Positive electrode sheet, and electrochemical device and electric device comprising same

Abstract

The present application relates to the technical field of electrochemistry. Particularly disclosed are a positive electrode sheet, and an electrochemical device and an electric device comprising same. The positive electrode sheet of the present application comprises a first active material having a particle size of 4-20 μm and a second active material having a particle size of 200-600 nm, wherein the first active material comprises lithium manganese iron phosphate with a manganese content of m%, the second active material comprises lithium manganese iron phosphate and / or lithium iron phosphate with the manganese content of n%, and m and n satisfy: 15≤m-n≤85. In the present application, by controlling the particle size distribution of the positive electrode active materials and the manganese content relationship, an electrochemical device comprising the positive electrode sheet has excellent fast charging performance and energy density.

Description

A positive electrode sheet and an electrochemical device and a power utilization device comprising the same

[0001] Cross-reference to Related Applications

[0002] This application claims priority to Chinese Patent Application No. 202411305169.8, filed on September 19, 2024, entitled “A positive electrode sheet and an electrochemical device and a power utilization device comprising the same”, the entire contents of which are incorporated herein by reference; this application claims priority to Chinese Patent Application No. 202411800897.6, filed on September 19, 2024, entitled “A positive electrode sheet and an electrochemical device and a power utilization device comprising the same”, the entire contents of which are incorporated herein by reference; this application claims priority to Chinese Patent Application No. 202411800883.4, filed on September 19, 2024, entitled “A positive electrode sheet and an electrochemical device and a power utilization device comprising the same”, the entire contents of which are incorporated herein by reference; this application also claims priority to Chinese Patent Application No. 202411800900.4, filed on September 19, 2024, entitled “A positive electrode sheet and an electrochemical device and a power utilization device comprising the same”, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present application relates to the technical field of electrochemistry, in particular to a positive electrode sheet and an electrochemical device and a power utilization device comprising the same. BACKGROUND

[0004] In recent years, with the rapid development of electric vehicles and energy storage systems, the demand for high-performance and high-safety power battery materials is also increasingly urgent. Lithium iron phosphate (LFP) positive electrode material has been widely concerned and applied due to its high safety, low cost and long cycle life. However, the traditional LFP material has certain limitations in energy density. In order to overcome these limitations of traditional LFP materials, lithium manganese iron phosphate (LMFP) has high voltage and high energy density compared with lithium iron phosphate, and has become a kind of alternative product that is concerned.

[0005] Compared with LFP, the diffusion coefficient of LMFP is lower, and the fast charging performance is poorer. Therefore, for LMFP, smaller particle size is needed, so as to reduce the diffusion path of lithium ions in the positive active material particles, so as to efficiently deintercalate, which helps to improve the electronic conductivity, thereby improving the fast charging performance. However, when the particle size of LMFP is small, the reaction surface with the electrolyte is too much, which leads to serious electrolyte side reactions, and for small particle size LMFP particles, the amount of binder needs to be increased, which leads to the decrease of the surface density of the battery, limiting the improvement of the energy density.

[0006] There are prior arts reporting that using LMFP agglomerates containing multiple small primary particles can reduce the amount of binder used and improve the energy density. However, the use of LMFP agglomerates limits the improvement of the compaction density of the pole piece, and the material inside may be broken during the processing of higher compaction, resulting in the deterioration of electrochemical performance. Moreover, agglomerates can also cause the deterioration of the bulk transport capacity of the material, and the kinetic performance, especially the fast charging performance, is reduced.

[0007] Therefore, it is necessary to develop a positive pole piece with good fast charging performance and energy density. SUMMARY

[0008] The purpose of the present application is to overcome the deficiencies in the prior art and provide a positive pole piece and an electrochemical device and an electric device comprising the same, which uses an LMFP material system, and by adjusting the particle size distribution of LMFP agglomerates and LMFP / LFP nanoscale particles and the manganese content of the material, the positive pole piece has excellent fast charging performance and energy density.

[0009] To achieve the above-mentioned purpose, in the first aspect of the present application, the present application provides a positive pole piece, which comprises a positive current collector and a positive active material layer arranged on at least one surface of the positive current collector, the positive active material layer comprising a positive active material, the positive active material comprising a first active material with a particle size of 4-20 μm and a second active material with a particle size of 200-600 nm;

[0010] The first active material comprises lithium manganese iron phosphate (LMFP), and the molar percentage content of manganese in the first active material is m% based on the total number of moles of metal elements other than lithium in the first active material;

[0011] The second active material comprises lithium manganese iron phosphate and / or lithium iron phosphate (LFP), and the molar percentage content of manganese in the second active material is n% based on the total number of moles of metal elements other than lithium in the second active material;

[0012] The m and the n satisfy the following relationship: 15≤m-n≤85.

[0013] As an optional embodiment of the present application, the m and the n satisfy the following relationship: 40≤m-n≤70.

[0014] As an optional embodiment of the present application, the m and the n satisfy the following relationship: 0.10≤n / m≤0.85.

[0015] As a further optional embodiment of the present application, the m and the n satisfy the following relationship: 0.18≤n / m≤0.45.

[0016] As an optional embodiment of the present application, the m% is 70-95%.

[0017] As an optional embodiment of the present application, the n% is 0-60%.

[0018] As an optional embodiment of the present application, the first active material comprises secondary particles formed by primary particles, the diameter of the primary particles being 20-130 nm.

[0019] As an optional embodiment of the present application, the molar ratio (Mn / Fe) of manganese element to iron element in the positive electrode active material is 1-4.

[0020] As an optional embodiment of the present application, the positive electrode tab satisfies the following relationship: 5≤(a×b) / c≤60;

[0021] The a is the value of m-n;

[0022] The b is the molar ratio of manganese element to iron element in the positive electrode active material;

[0023] The c is the peak intensity ratio of (101) crystal face to (020) crystal face diffraction peak in the XRD pattern of the positive electrode tab.

[0024] As an optional embodiment of the present application, the c ranges from 0.75 to 1.13.

[0025] In a second aspect of the present application, the present application provides an electrochemical device comprising the above-mentioned positive electrode tab.

[0026] In a third aspect of the present application, the present application provides a power utilization device comprising the above-mentioned electrochemical device.

[0027] The present application has the following beneficial effects:

[0028] The present application provides a positive electrode tab, an electrochemical device comprising the same, and a power utilization device. The positive electrode tab of the present application mainly adopts a LMFP material system, and by controlling the particle size distribution of LMFP / LFP agglomerates and nano-sized particles in the positive electrode active material, and the manganese content relationship of LMFP / LFP, the positive electrode tab has excellent fast charging performance and energy density. BRIEF DESCRIPTION OF DRAWINGS

[0029] FIG. 1 is an SEM image of the positive electrode active material of Example 1 at a 5K rate.

[0030] Fig. 2 is an SEM image of the positive electrode active material of Example 19 at a 10K rate.

[0031] Fig. 3 is an XRD pattern of the positive electrode sheet prepared in Example 1.

[0032] Fig. 4 is an XRD pattern of the positive electrode sheet prepared in Example 19. DETAILED DESCRIPTION

[0033] In order to make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0034] In the present application, the technical features described in an open manner include both the closed technical solutions consisting of the listed features and the open technical solutions containing the listed features.

[0035] In the present application, if no special description is provided, the numerical range is regarded as continuous and includes the minimum value and the maximum value of the range and each value between the minimum value and the maximum value. Further, when the range refers to an integer, each integer between the minimum value and the maximum value of the range is included. In addition, when multiple ranges are provided to describe a feature or a property, the ranges can be combined. In other words, unless otherwise specified, all the ranges disclosed herein should be understood as including any and all sub-ranges.

[0036] In the present application, the specific dispersion and stirring treatment method is not particularly limited.

[0037] The reagents or instruments used in the present application are all conventional products that can be obtained through market purchase, unless otherwise specified.

[0038] One embodiment of the present application provides a positive electrode sheet, which comprises a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector, and the positive electrode active material layer comprises a positive electrode active material, and the positive electrode active material comprises a first active material with a particle size of 4-20 μm and a second active material with a particle size of 200-600 nm.

[0039] The first active material comprises lithium manganese iron phosphate (LMFP), and the molar percentage content of manganese in the first active material is m% based on the total moles of metal elements other than lithium in the first active material.

[0040] The second active material includes lithium manganese iron phosphate and / or lithium iron phosphate (LFP), and the molar percentage content of manganese in the second active material is n% based on the total moles of metal elements other than lithium in the second active material;

[0041] The m and the n satisfy the following relationship: 15≤m-n≤85.

[0042] The present application researches and finds that by using LMFP agglomerates with high manganese content in combination with LMFP nano-sized particles with low manganese content and / or LFP nano-sized particles without manganese, the fast-charging performance and energy density of the lithium manganese iron phosphate system positive electrode sheet can be simultaneously improved.

[0043] In the present application, the positive electrode active material includes a first active material with a particle size of 4-20 μm and a second active material with a particle size of 200-600 nm. Agglomerates refer to secondary particles formed by the aggregation of two or more primary particles, and the first active material is in the form of highly agglomerated agglomerates. Generally, due to the process of highly agglomerated primary particles, the particle size of the first active material is large. The particle size of the second active material is relatively small, and it is a nano-sized particle. The second active material can be a non-agglomerated primary particle or a secondary particle with extremely low agglomeration (two or three primary particles are aggregated). The agglomeration state or non-agglomeration state of the particles and the number of agglomerated particles can be observed by using a scanning electron microscope (SEM) image. Combined with the particle size observed by SEM, the first active material and the second active material in the positive electrode active material layer can be distinguished.

[0044] In the present application, the manganese content (m%) in the first active material is high, and the manganese content (n%) in the second active material is low or zero. The form of high-manganese large-particle agglomerates combined with low-manganese or manganese-free nano-sized particles is used to fill the inter-particle voids formed by the large-particle first active material with the second active material with small particle size, thereby improving the compaction density. A certain amount of agglomerates is used as the positive electrode active material to reduce the amount of binder used, increase the coating amount per unit area, and increase the area density. The first active material is LMFP agglomerates with high manganese content. By using the positive electrode active material with high manganese content, the energy density of the battery is further improved. Through the improvement of the compaction density and the area density, and the specific manganese content, the battery can achieve higher energy density. In addition, by compounding low-manganese or manganese-free nano-sized particles, the fast-charging performance is greatly improved on the basis of maintaining high energy density of the battery.

[0045] The difference between m and n should be within a suitable range, and the manganese content difference between the two active materials should not be too large or too small. When 0≤m-n<15, the difference is too small, meaning that the manganese content of the first active material and the second active material is very close, and the high energy density and excellent fast charging performance brought by the high manganese and low manganese combination cannot be achieved, and the improvement effect of the high and low manganese content material combination cannot be reflected. When m-n>85, the difference is too large, meaning that the manganese content in the first active material is too high, and even if the second active material is mixed, the improvement of the ion transmission rate in the positive active material is also limited, resulting in a decrease in the fast charging performance of the battery. When the manganese content in the first active material is lower than that in the second active material, i.e. m<n, the second active material has a high manganese content, and since its particle size is only nanoscale, it is easy to cause manganese dissolution and intensify electrolyte side reactions, resulting in battery performance degradation. Although the first active material has a low manganese content, the particle size is too large and the agglomeration degree is too high, which also leads to the inability to effectively improve the fast charging performance of the battery.

[0046] For example, in the present application, the value of m-n can be 15, 20, 30, 50, 60, 70, 75, 80, 85, or an interval range formed by any two of the above values.

[0047] In one preferred embodiment, the m and the n satisfy the following relationship: 40≤m-n≤70.

[0048] When the difference between m and n is within the above preferred range, the energy density and fast charging performance of the battery containing the positive electrode sheet are more comprehensive.

[0049] In one embodiment, the m and the n satisfy the following relationship: 0.10≤n / m≤0.85.

[0050] For example, in the present application, the value of n / m can be 0.10, 0.15, 0.20, 0.30, 0.50, 0.70, 0.75, 0.80, 0.85, or an interval range formed by any two of the above values.

[0051] The difference between m and n (m-n) reflects the absolute value difference of the manganese content in the first and second active materials; unlike the difference, the ratio of n to m (n / m) reflects the relative size relationship of the manganese content in the second active material and the first active material. The present application found that when m and n satisfy the difference within the range defined in the present application, and further satisfy 0.10≤n / m≤0.85, the energy density and fast charging performance of the positive electrode sheet are relatively more balanced.

[0052] In one preferred embodiment, the m and the n satisfy the following relationship: 0.18≤n / m≤0.45.

[0053] In one embodiment, the m% is 70-95%. For example, the m% can be 70%, 75%, 80%, 85%, 90%, 95%.

[0054] In one preferred embodiment, the m% is 75-85%.

[0055] Although LMFP with higher manganese content has higher specific capacity, as the manganese content increases, the kinetic performance of the battery further decreases, and the fast-charging performance is poor. And when the manganese content is too high, such as more than 95%, it is easy to promote the Jahn-Teller effect, causing lattice distortion of the material, and the reaction between manganese dissolution and electrolyte may cause the stability of the material to decrease, too much heat is generated during the charging and discharging process, affecting the cycle stability and long-term life of the battery, especially after a certain cycle, the energy density of the battery will decrease.

[0056] In one embodiment, the n% is 0-60%, for example, the n% can be 0%, 10%, 15%, 20%, 30%, 40%, 50%, 55%, 58%, 60%.

[0057] In one preferred embodiment, the n% is 15-40%.

[0058] The n% of the second active material should not be too low, in the case of too low (such as less than 15%), it may cause the platform voltage to be insufficiently obvious, affecting the energy density of the overall material. And in the case of n% greater than 40%, the manganese-iron ratio of the overall positive active material may be too high, resulting in a decrease in the fast-charging performance of the battery; and after a certain cycle, the structural stability of the material with too high manganese-iron ratio is relatively low, and the energy density of the battery will also decrease.

[0059] When the m% and n% are within the above ranges, the high-manganese and low-manganese LMFP materials can better cooperate with each other, achieving better battery kinetic performance, and the fast-charging performance of the battery is greatly improved.

[0060] It should be noted that the second active material includes LMFP and / or LFP, when the second active material is LFP, the n% is 0%; when n%>0, the second active material can be LMFP, or a mixture of LMFP and LFP.

[0061] As for the detection method of m% and n%, the present application does not make any limitation, and those skilled in the art can detect the manganese content of the positive active material of a specific particle size according to conventional technical means.

[0062] For example, the m% and n% can be detected by the following method:

[0063] Disassemble the battery to obtain the positive electrode sheet, and obtain the positive electrode active material powder after treatment. The m% and n% are obtained by electron microscope (SEM) and energy spectrometer (EDS) test.

[0064] In one embodiment, the first active material comprises secondary particles formed by primary particles, and the average diameter of the primary particles is 20-130 nm.

[0065] In one preferred embodiment, the first active material comprises secondary particles formed by primary particles, and the average diameter of the primary particles is 40-90 nm.

[0066] In the positive electrode active material of the present application, the average diameter of the primary particles in the first active material is smaller than the particle size of the particles of the second active material. For high-manganese LMFP materials, due to the high manganese content, the lithium ion diffusion coefficient of the material itself decreases, and the charge and discharge rate slows down. In order to compensate for the fast-charging performance defects brought by high manganese content, the present application studies the use of high-manganese primary particles with extremely small particle size to form high-manganese agglomerates, and especially preferably uses primary particles with an average diameter of 40-90 nm to increase the contact between particles and enhance the internal conductivity of the high-manganese agglomerates, which can ensure good fast-charging performance of the battery.

[0067] For the agglomerated LMFP, after being coated on the surface of the positive electrode current collector as the positive electrode active material, some of the agglomerates may be loose during the processing of the positive electrode sheet, resulting in the presence of primary particles with a particle size of 20-130 nm in the positive electrode active material layer. It should be noted that the primary particles in this particle size range (20-130 nm) do not belong to the second active material.

[0068] In one embodiment, the molar ratio of manganese element to iron element (Mn / Fe) in the positive electrode active material is 1.0-4.0, for example, the Mn / Fe can be 1.0, 1.5, 1.8, 2.0, 2.5, 3.0, 3.5, 3.8, 4.0.

[0069] In one preferred embodiment, the molar ratio of manganese element to iron element in the positive electrode active material is 2.0-3.5.

[0070] In one embodiment, the positive electrode sheet satisfies the following relationship: 5≤(a×b) / c≤60;

[0071] The a is the value of m-n;

[0072] The b is the molar ratio of manganese element to iron element in the positive electrode active material;

[0073] The c is the peak intensity ratio (denoted as I) of the diffraction peaks of the (101) crystal plane and the (020) crystal plane in the XRD pattern of the positive electrode. 101 / I 020 ).

[0074] XRD analysis was performed on the positive electrode. In the XRD pattern, a diffraction peak (peak intensity denoted as I) was observed at the position 2θ = 20.7° ± 0.5°. 101 The diffraction peak (peak intensity denoted as I) at the position of 2θ = 29.5° ± 0.5° corresponding to the (101) crystal plane of the positive electrode active material is located at the position of 2θ = 29.5° ± 0.5°. 020 ) corresponds to the (020) crystal plane of the positive electrode active material.

[0075] In the positive electrode active materials of this application, both lithium manganese iron phosphate and lithium iron phosphate are olivine-type materials. For olivine-type materials, I... 020 The (020) crystal plane corresponding to the diffraction peaks extends along the b-axis of the crystal. Lithium-ion diffusion along the b-axis is the main pathway during battery charging and discharging; therefore, good development of the (020) crystal plane is a crucial factor in improving the fast-charging performance of the material. However, the rapid insertion and extraction of lithium ions can lead to abrupt changes in the crystal lattice, and these changes can cause a decrease in the energy density of the positive electrode. This study found that I... 101 The (101) crystal plane corresponding to the diffraction peaks plays an important role in maintaining lattice integrity and suppressing lattice abrupt changes. The (101) crystal plane is at a certain angle relative to the b-axis and c-axis in the crystal structure. During rapid charge and discharge, the (101) crystal plane can provide a relatively stable structural platform, helping to alleviate lattice stress caused by the rapid migration of lithium ions. 101 and I 020 The ratio (i.e., I) 101 / I 020 This can demonstrate the proportional relationship between the (101) and (020) crystal planes. In this application, by controlling I... 101 / I 020 During rapid charging and discharging, the material maintains structural stability while ensuring a good lithium-ion diffusion path, thereby achieving a balance between fast charging and maintaining energy density.

[0076] I 101 / I 020 The value of a, b, and c is related to the content and distribution of manganese and iron in the positive electrode active material; therefore, the values ​​of a, b, and c need to be comprehensively limited. This application's research found that when a, b, and c satisfy 5 ≤ a × b × c ≤ 60, the battery's fast-charging performance and energy density are superior overall.

[0077] This application does not limit the method for detecting the c-value. Those skilled in the art can perform XRD detection on the positive electrode sheet using conventional technical means.

[0078] In one preferred embodiment, the positive electrode sheet satisfies the following relationship: 15≤(a x b) / c≤30.

[0079] In one preferred embodiment, the value of c is in the range of 0.75-1.13.

[0080] In one further preferred embodiment, the value of c is in the range of 0.84-1.05.

[0081] When the value of c is in the above preferred range, it indicates that the (101) crystal plane and the (020) crystal plane are relatively more balanced, which helps to better the fast charging performance and energy density of the battery.

[0082] In the present application, the preparation method of LMFP and LFP is not limited, and those skilled in the art can prepare LMFP or LFP according to conventional technical means.

[0083] For example, the preparation method of LMFP can include the following steps:

[0084] Mix the manganese source, iron source, phosphorus source and lithium source in a certain molar ratio, use deionized water as a dispersant, and perform ball milling;

[0085] Spray dry the wet material after the above ball milling to obtain dry mixed powder;

[0086] Sinter the above dry powder in an atmosphere with a nitrogen concentration less than 150 ppm; and LMFP agglomerates can be obtained.

[0087] Break the LMFP agglomerates obtained in the above step, and then perform screening and grading to obtain LMFP nano-level particles with a specific particle size range.

[0088] The preparation method of LFP is similar to that of LMFP, except that no manganese source is added.

[0089] The lithium source can include at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxalate, lithium dihydrogen phosphate, lithium citrate or lithium acetate.

[0090] The phosphorus source can include at least one of diammonium hydrogen phosphate, lithium dihydrogen phosphate, ammonium phosphate or lithium phosphate.

[0091] The iron source can include at least one of ferrous oxalate, iron hydroxide, ferrous hydroxide, iron phosphate, ferrous phosphate, iron acetate, ferrous acetate, iron carbonate, ferrous carbonate, diiron trioxide, triiron tetroxide or iron oxalate.

[0092] The manganese source can include at least one of manganese carbonate, manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate or manganese acetate.

[0093] In the preparation of the LMFP and / or LFP, the carbon source can be mixed with the manganese source (if any), the iron source, the phosphorus source and the lithium source as needed to obtain the LMFP and / or LFP containing a carbon coating layer.

[0094] The carbon source can include at least one of glucose, sucrose, polyethylene glycol (PEG), and polyvinyl alcohol.

[0095] In the preparation of the LMFP and / or LFP, a certain amount of a doping element source can be mixed with the manganese source (if any), the iron source, the phosphorus source and the lithium source as needed to obtain the LMFP and / or LFP containing a certain amount of a doping element, the doping element source being, for example, a vanadium source (divanadium pentoxide), a tungsten source (ammonium metatungstate), a titanium source (titanium oxide), a magnesium source (magnesium carbonate), etc.

[0096] wherein the structural formula of the manganese-iron-lithium particles is: LiMn x Fe y M z n PO4, wherein 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, M refers to a doping element, and n refers to the valence of the doping element; and 2(x+y)+n*z=2 is satisfied.

[0097] The manganese-iron-phosphorus source can be used to simultaneously serve as the manganese source, the iron source and the phosphorus source; and the iron-phosphorus source can be used to simultaneously serve as the iron source and the phosphorus source.

[0098] Optionally, the solvent can be at least one of water and ethanol.

[0099] Optionally, the ball milling can use zirconium oxide as the ball milling beads. The diameter of the ball milling beads can be a conventional size in ball milling, such as 0.05-50 mm in diameter. In the ball milling, the mass ratio of the grinding material to the ball milling beads (ball-to-material ratio) can be adjusted as needed, such as the ball-to-material ratio being selected to be (2-10):1. The ball milling conditions can be: time 2-20 h, rotation speed 200-500 rpm.

[0100] Optionally, the sintering conditions can be: sintering at 600-1200 °C for 5-20 h at a temperature increasing rate of 5-20 °C / min from room temperature.

[0101] Optionally, the sintering can also use gradient sintering conditions.

[0102] By adjusting the addition amount of the manganese source and the iron source, the proportion of the manganese content in the LMFP can be controlled; and by adjusting the sintering conditions and the crushing and screening grading conditions, the particle size of the LMFP and the LFP can be controlled.

[0103] The positive electrode active material can be obtained by directly mixing the first active material and the second active material uniformly. The mixing mass ratio of the first active material and the second active material can be (40:60) to (99:1).

[0104] In addition to the positive electrode active material described above, the positive electrode active material layer can further include a conductive agent and a binder.

[0105] The conductive agent can be at least one of carbon nanotubes, carbon black, or graphene, without particular limitation on the type of the conductive agent in the present application, as long as the conductive agent has suitable electronic conductivity and does not cause adverse chemical changes in the battery.

[0106] The binder is used to improve the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector, and the binder can be a conventional choice in the field of batteries in the present application. Specifically, the conductive agent can be at least one of 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), or sodium alginate.

[0107] The positive electrode current collector is not particularly limited in the present application, as long as it has electrical conductivity without causing adverse chemical changes in the battery, and can be, for example, stainless steel, aluminum, nickel, titanium, baked carbon; or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc.

[0108] The positive electrode tab of the present application can be prepared according to conventional methods in the art. For example, the positive electrode active material, the conductive agent, and the binder are dispersed in a solvent to form a uniform positive electrode slurry, the positive electrode slurry is coated on the positive electrode current collector, and after processes such as drying and rolling, the positive electrode tab is obtained.

[0109] An embodiment of the present application provides an electrochemical device comprising the positive electrode tab described above.

[0110] In addition to the positive electrode tab, the electrochemical device further includes a negative electrode tab, a separator, and an electrolyte.

[0111] The negative electrode tab includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material. The type of the negative electrode active material is not particularly limited in the embodiments of the present application, and can be selected according to actual needs. As an example, the negative electrode active material can be natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, or silicon-carbon composite.

[0112] The separator is located between the positive electrode sheet and the negative electrode sheet, and is used to separate the positive electrode sheet and the negative electrode sheet, and prevent the positive electrode sheet and the negative electrode sheet from short circuiting. The separator can be various materials suitable for the separator of the electrochemical energy storage device in the art. Specifically, the separator comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fiber.

[0113] The electrolyte of the present application can be various electrolytes suitable for the electrochemical energy storage device in the art. The electrolyte comprises an electrolyte and a solvent, and the electrolyte can generally comprise a lithium salt.

[0114] Specifically, the lithium salt comprises at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). The concentration of the electrolyte in the electrolyte can be 0.5-5 mol / L.

[0115] Specifically, the solvent comprises at least one of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene 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), and diethyl sulfone (ESE).

[0116] An embodiment of the present application provides a power utilization device comprising the electrochemical device described above. The electrochemical device is used as a power supply of the power utilization device.

[0117] The power utilization device refers to any device that can utilize electric energy and convert it into mechanical energy, thermal energy, light energy, or other one or more forms of energy, such as an electric motor, an electric heating machine, an electric light source, etc. Specifically, it can include but is not limited to mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. The mobile device can be a mobile phone, a notebook computer, a drone, a sweeping robot, an electronic cigarette, etc. The electric vehicle can be a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.

[0118] The application is further described below with specific examples.

[0119] Examples 1-19 and Comparative Examples 1-3

[0120] Examples 1-19 and Comparative Examples 1-3 each provide a lithium ion battery, and the preparation method is as follows:

[0121] (1) Preparation of the positive electrode sheet

[0122] (1.1) Preparation of the positive active material

[0123] Preparation of the first active material:

[0124] According to the target chemical formula LiMn m / 100 Fe 1-m / 100 PO4(m values are shown in Table 2), lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate were weighed according to the molar ratio of each element Li, Mn, Fe, and P, respectively, and then mixed. The mixed material was mixed with glucose and ethanol for first ball milling. Zirconia with a diameter of 0.6 mm was used as the ball milling bead, and the ball-to-material ratio was 5:1. The first ball milling speed was 300 rpm, and the first ball milling time is shown in Table 1.

[0125] After filtering the above ground wet material, it was dried by blowing for 2h, and then spray dried for 5h to obtain a dry powder, i.e. a precursor;

[0126] The above dry powder was placed in a tube furnace and sintered in an atmosphere with an oxygen concentration less than 150ppm. The sintering conditions are shown in Table 1: the temperature was raised from room temperature to 850℃ at a rate of 12℃ / min, and maintained for 960min; and then cooled to room temperature.

[0127] The sintered product was sieved to obtain LMFP agglomerates with a particle size in the range of 4-20μm, which is the first active material.

[0128] Preparation of the second active material:

[0129] According to the target chemical formula LiMn n / 100 Fe 1-n / 100Li, Mn, Fe, P elements in PO4(n value see Table 2) were weighed respectively, and lithium carbonate, manganese carbonate, ferrous oxalate, diammonium hydrogen phosphate were mixed, and the mixed material was mixed with glucose and ethanol for second ball milling, zirconia with a diameter of 0.6 mm was used as the ball milling bead, the ball-to-material ratio was 5:1, the rotation speed of the second ball milling was 200 rpm, and the second ball milling time was shown in Table 1;

[0130] The above ground wet material was filtered, air dried and spray dried under the same conditions as in the first active material, and then sintered, the sintering conditions were: from room temperature to 850℃ at a heating rate of 12℃ / min, and kept for 960min; cooled to room temperature;

[0131] The sintered product was crushed and then screened, and the LMFP nano-sized particles with a particle size in the range of 200-600nm (when n is 0, it is LFP nano-sized particles) were obtained, which was the second active material;

[0132] (1.2) The above first active material and the above second active material were mixed uniformly according to the mass ratio shown in Table 1 to obtain a positive electrode active material;

[0133] The positive electrode active material, conductive agent (SP) and binder (PVDF) were mixed uniformly in NMP at a mass ratio of 96:1.5:2.5, then the mixed positive electrode slurry was uniformly coated on an aluminum foil with a thickness of 15μm, the coating density was 446m 2 / g, and the compaction density was 2.4m 3 / g; the positive electrode sheet was dried in a vacuum oven at 100℃, then was cut and rolled to obtain a positive electrode sheet.

[0134] (2) Preparation of negative electrode sheet

[0135] The negative electrode active material (artificial graphite), conductive agent (CNT) and binder (carboxymethyl cellulose, CMC) were mixed at a mass ratio of 96:1.5:2.5, and were dispersed in deionized water, and a negative electrode slurry was prepared by a wet process using a vacuum stirrer, the negative electrode slurry was uniformly coated on a negative electrode current collector (copper foil), and the negative electrode current collector coated with the negative electrode slurry was transferred to a vacuum oven for drying at 100℃ for 12h, and then was cut and rolled to obtain a negative electrode sheet.

[0136] (3) Preparation of electrolyte

[0137] Vinyl carbonate (EC) and methyl ethyl carbonate (EMC) were mixed at a weight ratio of 3:7 to obtain an organic solvent, and then the dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1.15mol / L.

[0138] (4) Preparation of the separator

[0139] A polyethylene (PE) separator was used.

[0140] (5) Preparation of the battery

[0141] The prepared positive electrode sheet, the separator, and the negative electrode sheet were stacked (the number of positive electrode stack layers was 40, and the number of negative electrode stack layers was 41) to obtain a bare cell without liquid injection; the bare cell was placed in an outer packaging foil, and the prepared electrolyte was injected into the dried bare cell; and the cell was subjected to vacuum packaging, standing, formation, shaping, sorting, and other processes to obtain a lithium ion battery with a size of 202 mm in length and 90 mm in width.

[0142] Table 1

[0143] The m% of the first active material, the n% of the second active material, the average diameter of the primary particles of the first active material, the Mn / Fe of the positive electrode active material, and the I of the positive electrode sheet were detected for each of the examples and the comparative examples. 101 / I 020 The detection methods of the above items are as follows:

[0144] The m% of the first active material and the n% of the second active material were detected as follows: a lithium ion battery was disassembled to obtain a positive electrode sheet; the positive electrode sheet was soaked in DMC (dimethyl carbonate) at room temperature for 60 min, taken out, and dried at room temperature with a humidity of ≤15% to obtain a sheet sample.

[0145] The sheet sample was adhered to a sample holder with a layer of conductive adhesive, and then a conductive film was plated thereon; the sample was observed under a scanning electron microscope (SEM) at a magnification of 5KX; the first active material and the second active material were determined according to the morphology and particle size of the agglomerates and the single particles; the molar content of the Mn element in the first active material and the second active material was analyzed by EDS testing to obtain the m% and the n%.

[0146] The average diameter of the primary particles of the first active material was detected as follows: the positive electrode active material powder obtained by disassembling the lithium ion battery was uniformly spread on conductive adhesive and directly placed in a SEM; a SEM photo with a clear image at a magnification of 30KN (30KX) was selected; the particle size distribution of the primary particles of the first active material was measured by particle size measurement software (Nano Measurer) (400 particles were measured); and the average number of the diameter of the primary particles was obtained.

[0147] The Mn / Fe of the positive electrode active material was detected as follows:

[0148] The positive electrode active material powder was obtained by disassembling the lithium ion battery, 0.5 g of the positive electrode active material powder was accurately weighed, dispersed in 20 ml of water, 10 ml of nitric acid was added, and after uniform mixing, heating treatment was carried out, after the positive electrode active material powder was dissolved, the material was diluted to 100 ml with water to obtain a test solution;

[0149] The test solution was subjected to ICP test, the ICP test conditions were: the selected element detection spectrum wavelength (Fe wavelength 259.94, 238.204, 239.562 nm, Mn wavelength 257.61 nm), according to the characteristics of the sample and the elements to be detected, the appropriate ICP instrument working conditions were set, including gas flow 0.5 L / min, power 1150 W;

[0150] The Mn / Fe content of the elements in the positive electrode active material was calculated by ICP test.

[0151] I 101 / I 020 : Disassembling the lithium ion battery, obtaining the positive electrode sheet, and performing XRD test on the positive electrode sheet, the XRD conditions were: using an X-ray diffractometer for testing; Cu target, Start angle (start angle) was set to 5°, Stop angle (end angle) was set to 90°, Sampling W (step angle) was set to 0.02, Scan speed (scanning speed) was 3° / min, acceleration voltage was set to 40KV, and acceleration current was set to 40mA.

[0152] The test results of each example and comparative example are shown in Table 2.

[0153] The SEM images of the positive electrode active materials of Example 1 and Example 19 are shown in Figures 1 and 2, respectively. In Figure 1, the agglomerates shown in "spectrum 2" are the first active material, and the particles shown in "spectrum 1", "spectrum 3" and "spectrum 4" are the second active material.

[0154] The XRD spectra of the positive electrode sheets of Example 1 and Example 19 are shown in Figures 3 and 4, respectively.

[0155] Table 2

[0156] The performance test of the fast charging performance and energy density of the lithium ion battery was carried out, and the specific method was as follows:

[0157] (1) Fast charging performance:

[0158] Lamella three-electrode test method, the positive and negative electrode sheets of the lithium ion battery are taken out, soaked and cleaned with DMC solvent for more than 72h, the sheets are dried in a vacuum oven, and then the positive and negative electrode sheets are assembled into a lamella three-electrode cell, wherein the copper wire is used as a reference electrode; a blue and charge-discharge device is used for testing;

[0159] 25℃, 0.33C charge-discharge for two cycles (upper limit voltage 4.25V, lower limit voltage 2.5V), and the charge capacity of the second cycle is used as the standard capacity;

[0160] After charging at 0.33C to 10% SOC, start charging at 4C (this time is recorded as time t1), and perform constant current charging with the upper limit voltage 4.25V or negative reference potential ≤0mv as the stopping condition, and after reaching the stopping condition, perform step-down charging at 0.2C until the current decreases to 0.05C, and the time when the charge capacity reaches 80% SOC is recorded as t2;

[0161] The time consumption from t1 to t2 (i.e. the time from 10% SOC to 80% SOC) is the fast charging time, and the unit is min.

[0162] (2) Volume energy density:

[0163] In a 25℃ constant temperature box, the lithium ion battery is subjected to charge-discharge cycle test, and the charge-discharge system is as follows: 0.33C constant current charging to 4.25V, then constant voltage charging until the current decreases to 0.05C, and then 1C constant current discharging to 2.5V after 5min, which is one cycle; after 10 cycles, the discharge capacity of the lithium ion battery at the 10th cycle is obtained;

[0164] The surface area S of the positive electrode active material layer and the total thickness T of the positive electrode active material layer in the prepared positive electrode sheet are measured;

[0165] The reversible capacity per unit area of the positive electrode active material layer after cycling C (Ah / cm 2 ) = discharge capacity of the lithium ion battery at the 10th cycle / surface area S of the positive electrode active material layer;

[0166] The ratio of the reversible capacity per unit area of the positive electrode active material to the total thickness of the positive electrode active material layer (C / T) (mAh / cm 3 ) = reversible capacity per unit area of the positive electrode active material layer after cycling C / total thickness T of the positive electrode active material layer.

[0167] The ratio of the reversible capacity per unit area of the positive electrode active material to the total thickness of the positive electrode active material layer is used to measure the volume energy density of the lithium ion battery after 10 cycles.

[0168] The test results are shown in Table 3.

[0169] Table 3

[0170] According to the test results of the examples and the comparative examples, it can be seen that the lithium ion battery using the positive electrode plate prepared by each embodiment of the present application has excellent fast charging performance and energy density, wherein the fast charging time is ≤25.3 min, the volume energy density is ≥398 mAh / cm 3 .

[0171] According to examples 1-5, it can be seen that when the average diameter of the primary particles of the first active material is 40-90 nm, the fast charging performance and energy density of the battery are more comprehensive. When the average diameter of the primary particles is slightly small, although the fast charging performance of the battery is improved, the energy density may be reduced, and the processing process is more difficult. When the average diameter of the primary particles is slightly large, the energy density of the battery is higher, but the fast charging time is longer, and the fast charging performance is decreased.

[0172] According to examples 6-8 and example 13, it can be seen that when the value of m exceeds 75-85, the value of n exceeds 15-40, or the value of n / m exceeds 0.18-0.45, the fast charging performance and energy density of the battery cannot be well balanced, and the comprehensive performance of the battery is slightly poor.

[0173] According to examples 9-12, it can be seen that when the positive electrode plate further satisfies that the Mn / Fe of the positive electrode active material is 2.0-3.5, the I 101 / I 020 of the positive electrode active material is 0.84-1.05, and (a / b)*c is 15-30, the fast charging performance and energy density of the battery are relatively more optimal.

[0174] According to example 19, when the second active material is LFP, as long as m-n is within the range of the technical solution of the present application, good fast charging performance and high energy density of the lithium ion battery can also be achieved.

[0175] According to comparative examples 1-2, it can be seen that when the value of m-n is too large, the manganese content of the first active material and the second active material cannot be effectively matched, causing the fast charging performance of the battery to deteriorate seriously. According to comparative example 3, it can be seen that when the value of m-n is too small, the manganese content of the first active material and the second active material is very close, and the improvement of the fast charging performance and energy density of the battery is not obvious. According to comparative example 4, when the manganese content of the second active material is higher than that of the first active material, the battery performance deteriorates, and the fast charging performance and energy density of the lithium ion battery are very poor.

[0176] It should be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A positive electrode sheet comprising a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector, the positive electrode active material layer containing a positive electrode active material, characterized in that, The positive electrode active material comprises a first active material with a particle size of 4-20 μm and a second active material with a particle size of 200-600 nm; The first active material comprises lithium iron manganese phosphate, and the molar percentage content of manganese in the first active material is m% based on the total number of moles of metal elements other than lithium in the first active material; the second active material comprises lithium iron manganese phosphate and / or lithium iron phosphate, and the molar percentage content of manganese in the second active material is n% based on the total number of moles of metal elements other than lithium in the second active material; The m and the n satisfy the following relationship: 15≤m-n≤85.

2. The positive electrode sheet according to claim 1, characterized by The m and the n satisfy the following relationship: 40≤m-n≤70.

3. The positive electrode sheet according to claim 1 or 2, characterized by The m and the n satisfy the following relationship: 0.10≤n / m≤0.

85.

4. The positive electrode sheet according to claim 3, wherein The m and the n satisfy the following relationship: 0.18≤n / m≤0.

45.

5. The positive electrode plate of claim 1, wherein, The m% is 70-95%.

6. The positive electrode plate of claim 1, wherein, The n% is 0-60%.

7. The positive electrode plate of claim 1, wherein, The first active material comprises secondary particles formed by primary particles, and the average diameter of the primary particles is 20-130 nm.

8. The positive electrode plate of claim 1, wherein, The molar ratio of manganese to iron in the positive electrode active material is 1-4.

9. The positive electrode plate of claim 1, wherein, The positive electrode tab satisfies the following relationship: 5≤(a×b) / c≤60; The a is the value of m-n; The b is the molar ratio of manganese to iron in the positive electrode active material; The c is the peak intensity ratio of the (101) crystal face to the (020) crystal face diffraction peak in the XRD pattern of the positive electrode tab.

10. The positive electrode plate of claim 9, wherein, The range of the c is 0.75-1.

13.

11. An electrochemical device, characterized by, The positive electrode tab comprises the positive electrode tab according to any one of claims 1-10.

12. An electrical device, comprising: The electrochemical device comprises the electrochemical device according to claim 11.

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