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 battery and electronic device TECHNICAL FIELD

[0001] The present application relates to the field of electrochemical energy storage, and in particular to a secondary battery and an electronic device using the same. BACKGROUND

[0002] Secondary batteries have been increasingly applied in various fields of new energy, and thus the requirements for their performance in various aspects have been improved.

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

[0004] The present application provides a secondary battery and an electronic device using the same.

[0005] The first aspect of the present application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, the positive electrode sheet comprising a composite current collector and a positive electrode material layer arranged on at least one surface of the composite current collector, the positive electrode material layer comprising lithium iron phosphate; the electrolyte comprising propylene carbonate and 1,3-propane sultone, the mass percentage of propylene carbonate being Z1 and the mass percentage of 1,3-propane sultone being Z2 based on the mass of the electrolyte, and 1≤Z1 / Z2≤40.

[0006] In the present application, the composite current collector and the lithium iron phosphate positive electrode material jointly act, and cooperate with propylene carbonate and 1,3-propane sultone present in the electrolyte at a specific ratio, so as to improve the capacity retention rate and lithium ion acceptance of the secondary battery after high-low temperature impact test.

[0007] Based on the first aspect, in some possible implementation manners, 5%≤Z1≤23%, which can further improve the capacity retention rate and lithium ion acceptance of the secondary battery after high-low temperature impact test.

[0008] Based on the first aspect, in some possible implementation manners, 0.5%≤Z2≤5%, which can further improve the capacity retention rate and lithium ion acceptance of the secondary battery after high-low temperature impact test.

[0009] Based on the first aspect, in some possible implementation manners, the electrolyte further comprises ethyl propionate, the mass percentage of ethyl propionate being Z3 based on the mass of the electrolyte, and 5%≤Z3≤40%, which can further improve the capacity retention rate and lithium ion acceptance of the secondary battery after high-low temperature impact test.

[0010] In some possible implementation manners based on the first aspect, the electrolyte further comprises propyl propionate, and a mass percentage of the propyl propionate in the electrolyte is Z4, 8%≤Z4≤60%, which can further improve the capacity retention rate and lithium ion acceptance of the secondary battery after the high and low temperature impact test.

[0011] In some possible implementation manners based on the first aspect, 7%≤Z1≤20%, which can further improve the capacity retention rate and lithium ion acceptance of the secondary battery after the high and low temperature impact test.

[0012] In some possible implementation manners based on the first aspect, 0.9%≤Z2≤3.5%, which can further improve the capacity retention rate and lithium ion acceptance of the secondary battery after the high and low temperature impact test.

[0013] In some possible implementation manners based on the first aspect, 8%≤Z3≤32%, which can further improve the capacity retention rate and lithium ion acceptance of the secondary battery after the high and low temperature impact test.

[0014] In some possible implementation manners based on the first aspect, 10%≤Z4≤50%, which can further improve the capacity retention rate and lithium ion acceptance of the secondary battery after the high and low temperature impact test.

[0015] In some possible implementation manners based on the first aspect, 30%≤Z1+Z2+Z3+Z4≤70%, which can further improve the capacity retention rate and lithium ion acceptance of the secondary battery after the high and low temperature impact test.

[0016] In some possible implementation manners based on the first aspect, the composite current collector comprises a polymer support layer and a metal conductive layer arranged on at least one surface of the polymer support layer, which can further improve the capacity retention rate and lithium ion acceptance of the secondary battery after the high and low temperature impact test.

[0017] In some possible implementation manners based on the first aspect, the polymer support layer comprises polyethylene terephthalate and / or polypropylene, which can further improve the capacity retention rate and lithium ion acceptance of the secondary battery after the high and low temperature impact test.

[0018] In some possible implementation manners based on the first aspect, the electrolyte further comprises trimethoxycycloborane, which can further improve the capacity retention rate and lithium ion acceptance of the secondary battery after the high and low temperature impact test.

[0019] In some possible implementation manners based on the first aspect, the negative electrode sheet comprises graphite and silicon material, and the graphite comprises artificial graphite and / or natural graphite, which can further improve the capacity retention rate and lithium ion acceptance of the secondary battery after the high and low temperature impact test.

[0020] The second aspect of the present application provides an electronic device comprising a secondary battery. The secondary battery powers the electronic device. In the secondary battery, the composite current collector and the lithium iron phosphate positive electrode material jointly act, and are matched with propylene carbonate and 1,3-propanesultone present in the electrolyte in a specific ratio, which can improve the capacity retention rate and lithium ion acceptance of the secondary battery after high-low temperature impact test, thereby improving the stability of the electronic device in the conversion between high and low temperatures, and improving the universality of the electronic device. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present application are described below clearly and in detail. Obviously, the described embodiments are some of the embodiments of the present application, rather than all the embodiments. Unless otherwise defined, all the technical and scientific terms used herein have the same meanings as those commonly understood by the person skilled in the art to which the present application belongs. The terms used in the specification of the present application are only for the purpose of describing the specific embodiments, and are not intended to limit the present application.

[0022] An embodiment of the present application provides a secondary battery, which comprises a shell, an electrode assembly and an electrolyte. The electrode assembly and the electrolyte are both located in the shell.

[0023] The shell can be a packaging bag obtained by packaging with a packaging film (such as an aluminum plastic film), and the secondary battery can be a soft package battery. In other embodiments, the secondary battery can also be a steel shell battery, an aluminum shell battery, etc.

[0024] The electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator, and the separator is arranged between the positive electrode sheet and the negative electrode sheet. The electrode assembly can be a laminated structure formed by alternately stacking the positive electrode sheet, the separator and the negative electrode sheet. In other embodiments, the electrode assembly can also be a winding structure formed by winding the positive electrode sheet, the separator and the negative electrode sheet after being stacked.

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

[0026] The secondary battery provided by the application utilizes the combined action of the composite current collector and the lithium ferrous phosphate positive electrode material, and cooperates with propylene carbonate and 1,3-propanesultone in the electrolyte in a specific ratio in the secondary battery, so that the capacity retention rate and lithium ion acceptance of the secondary battery after high-low temperature impact test can be improved. It is speculated that the positive electrode system and the electrolyte system in the application can improve the binding force between the composite current collector and the lithium ferrous phosphate, and enhance the stability of the electrolyte in the application in forming a film on the positive electrode interface, and can withstand the impact of high-low temperature conversion.

[0027] In some embodiments, the value 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 consisting of any two of the above values.

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

[0029] In some embodiments, 0.5%≤Z2≤5%. The capacity retention rate and lithium ion acceptance of the secondary battery after high-low temperature impact test can be further improved. In some alternative 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 consisting of any two of the above values.

[0030] In some embodiments, the electrolyte further comprises ethyl propionate (EP), and the mass percentage of ethyl propionate in the electrolyte is Z3, 5%≤Z3≤40%. When the electrolyte system in the application further satisfies the above requirements, it can better adapt to the positive electrode system in the application, and the capacity retention rate and lithium ion acceptance of the secondary battery after high-low temperature impact test can be further improved. In some alternative 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 consisting of any two of the above values.

[0031] In some embodiments, the electrolyte further comprises propyl propionate (PP) with a mass percentage of Z4, 8%≤Z4≤60% based on the mass of the electrolyte. When the electrolyte system in the present application further satisfies the above requirements, it can better adapt to the positive electrode system of the present application, and further improve the capacity retention rate and lithium ion acceptance of the secondary battery after high-low temperature impact test. In some alternative embodiments, Z4 can be 8%, 10%, 13%, 16%, 20%, 23%, 26%, 30%, 35%, 40%, 45%, 50%, 55%, 60% or any value within the range formed by any two of the above values.

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

[0033] In some embodiments, 0.9%≤Z2≤3.5%. It can further improve the capacity retention rate and lithium ion acceptance of the secondary battery after high-low temperature impact test.

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

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

[0036] In some embodiments, 30%≤Z1+Z2+Z3+Z4≤70%. It can further improve the capacity retention rate and lithium ion acceptance of the secondary battery after high-low temperature impact test. In some alternative 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 formed by any two of the above values.

[0037] In some embodiments, the electrolyte further comprises trimethoxyboroxine with a mass percentage of 0.3% to 0.5% based on the mass of the electrolyte, which is conducive to further improving the capacity retention rate and lithium ion acceptance of the secondary battery after high-low temperature impact test.

[0038] Electrolyte

[0039] According to some embodiments of the present application, the electrolyte comprises the above-described propylene carbonate, 1,3-propane sultone, ethyl propionate, propyl propionate, trimethoxyboroxine and lithium salt.

[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), dimethyl carbonate (DMC).

[0041] In some embodiments, the organic solvent further includes an ether solvent, which in some alternative embodiments includes at least one of 1,3-dioxolane (DOL) and dimethoxyethane (DME).

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

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

[0044] Positive electrode tab

[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 use of the polymer support layer has good structural strength, which can improve the structural strength of the composite current collector, thereby facilitating further improvement in the capacity retention rate and lithium ion acceptance of the secondary battery after a high-low temperature impact test.

[0046] The polymer support layer includes polyethylene terephthalate and / or polypropylene. The above-mentioned polymer material has good thermal stability and mechanical properties as a polymer support layer.

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

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

[0049] The positive electrode material layer can further include a conductive material, including but not limited to carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, the carbon-based materials can include, but are not limited to, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, or any combination thereof. In some embodiments, the metal-based materials can include, but are not limited to, metal powders or metal fibers, in some alternative embodiments, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymers can be polyphenylene derivatives.

[0050] Negative electrode tab

[0051] In some embodiments, the negative electrode tab includes a negative current collector and a negative electrode material layer disposed on the negative 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 silicon-based substance and a composite of a silicon-based substance and a carbon-based substance, or a silicon oxide (SiOx, 0 < x < 2). The silicon-based substance can be silicon particles, silicon alloy particles, or the like.

[0053] Since the graphite has a certain flexibility, it cooperates with the silicon material to relieve the volume expansion of the negative electrode material layer as a whole. Meanwhile, the graphite and the silicon material both serve as negative active materials, which can fully utilize the advantages of both the silicon material and the graphite to achieve better electrochemical performance.

[0054] In this application, the mass percentage of the graphite in the negative electrode material layer is 35 wt.% to 95 wt.%, and the mass percentage of the graphite in the negative electrode material layer within the above range can further improve the cycle performance of the negative electrode material layer, thereby improving the cycle performance of the secondary battery.

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

[0056] The negative electrode material layer further includes a binder for binding the negative active material particles to facilitate the formation of a film layer, and can also improve the bonding force between the negative electrode material layer and the negative current collector. In some embodiments, the binder can include, but is not limited to, 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, etc.

[0057] The negative material layer can further include a conductive material including, but not limited to, a carbon-based material, a metal-based material, a conductive polymer, or any combination thereof. In some embodiments, the carbon-based material can include, but is 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 material can include, but is not limited to, metal powder or metal fiber, and in some alternative embodiments, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer can be a polyphenylene derivative.

[0058] The negative material layer can further include a dispersant including at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, carboxymethyl cellulose, lithium hydroxypropyl carboxymethyl cellulose, sodium hydroxypropyl carboxymethyl cellulose, hydroxypropyl carboxymethyl cellulose, lithium hydroxyethyl carboxymethyl cellulose, sodium hydroxyethyl carboxymethyl cellulose, or hydroxyethyl carboxymethyl cellulose.

[0059] Separator film

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

[0061] In some alternative embodiments, the separator film can include a base layer and a surface treatment layer. The base layer is a non-woven fabric, a film, or a composite film having a porous structure, and the material of the base layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used.

[0062] The surface treatment layer is provided on at least one surface of the base layer and can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic material. The inorganic layer includes inorganic particles selected from 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, and a binder selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinylalkoxide, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer includes a polymer having a material selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinylalkoxide, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0063] The secondary battery described above is applied to electronic devices to supply power to loads in the electronic devices. The secondary battery provided by the present application has good capacity retention and lithium ion acceptance after a high-low temperature impact test, thereby facilitating the improvement of the stability of the electronic device when used in the conversion between high temperature and low temperature, and improving the versatility of the electronic device. The electronic device can include, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, an illuminating appliance, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a household large storage battery, and a lithium ion capacitor, etc.

[0064] The present application is described below through specific examples and comparative examples. Those skilled in the art should understand that the preparation methods described in the present application are only examples, and any other suitable preparation method is within the scope of the present application.

[0065] Example 1

[0066] 1. Preparation of the positive electrode tab

[0067] LiFePO4, Super-P and polyvinylidene fluoride were mixed with N-methyl pyrrolidone (NMP) in a mass ratio of 96:2:2, and stirred uniformly to obtain a positive electrode slurry. The positive electrode slurry was coated on a 12 μm composite aluminum foil (commercially available, which is a composite current collector made of polyethylene terephthalate (PET) as a base material, and a metal aluminum layer deposited on both sides thereof by advanced vacuum plating process), dried, cold-pressed, and then cut and tab-welded to obtain a positive electrode tab.

[0068] 2. Preparation of the negative electrode tab

[0069] Artificial graphite and SiO2 (mass ratio 90:10), butadiene styrene rubber, sodium hydroxyethyl carboxymethyl cellulose, and deionized water were mixed in a mass ratio of 96.5%:1.5%:2%, and then a triazine compound was added and stirred uniformly to obtain a slurry. The slurry was coated on a 9 μm copper foil, dried, cold-pressed, and then cut and tab-welded to obtain a negative electrode tab.

[0070] 3. Preparation of the electrolyte

[0071] A base electrolyte was prepared by mixing ethylene carbonate (EC), diethyl carbonate (DMC) and fluoroethylene carbonate (FEC) (2:2:3 by weight) and adding LiPF6, wherein the concentration of LiPF6 was 12.5%. The electrolyte of different examples and comparative examples was prepared by adding propylene carbonate (PC) and 1,3-propane sultone (PS) and optionally other substances to the base electrolyte in the amounts shown in Table 1.

[0072] 4. Preparation of separator

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

[0074] 5. Preparation of secondary battery

[0075] The obtained positive electrode sheet, separator and negative electrode sheet were wound in order, placed in an outer packaging foil, and a liquid injection port was left. The electrolyte was filled from the liquid injection port, and the secondary battery was prepared by encapsulation, formation, capacity and other processes.

[0076] Examples 2 to 19

[0077] Examples 2 to 19 are different from Example 1 in that, in addition to adjusting the electrolyte-related parameters according to Table 1, the rest is the same as Example 1.

[0078] Comparative Examples 1 to 5

[0079] Comparative Example 1 is the same as Example 1 except that a conventional positive electrode current collector with a thickness of 10 μm is used. Comparative Examples 2 to 5 are the same as Example 1 except that the electrolyte-related preparation parameters are adjusted according to Table 1.

[0080] Test method

[0081] 1. Capacity retention rate after high and low temperature impact test

[0082] Three pieces of the prepared secondary battery were taken from each group, and the three lithium ion batteries were charged and discharged by the following steps, and the discharge capacity retention rate of the battery was calculated.

[0083] First, in an environment of 25°C, the first charge and discharge were carried out, first using a current of 0.5C for constant current charging, charging to 4.3V for constant voltage charging, then discharging at a current of 1C for constant current discharging, discharging to 2.8V, and recording the discharge capacity of the first cycle; then the lithium ion battery was placed in an environment of -20°C for 100 cycles of charge and discharge. After the low temperature cycle, the lithium ion battery was transferred to an environment of 45°C within one hour for 200 cycles of charge and discharge, and the discharge capacity of the 200th cycle under the condition of 45°C was recorded.

[0084] Capacity retention rate = (discharge capacity at 200th cycle / discharge capacity at 1st cycle) x 100%.

[0085] The higher the capacity retention rate, the more excellent the performance of the secondary battery after the high-low temperature impact test.

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

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

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

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

[0090] 2. Lithium ion acceptance after the high-low temperature impact test

[0091] After the prepared secondary battery is left to stand for 24 hours in an environment of 35°C, high-temperature charge capacity (C0) is measured by performing a charge operation for 1 hour at a constant current of 1.0C in an environment of 35°C. Then, at the time when discharge is performed to 3V at a constant current of 0.1C in an environment of 35°C, the discharge is stopped. Next, low-temperature charge capacity (C1) is measured by performing a charge for 1 hour at a constant current of 1.0C in an environment of -15°C. Then, the ratio of C1 to C0 (C1 / C0) is calculated, and the following criteria are used for evaluation. The larger the value of C1 / C0, the more excellent the lithium ion acceptance of the secondary battery at low temperature.

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

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

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

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

[0096] Table 1

[0097] In the table, " / " indicates no relevant parameter.

[0098] As can be seen from Table 1, 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, the positive electrode material layer including lithium iron phosphate; and the electrolyte includes propylene carbonate and 1,3-propane sultone and satisfies the content range in the present application, which can improve the capacity retention rate and lithium ion acceptance of the secondary battery after the high-low temperature impact test.

[0099] In particular, when ethyl propionate and / or propyl propionate is included in the electrolyte in a suitable amount, it can further cooperate with the composite current collector and lithium iron phosphate, optimize the positive electrode interface protection film in the application, and further improve the capacity retention rate and lithium ion acceptance of the secondary battery.

[0100] In particular, when trimethoxycycloboroxane is included in the electrolyte, the uniformity of the positive electrode interface film under high and low temperature impact can be further improved, and the capacity retention rate and lithium ion acceptance of the secondary battery can be further improved.

[0101] Although the illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments cannot be interpreted as a limitation of the application, and changes, substitutions and modifications can be made to the embodiments without departing from the principles and scope of the 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, characterized by, 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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