Secondary batteries and power consumption devices

Abstract

This application discloses a secondary battery and a power consumption device. The secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator interposed between the positive electrode plate and the negative electrode plate. The positive electrode plate includes a positive electrode active material, and the positive electrode active material contains LiFe x M (1-x) PO4, where 0 < x < 1, and M contains at least one of Co, Mn, Ni, Mg, Zn, and Al. The electrolyte contains a lithium salt represented by the following formula (I). The secondary battery satisfies the condition of (aa), where C is the mass percentage content of the lithium salt in the electrolyte, U is the upper limit voltage of use of the secondary battery, and U0 is the stable voltage of the lithium salt. [Equation 1] TIFF2025539139000017.tif9168 [Chemical Formula 1] TIFF2025539139000018.tif42168

Description

[Technical Field]

[0001] The present application relates to the field of battery technology, and more particularly to secondary batteries and power consuming devices. [Background technology]

[0002] Lithium ion batteries have the advantages of high open circuit voltage, high energy density, long service life, no memory effect, no pollution, and small self-discharge, and are therefore widely applicable. The positive electrode active material of a lithium ion battery can be selected from lithium iron phosphate doped with transition metals, for example, LiFe x Mn (1-x) PO4, LiFe x Co (1-x) PO4, LiFe x Ni (1-x) Although a high-voltage solid solution material such as PO4 can be selected, the transition metal in the positive electrode active material is prone to leaching.

[0003] The transition metal ions in the positive electrode active material are dissolved from the positive electrode into the electrolyte. Under the driving of an electric field, the transition metal ions migrate and deposit on the surface of the graphite negative electrode, destroying the solid electrolyte interfacial film (SEI), causing the continuous decomposition and regeneration of the SEI film on the graphite surface, continuously consuming active lithium and causing the attenuation of the battery cycle performance.

[0004] Therefore, there is a need to improve lithium-ion batteries. Summary of the Invention

[0005] The inventors discovered that HF ​​is the main cause of the elution of transition metal ions in the positive electrode active material. Because the electrolyte is sensitive to moisture, when water is introduced from the external environment and the electrode plate, the LiPF6 in the electrolyte decomposes upon contact with water to produce HF, which makes the transition metals more susceptible to elution.

[0006] To improve the above technical problems, the present application provides a secondary battery, which includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator interposed between the positive electrode plate and the negative electrode plate. The positive electrode plate includes a positive electrode active material, and the positive electrode active material contains LiFe x M (1-x) PO4, where 0 < x < 1, and M contains at least one of Co, Mn, Ni, Mg, Zn, and Al. The electrolyte contains a lithium salt represented by the following formula (I).

Chemical formula

Number

[0007] The lithium salt represented by formula (I) of the present application has low sensitivity to water and high temperature and is difficult to decompose to generate HF. Therefore, by adding the lithium salt represented by formula (I) to the electrolyte, the present application can reduce the HF content in the secondary battery, further reduce the elution of transition metals in the positive electrode active material, and endow the secondary battery with good cycle performance and kinetic performance. The inventor has found through experiments that

Number

[0008] According to the examples of the present application, the value of C is in the range of 5 to 20 wt%, which can effectively reduce the HF content in the secondary battery, improve the performance of the secondary battery, and further ensure that the secondary battery has relatively low gas generation.

[0009] According to the examples of the present application, the value of U is in the range of 3.65 to 4.35 V. This allows the secondary battery to have excellent performance and can be used stably for a long period of time.

[0010] According to an embodiment of the present application, the U0 is 3.5 to 3.8V.

[0011] According to an embodiment of the present application, the lithium salt includes at least one of lithium bisfluorosulfonylimide, lithium bis(trifluoromethanesulfonyl)imide, (fluorosulfonyl)(trifluoromethanesulfonyl)imide lithium, bis(pentafluoroethylsulfonyl)imide lithium, and (trifluoromethylsulfonyl)(pentafluorobutylsulfonyl)imide lithium. These lithium salts are not easily decomposed to produce HF, and can effectively reduce the HF content in secondary batteries, resulting in good performance of the secondary batteries.

[0012] According to an embodiment of the present application, the electrolyte solution further includes a passivator, which includes at least one of vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, and 1,3-propane sultone. The addition of the passivator can form a highly electronically insulating SEI film at the negative electrode interface, which is advantageous for improving the deposition of transition metal ions at the negative electrode and improving the cycle capacity of the secondary battery.

[0013] According to an embodiment of the present application, the secondary battery comprises:

number

[0014] Therefore, when the mass percentage content of the passivator in the electrolyte and 1-x satisfy the above content relationship, the deposition of transition metals on the negative electrode can be reduced, and the cycle performance and dynamic performance of the secondary battery can be further improved.

[0015] According to the examples of the present application, the value of C2 is in the range of 1 to 6 wt%, which can further improve the deposition of transition metal ions on the negative electrode.

[0016] According to the examples of the present application, the value of C3 is in the range of 0.1 to 0.3. Using lithium iron phosphate doped with a transition metal as the electrode active material can improve the operating voltage of a secondary battery, rather than using lithium iron phosphate as the positive electrode active material.

[0017] According to an embodiment of the present application, the electrolyte solution further contains ethylene carbonate, which can increase the lithium ion concentration in the electrolyte solution, improve the liquid phase transport ability of the electrolyte solution, and further improve the performance of the secondary battery.

[0018] According to an embodiment of the present application, the mass percentage content of the ethylene carbonate in the electrolyte is 10 to 40 wt % based on the total mass of the electrolyte, which allows the electrolyte to have a relatively high conductivity and a relatively high oxygen resistance, which is advantageous for further reducing the battery DCR and gas generation.

[0019] According to the examples of the present application, the porosity of the separator is 30% to 50%, which allows the secondary battery to have good cycle performance and a relatively low DCR.

[0020] According to the embodiment of the present application, the thickness of the separator is 5 to 12 μm, which allows the secondary battery to have good cycle performance and a relatively low DCR.

[0021] According to an embodiment of the present application, the material forming the separator includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyester, polyimide, polyamide, glass fiber, cellulose, aramid, and spandex, which can provide the secondary battery with better cycle performance and lower DCR.

[0022] The present application further provides a power consuming device including the aforementioned secondary battery, whereby the power consuming device has all the features and advantages of the aforementioned secondary battery, which will not be further described herein. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will be described with reference to the following examples. Those skilled in the art should understand that the following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the present invention. Unless specific techniques or conditions are specified in the examples, they are carried out in accordance with the techniques or conditions described in the literature in the field or in accordance with the product instructions. Unless the manufacturer of the reagents or equipment used is specified, they are all commercially available products.

[0024] The inventor has discovered that in a secondary battery, the easy elution of metal ions in the positive electrode active material under the corrosion of HF is one of the factors that attenuate the battery cycle performance. The HF in the battery mainly originates from the electrolyte. The external environment and the electrode plates introduce water, and LiPF6 in the electrolyte decomposes when it comes into contact with water to generate HF. In order to reduce the HF in the battery, in the related art, generally additives for removing water and acid are added to the electrolyte. However, this type of additive itself causes redox reactions to occur on the positive and negative electrodes, and it cannot be guaranteed that the additive will continuously exist throughout the use process of the secondary battery. Moreover, the by-products of the reaction between this type of additive and water, or the by-products of the reaction between the additive and acid, still exist in the secondary battery. The by-products are still more or less involved in the redox reaction and deteriorate the performance of the secondary battery.

[0025] To improve the above technical problems, the present application provides a secondary battery, which includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator interposed between the positive electrode plate and the negative electrode plate. The positive electrode plate includes a positive electrode active material, and the positive electrode active material includes LiFe x M (1-x) PO4, where 0 < x < 1, and M includes at least one of Co, Mn, Ni, Mg, Zn, and Al. The electrolyte includes a lithium salt represented by the following formula (I).

Chemical formula

Number

number

[0026] In the present application, by adding the lithium salt represented by formula (I) to the electrolyte, the amount of LiPF6 used in the electrolyte can be reduced, and even LiPF6 does not need to be added to the electrolyte.

[0027] It should be noted that U is the upper limit voltage of the secondary battery, which is the upper limit voltage that the secondary battery can tolerate. If the voltage is higher than the upper limit voltage of the secondary battery, it will deteriorate the performance of the secondary battery and even pose a safety risk. The test method for U is to provide multiple secondary batteries with the same structural composition as multiple experimental groups, and charge the secondary batteries in each experimental group to different voltages. Specifically, the secondary batteries are first charged at a constant current of 0.3C to different voltages, and the voltage intervals are 0.05V (e.g., 3.6V, 3.65V, 3.7V, 3.75V, 3.8V, 3.85V, 3.9V, 3.95V, 4.0V, 4.05V, 4.1V, 4.15V, 4.2V, 4.25V, 4.3V, 4.35V). V, 4.4V), and then constant voltage charging until the current reached 0.05C. Then, the secondary batteries of each experimental group were disassembled, and the positive electrode active material was taken out and the Li content (referring to GBT19282-2014) in the positive electrode active material was measured using an inductively coupled plasma optical emission spectrometer (ICP-OES). If the Li content was ≦0.1 wt%, it indicated that the positive electrode had sufficiently desorbed lithium, and the battery voltage corresponding to this group could be considered the upper limit voltage for use of the secondary battery.

[0028] U0 is the stable voltage of the lithium salt, which is the voltage at which the secondary battery can be used stably. As a test method for U0, a number of secondary batteries with the same structural composition were prepared as a number of experimental groups, and each experimental group was prepared with an electrolyte solution using 1 wt% vinylene carbonate and 20 wt% of the lithium salt represented by formula (I), and LiFe 0.7 Mn 0.3 Pouch batteries were fabricated using PO4 as the positive electrode active material. Each experimental group of secondary batteries was charged at a different voltage. Specifically, the secondary batteries were first charged at a constant current of 0.3C to different voltages, with voltage intervals of 0.1V (e.g., 3.3V, 3.4V, 3.5V, 3.6V, 3.7V, 3.8V, and 3.9V). They were then charged at a constant voltage of 0.05C. Each experimental group of secondary batteries was then stored at 45°C for three days. The volumetric change rate of each experimental group of secondary batteries was measured before and after storage. The voltage of the secondary battery in the experimental group with a volumetric change rate of 5% was the stable voltage of the lithium salt. If the voltage of the secondary battery was greater than the stable voltage of the lithium salt, the volumetric change rate of the secondary battery was greater than 5%. If the voltage of the secondary battery was less than U0, the volumetric change of the secondary battery was not significant.

[0029] For ease of understanding, the principle by which the secondary battery of the present application can achieve the above beneficial effects will be briefly described below.

[0030] To improve the performance of lithium-ion batteries, the related art proposes a solution in which a mixed lithium salt is added to the electrolyte, while simultaneously combining an ether-based and a nitrile-based solvent, and the positive electrode active material is a ternary material of nickel, cobalt, and manganese. The positive electrode material in the related art requires the use of a ternary material of nickel, cobalt, and manganese, as well as a mixed lithium salt, which imposes many restrictions and a relatively narrow range of applications. The present application proposes adding a lithium salt represented by formula (I) to the electrolyte to effectively reduce the leaching of transition metals in the positive electrode active material, thereby providing secondary batteries with good cycle and dynamic performance. The lithium salt in the electrolyte of the present application may be a single type of lithium salt, i.e., only one lithium salt represented by formula (I) may be used in the electrolyte, and the electrolyte of the present application may be a carbonate-based electrolyte. Compared to the solutions of the related art, the solution of the present application imposes fewer restrictions and has a wider range of applications.

[0031] Specifically, the inventors discovered that the lithium salt represented by formula (I) has low sensitivity to water and high temperatures and is less likely to decompose to generate HF. Adding the lithium salt represented by formula (I) to the electrolyte effectively reduces the HF content in the secondary battery and further reduces the elution of transition metals in the positive electrode active material, thereby providing the secondary battery with good cycle performance and dynamic performance. However, the lithium salt represented by formula (I) has poor high-pressure stability, and is prone to oxidization at high voltages, generating gas, increasing the internal pressure of the battery and causing the housing to expand. At high voltages, it is necessary to adjust the amount of lithium salt represented by formula (I) used to improve gas generation. The inventors discovered that the performance of a secondary battery is related to the mass percentage content of the lithium salt in the electrolyte, the upper limit voltage for use of the battery, and the stable voltage of the lithium salt. The inventors conducted experiments to determine the following:

number

[0032] According to the examples of the present application, the value of C is in the range of 5 to 20 wt%, which can effectively reduce the HF content in the secondary battery and further ensure that the secondary battery has relatively low gas generation. If the value of C is too small, i.e., if the mass percentage content of the lithium salt in the electrolyte is too small, the HF generation in the secondary battery cannot be effectively reduced, and the effect of reducing the elution of transition metals is not significant, which is disadvantageous to improving battery performance. If the value of C is too large, i.e., if the mass percentage content of the lithium salt in the electrolyte is too high, the lithium salt is easily oxidized under high pressure and gases are generated, which is likely to cause excessive gas generation in the secondary battery.

[0033] According to the examples of the present application, the value of U is in the range of 3.65 to 4.35 V. This allows the secondary battery to have excellent performance and to be used stably for a long period of time.

[0034] According to the examples of the present application, U0 is 3.5 V. The lithium salt of the present application can exist stably at 3.5 V or less.

[0035] According to an embodiment of the present application, the lithium salt includes at least one of lithium bisfluorosulfonylimide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), (fluorosulfonyl)(trifluoromethanesulfonyl)imide lithium (LiFTFSI), bis(pentafluoroethylsulfonyl)imide lithium (LiBESI), and (trifluoromethylsulfonyl)(pentafluorobutylsulfonyl)imide lithium. These lithium salts have low sensitivity to water and high temperatures, and are not prone to decomposition to produce HF, which can effectively reduce the HF content in secondary batteries, resulting in good cycle performance and kinetic performance of the secondary batteries.

[0036] The corrosion of the positive electrode by HF and the high voltage can easily cause the dissolution of transition metals from the positive electrode active material, and the transition metal ions migrate and diffuse to the negative electrode due to the effects of the electric field and concentration. Although the SEI film at the negative electrode interface is theoretically electronically insulating, electrons still pass through the SEI and reach the SEI / electrolyte interface, where they combine with transition metal ions, causing a reduction reaction and deposition at the negative electrode interface. This further increases the electron conduction ability of the SEI, further exacerbating side reactions such as transition metal deposition, and deteriorating the performance of the secondary battery.

[0037] To address the issue of transition metal ion deposition at the negative electrode, the electrolyte further includes a passivator, such as at least one of vinylene carbonate (also known as 1,3-dioxol-2-one, ethylene carbonate, abbreviated as VC), vinyl ethylene carbonate (abbreviated as VEC), fluoroethylene carbonate (abbreviated as FEC), and 1,3-propane sultone (abbreviated as PS). Adding a passivator to the electrolyte can form a highly electronically insulating SEI film at the negative electrode interface, which is beneficial for addressing the issue of transition metal ion deposition at the negative electrode. Specifically, the passivator can contribute to the formation of the SEI film and produce inorganic components, such as Li2CO3, LiF, and Li2SO3, which reduce the electronic conductivity of the SEI, thereby reducing the electron reduction reaction of transition metal ions and improving the cycling capacity of the secondary battery.

[0038] According to an embodiment of the present application, the secondary battery comprises:

number

number

[0039] According to the examples of the present application, the value of C2 is in the range of 1 to 6 wt%. This allows for the formation of a highly electronically insulating SEI film at the negative electrode interface, effectively reducing the deposition of transition metal ions at the negative electrode. If the value of C2 is too small, i.e., if the amount of passivator used is too small, the degree to which the passivator reduces the electronic conductivity of the SEI is limited, and the improvement in the cycle capacity of the secondary battery is relatively small. If the value of C2 is too large, i.e., if the amount of passivator used is too large, the SEI film becomes too thick, which is unfavorable to lithium ion transport and deteriorates the dynamics of the battery.

[0040] According to the examples of the present application, the value of C3 is in the range of 0.1 to 0.3, that is, 0.7≦x≦0.9. Compared with using lithium iron phosphate as the positive electrode active material, LiFe x M (1-x) Using PO4 as an electrode active material can improve the operating voltage of secondary batteries.

[0041] According to an embodiment of the present application, the electrolyte solution further contains ethylene carbonate (EC), which has a relatively high dielectric constant and can promote dissociation of various lithium salts (e.g., the lithium salt represented by formula (I)) in the electrolyte solution, increase the lithium ion concentration in the electrolyte solution, improve the liquid phase transport ability of the electrolyte solution, and further improve the performance of the secondary battery.

[0042] According to the examples of the present application, the mass percentage content of ethylene carbonate in the electrolyte is 10 to 40 wt%, based on the total mass of the electrolyte. This allows the electrolyte to have relatively high conductivity and relatively high oxygen resistance, which is advantageous for reducing the DCR and gas generation of secondary batteries. If the ethylene carbonate content is too low, the improvement in lithium ion concentration in the electrolyte is relatively small, and the improvement in secondary battery performance is relatively small. However, ethylene carbonate has relatively low oxidation resistance, and on the one hand, ethylene carbonate is easily oxidized at relatively high voltages, causing gas generation. On the other hand, ethylene carbonate forms Li2CO3 in situ at the negative electrode and then migrates to the positive electrode and is oxidized. Ethylene carbonate or Li2CO3 also undergoes hydrolysis or thermal decomposition, resulting in an increase in CO2. If the ethylene carbonate content is too high, secondary batteries are likely to generate too much gas.

[0043] According to the examples of the present application, the porosity of the separator is 30% to 50%. This allows the secondary battery to have good cycle performance and a relatively low DCR. If the porosity of the separator is too small, the migration of lithium ions becomes too slow, resulting in a large DCR of the battery. If the porosity of the separator is too large, the migration of transition metal ions becomes too fast, resulting in an increase in side reactions in the battery and a deterioration in the performance of the secondary battery.

[0044] According to the examples of the present application, the thickness of the separator is 5 to 12 μm. This allows the battery to have good cycle performance and a relatively low DCR, while also providing the battery with relatively high safety performance. If the separator thickness is too small, safety risks are likely to occur, while if the separator thickness is too large, the migration of lithium ions is relatively slow, resulting in a relatively high secondary battery DCR.

[0045] According to an embodiment of the present application, the material forming the separator includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyester, polyimide, polyamide, glass fiber, cellulose, aramid, and spandex, which can provide the secondary battery with better cycle performance and lower DCR.

[0046] The present application further provides a power consuming device including the aforementioned secondary battery, whereby the power consuming device has all the features and advantages of the aforementioned secondary battery, which will not be further described herein.

[0047] Secondary batteries are used to supply electrical energy to power consuming devices, which may include, but are not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0048] In the examples described below in this application, unless otherwise specified, all reagents used are either commercially available or may be prepared by the methods described in this application.

[0049] Example 1 Positive electrode plate manufacturing: The iron source, M source, phosphorus source, lithium source, lithium fluoride, and carbon source are uniformly mixed and ball milled to obtain a precursor. The precursor is placed in a tubular furnace, and after introducing an inert gas, it is fired. After firing, it is cooled to room temperature, and the obtained solid is pulverized by an airflow crushing method to obtain the positive electrode active material LiFe. x M (1-x) PO4 samples were obtained.

[0050] The positive electrode active material, polyvinylidene fluoride (PVDF), and carbon black (SP) were mixed with a solvent in a mass ratio of 97:2:1, and stirred to obtain a uniformly dispersed positive electrode slurry. The positive electrode slurry was then uniformly applied to two surfaces of aluminum foil, followed by drying, cold pressing, and cutting to obtain a positive electrode plate.

[0051] Negative electrode plate manufacturing: The negative electrode active material (artificial graphite), carbon black (SP), styrene butadiene rubber (SBR), and sodium hydroxymethylcellulose (CMC) were mixed with a solvent in a ratio of 97:0.5:1.5:1, a pore-forming agent was added, and the mixture was stirred to obtain a uniformly dispersed negative electrode slurry. The negative electrode slurry was then evenly applied to the two surfaces of copper foil, which was then dried, cold-pressed, and cut to obtain a negative electrode plate.

[0052] Separator: A polyethylene film was used as the separator.

[0053] Electrolyte production: In a glove box under an argon atmosphere, 30% ethylene carbonate (EC), 40% dimethyl carbonate (DMC), 5% ethyl methyl carbonate (EMC), 7% diethyl carbonate (DEC), 3% vinylene carbonate (VC), 5% lithium hexafluorophosphate (LiPF), and 10% lithium bisfluorosulfonylimide (LiFSI) were mixed and dissolved by mass based on the content of each component in Table 1 to obtain an electrolyte solution.

[0054] Lithium-ion battery manufacturing: The positive electrode plate, the negative electrode plate, and the separator were fabricated into an electrode assembly by a winding process or a stacking process, and then placed in a housing made of an aluminum case, an aluminum plastic film, or the like. The above-mentioned electrolyte solution was poured into the assembly, and the assembly was left standing at a high temperature, subjected to chemical formation, and divided into volumes, to obtain a secondary battery.

[0055] Examples 2-25 and Comparative Examples 1-2 By following the procedures of Example 1 and referring to Table 1, secondary batteries of Examples 2-25 and Comparative Examples 1-2 were obtained.

[0056] The secondary batteries manufactured in Examples 1-25 and Comparative Examples 1-2 were subjected to performance tests. The specific measurement methods are as follows, and the test results are shown in Table 1.

[0057] (1) Measurement of high temperature cycle performance at 60℃ At 60°C, the secondary batteries of each example and comparative example were charged at a constant current of 0.5C to an upper limit voltage (4.2V in the case of Example 1), then charged at a constant voltage of 0.05C. The batteries were then left to stand for 5 minutes and discharged at a constant current of 1 / 3C to 2.5V. This was the first charge-discharge cycle of the secondary batteries, and the discharge capacity at this time is referred to as the first cycle discharge capacity of the secondary batteries. A cycle charge-discharge test was performed on the secondary batteries according to the above method, and the capacity retention rate after 500 cycles of battery cycling was recorded.

[0058] (2) Volume expansion test at 60°C At 60°C, the secondary battery is charged at a constant current of 0.5C up to the upper limit voltage (for example, in Example 1, the upper limit voltage is 4.2V). The secondary battery was then charged at a constant voltage until the current reached 0.05C. The volume of the secondary battery was then measured using the drainage method and recorded as V0. The secondary battery was then placed in a thermostatic chamber at 60°C and stored for 30 days, after which it was removed and the volume of the secondary battery was measured using the drainage method and recorded as V1. The volume expansion rate of the secondary battery after 30 days of storage at 60°C = [(V1-V0) / V0] × 100%.

[0059] (3) DCR test At 60°C, the secondary battery was charged at a constant current of 0.5C up to the upper limit of usable voltage (using Example 1 as an example, the upper limit of usable voltage is 4.2V), and then charged at a constant voltage of 0.05C. The battery was then discharged at 0.5C for 1 hour to adjust the battery to 50% SOC, and the voltage at this time was recorded as U1. The battery was then discharged at 4C for 30 seconds, and the voltage at this time was recorded as U2. DCR = (U1 - U2) / 4C.

[0060] (4) Porosity Test according to GB / T 24586-2009 method.

[0061] [Table 1-1] [Table 1-2]

[0062] As can be seen from Table 1, the overall performance of the secondary batteries of Examples 1-25 was superior to that of the secondary batteries of Comparative Examples 1-2. The secondary batteries of Examples 1-25 had relatively small volume expansion coefficients, relatively large capacity retention, and relatively small DCRs. The volume expansion coefficients of the secondary batteries of the examples of the present application may be as low as 24%, the capacity retention rates of the secondary batteries of the examples of the present application may be as high as 93.5%, and the DCRs of the secondary batteries of the examples of the present application may be as low as 25 mΩ. In Comparative Example 1, the electrolyte solution did not contain a passivator and a lithium salt represented by formula (I), so the resulting secondary battery had a large volume expansion coefficient and a small capacity retention rate. In Comparative Example 2, the content of the lithium salt represented by formula (I) added to the electrolyte solution was too low, so the resulting secondary battery had a relatively large volume expansion coefficient and poor overall performance.

[0063] Although the embodiments of the present application have been described in detail above, the present application is not limited to the specific details in the above embodiments, and various simple modifications can be made to the technical solutions of the present application within the scope of the technical idea of ​​the present application, and all of these simple modifications fall within the protection scope of the present application. It should be noted that the specific technical features described in the above specific embodiments can be combined in any suitable manner as long as they are not contradictory.

[0064] It should be noted that in the description of this specification, the reference terms "one embodiment," "some embodiments," "example," "specific example," or "some examples" mean that the specific features, structures, materials, or characteristics described in connection with this embodiment or example are included in at least one embodiment or example of the present application. In this specification, general expressions using the above terms do not necessarily refer to the same embodiment or example. Furthermore, the described specific features, structures, materials, or characteristics may be combined in any appropriate manner in any one or more embodiments or examples. Furthermore, if not inconsistent, those skilled in the art may combine and combine different embodiments or examples and features of different embodiments or examples described in this specification.

[0065] Although the embodiments of the present application have been shown and described above, it should be understood that the above embodiments are illustrative and should not be construed as limiting the present application, and that those skilled in the art may make changes, modifications, substitutions and variations to the above embodiments within the scope of the present application.

Claims

1. A secondary battery, wherein the secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator interposed between the positive electrode plate and the negative electrode plate, the positive electrode plate including a positive electrode active material, and the positive electrode active material is LiFe ｘ M （１－ｘ） P.O. ４ wherein 0<x<1 and M comprises at least one of Co, Mn, Ni, Mg, Zn, and Al; The electrolyte solution contains a lithium salt represented by the following formula (I): 【number】 Formula (I), Here, R １ , R ２ are independently F, C １－４ Alkyl or C substituted with one or more fluorines １－４ Contains alkyl, The secondary battery is [Equation 1] where C is the mass percentage content of the lithium salt in the electrolyte, U is the upper limit of usable voltage of the secondary battery, and U0 is a stable voltage of the lithium salt.

2. 2. The secondary battery according to claim 1, wherein the value of C is in the range of 5 to 20 wt %.

3. 3. The secondary battery according to claim 1, wherein the value of U is in the range of 3.65 to 4.35 V.

4. 4. The secondary battery according to claim 1, wherein U0 is 3.5 to 3.8 V.

5. 5. The secondary battery according to claim 1, wherein the lithium salt comprises at least one of lithium bisfluorosulfonylimide, lithium bis(trifluoromethanesulfonyl)imide, lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, and lithium (trifluoromethylsulfonyl)(pentafluorobutylsulfonyl)imide.

6. the electrolyte further comprises a passivator; 6. The secondary battery according to claim 1, wherein the passivator includes at least one of vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, and 1,3-propane sultone.

7. Secondary batteries are [Equation 2] 7. The secondary battery according to claim 6, wherein C2 is the mass percentage content of the passivating agent in the electrolyte solution, and C3 is 1-x.

8. 8. The secondary battery according to claim 7, wherein the value of C2 is in the range of 1 to 6 wt %.

9. 9. The secondary battery according to claim 7, wherein the value of C3 is in the range of 0.1 to 0.

3.

10. The secondary battery according to claim 1 , wherein the electrolyte solution further contains ethylene carbonate.

11. 11. The secondary battery according to claim 10, wherein the mass percentage content of the ethylene carbonate in the electrolyte solution is 10 to 40 wt %, based on the total mass of the electrolyte solution.

12. 12. The secondary battery according to claim 1, wherein the porosity of the separator is 30% to 50%.

13. 13. The secondary battery according to claim 1, wherein the separator has a thickness of 5 to 12 μm.

14. 14. The secondary battery according to claim 1, wherein a material forming the separator includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyester, polyimide, polyamide, glass fiber, cellulose, aramid, and spandex.

15. The power consuming device comprises a secondary battery according to any one of claims 1 to 14.

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