CN111525194A

CN111525194A - Electrochemical device and electronic device including the same

Info

Publication number: CN111525194A
Application number: CN202010349336.4A
Authority: CN
Inventors: 刘晓静
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2020-04-28
Filing date: 2020-04-28
Publication date: 2020-08-11
Anticipated expiration: 2040-04-28
Also published as: CN111525194B; CN114899361A

Abstract

The present application relates to an electrochemical device and an electronic device including the same. The electrochemical device includes: anodal, barrier film and negative pole, wherein the negative pole includes: the negative pole current collector, negative pole active material layer and negative pole utmost point ear, and the negative pole utmost point ear sets up on the major axis side of negative pole current collector and contacts with negative pole active material layer. The anode active material layer comprises a silicon-based material, the distance between the center position of the anode tab and any one end of the anode active material layer in the long axis direction is a first length, the length of the long axis of the anode active material layer is a second length, and the anode satisfies the following relational expression: d is more than or equal to 0.5 and more than or equal to 0.6 XG, wherein D is the ratio of the first length to the second length, G is the weight ratio of the silicon-based material, and the weight ratio of the silicon-based material is less than or equal to 70 percent. The electrochemical device can effectively reduce the impedance of the negative electrode and control the temperature of the battery core to be increased, and then the cyclic expansion rate of the electrochemical device is reduced and the cycle performance of the electrochemical device is improved.

Description

Electrochemical device and electronic device including the same

Technical Field

The present disclosure relates to the field of energy storage technologies, and particularly to a negative electrode structure, and an electrochemical device and an electronic device including the negative electrode structure.

Background

With the rapid development of mobile electronic technology, the frequency and experience requirements of people using mobile electronic devices such as mobile phones, tablets, notebook computers, unmanned planes and the like are higher and higher. Therefore, electrochemical devices (e.g., lithium ion batteries) that provide energy sources for electronic devices are required to exhibit higher energy density, greater rate, higher safety, and less capacity fade after repeated charge and discharge processes.

The energy density and cycling performance of an electrochemical device are closely related to its negative electrode material. Currently, since a silicon-based material of at least one of silicon-based simple substance, alloy, or compound thereof has a high theoretical gram capacity, the use of the silicon-based material instead of the existing graphite material is being widely studied. However, since the silicon-based material has problems of low conductivity and high expansion rate at high temperature, there is a need for further improvement and optimization of the structure of the negative electrode having the silicon-based material.

Disclosure of Invention

The present application provides an electrochemical device and an electronic device including the same in an attempt to solve at least one of the problems existing in the related art to at least some extent.

According to one aspect of the present application, there is provided an electrochemical device including: positive electrode, barrier film and negative pole, wherein the negative pole includes: negative current collector, negative active material layer and negative pole utmost point ear. The negative pole active material layer contains silicon-based material, just the negative pole utmost point ear set up in on the major axis side of the negative pole mass flow body and with the negative pole active material layer contacts, wherein the negative pole utmost point ear set up in on the major axis side of the negative pole mass flow body, the central point of negative pole utmost point ear put with the arbitrary end of negative pole active material layer is first length in the ascending distance of major axis direction, the major axis length of negative pole active material layer is the second length, just the negative pole satisfies following relational expression (I):

d is more than or equal to 0.5 and more than or equal to 0.6 XG formula (I), wherein D is the ratio of the first length to the second length, G is the weight ratio of the silicon-based material, and the weight ratio of the silicon-based material is less than or equal to 70%.

This application electrochemical device satisfies the above negative pole utmost point ear that sets up through the adoption, and the impedance that can effectual reduction negative pole and the temperature of control electric core promote, and then reduces electrochemical device's cyclic expansion rate and improve its cyclicity.

According to another aspect of the present application, there is provided an electronic device comprising the electrochemical device described above.

Additional aspects and advantages of embodiments of the present application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of embodiments of the present application.

Drawings

Drawings necessary for describing embodiments of the present application or the prior art will be briefly described below in order to describe the embodiments of the present application. It is to be understood that the drawings in the following description are only some of the embodiments of the present application. It will be apparent to those skilled in the art that other embodiments of the drawings can be obtained from the structures illustrated in these drawings without the need for inventive work.

Fig. 1 is a schematic cross-sectional view of a negative electrode structure according to the prior art.

Fig. 2 is a schematic top view of a negative electrode structure according to the prior art.

Fig. 3 is a schematic diagram of a winding type cell structure according to the prior art.

Fig. 4 is a schematic cross-sectional view of a negative electrode structure according to an embodiment of the present application.

Fig. 5 is a schematic top view of an anode structure according to an embodiment of the present disclosure.

Fig. 6 is a schematic view of a winding-type cell structure according to an embodiment of the present application.

Fig. 7 is a schematic view of current distribution of the negative electrode tab disposed at two ends of the long axis of the negative electrode.

Fig. 8 is a schematic view of current distribution in which a negative electrode tab is provided in the middle portion of the long axis of the negative electrode.

Fig. 9 shows a three-dimensional graph of the arrangement position of the negative electrode tab and the silicon-based material content in the negative electrode active material layer with the increase in cell temperature according to an example of the present application.

Detailed Description

Embodiments of the present application will be described in detail below. Throughout the specification, the same or similar components and components having the same or similar functions are denoted by like reference numerals. The embodiments described herein with respect to the figures are illustrative in nature, are diagrammatic in nature, and are used to provide a basic understanding of the present application. The embodiments of the present application should not be construed as limiting the present application.

As used herein, the terms "substantially", "substantially" and "about" are used to describe and illustrate minor variations. When used in conjunction with an event or circumstance, the terms can refer to instances where the event or circumstance occurs precisely as well as instances where the event or circumstance occurs in close proximity. For example, when used in conjunction with numerical values, the term can refer to a range of variation that is less than or equal to ± 10% of the stated numerical value, such as less than or equal to ± 5%, less than or equal to ± 4%, less than or equal to ± 3%, less than or equal to ± 2%, less than or equal to ± 1%, less than or equal to ± 0.5%, less than or equal to ± 0.1%, or less than or equal to ± 0.05%. For example, two numerical values are considered to be "substantially" identical if the difference between the two numerical values is less than or equal to ± 10% (e.g., less than or equal to ± 5%, less than or equal to ± 4%, less than or equal to ± 3%, less than or equal to ± 2%, less than or equal to ± 1%, less than or equal to ± 0.5%, less than or equal to ± 0.1%, or less than or equal to ± 0.05%) of the mean of the values.

In this specification, unless specified or limited otherwise, relative terms such as: terms of "central," "longitudinal," "lateral," "front," "rear," "right," "left," "inner," "outer," "lower," "upper," "horizontal," "vertical," "above," "below," "top," "bottom," and derivatives thereof (e.g., "horizontally," "downwardly," "upwardly," etc.) should be construed to refer to the orientation as then described in the discussion or as shown in the drawing figures. These relative terms are for convenience of description only and do not require that the present application be constructed or operated in a particular orientation.

Additionally, amounts, ratios, and other numerical values are sometimes presented herein in a range format. It is to be understood that such range format is used for convenience and brevity, and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited.

In the detailed description and claims, a list of items linked by the term "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items a and B are listed, the phrase "at least one of a and B" means a only; only B; or A and B. In another example, if items A, B and C are listed, the phrase "at least one of A, B and C" means a only; or only B; only C; a and B (excluding C); a and C (excluding B); b and C (excluding A); or A, B and C. Item a may comprise a single element or multiple elements. Item B may comprise a single element or multiple elements. Item C may comprise a single element or multiple elements.

The silicon-based material has semiconductor property, and the powder conductivity of the silicon-based material is far less than that of the existing graphite material, so that the impedance of the negative electrode material containing the silicon-based material is larger regardless of electrons or ions. In the charge-discharge cycle process, especially under the high-rate charge-discharge condition, the internal impedance of the electrical core containing the silicon-based material is high, so that the heat generation energy consumption of the electrical core is increased, the temperature of the electrical core is obviously increased, the reduction of the electrochemical properties such as the acceleration of the cycle capacity attenuation, the reduction of the discharge rate and the like is further caused, and the thermal runaway of an electrochemical device can be caused to cause potential safety hazards.

Fig. 1 and 2 are schematic cross-sectional and top views of a commercially available negative electrode structure in the prior art. Fig. 3 shows a schematic diagram of a prior art cell in a winding structure.

As shown in fig. 1 and 2, the negative active material layer 102 in the related art is disposed on the surface of the negative current collector 101, and at both ends of the negative current collector 101 in the length direction, there are empty foil regions where the negative active material layer 102 is not disposed, and the negative tab 103 is disposed in an uncoated region at one end of the negative current collector. The winding structure of the cell formed by winding the negative electrode, the positive electrode and the isolation film 107 is as shown in fig. 3, in the prior art, the negative electrode tab 103 is arranged in an empty foil area at one end of the negative electrode current collector 101, and the positive electrode tab 106 is arranged in an empty foil area at one end of the positive electrode current collector 104 without the positive electrode active material layer 105, so that the negative electrode tab 103 and the positive electrode tab 106 are positioned in the middle of the cell in the winding process. However, when a negative active material (e.g., a silicon-based material) having a high gram-volume is used, the greater the silicon-based material content of the negative active material, the smaller the electrical conductivity of the negative material layer, resulting in an increase in the internal resistance of the negative electrode and an increase in the heat-generating power, thereby reducing the cycle performance of the electrochemical device and implying a safety problem of runaway overheating. In addition, providing empty foil regions on the positive and negative electrodes can reduce the energy density of the electrochemical device.

According to one aspect of the application, the position of a cathode tab and the content of a silicon-based material are limited to reduce impedance in a cathode active material layer, and the current density of each part in the cathode is improved, so that the thermal power generated by internal resistance of the cathode during charge and discharge cycles is reduced, and the cycle performance and the safety performance of an electrochemical device are improved.

Fig. 4 and 5 are schematic sectional and top views of a negative electrode structure according to some embodiments of the present invention.

As shown in fig. 4 and 5, the present application provides a negative electrode including: the negative electrode current collector 201, the negative electrode active material layer 202, and the negative electrode tab 203 is disposed on the long axis side of the negative electrode current collector 201 and contacts with the negative electrode active material layer 202. The anode active material layer 202 includes a silicon-based material, wherein the distance between the center position of the anode tab 203 and either end of the anode active material layer 202 in the long axis direction is a first length 204, and the long axis length of the anode active material layer is a second length 205. The above negative electrode satisfies the following relational expression (I):

d is more than or equal to 0.5 and more than or equal to 0.6 XG of the formula (I).

Where D is a ratio of the first length 204 to the second length 205, G is a weight ratio of the silicon-based material in the negative electrode active material layer 202, and the weight ratio G of the silicon-based material is less than or equal to 70%.

An electrochemical device having a negative electrode according to the above relation (I) enables the temperature increase of less than 15 ℃ during operation due to the charge-discharge cycle. Compared with the prior art, the negative pole of this application can effectually reduce the conduction distance that partial current passes through negative pole active material layer in negative pole active material layer at the charge-discharge cycle in-process, and then reduces the internal impedance of negative pole itself and the current density in pole piece district around the negative pole utmost point ear, helps reducing its electric core polarization. In other embodiments, when the weight ratio G of the silicon-based material is greater than 70%, the temperature of the electrochemical device, which is increased during operation due to charge and discharge cycles, can still be reduced by centering the center of the anode tab 203 in the center of the anode active material layer 202 (i.e., when the ratio D of the first length 204 to the second length 205 is 0.5).

In some embodiments, as shown in fig. 4, the negative electrode satisfies the following relationship (II):

0.9×(S₁+2S₃)≤S₁+S₂≤1.1×(S₁+2S₃) A compound of the formula (II),

wherein the negative electrode current collector 201 has a thickness S₁The thickness of the negative electrode tab 203 is S₂The thickness of the anode active material layer 202 is S₃. Through the arrangement, the thickness of the negative pole piece can be more uniform. When the electrode plate is wound or stacked to form the battery cell, the defects of protrusion or recess and the like caused by uneven thickness of the electrode plate can be avoided, the structural stability of the battery cell in the circulating process is improved, and the safety performance and the circulating performance of the electrochemical device are improved.

In some embodiments, as shown in fig. 5, the negative active material layer 202 further comprises a groove 206, the groove 206 being defined by the negative active material layer 202 and exposing a portion of the negative current collector 201, wherein the negative tab 203 is disposed in the groove. In other embodiments, an insulating material and/or a bonding material may be disposed in the groove and around the anode tab 203 to prevent short circuits caused by contact of the anode tab with the positive active material layer or the positive tab. It is to be understood that the insulating material and the bonding material may be any suitable material commonly found in the art.

Fig. 7 and 8 are schematic views of current distribution of the negative electrode tabs respectively disposed at two ends and a middle portion of the long axis of the negative electrode.

The ohmic heat Q of the current passing through the current collector and its corresponding resistance value R can be calculated for each part of the negative current collector by the following formula:

Q_i＝I_i ²*R_i*t，

R_i＝ρ*dx/A，

wherein Qi is the current thermal power of each part of the negative current collector, Ri is the impedance of each part of the negative current collector, t is the current circulation time, ρ is the resistivity of the negative current collector, dx is the length of each part of the negative current collector, and a is the cross-sectional area of the negative current collector. As shown in fig. 7, when the negative electrode tab is disposed near one end of the current collecting body, X, which is the farthest end from the negative electrode tab_nPartial current derived from part of the cathode current collector needs to pass through X of the cathode current collector₁Moiety to X_nMoiety from X₃Part of the derived current needs to pass through X of the negative current collector₁Moiety to X₃And (4) partial. When the external discharge current is I and the reaction current of each section is Ia, X passing through the negative current collector₁Part of the current is n X Ia, X through the negative current collector₂Part of the current is (n-1) Ia, X through the negative current collector₃Part of the current is (n-2) Ia, X through the negative current collector_nThe partial current is Ia.

As shown in fig. 8, when the anode tab is disposed at the middle portion of the anode current collector, X, which is farthest from the anode tab_n/2Partial current derived at part only needs to pass through X₁Moiety to X_n/2Moiety of the other end X_n/2The partial current derived at the' part also only needs to pass through X₁' moiety to X_n/2Part (c). Under the intensity of the same discharge current, the negative electrode structure can effectively reduce the current intensity through the negative electrode current collector in the discharge process, further reduce the internal impedance of the negative electrode, reduce the overheating temperature rise condition of the negative electrode, and simultaneously avoid the thermal expansion condition of the silicon-based material in the negative electrode material.

In some embodiments, the negative electrode current collector 201 may be a copper foil or a nickel foil, however, other negative electrode current collectors commonly used in the art may be employed without limitation.

In some embodiments, the negative current collector 201 has a thickness of about 4 μm to about 30 μm. In other embodiments, the thickness of the negative current collector 201 is approximately, for example, about 4.0 μm, about 5.0 μm, about 10.0 μm, about 15.0 μm, about 20.0 μm, about 25.0 μm, about 30.0 μm, or a range consisting of any two of these values.

The anode active material layer 202 contains an anode material capable of absorbing and releasing lithium (Li) (hereinafter, sometimes referred to as "anode material capable of absorbing/releasing lithium Li") in addition to a silicon-based material. Examples of the material capable of absorbing/releasing lithium (Li) may include carbon materials, metal compounds, oxides, sulfides, lithium nitrides such as LiN3, lithium metal, metals and polymer materials that form alloys with lithium. In some embodiments, the silicon-based material comprises at least one of a simple substance of silicon, a compound of silicon, an alloy of silicon, and a silicon oxygen material. In some embodiments, the silicon oxygen material is of the general formula SiO_xSilicon oxide is represented wherein x is from about 0.5 to about 1.5 and the silicon oxygen material comprises crystalline, amorphous, or a combination thereof.

In some embodiments, the silicon-based material further comprises a material layer disposed on at least a portion of a surface of the silicon-based material, the material layer comprising at least one of a polymer, an inorganic particle, amorphous carbon, or a carbon nanotube.

In some embodiments, the inorganic particles comprise at least one of lithium cobaltate, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, elemental silicon, a compound of silicon, an alloy of silicon, and a silicone material, and the polymer comprises at least one of polyvinylidene fluoride, polyacrylic acid, polyvinyl chloride, carboxymethyl cellulose, polyethylene, polypropylene, polyethylene terephthalate, polyimide, and aramid.

In some embodiments, the weight ratio G of the silicon-based material in the negative active material layer is greater than about 0% and less than or equal to about 70%, based on the total weight of the negative active material layer. In other embodiments, the weight ratio G of the silicon-based material in the negative active material layer is approximately, for example, about 0%, about 10%, about 20%, about 30%, about 50%, about 70%, or a range consisting of any two of these values.

In some embodiments, a ratio of a long axis length of the negative active material layer to a long axis length of the negative current collector is about 0.8 to about 1.0. In other embodiments, the ratio of the length of the major axis of the negative active material layer to the length of the major axis of the negative current collector is about 0.9 to about 0.95. Through eliminating the area that the negative pole active material layer of negative pole mass flow body both ends set up the district to and the empty paper tinsel area of negative pole utmost point ear department, can effectively increase the utilization ratio of the negative pole mass flow body, further promoted its electrochemical device's energy density.

According to another aspect of the present application, there is provided an electrochemical device comprising the anode of the present application. In some embodiments, the electrochemical device is a lithium ion battery. The lithium ion battery includes: the negative electrode of the above embodiment, wherein the separator is disposed between the positive electrode and the negative electrode.

Fig. 6 is a schematic view illustrating a cell in a winding structure of an electrochemical device according to some embodiments of the present disclosure.

As shown in fig. 6, in some embodiments, the electrochemical device is a roll-to-roll structure in which a positive electrode, a negative electrode and a separator are sequentially stacked and rolled, the negative electrode includes a negative electrode current collector 201, a negative electrode active material layer 202 and a negative electrode tab 203, and the negative electrode tab 203 is disposed at a position other than three layers from the center of the roll-to-roll structure.

In some embodiments, the positive electrode tab 209 of the positive electrode is disposed at a position one layer inward or outward from the center of the wound structure from the position of the negative electrode tab 203. The risk of short circuit between the positive electrode tab 209 and the negative electrode tab 203 can be reduced by separating the positive electrode tab 209 and the negative electrode tab 203 by one layer.

In some embodiments, the negative electrode tab of the present application is disposed on the negative current collector by welding the negative electrode tab to the location of the disposition on the negative current collector. The arrangement part is formed by ultrasonically cleaning the negative electrode active material layer, so that the problem of watermarks of the positive electrode and the negative electrode of a commercial electrochemical device when coating the positive electrode active material layer and the negative electrode active material layer does not exist, the distance between the arrangement part of the welded negative electrode current collector and the negative electrode lug can be reduced, and the impedance at the negative electrode lug can be further reduced.

In some embodiments, as shown in fig. 6, the anode active material layer 202 and the cathode active material layer 208 further comprise a groove 206, the groove 206 being defined by the anode active material layer 202 or the cathode active material layer 208 and exposing a portion of the anode current collector 201 or the cathode current collector 207, wherein the groove is disposed around the anode tab 203 or the cathode tab 209. In other embodiments, the groove 206 can be further disposed in a region 206' of the positive or negative material layer corresponding to the negative or

positive tab

203 or 209. In other embodiments, an insulating material and/or an adhesive material can be disposed in the recess 206 and fill the recess. It is to be understood that the insulating material and the bonding material may be any suitable material commonly found in the art. Through above-mentioned recess, insulating material and bonding material setting, can further reduce the risk of electric core structure short circuit.

In some embodiments, the positive electrode further includes a positive current collector 207 and a positive active material layer 208.

In some embodiments, the positive electrode current collector 207 may be an aluminum foil or a nickel foil, however, other materials commonly used in the art may be used as the positive electrode current collector without limitation.

The positive electrode active material layer 208 contains a positive electrode material capable of absorbing and releasing lithium (Li) (hereinafter, sometimes referred to as "a positive electrode material capable of absorbing/releasing lithium Li"). In some embodiments, the positive electrode material capable of absorbing/releasing lithium (Li) may include one or more of lithium cobaltate, lithium nickel cobalt manganese, lithium nickel cobalt aluminate, lithium manganate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadyl phosphate, lithium iron phosphate, lithium titanate, and a lithium-rich manganese-based material.

In the above positive electrode material, the chemical formula of lithium cobaltate may be Li_yCo_aM1_bO_2-cWherein M1 represents at least one selected from the group consisting of nickel (Ni), manganese (Mn), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), tungsten (W), yttrium (Y), lanthanum (La), zirconium (Zr), and silicon (Si), and Y, a, B, and c values are respectively in the following ranges: y is more than or equal to 0.8 and less than or equal to 1.2, a is more than or equal to 0.8 and less than or equal to 1, b is more than or equal to 0 and less than or equal to 0.2, and c is more than or equal to-0.1 and less than or equal to 0.2;

in the above cathode material, the chemical formula of lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminate may be Li_zNi_dM2_eO_2-fWherein M2 represents at least one selected from the group consisting of cobalt (Co), manganese (Mn), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), tungsten (W), zirconium (Zr) and silicon (Si), and z, d, e and f values are respectively in the following ranges: z is more than or equal to 0.8 and less than or equal to 1.2, d is more than or equal to 0.3 and less than or equal to 0.98, e is more than or equal to 0.02 and less than or equal to 0.7, and f is more than or equal to 0.1 and less than or equal to 0.2;

in the cathode material, the chemical formula of lithium manganate is Li_uMn_2-gM_3gO_4-hWherein M3 represents at least one selected from the group consisting of cobalt (Co), nickel (Ni), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), and tungsten (W), and z, g, and h values are respectively in the following ranges: u is more than or equal to 0.8 and less than or equal to 1.2, and g is more than or equal to 0<H is more than or equal to 1.0 and less than or equal to-0.2 and less than or equal to 0.2.

In some embodiments, the positive electrode can further include at least one of a binder and a conductive agent. It is to be understood that those skilled in the art can select the binder and the conductive agent, which are conventional in the art, according to actual needs without being limited thereto.

In some embodiments, the release film includes, but is not limited to, at least one selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate, polyimide, and aramid. For example, the polyethylene includes at least one component selected from the group consisting of high density polyethylene, low density polyethylene, and ultra high molecular weight polyethylene. In particular polyethylene and polypropylene, which have a good effect on preventing short circuits and can improve the stability of lithium ion batteries by means of a shutdown effect.

The electrochemical device of the present application further includes an electrolyte, which may be one or more of a gel electrolyte, a solid electrolyte, and an electrolytic solution including a lithium salt and a non-aqueous solvent.

In some embodiments, the lithium salt is selected from LiPF₆、LiBF₄、LiAsF₆、LiClO₄、LiB(C₆H₅)₄、LiCH₃SO₃、LiCF₃SO₃、LiN(SO₂CF₃)₂、LiC(SO₂CF₃)₃、LiSiF₆One or more of LiBOB and lithium difluoroborate. For example, the lithium salt is LiPF₆Since it can give high ionic conductivity and improve cycle characteristics.

The non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvent, or a combination thereof.

The carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluoro carbonate compound, or a combination thereof.

Examples of such other organic solvents are dimethylsulfoxide, 1, 2-dioxolane, sulfolane, methyl sulfolane, 1, 3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters and combinations thereof.

In some embodiments, the non-aqueous solvent is selected from the group consisting of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, methyl acetate, ethyl propionate, fluoroethylene carbonate, and combinations thereof.

It is to be understood that the methods for preparing the positive electrode, the negative electrode, the separator, and the lithium ion battery in the examples of the present application may be any suitable conventional method in the art according to specific needs without departing from the spirit of the present application, and are not limited thereto. In one embodiment of the method of manufacturing an electrochemical device, the method of manufacturing a lithium ion battery includes: the positive electrode, the separator and the negative electrode in the above embodiments are sequentially wound into a cell, the cell is placed in, for example, an aluminum plastic film, and an electrolyte is injected, followed by vacuum packaging, standing, formation, shaping and other processes, so as to obtain the lithium ion battery.

The cell of the electrochemical device of the present application includes not only the winding structure, but also, in some embodiments, the cell of the electrochemical device of the present application includes a lamination structure and a folding structure.

Although illustrated above as a lithium ion battery, one skilled in the art will appreciate after reading this application that the negative electrode of the present application may be used in other suitable electrochemical devices. Such an electrochemical device includes any device in which electrochemical reactions occur, and specific examples thereof include all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

Some embodiments of the present application further provide an electronic device comprising the electrochemical device in the embodiments of the present application.

The electronic device of the embodiment of the present application is not particularly limited, and may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a cellular phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a handheld cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notebook, a calculator, a memory card, a portable recorder, a radio, a backup power source, a motor, an automobile, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game machine, a clock, a power tool, a flashlight, a camera, a large household battery, a lithium ion capacitor, and the like.

Examples

Some embodiments are listed below, and a direct current resistance test, a discharge rate test, a cycle performance test, and a cell surface temperature rise test are respectively performed on an electrochemical device (lithium ion battery) of the embodiment to better describe the technical scheme of the present application.

Test method

1.1 direct current resistance test:

the direct current resistance is calculated by the following formula, where R ═ U_0.1C-U_1C)/(I_1C-I_0.1C) Wherein R is a direct current resistance, I_1CIs the current of a lithium ion battery with a discharge rate of 1C, I_0.1CIs the current of the lithium ion battery with the discharge rate of 0.1C, U_1CThe terminal voltage, U, of the lithium ion battery after 1 second of discharge at a discharge rate of 1C_0.1CThe end voltage of the lithium ion battery after 10 seconds of discharge at a discharge rate of 0.1C. Direct current resistance test flow: after the lithium ion batteries of the following examples were fully charged, they were discharged at a constant current of 0.1C for 10 seconds, and the current I was recorded_0.1CAnd terminal voltage U_0.1CThen discharged at constant current of 1C for 1 second, and the current I is recorded_1CAnd terminal voltage U_1C. And 4 lithium ion batteries are taken for testing each group, and the average value of the direct current resistance of the lithium ion batteries is calculated.

1.2 discharge rate test:

the lithium ion battery of the following example was placed in a thermostat of 25 ℃. + -. 2 ℃ and left to stand for 2 hours, charged at a constant current of 0.5C to 4.35V, then charged at a constant voltage of 4.35V to 0.05C and left to stand for 15 minutes; then the discharge was carried out at a constant current of 0.2C to 3.0V. Then the lithium ion battery is charged to 4.35V at a constant current of 0.5C, then charged to 0.05C full charge at a constant voltage of 4.35V, and then discharged to 3.0V at a constant current of 1.0C. And recording the discharge capacity of the lithium ion battery discharged at a constant current of 0.2C and discharged at a constant current of 1.0C.

And 4 lithium ion batteries are taken for testing each group, and the average value of the discharge multiplying power of the lithium ion batteries is calculated. The discharge rate was 1.0C discharge capacity (mAh) for constant current discharge/0.2C discharge capacity (mAh) for constant current discharge.

1.3 cycle performance test:

the lithium ion battery of the following example was placed in a thermostat of 25 ℃. + -. 2 ℃ and left to stand for 2 hours, charged at a constant current of 0.5C to 4.35V, then charged at a constant voltage of 4.35V to 0.05C and left to stand for 15 minutes; discharging to 3.0V at a constant current of 0.5C, wherein the constant current is a charge-discharge cycle process, and recording the discharge capacity of the lithium ion battery in the first cycle; and repeating the charge-discharge cycle process for multiple times according to the method, and recording the discharge capacity after 100 cycles.

And 4 lithium ion batteries are taken for testing each group, and the average value of the capacity retention rate of the lithium ion batteries is calculated. The capacity retention ratio of the lithium ion battery at 100 cycles was equal to the discharge capacity (mAh) at 100 th cycle/the discharge capacity (mAh) after the first cycle × 100%.

1.4 testing the surface temperature rise of the battery core:

the lithium ion batteries of the following examples were placed in a 25 ℃ ± 2 ℃ thermostatically sealed box while monitoring the temperature at four different locations of the cell surface of the lithium ion batteries. The specific temperature rise test flow is as follows: the lithium ion battery is discharged to 2.8V at a constant current of 1.0C and is kept stand for 30 minutes. Then charging to 4.35V at a constant current of 1.0C, standing for 5 minutes, and then discharging to 2.8V at a constant current of 1.0C, which is a charge-discharge cycle process. The charge-discharge cycle was repeated three times. And calculating the average value of the surface temperature rise of the battery core of the lithium ion battery.

Second, preparation method

2.1 preparation of the Positive electrode

Mixing lithium cobaltate with acetylene black and polyvinylidene fluoride according to a weight ratio of 94: 3: 3 in the proportion of N-methylpyrrolidone (NMP) solution to form positive electrode slurry. And (3) adopting an aluminum foil as a positive current collector, coating the positive slurry on the positive current collector, and drying, cold pressing and cutting to obtain the positive electrode.

2.2 preparation of the isolating Membrane

Dissolving polyvinylidene fluoride in water, forming uniform slurry through mechanical stirring, coating the slurry on the two side surfaces of a porous base material (polyethylene) coated with ceramic coatings on the two sides, and drying to form an isolating membrane.

2.3 preparation of the electrolyte

Under the environment that the water content is less than 10ppm, lithium hexafluorophosphate and a nonaqueous organic solvent (ethylene carbonate (EC): diethyl carbonate (DEC): Propylene Carbonate (PC): Propyl Propionate (PP): Vinylene Carbonate (VC): 20; 30; 20; 28; 2) are mixed according to the weight ratio of 8: 92 are formulated to form an electrolyte.

Examples 1 to 1

Uniformly dispersing artificial graphite and simple substance silicon in deionized water according to a certain weight ratio to form cathode slurry. The copper foil is used as a negative current collector, the thickness of the negative current collector is 8 mu m, the negative slurry is coated on the negative current collector, the coating mass is 105mg, a negative pole tab is arranged at one end of the negative current collector in the long axis direction after drying, cold pressing and cutting procedures, the thickness of the negative pole tab is 80 mu m, a negative pole is obtained, and the weight ratio of simple substance silicon in a negative active material layer is 20%. And stacking the anode, the isolating membrane and the cathode in sequence to enable the isolating membrane to be positioned between the anode and the cathode to play an isolating role, and then winding the anode and the isolating membrane into a battery cell, wherein the number of the battery cell layers is 7 (one for each of the anode and the cathode on the double sides). The cell was then packed in an aluminum plastic film bag and dehydrated at 80 ℃ to obtain a dry cell. And then injecting the electrolyte into a dry battery core, and carrying out vacuum packaging, standing, formation, shaping and other processes to obtain the lithium ion battery.

Examples 1 to 2

The same procedure as in example 1-1 was repeated, except that in example 1-2, artificial graphite was mixed with silicon carbon and then dissolved in deionized water to form a negative electrode slurry, wherein the weight ratio of silicon carbon in the negative electrode active material layer was 40%.

Examples 1 to 3

The same procedure as in example 1-1 was repeated, except that in example 1-3, artificial graphite was mixed with silicon carbon and dissolved in deionized water to form a negative electrode slurry, wherein the silicon carbon content in the negative electrode active material layer was 50% by weight.

Examples 1 to 4

The same procedure as in example 1-1 was repeated, except that in examples 1-4, artificial graphite was mixed with silicon carbon and then dissolved in deionized water to form a negative electrode slurry, wherein the silicon carbon content in the negative electrode active material layer was 70% by weight.

Examples 1 to 5

The same procedure as in example 1-1 was repeated, except that in example 1-5, artificial graphite was mixed with silicon carbon and then dissolved in deionized water to form a negative electrode slurry, wherein the silicon carbon content in the negative electrode active material layer was 90% by weight.

Examples 2-1 to 2-5

The same manner as in example 1-1 was conducted except that in examples 2-1 to 2-5, the anode tab was disposed at a position spaced from the closest end of the anode active material layer in the longitudinal direction by 0.125 times the length of the longitudinal axis of the anode active material layer, and the cathode tab was disposed at a position one layer outside from the center of the wound structure. The negative electrode active materials in examples 2-1 to 2-5 included artificial graphite and silicon carbon, and the weight ratios of silicon carbon in the negative electrode active material layer were 20%, 40%, 50%, 70%, and 90%, in this order.

Examples 3-1 to 3-5

In the same manner as in example 1-1, except that the distance between the position of the anode tab and the nearest end in the long axis direction of the anode active material layer was 0.25 times the long axis length of the anode active material layer in examples 3-1 to 3-5, and the anode tab thereof were disposed one layer outside from the center of the wound structure, the anode active materials in examples 3-1 to 3-5 contained artificial graphite and silicon carbon, and the weight ratio of silicon carbon in the anode active material layer was 20%, 40%, 50%, 70%, and 90% in this order.

Examples 4-1 to 4-5

The same procedure as in example 1-1 was conducted except that in examples 4-1 to 4-5, the anode tab was disposed at a position spaced from the closest end of the anode active material layer in the long axis direction by 0.5 times the length of the long axis of the anode active material layer, and the cathode tab was disposed at a position one layer outside from the center of the wound structure. The negative electrode active materials in examples 4-1 to 4-5 contained artificial graphite and silicon carbon, and the weight ratios of silicon carbon in the negative electrode active material layer were 20%, 40%, 50%, 70%, and 90%, in this order.

Examples 5-1 to 5-2

In the same manner as in example 1-1, except that the distances between the position where the negative electrode tab is disposed and the closest end in the long axis direction of the negative electrode active material layer in examples 5-1 and 5-2 were 0.1 times and 0.15 times the long axis length of the negative electrode active material layer, respectively, and the thickness of the negative electrode active material coating layer coated on the negative electrode current collector was 35 μm and 45 μm, the positive electrode tab thereof was disposed and the negative electrode tab thereof was disposed one layer outside from the center of the wound structure. The negative electrode active materials in examples 5-1 and 5-2 contained artificial graphite and silicon carbon, and the weight ratio of silicon carbon in the negative electrode active material layer was 20%.

Examples 5-3 to 5-4

In the same manner as in example 1-1, except for examples 5-3 and 5-4, the distance between the position of the anode tab and the closest end in the long axis direction of the anode active material layer was 0.125 times the length of the long axis of the anode active material layer, and the anode tab thereof was positioned one layer outside from the center of the wound structure. The current collector thicknesses of the negative electrodes in examples 5-3 and 5-4 were 4 μm and 30 μm, respectively, and the weight ratio of silicon to carbon in the negative electrode active material layers in examples 5-3 and 5-4 was 20%.

The lithium ion battery of the above embodiment is subjected to direct current resistance test, discharge rate test, cycle performance test and cell surface temperature rise, and test results are recorded.

The results of the direct current resistance test, the discharge rate test, the cycle performance test, and the cell surface temperature rise of the lithium ion batteries of all the examples are shown in tables 1 to 5 below.

TABLE 1

TABLE 2

TABLE 3

TABLE 4

TABLE 5

Fig. 9 shows three-dimensional graphs of the arrangement position of the negative electrode tab and the silicon content in the negative electrode active material layer with the increase in cell temperature according to examples of tables 1 to 4 of the present application. As shown in fig. 9, the examples of the present application clearly show the effect of the location and silicon content of the negative electrode tab on the cycle performance and safety performance of the electrochemical device. Wherein, according to the results of table 1, the ratio D of the distance in the long axis direction from the center of the anode tab to either end of the anode active material layer to the length of the long axis of the anode active material layer and the ratio G of the weight of silicon in the anode active material layer of examples 1-1, 2-2, 3-1, 3-2, 3-3, 4-1, 4-2, 4-3, and 4-4 conform to the following relationship: d is more than or equal to 0.6 XG. According to the embodiment, the electrochemical device provided by the embodiment of the application can effectively reduce the temperature of the battery cell rising in the charge-discharge cycle process to be less than 15 ℃.

According to examples 5-1 to 5-4, when the tab thickness was 80 μm, the negative electrode current collector thickness S₁Is negativeThickness S of pole ear₂The thickness of the negative electrode active material layer is S₃Satisfies the following relational expression, 0.9 (S)₁+2S₃)≤S₁+S₂≤1.1(S₁+2S₃). The temperature rise of the battery cell is reduced along with the increase of the thickness of the negative current collector, and the current collector with the size of 8 microns is preferably selected in the embodiment by integrating the strength of the current collector and the energy density of the battery cell. By controlling the relationship between the arrangement position of the cathode tab and the silicon content, the electrochemical device provided by the embodiment of the application can have lower direct current resistance and better discharge rate and also show better cycle capacity under the condition of the cathode material with the same silicon content. In addition, the embodiment in the relation range between the arrangement position of the negative electrode tab and the silicon content in the embodiment of the application can effectively control the average rising temperature of the surface of the battery cell, and further ensure the safety performance of the electrochemical device.

Through comparison of the above embodiments, it can be clearly understood that the electrochemical device of the present application enables the cycle performance and the safety performance of the electrochemical device to be significantly improved by limiting the relationship between the arrangement position of the negative electrode tab and the weight ratio of silicon in the negative electrode active material layer.

Reference throughout this specification to "some embodiments," "one embodiment," "another example," "an example," "a specific example," or "some examples" means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present application. Thus, throughout the specification, descriptions appear, for example: "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in one example," "in a particular example," or "by example," which do not necessarily refer to the same embodiment or example in this application. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

Although illustrative embodiments have been illustrated and described, it will be appreciated by those skilled in the art that the above embodiments are not to be construed as limiting the application and that changes, substitutions and alterations can be made to the embodiments without departing from the spirit, principles and scope of the application.

Claims

1. An electrochemical device, comprising:

a positive electrode;

an isolation film; and

a negative electrode, wherein the negative electrode comprises:

a negative current collector;

a negative electrode active material layer, wherein the negative electrode active material layer comprises a silicon-based material; and

a negative electrode tab, wherein the negative electrode tab is disposed on the long axis side of the negative electrode current collector, the central position of the negative electrode tab and the distance of any end of the negative electrode active material layer in the long axis direction are a first length, the long axis length of the negative electrode active material layer is a second length, and the negative electrode satisfies the following relational expression (I):

2. The electrochemical device according to claim 1, wherein the negative electrode current collector has a thickness of 4 to 30 μm, and the negative electrode satisfies the following relational expression (II):

0.9×(S₁+2S₃)≤S₁+S₂≤1.1×(S₁+2S₃) Formula (II)

Wherein the negative current collector has a thickness of S₁The thickness of the negative pole tab is S₂The thickness of the negative electrode active material layer is S₃。

3. The electrochemical device according to claim 1, wherein the silicon-based material contains at least one of a simple substance of silicon, a compound of silicon, an alloy of silicon, and a silicon oxide material.

4. The electrochemical device according to claim 1, wherein a ratio of a long axis length of the anode active material layer to a long axis length of the anode current collector is 0.8 to 1.0.

5. The electrochemical device according to claim 1, wherein the electrochemical device is a wound structure, and the anode tab is disposed at a position other than three layers from a center of the wound structure.

6. The electrochemical device according to claim 5, wherein the positive electrode tab of the positive electrode is disposed at a position one layer outward from the center of the wound structure from the position of the negative electrode tab.

7. The electrochemical device of claim 1, wherein the silicon-based material further comprises a material layer disposed on at least a portion of a surface of the silicon-based material, the material layer comprising at least one of a polymer, an inorganic particle, amorphous carbon, or a carbon nanotube.

8. The electrochemical device of claim 7, wherein the inorganic particles comprise at least one of lithium cobaltate, lithium iron phosphate, lithium nickel cobalt manganese, lithium nickel cobalt aluminate, elemental silicon, a compound of silicon, an alloy of silicon, and a silicone material, the polymer comprising at least one of polyvinylidene fluoride, polyacrylic acid, polyvinyl chloride, carboxymethyl cellulose, polyethylene, polypropylene, polyethylene terephthalate, polyimide, and aramid.

9. The electrochemical device of claim 1, wherein a groove is disposed on the negative electrode, the negative electrode tab being disposed in the groove.

10. An electronic device comprising the electrochemical device of any one of claims 1 to 9.