Secondary battery and device

Abstract

The invention provides a secondary battery and a device, the secondary battery comprises a positive pole piece and an electrolyte, the electrolyte comprises a chain solvent, the positive pole piece comprises a positive active material, the secondary battery satisfies 1.5 < = M * 1000 / (N * rho) < = 15.0, M refers to the mass of the chain solvent corresponding to every 100g of the positive active material, and the unit is g; rho refers to the surface density of the positive pole piece, and the unit is g / m < 2 >; n is the OI value of the positive pole piece, and the OI value of the positive pole piece is the ratio of the peak area of the 003 crystal face diffraction peak of the positive pole piece to the peak area of the 110 crystal face diffraction peak of the positive pole piece. The lithium ion battery has the characteristics of high safety, excellent dynamic performance and long cycle life.

Description

Technical Field

[0001] The present application relates to the field of lithium batteries, and in particular to a secondary battery and a device. Background Art

[0002] With its many advantages, lithium-ion batteries have quickly occupied the 3C fields such as mobile phones and laptops, and even become a key component of various electric vehicles. In order to meet people's needs, lithium-ion batteries need to develop in the direction of higher energy density, safety, and longer life. In addition, in order to obtain higher energy density, its batteries are usually designed in the direction of high compaction density or high surface density. However, batteries with high compaction density or high surface density are prone to swelling during the cycle process, the internal electrolyte cannot evenly infiltrate the pole piece, the battery polarization increases, and lithium is easily precipitated at the negative electrode interface, which not only buries safety hazards, but also continues to deteriorate the performance of the battery, such as the battery's power performance continues to decline and the cycle life rapidly decays. In order to solve the above problems, researchers have conducted a lot of research, but the improvement effect is limited, and it cannot fundamentally improve the battery's safety, low temperature power problems, and cycle life problems.

[0003] Therefore, there is an urgent need to develop a novel secondary battery and device. Summary of the invention

[0004] In view of the above problems existing in the prior art, the present application proposes a secondary battery and a device. The secondary battery of the present application improves the low temperature performance and cycle performance of the lithium ion secondary battery by controlling the mass of the chain solvent in the electrolyte corresponding to each 100g of the positive electrode active material, the surface density of the positive electrode sheet and the relationship between the OI value of the positive electrode sheet.

[0005] A first aspect of the present application provides a secondary battery, wherein the secondary battery comprises a positive electrode sheet and an electrolyte, wherein the electrolyte comprises a chain solvent, and the positive electrode sheet comprises a positive electrode active material, and the secondary battery satisfies: 1.5≤M×1000 / (N×ρ)≤20.0, wherein M refers to the mass of the chain solvent per 100g of the positive electrode active material, in g; ρ refers to the surface density of the positive electrode sheet, in g / m 2 ; N refers to the OI value of the positive electrode plate, wherein the OI value of the positive electrode plate refers to the ratio of the peak area of ​​the 003 crystal plane diffraction peak of the positive electrode plate to the peak area of ​​the 110 crystal plane diffraction peak.

[0006] A second aspect of the present application provides a device including the aforementioned secondary battery.

[0007] The technical solution of this application can achieve the following beneficial effects:

[0008] The secondary battery of the present application can ensure that lithium ions are quickly released from the positive electrode and quickly migrate to the surface of the negative electrode and then quickly embedded in the negative electrode by reasonably adjusting the OI value of the positive electrode plate, the mass of the chain solvent used per 100g of positive electrode material, and the surface density of the positive electrode plate; and the positive electrode plate has a small chemical rebound and excellent kinetic performance during the charge and discharge process, which is conducive to the release of lithium ions and the migration of lithium ions, so that the lithium ion battery has a small expansion and a high discharge capacity, and at the same time ensures that the electrolyte uniformly infiltrates the plate, reduces battery polarization, and inhibits negative electrode lithium precipitation. Under the premise of improving the kinetic performance of the battery core, it also has a good cycle life and safety when used for long-term fast charging. At the same time, by adjusting the relationship between the viscosity of the electrolyte chain solvent and the porosity of the positive electrode plate, it can ensure that the electrolyte fully fills the gap of the positive electrode plate, thereby ensuring that lithium ions are quickly released and embedded from the positive electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a schematic diagram of the structure of the device used in the present application to measure the viscosity of the chain solvent. DETAILED DESCRIPTION

[0010] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The relevant embodiments described herein are illustrative and are used to provide a basic understanding of the present application. The embodiments of the present application should not be interpreted as limiting the present application.

[0011] For simplicity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and any upper limit can be combined with any other upper limit to form an unspecified range. In addition, each separately disclosed point or single value can itself be combined as a lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form an unspecified range.

[0012] In the description herein, unless otherwise specified, “above” and “below” include the number.

[0013] Unless otherwise specified, the terms used in this application have the commonly known meanings generally understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0014] A list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0015] The term "OI value of the positive electrode pole piece" refers to the ratio of the peak area of ​​the 003 crystal plane diffraction peak to the peak area of ​​the 110 crystal plane diffraction peak of the positive electrode pole piece.

[0016] Primary and secondary batteries

[0017] One or more embodiments of the present application provide a secondary battery, the secondary battery comprising a positive electrode plate and an electrolyte, the electrolyte comprising a chain solvent, the positive electrode plate comprising a positive electrode active material, the secondary battery satisfying: 1.5≤M×1000 / (N×ρ)≤20.0, wherein M refers to the mass of the chain solvent per 100g of the positive electrode active material, in units of g; ρ refers to the surface density of the positive electrode plate, in units of g / m 2 ; N refers to the OI value of the positive electrode sheet, wherein the OI value of the positive electrode sheet refers to the ratio of the peak area of ​​the 003 crystal plane diffraction peak of the positive electrode sheet to the peak area of ​​the 110 crystal plane diffraction peak. The present application reasonably controls the OI value of the positive electrode sheet, the mass of the electrolyte chain solvent used per 100g of positive electrode active material, and the surface density of the positive electrode sheet to ensure that lithium ions can be quickly released from the positive electrode sheet, so that the positive electrode sheet has excellent kinetic performance, and also makes the positive electrode sheet expand less during the cycle process, avoiding the adverse effect of the expansion of the positive electrode sheet on the battery performance. Therefore, the secondary battery of the present application can have the characteristics of high safety, excellent kinetic performance and long cycle life.

[0018] In some embodiments, 3≤1000×M / (N×ρ)≤15. In some embodiments, 1000×M / (N×ρ) is 1.5, 1.8, 2, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0, 17.0, 18.0, 20, or any range therebetween. If the value of M×1000 / (N×ρ) is too low, it means that the rate of lithium ion extraction from the positive electrode of the secondary battery is slow, and the transmission rate of lithium ions in the electrolyte is limited, the kinetic performance is limited, and the low temperature performance and fast charging performance of the secondary battery are affected; if the value of M×1000 / (N×ρ) is too high, the rate of lithium ion extraction from the positive electrode in the secondary battery is fast, and the transmission rate of lithium ions in the electrolyte is fast. In some embodiments, 2.5≤1000×M / (N×ρ)≤14.

[0019] In some embodiments, 2.5≤10×ε / η≤12.0, wherein η refers to the viscosity value of the chain solvent at 25°C, in mPa·s; ε refers to the porosity of the positive electrode sheet. In some embodiments, 10×η / ε is 2.5, 3.5, 4.5, 5.5, 6.5, 7.5, 8.5, 9.5, 10.5, 11, 12 or any range therebetween. If the value of 10×η / ε is too low, it means that the electrolyte cannot fully fill the positive electrode pores, affecting the embedding and extraction of lithium ions in the positive electrode, and affecting the low temperature performance and fast charging performance of the secondary battery; if the value of 10×η / ε is too high, the capacity of the positive electrode is affected due to the higher porosity, thereby reducing the battery capacity. In some embodiments, 3≤10×ε / η≤11. In some embodiments, 7≤10×ε / η≤10.

[0020] In some embodiments, 80 g / m 2 ≤ρ≤400g / m 2 In some embodiments, ρ is 80 g / m 2 , 100g / m 2 , 150g / m 2 , 200g / m 2 , 250g / m 2 , 300g / m 2 , 350g / m 2 , 400g / m 2 Or any range therebetween. If ρ is too large, it means that the mass of the positive electrode per unit area is high, and the ability of lithium ions to escape from the positive electrode is limited, which affects the low temperature performance and fast charging performance of the secondary battery. If ρ is too small, it means that the mass of the positive electrode per unit area is low, and lithium ions can easily escape from the positive electrode, but the mass of the positive electrode is low, which affects the energy density of the secondary battery. In some embodiments, 90 g / m2 ≤ρ≤350g / m 2 .

[0021] In some embodiments, 10g≤M≤70g; in some embodiments, M is 10g, 20g, 30g, 40g, 50g, 60g, 70g or any range therebetween. If the M value is too large, it means that the electrolyte composition contains a large amount of low-viscosity linear esters, which can effectively improve the kinetic performance of the secondary battery, but a high content of low-viscosity linear esters affects the battery cycle performance. If the M value is too small, it means that the electrolyte composition contains a small amount of low-viscosity linear esters, and the kinetic performance is limited, which affects the low temperature performance and fast charging performance of the secondary battery. In some embodiments, 15g≤M≤65g. In some embodiments, 35g≤M≤65g.

[0022] In some embodiments, 2≤N≤150. In some embodiments, N is 2, 10, 20, 30, 40, 50, 60, 70, 90, 110, 120, 130, 140, 150 or any range therebetween. The OI value of the positive electrode plate can reflect the stacking orientation degree of the layered lithium-containing compound particles in the positive electrode plate, and reflect the actual ability of the positive electrode plate to release lithium ions. Generally speaking, layered lithium-containing compounds have a strong C-axis orientation, that is, 003 crystal plane orientation, which will affect the release of lithium ions and further affect the kinetic performance of lithium-ion batteries. In layered lithium-containing compounds, the angle between the 003 crystal plane and the 110 crystal plane is 90°, so C 003 / C 110It can characterize the orientation degree of the layered lithium-containing compound. However, in addition to the layered lithium-containing compound, the positive electrode sheet also contains inactive substances such as conductive agents and binders, which cannot release lithium ions. In addition, in the preparation process of the positive electrode sheet, cold pressing, drying and other processes often change the orientation of the layered lithium-containing compound. Therefore, the powder OI value of the layered lithium-containing compound cannot reflect the actual ability of the positive electrode sheet to release lithium ions. The smaller the OI value of the positive electrode sheet, the easier it is for the layered lithium-containing compound particles to be preferentially oriented perpendicular to the positive current collector in the positive electrode sheet (that is, the 003 crystal plane is more perpendicular to the positive current collector), and the easier it is for lithium ions to be quickly released from the crystal structure of the layered lithium-containing compound, which is more conducive to improving the charging capacity of the lithium-ion battery. In addition, the smaller the OI value of the positive electrode sheet, the smaller the residual stress in the positive electrode sheet, and the smaller the expansion of the positive electrode sheet during the cycle. The smaller the expansion of the positive electrode sheet, the smaller the risk of the positive electrode sheet breaking or even causing a short circuit in the battery due to the expansion of the positive electrode sheet; the smaller the expansion of the positive electrode sheet, the smaller the probability of poor electrolyte infiltration caused by the compression of the negative electrode sheet due to the expansion of the positive electrode sheet, thereby avoiding the increase of battery polarization during charging, local lithium precipitation at the negative electrode interface, and excessive decay of the battery cycle capacity; the smaller the expansion of the positive electrode sheet, the smaller the probability of loosening the positive electrode active material particles and damaging the positive electrode conductive network due to the expansion of the positive electrode sheet, thereby avoiding the increase of battery polarization during charging, the decrease of battery charge and discharge power, and the increase of battery heat generation. If the OI value of the positive active material is too high, the positive active material (such as lithium iron phosphate particles and ternary NCM particles) tends to be arranged parallel to the positive current collector, and there are fewer end faces available for active lithium ions to be deintercalated, and the battery is prone to lithium precipitation during the cycle, and the battery has poor kinetic performance. In some embodiments, 5≤N≤100. In some embodiments, 8≤N≤80.

[0023] In some embodiments, 0.3≤η≤1.9. In some embodiments, η is 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 1.0, 1.3, 1.5, 1.7, 1.9 or any range therebetween. If the viscosity η of the linear ester is too high, it will affect the wetting of the positive and negative electrode sheets, which is not conducive to the formation of a stable solid electrolyte interface film on the surface of the positive and negative electrode sheets. If the viscosity η of the linear ester is too low, the battery will easily become soft and bloated during use, which is not conducive to the long-term performance of the battery. In some embodiments, 0.3≤η≤1.85.

[0024] In some embodiments, 22%≤ε≤45%. In some embodiments, ε is 22%, 24%, 26%, 28%, 30%, 35%, 40%, 42%, 45% or any range therebetween. If the porosity ε of the positive electrode sheet is too low, it will affect the infiltration of the electrolyte and will not be conducive to the formation of a stable solid electrolyte interface film on the surface of the positive electrode sheet. Controlling the porosity of the positive electrode sheet within the above range is conducive to ensuring a high energy density while ensuring the formation of a stable solid electrolyte interface film on the surface of the positive electrode sheet, thereby improving the cycle performance of the secondary battery. In some embodiments, 24%≤ε≤44%.

[0025] In some embodiments, the chain solvent includes at least one of a chain carbonate, a chain carboxylic acid ester, a fluorinated chain carbonate, a cyclic carbonate, and a fluorinated chain carboxylic acid ester.

[0026] In some embodiments, the linear carbonate compound includes, but is not limited to, one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), and ethylmethyl carbonate (MEC).

[0027] In some embodiments, the cyclic carbonate compound includes, but is not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinyl ethylene carbonate (VEC).

[0028] In some embodiments, the chain carboxylate compound includes but is not limited to one or more of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid, valerolactone and caprolactone.

[0029] The fluorinated chain carbonate ester includes monofluoro dimethyl carbonate and difluoro dimethyl carbonate; the fluorinated chain carboxylic acid ester includes at least one of ethyl fluoroacetate, ethyl difluoroacetate and ethyl trifluoroacetate.

[0030] In some embodiments, the electrolyte further includes a lithium salt comprising at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), trifluorosulfonyl lithium (LiOTf), lithium bis(oxalatoborate) (LiBOB), lithium bis(fluoromalonate) borate (LiBFMB), lithium bis(fluorosulfonyl)imide (LiFSi), and lithium difluorooxalatoborate (LiDFOB).

[0031] In some embodiments, the positive electrode plate includes a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode active material. In some embodiments, the positive electrode active material includes at least one of a lithium iron phosphate material and a nickel-cobalt ternary material, and the lithium iron phosphate material includes at least one of the materials represented by the formula LixFeyR(1-y)PO4, wherein R includes at least one of the elements Mn, Co, Ti, Mg, Ca, Cr, Cu, Ni, V, Mo, Zn, Al, B and Nb, 0.05≤x≤1.2, 0<y≤1. In some embodiments, the lithium iron phosphate material is a lithium manganese iron phosphate material. The conductivity and lithium ion diffusion capacity of the lithium iron phosphate material with an olivine structure are poor, especially at low temperatures, the lithium ion transmission rate is worse. Therefore, it is more necessary to improve the transmission rate of lithium ions in the electrolyte, at the interface between the electrolyte and the negative electrode plate, and in the negative electrode plate to improve the overall lithium ion transmission rate of the secondary battery and obtain better low temperature performance and rate performance.

[0032] In some embodiments, the nickel-cobalt ternary material includes at least one of LiNimConA(1-mn)O2 materials, where A is selected from at least one of manganese, aluminum, magnesium, chromium, calcium, zirconium, molybdenum, silver or niobium, 0.5≤m≤1, 0≤n≤0.5, and m+n≤1.

[0033] In some embodiments, m is 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or a range consisting of any two of these values. In some embodiments, n is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, or a range consisting of any two of these values.

[0034] In some embodiments, the nickel-cobalt-based ternary material includes at least one of NCA, NCM111, NCM523, NCM622, NCM811, Ni90, Ni92, or Ni95.

[0035] In some embodiments, there is a carbon coating on the surface of the lithium iron phosphate material. Based on the mass of the lithium iron phosphate material, the mass percentage of the carbon coating is 1% to 3%. It is understandable that if the carbon coating is too thin, it will not be able to effectively improve the inherent conductivity of the positive electrode material, and the power performance of the lithium-ion battery will be poor; if the carbon coating is too thick, the energy density of the lithium-ion battery will be significantly reduced, and the non-uniformity of the coating will be more obvious and the defects will increase, affecting the cycle performance of the lithium-ion battery. In some embodiments, the mass percentage of the carbon coating is 1%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 3% or a range consisting of any two of the above values.

[0036] In some embodiments, in addition to the aforementioned positive electrode active materials, the positive electrode active material may further include lithium nickel oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, lithium nickel manganese cobalt magnesium oxide, and lithium nickel manganese oxide.

[0037] In some embodiments, the positive electrode active material layer further includes a binder, and optionally a conductive material. The binder improves the bonding of the positive electrode active material particles to each other and also improves the bonding of the positive electrode active material to the current collector.

[0038] In some embodiments, the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin or nylon, etc.

[0039] In some embodiments, the conductive material includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0040] In some embodiments, the positive electrode further includes a positive electrode current collector, which may be a metal foil or a composite current collector. For example, aluminum foil may be used. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer substrate.

[0041] In some embodiments, the negative electrode active material layer includes a negative electrode active material, the negative electrode active material includes a carbon-based material, the carbon-based material includes at least one of graphite, soft carbon, hard carbon, carbon nanotubes and graphene. Exemplarily, the tin-based material includes at least one of tin, tin oxide and tin alloy. Exemplarily, the phosphorus-based material includes at least one of phosphorus and a phosphorus complex.

[0042] In some embodiments, the negative electrode active material layer also includes a binder and a conductive agent. The binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin and nylon, etc. At least one of the conductive agent includes, but is not limited to: at least one of carbon-based materials, metal-based materials, conductive polymers and mixtures thereof. In some embodiments, the carbon-based material includes natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber or any combination thereof. In some embodiments, the metal-based material includes metal powder, metal fiber, copper, nickel, aluminum or silver. In some embodiments, the conductive polymer includes a polyphenylene derivative.

[0043] In some embodiments, the negative electrode further includes a negative electrode current collector, and the negative electrode current collector includes at least one of: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof.

[0044] In some embodiments, a separator is provided between the positive electrode plate and the negative electrode plate to prevent short circuit. The material and shape of the separator that can be used in the embodiments of the present application are not particularly limited, and it can be any technology disclosed in the prior art. In some embodiments, the separator includes a polymer or an inorganic substance formed of a material that is stable to the electrolyte of the present application.

[0045] In some embodiments, the isolation film includes a base film and a coating disposed on the base film, the base film includes at least one of a polyethylene film, a polypropylene film, a PP / PE / PP composite film, a polyimide film, an aramid film, a polyethylene terephthalate film, or a non-woven fabric. In some embodiments, the coating includes at least one of a polymer layer, an inorganic ceramic layer, or a mixed layer of a polymer and an inorganic ceramic layer.

[0046] In some embodiments, the inorganic ceramic layer includes inorganic particles and a binder, the inorganic particles include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate. The binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.

[0047] The polymer layer contains polymers, and the polymer material includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride and poly(vinylidene fluoride-hexafluoropropylene).

[0048] In some embodiments, the secondary battery is a lithium secondary battery or a sodium secondary battery. In some embodiments, the lithium secondary battery includes, but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0049] In some embodiments, the secondary battery may include an outer package, which may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery may also be a soft shell. The material of the soft shell may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0050] In some embodiments, the shape of the secondary battery is not particularly limited, and it may be cylindrical, square, or any other shape.

[0051] In some embodiments, the present application also provides a battery module. The battery module includes the above-mentioned secondary battery. The battery module of the present application uses the above-mentioned secondary battery, and therefore has at least the same advantages as the secondary battery. The number of secondary batteries contained in the battery module of the present application can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0052] In some embodiments, the present application further provides a battery pack, which includes the above-mentioned battery module. The number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0053] 2. Device

[0054] The present application also provides a device, which includes at least one of the above-mentioned secondary battery, battery module or battery pack.

[0055] In some embodiments, the device includes, but is not limited to: electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, power storage systems, etc. In order to meet the device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module may be used.

[0056] In other embodiments, the 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 secondary battery may be used as a power source.

[0057] Hereinafter, the secondary battery of the present application will be further described in combination with specific embodiments and comparative examples.

[0058] Examples and Comparative Examples

[0059] Hereinafter, the present application will be described in more detail with reference to Examples and Comparative Examples, but the present application is not limited to these Examples unless departing from the gist of the present application.

[0060] The materials and solvents used in the following examples and comparative examples can all be obtained from commercial sources.

[0061] Example 1

[0062] Preparation of positive electrode sheets: Mix the positive electrode active material lithium iron phosphate, the conductive agent carbon black, and the binder PVDF in a mass ratio of 96:2:2, add the solvent NMP, and stir until the system is uniform under the action of a vacuum mixer to obtain a positive electrode slurry; evenly coat the positive electrode slurry on both surfaces of the positive electrode current collector aluminum foil, dry it at room temperature, transfer it to a 120°C oven for further drying, and then cold press and cut it to obtain a positive electrode sheet. In the preparation process of the positive electrode sheet, after selecting the appropriate positive active material, different positive electrode sheet OI values ​​can be obtained by reasonably adjusting the cold pressing process parameters or auxiliary magnetic field induction technology.

[0063] Preparation of negative electrode sheets: negative electrode active material graphite, conductive agent Super-P, thickener CMC, and binder SBR are mixed in a mass ratio of 96.4:1:1.2:1.4, deionized water solvent is added, and stirred under the action of a vacuum mixer until the system becomes uniform to obtain negative electrode slurry; the negative electrode slurry is evenly coated on both surfaces of the negative electrode collector copper foil, dried at room temperature, and then transferred to a 120°C oven for further drying, and then cold pressed and cut to obtain negative electrode sheets.

[0064] Preparation of electrolyte: In an argon-protected glove box (water content <0.1ppm, oxygen content <0.1ppm), take 25g of ethylene carbonate (EC) and 59g of ethyl acetate, then dissolve 14g of fully dried LiPF6 in the mixed organic solvent, and finally add 1g of electrolyte additives fluoroethylene carbonate and 1g of vinylene carbonate.

[0065] Isolation film: PE isolation film is used.

[0066] Preparation of lithium-ion secondary battery: stack the prepared positive electrode sheet, separator, and negative electrode sheet in order, so that the separator is between the positive electrode sheet and the negative electrode sheet, and wind them to obtain a bare battery cell. Place the bare battery cell in an aluminum-plastic film outer package, inject the prepared lithium-ion battery electrolyte after sufficient drying, and obtain a lithium-ion secondary battery after vacuum packaging, standing, formation, shaping and other processes.

[0067] Example 2-16

[0068] Examples 2-16 are achieved by adjusting the surface density of the positive electrode sheet, the OI value of the positive electrode sheet, and the type and content of the chain solvent in the electrolyte on the basis of Example 1. Specific adjustment measures and detailed data are shown in Table 1. The other preparation processes are the same as those of Example 1.

[0069] Comparative Examples 1-3

[0070] Comparative Examples 1-3 are achieved by adjusting the surface density of the positive electrode sheet, the OI value of the positive electrode sheet, and the type and content of the chain solvent in the electrolyte on the basis of Examples 1-16. The specific adjustment measures and detailed data are shown in Table 1. The other preparation processes are the same as those of Example 1.

[0071] Test Method

[0072] 1. Test of the porosity of the positive electrode

[0073] The porosity is measured by a mercury intrusion instrument, specifically: the dried electrode sample is cut into thin strips of a certain size, and the apparent volume of the electrode coating is measured using a micrometer, and the apparent volume = sample coating thickness × sample length × sample width. The electrode is then vacuum degassed, rolled up and placed in a sample pool, and the sample volume must be ensured to account for 40%-70% of the effective volume of the sample pool to ensure measurement accuracy. The pore volume of the sample is then measured using a mercury intrusion instrument, that is, the volume of mercury pressed into the sample. Porosity = pore volume / apparent volume.

[0074] 2. Test of positive electrode surface density

[0075] Cut a piece of positive electrode plate, weigh its mass and record it as M1, then scrape off the positive electrode active material layer on the plate, weigh its mass and record it as M2, measure the area of ​​the plate and record it as V, the surface density of the plate = (M1-M2) / V.

[0076] 3. Test of OI value of positive electrode

[0077] OI value C of positive electrode OI It can be obtained by using an X-ray powder diffractometer (X'pert PRO) and obtaining an X-ray diffraction pattern according to the general rules for X-ray diffraction analysis JIS K 01313-1996, OI value = C 003 / C 110 , where C 003 is the peak area of ​​the characteristic diffraction peak of the 003 crystal plane, C 110 It is the peak area of ​​the characteristic diffraction peak of the 110 crystal plane. Specifically, the OI value test method of the positive electrode piece is: directly placing the prepared positive electrode piece in an X-ray powder diffractometer, and obtaining the peak area of ​​the 003 crystal plane diffraction peak and the peak area of ​​the 110 crystal plane diffraction peak by X-ray diffraction analysis, and then obtaining the OI value of the positive electrode piece.

[0078] 4. Test of chain solvent viscosity

[0079] 1) Fix the Ubbelohde viscometer vertically on the iron frame and place it on the desktop. Use a hose to connect the external circulation of the constant temperature water bath to the constant temperature jacket of the Ubbelohde viscometer (the constant temperature jacket of the viscometer is connected in the bottom-in and top-out principle). Turn on the power button and circulation of the constant temperature water bath, set the temperature to 25.0℃, and wait for the temperature to stabilize at 25±0.1℃.

[0080] 2) Add the sample to be tested from tube 2 of the viscometer to between the two red lines of ball B, pinch the latex tube at tube 1 with your hand, use the ear cleaning bulb to absorb the solution from the latex tube at tube 3 to above ball C, remove the suction ball, loosen the latex tube at tube 1, make ball A communicate with the atmosphere, and let the solution flow out freely under its own gravity. When the liquid level reaches the scale m1, press the stopwatch to start timing, and when the liquid level drops to the scale m2, press the stopwatch to stop, and measure the time it takes for the solution between the scales m1 and m2 to flow through the capillary. Repeat the operation twice, and the difference between the two data should not be greater than 3s. Take the average value, which is the outflow time t.

[0081] 3) Test the viscosity of high-purity water simultaneously according to the above requirements to obtain the calibration coefficient of the viscometer;

[0082] 4) Calculation formula of kinematic viscosity: V = 0.8963 / T0xT1

[0083] Where V is the kinematic viscosity of the sample;

[0084] T0--The time it takes for water to flow from m1 to m2 in pipe 3 (s);

[0085] T1--The time (s) it takes for the sample to flow from m1 to m2 in tube 3;

[0086] 0.8963--Kinematic viscosity of water at 25.0℃

[0087] 5. Test of the maximum charging rate of the battery at 25°C

[0088] At 25°C, the battery prepared in the embodiment and the comparative example was charged to 3.75V at x C constant current and constant voltage, with a cut-off current of 1 / 20C, and discharged to 2.1V at 1C constant current for 10 times, and then the battery was charged to 3.75V at x C constant current and constant voltage, with a cut-off current of 1 / 20C, and then the negative electrode was disassembled and the lithium deposition on the surface of the negative electrode was observed. If no lithium is deposited on the negative electrode surface, the charging rate x C is increased by 0.1C as a gradient and tested again until lithium is deposited on the negative electrode surface, and the test is stopped. The charging rate (x-0.1) C at this time is the maximum charging rate of the battery.

[0089] 6. Cycle performance test

[0090] At 25°C, first charge at 0.5C constant current and constant voltage to 3.75V, then charge at 3.75V constant voltage to a current of 1 / 20C. After standing for 10 minutes, discharge at 1C constant current to 2.1V. Perform a cycle test in this full charge and discharge form until the discharge capacity of the lithium-ion battery decays to 80% of the initial capacity, and record the number of cycles at this time.

[0091] 7. Test of low temperature rate discharge performance at -20℃

[0092] At -20°C, the batteries prepared in the examples and comparative examples were charged at 0.5C to the upper limit voltage, and the discharge capacity was recorded and the batteries were disassembled to observe the lithium deposition on the surface of the negative electrode.

[0093] Please see Table 1 below for the test data.

[0094] Table 1

[0095]

[0096]

[0097]

[0098] As can be seen from Table 1, the secondary battery of the present application can improve the safety performance, dynamic performance and long cycle performance of the secondary battery by reasonably adjusting the relationship between the OI value of the positive electrode plate, the mass of the chain solvent used per 100g of positive electrode active material, and the surface density of the positive electrode plate, and further by adjusting the relationship between the viscosity value of the chain solvent and the porosity of the positive electrode plate.

[0099] Although some exemplary embodiments of the present application have been illustrated and described, the present application is not limited to the disclosed embodiments. On the contrary, those skilled in the art will recognize that some modifications and changes may be made to the described embodiments without departing from the spirit and scope of the present application as described in the appended claims.

Claims

1. A secondary battery, characterized in that The secondary battery comprises a positive electrode sheet and an electrolyte, wherein the electrolyte comprises a chain solvent, the positive electrode sheet comprises a positive electrode active material, and the secondary battery satisfies: 1.5≤M×1000 / (N×ρ)≤20, wherein: M refers to the mass of the chain solvent per 100g of the positive electrode active material, unit: g; ρ refers to the surface density of the positive electrode sheet, unit: g / m 2 ; N refers to the OI value of the positive electrode plate, wherein the OI value of the positive electrode plate refers to the ratio of the peak area of ​​the 003 crystal plane diffraction peak of the positive electrode plate to the peak area of ​​the 110 crystal plane diffraction peak.

2. The secondary battery according to claim 1, characterized in that: 3≤1000×M / (N×ρ)≤15.

3. The secondary battery according to claim 1 or 2, characterized in that: 2.5≤10×ε / η≤12, where η refers to the viscosity of the chain solvent at 25°C, unit: mPa·s; ε refers to the porosity of the positive electrode sheet.

4. The secondary battery according to claim 3, characterized in that: 3≤10×ε / η≤11.

5. The secondary battery according to claim 1 or 2, characterized in that: The secondary battery satisfies at least one of the following conditions: (1) 80≤ρ≤400; (2) 10≤M≤42； (3) 2≤N≤150。 6. The secondary battery according to claim 5, characterized in that: The secondary battery satisfies at least one of the following conditions: (1) 90≤ρ≤350; (2) 15≤M≤40； (3) 5≤N≤100。 7. The secondary battery according to claim 3, characterized in that: 0.3≤η≤1.9; and / or 22%≤ε≤45%.

8. The secondary battery according to claim 7, characterized in that: 0.3≤η≤1.5 and / or 24%≤ε≤44%.

9. The secondary battery according to claim 1 or 2, characterized in that: The chain solvent includes at least one of chain carbonate, chain carboxylic acid ester, fluorinated chain carbonate, cyclic carbonate and fluorinated chain carboxylic acid ester.

10. A device, characterized in that: The device includes the secondary battery according to any one of claims 1 to 9.

Images