Secondary battery, electric device
By adding solvents and additives with specific structures to the electrolyte and introducing grooves on the negative electrode, the performance problem of secondary batteries under high temperature conditions was solved, the stability of the electrolyte and interface was improved, and the thermal shock resistance and cycle performance of the battery were enhanced.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ZHEJIANG LIWINON ENERGY TECHNOLOGY CO LTD
- Filing Date
- 2026-04-27
- Publication Date
- 2026-07-14
AI Technical Summary
Existing secondary batteries have poor performance under high temperature conditions, poor cycle performance, and poor thermal shock resistance, and there are potential risks of electrolyte decomposition and safety hazards.
A first solvent and a first additive with a specific structure are added to the electrolyte, and multiple slots are introduced on the negative electrode sheet, limiting the mass percentage of the solvent and additive in the electrolyte and the slot distance to satisfy a specific relationship.
It improves the stability of the electrolyte under high voltage and high temperature conditions, reduces side reactions between the electrolyte and the electrode, and improves the thermal shock resistance and overall performance of the secondary battery.
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Abstract
Description
Technical Field
[0001] This application relates to the field of battery technology, and in particular to a secondary battery and an electrical device. Background Technology
[0002] As an important energy storage technology, the performance and stability of rechargeable batteries largely depend on the selection and performance of the electrolyte. The electrolyte in a rechargeable battery primarily functions as an ion transport medium. It not only provides a migration channel for lithium ions between the positive and negative electrodes, ensuring a stable ion concentration during operation, but also generates solid electrolyte interfaces (CEI and SEI films) at the positive and negative electrodes, thus ensuring continuous and stable power supply. However, in high-voltage systems (such as those where the positive electrode active material includes transition metal ions), the dissolution of transition metal ions and the continuous oxidation of conventional carbonate solvents, along with instability at the electrode / electrolyte interface, lead to a rapid decline in battery cycle performance. Simultaneously, the large amount of gas and heat generated by electrolyte decomposition poses certain safety concerns, severely hindering the practical application of rechargeable batteries.
[0003] Adding film-forming additives and nitrile additives such as fluoroethylene carbonate (FEC) and succinic anhydride (SN) to the electrolyte is considered an effective way to solve the above problems. FEC additives have a high film-forming potential, which can preferentially form an SEI film on the negative electrode surface without increasing impedance, and can prevent further decomposition of the electrolyte. However, under high temperature conditions, FEC is prone to desulfurization reaction under the action of Lewis acids (PF5) in the electrolyte, producing HF and other acids; resulting in significant performance degradation under high temperature conditions. Summary of the Invention
[0004] The purpose of this application is to solve the technical problems of poor high-temperature performance, poor cycle performance and poor thermal shock resistance of existing secondary batteries, and to propose a secondary battery and power supply device.
[0005] To achieve the above objectives, a first aspect of this application provides a secondary battery, the secondary battery comprising a negative electrode and an electrolyte, wherein the negative electrode is provided with a plurality of slots; The electrolyte comprises a first solvent and a first additive; The structural formula of the first solvent is shown in Formula I, and the structural formula of the first additive is shown in Formula II. Formula I Formula II; R1 and R2 are each independently selected from C1-C5 alkyl, fluorine-substituted C1-C5 alkyl, hydrogen or fluorine; wherein at least one of R1 and R2 is a fluorine-substituted C1-C5 alkyl. R3 is selected from C1~C6 alkyl, C1~C6 ester, C6~C9 benzenesulfonyl or C1~C6 isocyanate; The secondary battery satisfies: 5 < (a + 10b) / X < 60; a% is the mass percentage of the first solvent based on the total mass of the electrolyte; b% is the mass percentage of the first additive based on the total mass of the electrolyte; X mm is the distance between adjacent slots on the negative electrode sheet.
[0006] As an embodiment of this application, the mass percentage a of the first solvent is 5 to 30% based on the total mass of the electrolyte.
[0007] As an embodiment of this application, the mass percentage b of the first additive is 0.1-3% based on the total mass of the electrolyte.
[0008] As an embodiment of this application, the distance X between adjacent slots on the negative electrode sheet is 0.5~5mm.
[0009] As an embodiment of this application, R1 and R2 are each independently selected from ethyl, 2,2-difluoroethyl or trifluoroethyl.
[0010] As an embodiment of this application, R3 is selected from ethyl methacrylate, hexane isocyanate, or isopropyl.
[0011] As an embodiment of this application, the electrolyte further includes a second additive, which includes at least one of fluoroethylene carbonate (FEC), succinate (SN), adiponitrile (ADN), and 1,3,6-hexanetrionitrile (HTCN).
[0012] As an embodiment of this application, the secondary battery satisfies: 0.7≤(a+b) / d≤2.2; where d% is the mass percentage of the second additive based on the total mass of the electrolyte.
[0013] As an embodiment of this application, the mass percentage d of the second additive is 9-20% based on the total mass of the electrolyte.
[0014] As an embodiment of this application, the electrolyte further includes a second solvent, which includes at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), 2,2-difluoroethyl acetate (DFEA), ethyl propionate (EP), and propyl propionate (PP).
[0015] As an embodiment of this application, the mass percentage of the second solvent is 40-70% based on the total mass of the electrolyte.
[0016] In a second aspect, this application provides an electrical device including the secondary battery described in this application.
[0017] Compared with the prior art, the beneficial effects of this application are: This application provides a secondary battery that, by adding a first solvent and a first additive with a specific structure to the electrolyte and introducing multiple slots on the negative electrode, further defines the mass percentage of the first solvent in the electrolyte, the mass percentage of the first additive in the electrolyte, and the distance between adjacent slots on the negative electrode to satisfy a specific relationship. This can improve the stability of the electrolyte under high voltage and high temperature conditions, reduce the occurrence of side reactions between the electrolyte and the electrode, improve the thermal shock resistance of the secondary battery, and make the overall performance of the secondary battery better. Detailed Implementation
[0018] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0019] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.
[0020] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.
[0021] In one embodiment of this application, a secondary battery is proposed, the secondary battery comprising a negative electrode sheet and an electrolyte, wherein the negative electrode sheet is provided with a plurality of slots; The electrolyte comprises a first solvent and a first additive; The structural formula of the first solvent is shown in Formula I, and the structural formula of the first additive is shown in Formula II. Formula I Formula II; R1 and R2 are each independently selected from C1-C5 alkyl, fluorine-substituted C1-C5 alkyl, hydrogen or fluorine; wherein at least one of R1 and R2 is a fluorine-substituted C1-C5 alkyl. R3 is selected from C1~C6 alkyl, C1~C6 ester, C6~C9 benzenesulfonyl or C1~C6 isocyanate; The secondary battery satisfies: 5 < (a + 10b) / X < 60; a% is the mass percentage of the first solvent based on the total mass of the electrolyte; b% is the mass percentage of the first additive based on the total mass of the electrolyte; X mm is the distance between adjacent slots on the negative electrode sheet.
[0022] This application provides a secondary battery that, by adding a first solvent and a first additive with a specific structure to the electrolyte and introducing multiple slots on the negative electrode, further defines the mass percentage of the first solvent in the electrolyte, the mass percentage of the first additive in the electrolyte, and the distance between adjacent slots on the negative electrode to satisfy a specific relationship. This can improve the stability of the electrolyte under high voltage and high temperature conditions, reduce the occurrence of side reactions between the electrolyte and the electrode, improve the thermal shock resistance of the secondary battery, and make the overall performance of the secondary battery better.
[0023] Specifically, in the first aspect, this application selects a substance with the structure shown in Formula I as the first solvent, which can effectively improve the chemical stability of the electrolyte. The CF bond energy (approximately 485 KJ / mol) in the substance with the structure shown in Formula I is more stable than that of commonly used carbonates in electrolytes (such as EC and PC, with CH bond energies of approximately 414 KJ / mol). At the same time, the substance with the structure shown in Formula I can form a better-performing SEI film, enhancing the stability of the interface between the negative electrode and the electrolyte. Moreover, the formed SEI film structure is more compact without increasing impedance, and it can also prevent the electrolyte from being oxidized and decomposed by transition metal ions dissolved from the positive electrode during cycling. In addition, due to the electron-withdrawing effect of fluorine atoms, replacing hydrogen atoms with fluorine atoms can lower the HOMO and LUMO energy levels, thereby enhancing the stability of the positive electrode.
[0024] Secondly, this application selects a substance with the structure shown in Formula II as the first additive, which can effectively improve the interfacial stability between the electrolyte and the electrode material. The -N=C=O group in the substance with the structure shown in Formula II is a highly unsaturated electrophilic center. In particular, the carbonyl carbon atom at the end is easily attacked by nucleophiles (such as H2O, alcohol ROH, etc.). Furthermore, it has strong reactivity, enabling it to react irreversibly with the most destructive nucleophilic impurity HF in the electrolyte. Therefore, it can remove water and acid, and can also capture alcohol impurities to reduce the side reactions of the secondary battery.
[0025] Thirdly, this application provides multiple slots on the negative electrode sheet, which can effectively improve the wettability of the electrolyte; the through slots can increase the contact area between the negative electrode sheet and the electrolyte, accelerate the wetting of the electrolyte to the negative electrode interface and corners, improve the utilization rate of the electrolyte and the kinetics during the cycle of the secondary battery, and at the same time improve the lithium plating problem at the negative electrode interface and corners.
[0026] Fourthly, this application further specifies that the secondary battery satisfies 5 < (a + 10b) / X < 60. As the proportion of the first solvent in the electrolyte increases, the electrolyte's oxidation resistance is improved, ensuring the cycle stability of the secondary battery. However, the increased content of the first solvent also increases the electrolyte viscosity, leading to a decrease in the secondary battery's kinetics and causing lithium plating at the negative electrode interface during continuous charge and discharge. Introducing multiple pores into the negative electrode sheet can improve the electrolyte's wettability and enhance the secondary battery's kinetics, but this also intensifies the side reactions between the electrolyte and the negative electrode. Therefore, the addition of the first additive can remove H2O, HF, and alcohol impurities from the electrolyte, reducing the generation of side reactions. Furthermore, the introduction of the first additive also increases the secondary battery's impedance and leads to a decrease in kinetics. These three factors work synergistically to improve the cycle performance of the secondary battery. When the mass percentage 'a' of the first solvent is larger, the slot spacing 'X' also needs to be increased, and the mass percentage 'b' of the first additive also needs to be increased. When the three factors are controlled to satisfy the above relationship, the overall performance of the secondary battery can be effectively balanced, resulting in better high-temperature performance, cycle performance, and thermal shock resistance of the secondary battery.
[0027] For example, the value of (a+10b) / X can be any point value or any two-point range value between 5 and 60, such as 5.1, 6, 8, 10, 12, 15, 18, 20, 22, 25, 28, 30, 32, 35, 38, 40, 42, 45, 48, 50, 52, 55, 58, 59.9, etc.
[0028] In one embodiment, 5.6 ≤ (a+10b) / X ≤ 56. For example, it can be 5.6, 8, 10, 15, 20, 25, 30, 35, 40, 45, 50, 56, etc.
[0029] In one embodiment, 12 ≤ (a + 10b) / X ≤ 16. For example, it can be 12, 12.2, 12.5, 12.8, 13, 13.2, 13.5, 13.8, 14, 14.2, 14.5, 14.8, 15, 15.2, 15.5, 15.8, 16, etc.
[0030] This study found that when (a+10b) / X is further selected within the above range, the resulting secondary battery exhibits better high-temperature performance, better cycle performance, and better thermal shock resistance.
[0031] In one embodiment, the mass percentage a of the first solvent, based on the total mass of the electrolyte, is 5-30%.
[0032] For example, based on the total mass of the electrolyte, the mass percentage 'a' of the first solvent can be any point value or any two-point range value between 5% and 30%, such as 5%, 6%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 24%, 25%, 26%, 28%, 30%, etc.
[0033] In one embodiment, the mass percentage 'a' of the first solvent, based on the total mass of the electrolyte, is 7.2% to 25.2%. For example, it can be 7.2%, 12%, 18%, 22%, 25%, 25.2%, etc.
[0034] In one embodiment, the mass percentage 'a' of the first solvent, based on the total mass of the electrolyte, is 15-21%. For example, it can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, etc.
[0035] It should be noted that the method for determining the mass percentage of the first solvent in the electrolyte is as follows: Disassemble the secondary battery to obtain the electrolyte. Use gas chromatography-mass spectrometry (GC-MS) to obtain the mass spectrum of the first solvent in the electrolyte. Match the mass spectrum of the sample peak with a standard spectral library or compare it with the mass spectrum of a standard to accurately identify the substance. Then, prepare a series of mixed standard solutions of known concentrations using a diluent. Inject the standard solutions into the same method as the sample and analyze them. Plot a calibration curve with concentration on the x-axis and response value (peak area) on the y-axis. Analyze the diluted sample solution under identical test conditions to obtain the peak area of each component in the sample. Substitute this peak area into the corresponding standard curve equation to calculate the concentration in the diluted sample solution. Multiply this concentration by the dilution factor to obtain the actual content of that component in the original electrolyte, i.e., the mass percentage of the first solvent in the electrolyte.
[0036] This study found that the mass percentage of the first solvent affects the stability of the electrolyte, the structural compactness of the formed SEI film, and the degree of oxidation and decomposition of the electrolyte by transition metal ions dissolved from the positive electrode during cycling. When the mass percentage of the first solvent is further selected within the above range, the high-temperature stability, cycle performance, and thermal shock resistance of the secondary battery can be effectively improved.
[0037] In one embodiment, the mass percentage b of the first additive is 0.1-3% based on the total mass of the electrolyte.
[0038] For example, based on the total mass of the electrolyte, the mass percentage b of the first additive can be any point value or any two-point range value between 0.1% and 3%, such as 0.1%, 0.2%, 0.3%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, 2.2%, 2.5%, 2.8%, 3.0%, etc.
[0039] In one embodiment, the mass percentage b of the first additive, based on the total mass of the electrolyte, is 0.5% to 1.5%. For example, it can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, etc.
[0040] It should be noted that the method for determining the mass percentage of the first additive in the electrolyte is as follows: Disassemble the secondary battery to obtain the electrolyte. Use gas chromatography-mass spectrometry (GC-MS) to obtain the mass spectrum of the first additive in the electrolyte. Match the mass spectrum of the sample peak with a standard spectral library or compare it with the mass spectrum of a standard to accurately identify the substance. Then, prepare a series of mixed standard solutions of known concentrations using a diluent. Inject the standard solutions into the same method as the sample and analyze them. Plot a calibration curve with concentration on the x-axis and response value (peak area) on the y-axis. Analyze the diluted sample solution under identical test conditions to obtain the peak area of each component in the sample. Substitute this peak area into the corresponding standard curve equation to calculate the concentration in the diluted sample solution, and then multiply by the dilution factor to obtain the mass percentage of the first additive in the electrolyte.
[0041] This study found that the amount of the first additive affects the interfacial stability between the electrolyte and the electrode, as well as its control over side reactions. When the mass percentage of the first additive in the electrolyte is further selected within the above range, the high-temperature stability, cycle performance, and thermal shock resistance of the secondary battery are all better.
[0042] In one embodiment, the distance X between adjacent slots on the negative electrode sheet is 0.5~5mm.
[0043] For example, the distance X between adjacent slots on the negative electrode sheet can be any point value or any two-point range value between 0.5 and 5 mm, such as 0.5 mm, 0.6 mm, 0.8 mm, 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm, 3.5 mm, 4.0 mm, 4.5 mm, 5.0 mm, etc.
[0044] In one embodiment, the distance X between adjacent slots on the negative electrode sheet is 1.5~2.5 mm. For example, it can be 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2 mm, 2.1 mm, 2.2 mm, 2.3 mm, 2.4 mm, 2.5 mm, etc.
[0045] It should be noted that the test method for the distance between adjacent slots on the negative electrode sheet is as follows: Take a secondary battery, disassemble the negative electrode sheet, cut a small sample from the electrode sheet with holes, ensure that the area to be tested is flat and wrinkle-free, place the sample on the worktable of the measuring instrument, find the micro-slot to be tested through the optical lens, and adjust the focus until the image is clear. The measurement software will automatically identify the edge of the slot. Use the software's "width" or "distance" measurement tool to measure the width multiple times at different positions of the slot (such as both ends or the middle) and record the data. Finally, take the average value as the test result.
[0046] This study found that the distance between adjacent slots on the negative electrode sheet affects the wetting ability of the electrolyte and the degree of side reactions between the negative electrode sheet and the electrolyte. When the distance between adjacent slots is further selected within the above range, the high-temperature stability, cycle performance and thermal shock resistance of the secondary battery are better.
[0047] In one embodiment, R1 and R2 are each independently selected from ethyl, 2,2-difluoroethyl, or trifluoroethyl.
[0048] For example, the first solvent may be 2,2-difluoroethyl ethyl carbonate (A1, formula III, CAS: 916678-14-3), ethyl trifluoroethyl carbonate (A2, formula IV, CAS: 156783-96-9), bis(2,2-difluoroethyl) carbonate (A3, formula V, CAS: 916678-16-5), etc.; Formula III Formula IV Formula V.
[0049] This study found that further selecting R1 and R2 independently from ethyl, 2,2-difluoro-substituted ethyl, or trifluoro-substituted ethyl, especially substances with the above structures, can better enhance the compactness of the SEI film and reduce the oxidative decomposition of the electrolyte by transition metal ions dissolved from the positive electrode during cycling, thereby resulting in better overall performance of the prepared secondary battery.
[0050] In one embodiment, R3 is selected from ethyl methacrylate, hexane isocyanate, or isopropyl.
[0051] For example, the first additive may be ethyl isocyanate methacrylate (B1, formula VI, CAS: 30674-80-7), hexamethylene diisocyanate (B2, formula VII, CAS: 822-06-0), isopropyl isocyanate (B3, formula VIII, CAS: 1795-48-8), p-toluenesulfonyl isocyanate (B4, formula IX, CAS: 4083-64-1), etc.; Formula VI Formula VII Formula VIII Formula IX.
[0052] This application research found that when the structure of the first additive is further selected as a substance of the above type, the interfacial stability between the electrolyte and the electrode material can be better improved, and it also has stronger reactivity, thereby effectively removing water and acid, capturing impurities such as alcohols, and reducing side reactions of the secondary battery; thus, the overall performance of the obtained secondary battery is better.
[0053] In one embodiment, the electrolyte further includes a second additive, the second additive including at least one of fluoroethylene carbonate (FEC), succinate (SN), adiponitrile (ADN), and 1,3,6-hexanetrionitrile (HTCN).
[0054] This study found that selecting the above-mentioned type of second additive can better help control the electrolyte viscosity and SEI thickness, thereby improving the overall performance of the secondary battery.
[0055] In one embodiment, the secondary battery satisfies: 0.7≤(a+b) / d≤2.2; where d% is the mass percentage of the second additive based on the total mass of the electrolyte.
[0056] For example, the value of (a+b) / d can be any point value or any two-point range value between 0.7 and 2.2, such as 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, etc.
[0057] This study found that further constraining the secondary battery to satisfy the above-mentioned relationship can, on the one hand, regulate the viscosity of the electrolyte, and on the other hand, reduce the formation of SEI, so that it can both meet the requirement of continuous repair of SEI during cycling and avoid the increase in battery impedance caused by excessively thick SEI layers; thereby effectively improving the overall performance of the secondary battery.
[0058] In one embodiment, the mass percentage d of the second additive is 9-20% based on the total mass of the electrolyte.
[0059] For example, based on the total mass of the electrolyte, the mass percentage d of the second additive can be any point value or any two-point range value between 9 and 20%, such as 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, etc.
[0060] It should be noted that the test method for the mass percentage of the second additive in the electrolyte is as follows: Disassemble the secondary battery to obtain the electrolyte. Use gas chromatography-mass spectrometry (GC-MS) to obtain the mass spectrum of the second additive in the electrolyte. Match the mass spectrum of the sample peak with a standard spectral library or compare it with the mass spectrum of a standard to accurately identify the substance. Then, prepare a series of mixed standard solutions of known concentrations using a diluent. Inject the standard solutions into the same method as the sample and analyze them. Plot a calibration curve with concentration on the x-axis and response value (peak area) on the y-axis. Analyze the diluted sample solution under exactly the same test conditions to obtain the peak area of each component in the sample. Substitute this peak area into the corresponding standard curve equation to calculate the concentration in the diluted sample solution, and then multiply it by the dilution factor to obtain the mass percentage of the second additive in the electrolyte.
[0061] This study found that the mass percentage of the second additive affects the control of electrolyte viscosity and the density of the subsequently generated SEI film. When the mass percentage of the second additive is further selected within the above range, the overall performance of the secondary battery is better.
[0062] In one embodiment, the electrolyte further includes a second solvent, which includes at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), 2,2-difluoroethyl acetate (DFEA), ethyl propionate (EP), and propyl propionate (PP).
[0063] In one embodiment, the second solvent accounts for 40-70% of the total mass of the electrolyte.
[0064] For example, based on the total mass of the electrolyte, the mass percentage of the second solvent can be any point value or any two-point range value between 40% and 70%, such as 40%, 42%, 48%, 50%, 52%, 54%, 55%, 58%, 60%, 62%, 64%, 65%, 68%, 70%, etc.
[0065] In one embodiment, the mass percentage of the second solvent, based on the total mass of the electrolyte, is 46.80% to 54.68%. For example, it can be 46.8%, 48.8%, 50.8%, 52.8%, 54.68%, etc.
[0066] It should be noted that the method for determining the mass percentage of the second solvent in the electrolyte is as follows: Disassemble the secondary battery to obtain the electrolyte. Use gas chromatography-mass spectrometry (GC-MS) to obtain the mass spectrum of the second solvent in the electrolyte. Match the mass spectrum of the sample peak with a standard spectral library or compare it with the mass spectrum of a standard to accurately identify the substance. Then, prepare a series of mixed standard solutions of known concentrations using a diluent. Inject the standard solutions into the same method as the sample and analyze them. Plot a calibration curve with concentration on the x-axis and response value (peak area) on the y-axis. Analyze the diluted sample solution under identical test conditions to obtain the peak area of each component in the sample. Substitute this peak area into the corresponding standard curve equation to calculate the concentration in the diluted sample solution, and then multiply it by the dilution factor to obtain the mass percentage of the second solvent in the electrolyte.
[0067] This study found that further selecting the mass percentage of the second solvent within the above-mentioned range resulted in a secondary battery with superior overall performance.
[0068] In one embodiment, the electrolyte further includes a lithium salt.
[0069] In one embodiment, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis(trifluoromethanesulfonylimide) (LiTFSI), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalate)phosphate (LiDFOP), lithium di(oxalate)borate (LiBOB), and lithium difluoro(oxalate)borate (LiODFB).
[0070] In one embodiment, the lithium salt has a mass percentage of 8-25% based on the total mass of the electrolyte. For example, it can be 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 25%, etc.
[0071] It should be noted that the slot includes a through hole or a blind hole. The slot can be introduced using methods conventional in the art for introducing slots.
[0072] It should be noted that the slots are located on the negative electrode active material layer on the negative electrode surface.
[0073] For example, the slots can be introduced by laser drilling, that is, by using a high-precision laser beam combined with laser patterning technology to process a vertical array of holes, i.e., slots.
[0074] In some embodiments, the laser power is 200-1500W, the laser speed is 30000-34000m / s, and the laser frequency is 500kHz-5MHz.
[0075] In one embodiment, the depth of the slot is 5-30 μm and the width is 50-90 μm.
[0076] In one embodiment, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side of the negative current collector, wherein the negative active material layer includes a negative active material, a negative binder, a negative thickener, and a negative conductive agent.
[0077] This application does not restrict the choice of negative electrode active material; any known negative electrode active material can be used. For example, it can be graphite, silicon, or lithium.
[0078] This application does not restrict the choice of negative electrode conductive agent; any known negative electrode conductive agent can be used. For example, carbon nanotubes (CNTs), acetylene black, etc.
[0079] This application does not restrict the choice of negative electrode thickener; any known negative electrode thickener can be used. For example, carboxymethyl cellulose (CMC) can be used.
[0080] This application does not restrict the choice of negative electrode binder; any known negative electrode binder can be used. For example, polyacrylic acid (PAA) can be used.
[0081] In one embodiment, the secondary battery further includes a positive electrode sheet, which includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector.
[0082] In one embodiment, the positive electrode active material layer includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder.
[0083] This application does not restrict the selection of the positive electrode active material; any known positive electrode active material can be used. For example, lithium cobalt oxide (LiCoO2) or lithium nickel cobalt manganese oxide can be used.
[0084] When selecting the above-mentioned type of positive electrode active material, this application can achieve high voltage, and under the system of this application, it can achieve excellent high-temperature performance, cycle performance and thermal shock resistance under high voltage.
[0085] This application does not restrict the choice of positive electrode conductive agent; any known positive electrode conductive agent can be used. For example, conductive carbon black (SP), carbon nanotubes (CNT), etc.
[0086] This application does not restrict the choice of the positive electrode binder; any known positive electrode binder can be used. For example, it can be polyvinylidene fluoride (PVDF), etc.
[0087] In one embodiment, the secondary battery further includes a separator.
[0088] This application does not limit the diaphragm; any known diaphragm can be used.
[0089] For example, the diaphragm includes any one of polyethylene diaphragm, polypropylene diaphragm, polyvinylidene fluoride diaphragm, and multilayer composite membrane.
[0090] In one embodiment of this application, an electrical device is provided, the electrical device including the secondary battery described in this application.
[0091] Example 1 This application provides a secondary battery, the preparation method of which includes the following steps: (1) Preparation of electrolyte In an argon-filled glove box, the second solvent (a mixture of diethyl carbonate (DEC), ethyl propionate (EP), and propyl propionate (PP) in a mass ratio of 1:1:1) and the first solvent (A3) are mixed in a mass ratio of DEC:EP:PP:A3 = 3:1. Then, lithium salt (LiPF6) at 15% of the total mass of the electrolyte is slowly added to the mixed solution. Finally, the second additive (a mixture of fluoroethylene carbonate (FEC), adiponitrile (ADN), and 1,3,6-hexanetrionitrile (HTCN) in a mass ratio of 10:1:1) at 12% of the total mass of the electrolyte and the first additive B2 at 1% of the total mass of the electrolyte are added and stirred until homogeneous to obtain the electrolyte. (2) Preparation of positive electrode sheet Lithium cobalt oxide (LiCoO2) (Xiamen Tungsten New Energy), conductive agent Super P, and binder polyvinylidene fluoride (PVDF) were mixed in a weight ratio of LiCoO2:Super P:PVDF = 97:2:1. The mixture was then added to N-methylpyrrolidone (NMP) and mixed evenly to prepare a positive electrode slurry. The positive electrode slurry was coated onto a current collector aluminum foil, dried at 85°C, and then cold-pressed. After trimming and slitting, the slurry was dried under vacuum at 85°C for 6 hours and then the tabs were welded to obtain the positive electrode sheet. (3) Preparation of negative electrode sheet Graphite (Shenzhen BTR), conductive agent acetylene black, thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber were mixed in a weight ratio of graphite:acetylene black:CMC:styrene-butadiene rubber = 96:1:1.5:1.5. Deionized water was then added and mixed thoroughly to prepare a negative electrode slurry. The negative electrode slurry was coated onto a current collector copper foil, dried at 85℃, and then cold-pressed. After edge trimming and slitting, it was dried under vacuum at 85℃ for 12 hours. Subsequently, a high-precision laser beam was used to etch grooves into the negative electrode sheet (laser power 800W, laser speed 32000mm / s, laser type 2MHz). The width of the grooves was 70μm, the depth was 15μm, and the distance between adjacent grooves was 2mm. Finally, tabs were welded to obtain the negative electrode sheet. (4) Preparation of secondary batteries The positive electrode, separator (polyethylene porous film, Shenzhen Xingyuan), and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes, and then wound to obtain a bare cell. The cell is designed to have a capacity of 5.0 Ah and a voltage range of 3.0~4.55V. The bare cell is then placed in an aluminum-plastic film outer packaging for sealing, and then baked in an 85℃ vacuum oven for 48 hours. Electrolyte is injected into the dried battery at an injection rate of 1.5 g / Ah. After sealing, settling, formation, shaping, and capacity testing, a second sealing is performed, with a electrolyte retention rate of 1.3 g / Ah, resulting in a secondary battery.
[0092] Examples 2-4 This application provides a secondary battery, which differs from Embodiment 1 in that the type of the first additive is adjusted to achieve the parameters in Table 1.
[0093] Examples 5-6 This application provides a secondary battery, which differs from Embodiment 1 in that the type of the first solvent is adjusted to achieve the parameters in Table 1.
[0094] Examples 7-8 This application provides a secondary battery, which differs from Embodiment 1 in that the amounts of the first solvent and the second solvent are adjusted to achieve the parameters in Table 1.
[0095] Examples 9-10 This application provides a secondary battery, which differs from Embodiment 1 in that the amounts of the first solvent, the second solvent, and the first additive are adjusted to achieve the parameters in Table 1.
[0096] Examples 11-12 This application provides a secondary battery, which differs from Embodiment 1 in that the spacing of the slots is changed to achieve the parameters in Table 1.
[0097] Examples 13-14 This application provides a secondary battery, which differs from Embodiment 1 in that the amounts of the second additive and the first solvent are changed to achieve the parameters in Table 1.
[0098] Example 15 This application provides a secondary battery, which differs from Embodiment 1 in that the type of the second additive is changed.
[0099] Example 16 This application provides a secondary battery, which differs from Embodiment 1 in that the type of the second solvent is changed.
[0100] Examples 17-22 This application provides a secondary battery, which differs from Embodiment 1 in that the types of the first solvent and the first additive are changed to achieve the parameters in Table 1.
[0101] Comparative Example 1 This application provides a secondary battery in comparison, which differs from Example 1 in that it does not add a first solvent, does not add a first additive, and does not have slots on the negative electrode.
[0102] Comparative Example 2 This application provides a secondary battery in comparison, which differs from Example 1 in that it does not add a first solvent and does not create slots on the negative electrode.
[0103] Comparative Example 3 This application provides a secondary battery in comparison, which differs from Example 1 in that no first additive is added and no slots are made on the negative electrode.
[0104] Comparative Example 4 This application provides a secondary battery in comparison, which differs from Embodiment 1 in that it does not have slots on the negative electrode.
[0105] Comparative Example 5 This application provides a secondary battery as a comparative example, which differs from Example 1 in that it does not add a first solvent or a first additive.
[0106] Comparative Examples 6-7 This application provides a secondary battery as a comparative example, which differs from Example 1 in that the amount of the first solvent and the second solvent added, as well as the spacing between adjacent slots, are changed to achieve the parameters in Table 1.
[0107] The types of the first solvent, the mass percentage of the first solvent in the total mass of the electrolyte solvent (a%), the types of the first additive, the mass percentage of the first additive in the total mass of the electrolyte (b%), the types of the second solvent, the mass percentage of the second solvent in the total mass of the electrolyte solvent (c%), the types of the second additive, the mass percentage of the second additive in the total mass of the electrolyte (d%), the distance X mm between adjacent cells, (a+10b) / X, (a+b) / d, and the mass percentage of lithium salt in the total mass of the electrolyte (f%) are shown in Table 1. Wherein, A1 is 2,2-difluoroethyl ethyl carbonate (Formula III, CAS: 916678-14-3), A2 is ethyl trifluoroethyl carbonate (Formula IV, CAS: 156783-96-9), and A3 is bis(2,2-difluoroethyl) carbonate (Formula V, CAS: 916678-16-5). B1 is ethyl isocyanate methacrylate (Formula VI, CAS: 30674-80-7), B2 is hexamethylene diisocyanate (Formula VII, CAS: 822-06-0), B3 isopropyl isocyanate (Formula VIII, CAS: 1795-48-8), and B4 is p-toluenesulfonyl isocyanate (Formula IX, CAS: 4083-64-1). C1 is a mixture of DEC, EP and PP in a mass ratio of 1:1:1, and C2 is a mixture of DEC and EP in a mass ratio of 1:1. D1 is a mixture of FEC, AND, and HTCN in a mass ratio of 10:1:1; D2 is a mixture of FEC and AND in a mass ratio of 10:1. Table 1 The performance tests of the secondary batteries prepared in the examples and comparative examples include the following aspects: (1) Room temperature cycle performance test: The secondary battery was charged to 4.55V at a constant current and constant voltage of 1.2C in an environment of 25℃, and the cut-off current was 0.05C. Then it was discharged to 3.0V at a constant current of 0.5C. This cycle was repeated 400 times. After the cycle, the capacity retention rate and thickness expansion rate were calculated. The calculation formula is as follows: 400-week cycle capacity retention (%) = (400-week cycle discharge capacity / initial cycle discharge capacity) × 100%; The thickness growth rate at week 400 = (full-charge thickness at week 400 / full-charge thickness at the first cycle) × 100%; (2) High-temperature cycle performance test: In an environment of 45℃, the secondary battery was charged to 4.55V at a constant current and constant voltage of 0.7C, and the cutoff current was 0.05C. Then it was discharged to 3.0V at a constant current of 0.5C. This cycle was repeated 300 times. After the cycle, the capacity retention rate and thickness expansion rate were calculated on the 300th cycle. The calculation formula is as follows: 300-week cycle capacity retention (%) = (300-week cycle discharge capacity / initial cycle discharge capacity) × 100%; The thickness growth rate at week 300 = (full-charge thickness at week 300 / full-charge thickness at the first cycle) × 100%; (3) Static Cycling Performance Test: In an environment of 45℃, the secondary battery was charged to 4.55V at a constant current and constant voltage of 0.7C, with a cutoff current of 0.05C. It was then left to stand for 24 hours in a fully charged state, and then discharged to 3.0V at a constant current of 0.5C. This cycle was repeated 120 times. After the cycle, the capacity retention rate and thickness expansion rate of the 120th cycle were calculated. The calculation formula is as follows: Cycle capacity retention rate at week 120 (%) = (Cycle discharge capacity at week 120 / Initial cycle discharge capacity) × 100%; Thickness expansion rate at 120th cycle = (Fully charged thickness at 120th cycle / Fully charged thickness at first cycle) × 100%; (4) 85℃ / 24h high temperature storage test: The battery was charged and discharged once at 0.5C at room temperature (3.0V-4.55V), and the discharge capacity C0 before storage was recorded. Then the battery was charged to 4.55V at constant current and constant voltage (100% SOC). The thickness d1 of the battery before high temperature storage was measured using a PPG battery thickness gauge (600g). The battery was placed in an 85℃ constant temperature chamber for 24h. After storage, the battery was taken out and the thermal thickness d2 after storage was measured. The battery thickness expansion rate after 24h storage at 85℃ was calculated. After the battery cooled at room temperature for 24h, it was discharged again at 0.5C at constant current to 3.0V, and then charged to 4.55V at 0.5C at constant current and constant voltage. The discharge capacity C1 and charging capacity C2 after storage were recorded. The remaining capacity and recovery rate of the battery after 24h storage at 85℃ were calculated. The calculation formula is as follows: Thickness expansion rate after storage at 85℃ for 24 hours = (d2-d1) / d1×100%; Capacity retention rate after storage at 85℃ for 24 hours = C1 / C0 × 100%; Capacity recovery rate after storage at 85℃ for 24 hours = C2 / C0 × 100%.
[0108] (5) Thermal shock performance test: Under the ambient conditions of 25℃, discharge to 3.0V with a given current of 0.2C; rest for 5min; charge to 4.55V with a charging current of 0.2C. When the cell voltage reaches 4.55V, switch to constant voltage charging at 4.55V until the charging current is ≤ cut-off current of 0.05C; after resting for 1h, put the cell into the oven. The oven temperature rises to 135±2℃ at a rate of 5±2℃ / min and is maintained for 60min before stopping. The judgment standard is that the cell does not catch fire or explode. The results are shown in Table 2. Table 2 As shown in Table 2, the secondary battery prepared using the method provided in this application exhibits excellent high-temperature performance and cycle performance. Specifically, after 400 cycles at room temperature, the capacity retention rate is above 82.20%, and the thickness expansion rate is below 14.32%; after 300 cycles at high temperature, the capacity retention rate is above 80.60%, and the thickness expansion rate is below 13.96%; after 120 cycles of static cycling, the capacity retention rate is above 62.30%, and the thickness expansion rate is below 12.95%; the capacity retention rate at 85℃ / 24h is above 81.30%, and the thermal shock pass rate at 135℃ is 6 / 6. As can be seen from Examples 1-22 and Comparative Examples 6-7, when the secondary battery does not meet the scope of this application, the obtained product cannot achieve the effect of this application; as can be seen from Examples 1-22 and Comparative Examples 1-5, when the first solvent and / or the first additive are not introduced into the electrolyte, or when the groove is not introduced into the negative electrode, the obtained product also cannot achieve the effect of this application.
[0109] Furthermore, comparative studies of Examples 1-4 revealed that hexamethylene diisocyanate (B2) exhibits the best performance. Containing two isocyanate groups, it possesses a stable structure and can react stepwise on the electrode surface, promoting the formation of a dense and stable SEI film. Simultaneously, it possesses the ability to capture protonated hydrogen, inhibiting the autocatalytic decomposition of lithium salts and significantly improving the battery's cycle and storage performance under high-temperature conditions. Comparative studies of Examples 1, 5, and 6 showed that bis(2,2-difluoroethyl) carbonate (A3) exhibits the best performance. It possesses a stronger degree of fluorination and molecular symmetry, enabling the in-situ formation of a dense, LiF-rich SEI film on the lithium anode surface, effectively inhibiting lithium dendrite growth. Furthermore, it demonstrates excellent thermal stability, a short self-extinguishing time, and high safety. Therefore, the combination of bis(2,2-difluoroethyl) carbonate and hexamethylene diisocyanate offers superior performance.
[0110] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of this application and not to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.
Claims
1. A secondary battery, the secondary battery comprising a negative electrode and an electrolyte, characterized in that, The negative electrode sheet is provided with multiple slots; The electrolyte comprises a first solvent and a first additive; The structural formula of the first solvent is shown in Formula I, and the structural formula of the first additive is shown in Formula II. Formula I Formula II; R1 and R2 are each independently selected from C1-C5 alkyl, fluorine-substituted C1-C5 alkyl, hydrogen or fluorine; wherein at least one of R1 and R2 is a fluorine-substituted C1-C5 alkyl. R3 is selected from C1~C6 alkyl, C1~C6 ester, C6~C9 benzenesulfonyl or C1~C6 isocyanate; The secondary battery satisfies: 5 < (a + 10b) / X < 60; a% is the mass percentage of the first solvent based on the total mass of the electrolyte; b% is the mass percentage of the first additive based on the total mass of the electrolyte; X mm is the distance between adjacent slots on the negative electrode sheet.
2. The secondary battery according to claim 1, characterized in that, Satisfy at least one of the following: (1) The mass percentage a of the first solvent, based on the total mass of the electrolyte, is 5-30%; (2) The mass percentage b of the first additive, based on the total mass of the electrolyte, is 0.1-3%; (3) The distance X between adjacent slots on the negative electrode sheet is 0.5~5mm.
3. The secondary battery according to claim 1, characterized in that, R1 and R2 are each independently selected from ethyl, 2,2-difluoroethyl, or trifluoroethyl.
4. The secondary battery according to claim 1, characterized in that, R3 is selected from ethyl methacrylate, hexane isocyanate, or isopropyl.
5. The secondary battery according to claim 1, characterized in that, The electrolyte further includes a second additive, which includes at least one of fluoroethylene carbonate, succinic acid, adiponitrile, and 1,3,6-hexanetrionitrile.
6. The secondary battery according to claim 5, characterized in that, The secondary battery satisfies: 0.7≤(a+b) / d≤2.2; Wherein, d% is the mass percentage of the second additive based on the total mass of the electrolyte.
7. The secondary battery according to claim 6, characterized in that, The mass percentage of the second additive, d, is 9-20% based on the total mass of the electrolyte.
8. The secondary battery according to claim 1, characterized in that, The electrolyte further includes a second solvent, which includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, 2,2-difluoroethyl acetate, ethyl propionate, and propyl propionate.
9. The secondary battery according to claim 8, characterized in that, The mass percentage of the second solvent is 40-70% based on the total mass of the electrolyte.
10. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 1-9.