Electrochemical and Electronic Devices

Abstract

The present invention relates to electrochemical devices and electronic devices. Specifically, the present invention provides an electrochemical device comprising a cell, the cell comprising a positive electrode, a negative electrode, an electrolyte, and a separator, the outermost electrode of the cell having a curved portion and a straight portion, the straight portion having a length L mm and a radius D mm, where L / D is 5≦L≦10, the electrolyte containing propylene carbonate, and the propylene carbonate content A % based on the mass of the electrolyte, where A % is 5≦A≦15. The electrochemical device of the present invention has significantly improved room temperature cycle performance.

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) have been widely applied in fields such as electrical energy storage, portable electronic devices, and electric transportation due to their characteristics of high specific energy, high operating voltage, low self-discharge rate, small volume, and light weight. As the application fields of lithium-ion batteries expand, people are placing higher demands on lithium-ion batteries, such as lighter, thinner, and longer service life. However, the lightweight and thin shape of batteries causes electrolyte loss at the corners of the cell structure, which negatively affects room temperature cycling performance.

[0003] In light of this, there is a need to provide electrochemical devices that can provide improved ambient temperature cycling performance. Summary of the Invention

[0004] SUMMARY OF THE INVENTION The present invention provides electrochemical and electronic devices that attempt to solve, at least in part, at least one problem present in the related art.

[0005] According to one aspect of the present invention, there is provided an electrochemical device, the 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 including a curved portion and a straight portion, where L mm is the length of the straight portion and D mm is the radius of the curved portion, and where L / D is 5≦L / D≦10, the electrolyte includes propylene carbonate, and where A % is the content of propylene carbonate based on the mass of the electrolyte, the ratio is 5≦A≦15.

[0006] By controlling the ratio between the length of the straight portion of the cell and the radius of the curved portion, it is possible to structurally suppress the loss of electrolyte in the corner regions of the cell, and by using an electrolyte containing a specific content of propylene carbonate, it is possible to reduce the consumption of electrolyte at the negative electrode interface and significantly slow down the rate of loss of electrolyte in the corner regions of the cell, thereby improving the room temperature cycle performance of the electrochemical device.

[0007] According to an embodiment of the present invention, 7≦L / D≦9.

[0008] According to an embodiment of the present invention, 5≦L≦30 or 1≦D≦5.

[0009] According to an embodiment of the present invention, 10≦L≦20 or 1.5≦D≦2.5.

[0010] According to an embodiment of the present invention, when the width of the cell is W mm, 10≦W≦40.

[0011] The cells having the above-mentioned widths are small in size, and by combining them with the specific electrolyte of the present invention (containing 5% to 15% propylene carbonate), the room temperature cycle performance of small-sized electrochemical devices can be more significantly improved.

[0012] 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 Ti, Mg, and Al, and the content of the doping element, defined as C ppm based on the mass of the positive electrode active material, is 7000≦C≦9000.

[0013] The positive electrode active material contains a specific content of a doping element, and the doping element is at least one selected from Ti, Mg, and Al, which is advantageous for improving the structural stability of the positive electrode active material, achieving an excellent fixing effect on active oxygen, and further reducing the consumption rate of the propylene carbonate-containing electrolyte in small-sized cells, thereby further improving the room-temperature cycle performance of the electrochemical device.

[0014] According to an embodiment of the present invention, 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, halogenated ethyl propionate, halogenated propyl propionate, halogenated butyl propionate, and halogenated pentyl propionate, where the content of the propionic acid ester, M %, based on the mass of the electrolyte, is 20≦M≦60.

[0015] By adding a certain content of propionic acid ester, the viscosity of the electrolyte can be obviously reduced, the fluidity of the electrolyte can be improved, and the electrolyte can be quickly replenished in the area where the electrolyte is locally deficient, thereby further improving the high-temperature cycle performance of the electrochemical device.

[0016] 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.

[0017] 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% based on the mass of the electrolyte; b) The content of ethylene sulfate is 0.1% to 1% based on the mass of the electrolyte; c) The content of vinylene carbonate is 0.1% to 1% based on the mass of the electrolyte; d) The content of dimethyl carbonate is 0.1% to 30% based on the mass of the electrolyte; e) The content of diethyl carbonate is 0.1% to 30% based on the mass of the electrolyte; f) The content of ethyl methyl carbonate is 0.1% to 30% based on the mass of the electrolyte; and g) The content of γ-butyrolactone is 0.01% to 5% based on the mass of the electrolyte solution.

[0018] Adding a specific amount of the above compound to the electrochemical device contributes to the construction of a stable interfacial film, further reducing the consumption rate of the electrolyte at the interface, and thereby further improving the high-temperature cycle performance of the electrochemical device.

[0019] 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%, preferably 1% to 2.5%, based on the mass of the electrolyte. By adding the trinitrile compound in the above content to the electrochemical device, the stronger adsorption energy of the trinitrile compound can be utilized to preferentially form a film on the electrode surface, significantly suppressing the occurrence of side reactions on the electrode surface, thereby further improving the high-temperature cycle performance of small cells.

[0020] 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 bisoxalate borate, lithium difluorooxalate borate, and lithium difluorophosphate.

[0021] According to another aspect of the present invention, there is provided an electronic device comprising an electrochemical device according to the present invention.

[0022] The present invention provides an electrochemical device and an electronic device that use a cell having a specific structure (5≦L / D≦10) in combination with a specific electrolyte (containing 5% to 15% propylene carbonate), thereby significantly improving the room temperature cycle performance of the electrochemical device.

[0023] Additional aspects and advantages of the present invention are set forth in part in the description that follows, and in part are illustrated by, or may be learned through the practice of embodiments of the present invention. [Brief explanation of the drawings]

[0024] In order to explain the embodiments of the present invention, the drawings necessary for explaining the embodiments of the present invention or the prior art will be briefly described below. 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 from the structures illustrated in these drawings without requiring any labor equivalent to an inventive step.

[0025] [Figure 1] FIG. 1 shows a structural schematic diagram of a cell according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] 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.

[0027] 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.

[0028] Electrochemical devices (e.g., lithium-ion batteries) are widely used in various fields due to their excellent performance. Certain fields have certain requirements for the shape of batteries. For example, with technological developments, mobile phones are becoming thinner and lighter, which requires thinner and lighter batteries, placing higher demands on the performance of flat-type batteries. The cell structure of flat-type batteries has a high corner area occupancy rate, which makes it easy for the electrolyte to be extruded from the corner areas, resulting in local electrolyte deficiency, blocking the transport of lithium ions, and adversely affecting the room-temperature cycle performance of electrochemical devices.

[0029] In order to improve the room temperature cycle performance of an electrochemical device, the present invention provides an electrochemical device, the electrochemical device comprising a cell, the cell comprising a positive electrode, a negative electrode, an electrolyte and a separator, the outermost electrode of the cell comprising a curved portion and a straight portion, the length of the straight portion being L mm and the radius of the curved portion being D mm, where L / D is 5≦L / D≦10, the electrolyte comprising propylene carbonate, and the content of the propylene carbonate based on the mass of the electrolyte being A%, where A is 5≦A≦15.

[0030] As used herein, "curved portion" and "straight portion" refer to portions of the outermost electrode of a wound cell (i.e., the electrode directly facing the package in which the cell is enclosed), and the curved and straight portions are alternately joined to form the outermost electrode of the wound cell. A "curved portion" refers to an arc-shaped portion of the outermost electrode of a wound cell, including a first curved portion consisting of a first arc and a second curved portion consisting of a second arc. A "straight portion" refers to a straight portion of the outermost electrode of a wound cell, i.e., a portion of the electrode between the first curved portion and the second curved portion, including a first straight portion and a second straight portion. A "radius of curvature" refers to the distance between the perpendicular bisector of the line segment between the two end points of the first (or second) arc of the first (or second) curved portion and the intersection point of this perpendicular bisector with the first (or second) arc. 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. The "length of the straight portion" refers to the longer of the lengths of the first straight portion and the second straight portion, since one of the first straight portion and the second straight portion is the end of the winding of the cell.

[0031] FIG. 1 shows a schematic diagram of a cell structure according to an embodiment of the present invention. The cell 100 includes a positive electrode 101, a negative electrode 102, and a separator 103 between the positive electrode 101 and the negative electrode 102. The wound cell is flat, and in the width (W) direction of the cell, the outermost electrode of the cell includes a first curved portion (left side), a second curved portion (right side), a first straight portion (upper side), and a second straight portion (lower side). The second curved portion, the first straight portion, the first curved portion, and the second straight portion are connected in this order to form the outermost electrode of the cell. The first curved portion is formed by a first arc along points A, C, and B. Here, point A is the intersection of the first curved portion and the first straight portion, and point B is the intersection of the first curved portion and the second straight portion. The second curved portion is formed by a second arc along points A′, C′, and B′. Here, point A' is the intersection point of the second curved portion and the first straight portion, and point B' is the intersection point of the second curved portion and the straight portion of the secondary outer electrode corresponding to the second straight portion. The first straight portion is formed by the line segment between point A and point A', and the second straight portion is formed by the line segment between point B and point B" (point B" is the end point of the outermost electrode). Points A and B are the endpoints of the first circular arc, point C is the intersection point of the perpendicular bisector of the line segment between point A and point B and the first circular arc, and the distance between point C and the perpendicular bisector of the line segment between point A and point B is the radius D1 of the first curved portion. Points A' and B' are the endpoints of the second circular arc, point C' is the intersection point of the perpendicular bisector of the line segment between points A' and B' and the second circular arc, and the distance between point C' and the perpendicular bisector of the line segment between points A' and B' is the radius D2 of the second curved portion. The larger of both curved portions D1 and D2 is the radius D of the curved portion (i.e., the radius D1 of the first curved portion in Figure 1). The length of the line segment between points A and A' is the length L1 of the first straight portion, and the length of the line segment between points B and B" is the length L2 of the second straight portion. The larger of both L1 and L2 is the length L of the straight portion (i.e., the length L1 of the first straight portion in Figure 1).

[0032] By controlling the ratio of the length of the straight section to the radius of the curved section of the cell, it is possible to structurally suppress electrolyte loss in the corner regions of the cell. Using an electrolyte containing a specific amount of propylene carbonate reduces electrolyte consumption at the negative electrode interface and significantly slows the rate of electrolyte loss in the corner regions of the cell. When a cell with a specific structure (5≦L / D≦10) is combined with a specific electrolyte (containing 5% to 15% propylene carbonate), the room-temperature cycle performance of the electrochemical device can be significantly improved.

[0033] In some embodiments, 7≦L / D≦9. In some embodiments, L / D is 5, 6, 7, 8, 9, 10, or within a range consisting of any two of the above values.

[0034] In some embodiments, 5≦L≦30. In some embodiments, 8≦L≦25. In some embodiments, 10≦L≦20. In some embodiments, 12≦L≦15. In some embodiments, L is 5, 8, 10, 12, 15, 18, 20, 22, 25, 28, 30, or within a range consisting of any two of the above values.

[0035] In some embodiments, 1≦D≦5. In some embodiments, 1.5≦D≦2.5. In some embodiments, D is 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or a range formed by any two of the foregoing values.

[0036] In some embodiments, 8≦A≦10. In some embodiments, A is 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or a range consisting of any two of the above values.

[0037] In some embodiments, the cell width, W mm, is 10≦W≦40. The cell width W is equal to the sum of the length L of the straight portion of the cell and the radius of the two curved portions (D1+D2 shown in FIG. 1). In some embodiments, W is 10, 15, 20, 25, 30, 35, 40, or within a range consisting of any two of the above values. Cells having such widths have smaller sizes, and the corner area of ​​small-sized cells is more occupied, resulting in more significant electrolyte extrusion. Surprisingly, the specific electrolyte of the present invention (containing 5% to 15% propylene carbonate) can exhibit superior effects in small-sized cells and can significantly improve the room-temperature cycling performance of small-sized electrochemical devices.

[0038] 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, halogenated ethyl propionate, halogenated propyl propionate, halogenated butyl propionate, and halogenated pentyl propionate. 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 depleted, thereby further improving the room temperature cycle performance of the electrochemical device.

[0039] In some embodiments, when the content of the propionate ester is M % based on the mass of the electrolyte, 20≦M≦60. In some embodiments, 30≦M≦50. In some embodiments, M is 20, 25, 30, 35, 40, 45, 50, 55, 60, or a range formed by any two of the above values. When M is within the above range, the electrolyte has excellent ion transport properties, thereby further improving the room temperature cycle performance of the electrochemical device.

[0040] 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 room-temperature cycle performance of the electrochemical device.

[0041] In some embodiments, the content of 1,3-propane sultone is 0.5% to 5% by weight of the electrolyte. In some embodiments, the content of 1,3-propane sultone is 1% to 3% by weight of the electrolyte. In some embodiments, the content of 1,3-propane sultone is 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range consisting of any two of the above values, based on the weight of the electrolyte.

[0042] 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%, 1%, or a range consisting of any two of the above values, based on the weight of the electrolyte.

[0043] In some embodiments, the content of vinylene carbonate is 0.1% to 1% by weight of the electrolyte. In some embodiments, the content of vinylene carbonate is 0.3% to 0.6% by weight of the electrolyte. In some embodiments, the content of vinylene carbonate is 0.1%, 0.3%, 0.5%, 0.8%, 1%, or a range consisting of any two of the above values, based on the weight of the electrolyte.

[0044] In some embodiments, the content of dimethyl carbonate is 0.1% to 30% by weight of the electrolyte solution. In some embodiments, the content of dimethyl carbonate is 0.5% to 25% by weight of the electrolyte solution. In some embodiments, the content of dimethyl carbonate is 1% to 20% by weight of the electrolyte solution. In some embodiments, the content of dimethyl carbonate is 5% to 15% by weight of the electrolyte solution. In some embodiments, the content of dimethyl carbonate is 10% to 12% by weight of the electrolyte solution. In some embodiments, the content of dimethyl carbonate is 0.1%, 0.5%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, or a range consisting of any two of the above values, based on the weight of the electrolyte solution.

[0045] 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%, 30%, or a range consisting of any two of the above values.

[0046] In some embodiments, the content of the ethyl methyl carbonate is 0.1% to 30% by weight of the electrolyte solution. In some embodiments, the content of the ethyl methyl carbonate is 0.5% to 25% by weight of the electrolyte solution. In some embodiments, the content of the ethyl methyl carbonate is 1% to 20% by weight of the electrolyte solution. In some embodiments, the content of the ethyl methyl carbonate is 5% to 15% by weight of the electrolyte solution. In some embodiments, the content of the ethyl methyl carbonate is 10% to 12% by weight of the electrolyte solution. In some embodiments, the content of the ethyl methyl carbonate is 0.1%, 0.5%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, or a range consisting of any two of the above values.

[0047] In some embodiments, the content of γ-butyrolactone is 0.01% to 5% by weight of the electrolyte solution. In some embodiments, the content of γ-butyrolactone is 0.05% to 3% by weight of the electrolyte solution. In some embodiments, the content of γ-butyrolactone is 0.1% to 2% by weight of the electrolyte solution. In some embodiments, the content of γ-butyrolactone is 0.5% to 1% by weight of the electrolyte solution. In some embodiments, the content of γ-butyrolactone is 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or a range consisting of any two of the above values, based on the weight of the electrolyte solution.

[0048] 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 improvement in the room temperature cycle performance of the electrochemical device.

[0049] In some embodiments, the electrolyte further comprises a trinitrile compound, the trinitrile compound being 1,3,5-pentanetricarbonitrile, i.e., [ka] , 1,2,3-propanetricarbonitrile, i.e. [ka] , 1,3,6-hexanetricarbonitrile, i.e. [ka] , and 1,2,3-tris(2-cyanoethoxy)propane, i.e. [ka] When the electrolyte solution contains a trinitrile compound, it contributes to further improvement of the room temperature cycle performance of the electrochemical device.

[0050] In some embodiments, the content of the trinitrile compound is 0.5% to 3% by weight of the electrolyte. In some embodiments, the content of the trinitrile compound is 1% to 2.5% by weight of the electrolyte. In some embodiments, the content of the trinitrile compound is 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or a range consisting of any two of the above values, based on the weight of the electrolyte.

[0051] 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 bisoxalatoborate, lithium difluorooxalatoborate, and lithium difluorophosphate.

[0052] In some embodiments, the content of the lithium salt is 10% to 15% by mass of the electrolyte. In some embodiments, the content of the lithium salt is 12% to 15% by mass 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 improving the room temperature cycle performance of the electrochemical device.

[0053] 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 may be located 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 these are merely examples, and other appropriate thicknesses may be used.

[0054] 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 Mnz 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 0≦y≦1, 0≦x≦1, 0≦z≦1, and x+y+z≦1. In some embodiments, the active cathode material can 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, and the active cathode material can be doped and / or coated.

[0055] In some embodiments, the positive electrode active material contains a doping element, and the doping element is at least one selected from Ti, Mg, and Al. The presence of Ti, Mg, and / or Al is advantageous for improving the structural stability of the positive electrode active material and contributes to further improving the room-temperature cycle performance of the electrochemical device.

[0056] In some embodiments, when the content of the doping element is C ppm based on the mass of the positive electrode active material, 7000≦C≦9000. In some embodiments, C is 7000, 7500, 8000, 8500, 9000, or 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, excellent fixation of active oxygen is achieved, improving the structural stability of the positive electrode active material. In particular, in small-sized cells, the consumption rate of the propylene carbonate-containing electrolyte can be further reduced, thereby further improving the room-temperature cycle performance of the electrochemical device.

[0057] The method for doping the positive electrode active material with Ti, Mg, and / or Al is not limited, and any applicable preparation method in this 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), a magnesium-containing compound (e.g., MgO), or a Ti-containing compound (e.g., TiO2) to the positive electrode active material LiCoO2. In addition, the amount of Ti, Mg, and / or Al doped in the positive electrode active material layer can be changed by adjusting the amount of Ti, Mg, and / or Al doped in the positive electrode active material.

[0058] 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-acrylic acid ester copolymer, styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylate, 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, layered graphite, graphene, carbon nanotubes, and carbon fibers. In some embodiments, the mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode active material layer may be (70 to 98):(1 to 15):(1 to 15). It should be understood that the above are merely examples, and the positive electrode active material layer may employ any other suitable materials, thicknesses, and mass ratios.

[0059] 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 portion 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 these are merely examples, and other appropriate thicknesses may be used.

[0060] 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.

[0061] 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, layered 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, polyacrylate, polyvinylpyrrolidone, polyaniline, polyimide, polyamideimide, polysiloxane, styrene butadiene rubber, epoxy resin, polyester resin, polyurethane resin, and polyfluorene. It should be understood that the materials disclosed above are merely exemplary, and any other suitable materials may be used in the negative electrode active material layer. In some embodiments, the mass ratio of the negative electrode active material, the conductive agent, and the binder in the negative electrode active material layer may be (80-99):(0.5-10):(0.5-10). It should be understood that this is for illustrative purposes only and is not intended to limit the invention.

[0062] In some embodiments, the separator includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, and aramid. For example, the polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene. In particular, polyethylene and polypropylene are effective in preventing short circuits and can improve battery stability through their shutdown effect. In some embodiments, the thickness of the separator is within the range of approximately 3 μm to 20 μm.

[0063] In some embodiments, the separator includes a porous substrate and an adhesive porous layer formed on at least one side of the porous substrate, the adhesive porous layer containing a polyvinylidene fluoride resin, which can improve the heat resistance, oxidation resistance, and electrolyte wettability of the separator and can improve adhesion between the separator and the pole pieces.

[0064] 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 adhesion between the separator and the electrode is high, improving the contact between them and the separator's moldability. In the case of a wound cell having a high-adhesion separator, the anode bounce gradually increases as the cycle progresses, making it easier for the electrolyte to be extruded from the corner regions. However, surprisingly, it has been found that the use of a specific electrolyte of the present invention (containing 5% to 15% propylene carbonate), particularly applicable to wound cells having a high-adhesion separator, results in electrochemical devices with excellent room-temperature cycle performance.

[0065] 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 can be applied to any electronic device known in the prior art. In some embodiments, the electronic device includes, 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 minidisc 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, a 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.

[0066] The preparation processes for electrochemical devices and electronic devices are well known to those skilled in the art and are not particularly limited in the present invention. For example, a lithium-ion battery can be produced by stacking a positive electrode and a negative electrode with a separator interposed therebetween, wrapping or folding the stack as necessary, placing 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 internal pressure buildup and overcharging / discharging of the lithium-ion battery.

[0067] Hereinafter, the preparation of a lithium ion battery will be described with reference to specific examples, taking a lithium ion battery as an example. Those skilled in the art should understand that the preparation methods described in the present invention are merely exemplary, and any other suitable preparation methods are within the scope of the present invention. Example

[0068] Hereinafter, performance evaluation of examples and comparative examples of the lithium ion battery according to the present invention will be described.

[0069] 1. Preparation of lithium-ion batteries 1. Preparation of the positive electrode Non-doped positive electrode active material: Lithium cobalt oxide (LiCoO2) was used as the positive electrode active material.

[0070] Doped positive electrode active material: Lithium cobalt oxide (LiCoO2) and one or more oxides containing doping elements (e.g., a mixture of magnesium oxide (MgO), titanium dioxide (TiO2), and aluminum oxide (Al2O3)) were mixed and mixed in a high-speed mixer at 300 r / min for 20 minutes. The mixture was then placed in an air kiln, heated to 820°C at 5°C / min, held for 24 hours, naturally cooled, removed, and sieved through a 300-mesh sieve to obtain a modified positive electrode active material (i.e., modified lithium cobalt oxide).

[0071] The positive electrode active material, conductive carbon nanotubes (CNTs) and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 95:2:3, and N-methylpyrrolidone (NMP) was added as a solvent. The mixture was stirred under a vacuum mixer 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 100 μm-thick positive electrode active material layer. The above steps were then repeated on the other surface of the positive electrode piece to obtain a positive electrode piece with a positive electrode active material layer coated on both sides. The positive electrode piece was cut into a 74 mm x 867 mm size and used after tab welding.

[0072] 2. Preparation of the negative electrode Artificial graphite, styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 95:2:3, and then deionized water was added as a solvent to prepare a slurry with a solids content of 70 wt%. The slurry was then uniformly mixed. The slurry was uniformly coated on one surface 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 step was then repeated on the other surface of the negative electrode piece to obtain a negative electrode piece with a double-sided negative electrode active material layer. The negative electrode piece was cut into a 74 mm x 867 mm size and tabs were welded for use. The defect level Id / Ig of the negative electrode piece was 0.17.

[0073] 3. Preparation of separator A 15 μm thick polyethylene (PE) porous polymer film was used as the separator.

[0074] 4. Preparation of electrolyte In a glove box with an argon gas atmosphere containing less than 10 ppm of water, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were mixed uniformly in a weight ratio of 40:60, and LiPF was added as the base solvent and stirred uniformly to form an electrolyte solution. The LiPF concentration was 12.5 wt%, and the propylene carbonate content A was set according to the requirements of each example and comparative example.

[0075] Depending on the settings of each example or comparative example, additional components were added to the base electrolyte to obtain an electrolyte solution.

[0076] 5. Preparation of Lithium-ion Battery The positive electrode pieces, separator, and negative electrode pieces were stacked in this order, with a separator positioned between the positive and negative electrode pieces to separate them, 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 outer bag, dehydrated at 80°C, and the prepared electrolyte was injected. A lithium-ion secondary battery was obtained through processes such as vacuum sealing, standing, formation, and shaping.

[0077] 2.Measurement method 1. How to measure the length of the straight part of the cell and the radius of the curved part Using an electron computed tomography (CT) scanner, the corners and the body of the lithium-ion battery were scanned at a magnification of 300% to obtain cross-sectional images. The length of the first straight section was measured as L1, the length of the second straight section was measured as L2, and the maximum of both was taken as the length of the straight sections, L. The radius of the first curved section was measured as D1, and the radius of the second curved section was measured as D2, and the maximum of both was taken as the radius of the curved sections, D.

[0078] 2. Method for measuring the content of doping elements in positive electrode active materials The active material of the positive electrode piece washed with dimethyl carbonate (DMC) was scraped off with a scraper, and dissolved in a mixed solvent (for example, 0.4 g of the 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. Then, the content (unit: ppm) of metal elements such as Ti, Mg, or Al in the solution was measured using an ICP analyzer.

[0079] 3. Measurement method for cycle performance of lithium-ion batteries At 25°C, the lithium-ion battery was charged to 4.5 V at a rate of 0.7 C, then charged at a constant voltage until the current reached 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 was recorded for the first cycle. The lithium-ion battery was then subjected to charge-discharge cycles according to the method described above. The discharge capacity of each cycle was recorded until the discharge capacity of the lithium-ion battery decayed to 80% of the discharge capacity of the first cycle, and the number of charge-discharge cycles was recorded.

[0080] 3. Measurement results Table 1 shows the influence of the ratio of the length of the straight part to the radius of the curved part (L / D) of the cell and the amount of propylene carbonate and its content in the electrolyte on the room temperature cycle performance of the lithium ion battery.

[0081] [Table 1]

[0082] The electrolyte in Comparative Example 1 does not contain propylene carbonate, the electrolyte in Comparative Example 2 contains excessive propylene carbonate, the L / D of the cell in Comparative Example 3 is too large, the L / D of the cell in Comparative Example 4 is not only too large but also contains excessive propylene carbonate in the electrolyte, and the L / D of the cell in Comparative Example 5 is too small, so these lithium ion batteries have low cycle times and are difficult to meet usage needs.

[0083] As shown in Examples 1 to 17, when the L / D ratio of the cell is within the range of 5 to 10 and the electrolyte contains 5% to 15% propylene carbonate, the cycle count of the lithium ion battery can be significantly increased and the room temperature cycle performance of the lithium ion battery can be improved. When the L / D ratio is within the range of 7 to 9 and 5≦L≦30 and 1≦D≦5, or 10≦L≦20 and 1.5≦D≦2, the room temperature cycle performance of the lithium ion battery can be further improved.

[0084] Table 2 shows the influence of the doping elements and their contents in the positive electrode active material on the room temperature cycle performance of lithium ion batteries.

[0085] [Table 2]

[0086] The results show that when the positive electrode active material contains Ti, Mg, and / or Al as doping elements, it can further reduce the consumption rate of the propylene carbonate-containing electrolyte in small-sized cells, stabilize the interface between the positive electrode and the electrolyte, and improve the room-temperature cycle performance of the lithium-ion battery.When the content of the doping elements in the positive electrode active material is 7000 ppm to 9000 ppm, the room-temperature cycle performance of the lithium-ion battery is more excellent.

[0087] Table 3 shows the effect of propionate ester in the electrolyte on the room temperature cycling performance of lithium-ion batteries. Examples 25-28 were the same as Example 3 except for the propyl propionate content. Example 29 was the same as Example 18 except for the propyl propionate content.

[0088] [Table 3]

[0089] The results show that when the cell's L / D ratio is within the range of 5-10, the electrolyte contains 5%-15% propylene carbonate, and a propionic acid ester (e.g., propyl propionate) is further added to the electrolyte, the electrolyte consumption rate is reduced, the electrolyte's fluid replenishment ability is further improved, localized electrolyte loss is delayed, and the room-temperature cycle performance of the lithium-ion battery is further improved. Furthermore, when the proportion of propionic acid ester in the electrolyte is 20%-60%, the room-temperature cycle performance of the lithium-ion battery is even better. At the same time, when the positive electrode contains a specific amount of doping element, the electrode interface stability is further improved, the electrolyte's side decomposition reaction is significantly reduced, and the room-temperature cycle performance of the lithium-ion battery is even better.

[0090] Table 4 shows the effect of additives in the electrolyte on the room temperature cycle performance of lithium-ion batteries. Examples 30 to 32 were set the same as Example 3, and Example 33 was set the same as Example 18, except that the content of 1,3-propane sultone or 1,3,6-hexanetricarbonitrile was different.

[0091] [Table 4]

[0092] The results show that adding 1,3-propane sultone and / or a trinitrile compound (e.g., 1,3,6-hexanetricarbonitrile) to the electrolyte not only slows down the electrolyte consumption rate but also forms a specific protective film on the surface of the positive electrode active material, further improving the room-temperature cycling performance of lithium-ion batteries. At the same time, when the positive electrode contains a specific amount of doping elements, a more stable electrode interface is established, suppressing the consumption of electrolyte components due to interfacial side reactions, thereby improving the room-temperature cycling performance of lithium-ion batteries.

[0093] Throughout the specification, references to "an embodiment," "some embodiments," "one embodiment," "another example," "an example," "a specific example," or "some of the examples" mean that at least one embodiment or example of the 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 another example," "in one example," "in a particular example," or "an example" throughout the specification do not necessarily refer to the same embodiment or example of the invention. Furthermore, particular features, structures, materials, or characteristics herein may be combined in any suitable manner in one or more embodiments or examples.

[0094] While illustrative embodiments have been disclosed and described, those skilled in the art should understand that the above embodiments cannot be construed as limiting the present invention, and that modifications, 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: the electrochemical device includes a cell; the cell includes a positive electrode, a negative electrode, an electrolyte, and a separator; the outermost electrode of the cell includes a curved portion and a straight portion; When the length of the straight portion is L mm and the radius of the curved portion is D mm, 5≦L / D≦10; the electrolyte solution contains propylene carbonate; An electrochemical device, wherein, when the content of the propylene carbonate is A % based on the mass of the electrolyte solution, 5≦A≦15.

2. 2. The electrochemical device of claim 1, wherein 7≦L / D≦9.

3. 2. The electrochemical device of claim 1, wherein 5≦L≦30 or 1≦D≦5.

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

5.

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

6. the positive electrode includes a positive electrode active material, The positive electrode active material includes a doping element, the doping element is at least one selected from Ti, Mg, and Al; The electrochemical device according to claim 1 , wherein the content of the doping element is 7000≦C≦9000 ppm based on the mass of the positive electrode active material.

7. 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, halogenated ethyl propionate, halogenated propyl propionate, halogenated butyl propionate, and halogenated pentyl propionate; 2. The electrochemical device according to claim 1, wherein, when the content of the propionate ester is defined as M % based on the mass of the electrolyte solution, 20≦M≦60.

8. 2. The electrochemical device of claim 1, wherein the electrolyte further comprises at least one of 1,3-propane sultone, ethylene sulfate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and γ-butyrolactone.

9. The electrochemical device comprises: a) the content of the 1,3-propane sultone is 0.5% to 5% based on the mass of the electrolyte; b) the content of the ethylene sulfate is 0.1% to 1% based on the mass of the electrolyte; c) the content of the vinylene carbonate is 0.1% to 1% based on the mass of the electrolyte; d) the content of the dimethyl carbonate is 0.1% to 30% based on the mass of the electrolyte; e) the content of the diethyl carbonate is 0.1% to 30% based on the mass of the electrolyte; f) the content of the ethyl methyl carbonate is 0.1% to 30% based on the mass of the electrolyte; and g) the content of the γ-butyrolactone is 0.01% to 5% based on the mass of the electrolyte solution.

10. The electrolyte solution further contains a trinitrile compound, 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% based on the mass of the electrolyte solution.

11. the electrolyte solution further contains a lithium salt; 10. 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 bisoxalatoborate, lithium difluorooxalatoborate, and lithium difluorophosphate.

12. An electronic device comprising an electrochemical device according to any one of claims 1 to 11.

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