Positive electrode sheet, battery, and electric device

Abstract

The present disclosure provides a positive electrode sheet, a battery, and an electric device. The positive electrode sheet comprises a positive electrode active material, and the positive electrode active material comprises lithium manganese iron phosphate particles. The molar ratio of manganese to iron in the positive electrode active material is a; the acidity growth rate of the positive electrode sheet is h; k = b / L, wherein L is the depth of the XPS etching of the positive electrode sheet, and has a value of 10 nm; k is the peak intensity ratio of a B1s peak at the position with a binding energy of 188-192 eV in an XPS graph during XPS etching analysis of the positive electrode sheet; and b is the peak intensity of the B1s peak at the position with a binding energy of 188-192 eV in an XPS graph; and a, k and h satisfy the following relational expression: a×h / k=8×10-4-10. In the positive electrode plate, by controlling the manganese-iron ratio, the acidity growth rate and the peak intensity ratio when the positive electrode sheet is etched for a certain depth, a stable CEI film containing B is formed on the surface of the positive electrode sheet, thereby inhibiting the dissolution of manganese ions, reducing the consumption of active lithium, and improving the cycle.

Description

A positive electrode, a battery, and an electrical device Technical Field

[0001] This disclosure pertains to the field of battery technology, and particularly relates to a positive electrode, a battery, and an electrical device. Background Technology

[0002] With the development of technology and industry, the importance of the energy storage capacity of lithium-ion batteries has been gradually recognized; however, the problem of transition metal dissolution occurs frequently in almost all layered transition metal oxide cathodes.

[0003] For the LMFP (lithium manganese iron phosphate) system, the dissolution of Mn ions affects the stability of the cathode material itself, while the deposition of Mn ions on the anode leads to the loss of active lithium and the gradual deterioration of the SEI film on the anode, which is an important reason for the lifespan degradation.

[0004] Therefore, improving battery cycle life and extending battery life is an urgent problem that needs to be solved. Summary of the Invention

[0005] In this disclosure, the inventors unexpectedly discovered that by controlling the manganese-iron ratio, the acidity growth rate, and the peak intensity ratio at a certain etching depth in the positive electrode, a stable boron (B)-containing solid electrolyte interphase (CEI) film can be formed on the surface of the positive electrode, preventing manganese ion dissolution, reducing active lithium consumption, and improving cycle life.

[0006] Based on the above findings, this disclosure provides a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material, the positive electrode active material comprising lithium manganese iron phosphate particles;

[0007] The molar ratio of manganese to iron in the positive electrode active material is a; the acidity growth rate of the positive electrode sheet is h, in %; and

[0008] k = b / L, where L is the XPS etching depth of the positive electrode, taken as 10 nm; k is the peak intensity ratio of the B1s peak at the position of 188-192 eV binding energy in the XPS image when the positive electrode is etched at 10 nm, in units of counts / s / nm; b is the peak intensity of the B1s peak at the position of 188-192 eV binding energy in the XPS image when the positive electrode is etched, in units of counts / s;

[0009] Wherein, a, k, and h satisfy the following relationship: 8×10 -4 ≤a×h / k≤10.

[0010] By controlling the manganese-iron ratio, acidity growth rate, and peak intensity ratio at a certain etching depth, a stable CEI film containing boron can be formed on the surface of the positive electrode, preventing manganese ion dissolution, reducing active lithium consumption, and improving cycle life.

[0011] In the specific embodiments disclosed herein, 0.02 ≤ a × h / k ≤ 3.

[0012] In the specific embodiments disclosed herein, 0.1 ≤ a ≤ 9.

[0013] In the specific embodiments disclosed herein, 0.4 ≤ a ≤ 2.5.

[0014] In the specific embodiments disclosed herein, 5 ≤ k ≤ 400.

[0015] In the specific embodiments disclosed herein, 9 ≤ k ≤ 108.

[0016] In a specific embodiment of this disclosure, the acidity growth rate h is 3% to 18%.

[0017] In a specific embodiment of this disclosure, the acidity growth rate h is 4% to 16%.

[0018] In a specific embodiment of this disclosure, the lithium manganese iron phosphate particles comprise primary particles, the particle size of which ranges from 50 nm to 170 nm.

[0019] Preferably, the XPS etching depth is 10 nm and the peak intensity of the B1s peak is F1; the XPS etching depth is 35 nm and the peak intensity of the B1s peak is F2.

[0020] The difference between F1 and F2 is greater than 0 and less than or equal to 2000.

[0021] In another aspect, this disclosure provides a battery including a positive electrode, a negative electrode, a separator, and an electrolyte;

[0022] The positive electrode is the positive electrode described in the above technical solution.

[0023] In specific embodiments of this disclosure, the electrolyte and / or the positive electrode contains a boron-containing compound.

[0024] In specific embodiments of this disclosure, the electrolyte contains a boron-containing compound selected from one or more of lithium bis(trimethylsilane)borate, tri(trimethylsilane)borate, lithium difluorooxalate borate, lithium tetrafluoroborate, tributyl borate, and trimethyl borate.

[0025] In another aspect, this disclosure provides an electrical device that includes the battery described in the above technical solution.

[0026] This disclosure describes the use of the above-mentioned battery in the manufacture of electrical devices. The battery can be used as a power source for the electrical devices or as an energy storage unit for the electrical devices, thus expanding the application range of the battery. Attached Figure Description

[0027] Figure 1 shows the XPS pattern of the positive electrode prepared in Example 12 of this disclosure at an etching depth of 10 nm. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions in the embodiments of this disclosure will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this disclosure, not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0029] In this disclosure, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0030] In this disclosure, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0031] In this disclosure, there are no particular restrictions on the specific methods of dispersion and mixing.

[0032] Unless otherwise specified, all reagents or instruments used in this disclosure are commercially available products.

[0033] This disclosure provides a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material, the positive electrode active material comprising lithium manganese iron phosphate particles;

[0034] The molar ratio of manganese to iron in the positive electrode active material is a; the acidity growth rate of the positive electrode sheet is h, in %; and

[0035] k = b / L, where k is the peak intensity ratio of the B1s peak at the position of binding energy 188-192 eV in the XPS image when performing XPS etching analysis on the positive electrode, in units of counts / s / nm; L is the depth of XPS etching on the positive electrode, with a value of 10 nm; b is the peak intensity of the B1s peak at the position of binding energy 188-192 eV in the XPS image when performing XPS etching analysis on the positive electrode, in units of counts / s;

[0036] Wherein, a, k, and h satisfy the following relationship: 8×10 -4≤a×h / k≤10.

[0037] By controlling the manganese-iron ratio, acidity growth rate, and peak intensity ratio at a certain etching depth, a stable boron (B) CEI film is formed on the surface of the positive electrode, which prevents manganese ions from dissolving, reduces active lithium consumption, and improves cycle life.

[0038] In this disclosure, 'a' represents the molar ratio of manganese to iron.

[0039] In this disclosure, the preferred value of 'a' is 0.1 ≤ a ≤ 9. If the value of 'a' is too high, the transition metal dissolution will be severe, which may worsen the cycling process; if the value of 'a' is lower than the above preferred value, the specific capacity utilization may be worsened. Specifically, the value of 'a' can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4... 4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, or 9.0.

[0040] More preferably, within the range of 0.4≤a≤2.5, the battery has better cycle performance.

[0041] In specific embodiments of this disclosure, the value of 'a' is 0.1, 2.8, 0.5, 2.3, 1.5, 0.4, 2.5, 1.5, 2, 0.4, 0.2, 9, 0.08, or 10.

[0042] In this disclosure, k represents the peak intensity ratio of boron during XPS etching. Its value reflects the boron content in the surface layer of the positive electrode, indicating a certain amount of boron in the solid electrolyte interphase (CEI) film formed on the surface of the positive electrode active material. K is the peak intensity ratio of the B1s peak at the binding energy position of 188-192 eV in the XPS image during XPS etching analysis of the positive electrode, reflecting the boron content in the surface layer of the positive electrode, with units of counts / s / nm. Where k = b / L, b is the peak intensity of the B1s peak at the binding energy position of 188-192 eV in the XPS image during XPS etching analysis of the positive electrode. For example, peak intensity indirectly reflects the boron content; a higher peak intensity indicates a higher boron content at this depth. L is the depth of XPS etching of the positive electrode, with units of nm. The role of element B in the surface layer: Element B is electron-deficient and can combine with anions or anionic groups to form polyanionic groups. Its molecular orbital energy level is high and it is easily oxidized. It can also directly participate in the formation of CEI in the form of anionic groups, thereby protecting the positive electrode and reducing the risk of manganese leaching from the positive electrode active material.

[0043] Preferably, the value of k in this disclosure satisfies 5 ≤ ​​k ≤ 400; within the above preferred range, the positive electrode can be protected, and excessive dissolution of transition metals can be avoided; at the same time, the increase in impedance and the degradation of cycle performance can be avoided. The value of k can be 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200, 205, 21 0, 215, 220, 225, 230, 235, 240, 245, 250, 255, 260, 265, 270, 275, 280, 285, 290, 295, 300, 305, 310, 315, 320, 325, 330, 335, 340, 345, 350, 355, 360, 365, 370, 375, 380, 385, 390, 395 or 400.

[0044] More preferably, 9 ≤ k ≤ 108; the specific value of k can be 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104 or 105.

[0045] In specific embodiments of this disclosure, the value of k is 400, 5, 108, 12, 45, 95, 9, 380, 43, 90, 7, 125, 100 or 20.

[0046] In this disclosure, h represents the acidity growth rate, expressed as a percentage (%). The acidity growth rate is the rate of increase in hydrogen ion content generated when the positive electrode is immersed in a mixed solution containing lithium perchlorate, due to side reactions between the positive electrode active material and the electrolyte, electron gain and loss, EC borrowing electrons from LMFP during charging and discharging, and EC undergoing ring-opening dehydrogenation. Controlling the acidity growth rate within a certain range can protect the positive electrode, reduce excessive side reactions between the positive electrode and the electrolyte, and ensure kinetic performance. Excessive acidity growth rate increases side reactions between lithium manganese iron phosphate and the electrolyte, worsening cycle performance; insufficient acidity growth rate increases solid-phase diffusion of lithium ions, deteriorating kinetic performance. Therefore, the preferred acidity growth rate h is 3–18%, more preferably 4–16%.

[0047] In this disclosure, the specific values ​​of h can be 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, or 18%.

[0048] In specific embodiments of this disclosure, the acidity growth rate h can be 3.2, 17.5, 4.5, 15.5, 7, 4.2, 16, 15, 16.2, 5, 3, 18, 2 or 19.

[0049] This disclosure does not limit the testing of acidity growth rate; those skilled in the art can perform the test using conventional methods. For example, the test can be conducted using the following methods:

[0050] Take 3 pieces of 7×7cm 2The fully charged positive electrode was immersed in a mixed solution of EC, EMC, and lithium perchlorate (total mixed capacity 20 ml, EC to EMC mass ratio 3:7, lithium perchlorate addition 1 mol / L), stored at 60℃ for 2 days, and the H2 content in the solution was measured. + Measure m1ppm; continue storage at 60℃ for 3 days, and measure H in the solution. + Measure m2ppm; obtain H + The growth rate, i.e., the acidity growth rate h, is (m2-m1) / m1.

[0051] The a, k, and h described in this disclosure satisfy the following relationship: a × h / k = 8 × 10 -4 ~10; In the above formula, if the upper limit is exceeded, the manganese content is high and the acidity growth rate is relatively large, if the B content is too low, a dense and stable CEI film cannot be formed on the positive electrode, resulting in more manganese dissolution, greater consumption of active lithium, and deterioration of cycle performance; If the above formula exceeds the lower limit, the boron (B) content is too high, which leads to an increase in interfacial impedance (Rct), SEI film carbon source (Rsei), and diffusion impedance (Ws) during the cycle, resulting in poor cycle performance.

[0052] Specifically, a×h / k=0.0008, 0.0009, 0.001, 0.0015, 0.0020, 0.0025, 0.0030, 0.0035, 0.0040, 0.0045, 0.0050, 0.0060, 0.0070, 0.0080, 0.0090, 0.0095, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0 0.14, 0.1436, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2.0, 2.5, 3.0, 3.5, 4, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5 or 10.0.

[0053] In this disclosure, the preferred range of a×h / k is 0.02 to 3; within this range, the cycle performance of the battery is better.

[0054] In the specific embodiments of this disclosure, a×h / k = 0.0008, 9.800, 0.0208, 2.9708, 0.2333, 0.0177, 4.4444, 0.0592, 0.7200, 0.0222, 0.0857, 1.2960, 0.0016, or 9.5000.

[0055] The positive electrode sheet provided in this disclosure includes lithium manganese iron phosphate particles as the active material. These lithium manganese iron phosphate particles comprise primary particles, with an average particle size ranging from 50 to 170 nm, or possibly 70 to 160 nm. Specifically, the average particle size of the primary particles is 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, 105 nm, 110 nm, 115 nm, 120 nm, 125 nm, 130 nm, 135 nm, 140 nm, 145 nm, 150 nm, 155 nm, 160 nm, 165 nm, or 170 nm. This disclosure does not regulate the adjustment method of the primary particle size; the particle size can be changed by controlling the sintering process or the grinding process. In specific embodiments of this disclosure, the particle size of the primary particles can be 162nm, 76nm, 151nm, 95nm, 130nm, 155nm, 93nm, 92nm, 41nm, 202nm, 132nm, 200nm, or 136nm.

[0056] The positive electrode sheet disclosed herein uses XPS to characterize the intensity of boron (B) at a certain etching depth. In a preferred embodiment of this disclosure, the peak intensity (F1) at 10 nm and the peak intensity (F2) at 35 nm satisfy a value greater than 0 and less than or equal to 2000. In this disclosure, B is mainly present in the CEI film layer on the surface of the positive electrode sheet. B primarily participates in the formation of the CEI film layer on the positive electrode surface. The presence of B on the surface contributes to the stability and density of the CEI film layer. If B were present in the active material layer, the direct contact between the electrode and the electrolyte would cause corrosion of the positive electrode active material by the electrolyte, thereby reducing the cycle stability of the battery. By limiting the peak intensity to a value greater than 0 and less than or equal to 2000, B is present on the surface, playing a role in stabilizing the CEI film layer and avoiding the problem of excessive B on the surface. In this disclosure, the difference between F1 and F2 can specifically be 45, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, 1300, 1350, 1400, 1450, 1500, 1550, 1600, 1650, 1700, 1750, 1800, 1850, 1900, 1950, or 2000.

[0057] In specific embodiments of this disclosure, the difference between F1 and F2 can be 3950, 45, 600, 100, 420, 880, 75, 3550, 400, 750, 50, 980, 890 or 160.

[0058] This disclosure allows for the formation of a uniform CEI film on the positive electrode surface by adjusting the boron content in the positive electrode, thereby inhibiting manganese ion dissolution, reducing the consumption of active lithium, and improving the battery's cycle performance. The electrolyte and / or positive electrode may contain boron-containing compounds.

[0059] The boron element can be introduced by adding a boron-containing compound to the electrolyte, wherein the boron-containing compound is selected from one or more of lithium bis(trimethylsilane)borate (LiBOB), tri(trimethylsilane)borate (TMSB), lithium difluorooxalate borate (LIODFB), lithium tetrafluoroborate, tributyl borate, and trimethyl borate.

[0060] The boron element can be used to form a coating layer on the surface of the positive electrode active material; or a dopant M can be added during the slurry mixing process; the dopant M is selected from one or more of boric acid, organoborane, borohydride and metal borides; the boron-containing compound in the coating layer is selected from metal borides and / or borate LiMBO3.

[0061] The positive electrode sheet described in the above technical solution of this disclosure includes a positive electrode active material; the positive electrode active material includes lithium manganese iron phosphate particles (LMFP);

[0062] This disclosure does not limit the preparation method of the positive electrode active material; those skilled in the art can prepare the positive electrode active material using conventional techniques. Exemplarily, the preparation method of the positive electrode active material includes the following steps:

[0063] The lithium source, manganese source, iron source and phosphorus source required for the synthesis of lithium manganese iron phosphate material are weighed in proportion and added to deionized water, and then ground to obtain lithium manganese iron phosphate precursor slurry.

[0064] Add a coated carbon source and mix it evenly with the lithium manganese iron phosphate precursor slurry, grind it, adjust the solid content and spray dry it to obtain dry powder.

[0065] The dry powder is sintered under a protective atmosphere and then cooled to obtain the positive electrode active material.

[0066] The above method yields agglomerated lithium manganese iron phosphate with relatively large particle size; the agglomerated lithium manganese iron phosphate is composed of multiple primary particles.

[0067] In some other embodiments, the synthesized positive electrode active material can be crushed and graded for screening; thus, small particles of lithium manganese iron phosphate can be obtained, wherein small particles of lithium manganese iron phosphate refer to a single particle, or there may be two or three particles connected together without being broken.

[0068] In Table 1 below this disclosure, the primary particle size refers to the primary particle size in the aggregate; or the small particle size.

[0069] The lithium source described in this disclosure is selected from at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxalate, lithium dihydrogen phosphate, lithium citrate, and lithium acetate. The manganese source is selected from at least one of manganese carbonate, manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate. The iron source is selected from at least one of ferrous oxalate, ferric hydroxide, ferrous hydroxide, ferric phosphate, ferrous phosphate, ferric acetate, ferrous acetate, ferric carbonate, ferrous carbonate, ferric oxide, magnetite, and ferric oxalate. The phosphorus source is selected from at least one of diammonium hydrogen phosphate, lithium dihydrogen phosphate, ammonium phosphate, and lithium phosphate. Preferably, ferromanganese phosphate is used as the manganese, iron, and phosphorus source simultaneously; more preferably, ferric phosphate is used as the iron and phosphorus source simultaneously.

[0070] In preparing lithium manganese iron phosphate particles, this disclosure allows for the doping of other elements, such as vanadium, tungsten, titanium, and magnesium, as needed. To provide these elements, the vanadium source can be selected from vanadium pentoxide, the tungsten source from ammonium metatungstate, the titanium source from titanium oxide, and the magnesium source from magnesium carbonate. The content of other doped elements in this disclosure is based on the total molar ratio of manganese to iron, and is preferably 1000–5000 ppm. The structural formula of the lithium manganese iron phosphate particles described in this disclosure is: LiMn x Fe y M z n PO4, where x is greater than 0 and less than 1; y is greater than 0 and less than 1; z is greater than or equal to 0 and less than 1; n refers to the valence of the dopant element; 2(x+y)+n×z=2.

[0071] In this disclosure, the carbon source content is based on the total amount of solid matter in the lithium manganese iron phosphate precursor slurry, preferably 5% to 35%, and the specific carbon source content is 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, or 35%.

[0072] In specific embodiments of this disclosure, the carbon source content is 30%, 12%, 25%, 17%, 20%, 28%, 15%, 16%, 5%, 20%, 28%, 12%, 35%, or 10%.

[0073] This disclosure involves mixing a lithium source, a manganese source, an iron source, and a phosphorus source to obtain a lithium iron manganese slurry, which is then mixed with a coated carbon source. The coated carbon source is selected from at least one of glucose, polyethylene glycol, acetylene black, glycine, starch, acetylene black, sucrose, phenolic resin, and ascorbic acid. The solvent used in this disclosure is water and / or ethanol. The grinding method in this disclosure can be ball milling.

[0074] This disclosure describes sintering a precursor using a gradient sintering method; the gradient sintering includes:

[0075] Preheat the temperature to 150–630℃ at a rate of 4–6℃ / min for 280–330 min, then calcine at 300–950℃ at a rate of 9–11℃ / min for 700–750 min.

[0076] This disclosure preferably uses natural cooling to obtain lithium manganese iron phosphate particles.

[0077] The cathode active material in this disclosure preferably further comprises lithium iron phosphate (LFP), with the specific structural formula of LiFePO4. The mass ratio of lithium manganese iron phosphate particles to lithium iron phosphate in this disclosure is 0.14–56. In specific embodiments of this application, the mass ratio of LMFP to LFP is 0.14, 56.0, 0.81, 13.14, 4, 0.61, 20, 4, 8, 0.61, 0.29, 0.11, or 22.2.

[0078] In addition to the positive electrode active material, the positive electrode sheet provided in this disclosure may also include a conductive agent and a binder. The mass ratio of the positive electrode active material, the conductive agent, and the binder in this disclosure may be 96:(0.1-3):(3.9-1).

[0079] The conductive agent included in the positive electrode sheet provided in this disclosure only needs to have suitable electronic conductivity and not cause adverse chemical changes in the battery. This disclosure does not impose any particular limitation on the type of conductive agent. Specifically, the conductive agent can be at least one of carbon nanotubes, carbon black, and graphene.

[0080] The binder included in the positive electrode sheet provided in this disclosure is used to improve the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. In this disclosure, the binder can be a conventional choice in the battery industry. Specifically, the binder can be at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyacrylate, polyolefin, sodium carboxymethyl cellulose (CMC), and sodium alginate.

[0081] The positive electrode sheet provided in this disclosure also includes a positive electrode current collector. This disclosure does not impose any particular limitation on the positive electrode current collector, as long as it is conductive and will not cause adverse chemical changes in the battery, and materials such as stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel that has undergone a surface treatment of carbon, nickel, titanium, silver, etc. can be used.

[0082] In this disclosure, the positive electrode sheet can be prepared according to conventional methods in the art. For example, the positive electrode active material, conductive agent and binder are dispersed in a solvent such as NMP (N-methylpyrrolidone) to form a uniform positive electrode slurry. The positive electrode slurry is coated on the positive electrode current collector, and after drying, rolling and other processes, the positive electrode sheet is obtained.

[0083] This disclosure also provides a battery, including a positive electrode, a negative electrode, a separator, and an electrolyte;

[0084] The positive electrode is any one of the positive electrode sheets described in the above technical solutions.

[0085] The battery disclosed herein exhibits excellent cycle performance by employing the aforementioned positive electrode.

[0086] This disclosure introduces boron into the prepared battery by incorporating a boron-containing compound into the electrolyte and / or the positive electrode. The boron-containing compound in the electrolyte described in this disclosure is selected from one or more of lithium bis(trimethylsilane)borate (LiBOB), tris(trimethylsilane)borate (TMSB), lithium difluorooxalate borate (LIODFB), lithium tetrafluoroborate, tributyl borate, and trimethyl borate.

[0087] In this disclosure, boron is introduced into the positive electrode sheet, which can be used to form a coating layer on the surface of the positive electrode active material; alternatively, a dopant M can be added during the slurry mixing process. The boron-containing compound in the coating layer is selected from metal borides and / or borates such as LiMBO3; the dopant M is selected from one or more of boric acid, organoboranes, borohydrides, and metal borides.

[0088] In this disclosure, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector, the negative electrode film layer containing a negative electrode active material.

[0089] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer can be disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0090] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector; for example, copper foil can be used as the metal foil. The composite current collector can include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer substrate (such as polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0091] This disclosure provides an electrical device, including the battery described in the above technical solution.

[0092] The battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0093] To further illustrate this disclosure, the following detailed description of a positive electrode, battery, and electrical device provided by this disclosure is provided in conjunction with embodiments, but these should not be construed as limiting the scope of protection of this disclosure.

[0094] Example 1

[0095] (1) Lithium manganese iron phosphate (LiMn) 0.75 Fe 0.25 PO4) cathode material: according to LiMn 0.75 Fe 0.25 Lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate were weighed out according to the molar ratios of Li, Mn, Fe, and P in the chemical formula PO4, respectively. These were added to deionized water and mixed, then ball-milled to obtain a lithium manganese iron phosphate precursor slurry. 30% glucose was then weighed and mixed evenly with the lithium manganese iron phosphate precursor slurry, and ball-milled for 20 hours. The solid content was then adjusted and spray-dried to obtain a dry powder. The dry powder was then calcined in a tube furnace at a heating rate of 5℃ / min to 600℃ for 300 minutes, followed by a heating rate of 10℃ / min to 800℃ for 720 minutes. After natural cooling, a solid powder was obtained. The solid powder was then crushed, and after 8 hours of crushing, it was screened to obtain the target material LiMn. 0.75 Fe 0.25 PO4 cathode material.

[0096] (2) Preparation of positive electrode: The above-obtained lithium manganese iron phosphate (LiMn) is prepared by... 0.75 Fe 0.25 The cathode material is a homogeneous mixture of lithium iron phosphate (LiFePO4) and lithium iron phosphate (LiFePO4) at a Mn / Fe molar ratio of 1:10, with an LMFP to LFP blending ratio of 0.14. The main material, conductive agent SP, and binder polyvinylidene fluoride (PVDF) are mixed homogeneously in NMP at a mass ratio of 96:3:1. Subsequently, the mixed cathode slurry is prepared with a surface density of 400 g / m³. 2 The positive electrode is uniformly coated on aluminum foil and dried in a vacuum furnace at 100°C to obtain a positive electrode sheet, which is then slit; subsequently, it is rolled and cut to obtain a positive electrode sheet.

[0097] (3) The electrolyte uses ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 3:7wt% as the solvent system, 1.15M LiPF6 as the lithium salt, and additives containing 3300ppm of element B, lithium bis(oxalato)borate (LiBOB), 1% vinylene carbonate (VC), and 1% methanedisulfonate (MMDS) as film-forming additives.

[0098] (4) Preparation of negative electrode sheet

[0099] The negative electrode active material (artificial graphite), conductive agent (SP), and binder (carboxymethyl cellulose, CMC) are mixed in a mass ratio of 96.4:1:2.6 and dispersed in deionized water to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated onto the negative electrode current collector (copper foil). The negative electrode current collector coated with the negative electrode slurry is transferred to a vacuum environment in an oven and dried at 100°C. It is then rolled, cut, and baked to obtain the negative electrode sheet.

[0100] (5) Preparation of the diaphragm

[0101] A polyethylene (PE) diaphragm is used.

[0102] (6) Battery manufacturing

[0103] The prepared positive electrode, separator, and negative electrode are wound to obtain an unfilled bare cell; the bare cell is placed in an outer packaging foil, and the prepared electrolyte is injected into the dried bare cell. After vacuum sealing, settling, formation, shaping, and sorting, a lithium-ion battery is obtained.

[0104] Example 2

[0105] (1) Lithium manganese iron phosphate (LiMn) 0.75 Fe 0.25 PO4) cathode material: according to LiMn 0.75 Fe 0.25 Lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate were weighed out according to the molar ratios of Li, Mn, Fe, and P in the chemical formula PO4. These were then added to deionized water and mixed. The mixture was ball-milled to obtain a lithium manganese iron phosphate precursor slurry. 12% glucose was then weighed and mixed evenly with the lithium manganese iron phosphate precursor slurry. The mixture was ball-milled for 20 hours, and the solid content was adjusted before spray drying to obtain a dry powder. The dry powder was then calcined in a tube furnace at a heating rate of 5℃ / min to 200℃ for 300 minutes, followed by a heating rate of 10℃ / min to 400℃ for 720 minutes. After natural cooling, LiMn was obtained. 0.75 Fe 0.25 PO4 material.

[0106] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn) 0.75 Fe 0.25 The main material is a homogeneous mixture of lithium iron phosphate (LiFePO4) and lithium iron phosphate (LiFePO4) cathode materials at a Mn / Fe molar ratio of 2.8, with an LMFP to LFP blend ratio of 56.0. The main material, conductive agent SP, and binder are mixed uniformly in NMP at a mass ratio of 96:0.2:3.8. Finally, trimethyl borate containing 45 ppm of element B is added, and the mixture is stirred further. The resulting cathode slurry is then prepared with a surface density of 400 g / m³. 2The coating is evenly applied to aluminum foil and dried in a vacuum furnace at 100°C to obtain a positive electrode sheet, which is then slit; subsequently, it is rolled and cut to obtain a positive electrode sheet.

[0107] (3) The electrolyte uses EC:EMC = 3:7wt% as the solvent system, 1.15M LiPF6 as the lithium salt, and 1%VC and 1%MMDS as film-forming additives.

[0108] (4) Preparation of negative electrode sheet: Same as in Example 1.

[0109] (5) Preparation of the diaphragm: Same as in Example 1.

[0110] (6) Battery preparation: Same as in Example 1.

[0111] Example 3

[0112] (1) Lithium manganese iron phosphate (LiMn) 0.75 Fe 0.25 PO4) cathode material: according to LiMn 0.75 Fe 0.25 Lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate were weighed out according to the molar ratios of Li, Mn, Fe, and P in the chemical formula PO4. These were then added to deionized water and mixed, followed by ball milling to obtain a lithium manganese iron phosphate precursor slurry. 25% glucose was then weighed and mixed evenly with the lithium manganese iron phosphate precursor slurry, and ball milled for 20 hours. The solid content was then adjusted, and the mixture was spray-dried to obtain a dry powder. The dry powder was then mixed evenly with boric acid (900 ppm B content) and calcined in a tube furnace. The temperature was increased to 400℃ at a rate of 5℃ / min for 300 minutes, then increased to 750℃ at a rate of 10℃ / min for 720 minutes. After natural cooling, a solid powder was obtained. This solid powder was then crushed for 6 hours to obtain LiMn. 0.75 Fe 0.25 PO4 material.

[0113] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn) 0.75 Fe 0.25 The main material is a homogeneous mixture of lithium iron phosphate (LiFePO4) and lithium iron phosphate (LiFePO4) cathode materials at a Mn / Fe molar ratio of 0.5, with an LMFP to LFP blending ratio of 0.81. The main material, conductive agent SP, and binder are mixed homogeneously in NMP at a mass ratio of 96:2.5:1.5. Subsequently, the mixed cathode slurry is prepared with a surface density of 400 g / m³. 2 The positive electrode is uniformly coated on aluminum foil and dried in a vacuum furnace at 100°C to obtain a positive electrode sheet, which is then slit; subsequently, it is rolled and cut to obtain a positive electrode sheet.

[0114] (3) The electrolyte is the same as in Example 2.

[0115] (4) Preparation of negative electrode sheet: Same as in Example 1.

[0116] (5) Preparation of the diaphragm: Same as in Example 1.

[0117] (6) Battery preparation: Same as in Example 1.

[0118] Example 4

[0119] (1) Lithium manganese iron phosphate (LiMn) 0.75 Fe 0.25 PO4) cathode material: according to LiMn 0.75 Fe 0.25 Lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate were weighed out according to the molar ratios of Li, Mn, Fe, and P in the PO4 chemical formula. Deionized water was added, and the mixture was ball-milled to obtain a lithium manganese iron phosphate precursor slurry. Then, 17% glucose was weighed and mixed evenly with the lithium manganese iron phosphate precursor slurry, and ball-milled for 15 hours. The solid content was then adjusted, and the mixture was spray-dried to obtain a dry powder. The dry powder was then calcined in a tube furnace at a heating rate of 5℃ / min to 300℃ for 300 minutes, followed by a heating rate of 10℃ / min to 500℃ for 720 minutes. After natural cooling, LiMn was obtained. 0.75 Fe 0.25 PO4 material.

[0120] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn) 0.75 Fe0 .25 Lithium iron phosphate (LiFePO4) and lithium iron phosphate (LiFePO4) cathode materials were mixed uniformly as the main material at a Mn / Fe molar ratio of 2.3, with an LMFP to LFP blend ratio of 13.14. The main material, conductive agent SP, and binder were mixed uniformly in NMP at a mass ratio of 96:0.8:3.2. Subsequently, the mixed cathode slurry was prepared with a surface density of 400 g / m³. 2 The positive electrode is uniformly coated on aluminum foil and dried in a vacuum furnace at 100°C to obtain a positive electrode sheet, which is then slit; subsequently, it is rolled and cut to obtain a positive electrode sheet.

[0121] (3) The electrolyte is different from that in Example 1: LiBOB, an additive containing 130 ppm of element B, is used.

[0122] (4) Preparation of negative electrode sheet: Same as in Example 1.

[0123] (5) Preparation of the diaphragm: Same as in Example 1.

[0124] (6) Battery preparation: Same as in Example 1.

[0125] Example 5

[0126] (1) Lithium manganese iron phosphate (LiMn) 0.75 Fe 0.25 PO4) cathode material: according to LiMn 0.75 Fe 0.25 Lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate were weighed out according to the molar ratios of Li, Mn, Fe, and P in the chemical formula PO4. These were added to deionized water and mixed. The mixture was then ball-milled to obtain a lithium manganese iron phosphate precursor slurry. 20% glucose was then weighed and mixed evenly with the lithium manganese iron phosphate precursor slurry. The mixture was ball-milled for 20 hours, and the solid content was adjusted before spray drying to obtain a dry powder. The dry powder was then calcined in a tube furnace at a heating rate of 5℃ / min to 400℃ for 300 minutes, followed by a heating rate of 10℃ / min to 600℃ for 720 minutes. After natural cooling, a solid powder was obtained. The solid powder was crushed and, after 12 hours, LiMn was obtained. 0.75 Fe 0.25 PO4 material.

[0127] (2) Preparation of positive electrode sheet:

[0128] Lithium manganese iron phosphate (LiMn) 0.75 Fe 0.25 Lithium iron phosphate (LiFePO4) and lithium iron phosphate (LiFePO4) cathode materials are mixed uniformly as the main material at a Mn / Fe molar ratio of 1.5, with an LMFP to LFP blending ratio of 4. The main material, conductive agent SP, and binder are mixed uniformly in NMP at a mass ratio of 96:1:3. Subsequently, the mixed cathode slurry is prepared with a surface density of 400 g / m³. 2 The coating is evenly applied to aluminum foil and dried in a vacuum furnace at 100°C to obtain a positive electrode sheet, which is then slit; subsequently, it is rolled and cut to obtain a positive electrode sheet.

[0129] (3) Preparation of negative electrode: Same as in Example 1.

[0130] (4) Electrolyte preparation: Compared with Example 1, LIODFB additive containing 380ppm B element was selected.

[0131] (5) Preparation of the separator: PP is used as the separator.

[0132] (6) Battery preparation: Same as in Example 1.

[0133] Example 6

[0134] (1) Lithium manganese iron phosphate (LiMn) 0.75 Fe 0.25 PO4) cathode material: according to LiMn 0.75 Fe 0.25Lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate were weighed out according to the molar ratios of Li, Mn, Fe, and P in the chemical formula PO4. These were added to deionized water and mixed. The mixture was then ball-milled to obtain a lithium manganese iron phosphate precursor slurry. 28% glucose was then weighed and mixed evenly with the lithium manganese iron phosphate precursor slurry. The mixture was ball-milled for 20 hours, and the solid content was adjusted before spray drying to obtain a dry powder. The dry powder was then calcined in a tube furnace at a heating rate of 5℃ / min to 400℃ for 300 minutes, followed by a heating rate of 10℃ / min to 800℃ for 720 minutes. After natural cooling, a solid powder was obtained. This solid powder was then crushed for 6 hours to obtain LiMn. 0.75 Fe 0.25 PO4 material.

[0135] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn) 0.75 Fe 0.25 The main material is a homogeneous mixture of lithium iron phosphate (LiFePO4) and lithium iron phosphate (LiFePO4) cathode materials at a Mn / Fe molar ratio of 0.4, with an LMFP to LFP blending ratio of 0.61. The main material, conductive agent SP, and binder are mixed homogeneously in NMP at a mass ratio of 96:3:1. Subsequently, the mixed cathode slurry is prepared with a surface density of 400 g / m³. 2 The positive electrode is uniformly coated on aluminum foil and dried in a vacuum furnace at 100°C to obtain a positive electrode sheet, which is then slit; subsequently, it is rolled and cut to obtain a positive electrode sheet.

[0136] (3) Compared with the example, the electrolyte used is LIODFB, which contains 805 ppm of boron.

[0137] (4) Preparation of negative electrode sheet: Same as in Example 1.

[0138] (5) Preparation of the diaphragm: Same as in Example 1.

[0139] (6) Battery preparation: Same as in Example 1.

[0140] Example 7:

[0141] (1) Lithium manganese iron phosphate (LiMn) 0.75 Fe 0.25 PO4) cathode material: according to LiMn 0.75 Fe 0.25Lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate were weighed out according to the molar ratios of Li, Mn, Fe, and P in the PO4 chemical formula. Deionized water was added, and the mixture was ball-milled to obtain a lithium manganese iron phosphate precursor slurry. Then, 15% glucose was weighed and mixed evenly with the lithium manganese iron phosphate precursor slurry, and ball-milled for 22 hours. The solid content was then adjusted, and the mixture was spray-dried to obtain a dry powder. The dry powder was then calcined in a tube furnace at a heating rate of 5℃ / min to 250℃ for 300 minutes, followed by a heating rate of 10℃ / min to 450℃ for 720 minutes. After natural cooling, LiMn was obtained. 0.75 Fe 0.25 PO4 material.

[0142] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn) 0.75 Fe 0.25 The main material is a homogeneous mixture of lithium iron phosphate (LiFePO4) and lithium iron phosphate (LiFePO4) cathode materials at a Mn / Fe molar ratio of 2.5, with an LMFP to LFP blend ratio of 20. The main material, conductive agent SP, and binder are mixed homogeneously in NMP at a mass ratio of 96:0.3:3.7. Subsequently, the mixed cathode slurry is prepared with a surface density of 400 g / m³. 2 The positive electrode is uniformly coated on aluminum foil and dried in a vacuum furnace at 100°C to obtain a positive electrode sheet, which is then slit; subsequently, it is rolled and cut to obtain a positive electrode sheet.

[0143] (3) Compared with Example 1, the electrolyte is made of trimethyl borate, which contains 80 ppm of element B.

[0144] (4) Preparation of negative electrode sheet: Same as in Example 1.

[0145] (5) Preparation of the diaphragm: Same as in Example 1.

[0146] (6) Battery preparation: Same as in Example 1.

[0147] Example 8:

[0148] (1) Lithium manganese iron phosphate (LiMn) 0.75 Fe 0.25 PO4) cathode material: according to LiMn 0.75 Fe 0.25Lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate were weighed out according to the molar ratios of Li, Mn, Fe, and P in the PO4 chemical formula. Deionized water was added, and the mixture was ball-milled to obtain a lithium manganese iron phosphate precursor slurry. Then, 20% glucose was weighed and mixed evenly with the lithium manganese iron phosphate precursor slurry, and ball-milled for 20 hours. The solid content was then adjusted, and the mixture was spray-dried to obtain a dry powder. The dry powder was then calcined in a tube furnace at a heating rate of 5℃ / min to 400℃ for 300 minutes, followed by a heating rate of 10℃ / min to 480℃ for 720 minutes. After natural cooling, LiMn was obtained. 0.75 Fe 0.25 PO4 material.

[0149] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn) 0.75 Fe 0.25 The cathode materials are mainly composed of lithium iron phosphate (LiFePO4) and lithium iron phosphate (LiFePO4) mixed uniformly at a Mn / Fe molar ratio of 1.5, with an LMFP to LFP blending ratio of 4. The main materials, conductive agent SP, and binder are mixed uniformly in NMP at a mass ratio of 96:1:3. Subsequently, the mixed cathode slurry is prepared with a surface density of 400 g / m³. 2 The positive electrode is uniformly coated on aluminum foil and dried in a vacuum furnace at 100°C to obtain a positive electrode sheet, which is then slit; subsequently, it is rolled and cut to obtain a positive electrode sheet.

[0150] (3) Preparation of negative electrode: Same as in Example 1.

[0151] (4) Compared with Example 1, the electrolyte is made of tributyl borate additive containing 3210 ppm of element B.

[0152] (5) Preparation of the diaphragm: Same as in Example 1.

[0153] (6) Battery preparation: Same as in Example 1.

[0154] Example 9:

[0155] 1) Preparation of LMFP cathode material: according to LiMn 0.75 Fe 0.25Lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate were weighed out according to the molar ratios of Li, Mn, Fe, and P in the chemical formula PO4. These were then added to deionized water and mixed, followed by ball milling to obtain a lithium manganese iron phosphate precursor slurry. 20% glucose was then weighed and mixed evenly with the lithium manganese iron phosphate precursor slurry, and ball milled for 30 hours. The solid content was then adjusted, and the mixture was spray-dried to obtain a dry powder. The dried powder was then calcined in a tube furnace at a heating rate of 5℃ / min to 150℃ for 300 minutes, followed by a heating rate of 10℃ / min to 300℃ for 720 minutes. After natural cooling, LiMn was obtained. 0.75 Fe 0.25 PO4 material.

[0156] 2) Cathode preparation: Lithium manganese iron phosphate (LiMn) is prepared... 0.75 Fe 0.25 The cathode materials, namely lithium iron phosphate (LiFePO4) and lithium iron phosphate (LiFePO4), are mixed uniformly as the main material at a Mn / Fe molar ratio of 2, with an LMFP to LFP blending ratio of 8. The main material, conductive agent SP, and binder are mixed uniformly in NMP at a mass ratio of 96:1.5:2.5. Subsequently, the mixed cathode slurry is prepared with a surface density of 400 g / m³. 2 The positive electrode is uniformly coated on aluminum foil and dried in a vacuum furnace at 100°C to obtain a positive electrode sheet, which is then slit; subsequently, it is rolled and cut to obtain a positive electrode sheet.

[0157] 3) Preparation of negative electrode sheet: Same as in Example 1.

[0158] 4) Compared with Example 1, the electrolyte used is trimethyl borate additive containing 350 ppm of element B.

[0159] Example 10:

[0160] (1) Lithium manganese iron phosphate (LiMn) 0.75 Fe 0.25 PO4) cathode material: according to LiMn 0.75 Fe 0.25 Lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate were weighed out according to the molar ratios of Li, Mn, Fe, and P in the chemical formula PO4. These were added to deionized water and mixed. The mixture was then ball-milled to obtain a lithium manganese iron phosphate precursor slurry. 20% glucose was then weighed and mixed evenly with the lithium manganese iron phosphate precursor slurry. The mixture was ball-milled for 20 hours, and the solid content was adjusted before spray drying to obtain a dry powder. The dry powder was then calcined in a tube furnace at a heating rate of 5℃ / min to 650℃ for 300 minutes, followed by a heating rate of 10℃ / min to 900℃ for 720 minutes. After natural cooling, a solid powder was obtained. This solid powder was then crushed for 9 hours to obtain LiMn.0.75 Fe 0.25 PO4 material

[0161] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn) 0.75 Fe 0.25 The cathode materials, namely lithium iron phosphate (LiFePO4) and lithium iron phosphate (LiFePO4), are mixed uniformly as the main material at a Mn / Fe molar ratio of 0.4, with an LMFP to LFP blending ratio of 0.61. The main material, conductive agent SP, and binder are mixed uniformly in NMP at a mass ratio of 96:1.5:2.5. Subsequently, the mixed cathode slurry is prepared with a surface density of 400 g / m³. 2 The positive electrode is uniformly coated on aluminum foil and dried in a vacuum furnace at 100°C to obtain a positive electrode sheet, which is then slit; subsequently, it is rolled and cut to obtain a positive electrode sheet.

[0162] (3) Preparation of negative electrode: Same as in Example 1.

[0163] (4) Compared with Example 1, the electrolyte is made of trimethyl borate additive containing 760 ppm of element B.

[0164] (5) Preparation of the diaphragm: Same as in Example 1.

[0165] (6) Battery preparation: Same as in Example 1.

[0166] Example 11:

[0167] (1) Lithium manganese iron phosphate (LiMn) 0.75 Fe 0.25 PO4) cathode material: according to LiMn 0.75 Fe 0.25 Lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate were weighed out according to the molar ratios of Li, Mn, Fe, and P in the chemical formula PO4. These were added to deionized water and mixed. The mixture was then ball-milled to obtain a lithium manganese iron phosphate precursor slurry. 28% glucose was then weighed and mixed evenly with the lithium manganese iron phosphate precursor slurry. The mixture was ball-milled for 20 hours, and the solid content was adjusted before spray drying to obtain a dry powder. The dry powder was then calcined in a tube furnace at a heating rate of 5℃ / min to 400℃ for 300 minutes, followed by a heating rate of 10℃ / min to 600℃ for 720 minutes. After natural cooling, a solid powder was obtained and crushed for 10 hours to obtain LiMn. 0.75 Fe 0.25 PO4 material.

[0168] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn) 0.75 Fe 0.25The cathode materials, namely lithium iron phosphate (LiFePO4) and lithium iron phosphate (LiFePO4), are mixed uniformly as the main material at a Mn / Fe molar ratio of 0.2, with an LMFP to LFP blending ratio of 0.29. The main material, conductive agent SP, and binder are mixed uniformly in NMP at a mass ratio of 96:3:1. Subsequently, the mixed cathode slurry is prepared according to a surface density of 400 g / m³. 2 The positive electrode is uniformly coated on aluminum foil and dried in a vacuum furnace at 100°C to obtain a positive electrode sheet, which is then slit; subsequently, it is rolled and cut to obtain a positive electrode sheet.

[0169] (3) Preparation of negative electrode: Same as in Example 1.

[0170] (4) Compared with Example 1, the electrolyte is made of TMSB additive containing 70ppm B element.

[0171] (5) Preparation of the diaphragm: Same as in Example 1.

[0172] (6) Battery preparation: Same as in Example 1.

[0173] Example 12:

[0174] (1) Lithium manganese iron phosphate (LiMn) 0.9 Fe 0.1 PO4) cathode material: according to LiMn 0.9 Fe 0.1 Lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate were weighed out according to the molar ratios of Li, Mn, Fe, and P in the chemical formula of PO4. They were added to deionized water and mixed. The mixture was then ball-milled to obtain a lithium manganese iron phosphate precursor slurry. 12% glucose was then weighed out and mixed evenly with the lithium manganese iron phosphate precursor slurry. The mixture was ball-milled for 20 hours. The solid content was then adjusted and spray-dried to obtain a dry powder. The dry powder was then placed in a tube furnace for calcination. The temperature was increased to 400℃ at a rate of 5℃ / min for 300 minutes. The temperature was then increased to 600℃ at a rate of 10℃ / min for 720 minutes. After natural cooling, a solid powder was obtained. After crushing and screening for 14 hours, the primary particle size was obtained as shown in Table 1.

[0175] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn) 0.9 Fe 0.1 PO4) was mixed with conductive agent SP and binder in NMP at a mass ratio of 96:1:3. Then, the mixed positive electrode slurry was prepared according to a surface density of 400 g / m³. 2 The positive electrode is uniformly coated on aluminum foil and dried in a vacuum furnace at 100°C to obtain a positive electrode sheet, which is then slit; subsequently, it is rolled and cut to obtain a positive electrode sheet.

[0176] (3) Preparation of negative electrode: Same as in Example 1.

[0177] (4) Compared with Example 1, the electrolyte is TMSB additive containing 980ppm B element.

[0178] (5) Preparation of the diaphragm: Same as in Example 1.

[0179] (6) Battery preparation: Same as in Example 1.

[0180] Figure 1 shows the XPS spectrum of the positive electrode prepared in Example 12 of this disclosure at an etching depth of 10 nm. As can be seen from Figure 1, the peaks in the XPS spectrum represent the peaks of element B. The peak value represents the peak intensity of element B in the positive electrode at the 10 nm etching position, which is approximately 1250 counts / s.

[0181] Example 13:

[0182] (1) Lithium manganese iron phosphate (LiMn) 0.75 Fe 0.25 PO4) cathode material: according to LiMn 0.75 Fe 0.25 Lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate were weighed out according to the molar ratios of Li, Mn, Fe, and P in the chemical formula PO4. These were then added to deionized water and mixed, followed by ball milling to obtain a lithium manganese iron phosphate precursor slurry. 35% glucose was then weighed and mixed evenly with the lithium manganese iron phosphate precursor slurry, and ball milled for 20 hours. The solid content was then adjusted, and the mixture was spray-dried to obtain a dry powder. The dried powder was then calcined in a tube furnace at a heating rate of 5℃ / min to 650℃ for 300 minutes, followed by a heating rate of 10℃ / min to 900℃ for 720 minutes. After natural cooling, LiMn was obtained. 0.75 Fe 0.25 PO4 material. Then LiMn 0.75 Fe 0.25 The PO4 material was crushed and ground for 8 hours, and then screened to obtain the primary particle size shown in Table 1.

[0183] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn) 0.75 Fe 0.25 The cathode materials are mainly composed of lithium iron phosphate (LiFePO4) and lithium iron phosphate (LiFePO4) mixed uniformly at a Mn / Fe molar ratio of 0.08, with an LMFP to LFP blending ratio of 0.11. The main materials, conductive agent SP, and binder are mixed uniformly in NMP at a mass ratio of 96:3:1. Subsequently, the mixed cathode slurry is prepared with a surface density of 400 g / m³. 2 The positive electrode is uniformly coated on aluminum foil and dried in a vacuum furnace at 100°C to obtain a positive electrode sheet, which is then slit; subsequently, it is rolled and cut to obtain a positive electrode sheet.

[0184] (3) Preparation of negative electrode: Same as in Example 1.

[0185] (4) Compared with Example 1, the electrolyte is LiBOB additive containing 850ppm B element.

[0186] (5) Preparation of the diaphragm: Same as in Example 1.

[0187] (6) Battery preparation: Same as in Example 1.

[0188] Example 14:

[0189] (1) Lithium manganese iron phosphate (LiMn) 0.95 Fe 0.05 PO4) cathode material: according to LiMn 0.95 Fe 0.05 Lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate were weighed out according to the molar ratios of Li, Mn, Fe, and P in the chemical formula PO4. These were then added to deionized water and mixed. The mixture was ball-milled to obtain a lithium manganese iron phosphate precursor slurry. 10% glucose was then weighed and mixed evenly with the lithium manganese iron phosphate precursor slurry. The mixture was ball-milled for 25 hours, and the solid content was adjusted before spray drying to obtain a dry powder. The dry powder was then calcined in a tube furnace at a heating rate of 5℃ / min to 200℃ for 300 minutes, followed by a heating rate of 10℃ / min to 450℃ for 720 minutes. After natural cooling, LiMn was obtained. 0.95 Fe 0.05 PO4 material.

[0190] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn) 0.95 Fe 0.05 The main material is a homogeneous mixture of lithium iron phosphate (LiFePO4) and lithium iron phosphate (LiFePO4) cathode materials at a Mn / Fe molar ratio of 10, with an LMFP to LFP blending ratio of 22.2. The main material, conductive agent SP, and binder are mixed homogeneously in NMP at a mass ratio of 96:0.1:3.9. Subsequently, the mixed cathode slurry is prepared with a surface density of 400 g / m³. 2 The positive electrode is uniformly coated on aluminum foil and dried in a vacuum furnace at 100°C to obtain a positive electrode sheet, which is then slit; subsequently, it is rolled and cut to obtain a positive electrode sheet.

[0191] (3) Preparation of negative electrode: Same as in Example 1.

[0192] (4) Compared with Example 1, the electrolyte is LiBOB additive containing 190ppm B element.

[0193] (5) Preparation of the diaphragm: Same as in Example 1.

[0194] (6) Battery preparation: Same as in Example 1.

[0195] Comparative Example 1

[0196] (1) Lithium manganese iron phosphate (LiMn) 0.9 Fe 0.1 PO4) cathode material: according to LiMn 0.9 Fe 0.1 Lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate were weighed out according to the molar ratios of Li, Mn, Fe, and P in the chemical formula PO4. These were then added to deionized water and mixed. The mixture was ball-milled to obtain a lithium manganese iron phosphate precursor slurry. 10% glucose was then weighed and mixed evenly with the lithium manganese iron phosphate precursor slurry. The mixture was ball-milled for 20 hours, and the solid content was adjusted before spray drying to obtain a dry powder. The dry powder was then calcined in a tube furnace at a heating rate of 5℃ / min to 100℃ for 300 minutes, followed by a heating rate of 10℃ / min to 300℃ for 720 minutes. After natural cooling, LiMn was obtained. 0.9 Fe 0.01 PO4 material.

[0197] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn) 0.9 Fe 0.1 PO4) The positive electrode material, conductive agent SP, and binder are mixed uniformly in NMP at a mass ratio of 96:1:3. Subsequently, the mixed positive electrode slurry is prepared according to a surface density of 400 g / m³. 2 The positive electrode sheet is obtained by uniformly coating the aluminum foil and drying it in a vacuum furnace at 100°C. The positive electrode sheet is then slit, rolled, and cut to obtain the positive electrode sheet.

[0198] (3) Preparation of negative electrode sheet: Same as in Example 1;

[0199] (4) Compared with Example 1, the electrolyte contains 90 ppm B element, additives LiBF4, 1% VC, and 1% MMDS as film-forming additives.

[0200] (5) Preparation of the diaphragm: Same as in Example 1.

[0201] (6) Battery preparation: Same as in Example 1.

[0202] Comparative Example 2:

[0203] (1) Lithium manganese iron phosphate (LiMn) 0.75 Fe 0.25 PO4) cathode material: according to LiMn 0.75 Fe 0.25Lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate were weighed out according to the molar ratios of Li, Mn, Fe, and P in the chemical formula PO4, respectively. These were added to deionized water and mixed. The mixture was then ball-milled to obtain a lithium manganese iron phosphate precursor slurry. 40% glucose was then weighed and mixed evenly with the lithium manganese iron phosphate precursor slurry. The mixture was ball-milled for 20 hours, and the solid content was adjusted before spray drying to obtain a dry powder. The dry powder was then calcined in a tube furnace at a heating rate of 5℃ / min to 600℃ for 300 minutes, followed by a heating rate of 10℃ / min to 1000℃ for 720 minutes. After natural cooling, a solid powder was obtained. The solid powder was then crushed for 3.5 hours, screened, and the primary particle size is shown in Table 1.

[0204] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn) 0.75 Fe 0.25 The main material is a homogeneous mixture of lithium iron phosphate (LiFePO4) and lithium iron phosphate (LiFePO4) cathode materials at a Mn / Fe molar ratio of 0.1, with an LMFP to LFP blending ratio of 0.14. The main material, conductive agent SP, and binder are mixed homogeneously in NMP at a mass ratio of 96:2.5:1.5. Subsequently, the mixed cathode slurry is prepared with a surface density of 400 g / m³. 2 The positive electrode is uniformly coated on aluminum foil and dried in a vacuum furnace at 100°C to obtain a positive electrode sheet, which is then slit; subsequently, it is rolled and cut to obtain a positive electrode sheet.

[0205] (3) Preparation of negative electrode sheet: Same as in Example 1;

[0206] (4) Compared with Example 1, the electrolyte is LiBF4 containing 3260ppm of element B.

[0207] (5) Preparation of the diaphragm: Same as in Example 1.

[0208] (6) Battery preparation: Same as in Example 1.

[0209] Comparative Example 3:

[0210] (1) Lithium manganese iron phosphate (LiMn) 0.75 Fe 0.25 PO4) cathode material: according to LiMn 0.75 Fe 0.25Lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate were weighed out according to the molar ratios of Li, Mn, Fe, and P in the chemical formula PO4. These were then added to deionized water and mixed. The mixture was ball-milled to obtain a lithium manganese iron phosphate precursor slurry. 40% glucose was then weighed and mixed evenly with the lithium manganese iron phosphate precursor slurry. The mixture was ball-milled for 20 hours, and the solid content was adjusted before spray drying to obtain a dry powder. The dry powder was then calcined in a tube furnace at a heating rate of 5℃ / min to 400℃ for 300 minutes, followed by a heating rate of 10℃ / min to 600℃ for 720 minutes. After natural cooling, LiMn was obtained. 0.75 Fe 0.25 PO4 material. Then LiMn 0.75 Fe 0.25 The PO4 material was crushed, ground and crushed for 12 hours, and then screened to obtain the primary particle size shown in Table 1.

[0211] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn) 0.75 Fe 0.25 Lithium iron phosphate (LiFePO4) and lithium iron phosphate (LiFePO4) cathode materials are mixed uniformly at a Mn / Fe molar ratio of 1.5 as the main material, and the LMFP to LFP compound ratio is 4. After the main material, conductive agent SP, and binder are mixed uniformly in NMP at a mass ratio of 96:1:3, a portion of the slurry is taken out and 35ppm of LiBF4 is added to form the first slurry, and the remaining part is used as the second slurry.

[0212] The first slurry is evenly coated onto the aluminum foil and dried in a vacuum furnace at 100°C. The second slurry is coated onto the first slurry and dried in a vacuum furnace at 100°C. The slurry is then slit, rolled, and cut to obtain the positive electrode sheet.

[0213] (3) Preparation of negative electrode sheet: Same as in Example 1;

[0214] (4) Preparation of the diaphragm: Same as in Example 1.

[0215] (5) Battery preparation: Same as in Example 1.

[0216] Table 1 shows the values ​​and relationships of a, k, h, etc. in the positive electrode of the examples and comparative examples, and the battery performance test results.

[0217] Table 2. Raw material quantities and process conditions used in the preparation of positive electrode sheets in the examples and comparative examples.

[0218] Test: Manganese-to-iron ratio (a) Test method: ICP

[0219] ① Pretreatment: Disassemble the lithium-ion battery to obtain the positive electrode sheet. Soak the positive electrode sheet in DMC (dimethyl carbonate) at room temperature for 60 minutes, take it out, and air dry it at room temperature with humidity ≤15%. Scrape off the positive active material layer on the surface of the current collector and calcine it at 400℃ for 3 hours to remove the conductive agent, binder, surface by-reaction products, and residual electrolyte. After washing and drying, obtain the positive active material powder.

[0220] ② Accurately weigh 0.5g of positive electrode active material powder, disperse it in 20ml of water, add 10ml of nitric acid, mix thoroughly, and then heat to dissolve the powder. Dilute the solution to 100mL with water to obtain the test solution. Perform ICP testing on the test solution. Before testing, a standard solution must be prepared. The linear correlation coefficient of the standard concentration must be above 0.999 to be used as a normal standard. Dilute the 1000mg / L standard solution with deionized water to different concentrations (generally 0, 1mg / 100mL, 2mg / 100mL, 3mg / 100mL), and select the element detection wavelength. Set the experimental conditions: Based on the characteristics of the sample and the elements to be detected, set appropriate ICP instrument operating conditions: gas flow rate 0.5L / min, power 1150W, and select element detection wavelengths of 259.94nm for Fe and 257.61nm for Mn. The concentrations of Fe and Mn elements in the sample can be read using the self-analysis function of the ICP testing software.

[0221] Peak intensity ratio:

[0222] ①Pretreatment: Disassemble the lithium-ion battery to obtain the positive electrode sheet. Soak the positive electrode sheet in DMC (dimethyl carbonate) at room temperature for 60 minutes, take it out, and air dry it at room temperature with humidity ≤15%.

[0223] ②XPS etching peak intensity ratio (k):

[0224] XPS etching analysis was performed on the electrode under test, and the peak intensity b of the B1s peak at the binding energy position of 188-192 eV was obtained in the XPS image. Specifically, the etching depth L can be selected as 10 nm.

[0225] Where, k = b / L;

[0226] The sample is fixed in a suitable position, such as on conductive tape on a copper sheet, and then sent into the analysis chamber through a rapid sample introduction chamber. A 120W monochromatic Al Kα X-ray source is used; the energy resolution is less than or equal to 0.48 eV; the test beam spot size is 400 micrometers, and the instrument automatically supplements the test energy range according to the element to be measured; etching conditions: Ar ions are used for etching, and the etching depth is controlled by adjusting the etching rate or etching time. In this disclosure, the etching depth is 10 nm (or 35 nm). After the test, the instrument automatically provides the test results, and the peak intensity b can be obtained. Combined with the etching depth L, b / L, the peak intensity ratio k is obtained.

[0227] Acidity growth rate:

[0228] The battery was disassembled under full charge (the battery was first discharged at 0.33C to the lower limit voltage of 2.5V, then charged at a constant current of 0.33C to the upper limit voltage of 4.25V, and then charged at a constant voltage until the current was less than or equal to 0.05C) to obtain the positive electrode sheet under full charge. The electrode sheet was soaked in DMC (dimethyl carbonate) for 1 hour, cleaned, and then dried at 80℃ for 4 hours to obtain the positive electrode sheet. The positive electrode sheet was cut into 7cm×7cm electrode sheets to be tested.

[0229] At 60℃, the electrode to be tested was immersed in 20 ml of a mixed solution, which consisted of ethylene carbonate, methyl ethyl carbonate and lithium perchlorate, with a volume ratio of ethylene carbonate to methyl ethyl carbonate of 3:7 and a molar concentration of lithium perchlorate of 1 mol / L.

[0230] When the electrode to be tested is immersed in the mixed solution for 48 hours, the hydrogen ion content in the mixed solution is measured and recorded as h1ppm; when the electrode to be tested is immersed in the mixed solution for 72 hours, the hydrogen ion content in the mixed solution is measured again and recorded as h2ppm.

[0231] The growth rate of hydrogen ion content in the positive electrode immersed in a mixed solution containing lithium perchlorate is calculated as h = (h2-h1) / h1×100%; this is the acidity growth rate.

[0232] The hydrogen ion content (h1, h2) in the mixed solution was detected by the following method:

[0233] Prepare a 0.05 mol / L triethylamine titrant using triethylamine and ethyl methyl carbonate (EMC). Take the mixed solution impregnated with the positive electrode as the test solution, add 10–30 drops of methyl red as an indicator, and add the triethylamine titrant to the test solution containing methyl red. Record the amount of triethylamine titrant used when the test solution turns orange. Then, calculate the hydrogen ion content using the formula:

[0234] Hydrogen ion content = M × V × 20010 / m, where the unit of hydrogen ion content is ppm;

[0235] In the formula: M is the concentration of the triethylamine titrant, in mol / L.

[0236] V represents the volume of titrant consumed by triethylamine, in mL.

[0237] m is the mass of the solution to be tested, in grams.

[0238] 20010 = 20.01 × 10 3 20.01 is the molecular weight of HF. The fully charged positive electrode contains the electrolyte component LiPF6. The positive electrode active material reacts with EC and EMC to dehydrogenate and generates HF in the presence of LiPF6. The amount of HF represents the hydrogen ions.

[0239] Capacity retention test at 25℃ for 400 cycles:

[0240] The lithium-ion secondary batteries prepared in the examples and comparative examples were subjected to cycle tests at 25°C according to the following procedure:

[0241] 1) Charge the battery at a constant current rate of 1C to 4.25V, then charge it at a constant voltage rate until the current is less than 0.05C. Repeat this process at least 3 times and record the battery capacity C1.

[0242] 2) Charge at a constant current rate of 1C to 4.25V, then charge at a constant voltage rate until the current is less than 0.05C.

[0243] 3) Let it stand for 5 minutes;

[0244] 4) Discharge to 2.5V at a 1C rate;

[0245] 5) Let it stand for 5 minutes.

[0246] Perform cycle tests according to steps 2)-5) until the lithium-ion secondary battery completes 400 cycles, and record the capacity C2 of the battery after 400 cycles.

[0247] Capacity retention rate during 25℃ cycling = C2 / C1 × 100%.

[0248] DCR growth rate:

[0249] The lithium-ion battery was capacitated and charged to 4.25V at a constant current of 0.33C, then charged to the cutoff current of 0.05C at a constant voltage. It was then discharged at 0.33C to adjust the charge to 50% SOC, left to stand for 2 hours, and then discharged at 1C at 50% SOC. The initial internal resistance of the battery was measured to obtain DCR1.

[0250] The lithium-ion battery was placed in a 25°C constant temperature chamber and discharged at a constant current of 0.33C. Then, it was cycled in the constant temperature chamber at a charge / discharge test rate of 1C / 1C and a cycle voltage range of 2.5-4.25V for a total of 400 cycles.

[0251] After 400 cycles, the battery was discharged at 0.33C to adjust the charge to 50% SOC, left to stand for 2 hours, and then discharged at 1C at 50% SOC. The internal resistance of the battery after cycling was tested to obtain DCR2.

[0252] The battery internal resistance test method is as follows: take the voltage at the last second of rest as V0, the voltage after 18 seconds of discharge as V1, and the current during the discharge process as I. DCR = (V0 - V1) / I.

[0253] Calculate the DCR growth rate as (DCR2 - DCR1) / DCR1 × 100%.

[0254] As can be seen from the above embodiments, this disclosure provides a positive electrode sheet, which includes a positive electrode active material, the positive electrode active material including lithium manganese iron phosphate particles; the molar ratio of manganese to iron in the positive electrode active material is a; the acidity growth rate of the positive electrode sheet is h, in %; k = b / L, where L is the XPS etching depth of the positive electrode sheet, taken as 10 nm; k is the peak intensity ratio of the B1s peak at the binding energy position of 188-192 eV in the XPS image when performing XPS etching analysis on the positive electrode sheet, in counts / s / nm; b is the peak intensity of the B1s peak at the binding energy position of 188-192 eV in the XPS image when performing XPS etching analysis on the positive electrode sheet, in counts / s; the a, k, and h satisfy the following relationship: a × h / k = 8 × 10 - 4 ~10. By controlling the manganese-iron ratio, acidity growth rate, and peak intensity ratio at a certain etching depth, this positive electrode forms a stable boron-containing CEI film on its surface, preventing manganese ion dissolution, reducing active lithium consumption, and improving cycle life.

[0255] Experimental results show that the battery prepared in this disclosure retains a capacity of 60.3%–96.4% after 400 cycles at room temperature, and the DCR growth rate after 400 cycles is 24.3%–56.1%. In contrast, the battery prepared in the comparative example retains a capacity of 45.3%–50.4% after 400 cycles at room temperature, and the DCR growth rate after 400 cycles is 63%–71.5%. Therefore, the effect of this disclosure is significantly better than that of the comparative example. This disclosure, by controlling experimental parameters such as a, k, h, a×h / k, and F2–F1, forms a stable boron (B)-containing solid electrolyte interphase (CEI) film on the surface of the positive electrode, preventing manganese ion dissolution, reducing active lithium consumption, and improving cycle life.

[0256] In Embodiments 3 to 5 of this application, the values ​​of a×h / k, and the values ​​of a, h, and k are all within the preferred range. Combined with the peak intensity difference F2-F1, which is also within the preferred range, the resulting battery maintains a capacity retention rate of 91.5%–96.4% after 400 cycles at room temperature, and the DCR growth rate after 400 cycles is 24.3%–36.0%. The above description is merely a preferred embodiment of this disclosure. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this disclosure, and these improvements and modifications should also be considered within the scope of protection of this disclosure.

Claims

1. A positive electrode sheet comprising a positive electrode active material, said positive electrode active material comprising lithium manganese iron phosphate particles; The molar ratio of manganese to iron in the positive electrode active material is a; the acidity growth rate of the positive electrode sheet is h, in %; k = b / L, where k is the peak intensity ratio of the B1s peak at the position of binding energy 188-192 eV in the XPS image when performing XPS etching analysis on the positive electrode, in units of counts / s / nm; L is the depth of XPS etching on the positive electrode, with a value of 10 nm; b is the peak intensity of the B1s peak at the position of binding energy 188-192 eV in the XPS image when performing XPS etching analysis on the positive electrode, in units of counts / s; The following relationship is satisfied by a, k, and h: 8 x 10 -4 ≤ a x h / k ≤ 10.

2. The positive electrode according to claim 1, wherein 0.02 ≤ a × h / k ≤ 3.

3. The positive electrode according to claim 1 or 2, wherein 0.1 ≤ a ≤ 9.

4. The positive electrode according to claim 3, wherein 0.4 ≤ a ≤ 2.

5.

5. The positive electrode according to any one of claims 1 to 4, wherein 5 ≤ k ≤ 400.

6. The positive electrode according to claim 5, wherein 9 ≤ k ≤ 108.

7. The positive electrode according to any one of claims 1 to 6, wherein the acidity growth rate h is 3% to 18%.

8. The positive electrode according to claim 7, wherein the acidity growth rate h is 4% to 16%.

9. The positive electrode sheet according to any one of claims 1 to 8, wherein the lithium manganese iron phosphate particles comprise primary particles, the average particle size of the primary particles ranging from 50 nm to 170 nm.

10. The positive electrode according to any one of claims 1 to 9, wherein the peak intensity of the B1s peak is F1 when the XPS etching depth is 10 nm and the peak intensity of the B1s peak is F2 when the XPS etching depth is 35 nm; The difference between F1 and F2 is greater than 0 and less than or equal to 2000.

11. A battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte; The positive electrode is the positive electrode as described in any one of claims 1 to 10.

12. The battery according to claim 11, wherein the electrolyte and / or the positive electrode contains a boron-containing compound.

13. The battery according to claim 12, wherein the electrolyte contains a boron-containing compound selected from one or more of lithium bis(oxalato)borate, tris(trimethylsilane)borate, lithium difluorooxalatoborate, lithium tetrafluoroborate, tributyl borate, and trimethyl borate.

14. An electrical device comprising the battery according to any one of claims 11 to 13.

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