CN116097473A

CN116097473A - Electrochemical device and electronic device

Info

Publication number: CN116097473A
Application number: CN202180042402.6A
Authority: CN
Inventors: 刘胜奇; 王可飞; 蔡小虎; 郭俊
Original assignee: Dongguan Amperex Technology Ltd
Current assignee: Dongguan Amperex Technology Ltd
Priority date: 2021-12-31
Filing date: 2021-12-31
Publication date: 2023-05-09
Also published as: WO2023123353A1

Abstract

The present application relates to an electrochemical device and an electronic device. Specifically, the present application provides an electrochemical device including a positive electrode including: a positive electrode current collector; a positive electrode active material layer formed in a central region on at least one surface of the positive electrode current collector, the positive electrode active material layer including a positive electrode active material and a binder having a density of a g/cm ³ And a is more than or equal to 0.6 and less than or equal to 1.5; and an insulating layer formed on an edge region on the at least one surface of the positive electrode current collector, the insulating layer containing an aluminum element. The above configuration of the positive electrode of the present application can improve the high-temperature storage voltage drop and the safety performance of the electrochemical device.

Description

Electrochemical device and electronic device

Technical Field

The present application relates to the field of energy storage, and in particular to an electrochemical device and an electronic device, especially a lithium ion battery.

Background

In recent years, with rapid development of electronic products such as smart phones, tablet computers, and smart wear, consumers have increasingly demanded energy density of electrochemical devices (e.g., lithium ion batteries) in consideration of the difference in the use period and working environment of the electronic products. Currently, the energy density of lithium ion batteries is mainly improved by using high-voltage (4.4V and above) lithium cobalt oxide positive electrode active materials and high-capacity and high-compaction-density graphite negative electrode materials. However, as the temperature and voltage rise, the cycle performance and safety performance of such lithium ion batteries are significantly deteriorated. Meanwhile, as severe environments such as global warming are increased (e.g., special use regions of india, africa, etc.), this puts higher demands on the high-temperature performance of the battery.

In view of the foregoing, it is desirable to provide an electrochemical device and an electronic device having improved high temperature performance.

Disclosure of Invention

The present application provides an electrochemical device having improved high temperature performance at least by improving the positive electrode of the electrochemical device to solve the problems of the prior art to some extent.

According to one aspect of the present application, there is provided an electrochemical device including a positive electrode including: a positive electrode current collector; a positive electrode active material layer formed in a central region on at least one surface of the positive electrode current collector, the positive electrode active material layer including a positive electrode active material and a binder having a density of a g/cm ³ And a is more than or equal to 0.6 and less than or equal to 1.5; and an insulating layer formed on an edge region on the at least one surface of the positive electrode current collector, the insulating layer containing an aluminum element.

According to an embodiment of the present application, the insulating layer comprises the binder.

According to an embodiment of the present application, the positive electrode active material layer and the insulating layer overlap each other to form an interaction region having a width of W mm and 0 < W.ltoreq.4.

According to an embodiment of the present application, the positive electrode active material layer and the insulating layer do not overlap.

According to the embodiment of the application, the content of the aluminum element is x% based on the weight of the insulating layer, wherein x is 20-65.

According to embodiments of the present application, 20.ltoreq.x/a.ltoreq.70.

According to the embodiment of the application, a is more than or equal to 0.8 and less than or equal to 1.2.

According to embodiments of the present application, the binder has a porosity of b.ltoreq.b.ltoreq.60, and 14.ltoreq.b/a.ltoreq.55.

According to an embodiment of the present application, the mass fraction of the positive electrode active material is M% based on the total weight of the positive electrode active material layer, wherein 90.ltoreq.m.ltoreq.99.5 and 64.ltoreq.m/a.ltoreq.170.

According to an embodiment of the present application, the electrochemical device further comprises an electrolyte comprising an ether nitrile compound, wherein the mass fraction of the ether nitrile compound is c%, wherein 0.01.ltoreq.c.ltoreq.8, based on the total weight of the electrolyte.

According to embodiments of the present application, the ether nitrile compound includes at least one of ethylene glycol bis (2-cyanoethyl) ether, 1,2, 3-tris (2-cyanoethoxy) propane, 1,2, 4-tris (2-cyanoethoxy) butane, 1-tris (cyanoethoxymethylene) ethane, 1-tris (cyanoethoxymethylene) propane, 3-methyl-1, 3, 5-tris (cyanoethoxy) pentane, 1,2, 7-tris (cyanoethoxy) heptane, 1,2, 6-tris (cyanoethoxy) hexane, or 1,2, 5-tris (cyanoethoxy) pentane.

According to the examples of the present application, 0.4.ltoreq.c/a.ltoreq.2.

In another aspect of the present application, the present application provides an electronic device comprising an electrochemical device according to the present application.

The structural stability of the positive electrode at high temperature and high pressure can be remarkably improved by providing the insulating layer with aluminum element in the positive electrode and adopting the low-density binder in the positive electrode active material layer, thereby remarkably improving the high-temperature performance of the electrochemical device, in particular improving the overcharge safety performance of the electrochemical device and reducing the voltage drop of the electrochemical device under the high-temperature storage condition.

Additional aspects and advantages of embodiments of the 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 application.

Drawings

Fig. 1 is a schematic top view of a positive electrode according to some embodiments of the present application, wherein an insulating layer and a positive electrode active material layer are disposed along a width direction of the positive electrode.

Fig. 2 is a schematic top view of a positive electrode according to other embodiments of the present application, wherein an insulating layer and a positive electrode active material layer are disposed along the length of the positive electrode.

Fig. 3 is a schematic top view of a positive electrode according to further embodiments of the present application, wherein the insulating layer and the positive electrode active material layer are disposed along the width and length directions of the positive electrode.

Fig. 4 is a schematic top view of a positive electrode according to some embodiments of the present application, wherein the positive electrode active material layer does not overlap with the insulating layer.

Detailed Description

Embodiments of the present application will be described in detail below. The examples of the present application should not be construed as limiting the present application.

The following terms used herein have the meanings indicated below, unless explicitly indicated otherwise.

In the detailed description and claims, a list of items connected by the term "at least one of" 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 only a; only B; or A and B. In another example, if items A, B and C are listed, then the phrase "at least one of A, B and C" means only a; 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. At least one of the terms "has the same meaning as at least one of the terms".

I. Positive electrode

Common methods of increasing the energy density of electrochemical devices (e.g., lithium ion batteries) include the use of high voltage (4.4V and above) lithium cobaltate positive electrode active materials and high capacity, high compacted density graphite negative electrode materials. However, as the temperature and voltage are increased, the structural stability of lithium cobaltate is deteriorated, metal ions are easily eluted from the positive electrode and are reductively deposited on the surface of the negative electrode, destroying the structure of a negative electrode Solid Electrolyte Interface (SEI) film, leading to an increasing negative electrode resistance and battery thickness, and thus leading to capacity loss and deterioration of cycle performance of the electrochemical device. In addition, at high temperature and high pressure, the electrolyte is easily oxidized and decomposed at the surface of the positive electrode to generate a large amount of gas, causing swelling of the electrochemical device and destruction of the electrode interface, thereby deteriorating the electrochemical performance of the electrochemical device. Meanwhile, under high temperature and high voltage, the lithium cobaltate has higher oxidation activity, so that side reaction with the electrolyte is aggravated, decomposition products of the electrolyte are continuously deposited on the surface of the positive electrode, the internal resistance of the electrochemical device is further increased, and the high temperature circulation capacity retention rate and the high temperature storage cell residual capacity are reduced. These factors may cause a great safety hazard to the electrochemical device.

In at least one aspect, the present application overcomes the above-described drawbacks of the prior art by providing an insulating layer having an aluminum element in the positive electrode and employing a low density binder in the positive electrode active material layer.

Specifically, the positive electrode described herein includes a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode active material layer contains a positive electrode active material and is formed in a central region on at least one surface of the positive electrode current collector. The positive electrode active material layer may be one or more layers. Each layer of the multi-layer positive electrode active material may contain the same or different positive electrode active materials.

The positive electrode is characterized in that the positive electrode further comprises an insulating layer containing aluminum element, wherein the insulating layer is formed on the positive electrode current collectorAn edge region on the at least one surface; and the positive electrode active material layer further comprises a binder having a density of a g/cm ³ Wherein a is more than or equal to 0.6 and less than or equal to 1.5.

As used herein, the term "central region" refers to a region that is a distance from the edge of the positive electrode current collector in the width direction of the positive electrode or in the length direction of the positive electrode. The center region edge is 2mm to 80mm from the edge of the positive electrode current collector and extends in the length direction of the positive electrode when in the width direction of the positive electrode, and the center region may have the same length as the positive electrode current collector or be shorter than the positive electrode current collector (e.g., 2mm to 500 mm). The center region edge is 2mm to 80mm from the edge of the positive electrode current collector and extends in the width direction of the positive electrode when in the length direction of the positive electrode, and the center region may have the same width as the positive electrode current collector or be narrower than the width of the positive electrode current collector (e.g., 4mm to 160 mm). As used herein, the term "edge region" refers to all or a portion of the region other than the center region of the positive electrode current collector in the width direction of the positive electrode or in the length direction of the positive electrode. The edge region has at least the same length as the center region when in the width direction of the positive electrode; the edge region has at least the same width as the center region when in the length direction of the positive electrode. As shown in fig. 1, the edge region (insulating layer) and the center region (positive electrode active material layer) are disposed in the width direction of the positive electrode. As shown in fig. 2, the edge region (insulating layer) and the center region (positive electrode active material layer) are disposed along the length direction of the positive electrode. As shown in fig. 3, the edge region (insulating layer) and the center region (positive electrode active material layer) are disposed along the width and length directions of the positive electrode.

In some embodiments, when the insulating layer and the positive electrode active material layer are disposed in the width direction of the positive electrode, the insulating layer is at least as long as the positive electrode active material layer. In some embodiments, when the insulating layer and the positive electrode active material layer are disposed along the length direction of the positive electrode, the insulating layer is at least as wide as the positive electrode active material layer.

On the one hand, the insulating layer containing aluminum element is arranged at the edge area of the positive electrode current collector to enhance the structural stability of the positive electrode, thereby improving the structural stabilityElectrochemical performance of an electrochemical device at high temperatures. On the other hand, the binder used in the positive electrode active material layer of the present application has a density of usually more than 1.5g/cm ³ ) With a lower density. When the density of the positive electrode binder is more than 1.5g/cm ³ When the winding process is carried out, the flexibility of the positive electrode can be influenced to a certain extent, so that the positive electrode is easy to break in the winding process; and when the density of the positive electrode binder is less than 0.6g/cm ³ At this time, the adhesive force of the adhesive is insufficient, thereby adversely affecting the electrochemical stability of the electrochemical device. The density of the positive electrode binder was controlled to 0.6g/cm ³ To 1.5g/cm ³ Within the range of (2), not only can good cohesiveness be realized, but also the flexibility of the positive electrode can be enhanced, and the risk of breakage in the winding process can be reduced. Meanwhile, the low-density binder used in the application is easy to form a cavity structure with peripheral active materials, electrolyte can be contained in the cavity structure, and the structure improves the wettability of the electrolyte and the positive electrode active materials to a certain extent and simultaneously effectively reduces side reactions generated by the action of the electrolyte and the active materials. In addition, the low-density binder can also be coated on the surface of the positive electrode active material particles, so that the stability of the interface of the positive electrode active material particles is improved. The combination of the insulating layer containing aluminum element and the positive electrode active material layer containing a low-density binder not only contributes to the improvement of the high-temperature safety performance (e.g., high-temperature overcharge performance) of the electrochemical device, but also contributes to the reduction of the voltage drop thereof under high-temperature storage.

In some embodiments, 0.8.ltoreq.a.ltoreq.1.2. In some embodiments, a may be 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, or within a range consisting of any two of the above.

In some embodiments, the insulating layer includes the low density binder described above. By using the low-density binder in the insulating layer, the binder and the aluminum element can be promoted to be more uniformly mixed, the binding effect is optimized, and the risk of the insulating layer falling off from the current collector is reduced, thereby improving the use safety of the electrochemical device. In addition, the above configuration also contributes to improving the thermal stability of the insulating layer, thereby better functioning as the insulating layer. Based at least on the above factors, including the low density binder in the insulating layer can further improve the safety performance such as voltage drop and overcharge deformation rate of the battery cell.

In some embodiments, the insulating layer and the positive electrode active material layer overlap each other to form an interaction region having a width W mm, where 0 < W.ltoreq.4. As shown in fig. 1 to 3, the positive electrode active material layer is in contact with the insulating layer such that the components of the positive electrode active material layer and the insulating layer coexist at the interface (i.e., intersect), and the formed region is referred to as an "interaction region". In some embodiments, W may be 0.05, 0.01, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4 or within a range consisting of any two of the above values. The presence of the interaction region may improve the stability of the active material layer and insulating layer boundary, reducing the safety risk.

In some embodiments, the insulating layer and the positive electrode active material layer do not overlap, as shown in fig. 4.

In some embodiments, the aluminum element is present in an amount of x% based on the weight of the insulating layer, where 20.ltoreq.x.ltoreq.65. In some embodiments, 35.ltoreq.x.ltoreq.0. In some embodiments, 40.ltoreq.x.ltoreq.50. In some embodiments, x may be 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, or within a range consisting of any two of the above values. When the content of the aluminum element in the insulating layer is within the above range, the insulating layer is not easily detached during the cell manufacturing process or in the electrochemical device, and has good adhesion with the positive electrode current collector, which is advantageous for improving the high-temperature storage voltage drop and the safety performance of the electrochemical device.

In some embodiments, the insulating layer comprises Al ₂ O ₃ 、AlF ₃ 、AlCl ₃ Or AIN.

In some embodiments, 20.ltoreq.x/a.ltoreq.70. In some embodiments, 30.ltoreq.x/a.ltoreq.55. In some embodiments, x/a is 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70 or is in the range consisting of any two of the above. When x/a satisfies the above relationship, not only can the more uniform distribution of the binder in the insulating layer be promoted, the insulating layer is promoted to be firmly bonded on the current collector, but also the insulating layer can be ensured to contain enough aluminum element, shrinkage of the insulating layer in the preparation process is avoided, and under the combined action of the two, the safety performance of the electrochemical device can be further improved and the voltage drop of the electrochemical device in a high-temperature storage environment can be reduced.

In some embodiments, the binder has a porosity of b%, where 17.ltoreq.b.ltoreq.60. In some embodiments, 25.ltoreq.b.ltoreq.55. In some embodiments, b may be 17, 20, 25, 30, 35, 40, 45, 50, 55, 60 or be in the range consisting of any two of the above values. When the porosity of the binder is within the above range, the binder has good wettability and stability in the positive electrode active material slurry, which contributes to the uniform coating of the positive electrode active material layer on the positive electrode current collector, thereby improving the electrochemical uniformity and electrochemical performance of the electrochemical device. In some embodiments, the density a of the binder and its porosity b satisfy: b/a is more than or equal to 14 and less than or equal to 55. In some embodiments, 14.ltoreq.b/a.ltoreq.50. In some embodiments, b/a is 14, 15, 20, 25, 30, 35, 40, 45, 50, 55 or is in the range consisting of any two of the above. When the density and porosity of the binder satisfy the above-mentioned relationship, infiltration and dispersion of the binder in the positive electrode slurry are more facilitated, and the positive electrode slurry is more facilitated to be accommodated in the cavity-type structure of the binder, so that the safety performance of the electrochemical device can be further improved and the voltage drop thereof under a high-temperature storage environment can be reduced.

In some embodiments, the binder comprises polyvinylidene fluoride (PVDF).

In some embodiments, the mass fraction of the positive electrode active material is M% based on the total weight of the positive electrode active material layer, wherein 90.ltoreq.m.ltoreq.99.5. In some embodiments, 95.ltoreq.M.ltoreq.99. In some embodiments, M may be 90, 92, 94, 95, 96, 97, 98, or 99, or be in the range consisting of any two of the above. When the mass fraction of the positive electrode active material in the positive electrode active material layer satisfies the above-described relationship, the energy density of the electrochemical device can be significantly improved.

In some embodiments, the density a of the binder and the mass fraction m% of the positive electrode active material satisfy: m/a is 64-170. In some embodiments, 70.ltoreq.M/a.ltoreq.160. In some embodiments, M/a is 64, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, 130, 140, 150, 160, 170 or is in a range consisting of any two of the foregoing values. When the electrochemical device satisfies the above relationship, it is possible to promote the dissolution of the binder in the positive electrode slurry, and more advantageously to uniformly distribute the binder in the positive electrode active material, improving the uniformity of the electrode structure, thereby further improving the safety performance of the electrochemical device and reducing the voltage drop thereof under a high-temperature storage environment.

The kind of the positive electrode active material is not particularly limited as long as it is capable of electrochemically occluding and releasing metal ions (for example, lithium ions). In some embodiments, the positive electrode active material is a material containing lithium and at least one transition metal. Examples of the positive electrode active material may include, but are not limited to, lithium transition metal composite oxides and lithium-containing transition metal phosphate compounds.

In some embodiments, the transition metal in the lithium transition metal composite oxide includes V, ti, cr, mn, fe, co, ni, cu and the like. In some embodiments, the lithium transition metal composite oxide includes LiCoO ₂ Equal lithium cobalt composite oxide, liNiO ₂ Equal lithium nickel composite oxide, liMnO ₂ 、LiMn ₂ O ₄ 、Li ₂ MnO ₄ Equal lithium manganese composite oxide, liNi _1/3 Mn _1/3 Co _1/3 O ₂ 、LiNi _0.5 Mn _0.3 Co _0.2 O ₂ And lithium nickel manganese cobalt composite oxides in which a part of transition metal atoms which are the main body of these lithium transition metal composite oxides are substituted with other elements such as Na, K, B, F, al, ti, V, cr, mn, fe, co, li, ni, cu, zn, mg, ga, zr, si, nb, mo, sn, W. Examples of lithium transition metal composite oxides may include, but are not limited to, liNi _0.5 Mn _0.5 O ₂ 、LiNi _0.85 Co _0.10 Al _0.05 O ₂ 、LiNi _0.33 Co _0.33 Mn _0.33 O ₂ 、LiNi _0.45 Co _0.10 Al _0.45 O ₂ 、LiMn _1.8 Al _0.2 O ₄ And LiMn _1.5 Ni _0.5 O ₄ Etc. Examples of combinations of lithium transition metal composite oxides include, but are not limited to, liCoO ₂ With LiMn ₂ O ₄ In which LiMn ₂ O ₄ A part of Mn in (e.g., liNi) may be substituted with a transition metal _0.33 Co _0.33 Mn _0.33 O ₂ )，LiCoO ₂ A portion of Co in (c) may be replaced with a transition metal.

In some embodiments, the transition metal in the lithium-containing transition metal phosphate compound includes V, ti, cr, mn, fe, co, ni, cu, and the like. In some embodiments, the lithium-containing transition metal phosphate compound comprises LiFePO ₄ 、Li ₃ Fe ₂ (PO ₄ ) ₃ 、LiFeP ₂ O ₇ Isophosphates, liCoPO ₄ Cobalt phosphates in which a part of the transition metal atoms that are the main body of these lithium transition metal phosphate compounds are substituted with other elements such as Al, ti, V, cr, mn, fe, co, li, ni, cu, zn, mg, ga, zr, nb, si.

A material having a composition different from that of the positive electrode active material may be attached to the surface of the positive electrode active material. Examples of surface-adherent substances may include, but are not limited to: oxides such as alumina, silica, titania, zirconia, magnesia, calcia, boria, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; carbon, and the like. By attaching a substance to the surface of the positive electrode active material, the oxidation reaction of the electrolyte on the surface of the positive electrode active material can be suppressed, and the life of the electrochemical device can be improved. When the amount of the surface-adhering substance is too small, the effect thereof cannot be sufficiently exhibited; if the amount of the surface-adhering substance is too large, the ingress and egress of lithium ions are hindered, and thus the electrical resistance may be increased. In the present application, a positive electrode active material having a composition different from that of the positive electrode active material attached to the surface of the positive electrode active material is also referred to as a "positive electrode active material".

In some embodiments, a "positive electrode active material" may use lithium cobalt oxide or lithium nickel cobalt manganese oxide.

In some embodiments, the shape of the positive electrode active material particles includes, but is not limited to, block, polyhedral, spherical, ellipsoidal, plate-like, needle-like, columnar, and the like. In some embodiments, the positive electrode active material particles include primary particles, secondary particles, or a combination thereof. In some embodiments, the primary particles may agglomerate to form secondary particles.

The kind of the positive electrode conductive material is not limited, and any known conductive material may be used. Examples of the positive electrode conductive material may include, but are not limited to, graphite such as natural graphite, artificial graphite, and the like; carbon black such as acetylene black; amorphous carbon material such as needle coke; a carbon nanotube; graphene, and the like. The above positive electrode conductive materials may be used alone or in any combination.

The type of solvent used to form the positive electrode slurry is not limited as long as it is a solvent capable of dissolving or dispersing the positive electrode active material, the conductive material, the positive electrode binder, and the thickener, if necessary. Examples of the solvent used to form the positive electrode slurry may include any one of an aqueous solvent and an organic solvent. Examples of the aqueous medium may include, but are not limited to, water and a mixed medium of alcohol and water, and the like. Examples of the organic-based medium may include, but are not limited to, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N, N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and Tetrahydrofuran (THF); amides such as N-methylpyrrolidone (NMP), dimethylformamide, and dimethylacetamide; aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide.

Thickeners are typically used to adjust the viscosity of the slurry. In the case of using an aqueous medium, the sizing may be performed using a thickener and Styrene Butadiene Rubber (SBR) emulsion. The kind of the thickener is not particularly limited, and examples thereof may include, but are not limited to, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, salts thereof, and the like. The above thickeners may be used alone or in any combination.

The kind of the positive electrode current collector is not particularly limited, and it may be any material known to be suitable for use as a positive electrode current collector. Examples of the positive electrode current collector may include, but are not limited to, metal materials such as aluminum, stainless steel, nickel plating, titanium, tantalum, and the like; carbon materials such as carbon cloth and carbon paper. In some embodiments, the positive electrode current collector is a metal material. In some embodiments, the positive electrode current collector is aluminum.

In order to reduce the electronic contact resistance of the positive electrode current collector and the positive electrode active material layer, the surface of the positive electrode current collector may include a conductive auxiliary agent. Examples of the conductive aid may include, but are not limited to, carbon and noble metals such as gold, platinum, silver, and the like.

The positive electrode may be manufactured by forming a positive electrode active material layer containing a positive electrode active material and a binder on a current collector. The positive electrode using the positive electrode active material can be produced by a conventional method in which the positive electrode active material and the binder, and if necessary, the conductive material, the thickener, and the like are dry-mixed to form a sheet, and the resulting sheet is pressure-bonded to the positive electrode current collector; or these materials are dissolved or dispersed in a liquid medium to prepare a slurry, and the slurry is applied to a positive electrode current collector and dried to form a positive electrode active material layer on the current collector, whereby a positive electrode can be obtained.

When the positive electrode active material is primary particles, the average particle diameter of the positive electrode active material refers to the positive electrode active material particle primary particle diameter. When primary particles of the positive electrode active material particles are aggregated to form secondary particles, the average particle diameter of the positive electrode active material particles refers to the positive electrode active material particle secondary particle diameter.

In some embodiments, the average particle size of the positive electrode active material is D μm, and D has a value in the range of 5 to 30. In some embodiments, D ranges from 10 to 25. In some embodiments, D ranges from 12 to 20. In some embodiments, D is 5, 7, 9, 10, 12, 15, 18, 20, 25, 30 or is in the range consisting of any two of the above.

When the average particle diameter of the positive electrode active material is within the above range, a positive electrode active material with a high tap density can be obtained, and degradation of the performance of the electrochemical device can be suppressed. On the other hand, in the process of producing the positive electrode of the electrochemical device (that is, when the positive electrode active material, the conductive material, the binder, and the like are applied in a film form by slurrying them with a solvent), problems such as occurrence of streaks can be prevented. Here, by mixing two or more positive electrode active materials having different average particle diameters, the filling property at the time of positive electrode preparation can be further improved.

The average particle diameter of the positive electrode active material can be measured by a laser diffraction/scattering particle size distribution measuring device: when LA-920 manufactured by HORIBA was used as a particle size distribution meter, a 0.1% aqueous solution of sodium hexametaphosphate was used as a dispersion medium for measurement, and after 5 minutes of ultrasonic dispersion, the measurement refractive index was set to 1.24 for measurement. The average particle diameter of the positive electrode active material can also be measured by a laser diffraction particle size analyzer (Shimadzu SALD-2300) and a scanning electron microscope (ZEISS EVO18, the number of samples of which is not less than 100).

II. Electrolyte solution

The electrochemical device of the present application further comprises an electrolyte, wherein the electrolyte comprises an electrolyte, a solvent that dissolves the electrolyte, and an additive.

In some embodiments, the electrolyte includes an ether nitrile compound. The ether nitrile functional groups on the surface of the ether nitrile compound can form hydrogen bonds with the functional groups on the surface of the binder, promote the infiltration of electrolyte and form an SEI film, and reduce the occurrence of side reactions while protecting the structural stability of the positive electrode, thereby improving the performance of the battery cell.

In some embodiments, the ethernitrile compound includes at least one of ethylene glycol bis (2-cyanoethyl) ether, 1,2, 3-tris (2-cyanoethoxy) propane, 1,2, 4-tris (2-cyanoethoxy) butane, 1-tris (cyanoethoxymethylene) ethane, 1-tris (cyanoethoxymethylene) propane, 3-methyl-1, 3, 5-tris (cyanoethoxy) pentane, 1,2, 7-tris (cyanoethoxy) heptane, 1,2, 6-tris (cyanoethoxy) hexane, or 1,2, 5-tris (cyanoethoxy) pentane.

The above ether nitrile compounds may be used alone or in any combination. When two or more kinds of ether nitrile compounds are contained in the electrolyte, the content of the ether nitrile compounds described herein refers to the total content of the two or more kinds of ether nitrile compounds in the electrolyte.

In some embodiments, the ethernitrile compound is present in a mass fraction of c% based on the total weight of the electrolyte, wherein 0.01 c.ltoreq.8. In some embodiments, 0.1.ltoreq.c.ltoreq.5. In some embodiments, c may be 0.01, 0.05, 0.1, 0.2, 0.3, 0.5, 0.6, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, or within a range consisting of any two of the above.

In some embodiments, the mass fraction c% of the ether nitrile compound and the density a of the binder satisfy: c/a is more than or equal to 0.4 and less than or equal to 12. In some embodiments, 0.5.ltoreq.c/a.ltoreq.10. In some embodiments, c/a may be 0.4, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 7, 8, 9, 10, 11, 12 or within a range consisting of any two of the foregoing values. When the electrochemical device satisfies the above relationship, it is possible to further improve the safety performance of the electrochemical device and reduce the voltage drop thereof under a high-temperature storage environment.

In some embodiments, the electrolyte further comprises any nonaqueous solvent known in the art that can be used as a solvent for the electrolyte.

In some embodiments, the nonaqueous solvent includes, but is not limited to, one or more of the following: cyclic carbonates, chain carbonates, cyclic carboxylates, chain carboxylates, cyclic ethers, chain ethers, phosphorus-containing organic solvents, sulfur-containing organic solvents, or aromatic fluorine-containing solvents.

In some embodiments, examples of the cyclic carbonate may include, but are not limited to, one or more of the following: ethylene Carbonate (EC), propylene Carbonate (PC) or butylene carbonate. In some embodiments, the cyclic carbonate has 3 to 6 carbon atoms.

In some embodiments, examples of the chain carbonate may include, but are not limited to, one or more of the following: and chain carbonates such as dimethyl carbonate, methylethyl carbonate, diethyl carbonate (DEC), methyl n-propyl carbonate, ethyl n-propyl carbonate, and di-n-propyl carbonate. Examples of fluorine substituted chain carbonates may include, but are not limited to, one or more of the following: bis (fluoromethyl) carbonate, bis (difluoromethyl) carbonate, bis (trifluoromethyl) carbonate, bis (2-fluoroethyl) carbonate, bis (2, 2-difluoroethyl) carbonate, bis (2, 2-trifluoroethyl) carbonate, 2-fluoroethyl methyl carbonate, 2-difluoroethyl methyl carbonate or 2, 2-trifluoroethyl methyl carbonate, and the like.

In some embodiments, examples of the cyclic carboxylic acid esters may include, but are not limited to, one or more of gamma-butyrolactone or gamma-valerolactone. In some embodiments, a portion of the hydrogen atoms of the cyclic carboxylic acid ester may be substituted with fluorine.

In some embodiments, examples of the chain carboxylic acid esters may include, but are not limited to, one or more of the following: methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, sec-butyl acetate, isobutyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, methyl valerate, ethyl valerate, methyl pivalate, ethyl pivalate, or the like. In some embodiments, a portion of the hydrogen atoms of the chain carboxylate may be substituted with fluorine. In some embodiments, examples of fluorine substituted chain carboxylates may include, but are not limited to, methyl trifluoroacetate, ethyl trifluoroacetate, propyl trifluoroacetate, butyl trifluoroacetate, or 2, 2-trifluoroethyl trifluoroacetate, and the like.

In some embodiments, examples of the cyclic ether may include, but are not limited to, one or more of the following: tetrahydrofuran, 2-methyltetrahydrofuran, 1, 3-dioxolane, 2-methyl-1, 3-dioxolane, 4-methyl-1, 3-dioxolane, 1, 3-dioxane, 1, 4-dioxane or dimethoxypropane.

In some embodiments, examples of the chain ethers may include, but are not limited to, one or more of the following: dimethoxymethane, 1-dimethoxyethane, 1, 2-dimethoxyethane, diethoxymethane, 1-diethoxyethane, 1, 2-diethoxyethane, ethoxymethoxymethane, 1-ethoxymethoxyethane or 1, 2-ethoxymethoxyethane, etc.

In some embodiments, examples of the phosphorus-containing organic solvent may include, but are not limited to, one or more of the following: trimethyl phosphate, triethyl phosphate, dimethyl ethyl phosphate, methyl diethyl phosphate, ethylene methyl phosphate, ethylene ethyl phosphate, triphenyl phosphate, trimethyl phosphite, triethyl phosphite, triphenyl phosphite, tris (2, 2-trifluoroethyl) phosphate, tris (2, 3-pentafluoropropyl) phosphate, and the like.

In some embodiments, examples of the sulfur-containing organic solvent may include, but are not limited to, one or more of the following: sulfolane, 2-methylsulfanyl sulfone, 3-methylsulfanyl sulfone, dimethyl sulfone, diethyl sulfone, ethyl methyl sulfone, methyl propyl sulfone, dimethyl sulfoxide, methyl methanesulfonate, ethyl methanesulfonate, methyl ethanesulfonate, ethyl ethanesulfonate, dimethyl sulfate, diethyl sulfate or dibutyl sulfate. In some embodiments, a portion of the hydrogen atoms of the sulfur-containing organic solvent may be replaced with fluorine.

In some embodiments, the aromatic fluorine-containing solvent includes, but is not limited to, one or more of the following: fluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene or trifluoromethylbenzene.

In some embodiments, the solvents used in the electrolytes of the present application include cyclic carbonates, chain carbonates, cyclic carboxylates, chain carboxylates, and combinations thereof. In some embodiments, the solvent used in the electrolyte of the present application comprises an organic solvent selected from the group consisting of: ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, n-propyl acetate, ethyl acetate, or a combination thereof. In some embodiments, the solvent used in the electrolyte of the present application comprises: ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, gamma-butyrolactone, or a combination thereof.

In some embodiments, the electrolyte is not particularly limited, and a substance known as an electrolyte may be arbitrarily used. In the case of a lithium secondary battery, a lithium salt is generally used. Examples of electrolytes may include, but are not limited to, liPF ₆ 、LiBF ₄ 、LiClO ₄ 、LiAlF ₄ 、LiSbF ₆ 、LiWF ₇ An inorganic lithium salt; liWOF ₅ Lithium tungstate; HCO (hydrogen chloride) ₂ Li、CH ₃ CO ₂ Li、CH ₂ FCO ₂ Li、CHF ₂ CO ₂ Li、CF ₃ CO ₂ Li、CF ₃ CH ₂ CO ₂ Li、CF ₃ CF ₂ CO ₂ Li、CF ₃ CF ₂ CF ₂ CO ₂ Li、CF ₃ CF ₂ CF ₂ CF ₂ CO ₂ Lithium carboxylates such as Li; FSO (FSO) ₃ Li、CH ₃ SO ₃ Li、CH ₂ FSO ₃ Li、CHF ₂ SO ₃ Li、CF ₃ SO ₃ Li、CF ₃ CF ₂ SO ₃ Li、CF ₃ CF ₂ CF ₂ SO ₃ Li、CF ₃ CF ₂ CF ₂ CF ₂ SO ₃ Lithium sulfonate such as Li; liN (FCO) ₂ 、LiN(FCO)(FSO ₂ )、LiN(FSO ₂ ) ₂ 、LiN(FSO ₂ )(CF ₃ SO ₂ )、LiN(CF ₃ SO ₂ ) ₂ 、LiN(C ₂ F ₅ SO ₂ ) ₂ Cyclic 1, 2-perfluoroethane bissulfonylimide lithium, cyclic 1, 3-perfluoropropane bissulfonylimide lithium, liN (CF) ₃ SO ₂ )(C ₄ F ₉ SO ₂ ) Lithium imide salts; liC (FSO) ₂ ) ₃ 、LiC(CF ₃ SO ₂ ) ₃ 、LiC(C ₂ F ₅ SO ₂ ) ₃ Isomethylated lithium salts; lithium (malonate) borates such as lithium bis (malonate) borate and lithium difluoro (malonate) borate; lithium (malonate) phosphate salts such as lithium tris (malonate) phosphate, lithium difluorobis (malonate) phosphate, and lithium tetrafluoro (malonate) phosphate; liPF (liquid crystal display) and LiPF ₄ (CF ₃ ) ₂ 、LiPF ₄ (C ₂ F ₅ ) ₂ 、LiPF ₄ (CF ₃ SO ₂ ) ₂ 、LiPF ₄ (C ₂ F ₅ SO ₂ ) ₂ 、LiBF ₃ CF ₃ 、LiBF ₃ C ₂ F ₅ 、LiBF ₃ C ₃ F ₇ 、LiBF ₂ (CF ₃ ) ₂ 、LiBF ₂ (C ₂ F ₅ ) ₂ 、LiBF ₂ (CF ₃ SO ₂ ) ₂ 、LiBF ₂ (C ₂ F ₅ SO ₂ ) ₂ Fluorine-containing organolithium salts; lithium oxalato borate salts such as lithium difluorooxalato borate and lithium bis (oxalato) borate; lithium oxalate phosphates such as lithium tetrafluorooxalate phosphate, lithium difluorobis (oxalato) phosphate and lithium tris (oxalato) phosphate.

In some embodiments, the electrolyte is selected from LiPF ₆ 、LiSbF ₆ 、FSO ₃ Li、CF ₃ SO ₃ Li、LiN(FSO ₂ ) ₂ 、LiN(FSO ₂ )(CF ₃ SO ₂ )、LiN(CF ₃ SO ₂ ) ₂ 、LiN(C ₂ F ₅ SO ₂ ) ₂ Cyclic 1, 2-perfluoroethane bissulfonylimide lithium, cyclic 1, 3-perfluoropropane bissulfonylimide lithium, liC (FSO) ₂ ) ₃ 、LiC(CF ₃ SO ₂ ) ₃ 、LiC(C ₂ F ₅ SO ₂ ) ₃ 、LiBF ₃ CF ₃ 、LiBF ₃ C ₂ F ₅ 、LiPF ₃ (CF ₃ ) ₃ 、LiPF ₃ (C ₂ F ₅ ) ₃ Lithium difluorooxalato borate, lithium bis (oxalato) borate or lithium difluorobis (oxalato) phosphate, which contribute to improvement of output characteristics, high-rate charge-discharge characteristics, high-temperature storage characteristics, cycle characteristics, and the like of electrochemical devices.

The content of the electrolyte is not particularly limited as long as the effects of the present application are not impaired. In some embodiments, the total molar concentration of lithium in the electrolyte is greater than 0.3mol/L or greater than 0.4mol/L or greater than 0.5mol/L. In some embodiments, the total molar concentration of lithium in the electrolyte is less than 3mol/L, less than 2.5mol/L, or less than 2.0mol/L or less. In some embodiments, the total molar concentration of lithium in the electrolyte is within a range consisting of any two of the values recited above. When the electrolyte concentration is within the above range, lithium as charged particles is not excessively small, and the viscosity can be brought into an appropriate range, so that good conductivity is easily ensured.

In the case where two or more electrolytes are used, the electrolytes include at least one salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate. In some embodiments, the electrolyte comprises a salt selected from the group consisting of monofluorophosphate, oxalate, and fluorosulfonate. In some embodiments, the electrolyte comprises a lithium salt. In some embodiments, the salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate is present in an amount greater than 0.01% or greater than 0.1% based on the weight of the electrolyte. In some embodiments, the salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate is present in an amount of less than 20% or less than 10% based on the weight of the electrolyte. In some embodiments, the salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate is present in an amount within the range of any two values recited above.

In some embodiments, the electrolyte comprises one or more materials selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate, and one or more salts other than. As other salts, there may be mentioned the lithium salts exemplified hereinabove, in some embodiments LiPF ₆ 、LiN(FSO ₂ )(CF ₃ SO ₂ )、LiN(CF ₃ SO ₂ ) ₂ 、LiN(C ₂ F ₅ SO ₂ ) ₂ Cyclic 1, 2-perfluoroethane bissulfonylimide lithium, cyclic 1, 3-perfluoropropane bissulfonylimide lithium, liC (FSO) ₂ ) ₃ 、LiC(CF ₃ SO ₂ ) ₃ 、LiC(C ₂ F ₅ SO ₂ ) ₃ 、LiBF ₃ CF ₃ 、LiBF ₃ C ₂ F ₅ 、LiPF ₃ (CF ₃ ) ₃ 、LiPF ₃ (C ₂ F ₅ ) ₃ . In some embodiments, the other salt is LiPF ₆ 。

In some embodiments, the other salts are present in an amount greater than 0.01% or greater than 0.1% based on the weight of the electrolyte. In some embodiments, the other salts are present in an amount of less than 20%, less than 15%, or less than 10% based on the weight of the electrolyte. In some embodiments, the other salts are present in an amount within the range consisting of any two of the values recited above. The other salts with the above content help balance the conductivity and viscosity of the electrolyte.

III, negative electrode

The anode includes an anode current collector and an anode active material layer provided on at least one surface of the anode current collector, wherein the anode active material layer contains an anode active material. The anode active material layer may be one or more layers, and each of the multiple layers of anode active material may contain the same or different anode active material. The negative electrode active material is any material capable of reversibly intercalating and deintercalating metal ions such as lithium ions. In some embodiments, the chargeable capacity of the negative electrode active material is greater than the discharge capacity of the positive electrode active material to prevent the inadvertent precipitation of lithium metal on the negative electrode during charging.

As the current collector for holding the anode active material, a known current collector can be arbitrarily used. Examples of the negative electrode current collector include, but are not limited to, metal materials such as aluminum, copper, nickel, stainless steel, nickel-plated steel, and the like. In some embodiments, the negative current collector is copper.

In the case that the negative electrode current collector is a metal material, the negative electrode current collector form may include, but is not limited to, a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, a metal expanded metal, a punched metal, a foamed metal, and the like. In some embodiments, the negative electrode current collector is a metal thin film. In some embodiments, the negative current collector is copper foil. In some embodiments, the negative electrode current collector is a rolled copper foil based on a rolling method or an electrolytic copper foil based on an electrolytic method.

In some embodiments, the negative electrode current collector has a thickness of greater than 1 μm or greater than 5 μm. In some embodiments, the negative electrode current collector has a thickness of less than 100 μm or less than 50 μm. In some embodiments, the thickness of the negative electrode current collector is within a range consisting of any two of the values described above.

The negative electrode active material is not particularly limited as long as it can reversibly store and release lithium ions. Examples of the anode active material may include, but are not limited to, carbon materials such as natural graphite, artificial graphite, and the like; metals such as silicon (Si) and tin (Sn); or oxides of metallic elements such as Si and Sn. The negative electrode active material may be used alone or in combination.

The anode active material layer may further include an anode binder. The anode binder can improve the bonding of anode active material particles to each other and the bonding of anode active material to the current collector. The type of the negative electrode binder is not particularly limited as long as it is a material stable to the electrolyte or the solvent used in the electrode production. In some embodiments, the negative electrode binder includes a resin binder. Examples of the resin binder include, but are not limited to, fluorine resins, polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, and the like. When the negative electrode mixture slurry is prepared using an aqueous solvent, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or a salt thereof, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, and the like.

The negative electrode may be prepared by: the negative electrode can be obtained by applying a negative electrode mixture slurry containing a negative electrode active material, a resin binder, and the like to a negative electrode current collector, drying the slurry, and then rolling the dried slurry to form negative electrode active material layers on both surfaces of the negative electrode current collector.

IV, isolation film

In order to prevent short circuit, a separator is generally provided between the positive electrode and the negative electrode. In this case, the electrolyte of the present application is generally used by penetrating into the separator.

The material and shape of the separator are not particularly limited as long as the effect of the present application is not significantly impaired. The separator may be a resin, glass fiber, inorganic, or the like formed of a material stable to the electrolyte of the present application. In some embodiments, the separator includes a porous sheet or a substance in a nonwoven fabric-like form, etc., which is excellent in liquid retention. Examples of materials for the resin or fiberglass barrier film may include, but are not limited to, polyolefin, aromatic polyamide, polytetrafluoroethylene, polyethersulfone, and the like. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The materials of the above-mentioned separator may be used alone or in any combination.

The separator may be a laminate of the above materials, and examples thereof include, but are not limited to, a three-layer separator laminated in this order of polypropylene, polyethylene, and polypropylene.

Examples of the material of the inorganic substance may include, but are not limited to, oxides such as alumina, silica, nitrides such as aluminum nitride, silicon nitride, etc., sulfates (e.g., barium sulfate, calcium sulfate, etc.). The inorganic forms may include, but are not limited to, particulate or fibrous.

The form of the separator may be a film form, examples of which include, but are not limited to, nonwoven fabric, woven fabric, microporous film, and the like. In the form of a thin film, the separator has a pore diameter of 0.01 μm to 1 μm and a thickness of 5 μm to 50 μm. In addition to the above-described independent film-like separator, the following separator may be used: a separator formed by forming a composite porous layer containing the above inorganic particles on the surface of the positive electrode and/or the negative electrode using a resin-based binder, for example, a separator formed by forming porous layers on both surfaces of the positive electrode with 90% of alumina particles having a particle diameter of less than 1 μm using a fluororesin as a binder.

The thickness of the separator is arbitrary. In some embodiments, the thickness of the barrier film is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the separator is less than 50 μm, less than 40 μm, or less than 30 μm. In some embodiments, the thickness of the separator is in the range of any two values recited above. When the thickness of the separator is within the above range, insulation and mechanical strength can be ensured, and rate characteristics and energy density of the electrochemical device can be ensured.

When a porous material such as a porous sheet or a nonwoven fabric is used as the separator, the porosity of the separator is arbitrary. In some embodiments, the separator has a porosity of greater than 10%, greater than 15%, or greater than 20%. In some embodiments, the separator has a porosity of less than 60%, less than 50%, or less than 45%. In some embodiments, the separator has a porosity within a range consisting of any two of the values recited above. When the porosity of the separator is within the above range, insulation and mechanical strength can be ensured, and membrane resistance can be suppressed, resulting in an electrochemical device having good safety characteristics.

The average pore size of the separator is also arbitrary. In some embodiments, the separator has an average pore size of less than 0.5 μm or less than 0.2 μm. In some embodiments, the separator has an average pore size of greater than 0.05 μm. In some embodiments, the separator has an average pore size within a range consisting of any two of the values recited above. If the average pore diameter of the separator exceeds the above range, short-circuiting is liable to occur. When the average pore diameter of the separator is within the above range, the electrochemical device is provided with good safety characteristics.

V, electrochemical device

The electrochemical device of the present application includes any device in which an electrochemical reaction occurs, and specific examples thereof include a lithium metal secondary battery or a lithium ion secondary battery.

VI, electronic device

The present application further provides an electronic device comprising an electrochemical device according to the present application.

The use of the electrochemical device of the present application is not particularly limited, and it may be used in any electronic device known in the art. In some embodiments, the electrochemical devices of the present application may be used in, but are not limited to, notebook computers, pen-input computers, mobile computers, electronic book players, cellular telephones, portable fax machines, portable copiers, portable printers, headsets, video recorders, liquid crystal televisions, hand-held cleaners, portable CD players, mini compact discs, transceivers, electronic notepads, calculators, memory cards, portable audio recorders, radios, backup power supplies, motors, automobiles, motorcycles, mopeds, bicycles, lighting fixtures, toys, gaming machines, watches, power tools, flashlights, cameras, home-use large storage batteries, lithium-ion capacitors, and the like.

The preparation of lithium ion batteries is described below by way of example in connection with specific examples, and those skilled in the art will appreciate that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

1. Preparation of lithium ion batteries

1. Preparation of negative electrode

Mixing artificial graphite, styrene-butadiene rubber and sodium carboxymethyl cellulose with deionized water according to the mass ratio of 96-2% to 2%, and uniformly stirring to obtain slurry. The slurry was coated on a 9 μm copper foil. Drying, cold pressing, cutting, and welding the tab to obtain the negative electrode.

2. Preparation of the Positive electrode

Polyvinylidene fluoride (PVDF) with different densities is synthesized by controlling the temperature rising speed and pressure of the steps and the time of each step.

The positive electrode active material lithium cobaltate (Hunan fir LC 9000E), carbon nano tubes and PVDF with different densities are mixed with N-methyl pyrrolidone (NMP) according to the mass ratio of 97 percent to 1 percent to 2 percent, and the mixture is uniformly stirred to obtain positive electrode slurry. Alumina or aluminum nitride and PVDF with different densities are mixed with NMP according to the mass ratio of 90 percent to 10 percent to obtain insulating layer slurry. And coating the positive electrode slurry and the insulating layer slurry on an aluminum foil with the thickness of 12 mu m, drying, cold pressing, cutting and welding the tab to obtain the positive electrode.

3. Preparation of electrolyte

Mixing EC, PC and DEC (weight ratio 1:1:1) under dry argon, adding LiPF ₆ MixingUniform, form a base electrolyte, wherein LiPF ₆ The concentration of (2) was 12.5%. The electrolytes of the different examples and comparative examples were obtained by adding different amounts of additives to the base electrolyte as needed.

Abbreviations and names of components in the electrolyte are shown in the following table:

material name	Abbreviations (abbreviations)	Material name	Abbreviations (abbreviations)
				Ethylene carbonate	EC	Ethylene carbonate	PC
Diethyl carbonate	DEC	Ethylene glycol bis (2-cyanoethyl) ether	EDN
				1,2, 3-tris (2-cyanoethoxy) propane	TCEP	1,2, 4-tris (2-cyanoethoxy) butane	MJ-2
1, 1-tris (cyanoethoxymethylene) ethane	MJ-3	1,1,1-tris (cyanoethoxymethylene) propane	MJ-4
				3-methyl-1, 3, 5-tris (cyanoethoxy) pentane	MJ-5	1,2, 7-tris (cyanoethoxy) heptane	MJ-6
1,2, 6-tris (cyanoethoxy) hexane	MJ-7	1,2, 5-tris (cyanoethoxy) pentane	MJ-8

4. Preparation of a separator film

A porous polyethylene polymer film was used as a separator.

5. Preparation of lithium ion batteries

The obtained positive electrode, the separator and the negative electrode are wound in order and placed in an outer packaging foil, and a liquid injection port is left. And (3) pouring electrolyte from the liquid pouring port, packaging, and performing the working procedures of formation, capacity and the like to obtain the lithium ion battery.

2. Test method

1. Voltage drop test of lithium ion battery under high temperature storage

At 25 ℃, the lithium ion battery is charged to 4.7V at a constant current of 1C, then charged to 0.05C at a constant voltage, discharged to 3.2V at a constant current of 1C, and left standing for 5 minutes, and then the voltage is tested. After 24 hours of storage at 85 ℃, the voltage was retested. The voltage drop stored at high temperature for a lithium ion battery is calculated according to the following formula:

voltage drop = pre-storage voltage-post-storage voltage.

2. Overcharge deformation rate test of lithium ion battery

Standing the lithium ion battery at 25℃ for 3 DEG CCharging to 4.7V at constant current with 0.5C ratio for 0 min, charging to 0.05C at constant voltage of 4.7V, standing for 60 min, and measuring thickness T of lithium ion battery ₁ . Then charging for 60 min with constant current of 0.1C multiplying power, standing for 30 min, repeating this step for 5 times to make the lithium ion battery reach 150% state of charge (SOC), and measuring thickness T of the lithium ion battery ₂ . The overcharge deformation rate of the lithium ion battery is calculated according to the following formula:

rate of overcharge deformation = [ (T) ₂ -T ₁ )/T ₁ ]×100％。

3. Test results

Table 1 shows the effect of the content of aluminum element in the positive electrode insulating layer and the density of the binder in the positive electrode active material layer on the voltage drop and overcharge safety performance of the lithium ion battery under high temperature storage. In each embodiment, the aluminum element content x is adjusted by adjusting the mass ratio of the aluminum-containing material in the slurry to the binder in the insulating layer.

TABLE 1

The above results indicate that when the positive electrode includes an insulating layer having an aluminum element, it includes a material having a density of 0.6g/cm ³ To 1.5g/cm ³ When the binder is used in the positive electrode active material layer of the range of (c), the resulting electrochemical device exhibits excellent high-temperature safety performance and has a smaller voltage drop at high-temperature storage.

As is clear from examples 1-1 and comparative examples 1-4, by providing an insulating layer containing an aluminum element on the positive electrode, both the voltage drop and the overcharge deformation rate of the electrochemical device described in example 1-1 were significantly reduced in the high-temperature storage.

Further, comparing examples 1-8 to 1-15 with comparative examples 1-1 and 1-2, it can be seen that, in the case of the same insulating layer, when the density of the binder used for the positive electrode active material layer was 0.6g/cm ³ To 1.5g/cm ³ In the range of (2), voltage drop and oversubstance of the obtained electrochemical device under high temperature storageThe rate of deformation is significantly reduced.

Comparing examples 1-1 to 1-6, it can be seen that when the content of aluminum element in the insulating layer is in the range of 20% to 65%, the corresponding resultant electrochemical device exhibits more excellent high temperature safety performance and has less voltage drop at high temperature storage.

Furthermore, it can be seen from Table 1 that when 20.ltoreq.x/a.ltoreq.70, the electrochemical performance of the electrochemical device can be further optimized.

Table 2 shows the effect of the density and porosity of the positive electrode binder on the voltage drop and overcharge safety performance of the lithium ion battery in high temperature storage. Examples 2-1 to 2-12 in Table 2 differ from example 1-1 only in the parameters listed in Table 2.

TABLE 2

As can be seen from a review of the electrochemical test results in Table 2, when the density of the positive electrode binder is a g/cm ³ And when the porosity b% satisfies 17.ltoreq.b.ltoreq.60 and 14.ltoreq.b/a.ltoreq.55, the obtained electrochemical device exhibits more excellent high-temperature safety performance and has smaller voltage drop under high-temperature storage.

Table 3 shows the effects of the mass fraction of the positive electrode active material in the positive electrode active material layer and the density of the binder in the positive electrode active material layer on the voltage drop and overcharge safety performance of the lithium ion battery stored at high temperature. Examples 3-1 to 3-9 in Table 3 differ from example 1-1 only in the parameters listed in Table 3.

TABLE 3 Table 3

Referring to the results of the electrochemical test in Table 3, it can be seen that when the mass fraction M% of the positive electrode active material and the density of the binder in the positive electrode active material layer were a g/cm ³ When the M/a is more than or equal to 64 and less than or equal to 170, the obtained electrochemical device shows more excellent Gao Wenan Full performance and less voltage drop at high temperature storage.

Table 4 shows the effect of the ether nitrile compound content in the electrolyte and the density of the binder in the positive electrode active material layer on the voltage drop and overcharge safety performance of the lithium ion battery stored at high temperature. Examples 4-1 to 4-22 in Table 4 differ from example 1-1 only in the parameters listed in Table 4.

TABLE 4 Table 4

Referring to the electrochemical test results in table 4, it can be seen that after the ethernitrile compound is added to the electrolyte, the voltage drop and the overcharge deformation rate of the corresponding electrochemical device are significantly reduced. Further, when the mass fraction c% of the ether nitrile compound in the electrolyte and the density of the binder are a g/cm ³ When the ratio of c/a is more than or equal to 0.4 and less than or equal to 12, the performance improvement of the electrochemical device is more obvious.

Table 5 shows the effect of the binder in the insulating layer on the voltage drop and overcharge safety performance of the lithium ion battery in high temperature storage. Examples 5-1 to 5-6 in Table 5 differ from example 1-1 only in the parameters listed in Table 5.

TABLE 5

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When the insulating layer includes a low-density binder, it helps to further reduce the voltage drop and the overcharge deformation rate of the electrochemical device under high-temperature storage.

Reference throughout this specification to "an embodiment," "a portion of an embodiment," "one embodiment," "another example," "an example," "a particular example," or "a portion of an example" means that at least one embodiment or example in the present application includes the particular feature, structure, material, or characteristic described in the embodiment or example. Thus, descriptions appearing throughout the specification, for example: "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in one example," "in a particular example," or "example," which do not necessarily reference the same embodiments or examples 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 shown and described, it will be understood by those skilled in the art that the foregoing embodiments are not to be construed as limiting the application and that changes, substitutions and alterations of the embodiments may be made without departing from the spirit, principles and scope of the application.

Claims

1. An electrochemical device comprising a positive electrode, the positive electrode comprising:

a positive electrode current collector;

a positive electrode active material layer formed in a central region on at least one surface of the positive electrode current collector, the positive electrode active material layer including a positive electrode active material and a binder having a density of a g/cm ³ And a is more than or equal to 0.6 and less than or equal to 1.5; and

an insulating layer formed at an edge region on the at least one surface of the positive electrode current collector, and containing an aluminum element.

2. The electrochemical device of claim 1, wherein the insulating layer comprises the binder.

3. The electrochemical device according to claim 1, wherein the positive electrode active material layer and the insulating layer overlap each other to form an interaction region, the width of the interaction region being W mm and 0 < w.ltoreq.4.

4. The electrochemical device according to claim 1, wherein the positive electrode active material layer and the insulating layer do not overlap.

5. The electrochemical device according to claim 1, wherein the content of the aluminum element is x%, wherein 20.ltoreq.x.ltoreq.65, based on the weight of the insulating layer.

6. The electrochemical device of claim 5, wherein 20.ltoreq.x/a.ltoreq.70.

7. The electrochemical device according to claim 1, wherein 0.8.ltoreq.a.ltoreq.1.2.

8. The electrochemical device of claim 1, wherein the binder has a porosity of b%, 17-b-60, and 14-b/a-55.

9. The electrochemical device of claim 1, wherein the mass fraction of the positive electrode active material is m% based on the total weight of the positive electrode active material layer, wherein 90+.m+.99.5 and 64+.m/a+.170.

10. The electrochemical device of claim 1, wherein the electrochemical device further comprises an electrolyte comprising an ether nitrile compound, wherein the mass fraction of the ether nitrile compound is c%, based on the total weight of the electrolyte, wherein 0.01 c.ltoreq.8.

11. The electrochemical device of claim 10, wherein the ethernitrile compound comprises at least one of ethylene glycol di (2-cyanoethyl) ether, 1,2, 3-tris (2-cyanoethoxy) propane, 1,2, 4-tris (2-cyanoethoxy) butane, 1-tris (cyanoethoxymethylene) ethane, 1-tris (cyanoethoxymethylene) propane, 3-methyl-1, 3, 5-tris (cyanoethoxy) pentane, 1,2, 7-tris (cyanoethoxy) heptane, 1,2, 6-tris (cyanoethoxy) hexane, or 1,2, 5-tris (cyanoethoxy) pentane.

12. The electrochemical device of claim 10, wherein 0.4 c/a 12.

13. An electronic device comprising the electrochemical device according to any one of claims 1-12.