Secondary battery and electric device

Abstract

Provided in the present application are a secondary battery and an electric device. An electrolyte of the secondary battery comprises a first additive having a structure as represented by formula I and a second additive comprising at least one of an alkali metal salt of difluorophosphoric acid, an alkali metal salt of tetrafluoroboric acid, an alkali metal salt of fluorosulfonic acid and an alkali metal salt of difluoro oxalato boric acid, wherein the mass content W2 of the second additive in the electrolyte is 0.01%≤W2%≤5%; and the ratio of the mass content W2 of the second additive in the electrolyte to the mass content W1 of the first additive in the electrolyte is 0.02≤W2 / W1≤10. The secondary battery has a good cathode-anode interface membrane, thereby having excellent cycle performance and storage performance.

Description

Secondary batteries and electrical devices

[0001] Cross-references

[0002] This application refers to Chinese patent application No. 202410069759.9, entitled “Secondary Battery and Electrical Device”, filed on January 17, 2024, which is incorporated into this application in its entirety by reference. Technical Field

[0003] The present application relates to the technical field of secondary batteries, and in particular to a secondary battery and an electrical device. Background Art

[0004] Secondary batteries have attracted much attention due to their high specific energy, long cycle life, low self-discharge and good safety performance. The application of secondary batteries has penetrated into all aspects of daily life, such as cameras, laptops, electric vehicles, etc., and the requirements for battery power performance, cycle and storage life are also increasing.

[0005] During the cycle, side reactions between the electrolyte and active ions occur at the anode and cathode interfaces, leading to electrolyte decomposition or active ion precipitation, which reduces the cycle life and storage life of the secondary battery. Therefore, it is necessary to develop a secondary battery with good cycle life and storage life. Summary of the Invention

[0006] The secondary battery provided in the first aspect of the present application has both good cycle life and storage life.

[0007] The secondary battery provided in the first aspect includes an electrolyte, wherein the electrolyte includes: a first additive having a structure shown in Formula I,

[0008] R1 is selected from substituted or unsubstituted C3~C6 alkynyl, R2 is selected from substituted or unsubstituted C1~C6 alkyl;

[0009] The second additive comprises at least one of an alkali metal salt of difluorophosphoric acid, an alkali metal salt of tetrafluoroboric acid, an alkali metal salt of fluorosulfonic acid, and an alkali metal salt of difluorooxalatoboric acid;

[0010] Wherein, the mass content W2 of the second additive in the electrolyte is 0.01%≤W2%≤5%;

[0011] The ratio of the mass content W2 of the second additive in the electrolyte to the mass content W1 of the first additive in the electrolyte is 0.02≤W2 / W1≤10.

[0012] In a secondary battery, the first additive can effectively form a film at the anode of the secondary battery and participate in the formation of a "solid electrolyte interface" (SEI), which can effectively inhibit the decomposition of the electrolyte on the anode side; the second additive can preferentially undergo a reduction reaction on the anode side of the secondary battery, participate in the formation of a LiF-rich SEI film, and inhibit the reduction reaction of the first additive on the anode side and inhibit the increase of the anode interface impedance. The second additive can also participate in the formation of a film at the cathode interface, protect the cathode and inhibit the dissolution of transition metals or doping elements in the positive electrode active material. The first additive and the second additive can be used in combination to form a good interface film at the anode and cathode, reduce side reactions in the electrolyte of the secondary battery, and improve the cycle performance and storage performance of the secondary battery.

[0013] In any embodiment, R1 is an acetylenic ethyl group, and R2 is a methyl group or an ethyl group. The acetylenic ethyl group in the first additive helps to react at the anode, produce organic substances, and better participate in the formation of the anode interface film.

[0014] In any embodiment, the mass content W2 of the second additive in the electrolyte is 0.05%≤W2%≤5%, thereby further forming a good interface film at the anode and cathode, reducing side reactions on the anode side of the secondary battery and inhibiting the increase of the anode interface impedance.

[0015] In any embodiment, the ratio of the mass content W2 of the second additive in the electrolyte to the mass content W1 of the first additive in the electrolyte is 1≤W2 / W1≤9.5, which can effectively inhibit the deterioration of the anode interface impedance caused by the first additive, thereby improving the cycle performance and storage performance of the secondary battery.

[0016] In any embodiment, the mass content W1 of the first additive in the electrolyte is 0.01%≤W1%≤6.5%, and can be optionally 0.01%≤W1%≤0.1%, so that the first additive can form a good interface film on the anode side and reduce the increase in the anode interface film impedance.

[0017] In any embodiment, the alkali metal salt includes any one or a combination of lithium, sodium, potassium, rubidium, and cesium salts, and can be a lithium salt.

[0018] In any embodiment, the secondary battery includes a positive electrode active material, the positive electrode active material includes a doping element, and the doping element includes one or more of B, Zr, Ti, Li, Cr, Cu, Zn, Mg, and Al. The doping element helps improve the structural stability of the positive electrode active material during cycling.

[0019] In any embodiment, the mass content W3 of the doping element in the positive electrode active material is 0.01%≤W3%≤1%, and can be optionally 0.04%≤W3%≤1%, thereby improving the structural stability of the positive electrode active material in the secondary battery and inhibiting the structural phase change of the positive electrode active material caused by the deintercalation and insertion of active lithium ions during the charge and discharge process.

[0020] In any embodiment, the secondary battery satisfies the following conditions: 0.1 ≤ W1 / W3 ≤ 13; and / or 0.1 ≤ W2 / W3 ≤ 35. Controlling the W1 / W3 ratio helps control the increase in anode interface impedance and improve the structural stability of the positive electrode active material during cycling. Controlling the W2 / W3 ratio helps inhibit the dissolution of dopant element ions in the positive electrode active material, improve the structural stability of the positive electrode active material during cycling, and reduce the impact of the anode interface film on the active ion transport performance.

[0021] In any embodiment, the positive electrode active material comprises a molecular formula of Li[Ni x Co y Mn z M 1-x-y-z ]O2 lithium nickel cobalt manganese oxide, wherein M includes one or more of B, Zr, Ti, Li, Cr, Cu, Zn, Mg, Al, 0≤x<1, 0≤y≤1, 0≤z≤1, x+y+z≤1.

[0022] In any embodiment, the electrolyte salt in the electrolyte includes LiPF6 and lithium bis(fluorosulfonyl)imide, and the concentration C1 of LiPF6 and the concentration C2 of lithium bis(fluorosulfonyl)imide satisfy: 0.8M≤C1+C2≤1.5M, 0.1M≤C2≤1M. The electrolyte salt has good chemical stability and ionic conductivity. The combined use of the two can improve the conductivity of the electrolyte and reduce the risk of corrosion of the aluminum foil.

[0023] In any embodiment, the electrolyte includes a cyclic carbonate and / or linear carboxylate solvent, wherein the cyclic carbonate includes at least one of ethylene carbonate, fluoroethylene carbonate, and propylene carbonate; and the linear carboxylate includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl acetate, methyl acetate, methyl propionate, ethyl propionate, and propyl propionate. These solvents help reduce the viscosity of the electrolyte and enhance the transport properties of active ions, thereby improving the cycle performance of the secondary battery.

[0024] A second aspect of the present application provides an electric device including a secondary battery selected from the first aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application.

[0026] FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 1 .

[0027] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0028] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0029] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present application.

[0030] FIG6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0031] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0032] Below, the embodiments of the secondary battery, battery module, battery pack and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0033] The "ranges" disclosed herein are defined in terms of lower and upper limits, where a given range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits define the boundaries of the particular range. Ranges defined in this manner can be inclusive or exclusive of the end values ​​and can be combined arbitrarily, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise indicated, the numerical range "a to b" is a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0034] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0035] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0036] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0037] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0038] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0039] [Secondary battery]

[0040] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0041] The electrolyte includes solvents, electrolyte salts and additives. It is a carrier for transporting active ions and plays a vital role in the fast charging performance, specific capacity, cycle efficiency and safety performance of secondary batteries.

[0042] During the initial charge and discharge process of a secondary battery, the electrode material and electrolyte react at the solid-liquid interface, forming a passivation layer (also known as an interfacial film) covering the surface of the electrode material. The passivation layer formed on the anode side is called the "solid electrolyte interface," or SEI, and the passivation layer formed on the cathode side is called the "cathode electrolyte interphase," or CEI. During cycling, the solvent in the electrolyte undergoes side reactions at the interface between the electrode and the electrolyte, generating gas. This affects the stability of the electrode interface and the impedance of the interfacial film, thereby reducing the cycling and storage performance of the secondary battery.

[0043] Based on this, the present application provides a secondary battery including an additive, which helps the secondary battery form a good SEI film and / or CEI film, can reduce the gas production of the electrolyte, and improve the stability of the electrode interface and the impedance of the interface film.

[0044] The secondary battery provided in the present application includes an electrolyte, wherein the electrolyte includes: a first additive having a structure shown in Formula I,

[0045] R1 is selected from substituted or unsubstituted C3-C6 alkynyl groups, and R2 is selected from substituted or unsubstituted C1-C6 alkyl groups; and

[0046] A second additive comprising an alkali metal salt of difluorophosphoric acid, an alkali metal salt of tetrafluoroboric acid, an alkali metal salt of fluorosulfonic acid, or an alkali metal salt of difluorooxalatoboric acid, wherein the mass content W2 of the second additive in the electrolyte is 0.01%≤W2%≤5%;

[0047] The ratio of the mass content W2 of the second additive in the electrolyte to the mass content W1 of the first additive in the electrolyte is 0.02≤W2 / W1≤10.

[0048] As used herein, "C1-C6 alkyl" refers to a straight or branched hydrocarbon chain radical consisting solely of carbon and hydrogen atoms, with no unsaturation present, having from one to six carbon atoms, and attached to the remainder of the molecule by a single bond. In some embodiments, the C1-C6 alkyl radical includes any one of methyl, ethyl, n-propyl, isopropyl, n-butyl, and n-pentyl. Alternatively, the C1-C6 alkyl radical is selected from methyl and ethyl.

[0049] As used herein, a "C3-C6 alkynyl" group refers to an alkyl group having 3 to 6 carbon atoms and containing at least one alkynyl group. The C3-C6 alkynyl group includes any one of CH≡C-CH2-(alkynylethyl), CH≡C-CH2-CH2-, and CH≡CC≡C-CH2-. Optionally, the C3-C6 alkynyl group is selected from alkynylethyl.

[0050] As used herein, the term "substituted" refers to substitution by a substituent, wherein the substituent is independently selected from: a halogen atom, a C1-C6 alkyl group, such as a fluoro group.

[0051] In secondary batteries, the unsaturated alkenyl group in the first additive can undergo a reduction reaction at the anode of the secondary battery, producing loose organic matter that participates in the formation of the SEI film, but is not conducive to reducing the interfacial impedance of the SEI film. The second additive can be preferentially deposited at the anode of the secondary battery, preferentially undergo a reduction reaction during formation, and participate in the formation of a dense SEI film rich in LiF. The SEI film helps to reduce the reduction reaction of the first additive at the anode and inhibit the increase of the anode interface impedance; at the same time, the second additive can also participate in the cathode interface film formation, protect the cathode and inhibit the dissolution of transition metals or doping elements in the positive electrode active material. The combined use of the first additive and the second additive helps to obtain a SEI film that is both rigid and tough, inhibits the increase of the anode interface impedance and the reduction and decomposition of the electrolyte at the anode, and improves the cycle performance and storage performance of the secondary battery.

[0052] In some embodiments, R1 is an alkynylethyl group, and R2 is a methyl or ethyl group. In some embodiments, R1 is an alkynylethyl group, and R2 is a methyl group. In some embodiments, R1 is an alkynylethyl group, and R2 is an ethyl group. The unsaturated group contained in the first additive can react at the anode, better participating in the formation of the SEI film; and the R2 group has good chemical stability and structural toughness, which helps improve the electronic insulation of the SEI film and the flexibility of the interfacial film.

[0053] In some embodiments, the mass content W2 of the second additive in the electrolyte is 0.05% ≤ W2% ≤ 5%. In some embodiments, the mass content W2 of the second additive in the electrolyte is 0.1% ≤ W2% ≤ 2.5%, 0.05% ≤ W2% ≤ 3.0%, 0.2% ≤ W2% ≤ 2.5%, 0.1% ≤ W2% ≤ 5.0%, 0.3% ≤ W2% ≤ 2.5%, 0.75% ≤ W2% ≤ 5.0%. In some embodiments, the mass content W2 of the second additive in the electrolyte is 0.05%, 0.07%, 0.1%, 0.15%, 0.2%, 0.25%, 0.5%, 0.75%, 1%, 1.5%, 1.85%, 2%, 2.5%, 2.95%, 3%, 3.5%, 4%, 4.5%, 5%, or a range between any two of the above values. Controlling the mass content of the second additive in the electrolyte can form a good interface film at the anode and cathode, and help inhibit the reduction reaction of the first additive on the anode side of the secondary battery and inhibit the increase of the anode interface impedance.

[0054] In some embodiments, the ratio of the mass content W2 of the second additive in the electrolyte to the mass content W1 of the first additive in the electrolyte is 1≤W2 / W1≤10. In some embodiments, the ratio of the mass content W2 of the second additive in the electrolyte to the mass content W1 of the first additive in the electrolyte is 1≤W2 / W1≤9.5. In some embodiments, the ratio of the mass content W2 of the second additive in the electrolyte to the mass content W1 of the first additive in the electrolyte is 1≤W2 / W1≤7.5, 2≤W2 / W1≤10, 3≤W2 / W1≤10, 1≤W2 / W1≤9, 1≤W2 / W1≤8, or 3.5≤W2 / W1≤7. In some embodiments, the ratio of the mass content W2 of the second additive in the electrolyte to the mass content W1 of the first additive in the electrolyte is 1, 1.3, 1.5, 1.8, 2, 2.4, 3, 3.5, 3.7, 4, 5, 6, 7.5, 8.7, 9.2, 9.8 or a range between any two of the above values. If the ratio of the mass content W2 of the second additive in the electrolyte to the mass content W1 of the first additive in the electrolyte is too small, the first additive may worsen the anode interface impedance of the secondary battery, which is not conducive to the cycle performance of the secondary battery. When the ratio of the mass content W2 of the second additive in the electrolyte to the mass content W1 of the first additive in the electrolyte is too high, the second additive may worsen the conductivity of the electrolyte, which is not conducive to the migration of active ions and affects the cycle performance of the secondary battery. Controlling the ratio of the mass content W2 of the second additive in the electrolyte to the mass content W1 of the first additive in the electrolyte can take into account both the secondary battery anode interface impedance and the conductivity of the electrolyte, thereby improving the cycle performance and storage performance of the secondary battery.

[0055] In some embodiments, the mass content W1 of the first additive in the electrolyte is 0.01%≤W1%≤6.5%. In some embodiments, the mass content W1 of the first additive in the electrolyte is 0.01%≤W1%≤0.1%, 0.05%≤W1%≤5%, 0.01%≤W1%≤4%, 0.01%≤W1%≤3%, 0.01%≤W1%≤1%. In some embodiments, the mass content W1 of the first additive in the electrolyte is 0.03%, 0.08%, 0.1%, 0.5%, 0.8%, 1.2%, 2.3%, 3.4%, 4.1%, 4.9%, 5.5%, 6.3% or a range between any two of the above values. Adjusting the mass content of the first additive in the electrolyte helps it form a good interfacial film on the anode side, reduce side reactions on the anode side, and not excessively increase the interfacial impedance of the anode.

[0056] In some embodiments, in the secondary battery, the mass content W1 of the first additive in the electrolyte is 0.01%≤W1%≤1%, the mass content W2 of the second additive in the electrolyte is 0.1%≤W2%≤5%, and the ratio of W2 to W1 is 1≤W2 / W1≤10, which can further improve the cycle performance and storage performance of the secondary battery.

[0057] In some embodiments, the alkali metal salt includes any one or a combination of lithium, sodium, potassium, rubidium, and cesium salts. In some embodiments, the alkali metal salt includes lithium salt.

[0058] In some embodiments, the second additive includes lithium difluorophosphate and / or lithium tetrafluoroborate. In some embodiments, the second additive includes lithium difluorophosphate. In some embodiments, the second additive includes lithium tetrafluoroborate. The additive is widely available, cost-effective, and helps form a high-quality anode-cathode interface film.

[0059] In some embodiments, the secondary battery includes a positive electrode active material, which can be a positive electrode active material for batteries known in the art.

[0060] As an example, the positive electrode active material may also include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0061] In some embodiments, the positive electrode active material includes a doping element. In some embodiments, the doping element includes one or more of B, Zr, Ti, Li, Cr, Cu, Zn, Mg, and Al. The doping element helps improve the structural stability of the positive electrode active material during cycling. In some embodiments, the doping element includes Zr.

[0062] In some embodiments, the positive electrode active material comprises a material having the formula Li[Ni x Co y Mn z M 1-x-y-z ]O2 lithium nickel cobalt manganese oxide, wherein the doping element M includes one or more of B, Zr, Ti, Li, Cr, Cu, Zn, Mg, Al, 0≤x<1, 0≤y≤1, 0≤z≤1, x+y+z≤1.

[0063] In some embodiments, 0 <x<1,0≤y≤0.3,0≤z≤0.01,x+y+z≤1。

[0064] In some embodiments, the molecular formula is Li[Ni x Co y Mn z M 1-x-y-z ]O2 lithium nickel cobalt manganese oxide can be prepared using methods known in the prior art, for example, referring to the methods or part of the methods in CN117334860A, CN117334852A, and CN115986105A.

[0065] In some embodiments, the mass content W3 of the doping element in the positive electrode active material is 0.01% ≤ W3% ≤ 1%. In some embodiments, the secondary battery includes a positive electrode active material containing a doping element, and the mass content W3 of the doping element in the positive electrode active material is 0.04% ≤ W3% ≤ 1%, 0.1% ≤ W3% ≤ 1%, 0.05% ≤ W3% ≤ 0.9%, 0.05% ≤ W3% ≤ 0.8%, 0.05% ≤ W3% ≤ 0.7%, 0.2% ≤ W3% ≤ 1%, or 0.01% ≤ W3% ≤ 0.5%. The secondary battery includes a positive electrode active material containing a doping element, wherein the mass content W3 of the doping element in the positive electrode active material is 0.03%, 0.05%, 0.08%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.38%, 0.41%, 0.52%, 0.64%, 0.72%, 0.83%, 0.94% or a range between the above two values. The doping element can improve the crystalline stability of the positive electrode active material. Adjusting the content of the doping element in the positive electrode active material can inhibit the structural phase change of the positive electrode active material caused by the deintercalation of active ions during the charge and discharge process, thereby improving the structural stability of the positive electrode active material during the cycle; and reducing the influence of the doping element on the energy density of the secondary battery, thereby improving the cycle performance and storage performance of the secondary battery.

[0066] The mass content W3 of the doping element in the positive electrode active material can be determined using methods known in the art. As an example, it can be determined by inductively coupled plasma (ICP) spectrometry analysis, for example, it can be determined using an inductively coupled plasma emission spectrometer, or reference can be made to standards YS / T1006.2-2014, GB / T23367.2-2009 or YS / T1028.5-2015.

[0067] In some embodiments, in the secondary battery, the mass content W1 of the first additive in the electrolyte is 0.01% ≤ W1% ≤ 1%, the mass content W2 of the second additive in the electrolyte is 0.05% ≤ W2% ≤ 5%, and the mass content W3 of the doping element in the positive electrode active material is 0.02% ≤ W3% ≤ 1%, which can take into account both the cycle performance and storage performance of the secondary battery.

[0068] In some embodiments, the secondary battery satisfies: 0.1≤W1 / W3≤13. In some embodiments, the ratio of the mass content W1 of the first additive in the electrolyte to the mass content W3 of the doping element in the positive electrode active material is 0.5-13, 0.8-13, 1-13, 2-13, 3-13, 0.1-10, 0.1-7, 0.1-6.7, 0.1-5, or 0.1-3. In some embodiments, the ratio of the mass content W1 of the first additive in the electrolyte to the mass content W3 of the doping element in the positive electrode active material is 0.3, 0.7, 1, 1.3, 2, 2.7, 3, 3.8, 4, 4.3, 5, 5.7, 6, 6.3, 7, 7.8, 8, 8.8, 9, 9.4, 10, 11, 11.4, 12.1, 13, or a range between the above two values. Adjusting the ratio of W1 / W3 helps to control the increase of anode interface impedance and improve the structural stability of the positive electrode active material during the cycle process, which helps to improve the cycle performance and storage performance of the secondary battery.

[0069] In some embodiments, the secondary battery satisfies: 0.1≤W2 / W3≤35. In some embodiments, the ratio of W2 / W3 is 1-35, 0.5-35, 1-30, 2-25, 3-20, 0.1-33, 0.3-27, 0.7-30. In some embodiments, the ratio of W2 / W3 is 0.15, 0.55, 0.96, 1.7, 2.5, 3.5, 5.3, 8.7, 10.2, 13.4, 15, 17.6, 18.9, 21.5, 23.1, 24.8, 28.9, 34.5, or a range between any two of the above values. Adjusting the ratio of W2 / W3 helps to inhibit the dissolution of doped element ions in the positive electrode active material, improve the structural stability of the positive electrode active material during the cycle, and reduce the impact of the anode interface film on the active ion transport performance.

[0070] [Positive electrode]

[0071] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0072] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0073] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0074] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0075] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0076] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0077] [Negative electrode]

[0078] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0079] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0080] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0081] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0082] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0083] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0084] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0085] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0086] [Electrolyte]

[0087] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte; it can be selected based on needs. For example, the electrolyte can be liquid, gel, or solid.

[0088] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0089] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0090] In some embodiments, the electrolyte salt in the electrolyte includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. The electrolyte salt has good chemical stability, provides active ions for the electrolyte, and helps improve the rate performance and cycle performance of the secondary battery.

[0091] In some embodiments, the concentration C1 of lithium hexafluorophosphate (LiPF6) and the concentration C2 of lithium bis(fluorosulfonyl)imide (LiFSI) satisfy the following conditions: 0.8M≤C1+C2≤1.5M, and 0.1M≤C2≤1M. The high degree of dissociation of LiFSI in the electrolyte can significantly improve the electrolyte conductivity and increase the lithium ion transfer rate. However, LiFSI carries the risk of corroding aluminum foil. LiPF6, on the other hand, can form a dense passivation layer on the aluminum foil surface, inhibiting corrosion. The combined use of the two can improve electrolyte conductivity and reduce the risk of aluminum foil corrosion.

[0092] In some embodiments, the electrolyte solvent includes a cyclic carbonate and / or a linear carboxylate solvent. The cyclic carbonate includes at least one of ethylene carbonate, fluoroethylene carbonate, and propylene carbonate; and the linear carboxylate includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl acetate, methyl acetate, methyl propionate, ethyl propionate, and propyl propionate. These solvents help reduce the viscosity of the electrolyte and enhance the transport properties of active ions, thereby improving the cycling performance of the secondary battery.

[0093] [Isolation film]

[0094] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0095] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0096] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0097] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0098] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0099] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery 5 with a square structure as an example.

[0100] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0101] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0102] Figure 3 shows an example battery module 4. Referring to Figure 3 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured together using fasteners.

[0103] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0104] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0105] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0106] In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0107] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0108] Figure 6 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0109] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0110] Example

[0111] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0112] 1. Test Method

[0113] 1. Cycle performance test of secondary batteries

[0114] At an ambient temperature of 25°C, the battery cell is charged to 4.25V at 1C, then charged to 0.05C at a constant voltage, left to stand for 10 minutes, and discharged to 2.8V at 1C. The discharge capacity is recorded as C0. 300 cycles are performed according to the above charge and discharge process. The discharge capacity of the 300th cycle is C1, and the cycle capacity retention rate of the battery cell = C1 / C0×100%.

[0115] 2. Storage performance test of secondary batteries

[0116] The cell was charged at 1C to 4.25V, then charged at a constant voltage to 0.05C, allowed to rest for 5 minutes, and then discharged at 1C to 2.8V. The discharge capacity was recorded as D0. The cell was stored at 60°C for 60 days, removed and returned to 25°C, then discharged at 1C to 2.8V, allowed to rest for 2 hours, then charged at 1C to 4.25V, then charged at a constant voltage to 0.05C, allowed to rest for 2 hours, and then discharged at 1C to 2.8V. The discharge capacity was recorded as D1. Discharge capacity retention = D1 / D0 × 100%.

[0117] 3. Determination of doping element content in positive electrode active materials

[0118] The content was determined by inductively coupled plasma optical emission spectrometry according to the standard YS / T1006.2-2014.

[0119] 2. Preparation of Secondary Batteries

[0120] Example 1

[0121] 1) Preparation of electrolyte

[0122] In an argon-filled glove box (water content <10 ppm, oxygen content <1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3:7 to obtain a non-aqueous organic solvent. Dry lithium salt LiPF6 and lithium bis(fluorosulfonyl)imide were dissolved in the mixed organic solvent to prepare an electrolyte solution with concentrations of lithium salt LiPF6 and lithium bis(fluorosulfonyl)imide of 0.8 mol / L and 0.2 mol / L, respectively. A first additive (structural formula: R1 is an acetylenic ethyl group, R2 is a methyl group), and the second additive lithium tetrafluoroborate with a mass content W2 of 0.05%.

[0123] 2) Preparation of positive electrode sheet

[0124] The positive electrode active material Li[Ni 0.8 Co 0.1 Mn 0.098 Zr 0.002O2, conductive agent Super P, and binder polyvinylidene fluoride were mixed in a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) was added and stirred evenly to obtain a positive electrode slurry with a solid content of 50wt%. The positive electrode slurry was coated on a current collector aluminum foil, dried, cold pressed, and slit to obtain positive electrode sheets.

[0125] 3) Preparation of negative electrode sheet

[0126] The negative electrode active material graphite, conductive agent Super P, thickener sodium carboxymethyl cellulose, and binder styrene-butadiene rubber were mixed uniformly in deionized water at a mass ratio of 80:15:3:2 to prepare a negative electrode slurry with a solid content of 30 wt%. The negative electrode slurry was coated onto the current collector copper foil and dried, pressed, trimmed, cut, and slit to form the negative electrode sheet.

[0127] 4) Preparation of secondary batteries

[0128] A 16 μm thick polyethylene film (PE) was used as a separator. The prepared positive electrode sheet, separator, and negative electrode sheet were stacked in order, with the separator positioned between the positive and negative electrode sheets to separate the positive and negative electrodes. The electrode assembly was wound, and the tabs were welded. The electrode assembly was placed in an outer package. The prepared electrolyte was injected into the dried battery cell, and the battery was packaged, allowed to stand, formed, shaped, and capacity tested to obtain the lithium-ion battery of Example 1.

[0129] Examples 2 to 19 and Comparative Examples 1 to 2

[0130] The secondary batteries of Examples 2 to 18 and the secondary batteries of Comparative Examples 1 to 2 were prepared in a similar manner to the secondary battery of Example 1, except that the amounts of additives and the mass content of doping elements in the positive electrode active materials were adjusted, as shown in Table 1.

[0131] The secondary battery preparation method of Example 19 is similar to that of Example 1, except that the substituent R1 of the first additive is ethylenyl, R2 is ethyl, and the mass content is 0.10%; the second additive is lithium difluorophosphate, and the mass content is 0.10%, see Table 1 for details.

[0132] Table 1

[0133] The secondary batteries prepared in Examples 1 to 19 and Comparative Examples 1 to 2 were tested using the above method. The test results are shown in Table 2 below:

[0134] Table 2

[0135] It can be seen from Examples 1 to 19 and Comparative Examples 1 to 2 that when the mass content of the second additive is between 0.01% and 5%, and the ratio of the mass content W2 of the second additive to the mass content W1 of the first additive is within the range of 0.02 to 10, the secondary battery can form a good interface film at both the anode and cathode, so that the secondary battery has both good cycle performance and storage performance.

[0136] It can be seen from Examples 1 to 5 that a ratio of W2 to W1 in the range of 1 to 10 can further improve the deterioration of the anode interface impedance of the secondary battery, thereby further improving the cycle performance and storage performance of the secondary battery.

[0137] As shown in Examples 6 to 10, when the mass content W2 of the second additive is within the range of 0.01% to 5.00%, the second additive can participate in film formation at the anode and cathode interfaces, inhibit the deterioration of the anode interface impedance and the structural stability of the positive electrode active material, thereby improving the cycle performance and storage performance of the secondary battery. When the mass content W2 of the second additive is within the range of 1.00% to 5.00%, the cycle performance and storage performance of the secondary battery can be further improved.

[0138] Examples 10 to 14 show that when the mass content of the first additive is within the range of 0.5% to 6.5%, the secondary battery has good cycle performance and storage performance. It also shows that as the mass content of the first additive increases, the first additive's deteriorating effect on the anode interface impedance increases, resulting in a decrease in the first additive's improvement in the cycle performance and storage performance of the secondary battery. When the mass content of the first additive is within the range of 0.50% to 1.0%, the cycle performance and storage performance of the secondary battery can be significantly improved.

[0139] As shown in Examples 6 and 15 to 18, when the mass content of the doping element in the positive electrode active material is within the range of 0.01% to 1.00%, the structural stability of the positive electrode active material is improved, and the secondary battery has good cycle performance and storage performance. When the mass content of the doping element in the positive electrode active material is within the range of 0.02% to 1.00%, the cycle performance and storage performance of the secondary battery can be further improved.

[0140] As can be seen from Example 19, when R2 in the first additive containing an alkynyl group is selected from an ethyl group and the second additive is lithium difluorophosphate, the prepared secondary battery also has excellent cycle performance and storage performance.

[0141] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery, characterized in that, Contains an electrolyte, the electrolyte comprising: a first additive having the structure shown in Formula I, R1 is selected from substituted or unsubstituted C3-C6 alkynyl groups, and R2 is selected from substituted or unsubstituted C1-C6 alkyl groups; A second additive, which includes at least one of an alkali metal salt of difluorophosphoric acid, an alkali metal salt of tetrafluoroboric acid, an alkali metal salt of fluorosulfonic acid, and an alkali metal salt of difluorooxalic acid borate; Wherein, the mass content W2 of the second additive in the electrolyte is 0.01% ≤ W2% ≤ 5%; The ratio of the mass content W2 of the second additive in the electrolyte to the mass content W1 of the first additive in the electrolyte is 0.02 ≤ W2 / W1 ≤ 10.

2. The secondary battery according to claim 1, wherein R1 is ethynyl, and R2 is methyl or ethyl.

3. The secondary battery according to claim 1 or 2, characterized in that, The mass content W2 of the second additive in the electrolyte is 0.05% ≤ W2% ≤ 5%.

4. The secondary battery according to any one of claims 1 to 3, characterized in that The ratio of the mass content W2 of the second additive in the electrolyte to the mass content W1 of the first additive in the electrolyte is 1 ≤ W2 / W1 ≤ 9.

5.

5. The secondary battery according to any one of claims 1 to 4, characterized in that, The mass content W1 of the first additive in the electrolyte is 0.01% ≤ W1% ≤ 6.5%, and can be optionally 0.01% ≤ W1% ≤ 1%.

6. The secondary battery according to any one of claims 1 to 5, characterized in that, The alkali metal salt includes any one or combination of lithium, sodium, potassium, rubidium, and cesium salts, and can be optionally a lithium salt.

7. The secondary battery according to any one of claims 1 to 6, characterized in that, The secondary battery includes a positive electrode active material, the positive electrode active material includes a doping element, and the doping element includes one or more of B, Zr, Ti, Li, Cr, Cu, Zn, Mg, and Al.

8. The secondary battery according to claim 7, wherein The mass content W3 of the doping element in the positive electrode active material is 0.01% ≤ W3% ≤ 1%, and can be optionally 0.04% ≤ W3% ≤ 1%.

9. The secondary battery according to claim 7 or 8, characterized in that, The secondary battery satisfies: 0.1 ≤ W1 / W3 ≤ 13; and / or 0.1 ≤ W2 / W3 ≤ 35.

10. The secondary battery according to claim 7 or 8, characterized in that, The positive electrode active material includes lithium nickel cobalt manganese oxide with the molecular formula Li[Ni x Co y Mn z M 1-x-y-z O2, where M includes one or more of B, Zr, Ti, Li, Cr, Cu, Zn, Mg, and Al, 0 ≤ x < 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, and x + y + z ≤ 1.

11. The secondary battery according to any one of claims 1 to 10, characterized in that, The electrolyte salt in the electrolyte includes LiPF6 and lithium bis(fluorosulfonyl)imide, and the concentration C1 of LiPF6 and the concentration C2 of lithium bis(fluorosulfonyl)imide satisfy: 0.8M ≤ C1 + C2 ≤ 1.5M, 0.1M ≤ C2 ≤ 1M.

12. The secondary battery according to any one of claims 1 to 11, characterized in that, The electrolyte includes a cyclic carbonate and / or a linear carboxylate solvent, The cyclic carbonate includes at least one of ethylene carbonate, fluoroethylene carbonate, and propylene carbonate; The linear carboxylate includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl acetate, methyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

13. An electrical device, characterized in that, Including the secondary battery according to any one of claims 1 to 12.

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