Secondary battery and electronic device

Abstract

A secondary battery and an electronic device. The secondary battery comprises a positive electrode sheet, a negative electrode sheet and an electrolyte. The positive electrode sheet comprises a composite current collector and a positive electrode material layer provided on at least one surface of the composite current collector. The positive electrode material layer comprises lithium iron phosphate. The electrolyte comprises propylene carbonate and 1,3-propane sultone. On the basis of the mass of the electrolyte, the mass percentage content of propylene carbonate is Z1, and the mass percentage content of 1,3-propane sultone is Z2, wherein 1 ≤ Z1 / Z2 ≤ 40. The method can improve the capacity retention rate and the lithium ion acceptability of secondary batteries after high and low temperature impact tests.

Description

Secondary batteries and electronic devices Technical Field

[0001] This application relates to the field of electrochemical energy storage, and in particular to a secondary battery and an electronic device using the secondary battery. Background Technology

[0002] Secondary batteries are being used in an increasingly wider range of new energy fields, which has also raised the requirements for their performance in various aspects.

[0003] With the increasing diversification of usage scenarios and application fields, how to provide a rechargeable battery with more stable and efficient performance under high and low temperature conversion conditions has become an urgent problem to be solved. Summary of the Invention

[0004] This application provides a secondary battery and an electronic device using the secondary battery.

[0005] The first aspect of this application provides a secondary battery, including a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a composite current collector and a positive electrode material layer disposed on at least one surface of the composite current collector. The positive electrode material layer includes lithium iron phosphate. The electrolyte includes propylene carbonate and 1,3-propanesulfonic acid lactone. Based on the mass of the electrolyte, the mass percentage of propylene carbonate is Z1, the mass percentage of 1,3-propanesulfonic acid lactone is Z2, and 1 ≤ Z1 / Z2 ≤ 40.

[0006] In this application, the composite current collector and lithium iron phosphate cathode material work together, and cooperate with propylene carbonate and 1,3-propanesulfonic acid lactone present in a specific ratio in the electrolyte, which can improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature impact tests.

[0007] Based on the first aspect, in some possible implementations, 5% ≤ Z1 ≤ 23% can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0008] Based on the first aspect, in some possible implementations, 0.5% ≤ Z2 ≤ 5% can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0009] Based on the first aspect, in some possible implementations, the electrolyte also includes ethyl propionate, and the mass percentage of ethyl propionate is Z3 based on the mass of the electrolyte, with 5% ≤ Z3 ≤ 40%, which can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0010] Based on the first aspect, in some possible implementations, the electrolyte also includes propyl propionate, and the mass percentage of propyl propionate is Z4 based on the mass of the electrolyte, with 8% ≤ Z4 ≤ 60%, which can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0011] Based on the first aspect, in some possible implementations, 7% ≤ Z1 ≤ 20% can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0012] Based on the first aspect, in some possible implementations, 0.9% ≤ Z2 ≤ 3.5% can further improve the capacity retention and lithium-ion acceptance of secondary batteries after high and low temperature shock tests.

[0013] Based on the first aspect, in some possible implementations, 8% ≤ Z3 ≤ 32% can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0014] Based on the first aspect, in some possible implementations, 10% ≤ Z4 ≤ 50% can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0015] Based on the first aspect, in some possible implementations, 30% ≤ Z1 + Z2 + Z3 + Z4 ≤ 70% can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0016] Based on the first aspect, in some possible implementations, the composite current collector includes a polymer support layer and a metal conductive layer disposed on at least one surface of the polymer support layer, which can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0017] Based on the first aspect, in some possible implementations, the polymer support layer includes polyethylene terephthalate and / or polypropylene, which can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0018] Based on the first aspect, in some possible implementations, the electrolyte also includes trimethoxycycloboroxane, which can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0019] Based on the first aspect, in some possible implementations, the negative electrode sheet includes graphite and silicon materials, wherein the graphite includes artificial graphite and / or natural graphite, which can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0020] A second aspect of this application provides an electronic device including a secondary battery. The secondary battery powers the electronic device. In the secondary battery, a composite current collector and a lithium iron phosphate cathode material work together, and these materials interact with propylene carbonate and 1,3-propanesulfonic acid lactone present in a specific ratio in the electrolyte. This improves the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests, thereby enhancing the stability of the electronic device during high and low temperature transitions and improving the versatility of the electronic device. Detailed Implementation

[0021] The technical solutions in the embodiments of this application are described clearly and in detail below. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the specification of this application is for the purpose of describing particular embodiments only and is not intended to limit this application.

[0022] One embodiment of this application provides a secondary battery, which includes a casing, an electrode assembly, and an electrolyte. Both the electrode assembly and the electrolyte are located within the casing.

[0023] The outer casing can be a packaging bag sealed with an encapsulating film (such as aluminum-plastic film), for example, a pouch battery for a secondary battery. In other embodiments, the secondary battery can also be a steel-cased battery, an aluminum-cased battery, etc.

[0024] The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator disposed between the positive and negative electrode. The electrode assembly can be a stacked structure, formed by alternating layers of the positive electrode, separator, and negative electrode. In other embodiments, the electrode assembly can also be a wound structure, formed by winding layers of the positive electrode, separator, and negative electrode.

[0025] The positive electrode includes a composite current collector and a positive electrode material layer disposed on at least one surface of the composite current collector, the positive electrode material layer including lithium iron phosphate; the electrolyte includes propylene carbonate (PC) and 1,3-propanesulfonic acid lactone (PS), the mass percentage of propylene carbonate is Z1 based on the mass of the electrolyte, the mass percentage of 1,3-propanesulfonic acid lactone is Z2, and 1≤Z1 / Z2≤40.

[0026] The secondary battery provided in this application utilizes the combined action of a composite current collector and a lithium iron phosphate cathode material, which, together with propylene carbonate and 1,3-propanesulfonic acid lactone present in a specific ratio in the electrolyte, improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests. It is speculated that the cathode and electrolyte systems in this application can enhance the bonding force between the composite current collector and lithium iron phosphate, and strengthen the stability of the electrolyte film formed at the cathode interface, thus enabling it to withstand the shock of high and low temperature transitions.

[0027] In some embodiments, the values ​​of Z1 / Z2 can be 1, 2, 5, 7, 9, 12, 15, 17, 19, 22, 25, 30, 35, 37, 40, or any value within the range of any two of the above values.

[0028] In some embodiments, 5% ≤ Z1 ≤ 23%. This can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests. In some optional embodiments, Z1 can be 5%, 6%, 7%, 8%, 10%, 11%, 12%, 14%, 15%, 17%, 19%, 20%, 21%, 23%, or any value within the range of any two of the above values.

[0029] In some embodiments, 0.5% ≤ Z2 ≤ 5%. This can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests. In some optional embodiments, Z2 can be 0.5%, 0.9%, 1%, 1.2%, 1.5%, 2%, 2.2%, 2.5%, 3%, 3.5%, 3.7%, 3.9%, 4%, 4.5%, 4.7%, 5%, or any value within the range of any two of the above values.

[0030] In some embodiments, the electrolyte further includes ethyl propionate (EP), and the mass percentage of ethyl propionate is Z3, where 5% ≤ Z3 ≤ 40%, based on the mass of the electrolyte. When the electrolyte system in this application further meets the above requirements, it can be better adapted to the cathode system of this application, and can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests. In some optional embodiments, Z3 can be 5%, 7%, 8%, 10%, 12%, 15%, 17%, 19%, 20%, 22%, 25%, 27%, 29%, 31%, 32%, 35%, 37%, 40%, or any value within the range of any two of the above values.

[0031] In some embodiments, the electrolyte further includes propyl propionate (PP), and the mass percentage of propyl propionate is Z4, where 8% ≤ Z4 ≤ 60% based on the mass of the electrolyte. When the electrolyte system in this application further meets the above requirements, it can be better adapted to the cathode system of this application, and can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests. In some optional embodiments, Z4 can be 8%, 10%, 13%, 16%, 20%, 23%, 26%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or any value within the range of any two of the above values.

[0032] In some embodiments, 7% ≤ Z1 ≤ 20%. This can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0033] In some embodiments, 0.9% ≤ Z2 ≤ 3.5%. This can further improve the capacity retention and lithium-ion acceptance of secondary batteries after high and low temperature shock tests.

[0034] In some embodiments, 8% ≤ Z3 ≤ 32%. This can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0035] In some embodiments, 10% ≤ Z4 ≤ 50%. This can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0036] In some embodiments, 30% ≤ Z1 + Z2 + Z3 + Z4 ≤ 70%. This can further improve the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests. In some optional embodiments, the sum of Z1 + Z2 + Z3 + Z4 can be 30%, 35%, 38%, 40%, 43%, 47%, 50%, 53%, 56%, 60%, 63%, 65%, 70%, or any value within the range of any two of the above values.

[0037] In some embodiments, the electrolyte further includes trimethoxycycloboroxane, wherein the mass percentage of trimethoxycycloboroxane is 0.3% to 0.5% based on the mass of the electrolyte, which is beneficial for further improving the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature shock tests.

[0038] electrolyte

[0039] According to some embodiments of this application, the electrolyte includes propylene carbonate, 1,3-propanesulfonate lactone, ethyl propionate, propyl propionate, trimethoxycycloboroxane, and lithium salt as described above.

[0040] In some embodiments, the electrolyte further includes an organic solvent, which includes, but is not limited to, ethylene carbonate (EC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).

[0041] In some embodiments, the organic solvent further includes ether solvents, including at least one of 1,3-dioxapentane (DOL) and ethylene glycol dimethyl ether (DME) in some optional embodiments.

[0042] In some embodiments, the lithium salt includes at least one of organic lithium salts or inorganic lithium salts. In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalateborate)borate LiB(C2O4)2 (LiBOB), or lithium difluorooxalateborate LiBF2(C2O4) (LiDFOB).

[0043] In some embodiments, the additive includes at least one of fluoroethylene carbonate and adiponitrile.

[0044] Positive electrode sheet

[0045] In some embodiments, the composite current collector includes a polymer support layer and a metal conductive layer disposed on at least one surface of the polymer support layer. The polymer support layer provides good structural strength, which can improve the structural strength of the composite current collector, thereby facilitating further improvement in the capacity retention and lithium-ion acceptance of the secondary battery after high and low temperature impact tests.

[0046] The polymer support layer comprises polyethylene terephthalate and / or polypropylene. These polymer materials, when used as the polymer support layer, exhibit good thermal stability and mechanical properties.

[0047] The conductive metal layer includes at least one of aluminum or an aluminum alloy.

[0048] The positive electrode material layer also includes an adhesive for bonding the positive electrode active material particles to facilitate the formation of the film layer, and also to improve the bonding force between the positive electrode material layer and the positive electrode current collector. In some embodiments, the adhesive may include, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0049] The positive electrode material layer may further include a conductive material, which includes but is not limited to carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, the carbon-based materials may include but are not limited to natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based materials may include but are not limited to metal powders or metal fibers, and in some alternative embodiments, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0050] Negative electrode sheet

[0051] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer provided on the negative electrode current collector. The negative electrode material layer includes graphite and a silicon material. The graphite includes artificial graphite and / or natural graphite.

[0052] The silicon material includes at least one of (a composite of silicon-based substances and carbon-based substances) or silicon oxide (SiOx, 0 < x ≤ 2). The silicon-based substances may be silicon particles, silicon alloy particles, etc.

[0053] Since graphite has a certain flexibility, its combination with the silicon material can relieve the overall volume expansion of the negative electrode material layer. At the same time, graphite and the silicon material as the negative electrode active materials can also make full use of the advantages of both the silicon material and graphite to achieve better electrochemical performance.

[0054] In the present application, the mass ratio of graphite in the negative electrode material layer is 35 wt.% to 95 wt.%. When the mass ratio of graphite in the negative electrode material layer is within the above range, the cycle performance of the negative electrode material layer can be further improved, thereby improving the cycle performance of the secondary battery.

[0055] The negative electrode current collector can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or a carbon-based current collector, and can also be a composite current collector disclosed in any prior art. In some alternative embodiments, but not limited to, the current collector formed by combining the aforementioned conductive foil and a polymer substrate.

[0056] The negative electrode material layer further includes a binder for binding the negative electrode active material particles to facilitate the formation of a film layer, and at the same time can also improve the binding force between the negative electrode material layer and the negative electrode current collector. In some embodiments, the binder may include but is not limited to polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc.

[0057] The negative electrode material layer may further include a conductive material, which includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, carbon-based materials may include, but are not limited to, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, metal-based materials may include, but are not limited to, metal powder or metal fibers, and in some optional embodiments, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0058] The negative electrode material layer may also include a dispersant, which may include at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, carboxymethyl cellulose, lithium hydroxypropyl carboxymethyl cellulose, sodium hydroxypropyl carboxymethyl cellulose, lithium hydroxyethyl carboxymethyl cellulose, sodium hydroxyethyl carboxymethyl cellulose, or hydroxyethyl carboxymethyl cellulose.

[0059] Separating membrane

[0060] The material and shape of the separator used in the secondary battery of this application are not particularly limited, and can be any technology disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application.

[0061] In some optional embodiments, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, 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 selected.

[0062] A surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixture of polymer and inorganic material. The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from 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, and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer contains a polymer, and the polymer material is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0063] The aforementioned secondary batteries are applied to electronic devices to power their loads. The secondary batteries provided in this application exhibit good capacity retention and lithium-ion acceptance after high and low temperature shock tests, thereby improving the stability of electronic devices during transitions between high and low temperatures and enhancing their versatility. These electronic devices may 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.

[0064] The present application will be described below through specific embodiments and comparative examples. Those skilled in the art should 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.

[0065] Example 1

[0066] 1. Preparation of positive electrode sheet

[0067] LiFePO4, Super-P, and polyvinylidene fluoride were mixed with N-methylpyrrolidone (NMP) in a mass ratio of 96:2:2 and stirred until homogeneous to obtain a positive electrode slurry. This positive electrode slurry was coated onto a 12μm composite aluminum foil (commercially available, a composite current collector made by depositing aluminum layers on both sides of polyethylene terephthalate (PET) using an advanced vacuum deposition process), dried, cold-pressed, and then cut and welded to obtain the positive electrode sheet.

[0068] 2. Preparation of negative electrode sheet

[0069] Artificial graphite and SiO2 (mass ratio 90:10), styrene-butadiene rubber, sodium hydroxyethyl carboxymethyl cellulose, and deionized water were mixed in a mass ratio of 96.5%:1.5%:2%. A triazine compound was then added and the mixture was stirred until homogeneous to obtain a slurry. The slurry was coated onto a 9μm copper foil. After drying and cold pressing, the foil was cut and tabs were welded to obtain the negative electrode sheet.

[0070] 3. Preparation of electrolyte

[0071] In a dry argon atmosphere, ethylene carbonate (EC), diethyl carbonate (DMC), and fluoroethylene carbonate (FEC) (weight ratio 2:2:3) were mixed, and LiPF6 was added at a concentration of 12.5% ​​to obtain a basic electrolyte. Propylene carbonate (PC) and 1,3-propanesulfonic acid lactone (PS), along with other optional substances, were added to the basic electrolyte in the amounts shown in Table 1 to obtain electrolytes for different examples and comparative examples.

[0072] 4. Preparation of the separating membrane

[0073] A 7-micron porous polyethylene polymer film was used as the separator.

[0074] 5. Preparation of secondary batteries

[0075] The obtained positive electrode, separator, and negative electrode are wound in sequence and placed in an outer packaging foil, leaving an electrolyte injection port. Electrolyte is poured in through the injection port, the battery is sealed, and then processed through formation, capacity testing, and other procedures to produce a secondary battery.

[0076] Examples 2 to 19

[0077] The difference between Examples 2 to 19 and Example 1 is that, except for adjusting the electrolyte parameters according to Table 1, they are the same as Example 1.

[0078] Comparative Examples 1 to 5

[0079] Comparative Example 1 was identical to Example 1 except that it used a conventional positive electrode current collector with a thickness of 10 μm. Comparative Examples 2 to 5 were identical to Example 1 except that the electrolyte preparation parameters were adjusted according to Table 1.

[0080] Test methods

[0081] 1. Capacity retention rate after high and low temperature shock tests

[0082] Take three batteries from each group of the prepared secondary batteries, and charge and discharge the three lithium-ion batteries respectively through the following steps, and calculate the battery discharge capacity retention rate.

[0083] First, the initial charge and discharge cycles were performed at 25°C. The battery was initially charged at a constant current of 0.5C until it reached 4.3V, then charged at a constant voltage. Finally, it was discharged at a constant current of 1C until it reached 2.8V. The discharge capacity of the first cycle was recorded. Next, the lithium-ion battery was placed at -20°C for 100 charge and discharge cycles. After the low-temperature cycle, the battery was transferred to a 45°C environment within one hour for 200 charge and discharge cycles. The discharge capacity of the 200th cycle at 45°C was recorded.

[0084] Capacity retention rate = (Discharge capacity of the 200th cycle / Discharge capacity of the first cycle) × 100%.

[0085] The following benchmarks are used for evaluation. A higher capacity retention rate indicates better performance of the secondary battery after high and low temperature shock tests.

[0086] A: Capacity retention rate is greater than 85%;

[0087] B: Capacity retention rate is greater than or equal to 80% and less than 85%;

[0088] C: Capacity retention rate is greater than or equal to 75% and less than 80%;

[0089] D: Capacity retention rate is less than 75%.

[0090] 2. Lithium-ion acceptability after high and low temperature impact testing

[0091] After the secondary battery was left to stand at 35°C for 24 hours, it was charged at a constant current of 1.0C for 1 hour at 35°C, and the high-temperature charging capacity (C0) was measured. Then, at 35°C, it was discharged at a constant current of 0.1C until it reached 3V, at which point the discharge was stopped. Next, at -15°C, it was charged at a constant current of 1.0C for 1 hour, and the low-temperature charging capacity (C1) was measured. The ratio of C1 to C0 (C1 / C0) was then calculated and evaluated using the following criteria. A higher C1 / C0 value indicates better lithium-ion acceptance at low temperatures.

[0092] A: C1 / C0 is 0.65 or higher;

[0093] B: C1 / C0 is greater than 0.55 and less than 0.65;

[0094] C: C1 / C0 is greater than 0.5 and less than 0.55;

[0095] D: C1 / C0 is less than 0.5.

[0096] [Revised according to Detailed Rules 26, 2009.06.2026] Table 1

[0097] In the table, " / " indicates that there are no relevant parameters.

[0098] As can be seen from Table 1, the positive electrode sheet includes a composite current collector and a positive electrode material layer disposed on at least one surface of the composite current collector, the positive electrode material layer including lithium iron phosphate; the electrolyte includes propylene carbonate and 1,3-propanesulfonic acid lactone and meets the content range in this application, which can improve the capacity retention and lithium ion acceptance of the secondary battery after high and low temperature impact tests.

[0099] In particular, when the electrolyte contains an appropriate amount of ethyl propionate and / or propyl propionate, it can be further combined with the composite current collector and lithium iron phosphate to optimize the positive electrode interface protection film in this application and further improve the capacity retention and lithium-ion acceptance of the secondary battery.

[0100] In particular, when the electrolyte includes trimethoxycycloboroxane, it can further improve the uniformity of the positive electrode interface film under high and low temperature shocks, and further improve the capacity retention and lithium-ion acceptance of the secondary battery.

[0101] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the principles and scope of the present application.

Claims

1. A secondary battery characterized by comprising: The secondary battery includes a positive electrode tab, a negative electrode tab, and an electrolyte, the positive electrode tab includes a composite current collector and a positive electrode material layer provided on at least one surface of the composite current collector, and the positive electrode material layer includes lithium iron phosphate; The electrolyte includes propylene carbonate and 1,3-propane sultone, a mass percentage of the propylene carbonate is Z1, and a mass percentage of the 1,3-propane sultone is Z2, based on a mass of the electrolyte, and 1≤Z1 / Z2≤40.

2. The secondary battery according to claim 1, wherein The secondary battery satisfies at least one of the following conditions: (1)5％≤Z1≤23％； (2)0.5％≤Z2≤5％。 3. The secondary battery according to claim 1 or 2, wherein The electrolyte further includes ethyl propionate, a mass percentage of the ethyl propionate is Z3, based on a mass of the electrolyte, and 5%≤Z3≤40%.

4. The secondary battery according to any one of claims 1 to 3, wherein The electrolyte further includes propyl propionate, a mass percentage of the propyl propionate is Z4, based on a mass of the electrolyte, and 8%≤Z4≤60%.

5. The secondary battery according to any one of claims 1 to 4, the electrolytic solution further comprising ethyl propionate and propyl propionate, a mass percentage of the ethyl propionate being Z3 and a mass percentage of the propyl propionate being Z4, based on the mass of the electrolytic solution, characterized in that, The secondary battery satisfies at least one of the following conditions: (1)7％≤Z1≤20％； (2)0.9％≤Z2≤3.5％； (3)8％≤Z3≤32％； (4)10％≤Z4≤50％； (5) 30%≤Z1+Z2+Z3+Z4≤70%.

6. The secondary battery according to any one of claims 1 to 5, wherein The composite current collector includes a polymer support layer and a metal conductive layer provided on at least one surface of the polymer support layer.

7. The secondary battery according to claim 6, wherein The polymer support layer includes polyethylene terephthalate and / or polypropylene.

8. The secondary battery according to any one of claims 1 to 7, wherein The electrolyte further includes trimethoxycycloboroxane.

9. The secondary battery according to any one of claims 1 to 8, wherein The negative electrode tab includes a negative electrode material layer, the negative electrode material layer includes graphite and a silicon material, and the graphite includes artificial graphite and / or natural graphite.

10. An electronic device, comprising: The secondary battery includes the secondary battery according to any one of claims 1 to 9.

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