above-mentioned positive electrode active materials can be used for doping modification and / or surface coating modification of the positive electrode active materials.

[0157] In some embodiments, to further improve the energy density of the secondary battery, the positive electrode active material includes materials with the molecular formula Li. a Ni b Co c Mn d Al e M f O g A h Layered lithium transition metal oxide, M represents transition metal site doped cation, A represents oxygen site doped anion, 0.8≤a≤1.2, 0≤b≤1, 0≤c≤1, 0≤d≤1, 0≤e≤1, 0≤f≤0.2, 0≤g≤2, 0≤h≤2, b+c+d+e+f=1, g+h=2.

[0158] The molecular formula is Li a Ni b Co c Mn d Al e M f O g A h Layered lithium transition metal oxides can be selectively modified by M cation doping, A anion doping, or by simultaneous doping with both M cations and A anions. The resulting layered lithium transition metal oxides have a more stable crystal structure, which can further improve the electrochemical performance of secondary batteries, such as cycle performance and power performance.

[0159] In some embodiments, M includes one or more of Si, Ti, Mo, V, Ge, Se, Zr, Nb, Ru, Pd, Sb, Ce, Te, and W.

[0160] In some embodiments, A includes one or more of F, N, P, and S. Optionally, A is F. After F doping modification, Li a Ni b Co c Mn d Al e M f O g A h The crystal structure is more stable, which enables secondary batteries to have better cycle performance and power performance.

[0161] The values ​​of a, b, c, d, e, f, g, and h satisfy the following condition: that makes Li a Ni b Co c Mn d Al e M f O g A h It is electrically neutral.

[0162] In some embodiments, 0 < b < 0.98. Optionally, 0.50 ≤ b < 0.98, 0.55 ≤ b < 0.98, 0.60 ≤ b < 0.98, 0.65 ≤ b < 0.98, 0.70 ≤ b < 0.98, 0.75 ≤ b < 0.98, or 0.80 ≤ b < 0.98.

[0163] In some embodiments, c = 0.

[0164] In some embodiments, 0 < c ≤ 0.20. Optionally, 0 < c ≤ 0.15, 0 < c ≤ 0.10, 0 < c ≤ 0.09, 0 < c ≤ 0.08, 0 < c ≤ 0.07, 0 < c ≤ 0.06, 0 < c ≤ 0.05, 0 < c ≤ 0.04, 0 < c ≤ 0.03, 0 < c ≤ 0.02, or 0 < c ≤ 0.01. Cobalt is scarce in the Earth's crust, difficult to mine, and expensive; therefore, low-cobalt or cobalt-free materials have become an inevitable development trend for cathode active materials. However, cobalt contributes significantly to the ion diffusion rate of cathode active materials; low-cobalt or cobalt-free materials will reduce the ion diffusion rate of cathode active materials, affecting the cycle performance of secondary batteries. Researchers have been working to improve the ion diffusion rate of low-cobalt or cobalt-free cathode active materials, but a satisfactory solution has not yet been found.

[0165] The inventors of this application unexpectedly discovered during their research that the compound shown in Formula 1 in the electrolyte can form a low-resistance protective film on the surface of the positive electrode active material, and the B atoms in its molecular structure readily combine with the O atoms in the positive electrode active material, thereby reducing the diffusion resistance of ions within the bulk phase of the positive electrode active material. Therefore, when the electrolyte contains an appropriate amount of the compound shown in Formula 1, the low-cobalt or cobalt-free positive electrode active material exhibits a significantly improved ion diffusion rate, and ions within the bulk phase of the low-cobalt or cobalt-free positive electrode active material can be promptly replenished to the surface, stabilizing the crystal structure of the low-cobalt or cobalt-free positive electrode active material. Because the crystal structure of the low-cobalt or cobalt-free positive electrode active material is more stable, it can greatly reduce the probability of problems such as instability in the crystal structure, chemical properties, or electrochemical properties of the positive electrode active material, for example, reducing the probability of irreversible distortion and lattice defects in the positive electrode active material.

[0166] In some embodiments, d = 0 and 0 < e < 0.50. Alternatively, d = 0 and 0 < e ≤ 0.45, d = 0 and 0 < e ≤ 0.40, d = 0 and 0 < e ≤ 0.35, d = 0 and 0 < e ≤ 0.30, d = 0 and 0 < e ≤ 0.25, d = 0 and 0 < e ≤ 0.20, d = 0 and 0 < e ≤ 0.15, or d = 0 and 0 < e ≤ 0.10.

[0167] In some embodiments, e = 0 and 0 < d < 0.50. Optionally, e = 0 and 0 < d ≤ 0.45, e = 0 and 0 < d ≤ 0.40, e = 0 and 0 < d ≤ 0.35, e = 0 and 0 < d ≤ 0.30, e = 0 and 0 < d ≤ 0.25, e = 0 and 0 < d ≤ 0.20, e = 0 and 0 < d ≤ 0.15, or e = 0 and 0 < d ≤ 0.10.

[0168] In some embodiments, 0 < d < 0.50 and 0 < e < 0.50. Alternatively, 0 < d ≤ 0.30 and 0 < e ≤ 0.10.

[0169] In some embodiments, g = 2, h = 0.

[0170] In some embodiments, g = 0, h = 2.

[0171] In some embodiments, 0 < g < 2, 0 < h < 2, and g + h = 2.

[0172] As an example, the molecular formula is Li a Ni b Co c Mn d Al e M f O g A hLayered lithium transition metal oxides, including but not limited to LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co 0.05 Mn 0.15 O2, LiNi 0.7 Mn 0.3 O2, LiNi 0.69 Co 0.01 Mn 0.3 O2, LiNi 0.68 Co 0.02 Mn 0.3 O2, LiNi 0.65 Co 0.05 Mn 0.3 O2, LiNi 0.63 Co 0.07 Mn 0.3 O2 and LiNi 0.61 Co 0.09 Mn 0.3 One or more of O2.

[0173] Li a Ni b Co c Mn d Al e M f O g A h It can be prepared according to conventional methods in the art. An exemplary preparation method is as follows: a lithium source, a nickel source, a cobalt source, a manganese source, an aluminum source, an M-element precursor, and an A-element precursor are mixed and then sintered. The sintering atmosphere can be an oxygen-containing atmosphere, such as an air atmosphere or an oxygen atmosphere. The O2 concentration of the sintering atmosphere is, for example, 70% to 100%. The sintering temperature and sintering time can be adjusted according to actual conditions.

[0174] As an example, the lithium source includes, but is not limited to, one or more of lithium oxide (Li₂O), lithium phosphate (Li₃PO₄), lithium dihydrogen phosphate (LiH₂PO₄), lithium acetate (CH₃COOLi), lithium hydroxide (LiOH), lithium carbonate (Li₂CO₃), and lithium nitrate (LiNO₃). As an example, the nickel source includes, but is not limited to, one or more of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate. As an example, the cobalt source includes, but is not limited to, one or more of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate. As an example, the manganese source includes, but is not limited to, one or more of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate. As an example, the aluminum source includes, but is not limited to, one or more of aluminum sulfate, aluminum nitrate, aluminum chloride, aluminum oxalate, and aluminum acetate. As an example, the precursor of element M includes, but is not limited to, one or more of oxides, nitrate compounds, carbonate compounds, hydroxides, and acetate compounds of element M. As an example, the precursors of element A include, but are not limited to, one or more of the following: ammonium fluoride, lithium fluoride, hydrogen fluoride, ammonium chloride, lithium chloride, hydrogen chloride, ammonium nitrate, ammonium nitrite, ammonium carbonate, ammonium bicarbonate, ammonium phosphate, phosphoric acid, ammonium sulfate, ammonium bisulfate, ammonium bisulfite, ammonium sulfite, ammonium hydrogen sulfide, hydrogen sulfide, lithium sulfide, ammonium sulfide, and elemental sulfur.

[0175] In some embodiments, based on the total weight of the positive electrode film, the molecular formula is Li a Ni b Co c Mn d Al e M f O g A h The weight percentage of layered lithium transition metal oxide is 80% or more, and can be 85% or more, or 90% or more.

[0176] In some embodiments, the positive electrode film layer may optionally include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, based on the total weight of the positive electrode film layer, the weight percentage of the positive electrode conductive agent is less than 15%, optionally less than 10% or less than 5%.

[0177] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose any particular limitation on the type of positive electrode binder. As an example, the positive electrode binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. In some embodiments, based on the total weight of the positive electrode film layer, the weight percentage of the positive electrode binder is less than 5%, optionally less than 3% or less, or less than 2%.

[0178] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. An example of the metal material may be one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. An example of the polymer substrate may be one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0179] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP), but is not limited to this.

[0180] [Negative electrode plate]

[0181] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0182] The negative electrode active material may be any negative electrode active material known in the art for use in secondary batteries. As an example, the negative electrode active material includes one or more of carbon-based materials, silicon-based materials, tin-based materials, lithium titanate, and composite materials obtained by coating modification of the above materials.

[0183] In some embodiments, the negative electrode active material includes one or more of carbon-based materials and composite materials obtained by coating modification of the above materials. Optionally, the carbon-based material includes one or more of graphite (e.g., natural graphite, artificial graphite, or a combination thereof), soft carbon, hard carbon, and composite materials obtained by coating modification of the above materials.

[0184] In some embodiments, the weight percentage of the negative electrode active material, based on the total weight of the negative electrode film, is 80% or more, optionally 85% or more, or 90% or more.

[0185] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, based on the total weight of the negative electrode film layer, the weight percentage of the negative electrode conductive agent is less than 15%, optionally less than 10% or less than 5%.

[0186] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the weight percentage of the negative electrode binder is less than 5% based on the total weight of the negative electrode film layer.

[0187] In some embodiments, the negative electrode film may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc. In some embodiments, the weight percentage of the other additives is less than 2% based on the total weight of the negative electrode film.

[0188] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer substrate and a metal material layer formed on at least one surface of the polymer substrate. As an example, the metal material may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0189] The negative electrode film layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing a negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0190] [Isolation membrane]

[0191] In some embodiments, the secondary battery further includes a separator. The separator is disposed between the positive electrode and the negative electrode, primarily serving to prevent short circuits between the positive and negative electrodes while allowing ions to pass through. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0192] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0193] [Preparation Method]

[0194] The method for preparing the secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding process and / or a stacking process. The electrode assembly is placed in an outer packaging, dried, and then injected with an electrolyte. After vacuum sealing, settling, formation, and shaping processes, a battery cell is obtained. Multiple battery cells can be further connected in series, parallel, or a combination thereof to form a battery module. Multiple battery modules can also be connected in series, parallel, or a combination thereof to form a battery pack. In some embodiments, multiple battery cells can also be directly assembled into a battery pack.

[0195] This application also provides an electrical device, which includes the secondary battery of this application. The secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may be, but is not limited to, mobile devices (e.g., mobile phones, tablets, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0196] The electrical device can select the specific type of secondary battery according to its usage requirements, such as a battery cell, battery module, or battery pack.

[0197] Figure 6 This is a schematic diagram illustrating an example of an electrical device. This device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used as the power source.

[0198] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0199] Example

[0200] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0201] Example 1

[0202] Preparation of positive electrode sheet

[0203] LiNi, the positive electrode active material 0.6 Co 0.2 Mn 0.2O2 (spherical morphology, 60% secondary particles, Dv50 20μm), conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) were thoroughly mixed in an appropriate amount of NMP solvent at a weight ratio of 97.5:1.4:1.1 to form a uniform positive electrode slurry. The positive electrode slurry was then uniformly coated onto the surface of the positive electrode current collector aluminum foil. After drying and cold pressing, the positive electrode sheet was obtained. The compaction density of the positive electrode sheet was achieved to 3.4 g / cm³ by adjusting one or more of the cold pressing process parameters, such as cold pressing speed, cold pressing temperature, cold pressing pressure, and the number of cold pressing cycles. 3 The porosity is 25%.

[0204] Preparation of negative electrode sheet

[0205] A uniform negative electrode slurry is formed by thoroughly mixing graphite (quasi-spherical morphology, secondary particle content of over 80%, Dv50 of 11 μm), styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC-Na), and carbon black (Super P) in a weight ratio of 96.2:1.8:1.2:0.8 with an appropriate amount of deionized water. The negative electrode slurry is then uniformly coated onto the surface of a copper foil current collector. After drying and cold pressing, a negative electrode sheet is obtained. The compaction density of the negative electrode sheet is achieved by adjusting one or more of the cold pressing process parameters, such as cold pressing speed, cold pressing temperature, cold pressing pressure, and the number of cold pressing cycles. 3 The porosity is 27%.

[0206] Separating membrane

[0207] Porous polyethylene (PE) membrane is used as the separator.

[0208] Preparation of electrolyte

[0209] The components were mixed thoroughly according to the composition shown in Table 1 to obtain the electrolyte. In Table 1, the amount of each component added is based on the total weight of the electrolyte.

[0210] The first group is

[0211] The second component is lithium hexafluorophosphate.

[0212] The third component is lithium tetrafluoroborate.

[0213] The fourth component is fluoroethylene carbonate.

[0214] The fifth component is a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a weight ratio of 1:1:1.

[0215] Preparation of secondary batteries

[0216] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly. The electrode assembly is placed in an outer packaging, the electrolyte is added, and after processes such as encapsulation, standing, formation, and aging, a secondary battery is obtained.

[0217] Examples 2 to 7 and Comparative Examples 1 to 3

[0218] The preparation method of the secondary battery is similar to that in Example 1, except that the preparation parameters of the electrolyte are adjusted, as detailed in Table 1.

[0219] Examples 8 to 10 and Comparative Examples 4 to 5

[0220] The preparation method of the secondary battery is similar to that of Example 1, except that the cold pressing process parameters of the negative electrode sheet are adjusted. For example, one or more of the cold pressing speed, cold pressing temperature, cold pressing pressure, and number of cold pressing cycles can be adjusted. The parameters of the negative electrode active material itself are also adjusted to give the negative electrode sheets of each example and comparative example different porosities. The Dv50 of the negative electrode active material used in Comparative Example 4 is 12 μm, the Dv50 of the negative electrode active material used in Comparative Example 5 is 10 μm, the Dv50 of the negative electrode active material used in Example 8 is 11.7 μm, the Dv50 of the negative electrode active material used in Example 9 is 11.4 μm, and the Dv50 of the negative electrode active material used in Example 10 is 10.5 μm.

[0221] Examples 11 to 13 and Comparative Examples 6 to 7

[0222] The preparation method of the secondary battery is similar to that of Example 1, except that the cold pressing process parameters of the positive electrode sheet are adjusted. For example, one or more of the cold pressing speed, cold pressing temperature, cold pressing pressure, and number of cold pressing cycles can be adjusted. The parameters of the positive electrode active material itself are also adjusted to give the positive electrode sheets of each example and comparative example different porosities. The positive electrode active material used in Comparative Example 6 has a secondary particle content of 80%, the positive electrode active material used in Comparative Example 7 has a secondary particle content of 50%, the positive electrode active material used in Example 11 has a secondary particle content of 75%, the positive electrode active material used in Example 12 has a secondary particle content of 70%, and the positive electrode active material used in Example 13 has a secondary particle content of 55%.

[0223] Examples 14 to 22

[0224] The preparation method of the secondary battery is similar to that in Example 1, except that the preparation parameters of the electrolyte are adjusted, as detailed in Table 1.

[0225] Test section

[0226] (1) Cyclic performance test of secondary batteries at room temperature

[0227] At 25℃, the secondary battery was charged at a constant current of 1C to 4.3V, and then charged at a constant voltage until the current reached 0.05C. At this point, the secondary battery was fully charged, and the charging capacity was recorded, which is the first charge capacity. After the secondary battery was left to stand for 5 minutes, it was discharged at a constant current of 1C to 2.8V. This completes one charge-discharge cycle, and the discharge capacity was recorded, which is the first discharge capacity. The secondary battery was subjected to cyclic charge-discharge tests using the above method, and the discharge capacity after each cycle was recorded. The capacity retention rate (%) of the secondary battery after 600 cycles at 25℃ = discharge capacity after 600 cycles / discharge capacity of the first cycle × 100%.

[0228] (2) High-temperature cycle performance test of secondary batteries

[0229] At 45℃, the secondary battery was charged at a constant current of 1C to 4.3V, and then charged at a constant voltage until the current reached 0.05C. At this point, the secondary battery was fully charged, and the charging capacity was recorded, which is the first charge capacity. After the secondary battery was left to stand for 5 minutes, it was discharged at a constant current of 1C to 2.8V. This completes one charge-discharge cycle, and the discharge capacity was recorded, which is the first discharge capacity. The secondary battery was subjected to cyclic charge-discharge tests using the above method, and the discharge capacity after each cycle was recorded. The capacity retention rate (%) of the secondary battery after 600 cycles at 45℃ = discharge capacity after 600 cycles / discharge capacity of the first cycle × 100%.

[0230] (3) Initial DC internal resistance test of secondary battery

[0231] At 25℃, the secondary battery is charged at a constant current of 1C to 4.3V, and then charged at a constant voltage until the current is 0.05C, at which point the secondary battery is fully charged. The secondary battery is then discharged at a constant current of 0.5C and adjusted to 50% SOC, and the voltage of the secondary battery at this point is recorded as U1. The secondary battery is then discharged at a constant current of 4C I1 for 30 seconds, and the voltage at the end of the discharge is recorded as U2, using a 0.1-second sampling time. The initial DC internal resistance of the secondary battery is expressed as the DC internal resistance at 50% SOC, and the initial DC internal resistance (mΩ) of the secondary battery is given by (U1-U2) / I1.

[0232] (4) Low-temperature performance test of secondary batteries

[0233] At -10℃, the secondary battery was charged at a constant current of 0.2C to 4.3V, and then charged at a constant voltage until the current reached 0.05C. At this point, the secondary battery was fully charged, and the charging capacity was recorded, which is the first charge capacity. After the secondary battery was left to stand for 30 minutes, it was discharged at a constant current of 0.2C to 2.8V. This completes one charge-discharge cycle, and the discharge capacity was recorded, which is the first discharge capacity. The secondary battery was subjected to cyclic charge-discharge tests using the above method, and the discharge capacity after each cycle was recorded. The capacity retention rate (%) of the secondary battery after 200 cycles at -10℃ = discharge capacity after 200 cycles / discharge capacity of the first cycle × 100%.

[0234] Table 1

[0235]

[0236]

[0237] Table 2

[0238]

[0239]

[0240] As shown in Table 2, when the secondary battery simultaneously satisfies 0.80≤A / B≤1.20 and 0.14≤100D1 / B≤1.50, the secondary battery has low internal resistance and high capacity retention. Therefore, it can have good power performance and long cycle life while having high energy density. In addition, it can also have good low-temperature discharge performance.

[0241] The secondary batteries in Comparative Examples 2 and 3 do not meet the requirement of 0.14≤100D1 / B≤1.50, and the secondary batteries in Comparative Examples 4-7 do not meet the requirement of 0.80≤A / B≤1.20. Therefore, none of them can achieve good power performance, good low-temperature discharge performance and long cycle life while having high energy density.

[0242] The test results from Examples 1-13 also show that when the secondary battery further satisfies 0.85≤A / B≤1.15 and / or 0.16≤100D1 / B≤1.40, it helps to further improve the overall performance of the secondary battery.

[0243] Based on the test results of Examples 1-6 and Example 7, it can be seen that when the secondary battery further satisfies at least one of 0.16≤100D1 / A≤1.20, 1.43≤10000D1 / P1≤9.34, and 2.78≤10000D1 / P2≤21.40, especially when the secondary battery simultaneously satisfies 0.16≤100D1 / A≤1.20, 1.43≤10000D1 / P1≤9.34, and 2.78≤10000D1 / P2≤21.40, it helps to further improve the overall performance of the secondary battery.

[0244] Based on the test results of Examples 1 and 14-22, it can be seen that when the electrolyte further contains an appropriate amount of the third component and / or the fourth component, it helps to further improve at least one of the cycle performance, power performance and low-temperature discharge performance of the secondary battery.

[0245] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte, wherein, The porosity of the positive electrode is A, and the porosity of the negative electrode is B, satisfying: 0.80≤A / B≤1.20; The electrolyte comprises a first component, which includes one or more compounds of Formula 1, wherein R1 and R2 each independently represent a fluorine atom, or at least one of the following groups that are partially or fully fluorinated: C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C6-C8 aryl, C1-C10 alkoxy, C2-C10 alkenyloxy, C2-C10 alkynyloxy, C6-C8 aryloxy, and Me includes one or more alkali metals and alkaline earth metals; the weight percentage of the first component in the electrolyte is D1, 0.05% ≤ D1 ≤ 0.3%; Formula 1; The electrolyte further includes a second component and a fifth component, wherein the second component includes lithium hexafluorophosphate; The fifth component includes cyclic carbonate compounds and chain carbonate compounds; The electrolyte further includes a fourth component, which comprises fluoroethylene carbonate. The fourth component has a weight percentage of less than 5% in the electrolyte; The weight ratio of the fourth component to the first component is 5 to 100.

2. The secondary battery according to claim 1, wherein, 18% ≤ A ≤ 32%; and / or, 20%≤B≤35%。 3. The secondary battery according to claim 2, wherein, 20%≤A≤32%； and / or; 20%≤B≤33%。 4. The secondary battery according to claim 1, wherein, The secondary battery has a strength of 0.14 ≤ 100D1 / B ≤ 1.

50.

5. The secondary battery according to claim 1, wherein, 0.85 ≤ A / B ≤ 1.15; and / or, 0.16≤100D1 / B≤1.

40.

6. The secondary battery according to claim 5, wherein, 0.90 ≤ A / B ≤ 1.15; and / or, 0.20≤100D1 / B≤1.

20.

7. The secondary battery according to claim 1, wherein, The secondary battery also satisfies the following conditions: 0.16 ≤ 100D1 / A ≤ 1.

20.

8. The secondary battery according to claim 7, wherein, The secondary battery also satisfies the following condition: 0.20≤100D1 / A≤1.

10.

9. The secondary battery according to claim 1, wherein, The compaction density of the positive electrode sheet is P1g / cm³. 3 The compaction density of the negative electrode sheet is P2g / cm³. 3 Furthermore, the secondary battery also satisfies the following relationship: 1.75≤P1 / P2≤2.

50.

10. The secondary battery according to claim 9, wherein, 2.00≤P1 / P2≤2.

40.

11. The secondary battery according to claim 1, wherein, The compaction density of the positive electrode sheet is P1g / cm³. 3 Furthermore, the secondary battery also satisfies the following condition: 1.43≤10000D1 / P1≤9.

34.

12. The secondary battery according to claim 11, wherein, 2.00≤10000D1 / P1≤8.

00.

13. The secondary battery according to claim 1, wherein, The compaction density of the negative electrode sheet is P2g / cm³. 3 Furthermore, the secondary battery also satisfies the following condition: 2.78≤10000D1 / P2≤21.

40.

14. The secondary battery according to claim 13, wherein, 5.00≤10000D1 / P2≤15.

00.

15. The secondary battery according to claim 1, wherein, The compaction density of the positive electrode sheet is P1g / cm³. 3 , 2.8≤P1≤3.65; and / or, The compaction density of the negative electrode sheet is P2g / cm³. 3 , 1.2≤P2≤1.

85.

16. The secondary battery according to claim 15, wherein, 3.2≤P1≤3.5; and / or, 1.4≤P2≤1.8。 17. The secondary battery according to claim 1, wherein, One of R1 and R2 represents a fluorine atom, and the other represents at least one of the following groups that are partially or fully fluorinated: methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, vinyl, propenyl, allyl, butadienyl, ethynyl, propynyl, phenyl, methoxy, ethoxy, propoxy, ethyleneoxy, propynyloxy, ethynyloxy, propynyloxy, and phenoxy. and / or; The alkali metal includes one or more of Li, Na, and K, and the alkaline earth metal includes Ca, Mg, or a combination thereof.

18. The secondary battery according to claim 17, wherein, Me represents Li; and / or, The compound shown in Formula 1 includes one or more of the following compounds: 。 19. The secondary battery according to claim 1, wherein, The second component in the electrolyte has a weight percentage D2 of 5% or more.

20. The secondary battery according to claim 19, wherein, The second component has a weight percentage D2 of 8% or more in the electrolyte.

21. The secondary battery according to claim 20, wherein, The second component, D2, has a weight percentage of 8% to 30% in the electrolyte.

22. The secondary battery according to claim 1, wherein, The electrolyte further includes a third component, which includes one or more of lithium tetrafluoroborate, lithium difluorophosphate, lithium perchlorate, lithium hexafluoroarsenate, lithium difluorodioxarate phosphate, and lithium tetrafluorooxarate phosphate.

23. The secondary battery according to claim 22, wherein, The third component includes lithium tetrafluoroborate, lithium difluorophosphate, or a combination thereof.

24. The secondary battery according to claim 22, wherein, The third component, D3, has a weight percentage of less than 0.5% in the electrolyte.

25. The secondary battery according to claim 24, wherein, The third component, D3, has a weight percentage of less than 0.25% in the electrolyte.

26. The secondary battery according to claim 25, wherein, The weight percentage D3 of the third component in the electrolyte satisfies: 0 ≤ D3 ≤ 0.25%.

27. The secondary battery according to claim 22, wherein, The weight ratio of the third component to the first component, D3 / D1, is 0.5 to 2.

28. The secondary battery according to claim 1, wherein, The fifth component has a weight percentage (D5) of more than 60% in the electrolyte; The electrolyte contains a weight percentage of cyclic carbonate compounds greater than 0 and less than or equal to 40%. and / or; The electrolyte contains 40% to 85% by weight of chain carbonate compounds.

29. The secondary battery according to claim 28, wherein, The fifth component has a weight percentage (D5) of 75% or more in the electrolyte; The weight percentage of cyclic carbonate compounds in the electrolyte is selected to be 5% to 40%. and / or; The weight percentage of the chain carbonate compound in the electrolyte is selected to be 50% to 80%.

30. The secondary battery according to claim 1, wherein, The positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector and including a positive electrode active material.

31. The secondary battery according to claim 30, wherein, The positive electrode active material includes one or more of layered lithium transition metal oxides, lithium phosphates, and their respective modified compounds.

32. The secondary battery according to claim 31, wherein, The positive electrode active material includes one or more of layered lithium transition metal oxides and their modified compounds, or a mixture of layered lithium transition metal oxides and their modified compounds with lithium phosphates and their modified compounds.

33. The secondary battery according to claim 30, wherein, The positive electrode active material satisfies at least one of the following: (1) The morphology of the positive electrode active material includes one or more of spherical and near-spherical shapes; (2) The positive electrode active material includes primary particles, secondary particles, or a combination thereof; (3) The proportion of secondary particles in the positive electrode active material is more than 50%; (4) The volume average particle size of the positive electrode active material satisfies 2.5μm≤Dv50≤30μm; (5) The diameter of the positive electrode active material satisfies 1≤(Dv90-Dv10) / Dv50≤5.

34. The secondary battery according to claim 33, wherein, The positive electrode active material includes secondary particles or a combination of primary and secondary particles.

35. The secondary battery according to claim 33, wherein, The volume average particle size of the positive electrode active material satisfies 2.5μm≤Dv50≤25μm.

36. The secondary battery according to claim 33, wherein, The diameter of the positive electrode active material satisfies: 1≤(Dv90-Dv10) / Dv50≤2.

37. The secondary battery according to claim 30, wherein, The positive electrode active material has a primary particle morphology, and the volume average particle size of the primary particle morphology positive electrode active material satisfies 2.5μm≤Dv50≤7μm; and / or; The positive electrode active material includes a secondary particle morphology, and the volume average particle size of the positive electrode active material with the secondary particle morphology satisfies 6μm≤Dv50≤30μm.

38. The secondary battery according to claim 37, wherein, The volume average particle size of the primary particle morphology of the positive electrode active material satisfies 2.5μm≤Dv50≤5.5μm; and / or; The volume average particle size of the positive electrode active material with the secondary particle morphology satisfies 6μm≤Dv50≤25μm.

39. The secondary battery according to claim 30, wherein, The positive electrode active material includes materials with the molecular formula Li. a Ni b Co c Mn d Al e M f O g A h Layered lithium transition metal oxide, M represents a transition metal site doped cation, A represents an oxygen site doped anion, 0.8≤a≤1.2, 0≤b≤1, 0≤c≤1, 0≤d≤1, 0≤e≤1, 0≤f≤0.2, 0≤g≤2, 0≤h≤2, b + c + d + e + f = 1, g + h = 2.

40. The secondary battery according to claim 39, wherein, M includes one or more of Si, Ti, Mo, V, Ge, Se, Zr, Nb, Ru, Pd, Sb, Ce, Te, and W; and / or; A includes one or more of F, N, P, and S; and / or; 0＜b＜0.98； and / or; 0≤c≤0.20； and / or; 0≤d≤0.50； and / or; 0≤e＜0.50。 41. The secondary battery according to claim 39, wherein, The molecular formula is Li a Ni b Co c Mn d Al e M f O g A h Layered lithium transition metal oxides, including but not limited to LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co 0.05 Mn 0.15 O2, LiNi 0.7 Mn 0.3 O2, LiNi 0.69 Co 0.01 Mn 0.3 O2, LiNi 0.68 Co 0.02 Mn 0.3 O2, LiNi 0.65 Co 0.05 Mn 0.3 O2, LiNi 0.63 Co 0.07 Mn 0.3 O2 and LiNi 0.61 Co 0.09 Mn 0.3 One or more of O2.

42. The secondary battery according to claim 1, wherein, The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and including a negative electrode active material.

43. The secondary battery according to claim 42, wherein, The negative electrode active material includes one or more of carbon-based materials, silicon-based materials, tin-based materials, lithium titanate, and composite materials obtained by coating modification of the above materials.

44. The secondary battery according to claim 42, wherein, The negative electrode active material includes one or more of carbon-based materials and composite materials obtained by coating modification of the above materials.

45. The secondary battery according to claim 43 or 44, wherein, The carbon-based materials include one or more of graphite, soft carbon, hard carbon, and composite materials obtained by coating modification of the above materials.

46. ​​The secondary battery according to claim 42, wherein, The negative electrode active material satisfies at least one of the following: (1) The morphology of the negative electrode active material includes one or more of the following: spherical, near-spherical, blocky, and sheet-like. (2) The negative electrode active material includes primary particles, secondary particles, or a combination thereof; (3) The proportion of secondary particles in the negative electrode active material is more than 50%; (4) The volume average particle size of the negative electrode active material satisfies 8μm≤Dv50≤22μm; (5) The diameter of the negative electrode active material satisfies 0.5≤(Dv90-Dv10) / Dv50≤5.

47. The secondary battery according to claim 46, wherein, The negative electrode active material includes secondary particles or a combination of primary and secondary particles.

48. The secondary battery according to claim 46, wherein, The volume average particle size of the negative electrode active material satisfies 10μm≤Dv50≤16μm.

49. The secondary battery according to claim 46, wherein, The diameter of the negative electrode active material satisfies 0.5≤(Dv90-Dv10) / Dv50≤1.

5.

50. An electrical device comprising a secondary battery as described in any one of claims 1 to 49.

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