Electrochemical device and electronic device comprising the same

Abstract

The present application relates to an electrochemical device and an electronic device comprising the same. The electrochemical device of the present application comprises: a positive electrode, a negative electrode and an electrolyte, the positive electrode comprising a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material, wherein the mass percentage of the positive electrode active material is M% based on the mass of the positive electrode active material layer, M ranges from 95 to 99, and the cracking width of the surface of the positive electrode active material layer is W mm, wherein M and W satisfy: M / W≥47.5. The electrochemical device provided by the present application has reduced direct current internal resistance and improved capacity retention rate, low temperature performance and floating performance.

Description

[0001] This application is a divisional application of application number 202180012340.4, filed on September 30, 2021, entitled "Electrochemical Device and Electronic Device Including the Same". Technical Field

[0002] This application relates to the field of energy storage, specifically to an electrochemical device and an electronic device comprising the same, particularly a lithium-ion battery. Background Technology

[0003] In recent years, with the continuous expansion of the battery industry and the development of related technologies, the energy density of lithium-ion batteries has received increasing attention and challenges. Currently, the most effective solution for continuously improving and enhancing energy density is to increase the coating weight of the cathode and reduce the amount of inactive materials used. However, increasing the coating weight can lead to severe coating cracking due to increased stress, affecting battery consistency and electrochemical performance.

[0004] Although existing technologies can reduce the coating speed and oven temperature to slow down the electrode drying process and prevent the solvent in the electrode from evaporating too quickly and causing excessive stress that could lead to cracking of the electrode coating, this method inhibits industrial production, increases manufacturing costs, and makes it difficult to achieve mass production. Summary of the Invention

[0005] This application provides an electrochemical and electronic device that can effectively suppress the growth of DC internal resistance under high voltage and high temperature, and effectively improve the float charging performance under high voltage, thereby solving, to some extent, the problems existing in the prior art.

[0006] In one embodiment, this application provides an electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte. The positive electrode comprises a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector. The positive electrode active material layer comprises positive electrode active material, wherein the mass percentage of the positive electrode active material is M% based on the mass of the positive electrode active material layer, and M ranges from 95 to 99. The crack width on the surface of the positive electrode active material layer is W mm, wherein M and W satisfy: M / W ≥ 47.5.

[0007] In some embodiments, W≤2.

[0008] In some embodiments, the unit area mass of the positive electrode active material layer is M1 mg / 1540.25 mm². 2 The value of M1 ranges from 100 to 400, where M1 and W satisfy: M1 / W≥50.

[0009] In some embodiments, the solid content of the positive electrode active material layer coating slurry is M2%, and the value of M2 ranges from 55 to 80, wherein M2 and W satisfy: M2 / W≥27.5.

[0010] In some embodiments, the positive electrode comprises a fluorinated binder with a melting point in the range of 155°C to 270°C.

[0011] In some embodiments, the positive electrode active material layer comprises a polymeric compound having ether bonds, wherein the mass percentage of the polymeric compound having ether bonds is M4% based on the mass of the positive electrode active material layer, and M4 ≤ 0.3%.

[0012] In some embodiments, the oxidation potential of the polymeric compound having ether bonds is greater than or equal to 4.6V.

[0013] In some embodiments, the electrolyte includes additive A, which includes at least one of a compound having a cyano group or a compound having an FPO bond.

[0014] In some embodiments, the mass percentage of additive A is a%, where a ranges from 0.1 to 15%.

[0015] In some embodiments, M / a ≥ 6.33.

[0016] In some embodiments, the cyano-containing compound includes at least one of the following compounds: succinic anionyl, glutaronitrile, adiponitrile, 1,5-dicyanopentane, 1,6-dicyanohexane, tetramethylsuccinic anionyl, 2-methylglutaronitrile, 2,4-dimethylglutaronitrile, 2,2,4,4-tetramethylglutaronitrile, 1,4-dicyanopentane, 1,2-dicyanobenzene, 1,3-dicyanobenzene, 1,4-dicyanobenzene, and ethylene glycol bis(propionitrile) ether. 3,5-Dioxa-heptadionitrile, 1,4-Di(cyanoethoxy)butane, diethylene glycol di(2-cyanoethyl) ether, triethylene glycol di(2-cyanoethyl) ether, tetraethylene glycol di(2-cyanoethyl) ether, 1,3-Di(2-cyanoethoxy)propane, 1,4-Di(2-cyanoethoxy)butane, 1,5-Di(2-cyanoethoxy)pentane, ethylene glycol di(4-cyanobutyl) ether, 1,4-dicyano-2-butene, 1 4-Dicyano-2-methyl-2-butene, 1,4-dicyano-2-ethyl-2-butene, 1,4-dicyano-2,3-dimethyl-2-butene, 1,4-dicyano-2,3-diethyl-2-butene, 1,6-dicyano-3-hexene, 1,6-dicyano-2-methyl-3-hexene, 1,3,5-pentanetricarbonyl, 1,2,3-propanetricarbonyl, 1,3,6-hexanetricarbonyl, 1,2,6-hexanetricarbonyl 1,2,3-tris(2-cyanoethoxy)propane, 1,2,4-tris(2-cyanoethoxy)butane, 1,1,1-tris(cyanoethoxymethylene)ethane, 1,1,1-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.

[0017] In some embodiments, the compound having an FPO bond includes at least one of lithium difluorophosphate, a compound of formula 1, a compound of formula 2, a compound of formula 3, or a compound of formula 4:

[0018] Formula 1

[0019] Formula 2

[0020] Formula 3

[0021] Formula 4.

[0022] In some embodiments, the positive electrode active material satisfies one of the following conditions:

[0023] (1) The positive electrode active material includes lithium iron phosphate, and the D50 of the positive electrode active material is D1µm, wherein 2×D1≥W;

[0024] (2) The positive electrode active material includes lithium manganese iron phosphate, and the D50 of the positive electrode active material is D2µm, wherein 5×D2≥W;

[0025] (3) The positive electrode active material includes lithium manganese oxide, and the D50 of the positive electrode active material is D3µm, wherein 0.1×D3≥W;

[0026] (4) The positive electrode active material includes lithium nickel cobalt manganese oxide, and the D50 of the positive electrode active material is D4µm, wherein 0.15×D4≥W; and

[0027] (5) The positive electrode active material includes lithium cobalt oxide, and the D50 of the positive electrode active material is D5µm, wherein 0.15×D5≥W.

[0028] By selecting an appropriate particle size, this application can further adjust the flatness of the positive electrode surface, thereby improving the performance of lithium-ion batteries.

[0029] In some embodiments, the electrolyte further comprises additive B, which includes at least one of fluoroethylene carbonate, 1,3-propanesulfonate lactone, ethylene sulfate, ethylene ethylene carbonate, or cyclic anhydride phosphate.

[0030] In another embodiment, this application provides an electronic device that includes the electrochemical device described in the embodiments of this application.

[0031] The electrochemical device provided in this application has reduced DC internal resistance and improved capacity retention, low-temperature performance and float charge performance.

[0032] Additional aspects and advantages of the embodiments of this application will be described and shown in part in the following description, or illustrated by practice of the embodiments of this application. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0034] Figure 1 SEM images of the surface of the positive electrode active material layer in Examples 1-8 of this application are shown. Detailed Implementation

[0035] The technical solutions of this application will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0036] The embodiments of this application will be described in detail below. These embodiments should not be construed as limiting the scope of this application.

[0037] Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format in this document. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only the numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0038] In the detailed description and claims, a list of items connected by the terms "one of," "among," "a kind of," or other similar terms may mean any of the listed items. For example, if items A and B are listed, then the phrase "one of A and B" means only A or only B. In another example, if items A, B, and C are listed, then the phrase "one of A, B, and C" means only A; only B; or only C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0039] In the detailed description and claims, a list of items connected by the terms "at least one of," "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, then 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 all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0040] I. Electrochemical Device

[0041] In some embodiments, this application provides an electrochemical device, which includes a positive electrode, a negative electrode, and an electrolyte.

[0042] positive electrode

[0043] 1. Positive electrode active material layer

[0044] In some embodiments, the positive electrode includes a positive current collector and a layer of positive active material located on the positive current collector, the layer comprising positive active material. In some embodiments, the positive active material layer may be one or more layers. In some embodiments, each layer of multiple positive active materials may contain the same or different positive active materials. The positive active material is any material capable of reversibly inserting and deintercalating metal ions such as lithium ions. In some embodiments, the discharge capacity of the positive active material is less than the rechargeable capacity of the negative active material to prevent unintentional deposition of lithium metal onto the negative electrode during charging.

[0045] (1) Crack width on the surface of the positive electrode active material layer

[0046] In some embodiments, based on the mass of the positive electrode active material layer, the mass percentage of the positive electrode active material is M%, and the value of M ranges from 95 to 99%.

[0047] In some embodiments, M is a range of 95, 96, 97, 98, 99, or any combination of these values. When the mass percentage of the positive electrode active material in the positive electrode active material layer is higher than 95%, the energy density of the electrochemical device can be significantly improved.

[0048] In some embodiments, the crack width on the surface of the positive electrode active material layer is W mm, where W ≤ 2. In some embodiments, W is a range of 0.01, 0.02, 0.03, 0.05, 0.08, 0.1, 0.15, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.4, 1.5, 1.8, 2, or any combination of these values. When the crack width on the surface of the positive electrode active material layer is infinitely small, or especially when it is nonexistent, the float charge performance of the electrochemical device under high voltage can be significantly improved.

[0049] In some embodiments, M and W satisfy: M / W ≥ 47.5. In some embodiments, M / W is a range of 47.5, 50, 60, 80, 90, 100, 120, 150, 200, 300, 400, 500, 100, 1500, 1800, 2000, 5000, 8000, 9000, 10000, 15000, 18000, 20000, or any combination of these values.

[0050] When the positive electrode satisfies the above relationship, it can not only improve the interfacial stability of the positive electrode active material layer, but also fully suppress the increase of DC internal resistance of the electrochemical device at room temperature and high temperature, and unexpectedly improve the float charging performance at high voltage.

[0051] The crack width on the surface of the positive electrode active material layer reflects its surface properties and is one of the parameters characterizing it. A smaller crack width indicates better interface smoothness, which can significantly improve the cycle performance, rate performance, float charge performance, and reduce the DC internal resistance of the electrochemical device. The crack width of the positive electrode active material layer can be affected by various factors, mainly including the coating weight, compaction density, solid content of the coating slurry, particle size, content of the positive electrode active material, binder, additives, functional treatment layers on the surface, and porosity.

[0052] The cracking described in this application refers to the cracks that occur on the surface of the positive electrode active material layer due to internal stress, external impact, or environmental conditions. The crack width on the surface of the positive electrode active material layer described in this application refers to the largest crack width among all cracks, which can be measured by measuring with a ruler or other instruments for measuring dimensions.

[0053] (2) Mass of the positive electrode active material layer

[0054] In some embodiments, the unit area mass of the positive electrode active material layer is M1 mg / 1540.25 mm². 2 The value of M1 ranges from 100 to 400. In some embodiments, M1 is 100, 120, 140, 150, 160, 180, 200, 240, 250, 270, 280, 290, 300, 350, 380, 400, or any combination of these values. When the value of M1 is between 100 and 400, the positive electrode surface can maintain structural stability during charge-discharge cycles, further improving the performance of the lithium-ion battery. If the value of M1 exceeds 400, the active layer is too thick, reducing the permeability of the electrolyte and making electron transport in the battery difficult, leading to increased battery polarization and thus deteriorating the high-current-density charge-discharge characteristics. Furthermore, if the value of M1 is below 100, the active layer exerts a significant impact on the current collector during processing, damaging the current collector interface, and increasing the relative displacement between active materials, affecting performance.

[0055] In some embodiments, M1 and W satisfy: M1 / W ≥ 50. In some embodiments, M1 and W satisfy: M1 / W is a range of 50, 80, 100, 150, 200, 250, 300, 350, 400, 500, or any combination of these values. When the positive electrode satisfies the above relationship, further improved effects can be obtained.

[0056] (3) Solid content of the coating slurry for the positive electrode active material layer

[0057] In some embodiments, the solid content of the positive electrode active material layer coating slurry is M2%, where M2 ranges from 55 to 80. In some embodiments, M2 is a range of 55, 58, 60, 63, 65, 68, 70, 72, 75, 78, 80, or any combination of these values. When M2 is in the range of 55 to 80, there are fewer defects on the positive electrode surface, further improving the performance of the lithium-ion battery. If this range is exceeded, the electrode will crack severely during baking. Conversely, if the value is below this range, solvent will be wasted and baking time will be prolonged during the preparation of the positive electrode active material layer, resulting in process losses.

[0058] In some embodiments, M2 and W satisfy: M2 / W ≥ 27.5. In some embodiments, M2 / W is a range of 27.5, 30, 32, 35, 38, 40, 45, 50, 60, 70, 80, 90, 100, 120, 200, 300, 350, 370, 400, 500, 600, 700, 800, 1000, 1100, 1400, 1500, 3000, 5000, 7000, 9000, 10000, 16000, 20000, or any combination of these values. When the positive electrode satisfies the above relationship, further improvements can be achieved.

[0059] (4) Binder in the positive electrode active material layer

[0060] In some embodiments, the positive electrode comprises a fluorinated binder with a melting point in the range of 155°C to 270°C. In some embodiments, the melting point of the fluorinated binder is 155°C, 160°C, 165°C, 170°C, 172°C, 175°C, 180°C, 200°C, 220°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, or a range of any two of these values.

[0061] When using fluorine-based binders with melting points in the range of 155°C to 270°C, excellent DC internal resistance and float charge performance under high temperature and high pressure were also achieved. In particular, when using fluorine-based binders with melting points in the range of 155°C to 260°C, they can be further uniformly distributed on the surface of the cathode material particles during the baking or hot pressing process of electrode preparation, effectively improving the adhesion effect, suppressing electrode surface defects, and further improving the performance of lithium-ion batteries.

[0062] In some embodiments, the fluorinated binder comprises polyvinylidene fluoride (PVDF). In some embodiments, the PVDF comprises a homopolymer of PVDF as a monomer and a copolymer of PVDF (VdF) as a monomer. In some embodiments, the ends of the PVDF may be modified with maleic acid.

[0063] In some embodiments, the fluorinated binder comprises 0.5% to 3% by mass, based on the mass of the positive electrode active material layer. In some embodiments, the fluorinated binder comprises 0.5%, 0.8%, 1.0%, 1.5%, 1.8%, 2.0%, 2.2%, 2.5%, 2.8%, 3%, or any combination of these values, based on the mass of the positive electrode active material layer.

[0064] When the content of fluorinated binder is less than 0.5%, the coverage of the positive electrode active material particles by the fluorinated binder becomes insufficient, the adhesion decreases, and the cracking phenomenon is aggravated. On the other hand, when the content of fluorinated binder exceeds 3%, the positive electrode active material particles are over-covered by the fluorinated binder, resulting in an increase in DC resistance. This leads to the inability to obtain high discharge rate performance at low temperatures and good float charge performance at high temperatures.

[0065] (5) Additives in the positive electrode active material layer

[0066] In some embodiments, the positive electrode active material layer includes an additive. In some embodiments, the additive includes a polymeric compound having ether bonds, wherein the mass percentage of the polymeric compound having ether bonds is M4% based on the mass of the positive electrode active material layer, where M4 ≤ 0.3%.

[0067] In some embodiments, M4 is a range of 0.04, 0.05, 0.06, 0.07, 0.08, 0.1, 0.12, 0.14, 0.15, 0.18, 0.2, 0.25, 0.28, 0.3, or any combination of these values. When the content of the additive is within the above range, it helps to improve the following characteristics of the electrochemical device: output power characteristics, load characteristics, low-temperature characteristics, cycle characteristics, and high-temperature storage characteristics.

[0068] In some embodiments, the oxidation potential of the polymer compound having ether bonds is greater than or equal to 4.6V. In some embodiments, the oxidation potential of the polymer compound having ether bonds is 4.6V, 4.7V, 4.8V, 4.9V, 5.0V, 5.1V, 5.2V, 5.3V, 5.4V, 5.5V, 5.6V, 6V, or any combination of these values. When the oxidation potential of the additive is within the above range, the electrochemical performance of the electrochemical device is stable and resistant to high voltage, which helps to improve the float charging performance of the electrochemical device under high temperature and high pressure.

[0069] In some embodiments, the polymeric compound having ether bonds includes at least one of polyethylene oxide, polyether, polyol, or polyol ester.

[0070] (6) Positive electrode active material

[0071] In some embodiments, the type of positive electrode active material is not particularly limited, as long as it is capable of electrochemically adsorbing and releasing metal ions (e.g., lithium ions). In some embodiments, the positive electrode active material is a substance containing lithium and at least one transition metal. Examples of positive electrode active materials may include, but are not limited to, lithium transition metal composite oxides and lithium transition metal phosphate compounds.

[0072] In some embodiments, the transition metal in the lithium transition metal composite oxide includes V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. In some embodiments, the lithium transition metal composite oxide includes lithium cobalt composite oxides such as LiCoO2, lithium nickel composite oxides such as LiNiO2, lithium manganese composite oxides such as LiMnO2, LiMn2O4, and Li2MnO4, and LiNi... 1 / 3 Mn 1 / 3 Co 1 / 3 O2, LiNi 0.5 Mn 0.3 Co 0.2 Lithium-nickel-manganese-cobalt composite oxides, such as O2, in which a portion of the transition metal atoms that form the bulk of these lithium transition metal composite oxides are replaced by 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, and W. Examples of lithium transition metal composite oxides include, but are not limited to, LiNi. 0.5 Mn 0.5 O2, LiNi 0.85 Co 0.10 Al 0.05 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.45 Co 0.10 Al 0.45 O2, LiMn 1.8 Al 0.2 O4 and LiMn 1.5 Ni 0.5 O4, etc. Examples of combinations of lithium transition metal composite oxides include, but are not limited to, combinations of LiCoO2 and LiMn2O4, wherein a portion of the Mn in LiMn2O4 can be replaced by a transition metal (e.g., LiNi). 0.33 Co 0.33 Mn 0.33 In LiCoO2, some of the Co can be replaced by transition metals.

[0073] In some embodiments, the transition metal in the lithium transition metal phosphate compound includes V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. In some embodiments, the lithium transition metal phosphate compound includes iron phosphates such as LiFePO4, Li3Fe2(PO4)3, and LiFeP2O7, and cobalt phosphates such as LiCoPO4, wherein a portion of the transition metal atoms that constitute the main body of these lithium transition metal phosphate compounds are replaced by other elements such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, Si, etc.

[0074] In some embodiments, the positive electrode active material includes lithium phosphate, which can improve the continuous charging characteristics of the electrochemical device. There are no restrictions on the use of lithium phosphate. In some embodiments, the positive electrode active material and lithium phosphate are used in combination. In some embodiments, the mass percentage of lithium phosphate relative to the mass of the positive electrode active material and lithium phosphate is greater than 0.1%, greater than 0.3%, or greater than 0.5%. In some embodiments, the mass percentage of lithium phosphate relative to the mass of the positive electrode active material and lithium phosphate is less than 10%, less than 8%, or less than 5%. In some embodiments, the content of lithium phosphate is within the range of any two of the above values.

[0075] The surface of the aforementioned positive electrode active material may be coated with a substance of a different composition. Examples of such surface-coated substances may include, but are not limited to: oxides such as aluminum oxide, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, 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; and carbon, etc.

[0076] These surface-adhering substances can be attached to the surface of the positive electrode active material by methods such as: dissolving or suspending the surface-adhering substance in a solvent and adding it into the positive electrode active material followed by drying; dissolving or suspending the surface-adhering substance precursor in a solvent, adding it into the positive electrode active material, and then reacting it by heating or the like; and adding it to the positive electrode active material precursor while simultaneously calcining it, etc. In the case of carbon attachment, a method of mechanically attaching carbon materials (e.g., activated carbon) can also be used.

[0077] In some embodiments, based on the mass of the positive electrode active material layer, the content of the surface-adhered substance is greater than 0.1 ppm, greater than 1 ppm, or greater than 10 ppm. In some embodiments, based on the mass of the positive electrode active material layer, the content of the surface-adhered substance is less than 10%, less than 5%, or less than 2%. In some embodiments, based on the mass of the positive electrode active material layer, the content of the surface-adhered substance is within the range of any two of the above values.

[0078] 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, thereby improving the lifespan of the electrochemical device. When the amount of surface-attached substance is too small, its effect cannot be fully realized; when the amount of surface-attached substance is too large, it will hinder the entry and exit of lithium ions, thus sometimes increasing the resistance.

[0079] In this application, a positive electrode active material on which a substance with a different composition is attached to the surface of the positive electrode active material is also referred to as a "positive electrode active material".

[0080] In some embodiments, the shape of the positive electrode active material particles includes, but is not limited to, blocky, polyhedral, spherical, ellipsoidal, plate-like, needle-like, and columnar shapes. In some embodiments, the positive electrode active material particles include primary particles, secondary particles, or combinations thereof. In some embodiments, primary particles may aggregate to form secondary particles.

[0081] In some embodiments, the tap density of the positive electrode active material is greater than 0.5 g / cm³. 3 Greater than 0.8 g / cm 3 or greater than 1.0 g / cm 3 When the tap density of the positive electrode active material is within the above-mentioned range, the amount of dispersion medium required for the formation of the positive electrode active material layer, as well as the required amounts of conductive material and positive electrode binder, can be suppressed, thereby ensuring the filling rate of the positive electrode active material and the capacity of the electrochemical device. A high-density positive electrode active material layer can be formed by using composite oxide powder with high tap density. Generally, a higher tap density is preferred, with no particular upper limit. In some embodiments, the tap density of the positive electrode active material is less than 4.0 g / cm³. 3 Less than 3.7 g / cm 3 or less than 3.5 g / cm 3 When the tap density of the positive electrode active material has the upper limit mentioned above, the reduction in load characteristics can be suppressed.

[0082] The tap density of the positive electrode active material can be calculated as follows: Place 5g to 10g of positive electrode active material powder into a 10mL glass graduated cylinder and vibrate it 200 times with a stroke of 20mm to obtain the powder filling density (tap density).

[0083] When the positive electrode active material particles are primary particles, the median particle size (D50) of the positive electrode active material particles refers to the primary particle size. When the primary particles of the positive electrode active material aggregate to form secondary particles, the median particle size (D50) of the positive electrode active material particles refers to the secondary particle size.

[0084] In some embodiments, the median particle size (D50) of the positive electrode active material particles is greater than 0.3 μm, greater than 0.5 μm, greater than 0.8 μm, or greater than 1.0 μm. In some embodiments, the median particle size (D50) of the positive electrode active material particles is less than 30 μm, less than 27 μm, less than 25 μm, or less than 22 μm. In some embodiments, the median particle size (D50) of the positive electrode active material particles is within the range of any two of the above values. When the median particle size (D50) of the positive electrode active material particles is within the above range, a positive electrode active material with high tap density can be obtained, which can suppress the degradation of the performance of the electrochemical device. On the other hand, during the preparation process of the positive electrode of the electrochemical device (i.e., when the positive electrode active material, conductive material, and binder are slurried with a solvent and coated in a thin film), problems such as streaking can be prevented. Here, by mixing two or more positive electrode active materials with different median particle sizes, the filling properties during positive electrode preparation can be further improved.

[0085] The median particle size (D50) of the positive electrode active material particles can be determined using a laser diffraction / scattering particle size distribution measuring device: using the LA-920 manufactured by HORIBA as the particle size distributor, a 0.1% sodium hexametaphosphate aqueous solution is used as the dispersion medium for the measurement. After ultrasonic dispersion for 5 minutes, the refractive index is set to 1.24 for measurement.

[0086] In some embodiments, the positive electrode active material satisfies one of the following conditions:

[0087] (1) The positive electrode active material includes lithium iron phosphate, and the D50 of the positive electrode active material is D1µm, wherein 2×D1≥W;

[0088] (2) The positive electrode active material includes lithium manganese iron phosphate, and the D50 of the positive electrode active material is D2µm, wherein 5×D2≥W;

[0089] (3) The positive electrode active material includes lithium manganese oxide, and the D50 of the positive electrode active material is D3µm, wherein 0.1×D3≥W;

[0090] (4) The positive electrode active material includes lithium nickel cobalt manganese oxide, and the D50 of the positive electrode active material is D4µm, wherein 0.15×D4≥W; and

[0091] (5) The positive electrode active material includes lithium cobalt oxide, and the D50 of the positive electrode active material is D5µm, wherein 0.15×D5≥W.

[0092] In some embodiments, the aforementioned positive electrode active materials, such as lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium cobalt oxide, can be used alone or in any combination. By selecting a suitable particle size, the flatness of the positive electrode surface and the compaction density of the electrode can be further adjusted, thereby improving the performance of the lithium-ion battery.

[0093] In some embodiments, the positive electrode active material layer further comprises a conductive agent. In some embodiments, the conductive agent comprises at least one selected from carbon nanotubes, carbon fibers, acetylene black, graphene, Ketjen black, or carbon black.

[0094] In some embodiments, the positive current collector includes at least one of copper foil or aluminum foil.

[0095] In some embodiments, the positive electrode can be prepared by methods known in the art. For example, the positive electrode can be obtained by mixing a positive electrode active material, a conductive agent, and a binder in a solvent to prepare an active material composition, and then coating the active material composition onto a current collector. In some embodiments, the solvent may include, but is not limited to, N-methylpyrrolidone, etc.

[0096] 2. Electrolyte

[0097] In some embodiments, the electrolyte used in the electrochemical device of this application comprises an electrolyte and a solvent for dissolving the electrolyte. In some embodiments, the electrolyte comprises additive A, which comprises at least one of a compound having a cyano group or a compound having an FPO bond.

[0098] Adding compounds with cyano groups or FPO bonds to the electrolyte can result in excellent DC internal resistance and float charge performance under high temperature and high pressure. In particular, the combined use of compounds with cyano groups and compounds with FPO bonds can further suppress electrode surface defects caused by the decomposition and remodeling of the positive electrode surface protective film during cycling, thereby improving the performance of lithium-ion batteries.

[0099] In some embodiments, the mass percentage of additive A is a%, and the value of a ranges from 0.1 to 15. In some embodiments, a is 0.1, 0.4, 0.5, 0.8, 1, 1.5, 1.8, 2, 2.5, 3, 3.5, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or a range of any two of these values.

[0100] In some embodiments, M / a is a range of 6.33, 8, 10, 15, 20, 24, 28, 30, 32, 35, 40, 45, 50, 100, 150, 190, 200, 250, or any combination of these values. When the above relationship is satisfied, the uniformity of the electrode surface is well maintained during cycling, thus not only further improving the DC internal resistance and float charge performance under high temperature and high pressure, but also unexpectedly improving the capacity retention rate at high voltage and the rate performance at low temperature. This may be because the interface formed between the positive electrode and the electrolyte has good stability and low impedance under high voltage and low temperature, which makes it easier for lithium ions to be inserted and extracted.

[0101] In some embodiments, the cyano-containing compound includes at least one of the following compounds: succinic anionyl, glutaronitrile, adiponitrile, 1,5-dicyanopentane, 1,6-dicyanohexane, tetramethylsuccinic anionyl, 2-methylglutaronitrile, 2,4-dimethylglutaronitrile, 2,2,4,4-tetramethylglutaronitrile, 1,4-dicyanopentane, 1,2-dicyanobenzene, 1,3-dicyanobenzene, 1,4-dicyanobenzene, and ethylene glycol bis(propionitrile) ether. 3,5-Dioxa-heptadionitrile, 1,4-Di(cyanoethoxy)butane, diethylene glycol di(2-cyanoethyl) ether, triethylene glycol di(2-cyanoethyl) ether, tetraethylene glycol di(2-cyanoethyl) ether, 1,3-Di(2-cyanoethoxy)propane, 1,4-Di(2-cyanoethoxy)butane, 1,5-Di(2-cyanoethoxy)pentane, ethylene glycol di(4-cyanobutyl) ether, 1,4-dicyano-2-butene, 1 4-Dicyano-2-methyl-2-butene, 1,4-dicyano-2-ethyl-2-butene, 1,4-dicyano-2,3-dimethyl-2-butene, 1,4-dicyano-2,3-diethyl-2-butene, 1,6-dicyano-3-hexene, 1,6-dicyano-2-methyl-3-hexene, 1,3,5-pentanetricarbonyl, 1,2,3-propanetricarbonyl, 1,3,6-hexanetricarbonyl, 1,2,6-hexanetricarbonyl 1,2,3-tris(2-cyanoethoxy)propane, 1,2,4-tris(2-cyanoethoxy)butane, 1,1,1-tris(cyanoethoxymethylene)ethane, 1,1,1-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.

[0102] In some embodiments, the compound having an FPO bond includes at least one of lithium difluorophosphate, a compound of formula 1, a compound of formula 2, a compound of formula 3, or a compound of formula 4:

[0103] Formula 1

[0104] Formula 2

[0105] Formula 3

[0106] Formula 4.

[0107] In some embodiments, the electrolyte further includes additive B, which includes at least one of fluoroethylene carbonate, 1,3-propanesulfonate lactone, ethylene sulfate, ethylene ethylene carbonate, and cyclic phosphate anhydride.

[0108] In some embodiments, the electrolyte further comprises any non-aqueous solvent known in the art that can be used as a solvent for an electrolyte.

[0109] In some embodiments, the non-aqueous solvent includes, but is not limited to, one or more of the following: cyclic carbonates, chain carbonates, cyclic carboxylic esters, chain carboxylic esters, cyclic ethers, chain ethers, phosphorus-containing organic solvents, sulfur-containing organic solvents, and aromatic fluorine-containing solvents.

[0110] 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), and butylene carbonate. In some embodiments, the cyclic carbonate has 3-6 carbon atoms.

[0111] In some embodiments, examples of the chain carbonate may include, but are not limited to, one or more of the following: dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate (DEC), methyl n-propyl carbonate, ethyl n-propyl carbonate, di n-propyl carbonate, and other chain carbonates. 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(2,2,2-trifluoroethyl) carbonate, 2-fluoroethylmethyl carbonate, 2,2-difluoroethylmethyl carbonate, and 2,2,2-trifluoroethylmethyl carbonate, etc.

[0112] In some embodiments, examples of the cyclic carboxylic acid ester may include, but are not limited to, one or more of the following: γ-butyrolactone and γ-valerolactone. In some embodiments, some hydrogen atoms of the cyclic carboxylic acid ester may be substituted with fluorine.

[0113] In some embodiments, examples of the chain carboxylic acid ester 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, and ethyl pivalate. In some embodiments, some hydrogen atoms of the chain carboxylic acid ester may be substituted with fluorine. In some embodiments, examples of fluorinated chain carboxylic acid esters may include, but are not limited to, methyl trifluoroacetate, ethyl trifluoroacetate, propyl trifluoroacetate, butyl trifluoroacetate, and 2,2,2-trifluoroethyl trifluoroacetate.

[0114] 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, and dimethoxypropane.

[0115] In some embodiments, examples of the chain ether may include, but are not limited to, one or more of the following: dimethoxymethane, 1,1-dimethoxyethane, 1,2-dimethoxyethane, diethoxymethane, 1,1-diethoxyethane, 1,2-diethoxyethane, ethoxymethoxymethane, 1,1-ethoxymethoxyethane, and 1,2-ethoxymethoxyethane, etc.

[0116] 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 phosphate, ethylene phosphate, triphenyl phosphate, trimethyl phosphite, triethyl phosphite, triphenyl phosphite, tri(2,2,2-trifluoroethyl) phosphate, and tri(2,2,3,3,3-pentafluoropropyl) phosphate, etc.

[0117] 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-methylsulfolane, 3-methylsulfolane, dimethyl sulfone, diethyl sulfone, ethyl methyl sulfone, methylpropyl sulfone, dimethyl sulfoxide, methyl methanesulfonate, ethyl methanesulfonate, methyl ethanesulfonate, ethyl ethanesulfonate, dimethyl sulfate, diethyl sulfate, and dibutyl sulfate. In some embodiments, some hydrogen atoms of the sulfur-containing organic solvent may be substituted with fluorine.

[0118] In some embodiments, the aromatic fluorinated solvent includes, but is not limited to, one or more of the following: fluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, and trifluoromethylbenzene.

[0119] In some embodiments, the solvent used in the electrolyte of this application includes cyclic carbonates, linear carbonates, cyclic carboxylic acid esters, linear carboxylic acid esters, and combinations thereof. In some embodiments, the solvent used in the electrolyte of this 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, and combinations thereof. In some embodiments, the solvent used in the electrolyte of this application comprises: ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, γ-butyrolactone, and combinations thereof.

[0120] In some embodiments, the electrolyte is not particularly limited, and any substance known as an electrolyte can be used. In the case of lithium secondary batteries, lithium salts are typically used. Examples of electrolytes may include, but are not limited to, inorganic lithium salts such as LiPF6, LiBF4, LiClO4, LiAlF4, LiSbF6, and LiWF7; lithium tungstates such as LiWOF5; lithium carboxylate salts such as HCO2Li, CH3CO2Li, CH2FCO2Li, CHF2CO2Li, CF3CO2Li, CF3CH2CO2Li, CF3CF2CO2Li, CF3CF2CF2CO2Li, and CF3CF2CF2CF2CO2Li; and lithium carboxylate salts such as FSO3Li and CH3SO3Li. Lithium sulfonate salts such as CH2FSO3Li, CHF2SO3Li, CF3SO3Li, CF3CF2SO3Li, CF3CF2CF2SO3Li, and CF3CF2CF2CF2SO3Li; lithium sulfonate salts such as LiN(FCO)2, LiN(FCO)(FSO2), LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,2-perfluoroethane disulfonylimide lithium, and cyclic 1,3-perfluoropropane disulfonylimide. Lithium, imide lithium salts such as LiN(CF3SO2)(C4F9SO2); methylated lithium salts such as LiC(FSO2)3, LiC(CF3SO2)3, and LiC(C2F5SO2)3; lithium malonate lithium salts such as bis(malonate)borate and difluoro(malonate)borate; lithium tri(malonate)phosphate, lithium difluorobis(malonate)phosphate, and lithium tetrafluoro(malonate)phosphate; and lithium malonate phosphates such as LiPF4(CF3)2 and LiPF4(C2F5)2. Fluorine-containing organic lithium salts such as LiPF4(CF3SO2)2, LiPF4(C2F5SO2)2, LiBF3CF3, LiBF3C2F5, LiBF3C3F7, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, and LiBF2(C2F5SO2)2; lithium oxalate borate salts such as lithium difluorooxalate borate and lithium bis(oxalate) borate; and lithium oxalate phosphate salts such as lithium tetrafluorooxalate phosphate, lithium difluorobis(oxalate) phosphate, and lithium tri(oxalate) phosphate.

[0121] In some embodiments, the electrolyte is selected from LiPF6, LiSbF6, FSO3Li, CF3SO3Li, LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,2-perfluoroethane disulfonylimide lithium, cyclic 1,3-perfluoropropane disulfonylimide lithium, LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiBF3CF3, LiBF3C2F5, LiPF3(CF3)3, LiPF3(C2F5)3, lithium difluorooxalateborate, lithium bis(oxalate)borate, or lithium difluorobis(oxalate)phosphate, which helps to improve the output power characteristics, high-rate charge-discharge characteristics, high-temperature storage characteristics, and cycle characteristics of the electrochemical device.

[0122] There are no particular limitations on the content of the electrolyte, as long as it does not impair the effectiveness of this application. In some embodiments, the total molar concentration of lithium in the electrolyte is greater than 0.3 mol / L, greater than 0.4 mol / L, or greater than 0.5 mol / L. In some embodiments, the total molar concentration of lithium in the electrolyte is less than 3 mol / L, less than 2.5 mol / L, or less than 2.0 mol / L. In some embodiments, the total molar concentration of lithium in the electrolyte is within the range of any two of the above values. When the electrolyte concentration is within the above range, the amount of lithium as charged particles is not too low, and the viscosity can be kept within an appropriate range, thus easily ensuring good conductivity.

[0123] When using two or more electrolytes, the electrolyte includes at least one salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate. In some embodiments, the electrolyte includes a salt selected from the group consisting of monofluorophosphate, oxalate, and fluorosulfonate. In some embodiments, the electrolyte includes a lithium salt. In some embodiments, the content of a salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate is greater than 0.01% or greater than 0.1% based on the mass of the electrolyte. In some embodiments, the content of a salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate is less than 20% or less than 10% based on the mass of the electrolyte. In some embodiments, the content of a salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate is within the range of any two of the above values.

[0124] In some embodiments, the electrolyte comprises one or more substances selected from the group consisting of monofluorophosphates, borates, oxalates, and fluorosulfonates, and one or more other salts. Examples of other salts include lithium salts exemplified above, which in some embodiments are LiPF6, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,2-perfluoroethane disulfonylimide lithium, cyclic 1,3-perfluoropropane disulfonylimide lithium, LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiBF3CF3, LiBF3C2F5, LiPF3(CF3)3, and LiPF3(C2F5)3. In some embodiments, other than these, the salt is LiPF6.

[0125] In some embodiments, the content of other salts is greater than 0.01% or greater than 0.1% based on the mass of the electrolyte. In some embodiments, the content of other salts is less than 20%, less than 15%, or less than 10% based on the mass of the electrolyte. In some embodiments, the content of other salts is within the range of any two of the above values. The above-mentioned amounts of other salts help to balance the conductivity and viscosity of the electrolyte.

[0126] 3. Negative electrode

[0127] In some embodiments, the negative electrode includes a negative electrode current collector and a layer of negative electrode active material located on one or both surfaces of the negative electrode current collector. The negative electrode active material layer contains negative electrode active material. The negative electrode active material layer can be one or more layers, and each layer in a multilayer negative electrode active material layer can contain the same or different negative electrode active materials. The negative electrode active material is any material capable of reversibly inserting and deintercalating metal ions such as lithium ions. In some embodiments, the rechargeable capacity of the negative electrode active material is greater than the discharge capacity of the negative electrode active material to prevent unintentional deposition of lithium metal on the negative electrode during charging.

[0128] As the current collector for retaining the active material of the negative electrode, any known current collector can be used. Examples of negative electrode current collectors include, but are not limited to, metallic materials such as aluminum, copper, nickel, stainless steel, and nickel-plated steel. In some embodiments, the negative electrode current collector is copper.

[0129] When the negative electrode current collector is a metallic material, its form may include, but is not limited to, metal foil, metal cylinder, metal strip roll, metal plate, metal film, metal mesh, stamped metal, foamed metal, etc. In some embodiments, the negative electrode current collector is a metal film. In some embodiments, the negative electrode current collector is copper foil. In some embodiments, the negative electrode current collector is rolled copper foil based on rolling or electrolytic copper foil based on electrolysis.

[0130] In some embodiments, the thickness of the negative electrode current collector is greater than 1 μm or greater than 5 μm. In some embodiments, the thickness of the negative electrode current collector is less than 100 μm or less than 50 μm. In some embodiments, the thickness of the negative electrode current collector is within the range of any two of the above values.

[0131] There are no particular restrictions on the negative electrode active material, as long as it can reversibly absorb and release lithium ions. Examples of negative electrode active materials may include, but are not limited to, carbon materials such as natural graphite and artificial graphite; metals such as silicon (Si) and tin (Sn); or oxides of metal elements such as Si and Sn. Negative electrode active materials can be used alone or in combination.

[0132] In some embodiments, the negative electrode active material layer may further include a negative electrode binder. The negative electrode binder can improve the bonding between the negative electrode active material particles and the bonding between the negative electrode active material and the current collector. There are no particular limitations on the type of negative electrode binder, as long as it is a material stable to the electrolyte or the solvent used in electrode manufacturing. In some embodiments, the negative electrode binder includes a resin binder. Examples of resin binders include, but are not limited to, fluoropolymers, polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, etc. When preparing the negative electrode slurry using an aqueous solvent, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or its salts, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salts, polyvinyl alcohol, etc.

[0133] In some embodiments, the negative electrode can be prepared by coating a negative electrode slurry containing a negative electrode active material, a resin binder, etc. onto a negative electrode current collector, drying it, and then calendering it to form a negative electrode active material layer on both sides of the negative electrode current collector, thereby obtaining the negative electrode.

[0134] 4. Separating membrane

[0135] In some embodiments, a separator is typically provided between the positive and negative electrodes to prevent short circuits. In this case, the electrolyte of this application is typically used after penetrating the separator.

[0136] There are no particular limitations on the material and shape of the separator, as long as it does not significantly impair the effectiveness of this application. The separator may be a resin, glass fiber, inorganic material, or other material formed from a material stable to the electrolyte of this application. In some embodiments, the separator includes a porous sheet or non-woven fabric-like material with excellent liquid retention properties. Examples of materials for resin or glass fiber separators may include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, etc. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The above-mentioned separator materials can be used alone or in any combination.

[0137] The separator can also be a material formed by laminating the above-mentioned materials, examples of which include, but are not limited to, a three-layer separator formed by laminating polypropylene, polyethylene, and polypropylene in that order.

[0138] Examples of inorganic materials may include, but are not limited to, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates (e.g., barium sulfate, calcium sulfate, etc.). Inorganic materials may be in, but are not limited to, particulate or fibrous forms.

[0139] The separator can be in the form of a thin film, examples of which include, but are not limited to, nonwoven fabrics, woven fabrics, microporous membranes, etc. In the thin film form, the pore size of the separator is 0.01 μm to 1 μm, and the thickness is 5 μm to 50 μm. In addition to the above-mentioned independent thin film separator, the following separator can also be used: a separator formed by using a resin-based adhesive to form a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive electrode and / or negative electrode, for example, a separator formed by using fluororesin as an adhesive to form a porous layer of alumina particles with a particle size of less than 1 μm on both sides of the positive electrode.

[0140] The thickness of the separator is arbitrary. In some embodiments, the thickness of the separator 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 within the range of any two of the above values. When the thickness of the separator is within the above range, insulation and mechanical strength can be ensured, and the rate capability and energy density of the electrochemical device can be ensured.

[0141] When using porous materials such as porous sheets or nonwoven fabrics as the separator, the porosity of the separator is arbitrary. In some embodiments, the porosity of the separator is greater than 10%, greater than 15%, or greater than 20%. In some embodiments, the porosity of the separator is less than 60%, less than 50%, or less than 45%. In some embodiments, the porosity of the separator is within the range of any two of the above values. When the porosity of the separator is within the above range, insulation and mechanical strength can be ensured, and membrane resistance can be suppressed, giving the electrochemical device good safety characteristics.

[0142] The average pore size of the separator is also arbitrary. In some embodiments, the average pore size of the separator is less than 0.5 μm or less than 0.2 μm. In some embodiments, the average pore size of the separator is greater than 0.05 μm. In some embodiments, the average pore size of the separator is within the range of any two of the above values. If the average pore size of the separator exceeds the above range, a short circuit is likely to occur. When the average pore size of the separator is within the above range, the electrochemical device has good safety characteristics.

[0143] 5. Electrochemical device

[0144] In some embodiments, the electrochemical device includes an electrode assembly, a current collector, an outer housing, and protective elements.

[0145] Electrode group

[0146] The electrode assembly can be either a laminated structure formed by stacking the positive and negative electrodes with the separator membrane in between, or a structure formed by spirally winding the positive and negative electrodes with the separator membrane in between. In some embodiments, the proportion of the electrode assembly's mass in the battery's internal volume (electrode assembly occupancy) is greater than 40% or greater than 50%. In some embodiments, the electrode assembly occupancy is less than 90% or less than 80%. In some embodiments, the electrode assembly occupancy falls within the range of any two of the above values. When the electrode assembly occupancy is within the above range, the capacity of the electrochemical device can be ensured, while the degradation of repeated charge-discharge performance and high-temperature storage characteristics associated with increased internal pressure can be suppressed.

[0147] collector structure

[0148] There are no particular limitations on the current collector structure. In some embodiments, the current collector structure is one that reduces the resistance of the wiring portion and the joint portion. When the electrode group has the above-described laminated structure, it is suitable to use a structure formed by bundling the metal core portions of each electrode layer together and soldering them to the terminals. As the area of ​​an electrode increases, the internal resistance increases; therefore, it is also suitable to provide two or more terminals within the electrode to reduce the resistance. When the electrode group has the above-described wound structure, the internal resistance can be reduced by providing two or more lead structures on the positive and negative electrodes respectively and bundling them together on the terminals.

[0149] outer casing

[0150] There are no particular restrictions on the material of the outer casing, as long as it is a substance stable to the electrolyte used. The outer casing can be, but is not limited to, nickel-plated steel, stainless steel, aluminum or aluminum alloy, magnesium alloy, or a laminated film of resin and aluminum foil. In some embodiments, the outer casing is an aluminum or aluminum alloy metal or a laminated film.

[0151] Metal casings include, but are not limited to, encapsulated and hermetically sealed structures formed by fusing metals together using laser welding, resistance welding, or ultrasonic welding; or riveted structures formed using the aforementioned metals with a resin gasket in between. Casings using the aforementioned laminated films include, but are not limited to, encapsulated and hermetically sealed structures formed by thermally bonding resin layers together. To improve sealing, a resin different from the resin used in the laminated film can be sandwiched between the resin layers. When forming a hermetically sealed structure by thermally bonding resin layers using current collectors, a resin with polar groups or a modified resin with introduced polar groups can be used as the sandwiched resin due to the bonding between the metal and the resin. Furthermore, the shape of the casing is arbitrary, and can be, for example, any of the following: cylindrical, square, laminated, button-shaped, or large.

[0152] Protective components

[0153] Protective components can include positive temperature coefficient (PTC) devices that increase resistance when abnormal heat generation or excessive current flows, temperature fuses, thermistors, and valves (current cut-off valves) that cut off current flowing through the circuit by causing a rapid increase in internal battery pressure or temperature during abnormal heat generation. These protective components can be selected to avoid operation under normal high-current conditions, or they can be designed to prevent abnormal heat generation or thermal runaway even without the protective components.

[0154] 6. Application

[0155] The electrochemical device of this application includes any device in which an electrochemical reaction occurs, and specific examples 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 lithium metal secondary batteries or lithium-ion secondary batteries.

[0156] This application also provides an electronic device that includes the electrochemical device described in this application.

[0157] The application of the electrochemical device in this application is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, the electrochemical device of this application can be used in, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors, etc.

[0158] The following uses a lithium-ion battery as an example and combines specific embodiments to illustrate the preparation of a lithium-ion battery. Those skilled in the art will understand that the preparation method described in this application is only an example, and any other suitable preparation method is within the scope of this application.

[0159] Example

[0160] The following describes the performance evaluation based on the embodiments and comparative examples of the lithium-ion battery of this application.

[0161] I. Preparation of Lithium-ion Batteries

[0162] 1. Preparation of the negative electrode

[0163] Artificial graphite, styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed with deionized water in a mass ratio of 96%:2%:2% and stirred until homogeneous to obtain a slurry. The slurry was then coated onto a 9μm copper foil. After drying and cold pressing, the foil was cut and tabs were welded to obtain the negative electrode.

[0164] 2. Preparation of the positive electrode

[0165] The positive electrode active material (e.g., lithium cobalt oxide), Super-P, and polyvinylidene fluoride are mixed with N-methylpyrrolidone (NMP) in a mass ratio of (95-99%):(0.1-5%):(0.1-5%) and stirred evenly to obtain a positive electrode slurry. This positive electrode slurry is coated onto a 12 μm aluminum foil, dried, cold-pressed, and then cut and welded to obtain the positive electrode.

[0166] 3. Preparation of electrolyte

[0167] EC, PP, and DEC (mass ratio 1:1:1) were mixed under a dry argon atmosphere, and LiPF6 was added and mixed thoroughly to form a basic electrolyte, wherein the content of LiPF6 was 12%. Electrolytes of different embodiments and comparative proportions were obtained by adding different amounts of additives to the basic electrolyte. The mass percentage of each substance in the electrolyte was calculated based on the total mass of the electrolyte.

[0168] The abbreviations and names of the components in the electrolyte are shown in the table below:

[0169]

[0170] 4. Preparation of the separating membrane

[0171] A porous polyethylene membrane with an alumina coating and a thickness of 9µm was used as the separator.

[0172] 5. Preparation of lithium-ion batteries

[0173] The obtained positive electrode, separator, and negative electrode are wound in sequence and placed in an outer packaging foil, leaving an injection port. Electrolyte is poured in through the injection port, the battery is sealed, and then processed through formation, capacity testing, and other procedures to produce a lithium-ion battery.

[0174] II. Testing Methods

[0175] 1. Test method for DC internal resistance of lithium-ion batteries under high temperature and high pressure

[0176] At 65℃, the lithium-ion battery was charged at a constant current of 1.5C to 4.7V, then charged at a constant voltage of 4.7V to 0.05C, and left to stand for 30 minutes. It was then discharged at 0.1C for 10 seconds, and the voltage value was recorded as U1. Finally, it was discharged at 1C for 360 seconds, and the voltage value was recorded as U2. This charge-discharge cycle was repeated 5 times. "1C" refers to the current value required to completely discharge the lithium-ion battery within one hour.

[0177] The DC resistance R of a lithium-ion battery at 65°C can be calculated using the following formula:

[0178] R=(U2-U1) / (1C-0.1C).

[0179] 2. Test methods for the float charge performance of lithium-ion batteries under high temperature and high pressure

[0180] At 25°C, the lithium-ion battery was discharged to 4.7V at 0.5C, then charged to 4.7V at 0.5C, and then charged at a constant voltage of 0.05C at 4.7V. It was then placed in a 50°C oven and continuously charged at a constant voltage of 4.7V with a cutoff current of 20mA, and the change in lithium-ion battery thickness was monitored. Using the thickness at the initial 50% State of Charge (SOC) as a baseline, an increase in battery thickness exceeding 20% ​​was considered a failure point, and the float charge time to reach the failure point was recorded.

[0181] 3. Test method for capacity retention of lithium-ion batteries under high temperature and high pressure

[0182] At 45°C, the lithium-ion battery was charged at a constant current of 1C to 4.7V, then charged at a constant voltage to a current of 0.05C, and finally discharged at a constant current of 1C to 3.0V. This constituted the first cycle. The lithium-ion battery was subjected to 800 cycles under these conditions. The capacity retention after cycling was calculated using the following formula:

[0183] Capacity retention rate = (Discharge capacity after 800 cycles / Discharge capacity in the first cycle) × 100%.

[0184] 4. Test methods for low-temperature discharge performance of lithium-ion batteries

[0185] At 25℃, the battery was charged at a constant current of 0.5C to 4.7V, then charged at a constant voltage to 0.05C (cutoff), and finally discharged at a constant current of 0.5C to 3.0V (cutoff). This discharge capacity at 25℃ was recorded. Similarly, at 25℃, the battery was charged at a constant current of 0.5C to 4.7V, then charged at a constant voltage to 0.05C (cutoff). Afterward, the battery was placed in a -20℃ constant temperature chamber for 2 hours, and then discharged at a constant current of 0.5C to 3.0V (cutoff). This discharge capacity at -20℃ was recorded. The discharge percentage of the lithium-ion battery was calculated using the following formula:

[0186] Discharge percentage = [-20℃ discharge capacity / 25℃ discharge capacity] × 100%.

[0187] 5. Test method for crack width

[0188] Take the positive electrode sheet from the disassembled battery and cut it into rectangular samples of 40mm (width) × 100mm (length) along the crack direction using a knife. Then, clamp the sample between two smooth, clean glass plates of 2mm (thickness) × 70mm (width) × 140mm (length) to prepare the sample. Place the cracked side of the sample on the stage of a KEYENCE VHX-5000 optical microscope and observe and photograph it at 100x magnification. Then, use VHX-5000 software to measure the width of the widest part of the crack using the parallel line method (select the two adjacent widest points to form a straight line). Measure each crack 5 times and take the maximum value as the crack width, i.e., W mm.

[0189] 6. Test method for melting point of fluorinated adhesives

[0190] The melting point of fluorinated binders can be determined as follows: First, remove the positive electrode from the battery, wash it with dimethyl carbonate, dry it, remove the current collector, and heat and stir it in a suitable dispersion medium (e.g., N-methylpyrrolidone) to dissolve the binder in the dispersion medium. Then, remove the positive electrode active material by centrifugation, filter the supernatant, and remove the binder by evaporation or reprecipitation in water. Next, using a differential scanning calorimeter (DSC, such as Rigaku Thermo plus DSC8230 manufactured by Rigaku Corporation), heat a sample of several mg to tens of mg at a heating rate of 1 to 10 °C / min. The temperature representing the maximum heat absorption among the endothermic peaks appearing in the temperature range of 100 °C to 300 °C is set as the melting point of the fluorinated binder.

[0191] 7. Test method for the content of fluorine-based adhesives

[0192] The content of the fluorinated binder was determined by the following procedure: First, the positive electrode was removed from the battery, cleaned with dimethyl carbonate, and dried. Next, using a differential thermal balance (TG-DTA apparatus, such as Rigaku Thermo plus TG8120 manufactured by Rigaku Corporation), a sample of several mg to tens of mg was heated to 600°C in air at a heating rate of 1 to 5°C / min. The content of the fluorinated binder in the positive electrode active material layer was determined based on the mass reduction at this point. It should be noted that to determine whether the mass reduction was due to the binder, the binder was separated as described above using the binder melting point determination method. A TG-DTA determination of the binder alone was performed in air, and the result was confirmed by investigating the temperature at which the binder burned.

[0193] III. Test Results

[0194] Table 1 shows the effects of the mass percentage (M%) of the positive electrode active material in the positive electrode active material layer and the crack width (Wmm) on the surface of the positive electrode active material layer on the DC internal resistance and float charge performance of the lithium-ion battery under high temperature and high pressure. The positive electrode material in Table 1 is Hunan Shanshan Lithium Cobalt Oxide LC9000E; the electrolyte is the basic electrolyte. Examples 1-2 to 1-13 and Comparative Examples 1-1 to 1-3 differ from Example 1-1 only in the parameters listed in Table 1; all other parameters are the same.

[0195] Table 1

[0196]

[0197] The test results above show that when the mass fraction of the positive electrode active material is 95% to 99%, and the positive electrode satisfies M / W ≥ 47.5, the DC internal resistance and float charge performance of lithium-ion batteries under high temperature and high pressure are significantly improved. Specifically, a higher mass fraction of the positive electrode active material is more beneficial to improving the battery's energy density. However, when the mass fraction of the positive electrode active material exceeds 99%, the proportion of binder and conductive agent decreases, making electrode processing difficult and causing significant cracking. When W ≤ 2, both the ionic and electronic conductivities on the surface and inside the positive electrode are improved, resulting in lower DC internal resistance and better electrochemical device performance. Once the crack width of the electrode is large, such as exceeding 2 mm, it will seriously affect the ionic and electronic conductivities, degrading battery performance.

[0198] This application, by controlling M and M / W within a suitable range, can reduce defects on the positive electrode surface such as cracks, pits, craters, and pinholes, effectively suppressing the continuous damage to the passivation layer on the positive electrode surface during battery charge-discharge cycles, reducing the number of repairs, thereby enabling lithium ions to obtain a smooth insertion-extraction channel, and reducing the SOC unevenness on the electrode surface (i.e., the accumulation of charge carriers at defects), because the place where SOC unevenness occurs is often the starting point of electrode degradation.

[0199] Figure 1 SEM images of the surface of the positive electrode active material layer in Examples 1-8 of this application are shown. The images show that the surface of the positive electrode active material layer has a crack width of 0.3 mm.

[0200] B. Table 2 shows the unit area mass of the positive electrode active material layer (M1 mg / 1540.25 mm). 2 The effects of the crack width (Wmm) on the surface of the positive electrode active material layer on the DC internal resistance and float charge performance of lithium-ion batteries under high temperature and high pressure are investigated. Examples 2-1 to 2-15 differ from Example 1-1 only in the parameters listed in Table 2.

[0201] Table 2

[0202]

[0203] The test results above show that when M1 is in the range of 100 to 400 and M1 / W≥50, the positive electrode surface can maintain structural stability during charge and discharge cycles, further reducing the DC internal resistance of the lithium-ion battery and improving its float charge performance.

[0204] C. Table 3 shows the effects of the solid content (M2%) of the positive electrode active material coating slurry and the crack width (Wmm) on the surface of the positive electrode active material layer on the DC internal resistance and float charge performance of the lithium-ion battery under high temperature and high pressure. The only difference between Examples 3-1 to 3-15 and Example 1-1 is the parameters listed in Table 3.

[0205] Table 3

[0206]

[0207] The test results above show that when the solid content of the positive electrode active material coating slurry is 55% to 80% and meets the requirement of M2 / W≥27.5, there are fewer defects on the positive electrode surface, which further reduces the DC internal resistance of the lithium-ion battery and improves the float charging performance of the lithium-ion battery.

[0208] D. Table 4-1 shows the effect of the melting point of the positive electrode binder on the DC internal resistance and float charge performance of lithium-ion batteries under high temperature and high pressure. The only difference between Examples 4-1 to 4-12 and Example 1-1 is the parameters listed in Table 4-1.

[0209] Table 4-1

[0210]

[0211] The test results above show that using fluorine-based binders with melting points in the range of 155℃ to 270℃ further reduces the DC internal resistance of lithium-ion batteries and improves their float charging performance. This is likely because fluorine-based binders with melting points in the range of 155℃ to 270℃ can be evenly distributed on the surface of the positive electrode material particles during the baking or hot-pressing process in electrode preparation, effectively improving adhesion, suppressing surface defects, and further enhancing the performance of the lithium-ion battery.

[0212] Table 4-2 shows the effect of the type and mass percentage (M4%) of the positive electrode additive on the DC internal resistance and float charge performance of lithium-ion batteries under high temperature and high pressure. The only difference between Examples 4-13 to 4-21 and Example 1-1 is the parameters listed in Table 4-2. The preparation method of the positive electrode in Examples 4-13 to 4-21 is as follows: Lithium cobalt oxide (Hunan Shanshan LC9000E), Super-P, and polyvinylidene fluoride are mixed with N-methylpyrrolidone in a mass ratio of 95%:2%:3%. The additives listed in Table 4-2 are then added to the slurry and stirred until homogeneous to obtain the positive electrode slurry. This positive electrode slurry is coated onto a 12 μm aluminum foil, dried, cold-pressed, and then cut and welded to obtain the positive electrode.

[0213] Table 4-2

[0214]

[0215] The test results above show that adding 0.1%-0.3% of ether-bonded polymers to the cathode slurry resulted in excellent DC internal resistance and float charge performance under high temperature and high pressure. In particular, when the oxidation potential of the ether-bonded polymers was higher than 4.6V, the DC internal resistance of the lithium-ion battery was further reduced, and the float charge performance was improved. This is likely because adding ether-bonded polymers to the cathode slurry can reduce the crack width on the surface of the positive electrode active material layer, thereby further suppressing surface defects and improving the performance of the lithium-ion battery under high voltage.

[0216] F. Table 5 shows the effects of the type and particle size (D50) of the positive electrode active material and the crack width on the surface of the positive electrode active material layer on the DC internal resistance and float charge performance of the lithium-ion battery under high temperature and high pressure. The only difference between Examples 5-1 to 5-6 and Example 1-1 is the parameters listed in Table 5.

[0217] Table 5

[0218]

[0219] The test results above show that when the particle size of the positive electrode active material and the crack width on the surface of the positive electrode active material layer meet one of the following conditions, the DC internal resistance of the lithium-ion battery is further reduced and the float charging performance of the lithium-ion battery is improved:

[0220] (1) The positive electrode active material includes lithium iron phosphate, and the D50 of the positive electrode active material is D1µm, wherein 2×D1≥W;

[0221] (2) The positive electrode active material includes lithium manganese iron phosphate, and the D50 of the positive electrode active material is D2µm, wherein 5×D2≥W;

[0222] (3) The positive electrode active material includes lithium manganese oxide, and the D50 of the positive electrode active material is D3µm, wherein 0.1×D3≥W;

[0223] (4) The positive electrode active material includes lithium nickel cobalt manganese oxide, and the D50 of the positive electrode active material is D4µm, wherein 0.15×D4≥W; and

[0224] (5) The positive electrode active material includes lithium cobalt oxide, and the D50 of the positive electrode active material is D5µm, wherein 0.15×D5≥W.

[0225] The reason may be that by selecting an appropriate particle size, the flatness of the positive electrode surface can be further adjusted, thereby improving the performance of lithium-ion batteries.

[0226] G. Table 6 shows the effects of the type or content of electrolyte additives and the mass percentage (M%) of positive electrode active material on the DC internal resistance and float charge performance of lithium-ion batteries under high temperature and high pressure. The mass percentage of additives is a% based on the total mass of the electrolyte. The difference between Examples 6-1 to 6-41 and Example 1-1 is only in the parameters listed in Table 6.

[0227] Table 6

[0228]

[0229] The test results above show that adding compounds with cyano groups or FPO bonds to the electrolyte can achieve excellent DC internal resistance and float charge performance under high temperature and high pressure. In particular, when compounds with cyano groups and compounds with FPO bonds are used in combination, the surface defects of the electrode caused by the decomposition and remodeling of the protective film on the positive electrode surface during cycling can be further suppressed, thereby improving the performance of lithium-ion batteries.

[0230] More specifically, by controlling the content of additives and keeping M / a within a suitable range, the degradation of the electrode surface caused by uneven SOC during battery cycling can be compensated. The additives form a stable protective film on the positive electrode surface, which is especially important for repairing defective areas. When M / a ≥ 6.33, the uniformity of the electrode surface is well maintained during cycling. Therefore, it not only further improves the DC internal resistance and float charge performance under high temperature and high pressure, but also unexpectedly improves the capacity retention rate under high voltage and the rate performance under low temperature. This may be because the interface formed between the positive electrode and the electrolyte has good stability and low impedance under high pressure and low temperature, which makes it easier for lithium ions to be inserted and extracted.

[0231] Furthermore, when the electrolyte also includes at least one of fluoroethylene carbonate, 1,3-propanesulfonic acid lactone, ethylene sulfate, ethylene ethylene carbonate, and cyclic anhydride phosphate, the DC internal resistance and float charging performance under high temperature and high pressure can be further improved.

[0232] Throughout this specification, references to "some embodiments," "partial embodiments," "one embodiment," "another example," "example," "specific example," or "partial example" mean that at least one embodiment or example in this application includes a specific feature, structure, material, or characteristic described in that embodiment or example. Therefore, descriptions appearing throughout this specification, such as "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in an example," "in a specific example," or "example," do not necessarily refer to the same embodiments or examples in this application. Furthermore, specific features, structures, materials, or characteristics described herein can be combined in any suitable manner in one or more embodiments or examples.

[0233] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. An electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, the positive electrode active material layer including positive electrode active material. Wherein, based on the mass of the positive electrode active material layer, the mass percentage of the positive electrode active material is M%, and the value of M ranges from 95% to 99%. The crack width on the surface of the positive electrode active material layer is W mm. Where M and W satisfy: M / W≥47.5; The electrolyte includes additive A, and the mass percentage of additive A is a% based on the total mass of the electrolyte, where a ranges from 2 to 5, and M / a satisfies 20 ≤ M / a ≤ 50. Additive A includes compounds having a cyano group and compounds having an FPO bond. The cyano group compounds include at least one of the following compounds: succinic anionibacterium, glutaronitrile, adiponitrile, 1,5-dicyanopentane, 1,6-dicyanohexane, tetramethylsuccinic anionibacterium, 2-methylglutaronitrile, 2,4-dimethyl... 2,2,4,4-Tetramethylglutaronitrile, 1,4-Dicyanopentane, 1,2-Dicyanobenzene, 1,3-Dicyanobenzene, 1,4-Dicyanobenzene, ethylene glycol bis(propionitrile) ether, 3,5-dioxa-heptanedione, 1,4-di(cyanoethoxy)butane, diethylene glycol di(2-cyanoethyl) ether, triethylene glycol di(2-cyanoethyl) ether, tetraethylene glycol di(2-cyanoethyl) ether, 1,3-di(2-cyanoethoxy)propane, 1,4-di(2-cyanoethoxy)butane, 1 5-Di(2-cyanoethoxy)pentane, ethylene glycol di(4-cyanobutyl) ether, 1,4-dicyano-2-butene, 1,4-dicyano-2-methyl-2-butene, 1,4-dicyano-2-ethyl-2-butene, 1,4-dicyano-2,3-dimethyl-2-butene, 1,4-dicyano-2,3-diethyl-2-butene, 1,6-dicyano-3-hexene, 1,6-dicyano-2-methyl-3-hexene, 1,3,5-pentanetricarbonitrile, 1,2,3-propanetricarbonitrile 1,3,6-Hexamethylenetricarbonitrile, 1,2,6-Hexamethylenetricarbonitrile, 1,2,3-Tris(2-cyanoethoxy)propane, 1,2,4-Tris(2-cyanoethoxy)butane, 1,1,1-Tris(cyanoethoxymethylene)ethane, 1,1,1-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.

2. The electrochemical device according to claim 1, wherein W ≤ 2.

3. The electrochemical device according to claim 1, wherein the unit area mass of the positive electrode active material layer is M1 mg / 1540.25 mm². 2 The value of M1 ranges from 100 to 400, where M1 and W satisfy: M1 / W≥50.

4. The electrochemical device according to claim 1, wherein the solid content of the coating slurry of the positive electrode active material layer is M2, the value of M2 is in the range of 55 to 80, and M2 and W satisfy: M2 / W≥27.

5.

5. The electrochemical device according to claim 1, wherein the positive electrode comprises a fluorine-based binder with a melting point in the range of 155°C to 270°C.

6. The electrochemical device according to claim 1, wherein the positive electrode active material layer comprises a polymeric compound having ether bonds, wherein the mass percentage of the polymeric compound having ether bonds is M4% based on the mass of the positive electrode active material layer, M4≤0.3%.

7. The electrochemical device according to claim 6, wherein the oxidation potential of the polymeric compound having ether bonds is greater than or equal to 4.6V.

8. The electrochemical device according to claim 1, wherein the compound having an FPO bond comprises at least one of lithium difluorophosphate, a compound of formula 1, a compound of formula 2, a compound of formula 3, or a compound of formula 4: Formula 1 Formula 2 Formula 3 Formula 4.

9. The electrochemical device according to claim 1, wherein the positive electrode active material satisfies one of the following conditions: (1) The positive electrode active material includes lithium iron phosphate, and the D50 of the positive electrode active material is D1µm, wherein 2×D1≥W; (2) The positive electrode active material includes lithium manganese iron phosphate, and the D50 of the positive electrode active material is D2µm, wherein 5×D2≥W; (3) The positive electrode active material includes lithium manganese oxide, and the D50 of the positive electrode active material is D3µm, wherein 0.1×D3≥W; (4) The positive electrode active material includes lithium nickel cobalt manganese oxide, and the D50 of the positive electrode active material is D4µm, wherein 0.15×D4≥W; and (5) The positive electrode active material includes lithium cobalt oxide, and the D50 of the positive electrode active material is D5µm, wherein 0.15×D5≥W.

10. The electrochemical device according to claim 1, wherein the electrolyte further comprises additive B, said additive B comprising at least one of fluoroethylene carbonate, 1,3-propanesulfonate lactone, ethylene sulfate, ethylene ethylene carbonate, or cyclic anhydride phosphate.

11. An electronic device comprising an electrochemical device according to any one of claims 1-10.

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