Lithium-ion secondary battery, battery module, battery pack and power-consuming device

Abstract

The present application discloses a lithium-ion secondary battery, a battery module, a battery pack and an electric device. The lithium-ion secondary battery comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, the positive electrode sheet comprises a positive electrode collector and a positive electrode material layer arranged on at least one surface of the positive electrode collector, the positive electrode material layer comprises a first positive electrode material represented by the following formula (1) and a second positive electrode material represented by the following formula (2), the electrolyte comprises vinylene carbonate, and the content of the vinylene carbonate is greater than 0.1 wt% and less than 5 wt% relative to the total weight of the electrolyte. Li 1+x Fe y Mn z M 1‑y‑z PO 4‑t A t (1) (In the general formula (1), M includes one or more of Ti, Zr, V, and Cr, A includes one or more of S, N, F, Cl, and Br, and x, y, z, and t satisfy the following conditions: -0.1≤x<0.1, 0<y≤1, 0≤z<1, 0<y+z≤1, and 0≤t<0.2.) Li 2+r Ni 0.5‑p Cu 0.5‑q Ti v N p+q‑v O 2‑s B s (2) (In the general formula (2), N includes one or more of Mn, Fe, Co, Al, V, Cr, and Nb, B includes one or more of S, N, F, Cl, and Br, and r, p, q, v, and s respectively satisfy the following: ‑0.2≤r≤0.2, ‑0.5<p<0.5, ‑0.5<q<0.5, 0<v<0.01, 0≤p+q‑v<0.2, and 0≤s<0.2).

Description

Technical Field

[0001] The present application relates to a lithium-ion secondary battery, a battery module, a battery pack and an electrical device. Background Art

[0002] During the first charge and discharge process of lithium-ion secondary batteries, a solid electrolyte interface (SEI) will form on the negative electrode surface, causing irreversible capacity loss and reducing the energy density of lithium-ion energy storage devices. In devices using graphite negative electrodes, the first cycle will consume about 10% of the active lithium source. Furthermore, when using negative electrode materials with high specific capacity, such as alloys (silicon, tin, etc.), oxides (silicon oxide, tin oxide, etc.) and amorphous carbon negative electrodes, the consumption of active lithium sources will be further aggravated. Therefore, finding a suitable lithium supplementation method is of great significance to further improve the energy density of lithium-ion secondary batteries.

[0003] In response to this, the industry has proposed a method of using lithium powder, such as stabilized lithium metal powder (SLMP) to supplement negative electrode lithium. However, although this method can improve the energy density of the battery, the reaction activity of metal lithium powder is extremely high and it easily reacts with moisture in the air, posing a great safety hazard. In addition to requiring the use of non-aqueous organic solvents that do not react with lithium during the production process, the control of moisture is also extremely strict, increasing the difficulty of the process.

[0004] In view of the huge challenges faced by the negative electrode lithium replenishment strategy, the relatively safer and easier-to-operate positive electrode lithium replenishment method has received increasing attention in the industry. For example, Patent Document 1 discloses a positive electrode lithium replenishment material based on lithium oxygen compounds, lithium sources and alkyl lithium. However, the decomposition potential of the lithium-containing compound is relatively high, and oxygen and other byproducts are produced during the decomposition process, which will affect the life of the battery.

[0005] In addition, as lithium supplement materials, Li2NiO2-based lithium supplement materials are known. However, the surface free lithium content of this type of material is extremely high, which can easily cause gelation of the slurry during the slurry mixing process, seriously affecting the processing performance. In addition, during the first charge, a large amount of active lithium is embedded in the negative electrode, causing the real potential of the negative electrode to further decrease, and the solvent in the electrolyte continues to undergo a reduction reaction at the negative electrode, causing a continuous increase in impedance, affecting the battery's cycle performance.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent document 1: CN104037418A Summary of the invention

[0009] The present application has been developed in view of the above circumstances, and its purpose is to provide a lithium ion secondary battery that can achieve a balance between energy density, cycle life, and rate performance.

[0010] In order to achieve the above-mentioned object, the present application provides a lithium-ion secondary battery, which comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, and is characterized in that:

[0011] The positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector.

[0012] The positive electrode material layer comprises a first positive electrode material represented by the following general formula (1) and a second positive electrode material represented by the following general formula (2),

[0013] The electrolyte contains vinylene carbonate,

[0014] The content of the vinylene carbonate is greater than or equal to 0.1 wt % and less than or equal to 5 wt % relative to the total weight of the electrolyte. 1+x Fe y Mn z M 1-y-z PO 4-t A t (1)

[0015] (In the general formula (1), M includes one or more of Ti, Zr, V, and Cr, A includes one or more of S, N, F, Cl, and Br, and x, y, z, and t satisfy: -0.1≤x<0.1, 0<y≤1, 0≤z<1, 0<y+z≤1, and 0≤t<0.2.)

[0016] Li 2+r Ni 0.5-p Cu 0.5-q Ti v N p+q-v O 2-s B s (2)

[0017] (In the general formula (2), N includes one or more of Mn, Fe, Co, Al, V, Cr, and Nb, B includes one or more of S, N, F, Cl, and Br, and r, p, q, v, and s respectively satisfy: -0.2≤r≤0.2, -0.5<p<0.5, -0.5<q<0.5, 0<v<0.01, 0≤p+qv<0.2, and 0≤s<0.2.)

[0018] By using the positive electrode material layer containing both the first positive electrode material and the second positive electrode material for the positive electrode plate, the second positive electrode material forms a solid solution with a lower phase barrier and higher purity and specific capacity than the existing Li2NiO2 type lithium supplement material, which, in synergy with the first positive electrode material having an olivine structure, can effectively improve the energy density, cycle life and rate performance of the lithium-ion secondary battery. In addition, by adding a specific amount of vinylene carbonate additive to the electrolyte, a synergistic effect is produced with the first positive electrode material and the second positive electrode material of the present invention, so that a more uniform and dense SEI film is formed on the negative electrode after the first cycle of charging, which inhibits the continuous loss of active lithium and further improves the cycle life of the lithium-ion secondary battery.

[0019] In some embodiments, in the general formula (2), p, q, and v respectively satisfy: -0.1<p<0.1, -0.1<q<0.1, 0.002≤v≤0.008. By making p, q, and v satisfy the specific range, the content of free lithium on the surface of the material can be further reduced, and the problem of positive electrode slurry gel can be greatly improved, so that energy density, cycle life, and rate performance can be better taken into account.

[0020] In some embodiments, the positive electrode sheet satisfies the following formula (3).

[0021] 0.5≤R·P / Q≤16 (3)

[0022] In formula (3), R represents the resistance of the positive electrode sheet, and its unit is Ω; P represents the compaction density of the positive electrode sheet, and its unit is g / cm 3 , Q represents the single-sided surface density of the positive electrode sheet, and its unit is g / 1540.25mm 2 . )

[0023] By making the positive electrode sheet satisfy the above formula (3), the energy density, rate performance and cycle life of the lithium-ion secondary battery can be further improved.

[0024] In some embodiments, the positive electrode sheet further satisfies the following formula (4):

[0025] 1.5≤R·P / Q≤10 (4)

[0026] By making the positive electrode sheet further satisfy the above formula (4), the energy density, rate performance and cycle life of the lithium-ion secondary battery can be further improved.

[0027] In some embodiments, the resistance of the positive electrode sheet satisfies R≤3Ω, and optionally satisfies R≤1Ω. By making the resistance of the positive electrode sheet within the specific range, the cycle performance and rate performance of the lithium-ion secondary battery are improved.

[0028] In some embodiments, the compaction density P (unit: g / cm 3 ) satisfies 1.6<P<2.6. By making the compaction density P of the positive electrode sheet within the specific range, it is beneficial to the migration of electrons and ions in the positive electrode sheet, thereby improving the cycle performance of the lithium ion secondary battery.

[0029] In some embodiments, the single-sided surface density Q (unit: g / 1540.25mm 2 ) satisfies 0.16<Q<0.45. By setting the single-surface density Q of the positive electrode sheet to be within the specific range, the cycle performance and rate performance of the lithium-ion secondary battery can be improved while maintaining the charge and discharge capacity.

[0030] In some embodiments, the weight ratio of the first positive electrode material to the second positive electrode material is 5: 1 to 99: 1, and optionally 9: 1 to 99: 1. By making the weight ratio of the first positive electrode material to the second positive electrode material within the specific range, the first positive electrode material accounts for the majority of the combination of the first positive electrode material and the second positive electrode material, so that the positive electrode sheet has higher structural stability, the capacity loss and impedance increase caused by the destruction of the positive electrode material structure can be reduced, and the cycle stability and kinetic performance can be maintained.

[0031] In some embodiments, in the positive electrode material layer, the content of the first positive electrode material is 80% to 98% by weight, and optionally 85% to 98%. By making the content of the first positive electrode material in the positive electrode material layer within the specific range, it is further beneficial to stabilize the structure of the positive electrode sheet, further reduce the capacity loss and impedance increase caused by the destruction of the positive electrode material structure, and improve the cycle stability and kinetic performance.

[0032] The crystal structure of the second positive electrode material belongs to the Immm space group in the orthorhombic system.

[0033] In some embodiments, the second positive electrode material has a characteristic diffraction peak A at 36° to 38°, a characteristic diffraction peak B at 42° to 44°, and a characteristic diffraction peak C at 62° to 64° in the X-ray diffraction spectrum after the first cycle of charging.

[0034] A second aspect of the present application provides a battery module, which includes the secondary battery according to the first aspect of the present application.

[0035] A third aspect of the present application provides a battery pack, which includes a battery module according to the second aspect of the present application.

[0036] A fourth aspect of the present application provides a device comprising at least one of the secondary battery according to the first aspect of the present application, the battery module according to the second aspect of the present application, or the battery pack according to the third aspect of the present application.

[0037] The battery module, battery pack and device of the present application include the secondary battery provided by the present application, and thus have at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0039] Figure 2 yes Figure 1 An exploded view of a secondary battery according to one embodiment of the present application is shown.

[0040] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0041] Figure 4 is a schematic diagram of a battery pack according to one embodiment of the present application.

[0042] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of the present application is shown.

[0043] Figure 6 This is an X-ray diffraction spectrum of the positive electrode sheet of the lithium ion secondary battery obtained in Example 1 after the first cycle of charging. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical scheme and advantages of the present application clearer, the implementation mode of the application will be described in detail below in conjunction with the examples. However, it should be understood by those skilled in the art that these examples are only used to illustrate the technical scheme of the present application and are not intended to be limiting. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should all be included in the protection scope of the present invention.

[0045] For simplicity, the present application specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unclearly recorded range; and any lower limit can be combined with other lower limits to form an unclearly recorded range, and any upper limit can be combined with any other upper limit to form an unclearly recorded range. In addition, although not clearly recorded, each point or single value between the range endpoints is included in the range. In addition, each separately disclosed point or single value itself can be combined with any other point or single value as a lower limit or upper limit or with other lower limits or upper limits to form an unclearly recorded range.

[0046] In the description of this article, it should be noted that, unless otherwise specified, "above" and "below" are inclusive of the number itself, and "several" in "one or several" means two or more.

[0047] The above-mentioned summary of the invention of the present application is not intended to describe each disclosed embodiment or each implementation in the present application. The following description more specifically illustrates exemplary embodiments. In many places throughout the application, guidance is provided by a series of examples, which can be used in various combinations. In each example, enumeration is only used as a representative group and should not be interpreted as exhaustive.

[0048] In order to solve the above problems in the prior art, the inventors of the present application have conducted intensive research, and found that: by compounding the existing Li2NiO2 type lithium supplement material with Cu elements, Ti elements and other optional metal elements, the second positive electrode material forms a solid solution with lower phase barrier and higher purity and specific capacity than the Li2NiO2 type lithium supplement material, and cooperates with the first positive electrode material with an olivine structure. On the one hand, during the first cycle of battery charging, the second positive electrode material has the characteristics of high first charge specific capacity and low first efficiency, which effectively compensates for the loss of active lithium caused by the generation of SEI, and sufficient lithium ions are embedded back into the first positive electrode material during the first discharge, effectively improving the energy density of the battery. On the other hand, the first positive electrode material with an olivine structure of the present invention has a stable structure, small volume change during the charge and discharge process, and excellent cycle stability. Furthermore, the inventors of the present application have found that by adding a specific amount of vinylene carbonate to the electrolyte, a synergistic effect is produced with the positive electrode sheet containing the first positive electrode material and the second positive electrode material, so that a more uniform and dense SEI film is formed at the negative electrode after the first cycle of charging, which inhibits the continuous loss of active lithium and further improves the cycle life of the lithium-ion secondary battery. Therefore, according to the lithium-ion secondary battery of this embodiment, the lithium-ion secondary battery can achieve high energy density, good rate performance and long cycle life.

[0049] That is, the present application relates to a lithium-ion secondary battery, which comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector,

[0050] The positive electrode material layer comprises a first positive electrode material represented by the following general formula (1) and a second positive electrode material represented by the following general formula (2),

[0051] The electrolyte contains vinylene carbonate,

[0052] The content of the vinylene carbonate is greater than or equal to 0.1 wt % and less than or equal to 5 wt % relative to the total weight of the electrolyte. 1+x Fe y Mn z M 1-y-z PO 4-t A t (1)

[0053] (In the general formula (1), M includes one or more of Ti, Zr, V, and Cr, A includes one or more of S, N, F, Cl, and Br, and x, y, z, and t satisfy: -0.1≤x<0.1, 0<y≤1, 0≤z<1, 0<y+z≤1, and 0≤t<0.2.)

[0054] Li 2+r Ni 0.5-p Cu 0.5-q Ti v N p+q-v O 2-s B s (2)

[0055] (In the general formula (2), N includes one or more of Mn, Fe, Co, Al, V, Cr, and Nb, B includes one or more of S, N, F, Cl, and Br, and r, p, q, v, and s respectively satisfy: -0.2≤r≤0.2, -0.5<p<0.5, -0.5<q<0.5, 0<v<0.01, 0≤p+qv<0.2, and 0≤s<0.2.)

[0056] The lithium-ion battery, battery module, battery pack and electrical device of the present application are described in detail below with reference to the accompanying drawings as appropriate.

[0057] Lithium-ion secondary battery

[0058] A lithium-ion secondary battery is a battery that can be used continuously by activating the active materials by charging after the lithium-ion battery is discharged. Generally, a lithium-ion secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, which can insulate electrons and prevent internal short circuits, while allowing active ions to pass through and move between the positive and negative electrodes. It plays an isolating role. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet.

[0059] [Positive electrode]

[0060] The positive electrode sheet includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode material layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0061] The positive electrode material layer includes a first positive electrode material represented by the following general formula (1) and a second positive electrode material represented by the following general formula (2).

[0062] Li 1+x Fe y Mn z M 1-y-z PO 4-t A t (1)

[0063] (In the general formula (1), M includes one or more of Ti, Zr, V, and Cr, A includes one or more of S, N, F, Cl, and Br, and x, y, z, and t satisfy: -0.1≤x<0.1, 0<y≤1, 0≤z<1, 0<y+z≤1, and 0≤t<0.2.)

[0064] Li 2+r Ni 0.5-p Cu 0.5-q Ti v N p+q-v O 2-s B s (2)

[0065] (In the general formula (2), N includes one or more of Mn, Fe, Co, Al, V, Cr, and Nb, B includes one or more of S, N, F, Cl, and Br, and r, p, q, v, and s respectively satisfy: -0.2≤r≤0.2, -0.5<p<0.5, -0.5<q<0.5, 0<v<0.01, 0≤p+qv<0.2, and 0≤s<0.2.)

[0066] By simultaneously including the first positive electrode material and the second positive electrode material in the positive electrode material layer, the lithium-ion secondary battery can achieve high energy density, good rate performance and long cycle life.

[0067] In the general formula (1), x satisfies -0.1≤x<0.1. From the viewpoint of further reducing the volume change during charge and discharge and further improving the cycle stability of the battery, x is preferably -0.1≤x≤0.05, and more preferably -0.05≤x≤0. In addition, y satisfies 0<y≤1. From the viewpoint of further improving the cycle stability of the battery, y is preferably 0.5≤y≤1, and more preferably 0.5≤y≤0.95. In addition, z satisfies 0≤z<1. From the viewpoint of improving the cycle stability of the battery, z is preferably 0≤z≤0.5, and more preferably 0.025≤z≤0.45.

[0068] In the general formula (1), M is one or more selected from Ti, Zr, V, and Cr. From the perspective of producing a synergistic effect with the second positive electrode material and improving the energy density and cycle life of the lithium-ion secondary battery, M is preferably one or more selected from Ti, Zr, and V, and more preferably one or more selected from Ti and Zr. In addition, A includes one or more of S, N, F, Cl, and Br. From the perspective of maintaining excellent comprehensive performance, A is preferably one or more selected from F, Cl, and Br, and more preferably F. In addition, t satisfies 0≤t<0.2. From the perspective of maintaining excellent comprehensive performance, t is preferably 0≤t≤0.05.

[0069] In the general formula (1), y+z satisfies 0<y+z≤1. From the viewpoint of producing a synergistic effect with the second positive electrode material and improving the energy density and cycle life of the lithium ion secondary battery, y+z is preferably 0.95≤y+z≤1.

[0070] In the general formula (2), r satisfies -0.2≤r≤0.2. From the perspective of effectively compensating for the loss of active lithium caused by the formation of SEI and further improving the energy density of the battery, r is preferably -0.05≤r≤0.2, and more preferably 0≤r≤0.2. In addition, p satisfies -0.5<p<0.5. From the perspective of further improving the energy density of the battery, p is preferably -0.1<p<0.1, more preferably -0.046≤p≤0.058, and further preferably 0.002≤p≤0.054. In addition, q satisfies -0.5<q<0.5. From the perspective of effectively improving the energy density and cycle life of the battery, q is preferably -0.1<q<0.1, more preferably -0.046≤q≤0.058, and further preferably 0.002≤q≤0.054. Furthermore, v satisfies 0<v<0.01. From the perspective of better reducing the content of free lithium on the surface of the material, better improving the problem of positive electrode slurry gel, and effectively improving the energy density of the battery, v is preferably 0.002≤v≤0.008, and more preferably 0.004≤v≤0.008. Further, s satisfies 0≤s<0.2. From the perspective of improving the cycle performance and energy density of the battery, s is preferably 0≤s≤0.1, and more preferably 0≤s≤0.05.

[0071] In the general formula (2), N includes one or more of Mn, Fe, Co, Al, V, Cr, and Nb. From the viewpoint of improving the rate performance and cycle performance of the battery, N is preferably one or more selected from Mn, Fe, Co, and Cr, and more preferably one or more selected from Mn and Co. In addition, B includes one or more of S, N, F, Cl, and Br. From the viewpoint of maintaining excellent comprehensive performance, B is preferably one or more selected from F, Cl, and Br, and more preferably F.

[0072] In the general formula (2), p+qv satisfies 0≤p+qv<0.2. From the viewpoint of improving the rate performance and cycle performance of the battery, p+qv preferably satisfies 0≤p+qv≤0.1.

[0073] In some embodiments, the positive electrode sheet satisfies the following formula (3).

[0074] 0.5≤R·P / Q≤16 (3)

[0075] In formula (3), R represents the resistance of the positive electrode sheet, and its unit is Ω; P represents the compaction density of the positive electrode sheet, and its unit is g / cm 3 , Q represents the single-sided surface density of the positive electrode sheet, and its unit is g / 1540.25mm 2 . )

[0076] By making the positive electrode sheet satisfy the above formula (3), the energy density, rate performance and cycle life of the lithium-ion secondary battery can be further improved.

[0077] In some embodiments, the positive electrode sheet preferably further satisfies the following formula (4).

[0078] 1.5≤R·P / Q≤10 (4)

[0079] It should be noted that in this application, the calculation of R·P / Q only involves the calculation of numerical values. For example, the resistance R of the positive electrode is 0.5Ω and the compaction density P is 2.2g / cm 3 The single-surface density Q of the positive electrode is 0.3g / 1540.25mm 2 , then R·P / Q=3.7.

[0080] In some embodiments, the resistance of the positive electrode sheet satisfies R≤3Ω, preferably R≤1Ω. By making the resistance of the positive electrode sheet within the specific range, it is possible to avoid the deterioration of the cycle performance and rate performance of the lithium-ion secondary battery caused by the excessive resistance of the positive electrode sheet, thereby helping to improve the cycle performance and rate performance of the lithium-ion secondary battery. In this application, the resistance R of the positive electrode sheet is the value measured by the DC two-probe method, where the contact area between the probe and the positive electrode sheet is 49πmm 2 As an example, the upper and lower sides of the positive electrode plate are clamped between two conductive terminals (with a diameter of 14 mm) of a plate resistance tester (HIOKIE.E.CORPORATION manufactured HIOKIE BT23562 internal resistance tester), and a pressure of 15 MPa to 27 MPa is applied to fix it, and the resistance of the positive electrode plate is measured using the plate resistance tester.

[0081] In some embodiments, the compaction density P (unit: g / cm 3 ) satisfies 1.6<P<2.6. By making the compaction density P of the positive electrode plate within the specific range, the cycle performance and rate performance of the battery are avoided from being deteriorated, which is beneficial to the migration of electrons and ions in the positive electrode plate and improves the cycle performance of the lithium-ion secondary battery. In the present application, the compaction density P of the positive electrode can be calculated by the formula P=m / v, where m is the weight of the positive electrode material layer, in g; v is the volume of the positive electrode material layer, in cm 3 Wherein, the volume v of the positive electrode material layer can be the area A of the positive electrode material layer. r The product of the thickness of the positive electrode material layer.

[0082] In some embodiments, the single-sided surface density Q (unit: g / 1540.25mm 2 ) satisfies 0.16<Q<0.45. By making the single-sided surface density Q of the positive electrode plate within the specific range, it is possible to avoid the reduction of the cycle life of the battery, the impact on the rate performance of the battery and the reduction of the discharge capacity of the battery at a high rate due to the single-sided surface density of the positive electrode plate being too large, and to avoid the increase in the length of the collector and the separator and the increase in the internal resistance of the battery at the same battery capacity due to the single-sided surface density of the positive electrode plate being too small, thereby ensuring the charge and discharge capacity while improving the cycle performance and rate performance of the lithium-ion secondary battery. In the present application, the single-sided surface density Q of the positive electrode plate can be expressed by the formula Q=1540.25m / A r Calculated, where m is the weight of the positive electrode material layer, in g; A r is the area of ​​the positive electrode active material layer, in mm 2 .

[0083] In some embodiments, the weight ratio of the first positive electrode material to the second positive electrode material is 5: 1 to 99: 1, preferably 9: 1 to 99: 1, and more preferably 10: 1 to 48: 1. By making the weight ratio of the first positive electrode material to the second positive electrode material within the specific range, the first positive electrode material accounts for the majority of the combination of the first positive electrode material and the second positive electrode material, so that the positive electrode sheet has higher structural stability, the capacity loss and impedance increase caused by the destruction of the positive electrode material structure can be reduced, and the cycle stability and kinetic performance can be maintained.

[0084] In some embodiments, in the positive electrode material layer, the content of the first positive electrode material is 80% to 98% by weight, preferably 85% to 98%. By making the content of the first positive electrode material in the positive electrode material layer within the specific range, it is further beneficial to stabilize the structure of the positive electrode sheet, further reduce the capacity loss and impedance increase caused by the destruction of the positive electrode material structure, and improve the cycle stability and kinetic performance.

[0085] In some embodiments, the crystal structure of the second positive electrode material belongs to the Immm space group in the orthorhombic system. In some embodiments, the second positive electrode material has a characteristic diffraction peak A at 36° to 38°, a characteristic diffraction peak B at 42° to 44°, and a characteristic diffraction peak C at 62° to 64° in the X-ray diffraction spectrum after the first cycle of charging.

[0086] In addition to the first positive electrode material and the second positive electrode material, the positive electrode material layer of the present application may also include other positive electrode materials, such as lithium transition metal oxides, within a range that does not impair the effects of the present application.

[0087] The positive electrode material layer of the present application includes an optional binder and a conductive agent. The present invention does not specifically limit the types of the conductive agent and the binder, and they can be selected according to actual needs.

[0088] As an example, the binder may include one or more selected from styrene-butadiene rubber (SBR), water based acrylic resin, carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), ethylene-vinyl acetate copolymer (EVA) and polyvinyl alcohol (PVA). The conductive agent may include one or more selected from graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0089] In some embodiments, the weight percentage of the conductive agent in the positive electrode material layer is greater than 0.5 weight %. By setting the content of the conductive agent to the above range, it is beneficial to obtain a lower resistance of the positive electrode sheet.

[0090] In some embodiments, the weight percentage of the binder in the positive electrode material layer is less than 2.5 weight %. By setting the content of the binder to the above range, it is beneficial to obtain a lower resistance of the positive electrode sheet.

[0091] In the lithium-ion secondary battery of the present application, the positive electrode current collector may be a metal foil, a porous metal plate or a composite current collector. As metal foil and porous metal plate, for example, foil or porous plate of metals such as aluminum, copper, nickel, titanium or silver or their alloys can be used, preferably aluminum 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 (such as 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.). The thickness of the positive electrode current collector is 5μm to 20μm, preferably 6μm to 18μm, and more preferably 8μm to 16μm.

[0092] The positive electrode sheet of the present application can be prepared according to the usual methods in the art. Specifically, the above-mentioned components for preparing the positive electrode sheet, such as the first positive electrode material, the second positive electrode material, the optional conductive agent, the optional binder and any other components, can be dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained. Alternatively, the positive electrode sheet can be manufactured in the following manner: the positive electrode slurry for forming the positive electrode material layer is cast on a separate carrier, and then the film obtained by peeling from the carrier is laminated on the positive electrode collector. In addition, in the above embodiment, the first positive electrode material and the second positive electrode material are directly mixed to prepare the positive electrode slurry, but it is not limited to this. The second positive electrode material can also be slurried separately and coated on the upper or lower layer of the first positive electrode material.

[0093] [Negative electrode]

[0094] In a lithium-ion secondary battery, the negative electrode plate generally includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode material layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0095] In the lithium ion secondary battery of the present application, the negative electrode current collector can be made of materials such as metal foil, porous metal plate or composite current collector. For example, as metal foil or porous metal plate, a foil or porous plate of metals such as copper, nickel, titanium or iron or their alloys can be used, preferably copper foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of a polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper 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.).

[0096] In the lithium ion secondary battery of the present application, the negative electrode material layer generally includes a negative electrode material and optionally a conductive agent, a binder and a thickener.

[0097] The negative electrode material can be a negative electrode material commonly used in the art for preparing a negative electrode of a lithium ion secondary battery, for example, natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structure lithium titanate Li4Ti5O 12 , Li-Al alloy and one or more of metallic lithium.

[0098] As an example, the conductive agent may include one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0099] As an example, the binder may include one or more of styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), water-based acrylic resin, and carboxymethyl cellulose (CMC).

[0100] As an example, the thickener may be carboxymethyl cellulose (CMC) or the like.

[0101] The present application is not limited to these materials, and other materials that can be used as a lithium ion secondary battery except for the negative electrode material, the conductive agent, the binder, and the thickener can also be used in the present application.

[0102] The negative electrode sheet of the present application can be prepared according to the common method in the art. Specifically, the negative electrode material and the optional conductive agent, binder and thickener are dispersed in a solvent to form a uniform negative electrode slurry, and the negative electrode slurry is coated on the negative electrode current collector, and the negative electrode is obtained through drying, cold pressing and other processes. The solvent can be N-methylpyrrolidone (NMP) or deionized water.

[0103] [Electrolyte]

[0104] The electrolyte of the present application includes an organic solvent, an electrolyte lithium salt and an additive. The present application does not specifically limit the types of the organic solvent and the electrolyte lithium salt, and they can be selected according to actual needs.

[0105] As an example, the solvent can be one or more selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), cyclopentane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE), and it is preferred to use two or more.

[0106] As an example, the electrolyte lithium salt can be one or more selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0107] The electrolyte of the present application contains vinylene carbonate (VC) as an additive. The content of the vinylene carbonate is greater than 0.1% by weight and less than 5% by weight relative to the total weight of the electrolyte. By including a specific amount of vinylene carbonate as an additive in the electrolyte, a synergistic effect can be produced with the positive electrode sheet containing the first positive electrode material and the second positive electrode material, so that a more uniform and dense SEI film is formed on the negative electrode after the first cycle of charging, which inhibits the continuous loss of active lithium and further improves the cycle life of the lithium-ion secondary battery.

[0108] The electrolyte may also optionally include other additives. The other additives may be additives that can be used in lithium-ion secondary batteries at will, without specific restrictions, and may be selected according to actual needs. As an example, the additive may include one or more of vinyl ethylene carbonate (VEC), succinonitrile (SN), adiponitrile (AND), 1,3-propylene sultone (PST), sulfonate cyclic quaternary ammonium salt, tris(trimethylsilyl) phosphate (TMSP) and tris(trimethylsilyl) borate (TMSB).

[0109] The electrolyte can be prepared according to the common methods in the art. Specifically, an organic solvent, an electrolyte lithium salt, vinylene carbonate and other optional additives can be mixed evenly to obtain an electrolyte. There is no particular restriction on the order of adding the substances. For example, an electrolyte lithium salt, vinylene carbonate and other optional additives are added to an organic solvent and mixed evenly to obtain an electrolyte. Among them, the electrolyte lithium salt can be first added to the organic solvent, and then vinylene carbonate and other optional additives are added to the organic solvent separately or simultaneously.

[0110] [Isolation film]

[0111] The embodiments of the present application have no particular restrictions on the type of separator, and any known porous separator with electrochemical stability and chemical stability for lithium-ion secondary batteries can be selected. For example, the separator can be one or more selected from glass fiber film, non-woven film, polyethylene film, polypropylene film, polyvinylidene fluoride film, and multilayer composite films containing one or more of them.

[0112] In some embodiments, the positive electrode sheet, the separator and the negative electrode sheet are stacked in order, and the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, to obtain an electrode assembly, and the electrode assembly is placed in an outer package, and the electrolyte is injected and sealed to obtain a lithium-ion secondary battery. In addition to the above-mentioned stacking process, the positive electrode sheet, the separator and the negative electrode sheet can also be obtained by a winding process.

[0113] In some embodiments, the outer packaging of the lithium ion secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the lithium ion secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0114] The present application has no particular restrictions on the shape of the lithium-ion secondary battery, which may be cylindrical, square or any other shape. Figure 1 The lithium ion secondary battery 5 is a square structure as an example.

[0115] In some embodiments, reference 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 form 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 lithium-ion secondary battery 5 can be one or more, which can be adjusted according to demand.

[0116] In some embodiments, lithium-ion secondary batteries may be assembled into a battery module. The battery module may contain multiple secondary batteries, and the specific number may be adjusted according to the application and capacity of the battery module.

[0117] Figure 3 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of lithium-ion secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

[0118] 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.

[0119] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0120] Figure 4 and Figure 5 1 is a battery pack 1 as an example. Figure 4 and Figure 5 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0121] Device

[0122] Another aspect of the present application provides a device, the device comprising at least one of the lithium-ion secondary battery, battery module, or battery pack provided in the present application. The lithium-ion secondary battery can be used as a power source for the device, and can also be used as an energy storage unit for the device. The device can be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.

[0123] The device can select a lithium-ion secondary battery, a battery module or a battery pack according to its use requirements.

[0124] As an example, a device may be a mobile phone, a tablet computer, a notebook computer, etc. The device is usually required to be thin and light, and a lithium-ion secondary battery may be used as a power source.

[0125] Example

[0126] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0127] Example 1

[0128] (1) Preparation of positive electrode sheet

[0129] The first positive electrode material LiFePO4 and the second positive electrode material Li2Ni 0.498 Cu 0.498 Ti 0.002 O2, binder polyvinylidene fluoride (PVDF), and conductive agent carbon black are dissolved in solvent N-methylpyrrolidone (NMP) in a mass ratio of 92.4:4.0:2.1:1.5, and fully stirred and mixed under vacuum until a uniform transparent system is obtained to obtain a positive electrode slurry; then the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and then transferred to an oven for drying at 120°C, and cold pressed and cut to obtain a positive electrode. In the positive electrode material layer, the weight percentage of the first positive electrode material LiFePO4 is 92.4%, and the weight percentage of the second positive electrode material Li2Ni 0.498 Cu 0.498 Ti 0.002 The weight percentage of O2 is 4.0%.

[0130] (2) Preparation of negative electrode sheet

[0131] The negative electrode material artificial graphite, thickener sodium carboxymethyl cellulose (CMC-Na), binder styrene-butadiene rubber (SBR), and conductive agent carbon black are dissolved in solvent deionized water in a mass ratio of 95.7:1.0:1.8:1.5, and are evenly mixed under the action of a vacuum mixer to prepare a negative electrode slurry; the negative electrode slurry is then evenly coated on the negative electrode collector copper foil, and then transferred to an oven for drying at 120°C, and after cold pressing and slitting, the negative electrode sheet is obtained.

[0132] (3) Preparation of electrolyte

[0133] Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were mixed uniformly in a volume ratio of 1:1:1 to obtain an organic solvent. 1 mol / L LiPF6 was dissolved in the organic solvent, and 3% vinylene carbonate (VC) was added relative to the total mass of the electrolyte, and mixed uniformly to obtain an electrolyte.

[0134] (4) Preparation of separator: A polypropylene film with a thickness of 14 μm (manufactured by Celgard) was used as a separator.

[0135] (5) Preparation of lithium-ion batteries

[0136] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in sequence, with the separator placed between the positive electrode sheet and the negative electrode sheet to play an isolating role. The electrode assembly is then wound into an electrode assembly, the pole ears are welded, the electrode assembly is placed in a casing, the above-mentioned electrolyte is injected and sealed, and then a lithium-ion secondary battery is obtained through processes such as standing, forming, and shaping.

[0137] Examples 2 to 21 and Comparative Examples 1 to 7

[0138] A lithium ion secondary battery was prepared in the same manner as in Example 1 except that the type of the first positive electrode material, the type of the second positive electrode material, and the content of vinylene carbonate in the electrolyte were changed as shown in Table 1.

[0139] For the lithium ion secondary batteries prepared in the above-mentioned embodiments and comparative examples, battery performance tests were carried out by the following method, and the obtained results are shown in Table 1.

[0140] (1) High temperature cycle performance test of lithium-ion secondary batteries:

[0141] At 60°C, charge the lithium-ion secondary battery to 4.2V at a constant current of 1C, then charge at a constant voltage until the current is less than or equal to 0.05C, and then discharge at a constant current of 1C to 2.5V. This is a charge and discharge cycle, and record the discharge capacity of the first cycle of the lithium-ion secondary battery. Perform charge and discharge cycles on the lithium-ion secondary battery according to the above method, and record the discharge capacity of each cycle until the discharge capacity of the lithium-ion secondary battery decays to 80% of the discharge capacity of the first cycle, and record the number of charge and discharge cycles.

[0142] (2) Rate performance test of lithium-ion secondary batteries:

[0143] At 25°C, the lithium-ion secondary battery was charged at a constant current of 0.5C to 4.2V, then charged at a constant voltage to a current less than or equal to 0.05C, and then discharged at a constant current of 0.5C to 2.5V, and the discharge capacity at the 0.5C rate was recorded.

[0144] At 25°C, the lithium-ion secondary battery was charged at a constant current of 0.5C to 4.2V, then charged at a constant voltage to a current less than or equal to 0.05C, and then discharged at a constant current of 2C to 2.5V, and the discharge capacity at the 2C rate was recorded.

[0145] Then, the 2C rate discharge capacity retention rate (%) of the lithium ion secondary battery was obtained by the following formula, and this was defined as rate performance (%).

[0146] Lithium ion secondary battery 2C rate discharge capacity retention rate (%) = 2C rate discharge capacity / 0.5C rate discharge capacity × 100%

[0147] (3) Energy density test of lithium-ion secondary batteries:

[0148] At 25°C, charge the lithium-ion secondary battery to 4.2V at a constant current of 0.2C, then charge it at a constant voltage until the current is less than or equal to 0.05C, then let it stand for 30 minutes, and then discharge it to 2.5V at a constant current of 0.2C. Record the discharge capacity D0 (Ah) and discharge platform V0 (V) of the lithium-ion secondary battery at 0.2C. Weigh the weight of the lithium-ion battery and record it as m0 (kg). Then, calculate the energy density of the lithium-ion secondary battery (unit: Wh / Kg) by the following formula.

[0149] Energy density = D0*V0 / m0.

[0150] (4) XRD spectrum of the positive electrode of lithium-ion secondary battery:

[0151] At 25°C, the lithium ion secondary battery prepared in Example 1 was charged to 4.2V at a constant current rate of 1C, and then charged to a current of less than or equal to 0.05C at a constant voltage. The lithium ion secondary battery after the first cycle of charging was disassembled to obtain a positive electrode sheet. The positive electrode sheet was measured using an X-ray diffractometer. The XRD spectrum of the obtained positive electrode sheet after the first cycle of charging is shown in Figure 6 middle.

[0152] according to Figure 6 It can be seen that in the X-ray diffraction spectrum after the first cycle of charging, characteristic diffraction peaks appear at 36° to 38°, characteristic diffraction peaks appear at 42° to 44°, and characteristic diffraction peaks appear at 62° to 64°. The above characteristic diffraction peaks are characteristic peaks of rock salt phase materials. Therefore, it can be confirmed that the second positive electrode material has characteristic diffraction peaks at 36° to 38°, characteristic diffraction peaks appear at 42° to 44°, and characteristic diffraction peaks appear at 62° to 64° in the X-ray diffraction spectrum after the first cycle of charging.

[0153] [Table 1]

[0154]

[0155]

[0156] According to the results of Table 1 above, in Examples 1 to 21 having both the first positive electrode material and the second positive electrode material of the present application, the lithium-ion secondary battery can have high energy density, good rate performance and long cycle life. On the other hand, in Comparative Examples 1 to 5 not having the first positive electrode material or the second positive electrode material of the present application, the energy density of the lithium-ion secondary battery is reduced and the number of high-temperature cycles is reduced. Furthermore, by adding a specific content of vinyl carbonate additive to the electrolyte, a denser and thinner SEI layer can be induced to prevent the continuous consumption of the electrolyte, thereby further improving the cycle life of the lithium-ion secondary battery.

[0157] (Examples 22 to 27)

[0158] The preparation method is similar to that of Example 1, except for the differences shown in Table 2 below.

[0159] In addition, the performance of the prepared lithium ion secondary battery was tested by the above-mentioned battery performance testing method. The obtained results are shown in Table 2.

[0160] Furthermore, the sheet resistance of the positive electrode sheet was measured by the method shown below. In addition, the compaction density and single-surface density of the positive electrode sheet were calculated by the method shown below.

[0161] (1) The membrane resistance R of the positive electrode:

[0162] The resistance of the positive electrode sheet was measured using a Hioki BT3562 resistance tester. Specifically, the positive electrode sheet was clamped between two conductive terminals (14 mm in diameter) of the internal resistance tester and fixed with a pressure of 15 MPa to 27 MPa. The resistance R of the positive electrode sheet was tested, and the sampling time range was 5 s to 17 s.

[0163] (2) Compacted density P of positive electrode sheet:

[0164] The compaction density P of the positive electrode is calculated by the formula P = m / v, where m is the weight of the positive electrode material layer in g; v is the volume of the positive electrode material layer in cm 3 The volume v of the positive electrode material layer is calculated by the area A of the positive electrode material layer. r It is obtained by multiplying the thickness of the positive electrode material layer.

[0165] (3) Single-sided surface density Q of the positive electrode sheet:

[0166] The single-sided surface density Q of the positive electrode sheet is calculated by the formula Q = 1540.25m / A r Calculated, where m is the weight of the positive electrode material layer, in g; A r is the area of ​​the positive electrode active material layer, in mm 2 .

[0167] [Table 2]

[0168]

[0169] According to the results in Table 2 above, the energy density, rate performance and cycle life of lithium-ion secondary batteries can be further improved by making the positive electrode sheet satisfy the formula 0.5≤R·P / Q≤16. In addition, the energy density, rate performance and cycle life of lithium-ion secondary batteries can be further improved by making the positive electrode sheet further satisfy the formula 1.5≤R·P / Q≤10.

[0170] Those skilled in the art should understand that the above-mentioned embodiments are only some specific embodiments for implementing the present application, and in actual applications, various changes and modifications may be made thereto in form and details, all of which fall within the scope of protection of the present application.

Claims

1. A lithium-ion secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, characterized in that: The positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. The positive electrode material layer comprises a first positive electrode material represented by the following general formula (1) and a second positive electrode material represented by the following general formula (2), Li 1+x Feb y Mr z M 1-y-z NIGHT 4-t A t (1) In the general formula (1), M includes one or more of Ti, Zr, V or Cr, A includes one or more of S, N, F, Cl or Br, and x, y, z and t respectively satisfy: -0.1≤x<0.1, 0<y≤1, 0≤z<1, 0<y+z≤1, 0≤t<0.2, Li 2+r Ni 0.5-p Cu 0.5-q Tea v N p+q-v O 2-s B s (2) In the general formula (2), N includes one or more of Mn, Fe, Co, Al, V, Cr or Nb, B includes one or more of S, N, F, Cl or Br, r, p, q, v and s respectively satisfy: -0.2≤r≤0.2, -0.5<p<0.5, -0.5<q<0.5, 0<v<0.01, 0≤p+qv<0.2, 0≤s<0.2, The weight ratio of the first positive electrode material to the second positive electrode material is 5:1 to 99:1; The electrolyte contains vinylene carbonate, The content of the vinylene carbonate is greater than or equal to 0.1 wt % and less than or equal to 5 wt % relative to the total weight of the electrolyte.

2. The lithium ion secondary battery according to claim 1, characterized in that In the general formula (2), -0.1<p<0.1, -0.1<q<0.1, 0.002≤v≤0.

008.

3. The lithium ion secondary battery according to claim 1 or 2, characterized in that: The positive electrode sheet satisfies the following formula (3): 0.5≤R·P / Q≤16 (3) In formula (3), R represents the resistance of the positive electrode sheet, and its unit is Ω; P represents the compaction density of the positive electrode sheet, and its unit is g / cm 3 , Q represents the single-sided surface density of the positive electrode sheet, and its unit is g / 1540.25mm 2 .

4. The lithium ion secondary battery according to claim 3, characterized in that The positive electrode sheet satisfies at least one of the following conditions: (1) The positive electrode sheet satisfies the following formula (4): 1.5≤R·P / Q≤10 (4) (2) The resistance of the positive electrode sheet satisfies R≤3Ω; (3) The compaction density P of the positive electrode sheet satisfies 1.6 g / cm 3 <P<2.6g / cm 3 ; (4) The single-sided surface density Q of the positive electrode sheet satisfies 0.16g / 1540.25mm 2 <Q<0.45g / 1540.25mm 2 .

5. The lithium ion secondary battery according to claim 3, characterized in that: The resistance of the positive electrode plate satisfies R≤1Ω.

6. The lithium ion secondary battery according to any one of claims 1 to 2, characterized in that The first positive electrode material and the second positive electrode material satisfy at least one of the following conditions: (I) a weight ratio of the first positive electrode material to the second positive electrode material is 9:1 to 99:1; (II) In the positive electrode material layer, the content of the first positive electrode material is 80% to 98% by weight.

7. The lithium ion secondary battery according to any one of claims 1 to 2, characterized in that In the positive electrode material layer, the content of the first positive electrode material is 85% to 98% by weight.

8. The lithium ion secondary battery according to any one of claims 1 to 2, characterized in that The crystal structure of the second positive electrode material belongs to Immm Space group.

9. The lithium ion secondary battery according to any one of claims 1 to 2, characterized in that In the X-ray diffraction spectrum of the second positive electrode material after the first cycle of charging, a characteristic diffraction peak A appears at 36° to 38°, a characteristic diffraction peak B appears at 42° to 44°, and a characteristic diffraction peak C appears at 62° to 64°. 10 . A battery module comprising the lithium ion secondary battery according to claim 1 . A battery pack comprising the battery module according to claim 10 . 12 . An electrical device comprising at least one of the lithium-ion secondary battery according to claim 1 , the battery module according to claim 10 , or the battery pack according to claim 11 .

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