Electrolyte, and electrochemical device and electronic device including same

Abstract

The invention 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 with more than 2 cyano groups and a boron-containing lithium salt, and the weight percentages of the dinitrile compound, the polynitrile compound and the boron-containing lithium salt meet a certain relational expression, so that the electrochemical device comprising the electrolyte has improved cycle performance at high temperature and high electric quantity.

Description

[0001] This application is a divisional application of the Chinese patent application with the application number 202080106738.X, the invention title of "Electrolyte and Electrochemical Device and Electronic Device Comprising the Same" and filed with the Patent Office of the State Intellectual Property Office of China on October 27, 2020. Technical Field

[0002] This application relates to the field of energy storage technologies, and in particular to an electrolyte and an electrochemical device and an electronic device comprising the same, especially a lithium-ion battery. Background Art

[0003] Electrochemical devices, such as lithium-ion batteries, have the advantages of high energy density, high working voltage, low self-discharge rate, long cycle life, and no pollution, and have been widely used in fields such as computers, smart wearable devices, smart phones, drones, and electric vehicles. With the development of modern information technology and the expansion of the application scope of lithium-ion batteries, more performance requirements are put forward for lithium-ion batteries, such as cycle performance at high temperature and high battery charge.

[0004] At present, how to enable lithium-ion batteries to have good cycle performance at high temperature and high battery charge is the research focus in the battery field. Summary of the Invention

[0005] This application provides an electrolyte and an electrochemical device comprising the same in an attempt to solve at least one problem existing in the related art to at least some extent.

[0006] This application provides an electrolyte which at least contains a dinitrile compound, a polynitrile compound with more than 2 cyano groups, and a boron-containing lithium salt, and controls the weight percentages of the three to provide good cycle performance of the electrochemical device at high temperature and high battery charge.

[0007] On the one hand, this application provides an electrolyte which contains a dinitrile compound, a polynitrile compound with 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%, and wherein A, B, and C satisfy A / B≥1.2 and 0≤(A / B)-C + 1≤11.

[0008] According to some embodiments of this application, the dinitrile compound contains a compound represented by Formula I:

[0009]

[0010] wherein R 1 is selected from substituted or unsubstituted C 1 to C 9 alkylene, substituted or unsubstituted C2 to C 10 alkenylene, -R a -O-R b - or -R c -O-R d -O-R 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 b are not both a single bond at the same time, R d is selected from a substituted or unsubstituted C 1 to C 5 alkylene, where when substituted, the substituent is a halogen.

[0011] According to some embodiments of the present application, wherein the polynitrile compound comprises a compound represented by Formula II:

[0012]

[0013] where R 2 is selected from H, C, CH, CH 2 or CH 3 ; R 3 is 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 -O-R 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 alkylene, where when substituted, the substituent is a halogen; X 1 and X 2 are each independently selected from a single bond, oxygen, or a substituted or unsubstituted C 1 to C 5 alkylene, where 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 a value of 0 at the same time.

[0014] According to some embodiments of the present application, the dinitrile compound includes:

[0015]

[0016] at least one of. According to some embodiments of the present application, the polynitrile compound includes:

[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] In another aspect, the present application also provides an electronic device, which includes any one of the above-mentioned electrochemical devices.

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

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

[0029] Figures 1A to 1C They are respectively schematic diagrams of the negative electrode of a lithium-ion battery without lithium plating, with lithium plating, and with severe lithium plating. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] The embodiments of the present application will be described in detail below. The embodiments related to the drawings described herein are illustrative, diagrammatic, and are used to provide a basic understanding of the present application. The embodiments of the present application should not be construed as a limitation of the present application.

[0031] As used herein, the term "about" is used to describe and account for small variations. When used in conjunction with an event or circumstance, the term can refer to instances where the event or circumstance occurs precisely and instances where the event or circumstance occurs approximately. For example, when used in conjunction with a numerical value, the term can refer to a range of variation of ±10% less than or equal to 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 "about" the same.

[0032] In addition, sometimes quantities, ratios, and other numerical values are presented in a range format in this text. It should be understood that such range formats are for convenience and brevity, and should be understood flexibly, including not only the numerical values explicitly specified as range limits, but also all individual numerical values or sub-ranges covered within the range, as if each numerical value and sub-range were explicitly specified.

[0033] In the specific embodiments and claims, a list of items joined by the terms "at least one of", "at least one", "at least one kind 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 include a single component or multiple components. Item B may include a single component or multiple components. Item C may include a single component or multiple components.

[0034] As used herein, the term "alkylene" means a straight-chain or branched divalent saturated hydrocarbon group. For example, the alkylene may be an alkylene having 1 to 20 carbon atoms, an alkylene having 1 to 15 carbon atoms, an alkylene having 1 to 10 carbon atoms, an alkylene having 1 to 5 carbon atoms, an alkylene having 5 to 20 carbon atoms, an alkylene having 5 to 15 carbon atoms, or an alkylene having 5 to 10 carbon atoms. Representative alkylene groups 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. Additionally, the alkylene may be optionally substituted.

[0035] The term "alkenylene" encompasses straight-chain and branched alkenylene groups. When specifying an alkenylene group having a specific number of carbon atoms, all geometric isomers having that number of carbon atoms are expected to be encompassed. For example, the alkenylene may be an alkenylene having 2 to 20 carbon atoms, an alkenylene having 2 to 15 carbon atoms, an alkenylene having 2 to 10 carbon atoms, an alkenylene having 2 to 5 carbon atoms, an alkenylene having 5 to 20 carbon atoms, an alkenylene having 5 to 15 carbon atoms, or an alkenylene having 5 to 10 carbon atoms. Representative alkenylene groups include (for example) vinylidene, propenylene, butenylene, etc. Additionally, the alkenylene may 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 a lithium-ion battery undergoes charge and discharge cycles at high temperatures and high battery levels, the positive electrode is in an unstable state and is prone to deoxidation. The oxygen removed is likely to react with the electrolyte in a side reaction and is also likely to oxidize the electrolyte. Therefore, the lithium-ion battery has poor cycle performance at high temperatures and high battery levels.

[0040] The inventors of the present application have found through research that nitrile compounds can coordinate with transition metal elements to stabilize the positive electrode, but the structure of nitrile compounds will affect their improvement effect. Adding polynitrile compounds with more than 2 cyano groups to the electrolyte can increase the complexation efficiency of transition metal ions in the positive electrode. However, due to their large steric hindrance, gaps will be generated between polynitrile compounds, thus unable to fully protect the positive electrode. The dinitrile compound has a small steric hindrance and can compensate for the positive electrode interface not protected by polynitrile compounds. In addition, the inventors have also found that boron (B) in the boron-containing lithium salt forms a B-O bond with oxygen atoms (O) on the surface of the positive electrode, which can stabilize the positive electrode and can further compensate for the part of the positive electrode not protected due to steric effects and protect this part, so that the electrochemical device has good cycle performance at high temperatures and high battery levels.

[0041] I. Electrolyte

[0042] The electrolyte of the present application contains a dinitrile compound, a polynitrile compound with more than 2 cyano groups, and a boron-containing lithium salt. 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%. A, B, and C satisfy 0 ≤ (A / B) - C + 1 ≤ 11.

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

[0044]

[0045] In Formula I, R 1 is selected from a substituted or unsubstituted C 1 to C 9 alkylene group, a substituted or unsubstituted C 2 to C 10 alkenylene group, -R a -O-R b -, or -R c -O-R d -O-R 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 group, and R a and R bNot a single bond at the same time, R d Selected from substituted or unsubstituted C 1 to C 5 alkylene, where when substituted, the substituent is halogen.

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

[0047] Compound I-1, Compound I-2,

[0048] Compound I-3, Compound I-4,

[0049] Compound I-5, Compound I-6,

[0050] Compound I-7, Compound I-8 or at least one of Compound I-9.

[0051] In some embodiments, the polynitrile compound having more than 2 cyano groups comprises a compound represented by Formula II:

[0052]

[0053] In Formula II, R 2 is selected from H, C, CH, CH 2 or CH 3 ; R 3 is selected from C, CH or CH 2 ; R 4 , R 5 , R 6 , R 7 , R 8 , R 9 and R 10 each independently selected from a single bond, substituted or unsubstituted C 1 to C 5 alkylene or -R f -O-R g -, where R f and R g each independently selected from a single bond or substituted or unsubstituted C 1 to C 5 alkylene, where when substituted, the substituent is halogen; X 1 and X 2 each independently selected from a single bond, oxygen, or substituted or unsubstituted C 1 to C5 an alkylene group, wherein 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 simultaneously take a value of 0.

[0054] Those skilled in the art can easily understand that in order to conform to the chemical bonding principle, the selection of the groups of R 2 and R 3 has a linkage relationship with the values of c, d, e, f and g. For example, when R 2 is C, it means that c, d and e must take a value of 1.

[0055] In some embodiments, the polynitrile compound comprises:

[0056] Compound II-10, Compound II-11,

[0057] Compound II-12, Compound II-13,

[0058] Compound II-14, Compound II-15,

[0059] Compound II-16, Compound II-17, Compound II-18, Compound II-19,

[0060] Compound II-20, Compound II-21 or

[0061] at least one of Compound II-22.

[0062] 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 the range composed 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.

[0063] 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 the range composed of any two of the above values. For example, about 3 to about 10 or about 5 to about 15.

[0064] 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 the range composed of any two of the above values. For example, about 0.5 to about 5 or about 2.5 to about 7.

[0065] In some embodiments, the boron-containing lithium salt includes at least one of lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium tetrafluoroborate (LiBF 4 ) or lithium tetraborate among others.

[0066] 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.

[0067] 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 the range composed of any two of the above values. For example, about 0.01 to about 1.5 or about 0.1 to about 2.

[0068] In some embodiments, the electrolyte further includes a boron-free lithium salt. In some embodiments, the boron-free lithium salt is selected from at least one of 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 lithium bis(oxalato)borate.

[0069] 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 may 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 may have further improved cycling performance at high temperature and high charge.

[0070] 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 the range composed of any two of the above values, for example, about 9 to about 15 or about 10 to about 20.

[0071] 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 composed of any two of the above values, for example, about 6 to about 10 or about 15 to about 20.

[0072] 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 divinyl sulfone (DTD).

[0073] II. Electrochemical Device

[0074] Embodiments of the present application further provide an electrochemical device, which includes a positive electrode, a negative electrode, a separator, and the electrolyte of the present application. The electrochemical device of the present application may include any device that undergoes an electrochemical reaction, and specific examples thereof include all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery, including a lithium metal secondary battery, a lithium-ion secondary battery, a lithium polymer secondary battery, or a lithium-ion polymer secondary battery. In some embodiments, the electrochemical device of the present application includes a positive electrode having a positive electrode active material capable of occluding and releasing metal ions; a negative electrode having a negative electrode active material capable of occluding and releasing metal ions; a separator disposed between the positive electrode and the negative electrode; and the electrolyte of the present application.

[0075] 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 at intervals, 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 foregoing paragraphs.

[0076] Electrolyte

[0077] The electrolyte used in the electrochemical device of the present application is any of the above electrolytes of the present application. In addition, the electrolyte used in the electrochemical device of the present application may also contain other electrolytes within the scope not departing from the gist of the present application.

[0078] Negative electrode

[0079] The negative electrode of the present application includes negative electrode active material particles containing a negative electrode active material. In some embodiments, 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 about 1 μm to about 9 μm; (b) The Dv50 of the negative electrode active material particles is about 5 μm to about 18 μm. Dn10 represents the particle size corresponding to 10% of the number distribution of the negative electrode active material particles in microns. Dv50 represents the particle size corresponding to 50% of the volume distribution of the negative electrode active material particles in microns. When the negative electrode active material particles satisfy the above (a) or (b), the lithium precipitation situation of the negative electrode can be effectively alleviated; when the negative electrode active material particles satisfy both the above (a) and (b) at the same time, no lithium precipitation phenomenon will occur on the negative electrode.

[0080] Figures 1A to 1C They are respectively schematic diagrams of the negative electrode of the lithium-ion battery without lithium precipitation phenomenon, with lithium precipitation phenomenon and with serious lithium precipitation phenomenon. As Figure 1A shown, when there is no lithium precipitation phenomenon on the negative electrode of the lithium-ion battery, the surface of the negative electrode is smooth. As Figure 1B shown, when there is a lithium precipitation phenomenon 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 there is a serious lithium precipitation phenomenon 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 precipitation process is irreversible and will cause damage to the lithium-ion battery. When the negative electrode of the lithium-ion battery has serious lithium precipitation, the safety of the lithium-ion battery will deteriorate, especially when the lithium-ion battery is subjected to external extrusion and impact, etc.

[0081] 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 Dn10 of the negative electrode active material particles < 5 μm, 5Dn10 < Dv50 < 12Dn10; (d) when Dn10 of the negative electrode active material particles ≥ 5 μm, 1.5Dn10 < Dv50 < 4Dn10.

[0082] In some embodiments, the negative electrode active material may include graphite. In some embodiments, 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.

[0083] In some embodiments, 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.

[0084] 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.

[0085] 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 above-mentioned negative electrode active material.

[0086] 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, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin or nylon.

[0087] 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.

[0088] 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.

[0089] Positive electrode

[0090] 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.

[0091] 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.

[0092] 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 oxides of coating elements, hydroxides of coating elements, hydroxyoxides of coating elements, carbonate oxides of coating elements, and hydroxycarbonates of coating elements. The compound used for the coating may be amorphous or crystalline.

[0093] In some embodiments, the coating elements 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 have an adverse effect on 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.

[0094] The positive electrode active material layer further includes a binder, and optionally includes a conductive material. The binder improves the binding between the positive electrode active material particles and also improves the binding between the positive electrode active material and the current collector.

[0095] In some embodiments, the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0096] 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 materials are selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based materials are selected from metal powder, metal fiber, copper, nickel, aluminum, silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0097] In some embodiments, the current collector can be aluminum, but is not limited thereto.

[0098] The positive electrode can be prepared by methods well known in the art. For example, the positive electrode can be obtained by the following method: 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 can include N-methylpyrrolidone, etc., but is not limited thereto.

[0099] 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-based compound powder and a binder on a current collector.

[0100] In some embodiments, the positive electrode active material layer can generally be made by the following operations: dry-mixing the positive electrode material and the binder (conductive material, thickener, etc. used as needed) to form a sheet, pressing the obtained sheet onto the positive electrode current collector, or dissolving or dispersing these materials in a liquid medium to form a slurry, coating it on the positive electrode current collector and drying. In some embodiments, the materials of the positive electrode active material layer include any materials well known in the art.

[0101] Separator

[0102] 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 materials and shapes 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, an inorganic substance, etc. formed of a material stable to the electrolyte of the present application.

[0103] For example, the separator membrane may include a base material layer and a surface treatment layer. The base material layer is a non-woven fabric, a film, or a composite film having a porous structure, and the material of the base material 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.

[0104] In some embodiments, a surface treatment layer is provided on at least one surface of the base material layer. The surface treatment layer may be a polymer layer, an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

[0105] The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from one or a combination of several of alumina, silica, magnesia, 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 several of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, polyvinylpyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0106] The polymer layer contains a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate salt, polyvinylpyrrolidone, polyethylene ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0107] III. Electronic Device

[0108] The electrochemical device described in the present application is applicable to electronic devices in various fields.

[0109] 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, mobile phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, liquid crystal TVs, portable cleaners, portable CD players, mini-discs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, motorized bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0110] IV. Examples

[0111] Hereinafter, examples and comparative examples are given to further specifically illustrate the present application. However, the present application is not limited to these examples as long as it does not deviate from its gist.

[0112] Preparation of Lithium-Ion Battery

[0113] (1) Preparation of Positive Electrode

[0114] Lithium cobaltate, conductive carbon black, and polyvinylidene fluoride were mixed at a weight ratio of 97:1.4:1.6, and N-methylpyrrolidone (NMP) was added. The mixture was stirred in a vacuum mixer until the system was homogeneous to obtain a positive electrode slurry, where the solid content of the positive electrode slurry was 72 wt%. The positive electrode slurry was uniformly coated on the positive electrode current collector aluminum foil. The aluminum foil was dried at 85 °C, and then after cold pressing, slitting, and cutting, it was dried under vacuum conditions at 85 °C for 4 hours to obtain the positive electrode.

[0115] (2) Preparation of Negative Electrode

[0116] Artificial graphite, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were mixed at a weight ratio of 97:1:2, and deionized water was added. The mixture was stirred evenly in a vacuum mixer to obtain a negative electrode slurry, where the solid content of the negative electrode slurry was 54 wt%. The negative electrode slurry was uniformly coated on the negative electrode current collector copper foil. The copper foil was dried at 85 °C, and then after cold pressing, slitting, and cutting, it was dried under vacuum conditions at 120 °C for 12 hours to obtain the negative electrode.

[0117] (3) Preparation of Electrolyte

[0118] In a dry argon atmosphere glove box, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were mixed at a weight ratio of 1:2:7, and fluoroethylene carbonate (FEC) was added. The specific addition amount of FEC was 5% except for the examples in Table 4. Then, additives were added. After dissolution and sufficient stirring, lithium salt LiPF 6 was added. After mixing evenly, the electrolyte was obtained. The specific addition amounts of the additives are shown in Tables 1 to 4 below, and the specific addition amount of lithium salt LiPF 6 was 12% except for the examples in Table 2. The contents of the additives and lithium salt in the table are weight percentages calculated based on the total weight of the electrolyte.

[0119] (4) Separator

[0120] A 7-μm-thick polyethylene (PE) separator was selected.

[0121] (5) Preparation of Lithium-Ion Battery

[0122] Stack the positive electrode, separator, and negative electrode in sequence, with the separator positioned between the positive and negative electrodes to serve as an insulator, and then wind them to obtain a bare battery cell. After welding the tabs, place the bare battery cell in an outer packaging foil-aluminum plastic film, inject the prepared electrolyte after drying, and then perform processes such as vacuum packaging, standing, formation (constant current charging at 0.02C to 3.5V and then constant current charging at 0.1C to 3.9V), shaping, and capacity testing to obtain a soft-pack lithium-ion battery (thickness 3.3 mm, width 39 mm, length 96 mm).

[0123] Test method

[0124] Cycle test at high temperature and high state of charge:

[0125] First, measure the initial thickness of the prepared lithium-ion battery at a 50% state of charge (SOC), denoted as W 0 . Then, at a constant temperature of 45 °C, charge the lithium-ion battery at a constant current of 0.7C to 4.45V, then charge it at a constant voltage to 0.05C, and let it stand for 10 minutes; discharge it at a constant current of 0.05C for 60 minutes. This is one charge-discharge cycle. Repeat the charge-discharge cycle 1500 times. After completion, charge the lithium-ion battery at a constant current of 0.7C to 4.45V, then charge it at a constant voltage to 0.05C, and then measure its thickness W 1 . The cycle performance at high temperature and high state of charge can be characterized by the thickness growth rate. A lower thickness growth rate indicates better performance.

[0126] Thickness growth rate (%) = (W 1 - W 0 ) / W 0 × 100%

[0127] Lithium deposition on the negative electrode:

[0128] For the lithium-ion battery after the high-temperature and high-state-of-charge cycle test, charge it at a constant current of 1.5C to 4.45V at 25 °C, then charge it at a constant voltage to 0.05C, disassemble it, and observe the lithium deposition on the surface of the negative electrode. The evaluation of the lithium deposition is as follows:

[0129] No lithium deposition: No lithium deposition is found on the surface of the negative electrode or the lithium deposition area < 2%;

[0130] Slight lithium deposition: The lithium deposition area is between 2% and 20%;

[0131] Severe lithium deposition: The lithium deposition area > 20%.

[0132] Room temperature cycle test:

[0133] First, measure the prepared lithium-ion battery. Under the condition of a constant temperature of 25 °C, charge the lithium-ion battery at a constant current of 0.7C to 4.45V, then charge it at a constant voltage to 0.05C, and let it stand for 10 minutes; discharge it at a constant current of 0.5C to 3.0V. This is one charge-discharge cycle, and record the discharge capacity of this cycle as D 0 Repeat the charge-discharge cycle 700 times. After completion, record the discharge capacity after 700 cycles, denoted as D 1 .

[0134] Cycle retention rate (%) = D 1 / D 0 ×100%.

[0135] Low-temperature discharge test:

[0136] For the formed lithium-ion battery, at 25 °C, charge it at a constant current of 0.7C to 4.45V, then charge it at a constant voltage to 0.05C, and let it stand for 10 minutes; discharge it at a constant current of 0.2C to 3.0V. At this time, the discharge capacity is denoted as D 2 ; then keep the lithium-ion battery at 25 °C, charge it at a constant current of 0.7C to 4.45V, then after constant voltage charging to 0.05C, transfer it to an environment of -10 °C for storage for 2h, and then discharge it at 0.2C to 3.4V at -10 °C. This discharge capacity is denoted as D 3 .

[0137] Low-temperature discharge retention rate (%) = D 3 / D 2 ×100%.

[0138] Test results

[0139] Table 1 shows the electrolyte parameters and test results of Examples 1 to 31 and Comparative Examples 1 to 6

[0140] Table 1

[0141]

[0142]

[0143] (The "-" in Table 1 indicates not added or not applicable)

[0144] By comparing Examples 1 to 33 with Comparative Examples 1 to 3, it can be known that the cycle performance of the lithium-ion battery whose electrolyte contains dinitrile compounds, polynitrile compounds and boron-containing lithium salts is better than that of the lithium-ion battery whose electrolyte only contains one of them. The electrolyte containing dinitrile compounds, polynitrile compounds and boron-containing lithium salts results in a lower thickness growth rate during cycling at high temperature and high charge, effectively improving the cycle performance of the electrochemical device at high temperature and high charge

[0145] By comparing Examples 1 to 31 with Example 32, it can be seen that when A / B ≥ 1.2, the thickness growth rate of the lithium-ion battery is significantly less than that when A / B < 1.2. Therefore, meeting A / B ≥ 1.2 can further improve the cycling performance of the lithium-ion battery at high temperature and high charge.

[0146] 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, and C satisfy 0 ≤ (A / B) - C + 1 ≤ 11, the cycling performance of the lithium-ion battery at high temperature and high charge can be further improved.

[0147] Table 2 shows the electrolyte parameters and test results of Examples 34 to 48.

[0148] Table 2

[0149]

[0150] By comparing Examples 34 to 46 with Examples 47 and 48, it can be seen 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 cycling thickness growth rate of the lithium-ion battery at high temperature and high charge can be further reduced, thereby further improving the cycling performance of the lithium-ion battery at high temperature and high 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.

[0151] Table 3 shows the electrolyte parameters and test results of Examples 49 to 54.

[0152] Table 3

[0153]

[0154] As can be seen from Table 3, 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 further have a Dn10 of about 1 μm to about 9 μm, and / or a Dv50 of about 5 μm to about 18 μm, the lithium plating situation on the negative electrode can be alleviated. When the Dn10 of the negative active material particles <5 μm (such as in Examples 51 and 52), the lithium-ion battery has better cycling performance at high temperature and high charge when the negative active material particles satisfy 5Dn10<Dv50<12Dn10; when the Dn10 of the negative active material particles ≥5 μm (such as in Examples 49 and 50), the lithium-ion battery has better performance when the negative active material particles satisfy 1.5Dn10<Dv50<4Dn10. If Dn10 and Dv50 are too large, the ion and electron transport paths become larger, resulting in poor kinetic performance;

[0155] Table 4 shows the electrolyte parameters and test results of Examples 4 and Examples 55 to 65.

[0156] Table 4

[0157]

[0158] Comparing Examples 4, 55 to 65 in Table 4, it can be seen 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 cycling thickness growth at high temperature and high charge and better room-temperature cycling performance. This may be because the dinitrile compound is unstable to the negative electrode and requires FEC to form a film on the negative electrode for protection, while FEC is unstable at high temperature and requires the dinitrile compound to strengthen the protection of the positive electrode. Therefore, when the sum of the contents of the dinitrile compound and FEC is within a certain range, the performance is better.

[0159] The above are only several embodiments of the present invention and do not impose any form of limitation on the present invention. Although the present invention is disclosed as above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art, without departing from the scope of the technical solution of the present invention, making some changes or modifications using the above-disclosed technical content is equivalent to equivalent implementation cases and all belong to the scope of the technical solution.

[0160] References throughout this specification to "some embodiments", "certain embodiments", "one embodiment", "another example", "an example", "a specific example", or "a partial example" mean that at least one embodiment or example in this application includes the specific features, structures, materials, or characteristics described in that embodiment or example. Thus, descriptions that occur throughout this specification, such as "in some embodiments", "in embodiments", "in one embodiment", "in another example", "in an example", "in a specific example", or "an example" do not necessarily refer to the same embodiment or example in this application. Furthermore, the specific features, structures, materials, or characteristics described herein may be combined in any suitable manner in one or more embodiments or examples.

[0161] Although the illustrative embodiments have been shown and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the application, and that changes, substitutions, and modifications may be made to the embodiments without departing from the spirit, principles, and scope of the application.

Claims

1. An electrolyte solution, which comprises a dinitrile compound, a polynitrile compound with more than 2 cyano groups, a boron-containing lithium salt, and fluoroethylene carbonate, wherein based on the total weight of the electrolyte solution, the weight percentage of the dinitrile compound is A%, the weight percentage of the polynitrile compound is B%, the weight percentage of the boron-containing lithium salt is C%, and the weight percentage of the fluoroethylene carbonate is E%; wherein, 0 ≤ (A / B) - C + 1 ≤ 11, 5 ≤ A + E ≤ 25.

2. The electrolyte solution according to claim 1, wherein the dinitrile compound comprises a compound represented by formula I: wherein 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 -O-R b -, or -R c -O-R d -O-R e -, wherein R a 、R b 、R c and R e are each independently selected from a single bond or substituted or unsubstituted C 1 to C 5 alkylene, and R a and R b are not simultaneously a single bond, R d is selected from substituted or unsubstituted C 1 to C 5 alkylene, wherein when substituted, the substituent is a halogen; wherein the polynitrile compound comprises a compound represented by formula II: wherein R 2 is 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 each independently selected from a single bond, a substituted or unsubstituted C 1 to C 5 alkylene or -R f -O-R g -, where R f and R g each independently selected from a single bond or a substituted or unsubstituted C 1 to C 5 alkylene, and when substituted, the substituent is a halogen; X 1 and X 2 each independently selected from a single bond, oxygen, or a substituted or unsubstituted C 1 to C 5 alkylene group, wherein 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 simultaneously take a value of 0.

3. The electrolyte solution according to claim 2, wherein the dinitrile compound comprises: at least one of; wherein the polynitrile compound comprises: at least one of 4. The electrolyte solution according to claim 1, wherein 3 ≤ A + B ≤ 20.

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

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

8.

7. An electrochemical device, which comprises a positive electrode, a negative electrode, a separator, and the electrolyte solution according to any one of claims 1 to 6.

8. The electrochemical device according to claim 7, wherein the negative electrode comprises 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.

9. The electrochemical device according to claim 8, wherein 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.

10. An electronic device, which comprises the electrochemical device according to any one of claims 7 to 9.

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