Electrolyte, secondary battery and electronic device

Abstract

The embodiment of the invention provides an electrolyte, a secondary battery and an electronic device, the electrolyte comprises ethylene carbonate, a first component and tris (triR-silyl) phosphate, the structural general formula of the tris (triR-silyl) phosphate is # imgabs0 #, R represents a saturated or unsaturated alkyl group or an unsaturated alkenyl group, R represents an alkyl group or an unsaturated alkenyl group, and R represents an alkyl group or an unsaturated alkenyl group. The first component comprises one or more of fluoroethylene carbonate, vinylene carbonate and propylene carbonate, based on the total mass of the electrolyte, the mass content of ethylene carbonate is 10%-25%, the mass content of the first component is 1%-5%, the mass content of tris (triR-silyl) phosphate is 0.2%-1%, and the mass content of triR-silyl phosphate is 0.2%-1%. And the electrolyte does not contain lithium bis (sulfonimide) salt. According to the present invention, by optimizing the electrolyte formula design, removing the bis-sulfonimide lithium salt, optimizing the content of the first component, and adding the tri (tri-R-based silicon-based) phosphate, the high-temperature storage and cycle performance of the secondary battery can be significantly improved.

Description

Technical Field

[0001] The present application relates to the field of batteries, and more specifically, to electrolytes, secondary batteries and electronic devices. Background Art

[0002] With the development of the current new energy field, secondary batteries such as cylindrical batteries have developed rapidly in the fields of electric vehicles and large-scale energy storage, occupying a large market share. With the widespread application of batteries, consumers also have higher demands for the cycle life of lithium-ion batteries. Summary of the invention

[0003] In order to solve the above problems, the present application optimizes the electrolyte formula design. On the basis of the original electrolyte, the bissulfonyl imide lithium salt is removed through scheme optimization, the content of vinyl carbonate is optimized, and tris(tri-R-silicon) phosphate is added. This can significantly improve the storage performance and calendar life of secondary batteries such as positive electrode laser penetration welding pre-nickel-plated steel shell cylindrical batteries, reduce the risk of self-discharge of steel shell batteries, and thus improve the high temperature storage and cycle performance of secondary batteries.

[0004] Some embodiments of the present application provide an electrolyte, comprising: ethylene carbonate, a first component and tris(tri-R-silyl)phosphate,

[0005] Wherein, the general structural formula of the tris(tri-R-silyl)phosphate is:

[0006]

[0007] Wherein, the R group represents a saturated or unsaturated alkyl group, or an unsaturated alkenyl group,

[0008] Wherein, the first component includes one or more of fluoroethylene carbonate (FEC), vinylene carbonate (VC) and propylene carbonate (PC), wherein, based on the total mass of the electrolyte, the mass content of the vinyl carbonate is 10%-25%, the mass content of the first component is 1%-5%, the mass content of tris(tri-R-silicon) phosphate is 0.2%-1%, and wherein the electrolyte does not contain bissulfonyl imide lithium salt. In some embodiments, the bissulfonyl imide lithium salt includes one or both of bistrifluoromethanesulfonyl imide lithium salt (LiFSi) and bis(trifluoromethylsulfonyl) imide lithium salt (LiTFSi). In the present application, by optimizing the electrolyte formula design, on the basis of the original electrolyte, the bissulfonyl imide lithium salt is removed through scheme optimization, the content of the first component is optimized, and tris(tri-R-silicon) phosphate is added, which can significantly improve the storage performance and calendar life of secondary batteries such as positive electrode laser penetration welding pre-nickel-plated steel shell cylindrical batteries, reduce the risk of self-discharge of steel shell batteries, and the electrolyte reduces its corrosion in steel shell secondary batteries by removing the bissulfonyl imide lithium salt.

[0009] In some embodiments, based on the total mass of the electrolyte, the mass content of the first component is 1%-3%. In some embodiments, based on the total mass of the electrolyte, the mass content of the tris(tri-R-based silicon) phosphate is 0.5%-1%. When the first component and the tris(tri-R-based silicon) phosphate in the electrolyte are within this range, the comprehensive performance is the best, which can significantly improve the high temperature storage and cycle performance of the corresponding secondary battery.

[0010] In some embodiments, the electrolyte further comprises isocyanates, wherein the R group links an isocyanate functional group, wherein the mass content of the isocyanates is 0.1%-1% based on the total mass of the electrolyte. The present application can significantly optimize the corrosion of secondary batteries such as pre-nickel-plated steel shell cylindrical batteries by adding 0.1%-1%, optionally 0.2%-0.5%, of isocyanate additives to the electrolyte, thereby effectively optimizing the high-temperature self-discharge of the battery.

[0011] In some embodiments, the R group is a saturated straight chain or branched chain alkyl or an unsaturated alkenyl, wherein the saturated straight chain or branched chain alkyl is represented by C n H 2n+1 , unsaturated olefinic groups are represented by C n H 2n-1 , and wherein 4≤n≤8. In some embodiments, the tris(tri-R-silyl)phosphate is tris(trimethylsilyl)phosphate (TMSP). In some embodiments, the isocyanate includes 1,6-hexamethylene diisocyanate. In the present application, the Si-O bond in the TMSP structure is connected to H + Combined, the corrosion of H+ on the steel shell Ni\Fe in the battery system is reduced. In addition, the electrolyte of the present application can significantly improve the high-temperature storage and cycle performance of the corresponding secondary battery by adding TMSP and 1,6-hexamethylene diisocyanate, and reduce the risk of self-discharge of the steel shell battery.

[0012] Some embodiments of the present application also provide a secondary battery, which includes a positive electrode column, a shell and an electrolyte, wherein the shell is a steel shell containing a nickel layer, wherein the shell includes a surrounding side wall, one end of which is formed with an opening; the end of the shell near the opening includes a crimping portion recessed into the shell; a cover plate, mounted on the opening; an insulating seal, the insulating seal is arranged around the periphery of the cover plate to insulate and seal the cover plate and the shell; a negative current collector, arranged between the electrode assembly and the cover plate, and electrically connected to the shell, the connecting piece of the negative current collector is located on the side of the crimping portion facing the electrode assembly and is welded to the crimping portion; and a pole, the pole passes through the end wall and is insulated from the end wall, the positive current collector is electrically connected to the pole and the electrode assembly, the positive current collector and the pole are fixed by laser penetration welding, and the electrolyte is the above electrolyte. In some embodiments, the secondary battery is a cylindrical battery.

[0013] In this application, by optimizing the electrolyte system, the risk of high-temperature self-discharge of the positive electrode laser-welded pre-nickel-plated steel shell secondary battery can be significantly reduced, and the charge retention of the battery under high-temperature storage conditions can be improved. DETAILED DESCRIPTION

[0014] Figure 1 A vehicle provided with a battery pack is shown.

[0015] Figure 2 A detailed view of the battery pack is shown.

[0016] Figure 3 A cross-sectional view of a secondary battery according to an embodiment of the present application is shown.

[0017] Figure 4 A partial cross-sectional view of a secondary battery according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0019] The following disclosure provides many different embodiments or examples for realizing the different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present invention. Of course, these are merely examples and are not intended to limit the present invention. For example, in the following description, forming a first component above or on a second component may include an embodiment in which the first component and the second component are directly in contact with each other, and may also include an embodiment in which an additional component may be formed between the first component and the second component so that the first component and the second component may not be in direct contact. In addition, the present invention may repeat reference numerals and / or characters in various examples. This repetition is for the purpose of simplicity and clarity, and does not itself indicate the relationship between the various embodiments and / or configurations discussed.

[0020] Additionally, for ease of description, spatially relative terms such as "below," "beneath," "lower," "above," "upper," etc. may be used herein to describe the relationship of one element or component to another (or additional) elements or components as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein should likewise be interpreted accordingly.

[0021] However, in existing secondary batteries such as cylindrical batteries, specifically, in the existing 46 series cylindrical steel shell batteries commonly used in the art, the positive pole is connected to the top of the connecting piece through the upper plastic and welded to the cover plate by welding. Laser penetration welding is used on the positive pole side. During the high temperature storage process of the battery cell at 45℃-70℃, the laser welding between the positive pole and the upper plastic causes micropores L due to high temperature thermal expansion, and the external H 2 O (water) leakage leads to H 2 O and LiPF in electrolyte 6 HF is generated, which corrodes the steel shell, and high-temperature self-discharge is likely to occur in 30-90 days, resulting in a significantly lower voltage of the battery cell, even to 0 V. Therefore, slight leakage may occur on the positive pole side, and the probability of detecting such extremely small micropore leakage using the He detection method is low.

[0022] If the battery's outer steel shell is pre-nickel-plated, the battery is more likely to suffer from Ni and Fe corrosion during high-temperature storage, leading to self-discharge.

[0023] In summary, the existing positive electrode penetration welding 46 series cylindrical steel shell battery is prone to chemical corrosion inside the battery cell during high temperature storage, and the Ni\Fe metal on the surface of the steel shell battery is oxidized to Fe 2+ \Ni 2+ , Fe dissolved in the electrolyte 2+ \Ni 2+ Between the battery core and the steel shell, during the battery charge and discharge process, the electrolyte flows into the core and deposits on the negative electrode surface. During continuous storage and charge and discharge, Ni\Fe deposits continue to grow, piercing the diaphragm to cause a short circuit between the positive and negative electrodes, resulting in physical self-discharge and a significant voltage drop in the battery. Specifically, LiPF in the electrolyte 6 With the outside world 2 O and the chemical reaction corresponding to Ni\Fe on the surface of the steel shell battery is:

[0024] H 2 O+LiPF 6 ---HF+POF 3 +LiF

[0025] H++Ni / Fe---Fe 2+ \Ni 2+

[0026] In addition, when the pre-nickel plated steel is used as the battery housing seal, the above corrosion reaction is more serious. In view of this, it is necessary to provide an electrolyte to improve the above corrosion problem.

[0027] See also Figure 1 , Figure 1 An electronic device 1000 is shown, such as Figure 1 As shown, the electronic device 1000 includes a battery pack 100. The working unit 300 is electrically connected to the battery pack 100 to obtain electrical energy support. Figure 1 It can be seen that the battery pack 100 includes the above-mentioned secondary battery 1. As an example, the electronic device 1000 is a vehicle, and the vehicle can be a fuel vehicle, a gas vehicle or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc., but is not limited to this. The working part 300 is a vehicle body, and the battery pack 100 is arranged at the bottom of the vehicle body, and provides power support for the driving of the vehicle or the operation of electrical components in the vehicle. However, in some other embodiments, the electronic device 1000 can also be a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, an electric tool, etc. Spacecraft include airplanes, rockets, space shuttles, and spacecrafts, etc.; the working part 300 can be a unit component that can obtain the electric energy of the battery pack 100 and perform corresponding work, such as a fan blade rotation unit, a vacuum cleaner dust removal unit, etc. Electric toys include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Electric tools include metal cutting electric tools, grinding electric tools, assembly electric tools, and railway electric tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. The present application embodiment does not impose any special restrictions on the above-mentioned electronic device 1000.

[0028] like Figure 2 As shown, Figure 2 The battery pack 100 is shown. As mentioned above, the battery pack 100 includes a secondary battery 1. In the embodiment of the battery pack 100, the battery pack 100 includes a box body 310, a box cover 320 and a plurality of secondary batteries 1. The plurality of secondary batteries 1 are placed in the box body 310 and are connected in series or in parallel, or in a mixture of series and parallel. The box cover 320 is sealed on the box body 310 to protect the plurality of secondary batteries 1. It should be noted that the battery pack 100 may also include a battery pack 100 thermal management system, a circuit board and other parts in addition to the secondary battery 1 of the present application. The battery pack 100 may be a battery module or a battery pack, an energy storage cabinet, etc.; they will not be described one by one here.

[0029] like Figure 3 As shown, this embodiment provides a secondary battery 1. The secondary battery 1 includes: a shell 10 and an electrode assembly 20, and the electrode assembly 20 is accommodated in the shell 10. In this embodiment, the shell 10 includes a surrounding side wall 11, and an opening 12 is formed at one end of the side wall 11; the end of the shell 10 close to the opening 12 includes a crimping portion 30 recessed into the shell 10. The secondary battery 1 also includes: a cover plate 40, an insulating seal 50 and a negative electrode collector 62. The cover plate 40 is installed at the opening 12. The insulating seal 50 is arranged around the periphery of the cover plate 40 to insulate and seal the cover plate 40 and the shell 10. The negative electrode collector 62 is arranged between the electrode assembly 20 and the cover plate 40, and is electrically connected to the shell 10. The connecting piece of the negative electrode collector 62 is located on the side of the crimping portion 30 facing the electrode assembly 20 and is welded to the crimping portion 30. In this way, by arranging the connecting piece of the negative electrode collector 62 to be located on the side of the crimping portion 30 facing the electrode assembly 20 and being welded to the crimping portion 30, that is, the welding area between the negative electrode collector 62 and the pole ear is located closer to the electrode assembly 20 than the crimping portion 30, thereby preventing the crimping portion 30 from affecting the welding area between the pole ear and the negative electrode collector 62, thereby improving the welding strength between the pole ear and the negative electrode collector 62. The shell 10 is a steel shell containing a nickel layer.

[0030] Figure 4 Shows Figure 3 A magnified view of area A, Figure 3 and Figure 4 In the structure shown, the secondary battery 1 also includes a pole 70 and a positive current collector 61. The pole 70 passes through the end wall 13 and is insulated from the end wall 13. The positive current collector 61 electrically connects the pole 70 and the electrode assembly 20. The positive current collector 61 and the pole 70 are fixed by laser penetration welding. In the present application, a laser is fired from the side of the pole 70 to melt the side of the pole 70 and thus melt the positive current collector 61 to form a fusion portion, thereby welding them together. Specifically, the laser penetration welding device projects a laser spot on the upper surface of the pole 70. The thermal effect of the laser spot will quickly generate a large amount of heat locally, causing the local temperature to rise rapidly, melting the metal of the pole 70, and generating a molten pool. In addition, the local high temperature can not only melt the pole 70 through, but also the heat can be conducted to the upper surface of the positive current collector 61 through the pole 70, melting part of the metal material on the upper surface of the positive current collector 61, thereby forming a weld mark.

[0031] As mentioned above, for the current secondary batteries (such as cylindrical batteries) in the new energy field, there is a corrosion problem, which is crucial to the development of secondary batteries in the new energy field. Based on this, the present application provides an electrolyte to improve the above corrosion problem. Specifically, the present application can significantly reduce the risk of high-temperature self-discharge of secondary batteries such as pre-nickel-plated steel shell cylindrical batteries with laser welding of positive poles through the optimization of the electrolyte system, and improve the charge retention of secondary batteries under high-temperature storage conditions, thereby improving high-temperature storage and cycle performance.

[0032] Some embodiments of the present application provide an electrolyte, including: ethylene carbonate; a first component and tris(tri-R-silyl)phosphate, wherein the tris(tri-R-silyl)phosphate has a general structural formula of:

[0033]

[0034] Wherein, the R group represents a saturated or unsaturated alkyl group, or an unsaturated alkenyl group, wherein the first component includes one or more of fluoroethylene carbonate (FEC), vinylene carbonate (VC) and propylene carbonate (PC), wherein, based on the total mass of the electrolyte, the mass content of vinyl carbonate is 10%-25%, optionally, 15%-20%, the mass content of the first component is 1%-5%, the mass content of tris(tri-R-based silicon) phosphate is 0.2%-1%, and wherein the electrolyte does not contain a bissulfonyl imide lithium salt. In some embodiments, the bissulfonyl imide lithium salt includes one or both of a bistrifluoromethanesulfonyl imide lithium salt (LiFSi) and a bis(trifluoromethylsulfonyl) imide lithium salt (LiTFSi). In the present application, by optimizing the electrolyte formula design, on the basis of the original electrolyte, the bissulfonyl imide lithium salt is removed through the scheme optimization, the content of the first component is optimized, and tris(tri-R-silyl) phosphate is added, which can significantly improve the storage performance and calendar life of secondary batteries such as pre-nickel-plated steel shell cylindrical batteries with positive electrode laser penetration welding, reduce the risk of self-discharge of steel shell batteries, and the electrolyte reduces its corrosion in secondary batteries such as steel shell cylindrical batteries by removing the bissulfonyl imide lithium salt. In some embodiments, through the Si-O bond in the tris(tri-R-silyl) phosphate structure and H + Combined with reducing H in the secondary battery system + Corrosion of Ni\Fe on steel shell.

[0035] In some embodiments, the electrolyte further comprises other solvents, and the other solvents may comprise one or both of ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC). In some embodiments, the first component comprises fluoroethylene carbonate (FEC), and the mass content of fluoroethylene carbonate (FEC) is in the range of 1.5% to 5% of the total mass of the electrolyte.

[0036] In some embodiments, based on the total mass of the electrolyte, the mass content of the first component is 1%-3%. In some embodiments, based on the total mass of the electrolyte, the mass content of tris(tri-R-based silicon) phosphate is 0.5%-1%. When the first component and tris(tri-R-based silicon) phosphate in the electrolyte are within this range, the comprehensive performance is the best, which can significantly improve the high temperature storage and cycle performance of the corresponding secondary battery.

[0037] In some embodiments, the electrolyte further comprises isocyanates, wherein the R group links the isocyanate functional group, wherein the mass content of the isocyanates is 0.1%-1% based on the total mass of the electrolyte. The present application can significantly optimize the corrosion of secondary batteries such as pre-nickel-plated steel shell cylindrical batteries by adding 0.1%-1%, optionally 0.2%-0.5% of isocyanate additives to the electrolyte, thereby effectively optimizing the high temperature self-discharge of the battery.

[0038] In some embodiments, the R group is a saturated straight chain or branched alkyl group or an unsaturated alkenyl group, wherein the saturated straight chain or branched alkyl group is represented by C n H 2n+1 , unsaturated olefinic groups are represented by C n H 2n-1 , and wherein 4≤n≤8. In some embodiments, tris(tri-R-silyl)phosphate is tris(trimethylsilyl)phosphate (TMSP). In some embodiments, isocyanates include 1,6-hexamethylene diisocyanate. In some embodiments, isocyanates include but are not limited to at least one of hexamethylene diisocyanate, cyclohexane-1,2-diylbis(methylene)diisocyanate, and cyclohexane-1,3-diylbis(methylene)diisocyanate. In the present application, the Si-O bond in the TMSP structure is connected to H + Combined, the corrosion of H+ on the steel shell Ni\Fe in the battery system is reduced. In addition, the electrolyte of the present application can significantly improve the high-temperature storage and cycle performance of the corresponding secondary battery by adding TMSP and 1,6-hexamethylene diisocyanate, and reduce the risk of self-discharge of the steel shell battery.

[0039] Some embodiments of the present application also provide a secondary battery 1 including the above electrolyte, such as Figure 3 to Figure 4As shown, the secondary battery 1 includes a positive electrode column 70, a shell 10 and the above-mentioned electrolyte, wherein the shell 10 includes a surrounding side wall 11, and an opening 12 is formed at one end of the side wall 11; the end of the shell 10 close to the opening 12 includes a crimping portion 30 recessed into the shell 10; a cover plate 40, which is installed on the opening 12; an insulating seal 50, which is arranged around the periphery of the cover plate (40) to insulate and seal the cover plate 40 and the shell 10; a negative current collector 62, which is arranged between the electrode assembly 20 and the cover plate 40 and is electrically connected to the shell 10, and the connecting piece of the negative current collector 62 is located on the side of the crimping portion facing the electrode assembly 20 and is welded to the crimping portion 30; a column 70, which passes through the end wall 13 and is insulated from the end wall 13; and a positive current collector 61, which electrically connects the column 70 and the electrode assembly 20, and the positive current collector 61 and the column 70 are fixed by laser penetration welding. It can be seen that in the present application, the positive pole 70 is laser welded, and the shell 10 is a pre-nickel-plated steel shell. The present application can significantly reduce the risk of high-temperature self-discharge of secondary batteries such as positive pole laser welded pre-nickel-plated steel shell cylindrical batteries by optimizing the electrolyte system, and improve the charge retention of the battery under high-temperature storage of the battery. In addition, the electrode assembly 20 of the secondary battery includes a positive electrode sheet containing a positive active material, a negative electrode sheet containing a negative active material, and a diaphragm. The positive electrode active material can be coated on a positive electrode collector such as aluminum foil, and can include any one or a combination of at least two of lithium nickel manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide. The negative electrode active material can be coated on a negative electrode collector such as copper foil, and can include any one or a combination of at least two of soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxide, silicon carbon compound or lithium titanate. The separator may be a polypropylene (PP) separator or a polyethylene (PE) separator, and the above separators also include separators coated with an inorganic coating or an organic coating on the surface. However, those skilled in the art will understand that the positive active material, the negative active material and the separator of the present application may be other suitable materials.

[0040] The preparation of secondary batteries such as cylindrical batteries is described below in conjunction with specific examples. The secondary batteries in the following Examples 1-24 and Comparative Examples 1-3 are all prepared by the following method, and the difference between them is the type and amount of additives. Those skilled in the art will understand that the preparation method described in this application is only an example, and any other suitable preparation method is within the scope of this application.

[0041] The preparation process of the secondary battery of the embodiment and the comparative example of the present application is as follows:

[0042] Example 1

[0043] (1) Preparation of electrolyte

[0044] Prepare a mixed solution of ethylene carbonate (EC) and other solvents containing ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC), wherein the weight ratio of EC, DMC and EMC is 20:70:10, and the mass content of ethylene carbonate (EC) is 10%-25% based on the total mass of the electrolyte, optionally 15%-20%, which can be adjusted according to actual conditions. The electrolyte is LiPF 6 , LiPF 6 The total mass content is 14.5-16.0% of the total mass of the electrolyte. In the electrolyte, a first component and tris(tri-R-silyl) phosphate are added. In the present embodiment, the first component is vinylene carbonate (VC) and the tris(tri-R-silyl) phosphate is tris(trimethylsilane) phosphate (TMSP), and based on the total mass of the electrolyte, the mass content of vinylene carbonate (VC) is 5%, and the mass content of tris(trimethylsilane) phosphate (TMSP) is 0.5%. In addition, the electrolyte does not contain bissulfonyl imide lithium salt, and the bissulfonyl imide lithium salt includes one or two of bis(trifluoromethanesulfonyl) imide lithium salt (LiFSi) and bis(trifluoromethylsulfonyl) imide lithium salt (LiTFSi). Other additives are listed in the following table, and the above-mentioned ratios are all mass ratios.

[0045] (2) Preparation of secondary batteries

[0046] According to the commonly used methods in this field and the normal production process of cylindrical batteries, 46120 cylindrical cells are prepared. After the processes of liquid injection, formation, sealing, aging, and capacity division, cylindrical batteries are obtained. The cylindrical batteries use pre-nickel-plated steel shells. High-temperature storage: 1. After charging the battery to 100% SOC, place it in a specific incubator for a specific time; 2. Take out the battery cell; 3. Test the battery capacity and DC internal resistance during charge and discharge; 4. Repeat the above steps until a specific time. Specifically, charge the cylindrical battery to 100% SOC (4.25V) and place it in a 60°C constant temperature box at intervals of 30D, test the battery voltage, and test the battery capacity at 25°C. Charge it to 100% SOC and place it in a 60°C constant temperature box for storage. Repeat the above steps until the storage time at 60°C reaches 2 years. If it is determined that obvious self-discharge occurs, stop the test.

[0047] In this application, pre-nickel-plated steel shell cylindrical battery package refers to the steel used to produce the steel shell, which is deposited with 2-10um on the surface of the steel shell by chemical or electrochemical methods, and then stamped to produce cylindrical steel shells with different height series such as 46mm in diameter and 95mm, 120mm in height, and a cover plate that matches the steel shell.

[0048] Example 2

[0049] The preparation method is consistent with that of Example 1, except that in the electrolyte of Example 2, the mass content of vinylene carbonate (VC) is 4% based on the total mass of the electrolyte.

[0050] Example 3

[0051] The preparation method is consistent with that of Example 1, except that in the electrolyte of Example 3, the mass content of vinylene carbonate (VC) is 3% based on the total mass of the electrolyte.

[0052] Example 4

[0053] The preparation method is consistent with that of Example 1, except that in the electrolyte of Example 4, the mass content of vinylene carbonate (VC) is 2% based on the total mass of the electrolyte.

[0054] Example 5

[0055] The preparation method is consistent with that of Example 1, except that in the electrolyte of Example 5, the mass content of vinylene carbonate (VC) is 1% based on the total mass of the electrolyte.

[0056] Example 6

[0057] The preparation method is consistent with that of Example 1, except that in the electrolyte of Example 2, based on the total mass of the electrolyte, the mass content of vinylene carbonate (VC) is 1%, and the mass content of tris(trimethylsilyl)phosphate (TMSP) is 1%.

[0058] Example 7

[0059] The preparation method is consistent with that of Example 1, except that in the electrolyte of Example 7, based on the total mass of the electrolyte, the mass content of vinylene carbonate (VC) is 1%, and the mass content of tris(trimethylsilyl)phosphate (TMSP) is 0.8%.

[0060] Example 8

[0061] The preparation method is consistent with that of Example 1, except that in the electrolyte of Example 8, based on the total mass of the electrolyte, the mass content of vinylene carbonate (VC) is 1%, and the mass content of tris(trimethylsilyl)phosphate (TMSP) is 0.6%.

[0062] Example 9

[0063] The preparation method is consistent with that of Example 1, except that in the electrolyte of Example 9, based on the total mass of the electrolyte, the mass content of vinylene carbonate (VC) is 1%, and the mass content of tris(trimethylsilyl)phosphate (TMSP) is 0.4%.

[0064] Example 10

[0065] The preparation method is consistent with that of Example 1, except that in the electrolyte of Example 10, based on the total mass of the electrolyte, the mass content of vinylene carbonate (VC) is 1%, and the mass content of tris(trimethylsilyl)phosphate (TMSP) is 0.3%.

[0066] Embodiment 11

[0067] The preparation method is consistent with that of Example 1, except that in the electrolyte of Example 11, based on the total mass of the electrolyte, the mass content of vinylene carbonate (VC) is 1%, and the mass content of tris(trimethylsilyl)phosphate (TMSP) is 0.2%.

[0068] Example 12

[0069] The preparation method is consistent with that of Example 1, except that in the electrolyte of Example 12, based on the total mass of the electrolyte, the mass content of vinylene carbonate (VC) is 1%, and the mass content of tris(trimethylsilyl)phosphate (TMSP) is 0.1%.

[0070] Embodiment 13

[0071] The preparation method is consistent with that of Example 1, except that in the electrolyte of Example 13, the cyclic carbonate is fluoroethylene carbonate (FEC).

[0072] Embodiment 14

[0073] The preparation method is consistent with that of Example 1, except that in the electrolyte of Example 14, the cyclic carbonate is propylene carbonate (PC).

[0074] Embodiment 15

[0075] The preparation method is consistent with that of Example 1, except that in the electrolyte of Example 15, the cyclic carbonate is fluoroethylene carbonate (FEC) and propylene carbonate (PC) (mass ratio is 1:1).

[0076] Example 16

[0077] The preparation method is consistent with that of Example 1, except that in the electrolyte of Example 15, tris(tri-R-silyl)phosphate is tris(trivinylsilyl)phosphate.

[0078] Embodiment 17

[0079] The preparation method is consistent with that of Example 2, except that isocyanates are added to the electrolyte of Example 17. In this embodiment, the isocyanate is 1,6-hexamethylene diisocyanate. Based on the total mass of the electrolyte, the mass content of 1,6-hexamethylene diisocyanate is 0.1%.

[0080] Embodiment 18

[0081] The preparation method is consistent with that of Example 1, except that isocyanates are added to the electrolyte of Example 18. In this embodiment, the isocyanate is 1,6-hexamethylene diisocyanate. Based on the total mass of the electrolyte, the mass content of 1,6-hexamethylene diisocyanate is 0.2%.

[0082] Embodiment 19

[0083] The preparation method is consistent with that of Example 2, except that isocyanates are added to the electrolyte of Example 19. In this embodiment, the isocyanate is 1,6-hexamethylene diisocyanate. Based on the total mass of the electrolyte, the mass content of 1,6-hexamethylene diisocyanate is 0.4%.

[0084] Embodiment 20

[0085] The preparation method is consistent with that of Example 1, except that isocyanates are added to the electrolyte of Example 20. In this embodiment, the isocyanate is 1,6-hexamethylene diisocyanate. Based on the total mass of the electrolyte, the mass content of 1,6-hexamethylene diisocyanate is 0.5%.

[0086] Embodiment 21

[0087] The preparation method is consistent with that of Example 2, except that isocyanates are added to the electrolyte of Example 21. In this embodiment, the isocyanate is 1,6-hexamethylene diisocyanate. Based on the total mass of the electrolyte, the mass content of 1,6-hexamethylene diisocyanate is 0.7%.

[0088] Embodiment 22

[0089] The preparation method is consistent with that of Example 2, except that isocyanates are added to the electrolyte of Example 22. In this embodiment, the isocyanate is 1,6-hexamethylene diisocyanate. Based on the total mass of the electrolyte, the mass content of 1,6-hexamethylene diisocyanate is 0.9%.

[0090] Embodiment 23

[0091] The preparation method is consistent with that of Example 2, except that isocyanates are added to the electrolyte of Example 22. In this embodiment, the isocyanate is 1,6-hexamethylene diisocyanate, and the mass content of the 1,6-hexamethylene diisocyanate is 1% based on the total mass of the electrolyte.

[0092] Embodiment 24

[0093] The preparation method is consistent with that of Example 2, except that isocyanates are added to the electrolyte of Example 22. In this embodiment, the isocyanate is hexamethylene diisocyanate. Based on the total mass of the electrolyte, the mass content of hexamethylene diisocyanate is 1%.

[0094] Comparative Example 1

[0095] The preparation method is consistent with that in Example 1, except that bistrifluoromethanesulfonyl imide lithium salt (LiFSi) is added to the electrolyte of Comparative Example 1, and the mass content of the bistrifluoromethanesulfonyl imide lithium salt (LiFSi) is 1% based on the total weight of the electrolyte.

[0096] Comparative Example 2

[0097] The preparation method is consistent with that of Example 1, except that bis(trifluoromethanesulfonyl)imide lithium salt (LiTFSi) is added to the electrolyte of Comparative Example 2, and the mass content of the bis(trifluoromethanesulfonyl)imide lithium salt (LiFSi) is 1% based on the total weight of the electrolyte.

[0098] Comparative Example 3

[0099] The preparation method is consistent with that of Example 1, except that tris(tri-R-silyl)phosphate is not added to the electrolyte of Comparative Example 3.

[0100] Comparative Example 4

[0101] The preparation method is consistent with that of Example 1, except that in the electrolyte of Comparative Example 4, no cyclic carbonate and tris(tri-R-silyl)phosphate are added.

[0102] Voltage test: Use a conventional multimeter to test the voltage at both ends of the battery. If the battery voltage is lower than 4.0V, it is determined that the battery has self-discharged. For 3EA batteries in parallel, if the voltage of 1EA battery is lower than 4.0V, it is determined that the battery has self-discharged. If it is determined that obvious self-discharge has occurred, stop the test.

[0103] 25℃ cycle test: first adjust the temperature of the thermostat to 25℃, discharge at 0.5C constant current to 2.5V, rest for 30min; then charge at 0.5C constant current to 4.25V, switch to constant voltage charging until the current reaches 0.02C, rest for 30min. Repeat this cycle, collect the charge and discharge capacity, and calculate the capacity retention rate. The greater the number of cycles when the discharge capacity retention rate drops to 80%, the better the cycle stability of the battery.

[0104] The types and contents of the electrolytes in Examples 1-16 and Comparative Examples 1-3 and the test results are shown in Table 1 below.

[0105] Table 1 Types and contents of electrolytes in Examples 1-16 and Comparative Examples 1-3 and test results

[0106]

[0107]

[0108] Note: “ / ” in the table indicates that obvious self-discharge occurred during the high-temperature storage test, and the test was stopped in the next test cycle.

[0109] Comparing Example 1 with Comparative Examples 1-2, it can be seen that adding bissulfonyl imide lithium salt of LiFSi or LiTFSi into the electrolyte system significantly deteriorates the high temperature storage performance of the battery.

[0110] It can be seen from Examples 1-5 and Comparative Examples 3-4 that controlling the VC content in the first component to be between 1% and 5% can improve high-temperature storage and cycle performance. When the VC content in the first component is 5%, the improvement effect is limited, and the high-temperature self-discharge of the secondary battery is slightly deteriorated. It can be seen from Comparative Examples 3-4 that when the VC content in the first component is 0%, the high-temperature self-discharge performance of the secondary battery deteriorates. Therefore, it is better to control the VC content in the first component to be 1%-3%. At this time, the 25°C cycle of the battery is better, and the high-temperature storage and cycle performance of the battery can be better improved.

[0111] Comparing Examples 5-11 and 12, it can be seen that the mass content of TMSP in tris(tri-R-silyl)phosphate is 0.2%-1%, which can improve the performance of the battery. And from Example 12, it can be seen that when the mass content of TMSP is 0.1%, the high temperature self-discharge of the battery deteriorates. It can be further seen from Examples 5-11 that when the mass content of TMSP is controlled at 0.5%-1%, the performance of the battery is the best.

[0112] In addition, it can be seen from Examples 13 to 16 that when the first component includes one or more of FEC, VC and PC, and the tris(tris-R-silyl)phosphate includes TMSP, etc., the performance of the battery can be improved.

[0113] It can be seen from the above examples 1-16 and comparative examples 1-4 that the lithium bissulfonyl imide salt needs to be removed from the electrolyte system, and when the content of the first component is 1-3% and the addition amount of tris(tri-R-silyl)phosphate is 0.5-1%, the comprehensive performance of the battery is the best.

[0114] The types and contents of the electrolytes in Examples 17-24 and the test results are shown in Table 2 below.

[0115] Table 2 Types and contents of electrolytes in Examples 17-24 and test results

[0116]

[0117] Corrosion Degree Determination Method

[0118] After charging the battery to 100% SOC, place it in a 60°C constant temperature box and let it stand for a specific time interval. Then, take out the battery and disassemble it to observe whether there is black deposit on the battery shell and improvement. Calculate the ratio of the black deposit area to the total area of ​​the steel shell + cover. If the ratio is less than 1%, it is defined as no corrosion, if it is 1%-10%, it is defined as slight corrosion, if the ratio is 10-20%, it is defined as moderate corrosion, and if the ratio is greater than 20%, it is defined as severe corrosion.

[0119] It can be seen from Examples 2 and 17-24 that by adding 0.1-1% isocyanate additives to the electrolyte, the corrosion of the pre-nickel-plated steel shell battery is significantly optimized, and the high-temperature self-discharge of the battery is effectively optimized. Further, it can be seen from the above Examples 20-24 that the addition of 1,6-hexamethylene diisocyanate to the electrolyte can significantly optimize the corrosion of the pre-nickel-plated steel shell. At the same time, it can be seen from Example 24 that if the addition ratio is 1%, the battery cell cycle performance will be slightly deteriorated. In addition, when the amount of isocyanate additives is between 0.2% and 0.5%, the overall performance of the battery is optimal.

[0120] In summary, when secondary batteries use pre-nickel-plated steel as the outer packaging cylindrical shell and cover, Ni\Fe is easily corroded and self-discharge occurs during the high-temperature storage test of the battery. The present application can significantly reduce the risk of high-temperature self-discharge of secondary batteries such as laser-welded pre-nickel-plated steel shell cylindrical batteries with positive poles through optimization of the electrolyte system, improve the battery's charge retention under high-temperature storage conditions, and improve the battery's high-temperature storage and cycle performance.

[0121] The features of several embodiments are summarized above so that those skilled in the art can better understand various aspects of the present invention. Those skilled in the art should understand that they can easily use the present invention as a basis to design or modify other processes and structures for performing the same purpose and / or achieving the same advantages as the embodiments introduced herein. Those skilled in the art should also appreciate that such equivalent constructions do not deviate from the spirit and scope of the present invention, and that they can make various changes, substitutions and modifications herein without departing from the spirit and scope of the present invention.

Claims

1. An electrolyte, characterized in that: include: Ethylene carbonate, a first component and tris(tri-R-silyl)phosphate, Wherein, the general structural formula of the tris(tri-R-silyl)phosphate is: Wherein, the R group represents a saturated or unsaturated alkyl group, or an unsaturated alkenyl group, Wherein, the first component comprises one or more of fluoroethylene carbonate, vinylene carbonate and propylene carbonate, Wherein, based on the total mass of the electrolyte, the mass content of the ethylene carbonate is 10%-25%, the mass content of the first component is 1%-5%, the mass content of tris(tri-R-silyl)phosphate is 0.2%-1%, and wherein the electrolyte does not contain bissulfonyl imide lithium salt.

2. The electrolyte according to claim 1, characterized in that Based on the total mass of the electrolyte, the mass content of the first component is 1%-3%.

3. The electrolyte according to claim 1, characterized in that Based on the total mass of the electrolyte, the mass content of the tris(tri-R-silyl)phosphate is 0.5%-1%.

4. The electrolyte according to claim 1, characterized in that The electrolyte further comprises isocyanates, wherein the mass content of the isocyanates is 0.1%-1% based on the total mass of the electrolyte.

5. The electrolyte according to claim 1, characterized in that The R group is a saturated straight chain or branched chain alkyl or an unsaturated alkenyl group, wherein the saturated straight chain or branched chain alkyl group is represented by C n H 2n+1 , unsaturated olefinic groups are represented by C n H 2n-1 , and among them, 4≤n≤8.

6. The electrolyte according to claim 1, characterized in that The tris(tri-R-silyl)phosphate is tris(trimethylsilyl)phosphate.

7. The electrolyte according to claim 1, characterized in that The bissulfonyl imide lithium salt includes one or both of bistrifluoromethanesulfonyl imide lithium and bis(trifluoromethylsulfonyl)imide lithium. The mass content of the first component is 15%-20%.

8. The electrolyte according to claim 4, characterized in that The mass content of the isocyanate is 0.2%-0.5%, Wherein, the isocyanates include 1,6-hexamethylene diisocyanate.

9. A secondary battery (1), characterized in that: The invention comprises a positive electrode column (70), a shell (10) and an electrolyte, wherein the shell (10) comprises a surrounding side wall (11), one end of the side wall (11) is formed with an opening (12); one end of the shell (10) close to the opening (12) comprises a crimping portion (30) recessed into the shell (10), and the shell (10) is a steel shell containing a nickel layer; A cover plate (40) mounted on the opening (12); an insulating seal (50), the insulating seal (50) being arranged around the periphery of the cover plate (40) so as to insulate and seal the cover plate (40) and the housing (10); A negative electrode current collector (62) is disposed between the electrode assembly (20) and the cover plate (40) and is electrically connected to the housing (10); a connecting piece of the negative electrode current collector (62) is located on a side of the crimping portion (30) facing the electrode assembly (20) and is welded to the crimping portion (30); A pole (70), the pole (70) passes through the end wall (13) and is insulated from the end wall (13); and The positive electrode current collector (61) electrically connects the pole (70) and the electrode assembly (20), and the positive electrode current collector (61) and the pole (70) are fixed by laser penetration welding. Wherein, the electrolyte is the electrolyte according to any one of claims 1-8.

10. An electronic device (1000), characterized in that: Comprising the secondary battery (1) as claimed in claim 9.

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