Electrochemical devices and electronic equipment

Abstract

This application discloses an electrochemical device and an electronic device. The electrochemical device includes a positive electrode plate, which includes a positive electrode active material layer. In a fully charged state, the Raman spectrum of the positive electrode active material layer shows a value at 580 cm⁻¹. ‑1 Up to 640cm ‑1 A characteristic peak A1 exists within the range, at 420 cm⁻¹. ‑1 Up to 520cm ‑1 The characteristic peak B1 is present within the range. The electrochemical device of this application has high energy density and good cycle performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more particularly to an electrochemical device and electronic device. Background Technology

[0002] Lithium-ion batteries are widely used due to their advantages such as high energy density, high power density, high operating voltage, good cycle performance, low self-discharge, and good safety. However, during the first charge and discharge process, the formation of a solid electrolyte interphase (SEI) film on the negative electrode surface consumes a large amount of active lithium, causing irreversible capacity loss and leading to a decrease in the energy density of the lithium-ion battery. Furthermore, in subsequent cycles, the destruction and regeneration of the SEI film further consumes active lithium, resulting in a decrease in battery cycle life. Summary of the Invention

[0003] In view of this, this application provides an electrochemical device and an electronic device to improve the energy density of the electrochemical device and enhance its high-temperature cycle life.

[0004] In a first aspect, this application provides an electrochemical device including a positive electrode plate, the positive electrode plate comprising a positive electrode active material layer, wherein, in a fully charged state, the Raman spectrum of the positive electrode active material layer shows a positive electrode active material layer at 580 cm⁻¹. -1 Up to 640cm -1 A characteristic peak A1 exists within the range, at 420 cm⁻¹. -1 Up to 520cm -1 A characteristic peak B1 is present within the range. Specifically, characteristic peak B1 is the characteristic vibration peak of the Li-O-Li bond in the layered crystal structure of lithium manganese composite oxides, while characteristic peak A1 is the characteristic vibration peak of the metal-O bond in both layered crystal structures of lithium cobalt composite oxides and lithium manganese composite oxides. On one hand, the layered crystal structure of lithium manganese composite oxides exhibits high initial charge specific capacity and low initial coulombic efficiency. When used in conjunction with lithium cobalt composite oxides, which have high initial coulombic efficiency, it can significantly improve the cycle performance of the electrochemical device. On the other hand, during the first discharge of the electrochemical device, some active lithium is re-intercalated into the layered crystal structure of lithium manganese composite oxides. In the high-voltage range, as the active lithium is continuously consumed during subsequent cycles, the positive electrode potential increases synchronously. At this time, the active lithium that has been re-intercalated into the high-voltage range of the lithium manganese composite oxide with a layered crystal structure will be slowly released. The Raman spectrum of the positive electrode active material layer shows a characteristic peak A1. The lithium manganese composite oxide with a layered crystal structure has good structural stability in the fully charged state. In subsequent cycles, it can provide sufficient lithium source for the destruction and regeneration of the SEI film, suppress the structural destruction of the lithium cobalt composite oxide due to excessive delithiation during high-temperature cycling, and thus improve the high-temperature cycle life of the electrochemical device.

[0005] In some embodiments, the peak intensity of the characteristic peak A1 is I. A1 The peak intensity of the characteristic peak B1 is I. B1 , satisfying: 1.4≤I A1 / I B1 ≤36. In some implementations, 1.4≤I A1 / I B1 ≤21.

[0006] In some embodiments, the positive electrode active material layer includes a first material and a second material; the first material is a lithium cobalt composite oxide with a layered crystal structure; and the second material is a lithium manganese composite oxide with a layered crystal structure.

[0007] In some embodiments, the second material comprises an R-3m and a C2 / m crystal phase structure.

[0008] In some embodiments, the second material includes Mn, T, O, optional Ni, and optional T′, wherein the T element includes at least one of Fe or Co; and the T′ element includes at least one of Mg, Al, Ti, V, Cr, Cu, Y, Zr, Nb, Mo, La, Zn, Ga, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd, or W; wherein the molar amount of Mn in the second material is n. Mn The molar amount of element T is n T The molar amount of the O element is n. O The molar amount of Ni element is n. Ni The molar amount of element T′ is n T The sum of the molar amounts of Mn, Fe, Ni, and T is n. M The condition is satisfied that: 0.25 ≤ n Mn / n M ≤0.85, 0.05≤n T / n M ≤0.65, 0≤n Ni / n M ≤0.4, 0≤n T’ / n M ≤0.05, 0.35≤n M / n O ≤0.475. Adding appropriate amounts of nitrogen (Fe and / or Co) to the second material component makes the structure of the second material more stable after delithiation, and the Mn element in the delithiation product of the second material is mostly in the form of Mn. 4+ Therefore, it can effectively inhibit Mn 3+The Ginger-Taylor distortion effect reduces the damage to the SEI film caused by the dissolution of Mn, and can effectively improve the high-temperature cycle life of electrochemical devices.

[0009] In some embodiments, the first material includes Co and optionally Me, wherein the Me element includes at least one selected from Ni, Mn, Al, Mg, Ti, Zr, La, Y, Mo, V, Cu, Zn, Ga, Nb, Cr, Ba, W, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd, or Ca, and the molar amount of Co in the second material is m. Co The molar amount of the Me element is m. Me The sum of the molar amounts of the Co and Me elements is m. M Satisfying: 0.5≤m Co / m M ≤1, 0≤m Me / m M ≤0.5.

[0010] In some implementations, 0.05 ≤ n T / n M ≤0.5.

[0011] In some embodiments, the T element includes Fe, and the molar amount of Fe in the second material is n. Fe The condition is satisfied that: 0.05 ≤ n Fe / n M ≤0.5. The Fe content in the second material is within the above range, due to Fe 3+ To Fe 4+ The ionization energy is much higher than that of Co. 3+ To Co 4+ The ionization energy of Fe is lower than that of Co during high-voltage cycling. This reduces the oxidation of the electrolyte by high-valence metal ions at the interface and helps Mn maintain a high valence, suppressing the Jam-Taylor distortion effect of Mn and reducing the risk of Mn dissolution. At the same time, it can enhance the structural stability of the material and inhibit the migration of transition metals to the lithium layer, thereby improving the high-temperature cycle life of the electrochemical device.

[0012] In some embodiments, the average particle size of the first material is D1, and the average particle size of the second material is D2, satisfying: 0.3≤D2 / D1≤0.5.

[0013] In some embodiments, the average particle size D1 of the first material is 10 μm to 25 μm. In some embodiments, the average particle size D2 of the second material is 4 μm to 9 μm.

[0014] In some embodiments, the compaction density of the positive electrode active material layer is P, which satisfies: 3.5g / cm 3 ≤P≤4.5g / cm 3 .

[0015] In some embodiments, the second material comprises any one of the materials represented by Chemical Formula I:

[0016] Li 2-e Ni a T b Mn c T' d O₂ Chemical Formula I

[0017] wherein 0≤a≤0.35, 0<b≤0.6, 0.25≤c≤0.65, 0≤d≤0.05, 0.7≤a+b+c+d≤0.95, 0.7≤e≤0.95; T comprises at least one of Fe or Co; T' comprises at least one of Mg, Al, Ti, V, Cr, Cu, Y, Zr, Nb, Mo, La, Zn, Ga, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd or W.

[0018] In some embodiments, the first material comprises any one of the materials represented by Chemical Formula II;

[0019] Li x Co y Me 1-y O 2-t A t Chemical Formula II

[0020] wherein 0.6≤x≤1.2, 0.5≤y≤1, 0≤t≤0.2, Me comprises at least one of Ni, Mn, Al, Mg, Ti, Zr, La, Y, Mo, V, Cu, Zn, Ga, Nb, Cr, Ba, W, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd or Ca, and A comprises at least one of S, N, F, Cl or Br.

[0021] In a second aspect of the present application, an electronic device is provided, comprising any one of the above electrochemical devices.

[0022] The technical solution of the present application has at least the following beneficial effects: 1) In the present application, through the ingenious design of the composition of the positive electrode plate and the cut-off voltage during formation, the positive electrode plate has unique Raman spectrum characteristics, so that the positive electrode plate can have high structural stability during cycling. In particular, adding an appropriate amount of T element (Fe and / or Co) to the component of the second material makes the structure of the second material more stable after delithiation, and the morphology of Mn element in the product of the second material after delithiation is mostly Mn4+ Therefore, it can effectively inhibit Mn 3+ The Ginger-Taylor distortion effect reduces the damage to the SEI film caused by the dissolution of Mn, effectively improving the high-temperature cycle life of lithium-ion batteries. 2) Existing Li2NiO2-type materials have high specific capacity, but they are expensive and extremely sensitive to air, requiring processing in a dry room. Furthermore, these materials have extremely high surface free lithium content, easily causing slurry gelation during the slurry preparation process, resulting in poor processing performance. The second material described in this application is inexpensive and has good air stability, with higher compatibility with existing lithium-ion battery manufacturing processes. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 The Raman spectrum of the positive electrode active material layer in Example 1 of this application;

[0025] Figure 2 Li is the second material in the positive electrode of Embodiment 1 of this application. 1.2 Ni 0.133 Fe 0.133 Mn 0.534 SEM test image of O2. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0027] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, just as any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an undefined range.

[0028] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C.

[0029] Electrochemical device

[0030] The first aspect of this application provides an electrochemical device, including a positive electrode, a negative electrode, a separator, and an electrolyte.

[0031] Positive electrode sheet

[0032] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on the surface of the positive current collector. As an example, the positive current collector includes two opposing surfaces in its thickness direction, and the positive active material layer covers either or both of the two surfaces of the positive current collector.

[0033] In the fully charged state, the Raman spectrum of the positive electrode active material layer of the electrochemical device at 580 cm⁻¹ -1 Up to 640cm -1 A characteristic peak A1 exists within the range, at 420 cm⁻¹. -1 Up to 520cm -1 A characteristic peak B1 is present within the range. The Raman spectrum of the positive electrode active material layer was tested after disassembling the positive electrode sheet in the designed fully charged state of the electrochemical device.

[0034] In the Raman spectrum of the positive electrode active material layer described in the embodiments of this application, at 580 cm⁻¹ -1 Up to 640cm -1 The characteristic peak A1 exists within the range. The A1 peak is the characteristic vibrational peak of the MO bond, mainly contributed by lithium cobalt composite oxide and lithium manganese composite oxide with layered crystal structures, where M refers to a metal element; at 420 cm⁻¹ -1 Up to 520cm -1The characteristic peak B1 is present within the range. Peak B1 is the characteristic vibration peak of the Li-O-Li bond in the layered crystal structure of lithium manganese composite oxide. On the one hand, the layered crystal structure of lithium manganese composite oxide has the characteristics of high initial charge specific capacity and low initial coulombic efficiency. When used in combination with lithium cobalt composite oxide with high initial coulombic efficiency, it can significantly improve the cycle performance of the electrochemical device. On the other hand, during the first discharge of the electrochemical device, some active lithium is re-intercalated into the high-voltage range of the layered crystal structure of lithium manganese composite oxide. In subsequent cycles, as the active lithium is continuously consumed, the positive electrode potential increases synchronously. At this time, the active lithium re-intercalated into the high-voltage range of the layered crystal structure of lithium manganese composite oxide will be slowly released. The characteristic peak A1 is present in the Raman spectrum of the positive electrode active material layer. The layered crystal structure of lithium manganese composite oxide has good structural stability in the fully charged state. In subsequent cycles, it can provide sufficient lithium source for the destruction and regeneration of SEI film, suppress the structural destruction of lithium cobalt composite oxide due to excessive delithiation during high-temperature cycling, thereby improving the high-temperature cycle life of the electrochemical device.

[0035] In some embodiments, the peak intensity of the characteristic peak A1 is I. A1 The peak intensity of the characteristic peak B1 is I. B1 , satisfying: 1.4≤I A1 / I B1 ≤36.

[0036] For example, the peak intensity ratio I of the diffraction peak A1 and the diffraction peak B1 A1 / I B1 The range is 1.4, 2.0, 5.0, 10, 15, 20, 25, 30, 36, or any two of the above values. In some embodiments, 1.4 ≤ 1 A1 / I B1 ≤21.

[0037] In some embodiments, the positive electrode active material layer includes a first material and a second material; the first material is a lithium cobalt composite oxide with a layered crystal structure; and the second material is a lithium manganese composite oxide with a layered crystal structure.

[0038] In some embodiments, the second material comprises an R-3m and a C2 / m crystal phase structure.

[0039] In some embodiments, the second material includes Mn, T, O, optional Ni, and optional T′, wherein the T element includes at least one of Fe or Co; and the T′ element includes at least one of Mg, Al, Ti, V, Cr, Cu, Y, Zr, Nb, Mo, La, Zn, Ga, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd, or W; wherein the molar amount of Mn in the second material is n. Mn The molar amount of element T is n T The molar amount of the O element is n. O The molar amount of Ni element is n. Ni The molar amount of element T′ is n T′ The sum of the molar amounts of the elements Mn, T, Ni, and T' is n. M The condition is satisfied that: 0.25 ≤ n Mn / n M ≤0.85, 0.05≤n T / n M ≤0.65, 0≤n Ni / n M ≤0.4, 0≤n T′ / n M ≤0.05, 0.35≤n M / n O ≤0.475. Adding appropriate amounts of nitrogen (Fe and / or Co) to the second material component makes the structure of the second material more stable after delithiation, and the Mn element in the delithiation product of the second material is mostly in the form of Mn. 4+ Therefore, it can effectively inhibit Mn 3+ The Ginger-Taylor distortion effect reduces the damage to the SEI film caused by the dissolution of Mn, and can effectively improve the high-temperature cycle life of electrochemical devices.

[0040] Optionally, in one example, the second material includes Mn, T, and O elements; or in another example, the second material includes Mn, T, and O elements, and further includes at least one of Ni and T′ elements.

[0041] For example, n Mn and n M molar ratio n Mn / n M The range is 0.25, 0.30, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.85 or any two of the above values.

[0042] For example, n T and n M molar ratio nT / n M The range is 0.05, 0.06, 0.08, 0.1, 0.2, 0.3, 0.4, 0.5, 0.65, or any two of the above values. In some embodiments, n T and n M molar ratio n T / n M The value range is 0.05 ≤ n T / n M ≤0.5.

[0043] For example, n Ni and n M molar ratio n Ni / n M The range is 0, 0.001, 0.01, 0.05, 0.08, 0.1, 0.2, 0.3, 0.4 or any two of the above values.

[0044] For example, n T′ and n M molar ratio n T′ / n M The range is 0, 0.001, 0.01, 0.02, 0.03, 0.04, 0.05, or any two of the above values.

[0045] For example, n M and n O molar ratio n M / n O The range is 0.35, 0.40, 0.41, 0.42, 0.43, 0.44, 0.45, 0.475, or any two of the above values.

[0046] In some embodiments, the T element includes Fe, and in the second material, the molar amount of Fe is n. Fe The condition is satisfied that: 0.05 ≤ n Fe / n M ≤0.5. The Fe content in the second material is within the above range, due to Fe 3+ To Fe 4+ The ionization energy is much higher than that of Co. 3+ To Co 4+ The ionization energy of Fe is lower than that of Co during high-voltage cycling. This reduces the oxidation of the electrolyte by high-valence metal ions at the interface and helps Mn maintain a high valence, suppressing the Jam-Taylor distortion effect of Mn and reducing the risk of Mn dissolution. At the same time, it can enhance the structural stability of the material and inhibit the migration of transition metals to the lithium layer, thereby improving the high-temperature cycle life of the electrochemical device.

[0047] In some embodiments, the first material includes Co and optionally Me, wherein the Me element includes at least one selected from Ni, Mn, Al, Mg, Ti, Zr, La, Y, Mo, V, Cu, Zn, Ga, Nb, Cr, Ba, W, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd, or Ca, and the molar amount of Co in the second material is m. Co The molar amount of the Me element is m. Me The sum of the molar amounts of the Co and Me elements is m. M Satisfying: 0.5≤m Co / m M ≤1, 0≤m Me / m M ≤0.5.

[0048] For example, m Co / m M The range is 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 or any two of the above values.

[0049] For example, m Me / m M The range is 0, 0.01, 0.05, 0.1, 0.15, 0.2, 0.3, 0.4, 0.5 or any two of the above values.

[0050] In some embodiments, the average particle size of the first material is D1, and the average particle size of the second material is D2, satisfying: 0.3 ≤ D2 / D1 ≤ 0.5. In this case, the particles of the second material can be embedded between the particles of the first material, efficiently replenishing the active lithium of the first material while reducing the occurrence of surface side reactions, thereby improving the cycle life of the electrochemical device.

[0051] Specifically, the average particle size is tested using a scanning electron microscope. The specific test method is as follows: a sample of the positive electrode active material layer is observed under a scanning electron microscope (SEM), and SEM images are taken at an appropriate magnification. Using image processing software, the longest diameter of 50 first material particles is randomly counted, and their average value is taken as the average particle size D1 of the first material. The longest diameter of 50 second material particles is randomly counted, and their average value is taken as the average particle size D2 of the second material.

[0052] For example, the particle size ratio D2 / D1 is 0.3, 0.35, 0.4, 0.45, 0.5 or any combination of two of the above values.

[0053] In some embodiments, the average particle diameter D1 of the first material is 10 μm to 25 μm. Exemplarily, the average particle diameter D1 of the first material is 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, 22 μm, 25 μm, or a range consisting of any two of the above values;

[0054] In some embodiments, the average particle diameter D2 of the second material is 4 μm to 9 μm. Exemplarily, the average particle diameter D2 of the second material is 4 μm, 5 μm, 6 μm, 8 μm, 9 μm, or a range consisting of any two of the above values.

[0055] In some exemplary embodiments, the compacted density of the positive electrode active material layer is P, which satisfies: 3.5g / cm 3 ≤P≤4.5g / cm 3 . Exemplarily, the compacted density P of the positive electrode active material layer is 3.5g / cm 3 , 4.0g / cm 3 , 4.1g / cm 3 , 4.2g / cm 3 , 4.3g / cm 3 , 4.5g / cm 3 or a range consisting of any two of the above values.

[0056] The compacted density P can be calculated by the formula P = m / v, wherein m is the weight of the positive electrode active material layer, with a unit of g; v is the volume of the positive electrode active material layer, with a unit of cm 3 . Wherein the volume v of the positive electrode active material layer may be the product of the area S of the positive electrode active material layer and the thickness h of the positive electrode active material layer.

[0057] In some embodiments, the second material comprises any one of the materials represented by Chemical Formula I:

[0058] Li 2-e Ni a T b Mn c T' d O2 Chemical Formula I

[0059] Wherein, 0≤a≤0.35, 0<b≤0.6, 0.25≤c≤0.65, 0≤d≤0.05, 0.7≤a+b+c+d≤0.95, 0.7≤e≤0.95; T comprises at least one of Fe or Co; T' comprises at least one of Mg, Al, Ti, V, Cr, Cu, Y, Zr, Nb, Mo, La, Zn, Ga, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd or W.

[0060] In some embodiments, the first material includes any one of the materials having chemical formula II;

[0061] Li x Co y Me 1-y O 2-t A t Chemical Formula II

[0062] Wherein, 0.6≤x≤1.2, 0.5≤y≤1, 0≤t≤0.2, Me includes at least one of Ni, Mn, Al, Mg, Ti, Zr, La, Y, Mo, V, Cu, Zn, Ga, Nb, Cr, Ba, W, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd or Ca, and A includes at least one of S, N, F, Cl or Br.

[0063] In some embodiments, the weight ratio of the first material to the second material is 6.8:1 to 97:1. By controlling the content of the first material in the positive electrode to be higher than the content of the second material, so that the majority of the positive electrode is made of the first material, the structural stability is higher, and the capacity loss and impedance increase during cycling can be reduced.

[0064] In some embodiments, the weight percentage of the first material is 85 wt% to 97 wt% based on the total weight of the positive electrode active material layer. Exemplarily, the weight percentage of the first material is 85 wt%, 90 wt%, 92 wt%, 94 wt%, 96 wt%, 97 wt%, or a range consisting of any two of the above values.

[0065] In some embodiments, the weight percentage of the second material is 1 wt% to 12.5 wt% based on the total weight of the positive electrode active material layer. Exemplarily, the weight percentage of the second material is 1 wt%, 2 wt%, 3 wt%, 5 wt%, 8 wt%, 10 wt%, 11 wt%, 12 wt%, 12.5 wt%, or a range consisting of any two of the above values.

[0066] In some embodiments, the positive electrode active material layer further includes a conductive agent and a binder.

[0067] In some embodiments, the conductive agent comprises 0.1 wt% to 5 wt% of the total weight of the positive electrode active material layer. In some embodiments, the binder comprises 0.5 wt% to 5 wt% of the total weight of the positive electrode active material layer. Exemplarily, the conductive agent comprises one or more of graphite, conductive carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers. Exemplarily, the binder comprises one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), ethylene-vinyl acetate copolymer (EVA), or polyvinyl alcohol (PVA).

[0068] For example, the positive current collector includes at least one of a metal foil or a porous metal plate, such as a foil or porous plate made of metals or alloys thereof, such as aluminum foil, copper, nickel, titanium, or silver. Optionally, the thickness of the positive current collector is 4 μm to 20 μm.

[0069] The positive electrode sheet of this application can be prepared according to conventional methods in the art. For example, a positive electrode slurry containing a first material, a second material, a conductive agent and a binder is first coated on at least one surface of the positive electrode current collector to obtain a positive electrode active material coating. After drying, cold pressing and other processes, the positive electrode sheet is obtained.

[0070] other

[0071] The negative electrode sheet can be a lithium metal sheet, or it can include a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector.

[0072] The negative electrode active material layer typically includes the negative electrode active material and optional conductive agents and binders.

[0073] Exemplary examples include one or more of natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, SiO, Li-Sn alloys, Li-Sn-O alloys, Li-Al alloys, or metallic lithium; conductive agents include one or more of conductive carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers; and binders include one or more of styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), water-based acrylic resin, or carboxymethyl cellulose (CMC). However, this application is not limited to these materials, and other materials that can be used as negative electrode active materials, conductive agents, and binders in lithium-ion batteries may also be used.

[0074] For example, the negative current collector can be made of materials such as metal foil or porous metal plate, for example, using foil or porous plate of metals or alloys of them such as copper, nickel, titanium or iron, such as copper foil.

[0075] The negative electrode sheet can be prepared according to conventional methods in the art. For example, the negative electrode active material and optional conductive agent and binder are dispersed in a solvent, which may be N-methylpyrrolidone (NMP) or deionized water, to form a uniform negative electrode slurry. The negative electrode slurry is coated on a negative electrode current collector, and the negative electrode sheet is obtained by processes such as drying and cold pressing.

[0076] There are no particular restrictions on the above-mentioned separator membrane. Any well-known porous structure separator membrane with electrochemical and chemical stability can be selected, such as one or more single-layer or multi-layer films of glass fiber, non-woven fabric, polyethylene (PE), polypropylene (PP) and polyvinylidene fluoride (PVDF).

[0077] The electrolyte described above includes an organic solvent, a lithium electrolyte salt, and additives. This invention does not impose specific limitations on the types of electrolytes used; selection can be made according to actual needs.

[0078] For example, the organic solvents mentioned above include one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butenyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), or diethyl sulfone (ESE), preferably two or more.

[0079] For example, the above-mentioned electrolyte lithium salt includes one or more of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bisfluorosulfonylimide), LiTFSI (lithium bistrifluoromethanesulfonylimide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiBOB (lithium dioxalate borate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorodioxalate phosphate), or LiTFOP (lithium tetrafluorooxalate phosphate).

[0080] The electrolyte may optionally include other additives, which can be any additive that can be used in lithium-ion secondary batteries. This invention does not impose specific limitations and can select additives according to actual needs. As an example, the additives may be one or more of the following: vinylene carbonate (VC), ethylene ethylene carbonate (VEC), succinate (SN), adiponitrile (AND), 1,3-propenesulfonate lactone (PST), tris(trimethylsilane) phosphate (TMSP), or tris(trimethylsilane) borate (TMSB).

[0081] Electrochemical devices can be prepared according to conventional methods in the art. For example, the above-mentioned positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrode to obtain an electrode assembly. Alternatively, the electrode assembly can be obtained by winding. The electrode assembly is placed in a packaging shell, an electrolyte is injected, and the shell is sealed to obtain the electrochemical device.

[0082] The electrochemical device of this application can include any device in which an electrochemical reaction occurs, and specific examples include all types of primary or secondary batteries. In particular, the electrochemical device is a lithium secondary battery, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0083] electronic devices

[0084] The electronic device of this application includes any of the electrochemical devices described above. The electronic device of this application can be used in, but is not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0085] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Unless otherwise stated, all parts, percentages and ratios listed below are by weight, and all raw materials used are commercially available or synthesized by conventional methods.

[0086] Example 1

[0087] Preparation of positive electrode sheet

[0088] The first material LiCoO2 and the second material Li 1.2 Ni 0.133 Fe 0.133 Mn 0.534 O2, binder (PVDF), and conductive carbon black are mixed, wherein LiCoO2 and Li 1.2 Ni 0.133 Fe 0.133 Mn 0.534 The weight ratio of O2, PVDF and conductive carbon black is 92.5:5.0:1.5:1.0. NMP solvent is added and the mixture is stirred evenly under vacuum to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated on one side of the positive electrode current collector aluminum foil and dried to obtain a single-sided coated positive electrode sheet. The above steps are repeated on the other side of the aluminum foil to obtain a double-sided coated positive electrode sheet. After cold pressing and cutting, the positive electrode sheet is obtained.

[0089] Preparation of negative electrode sheet

[0090] The negative electrode active material graphite / SiO (graphite to SiO weight ratio of 4:1), binder polyacrylic acid (PAA) and conductive carbon black are mixed in a mass ratio of 95.7:3.2:1.1. Deionized water is added and the mixture is stirred evenly under vacuum to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated on one side of the negative electrode current collector copper foil and dried to obtain a single-sided coated negative electrode sheet. The above steps are repeated on the other side of the copper foil to obtain a double-sided coated negative electrode sheet. After cold pressing and slitting, the negative electrode sheet is obtained.

[0091] Preparation of electrolyte

[0092] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed thoroughly at a volume ratio of 1:1:1 to obtain an organic solvent. LiPF6 was dissolved in the above organic solvent, and then fluoroethylene carbonate was added and mixed thoroughly to obtain the electrolyte. Based on the total mass of the electrolyte, the mass percentage of LiPF6 was 12.5%, and the mass percentage of fluoroethylene carbonate was 5%.

[0093] Preparation of lithium-ion batteries

[0094] The positive electrode, separator, and negative electrode are stacked sequentially. The separator is a 14μm thick porous polypropylene (PP) membrane, which acts as a barrier between the positive and negative electrodes. The cells are then wound into a bare cell, which is placed in an aluminum-plastic film, injected with electrolyte, and sealed. After standing, formation, and shaping processes, a lithium-ion battery is obtained. The formation process is as follows: The first charge-discharge cycle is performed at 45℃, following this procedure: First, constant current charging at 0.1C for 10 minutes; then constant current charging at 0.5C to a specified voltage Q = 4.6V; then constant voltage charging until the current is less than or equal to 0.05C; finally, constant current discharging at 0.5C to 3.0V.

[0095] Examples 2-24

[0096] Unlike Example 1, the material composition in the positive electrode and the relevant parameters in the preparation steps were adjusted, as detailed in Table 1.

[0097] Comparative Examples 1-4

[0098] Unlike Example 1, the material composition in the positive electrode and the relevant parameters in the preparation steps were adjusted, as detailed in Table 1.

[0099] Test section

[0100] (1) Raman spectroscopy test

[0101] After fully charging the lithium-ion battery, it was disassembled to obtain the positive electrode. The HR Evolution Raman spectrometer from HORIBA, France, was used. The laser wavelength was 532nm (1MHz solid-state laser), the power was 100mW, and the XYZ automatic platform had X=75mm, Y=50mm, XY minimum step size of 50nm, Z minimum step size of 10nm, and imaging rate <10ms.

[0102] (2) SEM testing

[0103] The morphology of the samples and the average particle size were observed using a Carl Zeiss SIGMA-500 field emission scanning electron microscope. SEM images were taken at an appropriate magnification. Using image processing software, the longest diameter of 50 randomly selected particles of the first material was counted, and their average value was taken as the average particle size D1 of the first material. Similarly, the longest diameter of 50 randomly selected particles of the second material was counted, and their average value was taken as the average particle size D2 of the second material.

[0104] (3) High-temperature cycling performance test

[0105] At 45°C, the lithium-ion battery was charged at a constant current rate of 1C to 4.48V, then charged at a constant voltage of 4.48V to a current of 0.05C, and then discharged at a constant current rate of 1C to 3.0V. This constitutes one charge-discharge cycle. The discharge capacity of the lithium-ion battery in the first cycle was recorded. The lithium-ion battery was charged and discharged in the same manner, and the discharge capacity of each cycle was recorded until the discharge capacity of the lithium-ion battery decreased to 80% of the discharge capacity of the first cycle. The number of charge-discharge cycles was recorded.

[0106] (4) Energy density test

[0107] At 25°C, the lithium-ion battery was charged at a constant current rate of 0.2C to 4.48V, then charged at a constant voltage of 4.48V to a current of 0.05C. After resting for 30 minutes, it was discharged at a constant current rate of 0.2C to 3.0V. The discharge capacity D0 of the lithium-ion battery at the 0.2C rate was recorded. The volume of the lithium-ion battery was measured and recorded as V0.

[0108] Energy density = D0 / V0.

[0109] (5) Ratio Performance Test

[0110] At 25°C, the lithium-ion battery was charged at a constant current rate of 0.2C to 4.48V, then charged at a constant voltage of 4.48V to a current of 0.05C, and then discharged at a constant current rate of 0.2C to 3.0V. The discharge capacity at the 0.2C rate was recorded.

[0111] At 25°C, the lithium-ion battery was charged at a constant current rate of 0.2C to 4.48V, then charged at a constant voltage of 4.48V to a current of 0.05C, and then discharged at a constant current rate of 2C to 3.0V. The discharge capacity at the 2C rate was recorded.

[0112] Lithium-ion battery 2C rate discharge capacity retention rate (%) = 2C rate discharge capacity / 0.2C rate discharge capacity × 100%.

[0113] The test results of Examples 1-24 and Comparative Examples 1-4 are shown in Table 2.

[0114] Table 1

[0115]

[0116]

[0117] Table 2

[0118]

[0119]

[0120] From the parameter characteristics in Table 1 and the test data in Table 2, and combined with... Figure 1 and Figure 2 It can be seen that this application, by using lithium cobalt composite oxide and lithium manganese composite oxide with layered crystal structures together in the positive electrode sheet and activating them under high voltage, ensures that the Raman spectrum of the positive electrode active material layer after the lithium-ion battery is fully charged satisfies: 1.4 ≤ I A1 / I B1 With a value of ≤36, on the one hand, the energy density of lithium-ion batteries can be significantly improved, and on the other hand, the positive electrode sheet can have high structural stability during cycling, thereby enabling lithium-ion batteries to have significantly improved high-temperature cycle life.

[0121] Specifically, compared to Example 1, Comparative Example 1 contains only the first material, Comparative Example 2 contains only the second material, and although Comparative Examples 3 and 4 both contain the first material and the second material, the peak intensity ratio in the Raman spectra of Comparative Examples 3 and 4 is different. A1 / I B1 None of them are in the range of 1.4 to 36. Referring to Table 2, the number of high-temperature cycles for Comparative Examples 1 to 4 is only about 600 to 620, while the number of cycles for Example 1 is 813, which is much higher than that for Comparative Examples 1 to 4. It can be seen that a suitable I A1 / I B1 Peak intensity ratio can significantly improve the high-temperature cycling performance of lithium-ion batteries.

[0122] A comparison of Examples 1-23 with Example 24 shows that adding an appropriate amount of T element (Fe and / or Co) to the second material component, 0.05≤n T / n M When the concentration is ≤0.5, the high-temperature cycle life of lithium-ion batteries can be further improved. This is because adding an appropriate amount of T element to the second material component makes the structure of the second material more stable after delithiation, and the Mn element in the delithiation product of the second material is mostly in the form of Mn. 4+ Therefore, it can effectively inhibit Mn 3+ The Ginger-Taylor distortion effect reduces the damage to the SEI film caused by Mn leaching, thereby effectively improving the high-temperature cycle life of the electrochemical device. Furthermore, a comparison between Example 1 and Example 5 shows that the second material containing Fe can further improve the high-temperature cycle life of the lithium-ion battery compared to the second material containing Co. This is because Fe... 3+ To Fe 4+ The ionization energy is much higher than that of Co. 3+ To Co 4+ The ionization energy of Fe is lower than that of Co during high-voltage cycling. This reduces the oxidation of the electrolyte by high-valence metal ions at the interface and helps Mn maintain a high valence, suppressing the Jam-Taylor distortion effect of Mn and reducing the risk of Mn dissolution. At the same time, it can enhance the structural stability of the material and inhibit the migration of transition metals to the lithium layer, thereby improving the high-temperature cycle life of lithium-ion batteries.

[0123] Furthermore, the parameter characteristics in Table 1 and the test data in Table 2 further demonstrate that embodiments with an average particle size ratio (D2 / D1) of the second material to the first material in the range of 0.3-0.5 exhibit higher high-temperature cycle life. This is because, with a D2 / D1 ratio in the range of 0.3-0.5, the particles of the second material can be embedded between the particles of the first material, efficiently replenishing the active lithium of the first material while reducing the occurrence of surface side reactions, thereby improving the high-temperature cycle life of the electrochemical device.

[0124] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An electrochemical device comprising a positive electrode, the positive electrode comprising a positive active material layer, wherein, in a fully charged state, the Raman spectrum of the positive active material layer exhibits a positive electrode active material layer at 580 cm⁻¹. -1 Up to 640 cm -1 A characteristic peak A1 exists within the range, at 420 cm⁻¹. -1 Up to 520 cm -1 Characteristic peak B1 exists within the range; The peak intensity of characteristic peak A1 is I A1 The peak intensity of the characteristic peak B1 is I. B1 , satisfying: 1.4≤I A1 / I B1 ≤36; The positive electrode active material layer comprises a first material and a second material; The first material is a lithium-cobalt composite oxide having a layered crystal structure; The second material is a lithium-manganese composite oxide having a layered crystal structure; The second material includes Mn, T, O, Ni, and T′ elements; the T element includes at least one of Fe or Co; the T′ element includes at least one of Mg, Al, Ti, V, Cr, Cu, Y, Zr, Nb, Mo, La, Zn, Ga, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd, or W; in the second material, the molar amount of the Mn element is n. Mn The molar amount of element T is n T The molar amount of the O element is n. O The molar amount of Ni element is n. Ni The molar amount of element T′ is n T The sum of the molar amounts of the elements Mn, T, Ni, and T′ is n. M The condition is satisfied that: 0.25 ≤ n Mn / n M ≤0.85, 0.05≤n T / n M ≤0.65, 0≤n Ni / n M ≤0.4, 0≤n T’ / n M ≤0.05, 0.35≤n M / n O ≤0.475; The element T includes Fe, and in the second material, the molar amount of Fe is n. Fe The condition is satisfied that: 0.05 ≤ n Fe / n M ≤0.

5.

2. The electrochemical device according to claim 1, characterized in that, 1.4≤I A1 / I B1 ≤21。 3. The electrochemical device according to claim 1, characterized in that, At least one of the following conditions is satisfied: (i) the second material comprises R-3m and C2 / m crystal phase structures; (ii) The first material comprises Co and Me, wherein the Me element comprises at least one of Ni, Mn, Al, Mg, Ti, Zr, La, Y, Mo, V, Cu, Zn, Ga, Nb, Cr, Ba, W, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd, or Ca, and the molar amount of Co in the second material is m. Co The molar amount of the Me element is m. Me The sum of the molar amounts of the Co and Me elements is m. M Satisfying: 0.5≤m Co / m M ≤1, 0≤m Me / m M ≤0.

5.

4. The electrochemical device according to claim 3, characterized in that, the following condition is satisfied: 0.05≤n T / n M ≤0.5。 5. The electrochemical device according to claim 1, characterized in that, at least one of the following conditions is satisfied: (a) the average particle diameter of the first material is D1, the average particle diameter of the second material is D2, which satisfies: 0.3 ≤ D2 / D1 ≤ 0.5; (b) the average particle diameter D1 of the first material is 10μm to 25μm; (c) the average particle diameter D2 of the second material is 4μm to 9μm.

6. The electrochemical device according to claim 1, characterized in that, The compaction density of the positive electrode active material layer is P, which satisfies: 3.5 g / cm³. 3 ≤P≤4.5 g / cm 3 .

7. The electrochemical device according to claim 1, characterized in that, at least one of the following conditions is satisfied: (1) the second material comprises any one of the materials represented by Chemical Formula I: Li 2-e Ni a T b Mn c T′ d O2 Chemical Formula I wherein 0 ≤ a ≤ 0.35, 0 < b ≤ 0.6, 0.25 ≤ c ≤ 0.6, 0 ≤ d ≤ 0.05, 0.7 ≤ a+b+c+d ≤ 0.95, 0.7 ≤ e ≤ 0.95; T comprises at least one of Fe or Co; T' comprises at least one of Mg, Al, Ti, V, Cr, Cu, Y, Zr, Nb, Mo, La, Zn, Ga, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd or W; (2) the first material comprises any one of the materials represented by Chemical Formula II; Li x Co y Me 1-y O 2-t A t Chemical formula II wherein 0.6 ≤ x ≤ 1.2, 0.5 ≤ y ≤ 1, 0 ≤ t ≤ 0.2, Me comprises at least one of Ni, Mn, Al, Mg, Ti, Zr, La, Y, Mo, V, Cu, Zn, Ga, Nb, Cr, Ba, W, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd or Ca, and A comprises at least one of S, N, F, Cl or Br.

8. An electronic device, comprising the electrochemical device according to any one of claims 1-7.

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