Secondary battery and electric device

Abstract

The invention provides a secondary battery and electric equipment. The secondary battery comprises a positive pole piece, the positive pole piece comprises a positive current collector and a positive active material layer arranged on at least one side of the positive current collector, and the positive active material layer comprises a manganese-iron-lithium oxide; the positive pole piece meets the condition that S1 / (S1 + S2) is larger than or equal to 2.9% and smaller than or equal to 9.7%, S1 is the peak area located at the 531.1 ev position in the XPS map of the positive pole piece, and S2 is the peak area located at the 532.7 ev position in the XPS map of the positive pole piece. According to the invention, the peak area S1 at the 531.1 ev and the peak area S2 at the 532.7 ev in the XPS map of the positive pole piece containing the manganese-iron-lithium oxide are controlled to meet a certain relationship, so that the rate capability of the secondary battery is improved.

Description

Technical Field

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

[0002] Since their successful commercial application in the 1990s, secondary batteries have developed rapidly, not only dominating the field of portable electronic devices, but also expanding their applications to plug-in hybrid electric vehicles (PHEVs), electric vehicles (EVs), and large-scale energy storage power stations. The large-scale application of secondary batteries in these emerging fields urgently needs to improve the rate performance of batteries to consolidate their own advantages.

[0003] Lithium iron manganese oxide (LiMn x Fe 1-x PO4) cathode materials have attracted more and more attention because of their higher voltage platform. x Fe 1-x The PO4 positive electrode material has an olivine structure and belongs to the orthorhombic Pnma space group. During charging and discharging, the transmission of active ions is affected by FeO6, MnO6 and PO4, and can only be transmitted in one dimension in a wavy shape, which leads to low diffusion efficiency of active ions. During charging and discharging, the material transforms between lithium manganese iron phosphate and manganese iron phosphate. At the same time, FeO6, MnO6, LiO6 octahedrons and PO4 tetrahedrons share edges, which greatly limits their electronic conductivity. Summary of the invention

[0004] The purpose of the present application is to provide a secondary battery and an electrical device to improve the rate performance of the existing secondary battery using manganese iron lithium oxide as the positive electrode active material.

[0005] To achieve the above object, in a first aspect of the present application, a secondary battery is provided, the secondary battery comprising a positive electrode plate, the positive electrode plate comprising a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector, the positive electrode active material layer comprising manganese iron lithium oxide;

[0006] The positive electrode sheet satisfies: 2.9%≤S1 / (S1+S2)≤9.7%, wherein S1 is the peak area at 531.1ev in the XPS spectrum of the positive electrode sheet, and S2 is the peak area at 532.7ev in the XPS spectrum of the positive electrode sheet.

[0007] As an embodiment of the present application, the positive electrode active material layer further includes a positive electrode conductor, and the positive electrode conductor includes carbon aerogel.

[0008] As an embodiment of the present application, the manganese iron lithium oxide contains vanadium element.

[0009] As an embodiment of the present application, the positive electrode sheet satisfies: 0.46%≤M V / (M Mn +M Fe )≤3.35%, where M V is the mass percentage of vanadium in the positive electrode sheet, M Mn is the mass percentage of manganese element in the positive electrode sheet, M Fe is the mass percentage of the iron element in the positive electrode sheet.

[0010] As an embodiment of the present application, 0.16%≤M V ≤1.14%, of which M V is the mass percentage of vanadium element in the positive electrode plate.

[0011] As an implementation scheme of the present application, 9.44%≤M Fe ≤10.5%, of which M Fe is the mass percentage of the iron element in the positive electrode sheet.

[0012] As an embodiment of the present application, 3.8%≤S1 / (S1+S2)≤9.2%.

[0013] As an embodiment of the present application, the EPR test spectrum of the positive electrode sheet has a symmetrical peak at g=2.003.

[0014] As an implementation scheme of the present application, the manganese iron lithium oxide satisfies: Eg≤2.63 eV, wherein Eg is the band gap width of the manganese iron lithium oxide in an ultraviolet visible light diffuse reflection test.

[0015] A second aspect of the present application provides an electrical device, wherein the electrical device comprises the secondary battery described in the first aspect of the present application.

[0016] Compared with the prior art, the beneficial effects of this application are:

[0017] The present application provides a secondary battery, which improves the rate performance of the secondary battery by controlling the peak area S1 at 531.1 ev and the peak area S2 at 532.7 ev in the XPS spectrum of a positive electrode sheet containing manganese iron lithium oxide to satisfy a certain relationship. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application are described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

[0019] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0020] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0021] The reagents or instruments used in this application without indicating the manufacturer are all conventional products that can be obtained through commercial purchase.

[0022] An embodiment of the present application provides a secondary battery, the secondary battery comprising a positive electrode plate, the positive electrode plate comprising a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector, the positive electrode active material layer comprising manganese iron lithium oxide;

[0023] The positive electrode sheet satisfies: 2.9%≤S1 / (S1+S2)≤9.7%, wherein S1 is the peak area at 531.1ev in the XPS (X-ray photoelectron spectroscopy) spectrum of the positive electrode sheet, and S2 is the peak area at 532.7ev in the XPS spectrum of the positive electrode sheet.

[0024] In some embodiments, 3.8%≤S1 / (S1+S2)≤9.2%. Exemplarily, S1 / (S1+S2) can be any one of 3.8%, 4.2%, 4.8%, 5.5%, 6.1%, 6.8%, 7.3%, 7.9%, 8.7%, 9.2%, or a range between any two values. S1 and S2 satisfy the above relationship, which can further improve the rate performance of the secondary battery. S1 and S2 are obtained by performing XPS testing on the positive electrode sheet according to X-ray photoelectron spectroscopy to obtain an XPS spectrum, and obtaining the peak area S1 at 531.1ev in the XPS (X-ray photoelectron spectroscopy) spectrum and the peak area S2 at 532.7ev by fitting and analyzing the XPS spectrum.

[0025] In some embodiments, the manganese iron lithium oxide contains vanadium. The manganese iron lithium oxide further contains vanadium, which improves the lithium ion diffusion rate and electronic conductivity of the manganese iron lithium oxide, provides a fast channel for the diffusion of lithium ions and the transmission of electrons, thereby further improving the rate performance of the prepared secondary battery.

[0026] In some embodiments, the positive electrode sheet satisfies: 0.46%≤M V / (M Mn +M Fe )≤3.35%, where M V is the mass percentage of vanadium in the positive electrode sheet, M Mn is the mass percentage of manganese element in the positive electrode sheet, M Fe is the mass percentage of iron in the positive electrode sheet. V / (M Mn +M Fe ) can be any value among 0.46%, 0.75%, 1.08%, 1.55%, 1.88%, 2.12%, 2.63%, 2.99%, 3.35%, or a range between any two values. V / (M Mn +M Fe ) Within the above range, the rate performance of the secondary battery can be further improved. The contents of vanadium, iron and manganese in the positive electrode sheet are obtained by ICP testing.

[0027] In some embodiments, 0.16%≤M V ≤1.14%, of which M V is the mass percentage of vanadium in the positive electrode. Exemplarily, the mass percentage of vanadium in the positive electrode can be any one of 0.16%, 0.26%, 0.35%, 0.45%, 0.55%, 0.65%, 0.75%, 0.85%, 0.95%, 1.05%, 1.14%, or a range between any two values. The content of vanadium in the above range can further improve the lithium ion diffusion rate and electronic conductivity, thereby improving the rate performance of the secondary battery.

[0028] In some embodiments, 9.44%≤M Fe ≤10.5%, of which M Feis the mass percentage of the iron element in the positive electrode sheet. Exemplarily, the mass percentage of the iron element in the positive electrode sheet can be any one of 9.44%, 9.65%, 9.85%, 9.97%, 10.15%, 10.3%, 10.5%, or a range between any two values. The content of the iron element within the above range can ensure that the secondary battery has both high rate performance and long cycle life.

[0029] In some embodiments, the EPR (electron paramagnetic resonance) test spectrum of the positive electrode sheet has a symmetrical peak at g=2.003. The EPR test spectrum has a symmetrical peak at g=2.003, which can provide more channels for the diffusion and transmission of active ions and electrons in the material layer, thereby improving the rate performance of the secondary battery. The EPR test spectrum is obtained by performing an EPR test on the positive electrode sheet using electron paramagnetic resonance technology to obtain an EPR spectrum.

[0030] In some embodiments, the manganese iron lithium oxide satisfies: Eg≤2.63eV, where Eg is the band gap width of the manganese iron lithium oxide in the ultraviolet visible light diffuse reflection test. The band gap width of the manganese iron lithium oxide is less than or equal to 2.63eV, indicating that the conductivity of the manganese iron lithium phosphate is relatively high, which can further improve the rate performance of the secondary battery.

[0031] In some embodiments, the positive electrode active material layer comprises a positive electrode conductive agent, and the positive electrode conductive agent comprises carbon aerogel. In some embodiments, the mass percentage of the positive electrode conductive agent in the positive electrode active material layer is less than or equal to 1%.

[0032] In some embodiments, the manganese iron lithium oxide includes carbon-coated manganese iron lithium phosphate.

[0033] In some embodiments, the secondary battery includes a positive electrode sheet, the positive electrode sheet includes a positive current collector and a positive electrode active material layer disposed on at least one side of the positive current collector, the positive electrode active material layer includes manganese iron lithium oxide, and the manganese iron lithium oxide includes vanadium; the positive electrode sheet satisfies: 2.9%≤S1 / (S1+S2)≤9.7%, wherein S1 is the peak area at 531.1ev in the XPS spectrum of the positive electrode sheet, and S2 is the peak area at 532.7ev in the XPS spectrum of the positive electrode sheet. The manganese iron lithium oxide includes vanadium, and the positive electrode sheet satisfies the above relationship, which can further improve the rate performance of the secondary battery.

[0034] In some embodiments, the method for preparing the manganese iron lithium oxide comprises the following steps:

[0035] S1. A manganese source, an iron source, a vanadium source and deionized water are mixed, a protective atmosphere is introduced, and then phosphoric acid is added to produce ferromanganese phosphate precipitate and the pH value is adjusted to 2.5 to 5.5 so that the precipitate is uniformly nucleated, the formed precipitate is washed and dried, and then sintered for the first time in a protective atmosphere to obtain vanadium-doped ferromanganese phosphate spherical particles;

[0036] S2. The vanadium-doped ferromanganese phosphate particles are added to the prepared lithium source solution, spray-dried, and sintered for a second time in a protective atmosphere to obtain vanadium-doped spherical lithium manganese iron phosphate particles;

[0037] S3. The vanadium-doped spherical lithium manganese iron phosphate particles are placed in a mixed reducing atmosphere for a third sintering to obtain spherical lithium manganese iron phosphate particles containing oxygen vacancies and vanadium-doped;

[0038] S4. adding vanadium-doped spherical lithium manganese iron phosphate particles containing oxygen vacancies to the prepared carbon source solution, spray-drying the particles, and then sintering the particles for the fourth time in a protective atmosphere to obtain the lithium manganese iron oxide.

[0039] In some embodiments, the first sintering temperature is 650-750° C., and the sintering time is 6-12 hours.

[0040] In some embodiments, the second sintering temperature is 720-780° C., and the sintering time is 6-12 hours.

[0041] In some embodiments, the temperature of the third sintering is 680-920° C., and the sintering time is 0.5-1.5 h.

[0042] In some embodiments, the temperature of the fourth sintering is 650-750° C., and the sintering time is 2-6 hours.

[0043] In some embodiments, the manganese source includes one or more of manganese carbonate (MnCO3), manganese oxalate (MnC2O4), manganese acetate (Mn(CH3COO)2), manganese dioxide (MnO2), manganese trioxide (Mn2O3), and manganese tetraoxide (Mn3O4).

[0044] In some embodiments, the iron source includes but is not limited to one or more of ferric hydroxide (Fe(OH)3), ferric phosphate (FePO4), ferric acetate (C4H7FeO5), ferric carbonate (Fe2(CO3)3), ferrous oxide (Fe2O3), ferrosoferric oxide (Fe3O4), and ferrous oxalate (FeC2O4).

[0045] In some embodiments, the vanadium source includes, but is not limited to, one or more of vanadium dioxide (VO2) and vanadium pentoxide (V2O5).

[0046] In some embodiments, the lithium source includes but is not limited to one or more of lithium carbonate (Li2CO3), lithium acetate (CH3COOLi), lithium hydroxide (LiOH), lithium dihydrogen phosphate (LiH2PO4), and lithium phosphate (Li3PO4).

[0047] In some embodiments, the carbon source includes, but is not limited to, one or more of glucose, xylitol, and polyvinyl alcohol.

[0048] In some embodiments, the protective atmosphere includes but is not limited to argon, nitrogen, or a mixture of the two.

[0049] In some embodiments, the spray drying air inlet temperature is 250-300° C., and the spray drying air outlet temperature is 90-130° C. In some embodiments, the spray drying is performed using a centrifugal spray dryer or a two-fluid spray dryer.

[0050] In some embodiments, the mixed reducing atmosphere comprises reducing gas and inert gas, and the volume ratio of the reducing gas to the inert gas is 1 to 3:9 to 7. The reducing gas comprises hydrogen and / or carbon monoxide, and the inert gas comprises nitrogen and / or argon.

[0051] In some embodiments, the secondary battery further comprises a negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material.

[0052] The type of negative electrode active material is not specifically limited and can be selected according to actual needs. For example, the negative electrode material can be artificial graphite, natural graphite, silicon-carbon composite material, silicon oxide, hard carbon, lithium metal and lithium titanate.

[0053] The type of negative electrode current collector is not particularly limited and can be selected according to actual needs. Preferably, copper foil or carbon-coated copper foil can be used.

[0054] In some embodiments, the negative electrode active material layer further includes a negative electrode conductive agent, wherein the negative electrode conductive agent includes at least one of conductive carbon black, carbon nanotubes, and graphene.

[0055] In some embodiments, the secondary battery further comprises a separator. The type of separator is not particularly limited and can be selected according to actual needs. The separator can be a polypropylene film, a polyethylene film, a polyvinylidene fluoride, a spandex film, an aramid film, or a multilayer composite film modified by a coating.

[0056] In some embodiments, the preparation of a secondary battery includes: stacking the positive electrode sheet, the separator, and the negative electrode sheet in order, so that the separator is between the positive and negative electrode sheets to play an isolating role, and then winding them into a square bare cell, loading them into a battery casing, and then baking them at 65 to 95°C to remove water, injecting electrolyte, sealing, and obtaining a secondary battery after standing, hot and cold pressing, formation, capacity division and other processes.

[0057] In some embodiments, the secondary battery may include an outer package, which may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery may also be a soft package, such as a bag-type soft package, and the material of the soft package may be plastic, such as one or more of polypropylene, polybutylene terephthalate, polybutylene succinate, etc.

[0058] In some embodiments, the shape of the secondary battery is not particularly limited, and it can be cylindrical, square, or any other shape.

[0059] In some embodiments, the ratio of the secondary battery 10C discharge gram capacity to the 0.1C discharge gram capacity is greater than 0.5. For example, the ratio of the secondary battery 10C discharge gram capacity to the 0.1C discharge gram capacity can be any one of 0.54, 0.58, 0.60, 0.62, 0.64, 0.66 or a range between any two values.

[0060] In some embodiments, the ratio of the 10C discharge gram capacity to the 0.1C discharge gram capacity of the secondary battery is 0.54-0.65.

[0061] In some embodiments, the secondary battery 10C discharge capacity is greater than 158.8 mAh / g.

[0062] In some embodiments, the secondary battery has a 0.1C discharge capacity greater than 86.7 mAh / g.

[0063] The second aspect of the present application provides an electric device, which includes the secondary battery described in the first aspect of the present application. The electric device can be an application device such as a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, and an electric tool. The vehicle can be a new energy vehicle, and the new energy vehicle can be a pure electric vehicle, a hybrid vehicle, or an extended-range vehicle, etc.; the spacecraft includes an airplane, a rocket, a space shuttle, and a spacecraft, etc.; the electric toy includes a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric airplane toy, etc.; the electric tool includes a metal cutting electric tool, a grinding electric tool, an assembly electric tool, and a railway electric tool, such as an electric drill, an electric grinder, an electric wrench, an electric screwdriver, an electric hammer, an impact drill, a concrete vibrator, and an electric planer, etc. The embodiments of the present application do not impose any special restrictions on the above-mentioned devices.

[0064] The following are specific embodiments of the present application, and the technical scheme of the present application is further described in conjunction with the embodiments, but the present application is not limited to these embodiments. The reagents, methods and equipment used in the present application, unless otherwise specified, are conventional reagents, methods and equipment in the art.

[0065] Example 1

[0066] Embodiment 1 provides a secondary battery, and the specific preparation process of the secondary battery includes:

[0067] (1) Preparation of positive electrode active materials

[0068] S1. 80.5 g of manganese carbonate (MnCO3), 22.4 g of ferric oxide (Fe2O3), 1.82 g of vanadium pentoxide (V2O5) and 400 g of deionized water were added to a round-bottom flask, and argon protective gas was introduced into the container, 980 g of a 10% phosphoric acid solution was slowly added to the round-bottom flask to produce a ferromanganese phosphate precipitate, and the pH value was adjusted at any time to be stable at 5, so that the ferromanganese phosphate was uniformly nucleated, and the formed ferromanganese phosphate precipitate was washed 6 times with 800 g of deionized water, and then vacuum dried at 80 ° C for 2 hours, followed by sintering at 720 ° C in an argon atmosphere for 8 hours to obtain vanadium-doped ferromanganese phosphate particles;

[0069] S2. Take 37g of lithium carbonate (Li2CO3) and add an appropriate amount of deionized water to prepare a solution with a mass concentration of 10%, add vanadium-doped ferromanganese phosphate particles to the lithium carbonate solution, spray dry, sinter at 760 ° C in a tube furnace with argon as a protective atmosphere for 8 hours to obtain vanadium-doped spherical lithium manganese iron phosphate particles;

[0070] S3. Spherical lithium manganese iron phosphate particles were sintered at 700° C. for 1 hour in a mixed atmosphere of hydrogen and argon (volume ratio of 1:9) to obtain lithium manganese iron phosphate particles containing oxygen vacancies and doped with vanadium;

[0071] S4. Take 34g of glucose to prepare a 20% mass concentration solution, add lithium manganese iron phosphate particles containing oxygen vacancies and doped with vanadium and fully stir it, spray dry it, and sinter it at 720°C in an argon atmosphere for 4 hours to obtain a positive electrode active material.

[0072] (2) Preparation of positive electrode sheet

[0073] The positive electrode active material, conductive carbon aerogel and binder polyvinylidene fluoride (PVDF) are evenly mixed in a mass ratio of 98.6:0.7:0.7, and evenly dispersed with 1-methyl-2-pyrrolidone (NMP) in a disperser to form a positive electrode slurry. The obtained positive electrode slurry is coated on both sides of an aluminum foil using a coating machine, and then baked, rolled and cut to obtain a positive electrode sheet.

[0074] (3) Preparation of negative electrode sheet

[0075] The negative electrode material graphite, the conductive agent carbon black, the thickener CMC, and the binder SBR are mixed in a mass ratio of 94.3:1.5:1.2:3, and the solvent deionized water is added. The mixture is stirred in a stirrer until the system becomes uniform to obtain a negative electrode slurry. The negative electrode slurry is evenly coated on the negative electrode collector copper foil, placed in an oven for drying, and rolled and cut to obtain a negative electrode sheet.

[0076] (4) Preparation of electrolyte

[0077] Organic solvents ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate were mixed in a volume ratio of 1:1:1. In an argon atmosphere glove box with a water content of <10 ppm, fully dried lithium hexafluorophosphate was dissolved in the above organic solvents to a content of 1 mol / L, and mixed evenly to obtain an electrolyte.

[0078] (5) Preparation of secondary batteries

[0079] The positive electrode sheet, the separator (polyethylene), and the negative electrode sheet are wound in order to obtain a bare cell; the bare cell is placed in an outer packaging shell, vacuum dried, injected with electrolyte, left to stand, formed, shaped, and capacity divided to obtain a secondary battery.

[0080] Example 2

[0081] Embodiment 2 provides a secondary battery, which is mainly different from Embodiment 1 in that the volume ratio of the mixed atmosphere of hydrogen and argon in step S3 is 1:4.

[0082] Example 3

[0083] Embodiment 3 provides a secondary battery, which is mainly different from Embodiment 1 in that the volume ratio of the mixed atmosphere of hydrogen and argon in step S3 is 3:7.

[0084] Example 4

[0085] Embodiment 4 provides a secondary battery, which is mainly different from Embodiment 1 in that the sintering temperature in step S3 is 800°C.

[0086] Example 5

[0087] Embodiment 5 provides a secondary battery, which is mainly different from Embodiment 1 in that the volume ratio of the mixed atmosphere of hydrogen and argon in step S3 is 1:4, and the sintering temperature in step S3 is 800°C.

[0088] Example 6

[0089] Embodiment 6 provides a secondary battery, which is mainly different from Embodiment 1 in that the volume ratio of the mixed atmosphere of hydrogen and argon in step S3 is 3:7, and the sintering temperature in step S3 is 800°C.

[0090] Example 7

[0091] Embodiment 7 provides a secondary battery, which is mainly different from Embodiment 1 in that the sintering temperature in step S3 is 900°C.

[0092] Example 8

[0093] Embodiment 8 provides a secondary battery, which is mainly different from Embodiment 1 in that the volume ratio of the mixed atmosphere of hydrogen and argon in step S3 is 1:4, and the sintering temperature in step S3 is 900°C.

[0094] Example 9

[0095] Embodiment 9 provides a secondary battery, which is mainly different from Embodiment 1 in that the volume ratio of the mixed atmosphere of hydrogen and argon in step S3 is 3:7, and the sintering temperature in step S3 is 900°C.

[0096] Example 10

[0097] Embodiment 10 provides a secondary battery, which is mainly different from Embodiment 5 in that the mass of Fe2O3 in step S1 is 23.6 g, and the mass of V2O5 is 0.46 g.

[0098] Embodiment 11

[0099] Example 11 provides a secondary battery, which is mainly different from Example 5 in that the mass of Fe2O3 in step S1 is 21.2 g, and the mass of V2O5 is 3.19 g.

[0100] Example 12

[0101] Example 12 provides a secondary battery, which is mainly different from Example 5 in that vanadium pentoxide doping is not used in step S1, and the mass of Fe2O3 is 24g.

[0102] Comparative Example 1

[0103] Comparative Example 1 provides a secondary battery, which is different from Example 1 in that the preparation method of the positive electrode active material is different, as follows:

[0104] S1. 80.5 g of manganese carbonate (MnCO3), 24 g of ferric oxide (Fe2O3) and 400 g of deionized water were added to a round-bottom flask, and argon protective gas was introduced into the container. 980 g of a 10% phosphoric acid solution was slowly added to the round-bottom flask to produce ferromanganese phosphate precipitate, and the pH value was adjusted at any time to be stable at 5, so that the ferromanganese phosphate nucleated uniformly, and the formed ferromanganese phosphate precipitate was washed 6 times with 800 g of deionized water, and then vacuum dried at 80 ° C for 2 hours, and then sintered at 720 ° C in an argon atmosphere for 8 hours to obtain ferromanganese phosphate particles;

[0105] S2. Take 37g of lithium carbonate (Li2CO3) and add an appropriate amount of deionized water to prepare a solution with a mass concentration of 10%, add ferromanganese phosphate particles to the lithium carbonate solution, spray dry, sinter in a tube furnace at 760 ° C for 8 hours with argon as a protective atmosphere to obtain spherical lithium manganese phosphate particles;

[0106] S3. Take 34g of glucose to prepare a 20% mass concentration solution, add spherical lithium manganese iron phosphate particles and stir them thoroughly. After spray drying, sinter at 720°C in an argon atmosphere for 4 hours to obtain a positive electrode active material.

[0107] Comparative Example 2

[0108] Comparative Example 2 provides a secondary battery, which is different from Example 1 in that the preparation method of the positive electrode active material is different, as follows:

[0109] S1. 80.5 g of manganese carbonate (MnCO3), 22.4 g of ferric oxide (Fe2O3), 1.82 g of vanadium pentoxide (V2O5) and 400 g of deionized water were added to a round-bottom flask, and argon protective gas was introduced into the container, 980 g of a 10% phosphoric acid solution was slowly added to the round-bottom flask to produce a ferromanganese phosphate precipitate, and the pH value was adjusted at any time to be stable at 5, so that the ferromanganese phosphate was uniformly nucleated, and the formed ferromanganese phosphate precipitate was washed 6 times with 800 g of deionized water, and then vacuum dried at 80 ° C for 2 hours, followed by sintering at 720 ° C in an argon atmosphere for 8 hours to obtain vanadium-doped ferromanganese phosphate particles;

[0110] S2. Take 37g of lithium carbonate (Li2CO3) and add an appropriate amount of deionized water to prepare a solution with a mass concentration of 10%, add vanadium-doped ferromanganese phosphate particles to the lithium carbonate solution, spray dry, sinter at 760 ° C in a tube furnace with argon as a protective atmosphere for 8 hours to obtain vanadium-doped spherical lithium manganese iron phosphate particles;

[0111] S3. Take 34g of glucose to prepare a 20% mass concentration solution, add spherical lithium manganese iron phosphate particles and stir them thoroughly. After spray drying, sinter at 720°C in an argon atmosphere for 4 hours to obtain a positive electrode active material.

[0112] The physical properties of the positive electrode active materials and positive electrode sheets in Examples 1 to 12 and Comparative Examples 1 to 2 are shown in Table 1.

[0113] Table 1

[0114]

[0115] The rate performance of the secondary batteries prepared in each embodiment and comparative example was tested. Normal temperature rate performance test: At 25±2°C, the prepared soft-pack battery was charged and discharged at 0.1C / 10C for 5 cycles at each rate. Different rate performance data were obtained, and the respective average values ​​were recorded in Table 2.

[0116] Table 2

[0117]

[0118] It can be seen from the above embodiments and comparative examples that the rate performance of the secondary battery is improved by controlling the peak area S1 at 531.1 ev and the peak area S2 at 532.7 ev in the XPS spectrum of the positive electrode sheet containing manganese iron lithium oxide to satisfy: 2.9%≤S1 / (S1+S2)≤9.7%.

[0119] In addition, by comparing Example 5 with Examples 10 to 12, it can be seen that by using lithium manganese iron phosphate containing vanadium as the positive electrode active material and controlling the contents of vanadium, manganese and iron in the positive electrode sheet to satisfy a certain relationship, the rate performance of the secondary battery can be further improved.

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present application rather than to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, ordinary technicians in this field should understand that the technical solution of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present application.

Claims

1. A secondary battery, characterized in that: The invention comprises a positive electrode plate, wherein the positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode active material layer comprises manganese iron lithium oxide; The positive electrode sheet satisfies: 2.9%≤S1 / (S1+S2)≤9.7%, wherein S1 is the peak area at 531.1ev in the XPS spectrum of the positive electrode sheet, and S2 is the peak area at 532.7ev in the XPS spectrum of the positive electrode sheet.

2. The secondary battery according to claim 1, characterized in that: The manganese iron lithium oxide contains vanadium element.

3. The secondary battery according to claim 1, characterized in that: The positive electrode active material layer further includes a positive electrode conductor, and the positive electrode conductor includes carbon aerogel.

4. The secondary battery according to any one of claims 1 to 3, characterized in that: The positive electrode sheet satisfies: 0.46%≤M V / (M Mn +M Fe )≤3.35%, where M V is the mass percentage of vanadium in the positive electrode sheet, M Mn is the mass percentage of manganese element in the positive electrode sheet, M Fe is the mass percentage of the iron element in the positive electrode sheet.

5. The secondary battery according to claim 4, characterized in that: 0.16%≤M V ≤1.14%, of which M V is the mass percentage of vanadium element in the positive electrode plate.

6. The secondary battery according to claim 4, characterized in that: 9.44%≤M Fe ≤10.5%, of which M Fe is the mass percentage of the iron element in the positive electrode sheet.

7. The secondary battery according to any one of claims 1 to 3, characterized in that: 3.8%≤S1 / (S1+S2)≤9.2%.

8. The secondary battery according to any one of claims 1 to 3, characterized in that: The EPR test spectrum of the positive electrode sheet has a symmetrical peak at g=2.

003.

9. The secondary battery according to any one of claims 1 to 3, characterized in that: The manganese iron lithium oxide satisfies: Eg≤2.63 eV, wherein Eg is the band gap width of the manganese iron lithium oxide in an ultraviolet visible light diffuse reflection test.

10. An electrical device, characterized in that: The electrical equipment comprises the secondary battery according to any one of claims 1 to 9.

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