Secondary battery and electronic apparatus
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2025-02-10
- Publication Date
- 2026-08-13
Smart Images
Figure CN2025076699_13082026_PF_FP_ABST
Abstract
Description
Secondary batteries and electronic devices Technical Field
[0001] This application relates to the field of energy storage technology, and in particular to a secondary battery and electronic device. Background Technology
[0002] With increasing global awareness of sustainable development and environmental protection, and the rapid development of energy storage systems and other fields, higher demands are being placed on the discharge performance of secondary batteries in diverse scenarios. For example, under high-temperature conditions, the cycle performance and safety performance of secondary batteries become key factors restricting their application. Therefore, optimizing the high-temperature performance of secondary batteries has become an urgent problem to be solved. Summary of the Invention
[0003] This application provides a secondary battery and electronic device with superior overall performance.
[0004] In a first aspect, embodiments of this application provide a secondary battery, including a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive electrode flux layer disposed on at least one surface of the positive current collector; the positive electrode flux layer includes a first material and a second material, the first material including nickel and manganese, and the second material including lithium, iron and phosphorus; the capacity-voltage differential dQ / dV-V image of the secondary battery discharge includes a first peak and a second peak, the peak position of the first peak is from 3.05V to 3.45V, and the peak position of the second peak is from 3.95V to 4.3V.
[0005] The secondary battery based on the embodiments of this application includes a specific positive electrode material in the positive electrode compound layer, such that the relationship curve between the capacity-voltage differential dQ / dV and voltage V of the secondary battery discharge has characteristic peaks in the high-voltage region. These characteristic peaks can reflect the intrinsic structure and compositional characteristics of the positive electrode material of this application. The first peak is located at 3.05V to 3.45V, and the second peak is located at 3.95V to 4.3V, indicating that the positive electrode material of this application undergoes significant elemental redox reactions and a significant phase transition in its material structure within this voltage range. The potential of the characteristic peaks represents the redox activity of the positive electrode material. This phase transition structure is difficult to define using structural formulas and conventional phase transition types, and the redox activity is also difficult to reflect using simple material chemical formulas and material structures. However, through the aforementioned characteristic peaks in the capacity-voltage differential image of this application, it is shown that the positive electrode material of this application has unique physicochemical properties. Through the combination of its phase transition structure and redox activity, the secondary battery can have superior overall performance.
[0006] In some embodiments, the peak position of the first peak is 3.15V to 3.4V; and / or, the peak position of the second peak is 4.07V to 4.26V. Based on the above embodiments, when the characteristic peaks in the dQ / dV curve of the secondary battery discharge are further within the above ranges, it indicates that the cathode material has unique physicochemical properties and superior overall performance, exhibiting both higher discharge specific capacity and better high-temperature performance.
[0007] In some embodiments, the peak area of the first peak is S1, the peak area of the second peak is S2, and 0.08 ≤ S2 / S1 ≤ 1.62. Based on the above embodiments, when the ratio of the peak area of the second peak to the peak of the first peak in the dQ / dV curve of the secondary battery discharge is within the above range, it indicates that the elements in the cathode material have a suitable proportion, resulting in better overall performance. This means that the material exhibits both higher discharge capacity and better high-temperature performance.
[0008] In some embodiments, 0.12 ≤ S2 / S1 ≤ 0.72. Based on the above embodiments, when the ratio of the peak area of the second peak to the peak of the first peak of the dQ / dV curve of the secondary battery discharge is further within the preferred range described above, it indicates that the elements in the cathode material have a more balanced proportion, resulting in better overall performance. It has both higher discharge specific capacity and better high-temperature performance.
[0009] In some embodiments, the surface of the first material is coated with a coating layer comprising boron. The average thickness of the coating layer is 10 nm to 120 nm. Based on the total mass of the positive electrode binder layer, the mass percentage content of boron is E%, 0.01 ≤ E ≤ 0.5%. Based on the above embodiments, this application exhibits superior overall performance. By coating the surface of the first material with a boron coating layer, the specific surface area of the material can be reduced; and by controlling the content of the coating element within the above range, side reactions between the material and the electrolyte can be suppressed, thereby improving gas generation under high-temperature storage. This further enhances the discharge capacity of the secondary battery while simultaneously improving high-temperature performance.
[0010] In some embodiments, the first material includes element M, which is selected from at least one of sodium, calcium, or aluminum. In the fully discharged state, based on the total mass of the positive electrode binder layer, the mass percentage of element M is F%, 0.4 ≤ F ≤ 2. Based on the above embodiments, this application exhibits superior overall performance. By doping the first material with the aforementioned metal element, which has a larger atomic radius, the crystal structure of the first material can be stabilized, and gas generation under high-temperature storage can be improved. Furthermore, while increasing the discharge capacity of the secondary battery, it also improves high-temperature performance.
[0011] In some embodiments, 0.01 ≤ E / F ≤ 0.3. Based on the above embodiments, the present application has superior overall performance. By controlling the ratio of the mass content of the first material coating element to the mass content of the doping element within the above range, it is possible to further improve the discharge capacity of the secondary battery while also improving its high-temperature performance.
[0012] In some embodiments, based on the total mass of the positive electrode additive layer, the ratio of the mass percentage of iron to the mass percentage of nickel is P, where 0.11 ≤ P ≤ 2.7; and / or, based on the total mass of the positive electrode additive layer, the ratio of the mass percentage of iron to the mass percentage of M is Q, where 5 ≤ Q ≤ 25. Based on the above embodiments, this application has superior overall performance. By controlling the ratio of the mass percentage of iron to the mass percentage of nickel in the positive electrode material within the above range, or by controlling the ratio of the mass percentage of iron to the mass percentage of M within the above range, it is possible to further improve the discharge capacity of the secondary battery while also improving high-temperature performance.
[0013] In some embodiments, 0.26 ≤ P ≤ 1.4. Based on the above embodiments, the present application has superior overall performance. By further controlling the ratio of the mass percentage of iron to the mass percentage of nickel in the cathode material within the above range, the discharge capacity of the secondary battery can be further improved while also improving high-temperature performance.
[0014] In some embodiments, the first material is a secondary particle composed of primary particles, the diameter of which is D1 μm, 8 ≤ D1 ≤ 12; and / or, the second material is a primary particle, the diameter of which is D2 nm, 10 ≤ D2 ≤ 500. Based on the above embodiments, this application has superior overall performance. By controlling the particle sizes of the first and second materials within the above ranges, the lithium-ion diffusion path and the level of side reactions between the material and the electrolyte can be controlled at a relatively balanced level, reducing polarization and the consumption of active lithium, thereby improving gas generation under high-temperature storage, and improving both the discharge capacity of the secondary battery and its high-temperature performance.
[0015] In some embodiments, the first material mentioned above includes LiNi x Co y Mn (1-x-y)O2, wherein 0.4≤x≤0.6, 0≤y≤0.2; the second material mentioned above includes LiFePO4. Based on the above embodiments, the positive electrode mixture layer of this application includes the first and second materials used in combination. The first material is nickel-manganese material, which has high discharge specific capacity and energy density; the second material is lithium iron phosphate, which has excellent thermal stability and a stable crystal structure. Furthermore, lithium iron phosphate is less prone to forming a loose surface by-product layer during use, which can stabilize the electrolyte interface and reduce the decomposition of nickel-manganese material at high potentials. Therefore, the combined use of the first and second materials has superior overall performance, improving both the discharge specific capacity of the secondary battery and its high-temperature performance.
[0016] Secondly, embodiments of this application provide an electronic device that includes the aforementioned secondary battery. Attached Figure Description
[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0018] Figure 1 is a capacity voltage differential dQ / dV-V image of embodiments 1-2 of this application. Detailed Implementation
[0019] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.
[0020] The first aspect of this application provides a secondary battery, including a positive electrode, a negative electrode, an electrolyte, and a separator.
[0021] positive electrode
[0022] The positive electrode includes a positive electrode sheet, which includes a positive current collector and a positive electrode additive layer disposed on at least one surface of the positive current collector.
[0023] The positive electrode composite layer comprises a first material and a second material. The first material includes nickel and manganese, and the second material includes lithium, iron, and phosphorus. The capacity-voltage differential C-image of the secondary battery discharge includes a first peak and a second peak. The first peak is located between 3.05V and 3.45V, and the second peak is located between 3.95V and 4.3V. The inclusion of specific positive electrode materials in the positive electrode composite layer causes the relationship curve of the capacity-voltage differential dQ / dV versus voltage V to have characteristic peaks in the high-voltage region, indicating that the positive electrode material of this application has unique physicochemical properties and superior overall performance.
[0024] In some embodiments, the first peak is located at 3.15V to 3.4V. In some embodiments, the second peak is located at 4.07V to 4.26V. When the characteristic peaks in the dQ / dV curve of the secondary battery discharge are further located within the above ranges, it indicates that the cathode material has unique physicochemical properties, exhibiting both high discharge specific capacity and superior high-temperature performance.
[0025] In some embodiments, the peak area of the first peak is S1, the peak area of the second peak is S2, and 0.08 ≤ S2 / S1 ≤ 1.62, preferably 0.12 ≤ S2 / S1 ≤ 0.72. For example, the ratio of the peak area of the second peak to the peak area of the first peak can be 0.08, 0.12, 0.43, 0.66, 0.72, 0.96, 1.35, 1.48, 1.62, or a value within any two of these ranges. When the ratio of the peak area of the second peak to the peak area of the first peak in the dQ / dV curve of the secondary battery discharge is within the above range, it indicates that the elements in the cathode material have a relatively balanced proportion, resulting in higher discharge specific capacity and better high-temperature performance.
[0026] In some embodiments, the surface of the first material is coated with a coating layer comprising boron. The average thickness of the coating layer is from 10 nm to 120 nm. For example, the average thickness of the coating layer can be 23, 31, 51, 78, 96, 102, 120, or any combination thereof. Based on the total mass of the positive electrode additive layer, the mass percentage of boron is E%, 0.01 ≤ E ≤ 0.5. For example, the mass percentage of boron in the positive electrode additive layer can be 0.01, 0.03, 0.17, 0.19, 0.27, 0.39, 0.48, 0.5, or any combination thereof. By coating the surface of the first material with a boron coating layer and controlling the content of the coating element within the above range, gas generation under high-temperature storage can be improved, thereby further improving the discharge capacity of the secondary battery while also improving high-temperature performance.
[0027] In some embodiments, the first material includes element M, which is selected from at least one of sodium, calcium, or aluminum. In the fully discharged state, the mass percentage of element M is F%, 0.4 ≤ F ≤ 2, based on the total mass of the positive electrode binder layer. The mass percentage of element M in the positive electrode binder layer can be 0.4, 0.5, 0.8, 1.1, 1.3, 1.6, 1.9, 2, or a value within any two of these ranges. By doping the first material with the aforementioned metal element, gas generation under high-temperature storage can be improved, further enhancing the discharge capacity of the secondary battery while simultaneously improving high-temperature performance.
[0028] In some embodiments, 0.01 ≤ E / F ≤ 0.3. For example, the value of E / F can be 0.01, 0.05, 0.07, 0.14, 0.18, 0.22, 0.28, 0.3, or a range of any two of these values. By controlling the ratio of the mass content of the first material coating element to the mass content of the doping element within the above range, it is possible to further improve the specific discharge capacity of the secondary battery while also improving its high-temperature performance.
[0029] In some embodiments, the ratio of the mass percentage of iron to the mass percentage of nickel in the positive electrode mixture layer is P, where 0.11 ≤ P ≤ 2.7. For example, the ratio of the mass percentage of iron to the mass percentage of nickel in the positive electrode mixture layer can be 0.11, 0.52, 0.61, 1.04, 1.60, 1.91, 2.46, 2.7, or any value within the range of any two of these values. The ratio of the mass percentage of iron to the mass percentage of M element in the positive electrode mixture layer is Q, where 5 ≤ Q ≤ 25. For example, the ratio of the mass percentage of iron to the mass percentage of M element in the positive electrode mixture layer can be 5, 7, 11, 13, 18, 19, 22, 25, or any value within the range of any two of these values. By controlling the ratio of the mass percentage of iron to the mass percentage of nickel in the cathode material within the above-mentioned range, or by controlling the ratio of the mass percentage of iron to the mass percentage of M element within the above-mentioned range, it is possible to further improve the discharge capacity of the secondary battery while also improving its high-temperature performance.
[0030] In some embodiments, 0.26 ≤ P ≤ 1.4. Based on the above embodiments, this application further controls the ratio of the mass percentage of iron to the mass percentage of nickel in the cathode material within the above range, thereby further improving the discharge capacity of the secondary battery while also improving its high-temperature performance.
[0031] In some embodiments, the first material is a secondary particle composed of primary particles, and the diameter of the secondary particles of the first material is D1 μm, where 8 ≤ D1 ≤ 12. For example, the diameter of the secondary particles of the first material can be 8, 8.6, 9.0, 9.9, 10.6, 10.7, 11.5, 12, or any value within the range of any two of these values. The second material is a primary particle, and the diameter of the primary particles of the second material is D2 nm, where 10 ≤ D2 ≤ 500. For example, the diameter of the primary particles of the second material can be 10, 49, 146, 199, 260, 344, 459, 500, or any value within the range of any two of these values. By controlling the particle sizes of the first and second materials within the above ranges, gas generation under high-temperature storage can be improved, thereby increasing the discharge capacity of the secondary battery while also improving high-temperature performance.
[0032] In some embodiments, the first material mentioned above includes LiNi. x Co y Mn (1-x-y) O2, where 0.4 ≤ x ≤ 0.6, 0 ≤ y ≤ 0.2. For example, the first material could be LiNi. 0.5 Mn 0.5 O2, LiNi 0.6 Mn 0.4 O2 or LiNi 0.6 Co 0.1 Mn 0.3 O2. The second material mentioned above includes LiFePO4. The positive electrode mixture layer includes the aforementioned mixed first material (nickel-manganese) and second material (lithium iron phosphate). The mixed use of these two materials can improve the discharge capacity of the secondary battery while also improving its high-temperature performance.
[0033] In some embodiments, the positive electrode mixture layer includes a positive electrode conductive material. There is no limitation on the type of positive electrode conductive material; any known conductive material can be used. Examples of positive electrode conductive materials include, but are not limited to, acetylene black, Super-P carbon black, amorphous carbon such as needle coke, carbon nanotubes, and graphene. The above-mentioned positive electrode conductive materials can be used alone or in any combination.
[0034] In some embodiments, the positive electrode binder layer includes a positive electrode adhesive. There are no particular limitations on the type of positive electrode adhesive; in the case of a coating method, any material that is soluble or dispersible in the liquid medium used during electrode manufacturing is acceptable. Examples of positive electrode adhesives may include, but are not limited to, one or more of the following: resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; rubber-like polymers such as styrene-butadiene rubber, nitrile rubber, fluororubber, isoprene rubber, polybutadiene rubber, and ethylene-propylene rubber; thermoplastic elastomers such as styrene-butadiene-styrene block copolymers or their hydrides, ethylene-propylene-diene terpolymers, styrene-ethylene-butadiene-ethylene copolymers, and styrene-isoprene-styrene block copolymers or their hydrides; soft resin-like polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; fluorinated polymers such as polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymers; and polymer compositions with alkali metal ion conductivity. The above-mentioned positive electrode adhesives may be used alone or in any combination.
[0035] There are no restrictions on the type of solvent used to form the positive electrode slurry, as long as it can dissolve or disperse the positive electrode active material, conductive material, positive electrode binder, and thickener used as needed. Examples of solvents used to form the positive electrode slurry can include any of aqueous solvents and organic solvents. Examples of aqueous media include, but are not limited to, mixtures of alcohol and water or water. Examples of organic media include, but are not limited to, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran; amides such as N-methylpyrrolidone, dimethylformamide, and dimethylacetamide; and aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide.
[0036] Thickeners are typically used to adjust the viscosity of slurries. In the case of aqueous media, thickeners and styrene-butadiene rubber latex can be used for slurry preparation. There are no particular limitations on the types of thickeners, but examples include, but are not limited to, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and their salts. The above thickeners can be used alone or in any combination.
[0037] There are no particular limitations on the type of positive electrode current collector; it can be any known material suitable for use as a positive electrode current collector. Examples of positive electrode current collectors include, but are not limited to, metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and materials such as carbon cloth and carbon paper. In some embodiments, the positive electrode current collector is a metallic material. In some embodiments, the positive electrode current collector is aluminum.
[0038] To reduce the electronic contact resistance between the positive current collector and the positive electrode binder layer, the surface of the positive current collector may include a conductive additive or a conductive coating. Examples of conductive additives include, but are not limited to, carbon and precious metals such as gold, platinum, and silver. Examples of conductive coatings may include a mixture layer containing inorganic oxides, conductive agents, and binders.
[0039] negative electrode
[0040] The negative electrode includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, the negative electrode material layer containing a negative electrode active material. In some embodiments, the rechargeable capacity of the negative electrode active material is greater than the discharge capacity of the positive electrode active material, so as to reduce the deposition of lithium metal on the negative electrode during charging.
[0041] Negative electrode active materials may include natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), silicon, silicon-carbon composites, and SiO2. w (0.5 < w < 1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O 12 At least one of Li-Al alloys or metallic lithium. Optionally, the negative electrode active material may further include amorphous carbon materials, which may be soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, or calcined coke, etc.
[0042] The negative electrode material layer also includes a negative electrode binder. The negative electrode binder improves the bonding between the negative electrode active material particles and the bonding between the negative electrode active material and the current collector. This application does not particularly limit the type of negative electrode binder, as long as it is a material stable to the electrolyte or the solvent used in electrode manufacturing. In some embodiments, the negative electrode binder includes a resin binder. Examples of resin binders include, but are not limited to, fluoropolymers, polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, etc. When using an aqueous solvent to prepare the negative electrode slurry, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or its salts, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salts, polyvinyl alcohol, etc.
[0043] The negative electrode material layer also includes a conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent, as long as it achieves the purpose of this application. For example, the negative electrode conductive agent can be at least one of acetylene black, Ketjen black, carbon nanotubes, carbon fibers, carbon dots, or graphene, etc., and the aforementioned carbon nanotubes can include, but are not limited to, at least one of single-walled carbon nanotubes or multi-walled carbon nanotubes.
[0044] This application does not impose any particular limitation on the negative electrode current collector, as long as it achieves the purpose of this application. For example, the negative electrode current collector may comprise copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a polymer substrate coated with a conductive metal. The conductive metal includes, but is not limited to, copper, nickel, or titanium, and the polymer substrate material includes, but is not limited to, at least one of polyethylene, polypropylene, ethylene-propylene copolymer, polyethylene terephthalate, polyethylene terephthalate, or poly(p-phenylene terephthalate). In this application, there are no particular limitations on the thickness of the negative electrode current collector and the negative electrode material layer, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode current collector is 4 μm to 12 μm, and the thickness of the single-sided negative electrode material layer is 30 μm to 160 μm. In this application, the negative electrode mixture layer may be disposed on one surface or on two surfaces in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of the negative electrode current collector or only a part of it. This application has no particular restrictions, as long as the purpose of this application can be achieved.
[0045] This application does not impose any particular limitation on the compaction density of the negative electrode sheet, as long as it achieves the purpose of this application. For example, the compaction density of the negative electrode sheet can be 1.0 g / cm³. 3 Up to 1.85 g / cm 3 This application does not impose any particular limitation on the cold pressing pressure of the negative electrode sheet, as long as the purpose of this application can be achieved. For example, the cold pressing pressure of the negative electrode sheet can be from 3 tons to 30 tons.
[0046] Optionally, the negative electrode sheet may further include a conductive layer, which is located between the negative electrode current collector and the negative electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, and it can be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer, and it can be at least one of the aforementioned conductive agents and binders. This application does not impose any particular limitation on the mass ratio of the conductive agent to the binder in the conductive layer; those skilled in the art can choose according to actual needs, as long as the purpose of this application is achieved. This application does not impose any particular limitation on the thickness of the conductive layer, as long as the purpose of this application is achieved; for example, the thickness of the conductive layer is 1 μm to 10 μm.
[0047] electrolyte
[0048] The electrolyte used in the secondary battery of this application includes a lithium salt and a non-aqueous solvent for dissolving the lithium salt.
[0049] This application does not impose any particular limitation on the type of lithium salt, as long as it achieves the purpose of this application. For example, the lithium salt may include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(fluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalateborate)borate (LiBOB), or lithium difluorooxalateborate (LiDFOB). Based on the mass of the electrolyte, the mass percentage of the lithium salt may be from 8% to 15%, for example, the mass percentage of the lithium salt may be 8%, 9%, 10%, 11%, 12.5%, 13%, 15%, or a range of any two of these values.
[0050] This application does not impose any particular limitation on the types of non-aqueous solvents mentioned above, as long as they can achieve the purpose of this application. For example, they may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The carbonate compounds mentioned above may include, but are not limited to, at least one of chain carbonate compounds or cyclic carbonate compounds. The chain carbonate compounds mentioned above may include, but are not limited to, at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, or methyl ethyl carbonate. The cyclic carbonate compounds mentioned above may include, but are not limited to, at least one of ethylene carbonate, propylene carbonate, butyl carbonate, or ethylene ethylene carbonate. The carboxylic acid ester compounds mentioned above may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of ethylene glycol dimethyl ether, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The aforementioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.
[0051] diaphragm
[0052] This application typically includes a separator between the positive and negative electrodes. The separator is used to separate the positive and negative electrode plates, reducing the problem of internal short circuits in the secondary battery, allowing electrolyte ions to pass freely, and not affecting the electrochemical charging and discharging process.
[0053] This application does not impose any particular limitation on the diaphragm, as long as it can achieve the purpose of this application. For example, the diaphragm material may include, but is not limited to, at least one of polyethylene (PE), polyolefin (PO) based on polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid; the diaphragm type may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.
[0054] In this application, the diaphragm may include a substrate and a surface treatment layer. The substrate may be a nonwoven fabric or composite membrane with a porous structure, and the material of the substrate may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials. For example, the inorganic layer includes inorganic particles and a binder. This application does not have any particular limitation on the aforementioned inorganic particles, and may include at least one of alumina, 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, or barium sulfate. This application does not have any particular limitation on the aforementioned binders, and may include at least one of the aforementioned binders. The polymer layer contains a polymer, the polymer material of which includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).
[0055] In this application, the pore size of the separator is from 0.01 μm to 1 μm, and the thickness is from 5 μm to 50 μm. In some embodiments, the separator thickness is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the separator thickness is less than 50 μm, less than 40 μm, or less than 30 μm. When the separator thickness is within the above ranges, insulation and mechanical strength can be ensured, and the rate performance and energy density of the secondary battery can be guaranteed.
[0056] This application also provides an electronic device, which includes the secondary battery described in this application. Electronic devices include, but are not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.
[0057] Example
[0058] The following examples, using lithium-ion batteries as an example, provide more specific illustrations of the implementation methods of the secondary battery of this application. Those skilled in the art will understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" refer to mass measurements.
[0059] Example 1-1
[0060] 1. Preparation of the positive electrode
[0061] <Preparation of Positive Electrode Active Material 1>
[0062] (1) A mixed solution containing NiSO4 and MnSO4 was prepared according to the element molar ratio Ni:Mn=50:50. The solution was then mixed with a precipitant (NaOH solution) and a complexing agent (ammonia water) and reacted. By controlling the reaction time, ammonia water concentration and pH value, a nickel-manganese precursor TM(OH)2 (TM=Ni / Mn) with an average particle size Dv50 of 11μm was obtained.
[0063] (2) The nickel manganese precursor and lithium nitrate were mixed in a molar ratio of Li:(Ni+Mn)=1.15:1, heated to 800℃ at a rate of 10℃ / min and held for 6h, and then quenched to room temperature in air at a certain cooling rate of 50℃ / min.
[0064] (3) Wash and soak the reaction product in deionized water and then dry it;
[0065] (4) The positive electrode active material 1, namely the first material LiNi, is obtained by crushing and sieving. 0.5 Mn 0.5 O2.
[0066] <Preparation of Positive Electrode Active Material II>
[0067] The second positive electrode active material is commercially available LiFePO4.
[0068] <Preparation of the positive electrode>
[0069] The positive electrode active material (including the first and second materials, with a mixing mass ratio as shown in Table 1), conductive carbon black, and polyvinylidene fluoride (PVDF) prepared in the above steps are mixed at a mass ratio of 95:2:3. N-methylpyrrolidone (NMP) is added, and the mixture is stirred evenly under vacuum to obtain a positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry is uniformly coated onto one surface of a 9 μm thick positive electrode current collector aluminum foil and dried to obtain a positive electrode sheet with a single-sided coating of the positive electrode mixture layer. The above steps are repeated on the other surface of the positive electrode current collector aluminum foil to obtain a positive electrode sheet with a double-sided coating of the positive electrode mixture layer. By adjusting the cold pressing pressure, positive electrode sheets with different compaction densities and surface roughness can be obtained. After cold pressing, slitting, and welding of electrode tabs, the sheets are dried to obtain a positive electrode sheet with a specification of 74 mm × 867 mm.
[0070] 2. Preparation of electrolyte
[0071] In a dry argon atmosphere glove box, diethyl carbonate was used as the base solvent, and lithium hexafluorophosphate (LiPF6) was dissolved in the base solvent. Ethylene carbonate was added as an additive to obtain the electrolyte. Based on the total mass of the electrolyte, the mass percentage of LiPF6 was 12.5%, and the mass percentage of vinylene carbonate was 2%.
[0072] 3. Preparation of the negative electrode
[0073] Using artificial graphite as the negative electrode active material, a mixture of the negative electrode active material, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), carbon nanotubes (CNTs), and carboxymethyl cellulose (CMC) was prepared in a mass ratio of 95.8:2.4:0.5:0.5:0.8. Deionized water was then added as a solvent and the mixture was stirred until homogeneous, resulting in a negative electrode slurry with a solid content of 45 wt%. The negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil current collector, and then dried to obtain a negative electrode sheet with a single-sided coating of the negative electrode mixture layer. The above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of the negative electrode mixture layer. By adjusting the cold pressing pressure, negative electrode sheets with different compaction densities and surface roughness could be obtained. After cold pressing, slitting, and welding of tabs, the sheets were dried to obtain negative electrode sheets with dimensions of 76.6 mm × 875 mm.
[0074] 4. Preparation of the diaphragm
[0075] A porous polyethylene film with a thickness of 15μm was used as the diaphragm.
[0076] 5. Preparation of lithium-ion batteries
[0077] The positive electrode, negative electrode, and separator are stacked sequentially, with the separator positioned between the positive and negative electrodes for isolation. The electrode assembly is then wound to form an electrode assembly. The electrode assembly is placed in a packaging bag, dehydrated at 80°C, injected with the aforementioned electrolyte, and sealed. After processing including formation hot pressing (at 80°C / 1–2.5 MPa for 0.5–2 hours), degassing, edge trimming, and capacity testing, a lithium-ion battery is obtained.
[0078] 6. Testing Methods
[0079] (1) Characteristic peaks and peak areas
[0080] Take a lithium-ion battery and charge and discharge it with a current of 0.2C within the voltage range of 2.8V to 4.35V. Obtain the relationship curve between the capacity-voltage differential dQ / dV and the voltage V. Calculate the discharge capacity in the voltage range of ±0.05V at the peak position of the first peak and obtain the peak area S1 mAh of the first peak. Calculate the discharge capacity in the voltage range of ±0.11V at the peak position of the second peak and obtain the peak area S2 mAh of the second peak.
[0081] (2) Particle morphology and diameter
[0082] Take a lithium-ion battery, cut the positive electrode sheet using ion polishing, and then observe the morphology of the positive electrode active material particles in the cross-section of the positive electrode sheet using a scanning electron microscope (instrument model: ZEISS SEM, accelerating voltage: 0.1kV~30kV). In the cross-sectional photograph, randomly select either the first material particle or the second material particle, and take its longest diameter as the diameter of the first material or the second material.
[0083] (3) Content of metallic elements and boron
[0084] Take a lithium-ion battery and discharge it to 2.8V to obtain a fully discharged secondary battery. Then remove the positive electrode and dissolve it in a mixed solvent (for example, 0.4g of positive electrode is dissolved in a mixed solvent of 5ml aqua regia and 5ml deionized water), and bring the volume to 100mL. Then use an ICP analyzer to test the mass percentage of each metal element and boron element in the solution.
[0085] (4) Discharge capacity
[0086] Take a lithium-ion battery and charge it at a constant current of 0.5C under constant temperature conditions of 25℃ until it reaches 4.35V. Then charge it at a constant voltage until the current reaches 0.05C. Finally, discharge it at a constant current of 0.2C until it reaches 2.8V.
[0087] Discharge capacity = Discharge capacity at 0.2C / Mass of positive electrode active material.
[0088] (5) Thermal runaway initiation temperature
[0089] A lithium-ion battery was charged to 4.35V at a constant current of 0.5C under constant temperature conditions of 25℃. Then, the thermocouple was fixed to the middle of the cell with Teflon glue. The sample was placed in the calorimetric chamber of an adiabatic accelerated calorimeter with an initial temperature of 40℃. The battery temperature was continuously heated and recorded in real time. A 5℃ increase in battery temperature within 1 minute was taken as the standard for thermal runaway. The temperature at which the battery thermal runaway occurred was recorded as the thermal runaway initiation temperature.
[0090] (6) High-temperature cycling performance
[0091] Take a lithium-ion battery and perform its first charge and discharge cycle at 45°C. First, use a constant current of 0.5C to charge it to 4.35V, then use a constant voltage to charge it. Then, use a constant current of 0.5C to discharge it to 2.8V. Record the discharge capacity of the third cycle. Then, perform 500 charge and discharge cycles and record the discharge capacity of the 500th cycle.
[0092] 45℃ cycle capacity retention % = (discharge capacity of the 500th cycle / discharge capacity of the 3rd cycle) × 100%.
[0093] Overall performance
[0094] If the above discharge capacity, thermal runaway initiation temperature, and high-temperature cycling performance test results simultaneously meet the following conditions, the overall performance is deemed to have passed and meets customer requirements; otherwise, it is deemed to have failed.
[0095] Discharge capacity: not less than 146mAh / g;
[0096] Thermal runaway initiation temperature: not lower than 232℃;
[0097] High-temperature cycling performance: not less than 72%.
[0098] The lithium-ion batteries in the following embodiments or comparative examples differ from those in Examples 1-1 only in that the mixing ratio of the first and second materials is adjusted according to Table 1. The performance test results of the lithium-ion batteries in each embodiment and comparative example are shown in Table 1 below.
[0099] Table 1
[0100] *In the table above, "First Material: Second Material" indicates the weight percentage of the first material and the second material in 100 parts of positive electrode active material; Fe and Ni represent the mass percentage of iron and nickel in the positive electrode mixture layer, respectively; the calculation results of S2 / S1 and P are both rounded to two decimal places.
[0101] As shown in Table 1, the lithium-ion batteries prepared in the embodiments of this application have better overall performance than Comparative Example 1, which uses only the first material. The thermal runaway initiation temperature and high-temperature cycle capacity retention of the lithium-ion batteries in Examples 1 to 10 are improved. Compared with Comparative Example 2, which uses only the second material, the lithium-ion batteries in Examples 1 to 10 have better overall performance and improved discharge capacity.
[0102] Specifically, the lithium-ion batteries prepared in the embodiments of this application exhibit excellent overall performance in terms of discharge specific capacity, thermal runaway initiation temperature, and high-temperature cycle capacity retention when the ratio of iron to nickel in the positive electrode binder layer is 0.08 ≤ S2 / S1 ≤ 1.62, and especially 0.12 ≤ S2 / S1 ≤ 0.72. In particular, the lithium-ion batteries prepared in the embodiments of this application exhibit excellent overall performance in terms of discharge specific capacity, thermal runaway initiation temperature, and high-temperature cycle capacity retention when the ratio P of iron to nickel in the positive electrode binder layer is 0.11 ≤ P ≤ 2.7, and especially 0.26 ≤ P ≤ 1.4.
[0103] The lithium-ion batteries in Examples 2-1 to 2-17 differ from those in Examples 1-4 only in that the mass percentage of boron and M elements in the positive electrode binder layer is adjusted according to Table 2.
[0104] The coating method for the boron coating layer on the surface of the first material is as follows: The prepared positive electrode active material one, namely the first material LiNi, is coated with the boron coating layer. 0.5 Mn 0.5 O2 is mixed with a certain amount of boric acid and calcined at 300℃ for 5 hours to obtain the first boron-coated material. The coating thickness is controlled by controlling the amount of boric acid mixed.
[0105] The doping method of element M in the first material is as follows: The nickel-manganese precursor obtained in step (1) of the preparation of the positive electrode active material and the salt of element M are ground and mixed evenly in a molar ratio of M:(Ni+Mn) of 1.15:1. The mixture is then calcined at 800℃ in an air atmosphere for 20h to obtain a reaction product with a molar ratio of Ni:Mn = 50:50. After crushing, sieving and demagnetizing, the product precursor MNi is obtained. 0.5 Mn 0.5 O2 is then used to react the precursor product with lithium nitrate in the steps described above.
[0106] The performance test results of the lithium-ion batteries in each embodiment are shown in Table 2 below.
[0107] Table 2
[0108] *In the table above, the calculation result of E / F is rounded to two decimal places.
[0109] As shown in Table 2, the lithium-ion batteries prepared in the embodiments of this application exhibit excellent overall performance in terms of discharge capacity, thermal runaway initiation temperature, and high-temperature cycle capacity retention when the first material is coated with a boron coating layer and the mass percentage of boron in the positive electrode additive layer satisfies 0.01≤E≤0.5. Specifically, the lithium-ion batteries prepared in the embodiments of this application also exhibit excellent overall performance in terms of discharge capacity, thermal runaway initiation temperature, and high-temperature cycle capacity retention when the first material includes element M and the mass percentage of element M in the positive electrode additive layer satisfies 0.4≤F≤2. Furthermore, the lithium-ion batteries prepared in the embodiments of this application exhibit excellent overall performance in terms of discharge capacity, thermal runaway initiation temperature, and high-temperature cycle capacity retention when 0.01≤E / F≤0.3 is satisfied. Specifically, in the lithium-ion batteries prepared according to the embodiments of this application, when the ratio Q of the mass percentage of iron to the mass percentage of M in the positive electrode binder layer satisfies 5 ≤ Q ≤ 25, the lithium-ion batteries exhibit excellent overall performance in terms of discharge specific capacity, thermal runaway initiation temperature, and high-temperature cycle capacity retention. Specifically, in the lithium-ion batteries prepared according to the embodiments of this application, when the diameter of the secondary particles of the first material satisfies 8 ≤ D1 ≤ 12, or the diameter of the primary particles of the second material satisfies 10 ≤ D2 ≤ 500, the lithium-ion batteries exhibit excellent overall performance in terms of discharge specific capacity, thermal runaway initiation temperature, and high-temperature cycle capacity retention.
[0110] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.
Claims
1. A secondary battery, characterized in that, The positive electrode includes a positive current collector and a positive electrode mixture layer disposed on at least one surface of the positive current collector; The positive electrode mixture layer includes a first material and a second material, wherein the first material includes nickel and manganese, and the second material includes lithium, iron and phosphorus. The capacity-voltage differential dQ / dV-V image of the secondary battery discharge includes a first peak and a second peak, with the first peak ranging from 3.05V to 3.45V and the second peak ranging from 3.95V to 4.3V.
2. The secondary battery according to claim 1, characterized in that, The peak position of the first peak is 3.15V to 3.4V; and / or, the peak position of the second peak is 4.07V to 4.26V.
3. The secondary battery according to claim 1 or 2, characterized in that, The peak area of the first peak is S1, the peak area of the second peak is S2, and 0.08≤S2 / S1≤1.
62.
4. The secondary battery according to claim 3, characterized in that, 0.12≤S2 / S1≤0.
72.
5. The secondary battery according to claim 1 or 2, characterized in that, The surface of the first material is covered with a coating layer, and the coating layer includes boron. Based on the total mass of the positive electrode mixture layer, the mass percentage of boron is E%, where 0.01 ≤ E ≤ 0.
5.
6. The secondary battery according to claim 5, characterized in that, The first material includes element M, wherein element M is selected from at least one of sodium, calcium, or aluminum; In the fully charged state, based on the total mass of the positive electrode mixture layer, the mass percentage of element M is F%, 0.4≤F≤2.
7. The secondary battery according to claim 6, characterized in that, 0.01≤E / F≤0.
3.
8. The secondary battery according to claim 6, characterized in that, Based on the total mass of the positive electrode mixture layer, the ratio of the mass percentage of iron to the mass percentage of nickel is P, where 0.11 ≤ P ≤ 2.7; and / or, Based on the total mass of the positive electrode mixture layer, the ratio of the mass percentage of iron to the mass percentage of M is Q, where 5 ≤ Q ≤ 25.
9. The secondary battery according to claim 8, characterized in that, 0.26≤P≤1.4。 10. The secondary battery according to claim 1 or 2, characterized in that, The first material is a secondary particle composed of primary particles, wherein the diameter of the secondary particles of the first material is D1 μm, 8 ≤ D1 ≤ 12; and / or, The second material is a primary particle, and the diameter of the primary particle of the second material is D2nm, 10≤D2≤500.
11. An electronic device, characterized in that, Includes the secondary battery as described in any one of claims 1 to 10.