Electrolyte, electrochemical device and electronic device including the same

Abstract

The present application relates to an electrolyte and an electrochemical device and an electronic device comprising the same. Specifically, the electrolyte comprises a dinitrile compound, a polynitrile compound having a cyano group number greater than 2, and a boron-containing lithium salt, wherein the weight percentages of the dinitrile compound, the polynitrile compound, and the boron-containing lithium salt satisfy a certain relationship, so that the electrochemical device comprising the electrolyte has improved cycle performance at high temperature and high power.

Description

Technical Field

[0001] The present application relates to the field of energy storage technology, and in particular to an electrolyte and an electrochemical device and an electronic device comprising the electrolyte, in particular a lithium-ion battery. Background Art

[0002] Electrochemical devices, such as lithium-ion batteries, have the advantages of high energy density, high operating voltage, low self-discharge rate, long cycle life and no pollution, and have been widely used in computers, smart wearable devices, smart phones, drones, electric vehicles and other fields. With the development of modern information technology and the expansion of the application range of lithium-ion batteries, more performance requirements have been put forward for lithium-ion batteries, such as cycle performance under high temperature and high power.

[0003] At present, how to make lithium-ion batteries have good cycle performance under high temperature and high power is the research and development focus in the battery field. Summary of the invention

[0004] The present application provides an electrolyte and an electrochemical device including the same in an attempt to solve at least one problem existing in the related art to at least some extent.

[0005] The present application provides an electrolyte, which at least comprises a dinitrile compound, a polynitrile compound having a cyano group number greater than 2, and a boron-containing lithium salt, and provides an electrochemical device with good cycle performance at high temperature and high power by controlling the weight percentages of the three.

[0006] On the one hand, the present application provides an electrolyte comprising a dinitrile compound, a polynitrile compound having a cyano group number greater than 2, and a boron-containing lithium salt, wherein based on the total weight of the electrolyte, the weight percentage of the dinitrile compound is A%, the weight percentage of the polynitrile compound is B%, and the weight percentage of the boron-containing lithium salt is C%, wherein A, B and C satisfy A / B≥1.2 and 0≤(A / B)-C+1≤11.

[0007] According to some embodiments of the present application, the dinitrile compound comprises a compound represented by formula I:

[0008]

[0009] Where R 1 is selected from substituted or unsubstituted C 1 To C 9 Alkylene, substituted or unsubstituted C 2 To C 10 Alkenylene, -R a -OR b -or-R c -OR d -OR e -, where Ra , R b , R c and R e are each independently selected from a single bond or a substituted or unsubstituted C 1 To C 5 alkylene, and R a and R b Not single bond at the same time, R d is selected from substituted or unsubstituted C 1 To C 5 wherein when substituted, the substituent is halogen.

[0010] According to some embodiments of the present application, the polynitrile compound comprises a compound represented by formula II:

[0011]

[0012] Where R 2 Selected from H, C, CH, CH 2 or CH 3 ; R 3 Selected from C, CH or CH 2 ; R 4 , R 5 , R 6 , R 7 , R 8 , R 9 and R 10 are each independently selected from a single bond, a substituted or unsubstituted C 1 To C 5 Alkylene or -R f -OR g -, where R f and R g are each independently selected from a single bond or a substituted or unsubstituted C 1 To C 5 An alkylene group, wherein when substituted, the substituent is a halogen; X 1 and X 2 are each independently selected from a single bond, oxygen, or substituted or unsubstituted C 1 To C 5 wherein when substituted, the substituent is halogen; and a, b, c, d, e, f and g are each independently 0 or 1, and at least three of them are not 0 at the same time.

[0013] According to some embodiments of the present application, the dinitrile compound comprises:

[0014] At least one of .

[0015] According to some embodiments of the present application, the polynitrile compound includes:

[0016]

[0017]

[0018] at least one of

[0019] According to some embodiments of the present application, A and B further satisfy 3 ≤ A + B ≤ 20.

[0020] According to some embodiments of the present application, the boron-containing lithium salt includes at least one of lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, or lithium tetraborate, and / or C ≤ A.

[0021] According to some embodiments of the present application, the electrolyte further includes a boron-free lithium salt, and based on the total weight of the electrolyte, the weight percentage of the boron-free lithium salt is D%, where 0.01 ≤ C / D × 12.5 ≤ 3.8.

[0022] According to some embodiments of the present application, the electrolyte further includes fluoroethylene carbonate, and based on the total weight of the electrolyte, the weight percentage of the fluoroethylene carbonate is E%, and 5 ≤ A + E ≤ 25 is satisfied.

[0023] On the other hand, the present application also provides an electrochemical device, which includes a positive electrode, a negative electrode, a separator, and any one of the above electrolytes.

[0024] According to some embodiments of the present application, the negative electrode includes negative electrode active material particles, and the negative electrode active material particles satisfy at least one of the conditions (a) or (b): (a) The Dn10 of the negative electrode active material particles is 1 μm to 9 μm; (b) The Dv50 of the negative electrode active material particles is 5 μm to 18 μm.

[0025] According to some embodiments of the present application, when the negative electrode active material particles at least satisfy the condition (a), the negative electrode active material particles further satisfy at least one of the conditions (c) or (d): (c) When the Dn10 of the negative electrode active material particles < 5 μm, 5Dn10 < Dv50 < 12Dn10; (d) When the Dn10 of the negative electrode active material particles ≥ 5 μm, 1.5Dn10 < Dv50 < 4Dn10.

[0026] On another aspect, the present application also provides an electronic device, and the electronic device includes any one of the above electrochemical devices.

[0027] Additional aspects and advantages of the embodiments of the present application will be described, shown, or explained in part in the subsequent description through implementation of the embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The following will briefly describe the drawings necessary for describing the embodiments of the present application or the prior art to facilitate the description of the embodiments of the present application. Obviously, the drawings described below are only some of the embodiments in the present application. For those skilled in the art, without the need for creative work, drawings of other embodiments can still be obtained based on the structures illustrated in these drawings.

[0029] Figures 1A to 1C The schematic diagrams respectively show that no lithium deposition occurs at the negative electrode of a lithium-ion battery, lithium deposition occurs, and lithium deposition is severe. DETAILED DESCRIPTION

[0030] The embodiments of the present application will be described in detail below. The embodiments of the drawings described herein are illustrative and graphic and are used to provide a basic understanding of the present application. The embodiments of the present application should not be interpreted as limiting the present application.

[0031] As used herein, the term "about" is used to describe and illustrate small changes. When used in conjunction with an event or situation, the term may refer to an example in which the event or situation occurs exactly as well as an example in which the event or situation occurs very approximately. For example, when used in conjunction with a numerical value, the term may refer to a range of variation of less than or equal to ±10% of the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. For example, if the difference between two numerical values ​​is less than or equal to ±10% of the average value of the values ​​(e.g., less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%), then the two numerical values ​​can be considered to be "about" the same.

[0032] In addition, sometimes amounts, ratios and other numerical values ​​are presented in range format herein. It should be understood that such range format is for convenience and brevity, and should be flexibly understood to include not only the numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or sub-ranges encompassed within the range, as if each numerical value and sub-range were explicitly specified.

[0033] 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, 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, 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 component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0034] As used herein, the term "alkylene" means a straight or branched divalent saturated hydrocarbon radical. For example, the alkylene can be an alkylene of 1 to 20 carbon atoms, an alkylene of 1 to 15 carbon atoms, an alkylene of 1 to 10 carbon atoms, an alkylene of 1 to 5 carbon atoms, an alkylene of 5 to 20 carbon atoms, an alkylene of 5 to 15 carbon atoms, or an alkylene of 5 to 10 carbon atoms. Representative alkylenes include, for example, methylene, ethane-1,2-diyl ("ethylene"), propane-1,2-diyl, propane-1,3-diyl, butane-1,4-diyl, pentane-1,5-diyl, and the like. In addition, the alkylene can be optionally substituted.

[0035] The term "alkenylene" encompasses straight and branched alkenylene. When specifying an alkenylene with a specific carbon number, it is contemplated that all geometric isomers with that carbon number are encompassed. For example, alkenylene can be an alkenylene of 2 to 20 carbon atoms, an alkenylene of 2 to 15 carbon atoms, an alkenylene of 2 to 10 carbon atoms, an alkenylene of 2 to 5 carbon atoms, an alkenylene of 5 to 20 carbon atoms, an alkenylene of 5 to 15 carbon atoms, or an alkenylene of 5 to 10 carbon atoms. Representative alkenylene includes, for example, vinylene, propenylene, butenylene, etc. In addition, alkenylene can be optionally substituted.

[0036] As used herein, the term "halogen" may be F, Cl, Br or I.

[0037] When the above substituents are substituted, the substituents may be selected from the group consisting of halogen, alkyl, cycloalkyl, alkenyl, aryl and heteroaryl.

[0038] Some embodiments of the present application relate to an electrochemical device, which includes a positive electrode, a negative electrode, a separator and an electrolyte. In some embodiments, the electrochemical device is a lithium ion battery.

[0039] When lithium-ion batteries are charged and discharged in cycles at high temperature and high charge, the positive electrode is in an unstable state and is easily deoxygenated. The deoxygenated oxygen easily undergoes side reactions with the electrolyte and easily oxidizes the electrolyte. Therefore, the cycle performance of lithium-ion batteries at high temperature and high charge is poor.

[0040] The inventors of the present application have found that nitrile compounds can coordinate with transition metal elements to stabilize the positive electrode, but the structure of the nitrile compounds will affect the improvement effect. Adding a polynitrile compound with a cyano group number greater than 2 in the electrolyte can increase the complexing efficiency of the positive electrode transition metal ions, but due to its large steric hindrance, gaps will be generated between the polynitrile compounds, thereby failing to fully protect the positive electrode; the dinitrile compound has a small steric hindrance and can make up for the positive electrode interface that the polynitrile compound fails to protect. In addition, the inventors have also found that the boron (B) in the boron-containing lithium salt reacts with the oxygen atom (O) on the surface of the positive electrode to form a BO bond, which can stabilize the positive electrode, and can further make up for the positive electrode portion that is not protected due to the steric effect, and protect this portion, so that the electrochemical device has good cycle performance at high temperature and high power.

[0041] 1. Electrolyte

[0042] The electrolyte of the present application comprises a dinitrile compound, a polynitrile compound having a cyano group number greater than 2, and a boron-containing lithium salt, wherein based on the total weight of the electrolyte, the weight percentage of the dinitrile compound is A%, the weight percentage of the polynitrile compound is B%, and the weight percentage of the boron-containing lithium salt is C%, and A, B and C satisfy 0≤(A / B)-C+1≤11.

[0043] In some embodiments, the dinitrile compound comprises a compound represented by Formula I:

[0044]

[0045] In Formula I, R 1 is selected from substituted or unsubstituted C 1 To C 9 Alkylene, substituted or unsubstituted C 2 To C 10 Alkenylene, -R a -OR b -or-R c -OR d -OR e -, where R a , R b , R c and R e are each independently selected from a single bond or a substituted or unsubstituted C 1 To C 5 alkylene, and R a and R bNot single bond at the same time, R d is selected from substituted or unsubstituted C 1 To C 5 wherein when substituted, the substituent is halogen.

[0046] In some embodiments, the dinitrile compound comprises:

[0047]

[0048]

[0049] At least one of .

[0050] In some embodiments, the polynitrile compound having more than 2 cyano groups comprises a compound represented by formula II:

[0051]

[0052] In Formula II, R 2 Selected from H, C, CH, CH 2 or CH 3 ; R 3 Selected from C, CH or CH 2 ; R 4 , R 5 , R 6 , R 7 , R 8 , R 9 and R 10 are each independently selected from a single bond, a substituted or unsubstituted C 1 To C 5 Alkylene or -R f -OR g -, where R f and R g are each independently selected from a single bond or a substituted or unsubstituted C 1 To C 5 An alkylene group, wherein when substituted, the substituent is a halogen; X 1 and X 2 are each independently selected from a single bond, oxygen, or substituted or unsubstituted C 1 To C 5 wherein when substituted, the substituent is halogen; and a, b, c, d, e, f and g are each independently 0 or 1, and at least three of them are not 0 at the same time.

[0053] Those skilled in the art can easily understand that in order to comply with the chemical bonding principle, R 2 and R 3The group selection of is linked to the values ​​of c, d, e, f, and g. For example, when R 2 When it is C, it means that c, d and e must be 1.

[0054] In some embodiments, the polynitrile compound comprises:

[0055]

[0056]

[0057] At least one of .

[0058] In some embodiments, based on the total weight of the electrolyte, the weight percentage A% of the dinitrile compound and the weight percentage B% of the polynitrile compound may satisfy 3≤A+B≤20. In some embodiments, the value of A+B may be about 3, about 4, about 5, about 6, about 7, about 8, about 9, about 10, about 12, about 15, about 17, about 20, or may satisfy a range consisting of any two of the above values, for example, about 3 to about 10, about 5 to about 15, or about 10 to about 20.

[0059] In some embodiments, based on the total weight of the electrolyte, the weight percentage A% of the dinitrile compound may satisfy 2≤A≤16. In some embodiments, the value of A may be about 2, about 3, about 4, about 5, about 6, about 7, about 8, about 9, about 10, about 12, about 15, about 16, or may satisfy a range consisting of any two of the above values, for example, about 3 to about 10 or about 5 to about 15.

[0060] In some embodiments, based on the total weight of the electrolyte, the weight percentage B% of the polynitrile compound may satisfy 0.5≤B≤7. In some embodiments, the value of B may be about 0.5, about 1, about 1.5, about 2, about 2.5, about 3, about 3.5, about 4, about 4.5, about 5, about 5.5, about 6, about 6.5, about 7, or may satisfy a range consisting of any two of the above values, for example, from about 0.5 to about 5 or from about 2.5 to about 7.

[0061] In some embodiments, the boron-containing lithium salt comprises lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiDFOB), lithium tetrafluoroborate (LiBF 4 ) or lithium tetraborate At least one of .

[0062] In some embodiments, based on the total weight of the electrolyte, the weight percentage C% of the boron-containing lithium salt and the weight percentage A% of the dinitrile compound may satisfy C≤A.

[0063] In some embodiments, based on the total weight of the electrolyte, the weight percentage C% of the boron-containing lithium salt may satisfy 0.007≤C≤2. In some embodiments, the value of C may be about 0.007, about 0.01, about 0.05, about 0.1, about 0.25, about 0.5, about 1, about 1.5, about 1.8, about 2, or may satisfy a range consisting of any two of the above values, for example, about 0.01 to about 1.5 or about 0.1 to about 2.

[0064] In some embodiments, the electrolyte further comprises a boron-free lithium salt. In some embodiments, the boron-free lithium salt is selected from lithium hexafluorophosphate (LiPF 6 ), lithium difluorophosphate (LiPO 2 F 2 ), lithium hexafluoroarsenate, lithium perchlorate, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or at least one of bis(oxalate)boron.

[0065] In some embodiments, based on the total weight of the electrolyte, the weight percentage D% of the boron-free lithium salt and the weight percentage C% of the boron-containing lithium salt can satisfy 0.01≤C / D×12.5≤3.8. When A, B, C, and D of the electrolyte simultaneously satisfy A / B≥1.2, 0≤(A / B)-C+1≤11, and 0.01≤C / D×12.5≤3.8, the lithium-ion battery can have further improved cycle performance under high temperature and high power.

[0066] In some embodiments, based on the total weight of the electrolyte, the weight percentage D% of the boron-free lithium salt may satisfy 8.75≤D≤20. In some embodiments, the value of D may be about 8.75, about 9, about 10, about 11, about 12, about 13, about 14, about 15, about 16, about 17, about 18, about 19, about 20, or may satisfy a range consisting of any two of the above values, for example, about 9 to about 15 or about 10 to about 20.

[0067] In some embodiments, the electrolyte may further include fluoroethylene carbonate (FEC). In some embodiments, based on the total weight of the electrolyte, the weight percentage E% of fluoroethylene carbonate and the weight percentage A% of the dinitrile compound may satisfy 5≤A+E≤25. In some embodiments, the value of A+E may be about 5, about 6, about 7, about 8, about 9, about 10, about 11, about 12, about 13, about 14, about 15, about 16, about 17, about 18, about 19, about 20, about 21, about 22, about 23, about 24, about 25, or may satisfy the range of any two of the above values, for example, from about 6 to about 10 or from about 15 to about 20.

[0068] In some embodiments, the electrolyte may further include at least one of 1,3-propane sultone (PS), 1,4-butane sultone, vinylene carbonate (VC), or dithiothreitol (DTD).

[0069] 2. Electrochemical Device

[0070] The embodiments of the present application also provide an electrochemical device, which includes a positive electrode, a negative electrode, a separator and an electrolyte of the present application. The electrochemical device of the present application may include any device in which an electrochemical reaction occurs, and its 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 a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery. In some embodiments, the electrochemical device of the present application includes a positive electrode having a positive electrode active material capable of absorbing and releasing metal ions; a negative electrode having a negative electrode active material capable of absorbing and releasing metal ions; a separator disposed between the positive electrode and the negative electrode; and the electrolyte of the present application.

[0071] In some embodiments, the electrochemical device is a lithium-ion battery, which includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte. In some embodiments, the positive electrode includes a positive electrode current collector and a positive electrode active material layer coated on the positive electrode current collector, and the negative electrode includes a negative electrode current collector and a negative electrode active material layer coated on the negative electrode current collector; the electrolyte is the non-aqueous electrolyte described in any of the preceding paragraphs.

[0072] Electrolyte

[0073] The electrolyte used in the electrochemical device of the present application is any of the above-mentioned electrolytes of the present application. In addition, the electrolyte used in the electrochemical device of the present application may also include other electrolytes within the scope not departing from the gist of the present application.

[0074] negative electrode

[0075] The negative electrode of the present application includes negative electrode active material particles containing negative electrode active material. In some embodiments, the negative electrode active material particles meet at least one of the conditions (a) or (b): (a) the negative electrode active material particles Dn10 are about 1 μm to about 9 μm; (b) the negative electrode active material particles Dv50 are about 5 μm to about 18 μm. Dn10 represents the particle size corresponding to 10% of the number distribution of negative electrode active material particles in microns. Dv50 represents the particle size corresponding to 50% of the volume distribution of negative electrode active material particles in microns. When the negative electrode active material particles meet the above (a) or (b), the lithium precipitation of the negative electrode can be effectively alleviated; when the negative electrode active material particles meet the above (a) and (b) at the same time, lithium precipitation will not occur at the negative electrode.

[0076] Figures 1A to 1C Schematic diagrams showing respectively the case where no lithium deposition occurs on the negative electrode of a lithium-ion battery, the case where lithium deposition occurs, and the case where severe lithium deposition occurs. As Figure 1A shown, when no lithium deposition occurs on the negative electrode of the lithium-ion battery, the surface of the negative electrode is smooth. As Figure 1B shown, when lithium deposition occurs on the negative electrode of the lithium-ion battery, metallic lithium will precipitate on a part of the surface of the negative electrode, making a part of the surface of the negative electrode rough. As Figure 1C shown, when severe lithium deposition occurs on the negative electrode, most of the surface of the negative electrode will be covered by the precipitated metallic lithium, making most of the surface of the negative electrode rough. The lithium deposition process is irreversible and will damage the lithium-ion battery. When severe lithium deposition occurs on the negative electrode of the lithium-ion battery, the safety of the lithium-ion battery will deteriorate, especially when the lithium-ion battery is subjected to external extrusion and impact, etc.

[0077] In some embodiments, when the negative electrode active material particles satisfy at least condition (a), the negative electrode active material particles may further satisfy at least one of conditions (c) or (d): (c) when the Dn10 of the negative electrode active material particles < 5 μm, 5Dn10 < Dv50 < 12Dn10; (d) when the Dn10 of the negative electrode active material particles ≥ 5 μm, 1.5Dn10 < Dv50 < 4Dn10.

[0078] In some embodiments, the negative electrode active material may include graphite. In some embodiments, the Dv50 of the graphite particles is about 5 μm to about 18 μm, for example, about 5 μm, about 7 μm, about 10 μm, about 12 μm, about 15 μm, about 18 μm, or may satisfy the range composed of any two of the above values, such as about 7 μm to about 15 μm.

[0079] In some embodiments, the Dn10 of the graphite particles is about 1 μm to about 9 μm, for example, about 1 μm, about 2 μm, about 3 μm, about 5 μm, about 7 μm, about 9 μm, or may satisfy the range composed of any two of the above values, such as about 2 μm to about 9 μm.

[0080] In some embodiments, the negative electrode active material may further include lithium metal, structured lithium metal, natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, silicon-oxygen material, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO 2 、spinel-structured lithiated TiO 2 -Li 4 Ti 5 O 12 、Li-Al alloy or any combination thereof.

[0081] In some embodiments, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector, and the negative electrode active material layer includes the negative electrode active material described above.

[0082] In some embodiments, the negative electrode active material layer may further include a binder. In some embodiments, the binder includes, but is not limited to: polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin or nylon.

[0083] In some embodiments, the negative electrode active material layer includes a conductive material. In some embodiments, the conductive material includes, but is not limited to: natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, metal powder, metal fiber, copper, nickel, aluminum, silver or polyphenylene derivatives.

[0084] In some embodiments, the negative electrode current collector includes, but is not limited to, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a polymer substrate coated with a conductive metal.

[0085] positive electrode

[0086] In some embodiments, the positive electrode includes a current collector and a positive electrode active material layer located on the current collector. The positive electrode active material layer contains a positive electrode active material, and the positive electrode active material includes at least one lithiated intercalation compound that reversibly intercalates and deintercalates lithium ions. In some embodiments, the positive electrode active material includes a composite oxide. In some embodiments, the composite oxide contains lithium and at least one element selected from cobalt, manganese and nickel.

[0087] In some embodiments, the positive electrode active material is selected from lithium cobalt oxide LiCoO 2 (LCO), lithium nickel cobalt manganese ternary material (NCM), lithium iron phosphate, lithium manganese oxide or any combination thereof.

[0088] In some embodiments, the positive electrode active material may have a coating on its surface, or may be mixed with another compound having a coating. The coating may include at least one coating element compound selected from an oxide of a coating element, a hydroxide of a coating element, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, and a hydroxycarbonate of a coating element. The compound for the coating may be amorphous or crystalline.

[0089] In some embodiments, the coating element contained in the coating may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, F or any combination thereof. The coating may be applied by any method as long as the method does not adversely affect the performance of the positive electrode active material. For example, the method may include any coating method known in the art, such as spraying, dipping, etc.

[0090] The positive electrode active material layer also includes a binder, and optionally a conductive material. The binder improves the bonding between the positive electrode active material particles and also improves the bonding between the positive electrode active material and the current collector.

[0091] In some embodiments, the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0092] In some embodiments, the conductive material includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0093] In some embodiments, the current collector may be aluminum, but is not limited thereto.

[0094] The positive electrode can be prepared by a preparation method known in the art. For example, the positive electrode can be obtained by mixing an active material, a conductive material, and a binder in a solvent to prepare an active material composition, and coating the active material composition on a current collector. In some embodiments, the solvent may include N-methylpyrrolidone, etc., but is not limited thereto.

[0095] In some embodiments, the positive electrode is made by forming a positive electrode material using a positive electrode active material layer including a lithium transition metal compound powder and a binder on a current collector.

[0096] In some embodiments, the positive electrode active material layer can be generally prepared by dry mixing the positive electrode material and the binder (conductive material and thickener used as needed) to form a sheet, pressing the obtained sheet to the positive electrode collector, or dissolving or dispersing these materials in a liquid medium to form a slurry, coating the slurry on the positive electrode collector and drying. In some embodiments, the material of the positive electrode active material layer includes any material known in the art.

[0097] Isolation film

[0098] In some embodiments, the electrochemical device of the present application is provided with a separator between the positive electrode and the negative electrode to prevent short circuit. The material and shape of the separator used in the electrochemical device of the present application are not particularly limited, and it can be any technology disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic substance formed of a material that is stable to the electrolyte of the present application.

[0099] For example, the isolation film may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film having a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be selected.

[0100] In some embodiments, a surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic layer.

[0101] The inorganic layer includes inorganic particles and a binder, wherein the inorganic particles are selected from one or a combination of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate. The binder is selected from one or a combination of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.

[0102] The polymer layer contains polymers, and the polymer material includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0103] 3. Electronic Devices

[0104] The electrochemical device described in this application is applicable to electronic devices in various fields.

[0105] The use of the electrochemical device of the present application is not particularly limited, and it can be used for any use known in the prior art. In one embodiment, the electrochemical device of the present application can be used for, but not limited to, laptop computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.

[0106] 4. Embodiment

[0107] Hereinafter, the present application will be described in more detail with reference to Examples and Comparative Examples, but the present application is not limited to these Examples unless departing from the gist of the present application.

[0108] Preparation of lithium-ion batteries

[0109] (1) Preparation of positive electrode

[0110] Lithium cobalt oxide, conductive carbon black and polyvinylidene fluoride were mixed in a weight ratio of 97:1.4:1.6, N-methylpyrrolidone (NMP) was added, and the system was stirred in a vacuum mixer until the system was uniform to obtain a positive electrode slurry, wherein the solid content of the positive electrode slurry was 72wt%. The positive electrode slurry was evenly coated on the positive electrode current collector aluminum foil, and the aluminum foil was dried at 85°C, and then cold pressed, cut and slit, and dried at 85°C under vacuum conditions for 4 hours to obtain a positive electrode.

[0111] (2) Preparation of negative electrode

[0112] Artificial graphite, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were mixed in a weight ratio of 97:1:2, deionized water was added, and the mixture was stirred evenly under the action of a vacuum mixer to obtain a negative electrode slurry, wherein the solid content of the negative electrode slurry was 54wt%. The negative electrode slurry was evenly coated on a negative electrode current collector copper foil, and the copper foil was dried at 85°C, and then cold pressed, cut into pieces, and slit, and then dried under vacuum conditions at 120°C for 12 hours to obtain a negative electrode.

[0113] (3) Preparation of electrolyte

[0114] In a dry argon atmosphere glove box, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were mixed in a weight ratio of 1:2:7, and fluoroethylene carbonate (FEC) was added. The specific amount of FEC added was 5% except for the examples in Table 4. Then, the additives were added, dissolved, and stirred thoroughly, and then lithium salt LiPF was added. 6 , and then mixed evenly to obtain an electrolyte. The specific amounts of additives are shown in Tables 1 to 4 below. Lithium salt LiPF 6 The specific addition amount is 12% except for the examples in Table 2. The contents of the additives and lithium salts in the table are weight percentages calculated based on the total weight of the electrolyte.

[0115] (4) Isolation film

[0116] A 7μm thick polyethylene (PE) isolation film is selected.

[0117] (5) Preparation of lithium-ion batteries

[0118] The positive electrode, the separator, and the negative electrode are stacked in order, so that the separator is between the positive electrode and the negative electrode to play an isolating role, and then wound to obtain a bare cell. After welding the pole ear, the bare cell is placed in the outer packaging foil aluminum plastic film, and after drying, the prepared electrolyte is injected, and after vacuum packaging, standing, formation (0.02C constant current charging to 3.5V, and then 0.1C constant current charging to 3.9V), shaping, capacity testing and other processes, a soft-pack lithium-ion battery (thickness 3.3mm, width 39mm, length 96mm) is obtained.

[0119] Test Method

[0120] Cyclic test under high temperature and high power:

[0121] First, the initial thickness of the prepared lithium-ion battery at 50% state of charge (SOC) is measured and recorded as W 0 Then, at a constant temperature of 45°C, the lithium-ion battery was charged to 4.45V at 0.7C constant current, then charged to 0.05C at constant voltage, and left to stand for 10 minutes; it was discharged at 0.05C constant current for 60 minutes, which was a charge and discharge cycle. This charge and discharge cycle was repeated 1500 times, and after the end, the lithium-ion battery was charged to 4.45V at 0.7C constant current, then charged to 0.05C at constant voltage, and then its thickness W was tested. 1 The cycling performance at high temperature and high charge can be characterized by the thickness growth rate. A lower thickness growth rate indicates better performance.

[0122] Thickness growth rate (%) = (W 1 -W 0 ) / W 0 ×100%

[0123] Negative electrode lithium plating situation:

[0124] After the high temperature and high power cycle test, the lithium-ion battery was charged to 4.45V at 1.5C constant current at 25°C, and then charged to 0.05C at constant voltage. The battery was disassembled and the lithium deposition on the negative electrode surface was observed. The evaluation of lithium deposition is as follows:

[0125] No lithium deposition: No lithium deposition is found on the negative electrode surface or the lithium deposition area is less than 2%;

[0126] Slight lithium deposition: The lithium deposition area is between 2% and 20%;

[0127] Severe lithium deposition: lithium deposition area > 20%.

[0128] Normal temperature cycle test:

[0129] First, measure the prepared lithium-ion battery. At a constant temperature of 25°C, charge the lithium-ion battery to 4.45V at 0.7C constant current, then charge it to 0.05C at constant voltage, and let it stand for 10 minutes; discharge it to 3.0V at 0.5C constant current. This is a charge and discharge cycle, and the discharge capacity of this cycle is recorded as D 0 Repeat the charge and discharge cycle 700 times, and record the discharge capacity after 700 cycles, which is recorded as D 1 .

[0130] Cycle retention rate (%) = D 1 / D 0 ×100%.

[0131] Low temperature discharge test:

[0132] The formed lithium-ion battery is charged to 4.45V at 0.7C constant current at 25°C, then charged to 0.05C at constant voltage, and left to stand for 10 minutes; discharged to 3.0V at 0.2C constant current, at which point the discharge capacity is recorded as D 2 ; Then the lithium-ion battery is charged to 4.45V at 0.7C constant current at 25℃, then charged to 0.05C at constant voltage, transferred to -10℃ environment for storage for 2h, and then discharged to 3.4V at 0.2C at -10℃. This discharge capacity is recorded as D 3 .

[0133] Low temperature discharge retention rate (%) = D 3 / D 2 ×100%.

[0134] Test Results

[0135] Table 1 shows the electrolyte parameters and test results of Examples 1 to 31 and Comparative Examples 1 to 6.

[0136] Table 1

[0137]

[0138]

[0139]

[0140] (“-” in Table 1 means no addition or not applicable)

[0141] By comparing Examples 1 to 33 with Comparative Examples 1 to 3, it can be seen that the cycle performance of a lithium ion battery in which the electrolyte includes a dinitrile compound, a polynitrile compound, and a boron-containing lithium salt is better than the cycle performance of a lithium ion battery in which the electrolyte includes only one of them. The electrolyte including the dinitrile compound, the polynitrile compound, and the boron-containing lithium salt makes the thickness growth rate of the electrochemical device cycled at high temperature and high power lower, effectively improving the cycle performance of the electrochemical device at high temperature and high power.

[0142] By comparing Examples 1 to 31 with Example 32, it can be seen that the thickness growth rate of the lithium-ion battery when A / B≥1.2 is significantly smaller than the thickness growth rate of the lithium-ion battery when A / B<1.2. Therefore, satisfying A / B≥1.2 can further improve the cycle performance of the lithium-ion battery under high temperature and high power.

[0143] By comparing Examples 1 to 31 with Comparative Examples 4 to 5, it can be seen that when A / B≥1.2, when A, B, C satisfy 0≤(A / B)-C+1≤11, the cycle performance of the lithium-ion battery under high temperature and high power can be further improved.

[0144] Table 2 shows the electrolyte parameters and test results of Examples 34 to 48.

[0145] Table 2

[0146]

[0147]

[0148] By comparing Examples 34 to 46 with Examples 47 and 48, it can be known that when A, B, and C of the electrolyte satisfy A / B≥1.2 and 0≤(A / B)-C + 1≤11, if the weight percentage C% of the boron-containing lithium salt and the weight percentage D% of the boron-free lithium salt further satisfy 0.01≤C / D×12.5≤3.8, the cyclic thickness growth rate of the lithium-ion battery at high temperature and high state of charge can be further reduced, thereby further improving the cycling performance of the lithium-ion battery at high temperature and high state of charge, and at the same time, the low-temperature discharge capacity retention rate can be improved. If C / D is too high, the film formed on the negative electrode may be too thick due to the high concentration of the boron-containing lithium salt, affecting the performance. If C / D is too low, the boron-containing lithium salt concentration may be too low to effectively stabilize the positive electrode and form a relatively thin cathode electrolyte interface (CEI) film layer.

[0149] Table 3 shows the electrolyte parameters and test results of Examples 49 to 54.

[0150] Table 3

[0151]

[0152] According to Table 3, it can be known that when A, B, and C of the electrolyte of the lithium-ion battery satisfy A / B≥1.2 and 0≤(A / B)-C + 1≤11, if the negative active material particles of the lithium-ion battery are further in the range of Dn10 being about 1 μm to about 9 μm, and / or Dv50 being about 5 μm to about 18 μm, it can alleviate the lithium deposition on the negative electrode. When the negative active material particles Dn10 < 5 μm (such as Examples 51 and 52), when the negative active material particles satisfy 5Dn10 < Dv50 < 12Dn10, the lithium-ion battery has better cycling performance at high temperature and high state of charge; when the negative active material particles Dn10≥5 μm (such as Examples 49 and 50), when the negative active material particles satisfy 1.5Dn10 < Dv50 < 4Dn10, the performance of the lithium-ion battery is better. If Dn10 and Dv50 are too large, the ion and electron transport paths become larger, resulting in poor kinetic performance;

[0153] Table 4 shows the electrolyte parameters and test results of Example 4 and Examples 55 to 65.

[0154] Table 4

[0155]

[0156]

[0157] It can be seen from Example 4, Example 55 to Example 65 of Table 4 that when A, B, and C of the electrolyte of the lithium ion battery satisfy A / B≥1.2 and 0≤(A / B)-C+1≤11, if the electrolyte of the lithium ion battery further satisfies 5≤A+E≤25, the lithium ion battery has a lower cycle thickness growth at high temperature and high power and better room temperature cycle performance. This may be because the dinitrile compound is unstable to the negative electrode, and FEC is required to form a film at the negative electrode for protection, while FEC is unstable at high temperature, and the dinitrile compound is required to strengthen the protection of the positive electrode, so the sum of the content of the dinitrile compound and the content of FEC is within a certain range, and the performance is better.

[0158] The above are only several embodiments of the present invention and are not intended to limit the present invention in any form. Although the present invention is disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with the profession, without departing from the scope of the technical solution of the present invention, using the above disclosed technical content to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

[0159] References throughout the specification to "some embodiments", "partial embodiments", "one embodiment", "another example", "example", "specific example" or "partial example" mean that at least one embodiment or example in the present application includes the specific features, structures, materials or characteristics described in the embodiment or example. Therefore, descriptions appearing in various places throughout the 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 embodiment or example in the present application. In addition, the specific features, structures, materials or characteristics herein may be combined in one or more embodiments or examples in any suitable manner.

[0160] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and that changes, substitutions and modifications may be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. An electrochemical device, which includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte contains a dinitrile compound, a polynitrile compound having more than 2 cyano groups, and a boron-containing lithium salt, wherein based on the total weight of the electrolyte, the weight percentage of the dinitrile compound is A%, the weight percentage of the polynitrile compound is B%, and the weight percentage of the boron-containing lithium salt is C%; in, A, B, and C satisfy 0 ≤ (A / B) - C + 1 ≤ 11; and wherein the negative electrode includes negative electrode active material particles, and the negative electrode active material particles satisfy that the Dn10 of the negative electrode active material particles is from 1 μm to 9 μm; and when the Dn10 of the negative electrode active material particles < 5 μm, 5Dn10 < Dv50 < 12Dn10; or when the Dn10 of the negative electrode active material particles ≥ 5 μm, 1.5Dn10 < Dv50 < 4Dn10.

2. The electrochemical device according to claim 1, wherein the dinitrile compound contains a compound represented by Formula I: wherein R1 is selected from substituted or unsubstituted C1 to C9 alkylene, substituted or unsubstituted C2 to C 10 Alkenylene, -R a -OR b -or-R c -OR d -OR e -, where R a , R b , R c and R e are each independently selected from a single bond or a substituted or unsubstituted C1 to C5 alkylene group, and R a and R b Not single bond at the same time, R d is selected from substituted or unsubstituted C1 to C5 alkylene, wherein when substituted, the substituent is halogen; wherein the polynitrile compound contains a compound represented by Formula II: wherein R2 is selected from H, C, CH, CH2, or CH3; R3 is selected from C, CH, or CH2; R4, R5, R6, R7, R8, R9 and R 10 are each independently selected from a single bond, a substituted or unsubstituted C1 to C5 alkylene group or -R f -OR g -, where R f and R g Each is independently selected from a single bond or a substituted or unsubstituted C1 to C5 alkylene group, wherein when substituted, the substituent is halogen; X1 and X2 are each independently selected from a single bond, oxygen, or a substituted or unsubstituted C1-C5 alkylene group, and when substituted, the substituent is a halogen; and a, b, c, d, e, f, and g each independently take a value of 0 or 1, and at least three of them do not take the value of 0 simultaneously.

3. The electrochemical device according to claim 2, wherein the dinitrile compound contains: At least one of; wherein the polynitrile compound contains: At least one of .

4. The electrochemical device according to claim 1, wherein 3 ≤ A + B ≤ 20.

5. The electrochemical device according to claim 1, wherein the boron-containing lithium salt contains at least one of lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, or lithium tetraborate, and / or wherein C ≤ A.

6. The electrochemical device according to claim 1, wherein the electrolyte further contains a boron-free lithium salt, and based on the total weight of the electrolyte, the weight percentage of the boron-free lithium salt is D%, and 0.01 ≤ C / D × 12.5 ≤ 3.

8.

7. The electrochemical device according to claim 1, wherein the electrolyte further contains fluoroethylene carbonate, and based on the total weight of the electrolyte, the weight percentage of the fluoroethylene carbonate is E%, and 5 ≤ A + E ≤ 25.

8. The electrochemical device according to claim 1, wherein the Dv50 of the negative electrode active material particles is from 5 μm to 18 μm.

9. An electronic device, which includes the electrochemical device according to any one of claims 1-8.

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