Electrochemical and electronic devices

Abstract

The present invention relates to electrochemical devices and electronic devices. Specifically, the present invention provides an electrochemical device including a cell, the cell including a positive electrode, a negative electrode, an electrolyte, and a separator, the outermost electrode of the cell having a curved portion and a flat portion, where L and D satisfy the relationship 5≦L / D≦10, where L is the length of the flat portion and D is the radius of the curved portion, and the electrolyte contains a dinitrile compound, where A is the content of the dinitrile compound relative to the mass of the electrolyte, and A satisfies the relationship 4≦A≦10. The electrochemical device of the present invention has significantly improved high-temperature cycle characteristics.

Description

[Technical Field]

[0001] The present invention relates to the field of energy storage, and in particular to electrochemical and electronic devices. [Background technology]

[0002] Electrochemical devices (e.g., lithium-ion batteries) are widely used in fields such as power storage, portable electronic devices, and electric vehicles due to their high specific energy, high operating voltage, low self-discharge rate, small volume, and light weight. As the range of lithium-ion battery applications expands, further improvements in their performance, such as thinner and lighter batteries and longer battery life, are required. However, in thinner and lighter batteries, the shape of the battery can lead to a lack of electrolyte at the corners of the cell structure, which can affect high-temperature cycling performance.

[0003] In view of the above, there is a need to provide electrochemical devices with improved high temperature cycling characteristics. Summary of the Invention

[0004] SUMMARY OF THE INVENTION The present invention is intended to solve, at least in part, at least one problem that has existed in the related art by providing electrochemical and electronic devices.

[0005] According to one aspect of the present invention, there is provided an electrochemical device including a cell, the cell including a positive electrode, a negative electrode, an electrolyte, and a separator, the outermost electrode of the cell having a curved portion and a flat portion, where L and D satisfy 5≦L / D≦10, where L is the length of the flat portion and D is the radius of the curved portion, and the electrolyte contains a dinitrile compound, where A is the content of the dinitrile compound relative to the mass of the electrolyte, and A satisfies 4≦A≦10. According to an embodiment of the present invention, L and D satisfy 7≦L / D≦9.

[0006] According to an embodiment of the present invention, L satisfies 5≦L≦30, or D satisfies 1≦D≦5.

[0007] According to an embodiment of the present invention, L satisfies 10≦L≦20, or D satisfies 1.5≦D≦2.5.

[0008] By controlling the ratio of the length of the flat part to the radius of the curved part of the cell, it is possible to structurally suppress the lack of electrolyte in the corner area of ​​the cell. Using an electrolyte containing a specific amount of dinitrile compound can improve the stability of the negative electrode, reduce the consumption of electrolyte at the negative electrode interface, and significantly slow down the rate of electrolyte loss in the corner area of ​​the cell. This improves the high-temperature cycle characteristics of the electrochemical device.

[0009] According to an embodiment of the present invention, the dinitrile compound has the structure of Formula 1: [ka] R1, R2, R3, and R4 are each independently selected from hydrogen, halogen, or a substituted or unsubstituted C1-C5 alkyl group; n is selected from an integer from 0 to 8, and when substituted, the substituent is halogen.

[0010] According to an embodiment of the present invention, the dinitrile compound is the following compound: [ka] It includes at least one of the following.

[0011] According to an embodiment of the present invention, when the width of a cell is W mm, W satisfies 10≦W≦40.

[0012] A cell having the above width is small, and by combining it with the specific electrolyte of the present invention (containing 4% to 10% of a dinitrile compound), the high-temperature cycle characteristics of a small electrochemical device can be significantly improved.

[0013] According to an embodiment of the present invention, a positive electrode includes a positive electrode active material, and the positive electrode active material includes a doping element, the doping element being at least one selected from Ni and Al, and when the content of the doping element is C ppm with respect to the mass of the positive electrode active material, C satisfies 3000≦C≦5000.

[0014] The presence of Ni and / or Al contributes to improving the structural stability of the positive electrode active material, and when the content of the doping element in the positive electrode active material is within the above range, it can achieve an excellent fixing effect on active oxygen and reduce the consumption rate of the electrolyte on the positive electrode side, thereby further improving the high-temperature cycle characteristics of the electrochemical device.

[0015] According to an embodiment of the present invention, the electrolyte further includes a propionic acid ester, the propionic acid ester including at least one of ethyl propionate, propyl propionate, butyl propionate, pentyl propionate, ethyl fluoropropionate, propyl fluoropropionate, butyl fluoropropionate, and pentyl fluoropropionate, where M % of the propionic acid ester is based on the mass of the electrolyte, and M satisfies 20≦M≦60.

[0016] Adding a certain amount of propionic acid ester can significantly reduce the viscosity of the electrolyte, improve the fluidity of the electrolyte, and quickly replenish the electrolyte in areas where the electrolyte is locally deficient, thereby further improving the high-temperature cycle properties of the electrochemical device.

[0017] According to an embodiment of the present invention, the electrolyte further includes at least one of 1,3-propane sultone, ethylene sulfate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and γ-butyrolactone.

[0018] According to an embodiment of the present invention, an electrochemical device comprises: a) The content of 1,3-propane sultone is 0.5% to 5% by mass of the electrolyte; b) The content of ethylene sulfate is 0.1% to 1% by mass of the electrolyte; c) The content of vinylene carbonate is 0.1% to 1% by mass of the electrolyte; d) The content of dimethyl carbonate is 0.1% to 30% by mass of the electrolyte; e) The content of diethyl carbonate is 0.1% to 30% by mass of the electrolyte; f) The content of ethyl methyl carbonate is 0.1% to 30% by mass of the electrolyte; g) The content of γ-butyrolactone is 0.01% to 5% by mass of the electrolyte; Satisfy at least one of the following:

[0019] Adding a specific amount of the above compound to an electrochemical device contributes to the construction of a stable interfacial film, further reducing the rate of electrolyte consumption at the interface, thereby further improving the high-temperature cycle characteristics of the electrochemical device.

[0020] According to an embodiment of the present invention, the electrolyte further contains a trinitrile compound, which includes at least one of 1,3,5-pentanetricarbonitrile, 1,2,3-propanetricarbonitrile, 1,3,6-hexanetricarbonitrile, and 1,2,3-tris(2-cyanoethoxy)propane. The content of the trinitrile compound is 0.5% to 3% by mass of the electrolyte, and preferably 1% to 2.5%. By adding the trinitrile compound in the above content to the electrochemical device, the trinitrile compound's stronger adsorption ability is utilized to preferentially form a film on the electrode surface, significantly suppressing the occurrence of side reactions on the electrode surface and further improving the high-temperature cycle performance of small cells.

[0021] According to an embodiment of the present invention, the electrolyte solution further includes a lithium salt, and the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, and lithium difluorophosphate.

[0022] According to an embodiment of the present invention, the separator includes a porous substrate and a porous layer on the surface of the porous substrate, and the porous layer includes polyvinylidene fluoride.

[0023] According to an embodiment of the present invention, the weight average molecular weight of polyvinylidene fluoride is 600,000 to 3,000,000.

[0024] When the porous layer in the separator contains polyvinylidene fluoride of a specific molecular weight, good bonding strength is achieved between the separator and the electrodes, thereby ensuring that the various characteristics of the electrochemical device are exhibited.

[0025] According to another aspect of the present invention, there is provided an electronic device comprising an electrochemical device according to the present invention.

[0026] The present invention provides electrochemical devices and electronic devices that can structurally suppress electrolyte shortages in the corner regions of cells by controlling the ratio of the length of the flat portion to the radius of the curved portion of the cell. Using an electrolyte containing a specific amount of dinitrile compound can improve the stability of the negative electrode, reduce electrolyte consumption at the negative electrode interface, and significantly slow the rate of electrolyte loss in the corner regions of the cell. The combination of a cell with a specific structure (5≦L / D≦10) and a specific electrolyte (containing 4% to 10% dinitrile compound) can significantly improve the high-temperature cycle characteristics of the electrochemical device.

[0027] Other aspects and advantages of the present invention are set forth in part in the description that follows, are illustrated in part, or are explained through the practice of embodiments of the present invention. [Brief explanation of the drawings]

[0028] In the following, in order to explain the embodiments of the present invention, drawings necessary for explaining the embodiments of the present invention or the prior art will be briefly described. It is obvious that the drawings described below are only a part of the embodiments of the present invention. Those skilled in the art can still obtain drawings of other embodiments based on the structures illustrated in these drawings without any creative effort.

[0029] [Figure 1] FIG. 1 is a schematic diagram showing the structure of a cell according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0030] Examples of the present invention will be described in detail below, but the examples of the present invention should not be construed as limiting the present invention.

[0031] In the detailed description and claims, a list of terms connected by the term "at least one of" can refer to any combination of the listed terms. For example, if terms A and B are listed, the phrase "at least one of A and B" means A only, B only, or A and B. In another example, if terms A, B, and C are listed, the phrase "at least one of A, B, and C" means A only, B only, C only, A and B (excluding C), A and C (excluding B), B and C (excluding A), or all of A, B, and C. Term A may include a single element or multiple elements. Term B may include a single element or multiple elements. Term C may include a single element or multiple elements.

[0032] Electrochemical devices (e.g., lithium-ion batteries) are widely used in various fields due to their excellent performance. Some fields have certain requirements for battery shape. For example, as technology advances, mobile phones become thinner and lighter, necessitating thinner and lighter batteries, which in turn requires further improvements in the performance of flat-type batteries. The cell structure of flat-type batteries has a relatively high proportion of bends, which tend to extrude the electrolyte in the bends, resulting in localized electrolyte shortages, blocking the transport of lithium ions and adversely affecting the high-temperature cycle characteristics of electrochemical devices.

[0033] In order to improve the high-temperature cycle characteristics of an electrochemical device, the present invention provides an electrochemical device including a cell, the cell including a positive electrode, a negative electrode, an electrolyte, and a separator, the outermost electrode of the cell having a curved portion and a flat portion, where L and D satisfy 5≦L / D≦10, where L is the length of the flat portion and D is the radius of the curved portion, and the electrolyte contains a dinitrile compound, where A is the content of the dinitrile compound relative to the mass of the electrolyte, and A satisfies 4≦A≦10.

[0034] As used herein, the terms "curved portion" and "flat portion" refer to the portion of the outermost electrode of the cell after winding (i.e., the electrode directly facing the package enclosing the cell), and the curved portions and flat portions are alternately connected to form the outermost electrode of the cell after winding. The term "curved portion" refers to the arc-shaped portion of the outermost electrode of the cell after winding, and includes a first curved portion formed by a first arc wire and a second curved portion formed by a second arc wire. The term "flat portion" refers to the flat portion of the outermost electrode of the cell after winding, i.e., the electrode portion between the first curved portion and the second curved portion, and includes a first flat portion and a second flat portion. The term "radius of curvature" refers to the distance between the perpendicular bisector of the line segment connecting the end points of the first (or second) arc line of the first (or second) curved portion and the intersection point of the perpendicular bisector and the first (or second) arc line. Since the cell has two curved portions, the radius of the curved portion of the cell is the larger of the radii of the two curved portions. Since one of the first flat portion and the second flat portion is the winding end of the cell, the "length of the flat portion" refers to the larger of the lengths of the first flat portion and the second flat portion.

[0035] FIG. 1 is a schematic diagram showing the structure of a cell according to an embodiment of the present invention. The cell 100 includes a positive electrode 101, a negative electrode 102, and a separator 103 positioned between the positive electrode 101 and the negative electrode 102. After winding, the cell is flattened, and the outermost electrode of the cell in the width (W) direction of the cell includes a first curved portion (left side), a second curved portion (right side), a first flat portion (upper side), and a second flat portion (lower side). The second curved portion, the first flat portion, the first curved portion, and the second flat portion are sequentially connected to form the outermost electrode of the cell. The first curved portion is formed by a first arc line along points A, C, and B, where point A is the intersection of the first curved portion and the first flat portion, and point B is the intersection of the first curved portion and the second flat portion. The second curved portion is formed by a second arc line along points A', C', and B', where A' is the intersection point of the second curved portion and the first flat portion, and B' is the intersection point of the second curved portion and the flat portion of the electrode on the layer one layer inward from the outermost layer, which corresponds to the second flat portion. The first flat portion is formed by the line segment from A to A', and the second flat portion is formed by the line segment from B to B" (point B" is the end of the outermost electrode). Points A and B are the endpoints of the first arc line, and point C is the intersection point of the perpendicular bisector of the line segment connecting A and B and the first arc line. The distance between point C and the perpendicular bisector of the line segment connecting A and B is the radius D1 of the first curved portion. Points A' and B' are the endpoints of the second arc line, and point C' is the intersection of the perpendicular bisector of the line segment connecting points A' and B' with the second arc line. The distance between point C' and the perpendicular bisector of the line segment connecting points A' and B' is the radius D2 of the second curved portion. The larger of D1 and D2 of the curved portion is recorded as the radius D of the curved portion (i.e., in Figure 1, this refers to the radius D1 of the first curved portion). The length of the line segment from point A to point A' is the length L1 of the first flat portion, and the length of the line segment from point B to point B'' is the length L2 of the second flat portion. The larger of L1 and L2 is recorded as the length L of the flat portion (i.e., in Figure 1, this refers to the length L1 of the first flat portion).

[0036] By controlling the ratio of the length of the flat part to the radius of the curved part of the cell, it is possible to suppress electrolyte shortage in the corner area of ​​the cell from a structural level. Using an electrolyte containing a specific amount of dinitrile compound can improve the stability of the negative electrode, reduce electrolyte consumption at the negative electrode interface, and significantly slow the rate of electrolyte loss in the corner area of ​​the cell. The combination of a cell with a specific structure (5≦L / D≦10) and a specific electrolyte (containing 4% to 10% dinitrile compound) can significantly improve the high-temperature cycle characteristics of electrochemical devices.

[0037] In some embodiments, L and D satisfy the relationship 7≦L / D≦9. In some embodiments, L / D is 5, 6, 7, 8, 9, or 10, or is within a range consisting of any two of the foregoing values.

[0038] In some embodiments, L satisfies 5≦L≦30. In some embodiments, L satisfies 8≦L≦25. In some embodiments, L satisfies 10≦L≦20. In some embodiments, L satisfies 12≦L≦15. In some embodiments, L is 5, 8, 10, 12, 15, 18, 20, 22, 25, 28, or 30, or within a range formed by any two of the foregoing values.

[0039] In some embodiments, D satisfies the range 1≦D≦5. In some embodiments, D satisfies the range 1.5≦D≦2.5. In some embodiments, D is 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, or 5, or within a range formed by any two of the foregoing values.

[0040] In some embodiments, A satisfies 5≦A≦8. In some embodiments, A is 4, 5, 6, 7, 8, 9, or 10, or is within a range consisting of any two of the foregoing values.

[0041] In some embodiments, the dinitrile compound has the structure of Formula 1: [ka] R1, R2, R3, and R4 are each independently selected from hydrogen, halogen, or a substituted or unsubstituted C1-C5 alkyl group; n is selected from an integer from 0 to 8, and when substituted, the substituent is halogen.

[0042] In some embodiments, the dinitrile compound is the following compound: [ka] It includes at least one of the following.

[0043] In some embodiments, where W mm is the width of the cell, W satisfies the relationship 10≦W≦40. The cell width W is equal to the sum of the length L of the flat portion of the cell and the radii of the two curved portions (D1+D2 shown in FIG. 1). In some embodiments, W is 10, 15, 20, 25, 30, 35, or 40, or within a range formed by any two of the above values. Cells having the above widths are small, and in small cells, the corner area occupies a higher proportion, resulting in a more pronounced electrolyte extrusion phenomenon. Surprisingly, the specific electrolyte of the present invention (containing 4% to 10% dinitrile compound) can exhibit superior performance in small cells and significantly improve the high-temperature cycle characteristics of small electrochemical devices.

[0044] In some embodiments, the electrolyte further comprises a propionic acid ester, the propionic acid ester comprising at least one of ethyl propionate, propyl propionate, butyl propionate, pentyl propionate, ethyl fluoropropionate, propyl fluoropropionate, butyl fluoropropionate, and pentyl fluoropropionate. The addition of the propionic acid ester significantly reduces the viscosity of the electrolyte, improves the fluidity of the electrolyte, and allows the electrolyte to be quickly replenished in areas where the electrolyte is locally deficient, thereby further improving the high-temperature cycle characteristics of the electrochemical device.

[0045] In some embodiments, when the content of the propionate ester is M % with respect to the mass of the electrolyte, M satisfies 20≦M≦60. In some embodiments, M satisfies 30≦M≦50. In some embodiments, M is 20, 25, 30, 35, 40, 45, 50, 55, or 60, or is within a range formed by any two of the foregoing values. When M is within the above range, the electrolyte has excellent ion transport properties, which can further improve the high-temperature cycle properties of the electrochemical device.

[0046] In some embodiments, the electrolyte solution further comprises at least one of 1,3-propane sultone, ethylene sulfate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and γ-butyrolactone. The presence of these compounds contributes to the construction of a stable interfacial film, further reducing the rate of electrolyte consumption at the interface, thereby further improving the high-temperature cycle characteristics of the electrochemical device.

[0047] In some embodiments, the content of the 1,3-propane sultone is 0.5% to 5% by weight of the electrolyte. In some embodiments, the content of the 1,3-propane sultone is 1% to 3% by weight of the electrolyte. In some embodiments, the content of the 1,3-propane sultone is 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5% by weight of the electrolyte, or within a range consisting of any two of the foregoing values.

[0048] In some embodiments, the ethylene sulfate content is 0.1% to 1% by weight of the electrolyte. In some embodiments, the ethylene sulfate content is 0.3% to 0.6% by weight of the electrolyte. In some embodiments, the ethylene sulfate content is 0.1%, 0.3%, 0.5%, 0.8%, or 1%, or any range consisting of any two of the foregoing values, by weight of the electrolyte.

[0049] In some embodiments, the vinylene carbonate content is 0.1% to 1% by weight of the electrolyte, 0.3% to 0.6% by weight of the electrolyte, or 0.1%, 0.3%, 0.5%, 0.8%, or 1%, or any combination of the above values.

[0050] In some embodiments, the dimethyl carbonate content is 0.1% to 30% by weight of the electrolyte. In some embodiments, the dimethyl carbonate content is 0.5% to 25% by weight of the electrolyte. In some embodiments, the dimethyl carbonate content is 1% to 20% by weight of the electrolyte. In some embodiments, the dimethyl carbonate content is 5% to 15% by weight of the electrolyte. In some embodiments, the dimethyl carbonate content is 10% to 12% by weight of the electrolyte. In some embodiments, the dimethyl carbonate content is 0.1%, 0.5%, 1%, 5%, 10%, 15%, 20%, 25%, or 30% by weight of the electrolyte, or a range consisting of any two of the foregoing values.

[0051] In some embodiments, the diethyl carbonate content is 0.1% to 30% by weight of the electrolyte solution. In some embodiments, the diethyl carbonate content is 0.5% to 25% by weight of the electrolyte solution. In some embodiments, the diethyl carbonate content is 1% to 20% by weight of the electrolyte solution. In some embodiments, the diethyl carbonate content is 5% to 15% by weight of the electrolyte solution. In some embodiments, the diethyl carbonate content is 10% to 12% by weight of the electrolyte solution. In some embodiments, the diethyl carbonate content is 0.1%, 0.5%, 1%, 5%, 10%, 15%, 20%, 25%, or 30% by weight of the electrolyte solution, or a range consisting of any two of the foregoing values.

[0052] In some embodiments, the content of the ethyl methyl carbonate is 0.1% to 30% by weight of the electrolyte. In some embodiments, the content of the ethyl methyl carbonate is 0.5% to 25% by weight of the electrolyte. In some embodiments, the content of the ethyl methyl carbonate is 1% to 20% by weight of the electrolyte. In some embodiments, the content of the ethyl methyl carbonate is 5% to 15% by weight of the electrolyte. In some embodiments, the content of the ethyl methyl carbonate is 10% to 12% by weight of the electrolyte. In some embodiments, the content of the ethyl methyl carbonate is 0.1%, 0.5%, 1%, 5%, 10%, 15%, 20%, 25%, or 30% by weight of the electrolyte, or any two of the above ranges.

[0053] In some embodiments, the γ-butyrolactone content is 0.01% to 5% by weight of the electrolyte. In some embodiments, the γ-butyrolactone content is 0.05% to 3% by weight of the electrolyte. In some embodiments, the γ-butyrolactone content is 0.1% to 2% by weight of the electrolyte. In some embodiments, the γ-butyrolactone content is 0.5% to 1% by weight of the electrolyte. In some embodiments, the γ-butyrolactone content is 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, or 5% by weight of the electrolyte, or within a range consisting of any two of the foregoing values.

[0054] When the content of 1,3-propane sultone, ethylene sulfate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, or γ-butyrolactone in the electrolyte is within the above range, it contributes to further improving the high-temperature cycle characteristics of the electrochemical device.

[0055] In some embodiments, the electrolyte further comprises a trinitrile compound, the trinitrile compound comprising: [ka] When the electrolyte contains a trinitrile compound, it contributes to further improving the high-temperature cycle characteristics of the electrochemical device.

[0056] In some embodiments, the trinitrile compound is present in an amount of 0.5% to 3% by weight of the electrolyte. In some embodiments, the trinitrile compound is present in an amount of 1% to 2.5% by weight of the electrolyte. In some embodiments, the trinitrile compound is present in an amount of 0.5%, 1%, 1.5%, 2%, 2.5%, or 3% by weight of the electrolyte, or in any range consisting of any two of the foregoing values.

[0057] In some embodiments, the electrolyte further comprises a lithium salt, the lithium salt comprising at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, and lithium difluorophosphate.

[0058] In some embodiments, the content of the lithium salt is 10% to 15% by weight of the electrolyte. In some embodiments, the content of the lithium salt is 12% to 15% by weight of the electrolyte. When the content of the lithium salt is within the above range, the electrolyte has appropriate ionic conductivity and viscosity, which contributes to further improving the high-temperature cycle characteristics of the electrochemical device.

[0059] In some embodiments, the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. The positive electrode active material layer can be disposed on one or both sides of the positive electrode current collector. In some embodiments, the positive electrode current collector may be aluminum foil, or other positive electrode current collectors commonly used in the art may be used. In some embodiments, the thickness of the positive electrode current collector may be 1 μm to 200 μm. In some embodiments, the positive electrode active material layer may be applied to only a portion of the positive electrode current collector. In some embodiments, the thickness of the positive electrode active material layer may be 10 μm to 500 μm. It should be understood that this is merely an example, and other suitable thicknesses may be used.

[0060] In some embodiments, the positive electrode active material layer includes a positive electrode active material, such as LiCoO2, LiNiO2, LiMn2O4, LiCo 1-y M y O2, LiNi 1-y M y O2, LiMn 2-y M y O4, LiNi x Co y Mn z M 1-x-y-z O2, where M is at least one selected from Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, and Ti, and x, y, and z satisfy the following relationships: 0≦y≦1, 0≦x≦1, 0≦z≦1, and x+y+z≦1. In some embodiments, the positive electrode active material may include at least one of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, and lithium nickel manganese oxide. The positive electrode active material may be doped and / or coated.

[0061] In some embodiments, the positive electrode active material includes a doping element, and the doping element is at least one selected from Ni and Al. The presence of Ni and / or Al contributes to improving the structural stability of the positive electrode active material and further improving the high-temperature cycle characteristics of the electrochemical device.

[0062] In some embodiments, when the content of the doping element is C ppm relative to the mass of the positive electrode active material, C satisfies the range of 3000≦C≦5000. In some embodiments, C is 3000, 3500, 4000, 4500, or 5000, or is within a range formed by any two of the above values. When the content of the doping element in the positive electrode active material is within the above range, an excellent fixing effect for active oxygen is achieved, the structural stability of the positive electrode active material is improved, and the consumption rate of the electrolyte on the positive electrode side is reduced, thereby further improving the high-temperature cycle characteristics of the electrochemical device.

[0063] There are no limitations on the method for doping Ni and / or Al into the positive electrode active material, and any preparation method applicable in the field can be used. For example, the modified positive electrode active material can be obtained by adding an aluminum-containing compound (e.g., Al2O3, Al(OH)3, AlF3) or a nickel-containing compound (e.g., NiO) to the positive electrode active material LiCoO2. In addition, by adjusting the amount of Ni and / or Al added to the positive electrode active material, the amount of Ni and / or Al added can be changed.

[0064] In some embodiments, the positive electrode active material layer further includes a binder and a conductive agent. In some embodiments, the binder in the positive electrode active material layer may include at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, styrene-acrylate copolymer, styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylic acid ester, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. In some embodiments, the conductive agent in the positive electrode active material layer may include at least one of conductive carbon black, acetylene black, ketjen black, flake graphite, graphene, carbon nanotubes, and carbon fibers. In some embodiments, the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode active material layer may be positive electrode active material:conductive agent:binder=(70 to 98):(1 to 15):(1 to 15). It should be understood that the above descriptions are merely examples, and the positive electrode active material layer may employ any other suitable materials, thicknesses, and mass ratios.

[0065] In some embodiments, the negative electrode may include a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector. The negative electrode active material layer may be provided on one or both sides of the negative electrode current collector. In some embodiments, the negative electrode current collector may be made of at least one of copper foil, aluminum foil, nickel foil, and a carbon-based current collector. In some embodiments, the thickness of the negative electrode current collector may be 1 μm to 200 μm. In some embodiments, the negative electrode active material layer may be applied to only a partial area of ​​the negative electrode current collector. In some embodiments, the thickness of the negative electrode active material layer may be 10 μm to 500 μm. It should be understood that this is merely an example and other suitable thicknesses may be used.

[0066] In some embodiments, the negative electrode active material layer includes a negative electrode active material. In some embodiments, the negative electrode active material in the negative electrode active material layer includes at least one of lithium metal, natural graphite, artificial graphite, and a silicon-based material. In some embodiments, the silicon-based material includes at least one of silicon, a silicon-oxygen compound, a silicon-carbon compound, and a silicon alloy.

[0067] In some embodiments, the negative electrode active material layer may further include a conductive agent and / or a binder. The conductive agent in the negative electrode active material layer may include at least one of carbon black, acetylene black, ketjen black, flake graphite, graphene, carbon nanotubes, carbon fibers, and carbon nanowires. In some embodiments, the binder in the negative electrode active material layer may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyacrylate, polyacrylic acid ester, polyvinylpyrrolidone, polyaniline, polyimide, polyamideimide, polysiloxane, styrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin, and polyfluorene. It should be understood that the above-disclosed materials are merely exemplary, and any other suitable materials may be employed in the negative electrode active material layer. In some embodiments, the mass ratio of the negative electrode active material, conductive agent, and binder in the negative electrode active material layer may be negative electrode active material:conductive agent:binder=(80-99):(0.5-10):(0.5-10). It should be understood that this is merely an example and is not intended to limit the invention.

[0068] In some embodiments, the separator includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene glycol terephthalate, polyimide, and aramid. For example, the polyethylene includes at least one of high-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene. In particular, polyethylene and polypropylene have a high short-circuit prevention effect and can improve battery stability through their shutdown effect. In some embodiments, the thickness of the separator is within a range of approximately 3 μm to 20 μm.

[0069] In some embodiments, the separator includes a porous substrate and an adhesive porous layer formed on at least one surface of the porous substrate, the adhesive porous layer including a polyvinylidene fluoride resin, which can improve the heat resistance, oxidation resistance, and electrolyte wettability of the separator and can enhance adhesion between the separator and the pole pieces.

[0070] In some embodiments, the weight-average molecular weight of the polyvinylidene fluoride resin is 600,000 to 3,000,000. In some embodiments, the weight-average molecular weight of the polyvinylidene fluoride resin is 1,000,000 to 2,000,000. When the weight-average molecular weight of the polyvinylidene fluoride resin is within the above range, the adhesive strength between the separator and the electrode is high, thereby improving the contact between them and providing excellent separator formability. In a wound cell equipped with a highly adhesive separator, the repulsion of the anode gradually increases as the cycle progresses, making it easier for the electrolyte to be extruded from corner regions. However, surprisingly, it has been discovered that a specific electrolyte of the present invention (containing 4% to 10% dinitrile compound) is particularly suitable for wound cells equipped with a highly adhesive separator, and the resulting electrochemical device exhibits excellent high-temperature cycling characteristics.

[0071] The present invention further provides an electronic device comprising an electrochemical device according to the present invention. The electronic device according to the present invention is not particularly limited and may be any known electronic device used in the prior art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-based computer, a mobile computer, an electronic book player, a mobile phone, a portable facsimile machine, a portable copier, a portable printer, a stereo headset, a video recorder, an LCD television, a portable vacuum cleaner, a portable CD player, a mini CD player, a walkie-talkie, an electronic notebook, a calculator, a memory card, a portable tape recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, an electric bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household storage battery, and a lithium-ion capacitor.

[0072] The preparation process for electrochemical devices and electronic devices is well known to those skilled in the art, and is not particularly limited in the present invention. A lithium-ion battery may be prepared, for example, by stacking a positive electrode and a negative electrode with a separator interposed therebetween, wrapping or folding the stack as necessary to place the stack in a case, injecting an electrolyte into the case, and sealing the case. Furthermore, an overcurrent protection element, lead plates, etc. may be provided in the case as needed to prevent an internal pressure rise in the lithium-ion battery and overcharging and discharging.

[0073] Hereinafter, a lithium ion battery will be taken as an example, and the preparation of a lithium ion battery will be described with reference to specific examples. Those skilled in the art should understand that the preparation method described in the present invention is merely exemplary, and any other suitable preparation method is also within the scope of the present invention. Example

[0074] In the following, examples and comparative examples of the lithium ion battery according to the present invention will be described, and performance evaluation will be carried out.

[0075] 1. Preparation of lithium-ion batteries 1. Preparation of the positive electrode For the undoped positive electrode active material, lithium cobalt oxide (LiCoO2) was used as the positive electrode active material.

[0076] Regarding the doped positive electrode active material, lithium cobalt oxide (LiCoO) and one or more oxides containing a doping element (e.g., a mixture of nickel oxide (NiO) and aluminum oxide (AlO)) were mixed and mixed in a high-speed mixer at 300 r / min for 20 minutes. The mixture was then placed in an air furnace, heated to 820°C at a rate of 5°C / min, and held for 24 hours. After natural cooling, the mixture was removed and passed through a 300-mesh sieve to obtain a modified positive electrode active material (i.e., modified lithium cobalt oxide).

[0077] The positive electrode active material, conductive carbon nanotubes (CNTs), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 95:2:3 (positive electrode active material:CNT:PVDF). N-methylpyrrolidone (NMP) was added as a solvent and the mixture was stirred with a vacuum stirrer until the mixture was homogeneous, resulting in a positive electrode slurry with a solids content of 75 wt%. The positive electrode slurry was uniformly applied to a 12 μm thick aluminum foil positive electrode current collector, dried at 85°C, and cold-pressed to obtain a positive electrode piece with a positive electrode active material layer thickness of 100 μm. The above process was then repeated on the other surface of the positive electrode piece, resulting in a positive electrode piece with a positive electrode active material layer coated on both sides. The positive electrode piece was cut to dimensions of 74 mm x 867 mm, tabs were welded, and it was then prepared for the next step. 2. Preparation of the negative electrode

[0078] Artificial graphite, styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 95:2:3, and deionized water was added as a solvent to prepare a slurry with a solids content of 70 wt%. The mixture was then uniformly stirred. The slurry was uniformly applied to one side of an 8 μm-thick copper foil, dried at 110°C, and cold-pressed to obtain a negative electrode piece with a 150 μm-thick negative electrode active material layer coated on one side. The above coating process was then repeated on the other surface of the negative electrode piece, resulting in a negative electrode piece with a negative electrode active material layer coated on both sides. The negative electrode piece was cut to a size of 74 mm x 867 mm, and a tab was welded. The Id / Ig ratio, which indicates the degree of defects in the negative electrode piece, was 0.17.

[0079] 3. Preparation of separator A polyethylene (PE) porous polymer film with a thickness of 15 μm was used as the separator.

[0080] 4. Preparation of electrolyte In an argon atmosphere glove box with a water content of less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were uniformly mixed in a weight ratio of EC:PC:DEC of 40-A:A:60 to prepare a base solvent. LiPF6 was added to the base solvent and stirred uniformly to prepare an electrolyte solution with a LiPF6 concentration of 12.5 wt% and a propylene carbonate content A set according to the requirements of each example and comparative example.

[0081] Depending on the settings of each Example or Comparative Example, an additional component was added to the base electrolyte to obtain an electrolyte solution.

[0082] 5. Preparation of Lithium-ion Battery The positive electrode pieces, separator, and negative electrode pieces were stacked in this order, with the separator interposed between the positive electrode pieces and the negative electrode pieces to act as an insulator, and then wound to obtain an electrode assembly. The L / D value was controlled by adjusting the winding parameters depending on the settings of each example or comparative example. The electrode assembly was placed in an aluminum plastic film packaging bag, and after removing moisture at 80°C, the prepared electrolyte was injected. The lithium-ion battery was obtained through processes such as vacuum packaging, standing, formation, and molding.

[0083] 2.Measurement method 1. How to measure the length of the flat part of the cell and the radius of the curved part A computed tomography (CT) scanner was used to scan the bend and body of the lithium-ion battery at 300% magnification to obtain cross-sectional images. The length of the first flat section was measured and recorded as L1, the length of the second flat section was measured and recorded as L2, and the larger of the two was recorded as the flat length L. The radius of the first curved section was measured and recorded as D1, and the radius of the second curved section was measured and recorded as D2, and the larger of the two was recorded as the curved radius D.

[0084] 2. Method for measuring the content of doping elements in positive electrode active material The active material was scraped off from the positive electrode pieces washed with dimethyl carbonate (DMC) using a scraper and dissolved in a mixed solvent (for example, 0.4 g of positive electrode active material was dissolved in a mixed solvent of 10 ml of aqua regia (a 1:1 mixture of nitric acid and hydrochloric acid) and 2 ml of HF), and the volume was adjusted to 100 ml. The content of metal elements such as Ni or Al in the solution was then measured using an ICP analyzer. The unit was ppm.

[0085] 3. Measurement method for cycle characteristics of lithium-ion batteries At 45°C, the lithium-ion battery was charged to 4.5 V at a rate of 0.7 C, then charged at a constant voltage of 0.05 C, and then discharged at a constant current of 1 C to 3.0 V. This constituted one charge-discharge cycle. The discharge capacity of the lithium-ion battery in the first cycle was recorded. The lithium-ion battery was then subjected to repeated charge-discharge cycles according to the method described above, and the discharge capacity of each cycle was recorded. The number of charge-discharge cycles at which the discharge capacity of the lithium-ion battery dropped to 80% of the discharge capacity of the first cycle was recorded.

[0086] 3. Measurement results Table 1 shows the effects of the ratio of the length of the flat part to the radius of the curved part of the cell (L / D), and the dinitrile compound and its content in the electrolyte on the high-temperature cycle characteristics of lithium-ion batteries.

[0087] [Table 1]

[0088] In Comparative Example 1, the content of the dinitrile compound in the electrolyte was too low, in Comparative Example 2, the content of the dinitrile compound in the electrolyte was too high, in Comparative Examples 3 and 4, not only was the L / D ratio of the cell too high, but the content of the dinitrile compound in the electrolyte was either too low or too high, and in Comparative Example 5, the L / D ratio of the cell was too low. In these Comparative Examples, the number of cycles was low, making it difficult to meet the usage requirements.

[0089] As shown in Examples 1 to 15, when the L / D ratio of the cell is within the range of 5 to 10 and the electrolyte contains 4% to 10% dinitrile compound, the lack of electrolyte in the corner region of the cell is suppressed at the structural level, the consumption of electrolyte at the negative electrode interface is reduced, and the rate of electrolyte loss in the corner region of the cell is significantly slowed, significantly increasing the cycle count of the lithium-ion battery and improving the high-temperature cycle performance of the lithium-ion battery.When the L / D ratio is within the range of 7 to 9 and L and D satisfy 5≦L≦30 and 1≦D≦5, or 10≦L≦20 and 1.5≦D≦2, the high-temperature cycle performance of the lithium-ion battery can be further improved.

[0090] Table 2 shows the influence of the doping elements and their contents in the positive electrode active material on the high-temperature cycle characteristics of lithium-ion batteries.

[0091] [Table 2]

[0092] As is clear from the results, when the positive electrode active material contains Ni and / or Al as a dopant, it reduces electrolyte shortage in the corner area, improves the structural stability of the positive electrode active material, and forms a more stable lithium ion transport interface on the surface of the positive electrode active material, thereby further improving the high-temperature cycle performance of the lithium ion battery.When the content of the dopant in the positive electrode active material is 3000 ppm to 5000 ppm, the lithium ion battery has better high-temperature cycle performance.

[0093] Table 3 shows the effect of propionate ester in the electrolyte on the high-temperature cycle characteristics of a lithium-ion battery. Examples 23 to 26 are identical to Example 3 except for the content of propyl propionate. Example 27 is identical to Example 17 except for the content of propyl propionate.

[0094] [Table 3]

[0095] The results show that the addition of a propionic acid ester (e.g., propyl propionate) to the electrolyte can enhance interface protection, further improve battery dynamics, suppress polarization, delay side reactions, and further improve the high-temperature cycling performance of lithium-ion batteries. When the amount of propionic acid ester added to the electrolyte is 20% to 60%, the lithium-ion battery has better high-temperature cycling performance.

[0096] Table 4 shows the effects of additives in the electrolyte on the high-temperature cycle characteristics of lithium-ion batteries. Examples 28 to 30 are identical to Example 3 except for the content of 1,3-propane sultone or 1,3,6-hexanetricarbonitrile. Example 31 is identical to Example 17 except for the content of 1,3-propane sultone or 1,3,6-hexanetricarbonitrile.

[0097] [Table 4]

[0098] As is clear from the results, the further addition of 1,3-propane sultone and / or trinitrile compounds (e.g., 1,3,6-hexanetricarbonitrile) to the electrolyte can synergistically construct a more stable electrode interface, reduce the occurrence of side reactions, and further improve the high-temperature cycle properties of lithium-ion batteries.

[0099] Throughout the specification, references to "in some embodiments," "in one embodiment," "another example," "an example," "embodiment," or "some examples" mean that at least one embodiment or example of the present invention includes the particular feature, structure, material, or characteristic described in that embodiment or example. Thus, the appearances of, for example, "in some embodiments," "in embodiments," "in one embodiment," "in other examples," "in one example," "in a particular example," or "example" throughout the specification do not necessarily refer to the same embodiment or example of the present invention. Furthermore, particular features, structures, materials, or characteristics herein may be combined in any suitable manner in one or more embodiments or examples.

[0100] Although illustrative embodiments have been disclosed and described, those skilled in the art should understand that the above-described embodiments are not to be construed as limiting the present invention, and that changes, substitutions, and alterations can be made to the embodiments without departing from the spirit, principle, and scope of the present invention.

Claims

1. 1. An electrochemical device comprising a cell, the cell includes a positive electrode, a negative electrode, an electrolyte, and a separator; The outermost electrode of the cell has a curved portion and a flat portion, and when the length of the flat portion is L mm and the radius of the curved portion is D mm, L and D satisfy 5≦L / D≦10, and The electrochemical device according to the present invention, wherein the electrolytic solution contains a dinitrile compound, and when the content of the dinitrile compound is A % relative to the mass of the electrolytic solution, A satisfies 4≦A≦10.

2. The electrochemical device according to claim 1 , wherein L and D satisfy the relationship 7≦L / D≦9.

3. L satisfies 5≦L≦30, or The electrochemical device according to claim 1 , wherein D satisfies 1≦D≦5.

4. L satisfies 10≦L≦20, or The electrochemical device according to claim 1 , wherein D satisfies 1.5≦D≦2.

5.

5. The dinitrile compound has the structure of Formula 1: 【Chemistry 1】 R １ , R ２ , R ３ , and R ４ are each independently selected from hydrogen, halogen, or a substituted or unsubstituted C1-C5 alkyl group; n is selected from an integer from 0 to 8, and 10. The electrochemical device of claim 1, wherein, when substituted, the substituents are halogens.

6. The dinitrile compound is the following compound: 【Chemistry 2】 The electrochemical device of claim 1 , comprising at least one of:

7. 2. The electrochemical device according to claim 1, wherein when the width of the cell is W mm, W satisfies 10≦W≦40.

8. the positive electrode includes a positive electrode active material, the positive electrode active material contains a doping element, the doping element is at least one selected from Ni and Al, The electrochemical device according to claim 1 , wherein when the content of the doping element is C ppm with respect to the mass of the positive electrode active material, C satisfies 3000≦C≦5000.

9. The electrolyte solution further comprises a propionic acid ester; the propionate ester comprises at least one of ethyl propionate, propyl propionate, butyl propionate, pentyl propionate, ethyl fluoropropionate, propyl fluoropropionate, butyl fluoropropionate, and pentyl fluoropropionate; 2. The electrochemical device according to claim 1, wherein when a content of the propionate ester is M % with respect to a mass of the electrolyte solution, M satisfies 20≦M≦60.

10. The electrolyte solution further includes at least one of 1,3-propane sultone, ethylene sulfate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and γ-butyrolactone; and The electrochemical device comprises: a) the content of the 1,3-propane sultone is 0.5% to 5% by mass of the electrolyte; b) the content of the ethylene sulfate is 0.1% to 1% by mass of the electrolyte; c) the content of the vinylene carbonate is 0.1% to 1% by mass of the electrolyte; d) the content of the dimethyl carbonate is 0.1% to 30% by mass of the electrolyte; e) the content of the diethyl carbonate is 0.1% to 30% by mass of the electrolyte; f) the content of the ethyl methyl carbonate is 0.1% to 30% by mass of the electrolyte; g) the content of the γ-butyrolactone is 0.01% to 5% by mass of the electrolyte; The electrochemical device according to claim 1 , wherein at least one of the following is satisfied:

11. The electrolyte solution further contains a trinitrile compound, and the trinitrile compound includes at least one of 1,3,5-pentanetricarbonitrile, 1,2,3-propanetricarbonitrile, 1,3,6-hexanetricarbonitrile, and 1,2,3-tris(2-cyanoethoxy)propane; 2. The electrochemical device according to claim 1, wherein the content of the trinitrile compound is 0.5% to 3% by mass of the electrolyte solution.

12. 12. The electrochemical device according to claim 11, wherein the content of the trinitrile compound is 1% to 2.5% by mass of the electrolyte solution.

13. the electrolyte solution further contains a lithium salt; 2. The electrochemical device of claim 1, wherein the lithium salt comprises at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, and lithium difluorophosphate.

14. The separator includes a porous substrate and a porous layer on a surface of the porous substrate, 2. The electrochemical device according to claim 1, wherein the porous layer contains polyvinylidene fluoride, and the weight average molecular weight of the polyvinylidene fluoride is 600,000 to 3,000,000.

15. An electronic device comprising an electrochemical device according to any one of claims 1 to 14.

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