Lithium-ion secondary battery, battery assembly, preparation method, and electric apparatus

Abstract

A lithium-ion secondary battery, a battery assembly, a preparation method, and an electric apparatus. The lithium-ion secondary battery comprises: a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the separator is located between the positive electrode sheet and the negative electrode sheet; the electrolyte fills the space among the positive electrode sheet, the separator, and the negative electrode sheet; the positive electrode sheet is provided with a current collector and a positive electrode active layer; the positive electrode active layer comprises a lithium nickel cobalt manganese oxide; the electrolyte comprises cyclic sulfur-containing organic matter; on the basis of the total mass of the electrolyte, the content of the cyclic sulfur-containing organic matter is 0.01-4.9%; and the cyclic sulfur-containing organic matter comprises cyclic sulfate and cyclic sulfonate, the content of the cyclic sulfate is 0.01-3.9%, and the content of the cyclic sulfonate is less than or equal to 1%.

Description

Lithium-ion secondary batteries, battery modules, manufacturing methods, and electrical devices

[0001] This application claims priority to Chinese application filed on January 22, 2025, entitled “Lithium-ion secondary battery, battery module, preparation method and power supply device”, application number 202510103789.1, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of batteries, specifically to lithium-ion secondary batteries, battery modules, preparation methods, and electrical devices. Background Technology

[0003] Lithium-ion secondary batteries, as a new energy storage device, have been widely researched and applied. Currently, the most widely studied and applied cathode materials for lithium-ion secondary batteries include ternary cathode materials (lithium nickel cobalt manganese oxide) and lithium iron phosphate materials.

[0004] However, current ternary lithium-ion rechargeable batteries still suffer from issues such as limited cycle life and rapid increases in cell DC resistance (DCR) over time. Furthermore, modifying ternary materials is challenging, and developing new materials is costly. Improving battery components, such as the electrolyte, to alleviate or resolve these problems would significantly address the issue. Therefore, current lithium-ion rechargeable batteries, electrolytes, and power devices still require further improvement. Summary of the Invention

[0005] In view of the above problems, this application provides a lithium-ion secondary battery and an electrolyte. By adjusting the composition of the electrolyte, a more stable solid interface film can be formed, thereby improving the cycle life of the secondary battery and alleviating problems such as a significant increase in DCR.

[0006] In one aspect of this application, a lithium-ion secondary battery is disclosed. The lithium-ion secondary battery includes: a positive electrode, a negative electrode, a separator, and an electrolyte. The separator is located between the positive and negative electrode. The electrolyte fills the space between the positive electrode, the separator, and the negative electrode. The positive electrode has a current collector and a positive active layer, the positive active layer comprising lithium nickel cobalt manganese oxide. The electrolyte comprises a cyclic sulfur-containing organic compound. Based on the total mass of the electrolyte, the content of the cyclic sulfur-containing organic compound is 0.01-4.9%, the cyclic sulfur-containing organic compound includes cyclic sulfates, the content of the cyclic sulfates is 0.01-3.9%, and the content of cyclic sulfonates in the cyclic sulfur-containing organic compound is ≤1%.

[0007] This lithium-ion secondary battery, by adjusting the particle size of the positive electrode active material and the composition of the electrolyte, can form a thin but relatively uniform and dense solid interface film on the electrode surface in the early stage of battery cycling. The electrolyte composition has good stability, and the solid interface film thickness increases little after formation. Therefore, it has a good cycle capacity retention rate, a low cycle DCR growth rate, and low gas production.

[0008] According to embodiments of this application, the cyclic sulfate ester comprises at least one of the following compounds:

[0009] According to an embodiment of this application, the cyclic sulfate ester includes the compound shown in formula (4), and the content of the compound shown in formula (4) in the electrolyte is 0.1-2%.

[0010] According to embodiments of this application, the cyclic sulfonate ester includes 1,3-propanesulfonate lactone, and the content of 1,3-propanesulfonate lactone in the electrolyte is 0.1-0.5%.

[0011] According to embodiments of this application, the electrolyte further comprises cyclic carbonates, and the content of the cyclic carbonates is 5-35% based on the total mass of the electrolyte, wherein the cyclic carbonates include ethylene carbonate.

[0012] According to embodiments of this application, the electrolyte further comprises chain carbonates, and the content of the chain carbonates is 45-80% based on the total mass of the electrolyte. The chain carbonates include at least one of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dimethyl carbonate (DMC).

[0013] According to embodiments of this application, the content of dimethyl carbonate is 25-50% based on the total mass of the electrolyte.

[0014] In another aspect of this application, a battery assembly is proposed, comprising a positive electrode, a negative electrode, a separator, and an electrolyte. The separator is located between the positive and negative electrode, and the electrolyte fills the spaces between the positive electrode, the separator, and the negative electrode. The positive electrode has a current collector and a positive active layer, the positive active layer comprising lithium nickel cobalt manganese oxide. The electrolyte comprises cyclic sulfur-containing organic compounds. Based on the total mass of the electrolyte, the content of the cyclic sulfur-containing organic compounds is 0.5-5%, and the cyclic sulfur-containing organic compounds include cyclic sulfates and cyclic sulfonates. The content of the cyclic sulfates is 0.4-4%, and the content of the cyclic sulfonates is ≤1.1%. This electrolyte facilitates the formation of a thin, uniform, and dense solid interface film on the electrode surface during the initial stage of battery cycling, thereby improving the cycle performance of the secondary battery utilizing this electrolyte.

[0015] According to embodiments of this application, the cyclic sulfate ester comprises at least one of the following compounds:

[0016] The content of the cyclic sulfate is 0.5-2%, and the cyclic sulfonate includes 1,3-propanesulfonate lactone, with a content of 0.3-0.8%.

[0017] According to an embodiment of this application, the electrolyte further comprises a lithium salt, and the lithium salt content is 10-15% based on the total mass of the electrolyte.

[0018] According to an embodiment of this application, the kinematic viscosity of the electrolyte at 25°C is 1.8–3 mm. 2 / s.

[0019] In another aspect of this application, a method for preparing a lithium-ion secondary battery is proposed. The method includes placing a positive electrode, a negative electrode, and a separator in an encapsulation structure, the separator being located between the positive and negative electrode; injecting an electrolyte into the encapsulation structure, wherein, based on the total mass of the electrolyte, the content of a cyclic sulfur-containing organic compound is 0.5-5%, the cyclic sulfur-containing organic compound including cyclic sulfates and cyclic sulfonates, the content of the cyclic sulfates being 0.4-4%, and the content of the cyclic sulfonates being ≤1.1%; sealing the encapsulation structure; and performing a formation treatment on the sealed battery assembly to obtain the lithium-ion secondary battery.

[0020] According to an embodiment of this application, the content of the cyclic sulfate in the electrolyte is 0.5-2%, and the formation treatment includes: constant current charging at 0.1C to 50% SOC. After the formation treatment, the content of the cyclic sulfate in the electrolyte is 0.1-1.8%.

[0021] In another aspect of this application, a lithium-ion secondary battery is provided, which is prepared using the aforementioned method.

[0022] In another aspect of this application, an electrical device is provided. The electrical device includes the aforementioned lithium-ion secondary battery, which is used to provide electrical energy. Attached Figure Description

[0023] To more clearly illustrate the technical solution of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application; those skilled in the art can obtain other drawings based on the drawings without any creative effort.

[0024] Figure 1 is a schematic diagram of the structure of a lithium-ion secondary battery according to some embodiments of this application;

[0025] Figure 2 is a schematic diagram of the structure of an electrical device according to some embodiments of this application. Detailed Implementation

[0026] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion.

[0028] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0029] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0030] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0031] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0032] In the description of the embodiments of this application, the technical terms "upper", "lower", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0033] Unless otherwise stated, the terms used in this application have their common meanings as understood by those skilled in the art. Unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application). As mentioned above, ternary cathode material systems, especially batteries with high-voltage ternary cathode materials (charging upper limit cutoff voltage greater than or equal to 4.35V), generally suffer from problems with unimproved cycle performance: during the charging and discharging process of lithium-ion batteries, the side reactions between the electrolyte and the positive and negative electrode materials are one of the important factors leading to rapid capacity decay, and these side reactions are more serious in high-voltage systems. Because the higher the charging voltage, the stronger the oxidizing power of the positive electrode when it is in a highly delithiated state, and the easier it is for the electrolyte to be oxidized, while the negative electrode is in a highly lithium-intercalated state, the electrolyte will accept electrons from the negative electrode, triggering a reduction reaction. These reactions also lead to severe gas generation in the cell during the cycle process, thus affecting the cell life. If the cycle stability can be improved through the design and coordination of the battery system, the above problems will be greatly alleviated or even solved.

[0034] Therefore, in one aspect of this application, a lithium-ion secondary battery and an electrolyte are proposed. By selecting the particle size of the positive electrode material and combining it with an electrolyte containing specific components and amounts, this application can form a thin, stable, and uniform solid interface film in the early stages of battery cycling, mitigating or even preventing the deterioration of the cell's damping coefficient (DCR) caused by the continuous thickening of the solid interface film during battery cycling. This is beneficial for improving the cycle performance of the secondary battery.

[0035] In one aspect of this application, a lithium-ion secondary battery is disclosed. The lithium-ion secondary battery includes: a positive electrode, a negative electrode, a separator, and an electrolyte. The separator is located between the positive and negative electrode, and the electrolyte fills the space between the positive electrode, the separator, and the negative electrode. The positive electrode has a current collector and a positive active layer, the positive active layer comprising lithium nickel cobalt manganese oxide. The electrolyte includes cyclic sulfur-containing organic matter, and the content of the cyclic sulfur-containing organic matter is 0.01-4.9% based on the total mass of the electrolyte. The cyclic sulfur-containing organic matter includes cyclic sulfates and cyclic sulfonates, the content of the cyclic sulfates is 0.01-3.9%, and the content of the cyclic sulfonates in the cyclic sulfur-containing organic matter is ≤1%.

[0036] This lithium-ion secondary battery utilizes a modified electrolyte composition, employing cyclic sulfates with highly electrochemical activity and -O-SO2-O groups. This allows for the formation of a thin, uniform, and dense solid-state interfacial film on the electrode surface during the initial cycling phase. Furthermore, the electrolyte contains a low content of cyclic sulfonates, which have lower electrochemical activity and can continuously participate in the solid-state interfacial film formation during cycling. Consequently, the electrolyte composition exhibits good stability, and the solid-state interfacial film shows minimal increase in thickness with cycling, resulting in good cycle capacity retention and a low cycle DCR (discharge rate reduction) growth rate. Additionally, since cyclic sulfates also reduce gas production, the gas production level can be kept from significantly increasing while reducing the content of cyclic sulfonates.

[0037] As mentioned earlier, lithium-ion secondary batteries using lithium nickel cobalt manganese oxide as the positive electrode active material generally suffer from poor cycle performance. This is especially true when these batteries are used in high-voltage systems, where the increased side reactions between the electrolyte and the positive electrode active material lead to poor cycle performance. Using the aforementioned electrolyte helps to rapidly form a stable and dense positive electrode solid-state interface film in the early stages of cycling, thereby mitigating the occurrence of side reactions between the positive electrode and the electrolyte to some extent.

[0038] In some embodiments, the Dv50 of lithium nickel cobalt manganese oxide can be 3-6 micrometers. When the Dv50 of lithium nickel cobalt manganese oxide in the positive electrode active layer is 3-6 micrometers, the specific surface area of ​​the positive electrode active material is moderate, which can alleviate the aggravation of side reactions caused by excessive contact area with electrolyte, while maintaining good kinetic performance and mitigating the impact on the ion conduction characteristics of the positive electrode sheet caused by excessively large particle size and excessively long lithium ion transport paths.

[0039] In this application, Dv50 can be defined using methods commonly used in this application and measured using methods commonly used in this application. For example, Dv50 can be the median particle size of powder, i.e., the volume average particle size, where the diameter of particles accounting for 50% of the total volume of the particles being measured is greater than this value, and the diameter of particles accounting for another 50% of the total volume is smaller than this value. Dv50 can be measured using a laser particle size analyzer (e.g., Malvern Master Sizer 3000) with reference to standard GB / T 19077-2016.

[0040] According to embodiments of this application, the electrolyte may contain a certain amount of cyclic sulfur-containing organic compounds, particularly a certain amount of cyclic sulfates. Cyclic sulfates have high electrochemical activity, and their reduction potential allows them to participate in the solid-state interface film formation reaction on the electrode surface earlier than common electrolyte additives, such as FEC, thereby facilitating the formation of a thinner, more uniform, and denser solid-state interface film. A uniform and dense solid-state interface film helps protect the positive electrode active material and mitigates side reactions caused by contact between the active material and the electrolyte. Forming a chemically stable and moderately thick solid-state interface film in the early stages of cycling is beneficial for improving the cycle performance of the lithium-ion secondary battery. Specifically, the content of cyclic sulfates in the electrolyte can be 0.01-4.9 wt%. When the content of cyclic sulfates in the electrolyte is within the above range, it can effectively improve the formation of the solid-state interface film on the electrode surface and alleviate the problem of excessively thick solid-state interface film formation in the early stages of cycling due to excessive addition, which affects lithium-ion insertion / extraction.

[0041] Furthermore, cyclic sulfonates also have a certain effect in improving gas production. Therefore, the content of cyclic sulfonates with similar functions in this electrolyte can be low, for example, 0.1-1 wt%, or 0.1-0.5 wt%, specifically 0.1 wt%, 0.2 wt%, 0.3 wt%, or 0.4 wt%. Although cyclic sulfonates with -O-SO2 groups have a certain effect in inhibiting gas production, their low reduction potential leads to their slow consumption during battery cycling, thus prolonging the electrolyte reaction process and causing the cell's DCR to increase with each cycle. Especially when the cyclic sulfonate is 1,3-propanesulfonate lactone, its electrochemical activity is low. Therefore, a low content of cyclic sulfonates is beneficial for improving the battery's environmental performance and cycle performance.

[0042] In some embodiments, cyclic sulfates include at least one of the following compounds:

[0043] Where p is 1-6, specifically 1, 2, 3, 4, 5 or 6.

[0044] The above compounds all have multiple cyclic structures containing -O-SO2-O groups, have more active sites, and have higher reactivity. Furthermore, compounds with multiple active sites can improve film density through self-crosslinking polymerization, which is beneficial to further enhance the ability of electrolytes to quickly form high-quality solid interface films.

[0045] According to a specific example of this application, cyclic sulfates may include compounds shown in formula (4). The compounds in formula (4) contain more active sites, which better facilitates the formation of high-quality solid interfacial films. The content of the compound in formula (4) in the electrolyte may be 0.5 wt%, 0.8 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, or 2 wt%. For example, it may be 0.1-1.8 wt%.

[0046] According to embodiments of this application, when the electrolyte contains a certain amount of cyclic sulfates, particularly compounds of formula (4), the content of cyclic sulfonates in the electrolyte can be low, for example, less than 1 wt%. Specifically, when the cyclic sulfonate is 1,3-propanesulfonyl lactone, its content can be 0.8 wt%, 0.6 wt%, 0.5 wt%, 0.3 wt%, etc. Since the electrolyte in the secondary battery of this application contains a certain amount of cyclic sulfates, even with a low content of cyclic sulfonates, the secondary battery exhibits low gas production.

[0047] According to embodiments of this application, the electrolyte further comprises cyclic carbonates, the content of which can be 5-35% based on the total mass of the electrolyte. In some embodiments, the content of cyclic carbonates in the electrolyte can be slightly lower: compared to chain carbonates, cyclic carbonates such as ethylene carbonate have slightly lower stability and can be added in small amounts. For example, in some examples, the content of cyclic carbonates can be 10-27 wt%.

[0048] Specifically, cyclic carbonates can include ethylene carbonate (EC). Ethylene carbonate has a high dielectric constant, which can effectively dissociate lithium salts, thereby improving the conductivity of the electrical system and suppressing the growth of the dielectric constant (DCR) of the secondary battery. However, ethylene carbonate has a high viscosity and poor stability. Therefore, the appropriate addition of ethylene carbonate can reduce electrolyte gas production while ensuring the conductivity of the system. For example, the content of ethylene carbonate in the electrolyte can be 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt%, 30 wt%, 31 wt%, 32 wt%, 33 wt%, 34 wt%, or 35 wt%.

[0049] In some embodiments, the electrolyte may further comprise chain carbonates. Using chain carbonates in combination with cyclic carbonates as solvents results in an electrolyte with better stability and reduces the overall viscosity of the electrolyte due to the addition of cyclic carbonates. Lower viscosity electrolytes exhibit better lithium-ion liquid-phase transport performance, thus improving battery power performance. However, low-viscosity electrolytes are more likely to diffuse to the surfaces of the positive and negative electrodes, increasing the risk of redox reactions at the interface, which may lead to decreased cell lifespan and gas generation. Therefore, adjusting the content of cyclic and chain carbonates in the electrolyte can balance the lifespan and DCR (Discharge Rate of Change) growth performance of the secondary battery.

[0050] In some embodiments, the content of chain carbonates in the electrolyte can be 45-80%, specifically 55-75 wt%.

[0051] In some embodiments, the chain carbonate may include at least one of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dimethyl carbonate (DMC). For example, in some embodiments, the electrolyte may include ethylene carbonate (EC) and ethyl methyl carbonate (EMC).

[0052] In some embodiments, the chain carbonate includes dimethyl carbonate (DMC). Dimethyl carbonate has a better effect on improving the power performance of the electrolyte. In some embodiments, the content of dimethyl carbonate can be not less than 20% based on the total mass of the electrolyte, for example, it can be 25-50%. When the electrolyte contains 35-50% dimethyl carbonate, the content of cyclic sulfonates in the electrolyte can be appropriately increased to enhance the effect of inhibiting gas production. For example, in this set of embodiments, the electrolyte may contain 0.1-0.5% 1,3-propanesulfonate lactone.

[0053] In some embodiments, the electrolyte may further include at least one selected from butylene carbonate (BC), fluoroethylene carbonate (FEC), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl sulfone (EMS), and diethyl sulfone (ESE).

[0054] According to embodiments of this application, the electrolyte may further contain lithium salts. The lithium salts may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobis(oxalato)phosphate, lithium bis(oxalato)borate, or lithium difluorooxalato)borate. In some embodiments, the lithium salt content in the electrolyte may be 10–15 wt%. The above-mentioned concentration of lithium salt, combined with the aforementioned solvent system, can improve the lithium-ion transport rate, further improving cycle life and DCR growth during the process.

[0055] In some embodiments, the kinematic viscosity of the electrolyte at 25°C can be 1.8–3 mm. 2 / s. By adjusting the chemical components and their contents in the electrolyte, the electrolyte can be made to have a lower viscosity, thereby improving the liquid phase transport capability of lithium ions, enhancing power performance during battery cycling, and reasonably controlling the diffusion rate of the electrolyte, thus achieving the goal of balancing the lifespan and DCR growth performance of the secondary battery.

[0056] In this application, the kinematic viscosity of the electrolyte can be determined according to GB / T 9725-2007 "Determination of Dynamic Viscosity and Density of Petroleum Products and Calculation of Kinematic Viscosity - Stabinger Method". The test temperature can be 25 or 45 degrees Celsius. Using a Stabinger viscometer based on the Couette viscosity measurement principle, the test liquid is rotated at a constant speed, and a measuring rotor with a built-in magnet is allowed to float freely in the sample. The shear force of the sample drives the rotor to rotate, while the magnetic effect inhibits the rotor's rotation. After the measurement begins and the rotor reaches its equilibrium speed, the dynamic viscosity of the liquid can be calculated based on the equilibrium speed. Then, the kinematic viscosity of the liquid can be calculated based on the dynamic viscosity and the sample density.

[0057] In some embodiments, the upper limit cutoff voltage for charging of the lithium-ion secondary battery can be greater than or equal to 4.35V. Due to the interaction between the particle size of the positive electrode active material and the electrolyte, the lithium-ion secondary battery can maintain good cycle capacity retention in high-voltage application scenarios.

[0058] Those skilled in the art will understand that this lithium-ion secondary battery also possesses conventional structures required for secondary batteries, such as a negative electrode and a separator. For example, the lithium-ion secondary battery further includes a negative electrode with a negative active layer disposed thereon. The negative active material in the negative active layer is not particularly limited, and those skilled in the art can select it according to actual needs; for example, it can be one or more of carbon-based materials and silicon-based materials. Carbon-based materials may include one or more of graphite (e.g., artificial graphite, natural graphite, etc.), soft carbon, and hard carbon. Silicon-based materials may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.

[0059] According to embodiments of this application, the material of the diaphragm is not particularly limited, and those skilled in the art can choose familiar materials to form the diaphragm. For example, the diaphragm may include a porous substrate. The porous substrate may be made of at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, polyester, and polyimide. The porous substrate may be a single-layer film or a multi-layer composite film. When the porous substrate is a multi-layer composite film, the materials of each layer may be the same or different.

[0060] In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding process or a stacking process.

[0061] In some embodiments, the lithium-ion secondary battery may include an outer packaging. This outer packaging can be used to encapsulate the electrode components and electrolyte described above. In some embodiments, the outer packaging of the lithium-ion secondary battery can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging of the lithium-ion secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0062] This application does not impose any particular limitation on the shape of the lithium-ion secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square-structured lithium-ion secondary battery 1 as an example. Referring to Figure 1, the outer packaging may include a housing 200 and a cover plate 300. The housing 200 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 200 has an opening communicating with the receiving cavity, and the cover plate 300 can be placed over the opening to close the receiving cavity. The electrode assembly 100 described in this application is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 100. The lithium-ion secondary battery 1 may contain one or more electrode assemblies 100, which can be selected by those skilled in the art according to specific practical needs.

[0063] In another aspect of this application, an electrolyte is proposed. The electrolyte contains 0.5-5% cyclic sulfur-containing organic compounds. These cyclic sulfur-containing organic compounds include cyclic sulfates and cyclic sulfonates. The cyclic sulfates have -O-SO2-O groups, and the cyclic sulfonates have -O-SO2 groups. Based on the total mass of the electrolyte, the content of cyclic sulfates is 0.4-4%, and the content of cyclic sulfonates is ≤1.1%. This electrolyte facilitates the formation of a thin, uniform, and dense solid interface film on the electrode surface during the initial stage of battery cycling, thereby improving the cycle performance of secondary batteries using this electrolyte and exhibiting good performance in suppressing gas generation in lithium-ion secondary batteries using this electrolyte.

[0064] In some embodiments, the electrolyte may have all the characteristics and advantages of the electrolytes in the aforementioned lithium-ion secondary batteries, which will not be repeated here. For example, as a specific example, the electrolyte may include 0.5-2 wt% of the cyclic sulfate ester shown in formula (4) above, 0.3-0.8% of 1,3-propanesulfonate lactone, and may further include ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, lithium salt, and fluoroethylene carbonate.

[0065] According to embodiments of this application, the kinematic viscosity of the electrolyte at 25°C is 1.8–3 mm. 2 / s.

[0066] In summary, the electrolyte has at least one of the following advantages: high stability, low gas production, and the ability to form a thin, uniform, and dense solid interface film in the early stages of battery cycling.

[0067] In another aspect of this application, a battery assembly is proposed. The battery assembly includes a positive electrode, a negative electrode, a separator, and an electrolyte. The separator is located between the positive and negative electrode, and the electrolyte fills the spaces between the positive electrode, the separator, and the negative electrode. The positive electrode has a current collector and a positive active layer, the positive active layer comprising lithium nickel cobalt manganese oxide. The electrolyte includes cyclic sulfur-containing organic compounds, the content of which is 0.5-5% based on the total mass of the electrolyte. Specifically, the cyclic sulfur-containing organic compounds include cyclic sulfates and cyclic sulfonates, the cyclic sulfates having -O-SO2-O groups and the cyclic sulfonates having -O-SO2 groups. The mass percentage of cyclic sulfates in the electrolyte is 0.4-4%, and the mass percentage of cyclic sulfonates is ≤1.1%. This battery assembly exhibits good cycle stability, a low cycle DCR growth rate, and a low gas production level.

[0068] In some specific embodiments, the cyclic sulfate ester includes at least one of the following compounds:

[0069] The aforementioned cyclic sulfates contain multiple cyclic structures with -O-SO2-O groups, thus possessing more active sites and capable of forming a denser solid interfacial film through self-crosslinking polymerization.

[0070] In some embodiments, the content of cyclic sulfates may specifically be 0.5-2%, and the cyclic sulfonate may include 1,3-propanesulfonate lactone, the content of which may be 0.3-0.8 wt%. Furthermore, the electrolyte may further include additives such as lithium salts, the content of which may be 10-15% based on the total mass of the electrolyte.

[0071] In some embodiments, the viscosity of the electrolyte can be adjusted by controlling the chemical composition and content of each component to obtain better lithium-ion liquid-phase transport capability, thereby improving power performance during battery cycling and reasonably controlling the diffusion rate of the electrolyte, thus achieving the goal of balancing the lifespan and DCR growth performance of the secondary battery. For example, cyclic carbonates and chain carbonates can be used as solvents in the electrolyte. In some embodiments, the kinematic viscosity of the electrolyte at 25°C can be 1.8–3 mm. 2 / s.

[0072] In some embodiments, the battery assembly may be unformed. The positive electrode, negative electrode, and separator contained in the electrolyte of this battery assembly may all possess the structural characteristics of the aforementioned lithium-ion secondary batteries. The electrolyte used in this battery assembly may also be the same composition as the electrolyte of the aforementioned lithium-ion secondary batteries before formation.

[0073] Overall, the battery module exhibits good cycle capacity retention, low cycle DCR growth rate, and low gas production.

[0074] In another aspect of this application, a method for preparing a lithium-ion secondary battery is proposed. The method includes: placing a positive electrode, a negative electrode, and a separator in an encapsulation structure, the separator being located between the positive and negative electrode; filling the encapsulation structure with an electrolyte, wherein, based on the total mass of the electrolyte, the content of a cyclic sulfur-containing organic compound is 0.5-5%, the cyclic sulfur-containing organic compound comprising cyclic sulfates and cyclic sulfonates, the cyclic sulfates having -O-SO2-O groups, the content of the cyclic sulfates being 0.4-4%, and the content of the cyclic sulfonates in the cyclic sulfur-containing organic compound being ≤1.1%, the cyclic sulfonates having -O-SO2 groups; sealing the encapsulation structure; and performing a formation treatment on the sealed battery assembly to obtain the lithium-ion secondary battery. The resulting lithium-ion secondary battery exhibits better cycle capacity retention, a lower cycle DCR growth rate, and lower gas production.

[0075] In some embodiments, the lithium-ion secondary battery prepared by this method may possess all the features and advantages of the aforementioned lithium-ion secondary battery, which will not be repeated here. For example, according to some specific embodiments of this application, the content of cyclic sulfates in the filled electrolyte may be 0.5-2%. The cyclic sulfates may include the compounds shown in formula (4) above, and the cyclic sulfonates may include 1,3-propanesulfonate lactone, the content of which may be 0.3-0.8%.

[0076] In some embodiments, the formation process may include: charging to 50% SOC at a constant current of 0.1C, specifically, charging to 50% SOC at a constant current of 0.1C to achieve a nominal capacity of 100% SOC.

[0077] After the formation process, the content of the cyclic sulfate in the electrolyte is consumed. After formation, the content of the cyclic sulfate can be 0.1-1.8%, and the content of the cyclic sulfonate can be 0.1-0.5%.

[0078] In another aspect of this application, an electrical device is provided. The electrical device includes the aforementioned lithium-ion secondary battery, which is used to provide electrical energy.

[0079] In this application, the electrical device can be such as a mobile phone, tablet, laptop, electric toy, power tool, electric vehicle, electric car, ship, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0080] As the electrical device, a sodium metal battery can be selected according to its usage requirements.

[0081] Figure 2 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of sodium metal batteries for this device, a battery pack or battery module can be used.

[0082] 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 utilize sodium metal batteries as their power source.

[0083] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0084] Example 1

[0085] 1. Preparation of positive electrode sheet

[0086] Ni, the positive electrode active material 0.65 Co 0.1 Mn 0.25 O2 (Dv50 is 3.7μm), polyvinylidene fluoride binder, and super P conductive agent are mixed in a weight ratio of 96:2:2, and N-methylpyrrolidone (NMP) solvent is added and stirred to form a positive electrode slurry. The slurry is then coated onto a current collector aluminum foil, dried, and cold-pressed, slit, and cut to form the positive electrode sheet of a lithium-ion battery.

[0087] 2. Preparation of negative electrode sheet

[0088] The negative electrode active material graphite, conductive agent carbon black, thickener sodium carboxymethyl cellulose (CMC-Na), and binder styrene-butadiene rubber (SBR) are mixed in a weight ratio of 97:0.5:1:1.5, added to deionized water as a solvent, and stirred to form a negative electrode slurry. The negative electrode slurry is then obtained under the action of a vacuum mixer. The slurry is then coated onto a current collector copper foil, dried, and cold-pressed, slit, and cut into sheets to form the negative electrode sheet of a lithium-ion battery.

[0089] 3. Preparation of electrolyte

[0090] In an argon atmosphere glove box with a water content of <1ppm and an oxygen content of <1ppm, non-aqueous solvents ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are mixed to obtain a mixed solvent. The compound shown in Formula 4 (cyclic sulfate), PS, FEC, and other additives are added to the mixed solvent. Finally, lithium salt LiPF6 is added, and the mixture is stirred until dissolved to complete the preparation of the electrolyte. The content of each component is detailed in Table 1 below.

[0091] 4. Separating membrane

[0092] Polyethylene (PE) film is used as the separator.

[0093] 5. Preparation of secondary batteries

[0094] Prepare the above-mentioned positive electrode, separator, and negative electrode in sequence, with the separator positioned between the positive and negative electrode to provide isolation. Then, wind them to obtain a bare cell and weld the tabs. Place the bare cell in an outer packaging shell, dry it, and inject electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained.

[0095] Examples 2-18 and the differences between the comparative examples and Example 1 are detailed in Table 1 below.

[0096] For ease of comparison, the differences between Comparative Examples 1-4 and the Examples are briefly described below:

[0097] Comparative Example 1 did not use cyclic sulfates and had a high content of cyclic sulfonates;

[0098] Cyclic sulfates and cyclic sulfonates were not used in Comparative Example 2;

[0099] In Comparative Example 3, the content of cyclic sulfate esters was 0.01-4%, but the content of cyclic sulfonates was greater than 1%;

[0100] In Comparative Example 4, the content of cyclic sulfate esters was greater than 4%, while the content of cyclic sulfonates was greater than 1%.

[0101] The electrolyte components and contents used in the above embodiments and comparative examples are detailed in Table 1 below.

[0102] Electrolyte and cathode material analysis and testing

[0103] The content of LiPF6 in electrolyte is quantitatively analyzed by ion chromatography, according to the reference standard JY / T020-1996.

[0104] The reference standard GB / T9722-2006 specifies the quantitative analysis of the content of PS and solvent in the components and electrolyte using gas chromatography.

[0105] The mass fraction of the additive (compound shown in Formula 4) in the electrolyte can be determined using nuclear magnetic resonance spectroscopy (NMR). The specific testing procedure is as follows: 500 μL of deuterated reagent is added to the NMR tube in a nitrogen-filled glove box. 100 μL of the non-aqueous electrolyte sample is then added to the NMR tube. The NMR tube is shaken to dissolve the non-aqueous electrolyte in the deuterated reagent. The test is performed using an Oxford Instruments X-Pulse benchtop NMR spectrometer. Because the non-aqueous electrolyte is highly sensitive to moisture, both the NMR test and sample preparation are conducted in a nitrogen atmosphere (H2O content less than 0.1 ppm, O2 content less than 0.1 ppm). Simultaneously, all instruments used in the test must be pre-washed with pure water and dried in a vacuum environment at 60°C for at least 48 hours. The deuterated reagent was prepared as follows: Deuterated dimethyl sulfoxide (DMSO-d6), deuterated acetonitrile, and trifluoromethylbenzene were dried using a 4A molecular sieve at a temperature above 25°C for at least 3 days, ensuring that the water content of all reagents was less than 3 ppm. A Metrohm 831KF coulometric moisture analyzer was used for moisture testing. Then, 10 mL of dried DMSO-d6 and 300 μL of dried internal standard trifluoromethylbenzene were mixed thoroughly in a nitrogen-filled glove box to obtain the first solution. 10 mL of dried deuterated acetonitrile and 300 μL of dried internal standard trifluoromethylbenzene were then mixed thoroughly to obtain the second solution. The first and second solutions were then mixed thoroughly to obtain the deuterated reagent.

[0106] Referring to standard GB / T 19077-2016, the volume average particle size Dv50 can be obtained by testing the positive electrode active material using a laser particle size analyzer (e.g., Malvern Master Sizer 3000). (Dv50: The diameter of 50% of the total volume particles is greater than this value, and the diameter of another 50% of the total volume particles is smaller than this value. Dv50 represents the median particle size of the powder).

[0107] According to the standard NB / SH / T 0870-2020, the kinematic viscosity of the electrolyte is tested by the Stabinger viscometer method.

[0108] Examples 1-18 and Comparative Examples 1-4 were tested using the above standards, and the test results are shown in Table 1 below.

[0109] Table 1

[0110] In the electrolytes of the batteries prepared in the above embodiments and comparative examples, the compound shown in Formula 4 is expected to be consumed in 45% to 80% after formation. For example, in Example 4, the content of the compound shown in Formula 4 after formation is approximately 0.17%. In Example 5, the content of the compound shown in Formula 4 after formation is approximately 1.04%. In Example 7, the content of the compound shown in Formula 4 after formation is approximately 0.6%.

[0111] Battery performance test

[0112] 1. Testing of the cycle capacity retention rate and cycle DCR growth rate of individual battery cells:

[0113] At 45℃, charge the battery cell at a constant current of 0.33C to 4.4V, then charge it at a constant voltage of 4.4V to a current of 0.05C, then discharge it at 0.5C for 1 hour, and discharge it at a current of 4C for 30s. Record the initial voltage V1 at the start of discharge and the voltage V2 after 30s of discharge. The initial DCR = (V1-V2) / I1, where I1 is the current corresponding to 4C.

[0114] Then, the battery cell is charged at a constant current of 0.5C to 4.4V, then charged at a constant voltage of 4.4V to a cutoff current of 0.05C, and finally discharged at a constant current of 1C to 2.8V. This constitutes one charge-discharge cycle. The discharge capacity of this cycle is recorded as the discharge capacity of the lithium-ion battery cell in the first cycle. This cycle is repeated for the same battery cell. After 600 cycles, the discharge capacity of the 600th cycle is recorded.

[0115] Then, the battery cells were charged at a constant current of 0.33C to 4.4V, then charged at a constant voltage of 4.4V to a current of 0.05C, then discharged at 0.5C for 1 hour, and discharged at a current of 4C for 30 seconds. The initial voltage V3 at the start of discharge and the voltage V4 after 30 seconds of discharge were recorded. The DCR of the 600th cycle was calculated as (V3-V4) / I2, where I2 is the current corresponding to 4C.

[0116] Cyclic DCR growth rate (%) = (DCR at 600th cycle - Initial DCR) / Initial DCR × 100%. Capacity retention rate of a lithium-ion battery cell after 600 cycles at 0.5C / 1C at 45℃ = Discharge capacity at 600th cycle / Discharge capacity at 1st cycle × 100%.

[0117] 3. Gas generation performance test of individual battery cells

[0118] In this embodiment of the application, the gas generation performance of a single battery cell is reflected by the volume expansion rate of the single battery cell. The test method for the volume expansion rate is described below.

[0119] The battery cells were fully charged to 4.4V at 0.5C and then left to stand in a 70℃ constant temperature chamber for 30 days. The volume expansion rate of the battery cells was obtained by measuring the initial volume and the volume after 30 days of standing using the water displacement method.

[0120] The volume expansion rate (%) of a single battery cell = [(volume after 30 days of rest / initial volume) - 1] × 100%.

[0121] The battery performance of Examples 1-18 and Comparative Examples 1-4 was tested, and the test results are shown in Table 2 below.

[0122] Table 2

[0123] Referring to the test results in Table 2, it can be seen that, compared with the comparative examples, Examples 1-18 of this application have better cycle capacity retention and smaller cycle DCR growth. This indicates that simultaneously adding appropriate amounts of cyclic sulfates and cyclic sulfonates to the electrolyte is beneficial for controlling cell gas production to maintain a certain level, improving cycle performance, and reducing cycle DCR growth. Furthermore, when too much cyclic sulfonate is added (refer to Comparative Example 3), the electrolyte's ion transport capacity is affected, resulting in a deterioration in both cycle performance and DCR growth. When the cyclic sulfate content is too high (refer to Comparative Example 4), the electrolyte viscosity increases significantly, and the ion transport capacity further deteriorates, thus further worsening both cycle performance and DCR growth.

[0124] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A lithium-ion secondary battery, wherein, The lithium-ion secondary battery includes: a positive electrode, a negative electrode, a separator, and an electrolyte. The separator is located between the positive electrode and the negative electrode, and the electrolyte fills the space between the positive electrode, the separator, and the negative electrode. The positive electrode has a current collector and a positive active layer, the positive active layer comprising lithium nickel cobalt manganese oxide. The electrolyte comprises cyclic sulfur-containing organic compounds. Based on the total mass of the electrolyte, the content of the cyclic sulfur-containing organic compounds is 0.01-4.9%. The cyclic sulfur-containing organic compound includes cyclic sulfates and cyclic sulfonates, wherein the content of the cyclic sulfates is 0.01-3.9% and the content of the cyclic sulfonates is ≤1%.

2. The lithium-ion secondary battery according to claim 1, wherein, The content of the cyclic sulfonate is 0.1-1 wt%, optionally 0.1-0.5 wt%.

3. The lithium-ion secondary battery according to claim 1 or 2, wherein the cyclic sulfate comprises at least one of the following compounds:

4. The lithium-ion secondary battery according to claim 3, wherein, The cyclic sulfate ester includes the compound shown in formula (4), and the content of the compound shown in formula (4) in the electrolyte is 0.1-2%.

5. The lithium-ion secondary battery according to any one of claims 1-4, wherein, The cyclic sulfonate includes 1,3-propanesulfonate lactone, and the content of 1,3-propanesulfonate lactone in the electrolyte is 0.1-0.5%.

6. The lithium-ion secondary battery according to any one of claims 1-5, wherein, The electrolyte further comprises cyclic carbonates, the content of which is 5-35% based on the total mass of the electrolyte. Optionally, the content of the cyclic carbonate is 10-27%.

7. The lithium-ion secondary battery according to claim 6, wherein, The cyclic carbonates include ethylene carbonate.

8. The lithium-ion secondary battery according to claim 7, wherein, Based on the total mass of the electrolyte, the content of ethylene carbonate is 5-35%, optionally 8-30%, and more preferably 10-27%.

9. The lithium-ion secondary battery according to any one of claims 1-5, wherein, The electrolyte further comprises chain carbonates, the content of which is 45-80% based on the total mass of the electrolyte.

10. The lithium-ion secondary battery according to claim 9, wherein, The chain carbonate includes at least one of ethyl methyl carbonate, diethyl carbonate, and dimethyl carbonate.

11. The lithium-ion secondary battery according to claim 10, wherein, Based on the total mass of the electrolyte, the content of dimethyl carbonate is 25-50%.

12. The lithium-ion secondary battery according to any one of claims 1-11, wherein, The electrolyte further comprises at least one selected from butylene carbonate, fluoroethylene carbonate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl sulfone, and diethyl sulfone.

13. The lithium-ion secondary battery according to any one of claims 1-12, wherein, The Dv50 of the lithium nickel cobalt manganese oxide is 3-6 micrometers.

14. A battery assembly, wherein, It includes a positive electrode, a negative electrode, a separator, and an electrolyte. The separator is located between the positive and negative electrode, and the electrolyte fills the space between the positive electrode, the separator, and the negative electrode. The positive electrode has a current collector and a positive active layer. The positive active layer includes lithium nickel cobalt manganese oxide. The content of the cyclic sulfur-containing organic matter is 0.5-5%. The cyclic sulfur-containing organic matter includes cyclic sulfates and cyclic sulfonates. The content of the cyclic sulfates is 0.4-4%, and the content of the cyclic sulfonates is ≤1.1%.

15. The battery assembly of claim 14, wherein, The cyclic sulfate ester includes at least one of the following compounds: The content of the cyclic sulfate is 0.5-2%, and the cyclic sulfonate includes 1,3-propanesulfonate lactone, with a content of 0.3-0.8%.

16. The battery assembly according to claim 14 or 15, wherein, The electrolyte further comprises a lithium salt, the lithium salt content being 10-15% based on the total mass of the electrolyte.

17. The battery assembly according to any one of claims 14-16, wherein, The electrolyte has a kinematic viscosity of 1.8-3 mm 2 / s at 25°C.

18. A method for preparing a lithium-ion secondary battery, wherein, include: A positive electrode, a negative electrode, and a separator are placed in an encapsulation structure, with the separator located between the positive electrode and the negative electrode. An electrolyte is injected into the encapsulation structure, and based on the total mass of the electrolyte, the content of cyclic sulfur-containing organic matter is 0.5-5%, wherein the cyclic sulfur-containing organic matter includes cyclic sulfate esters and cyclic sulfonates, wherein the content of cyclic sulfate esters is 0.4-4%, and the content of cyclic sulfonates is ≤1.1%. The encapsulation structure is sealed, and the sealed battery assembly is subjected to formation treatment to obtain the lithium-ion secondary battery.

19. The method according to claim 18, wherein, The electrolyte contains 0.5-2% cyclic sulfates, and the formation treatment includes: constant current charging at 0.1C to 50% SOC. After the formation treatment, the content of the cyclic sulfate ester in the electrolyte is 0.1-1.8%.

20. A lithium-ion secondary battery, wherein, The lithium-ion secondary battery is prepared using the method described in claim 18 or 19.

21. An electrical appliance, wherein, The electrical device includes a lithium-ion secondary battery as described in any one of claims 1-13, the lithium-ion secondary battery being used to provide electrical energy.

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