A positive electrode plate, an electrochemical device including the same, and an electrical device using the same

Abstract

The present invention relates to the field of electrochemistry technology, and specifically discloses a positive electrode plate, an electrochemical device including the positive electrode plate, and an electrical device using the same. The positive electrode plate of the present invention 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; the first active material includes lithium iron manganese phosphate, and the manganese content is m%; the second active material includes lithium iron manganese phosphate and / or lithium iron phosphate, and the manganese content is n%, and m and n satisfy: 15 ≤ m - n ≤ 85. By controlling the particle size distribution and the manganese content relationship in the positive electrode active material, the electrochemical device containing the positive electrode plate has excellent fast charging performance and energy density.

Description

[0001] This application is a divisional application of CN118867136A (with an application date of September 19, 2024, an application number of 202411305169.8, and an invention title of a positive electrode sheet and an electrochemical device and an electrical device including the same). Technical Field

[0002] The present invention relates to the field of electrochemistry technology, and particularly to a positive electrode sheet and an electrochemical device and an electrical device including the same. Background Art

[0003] 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 has become increasingly urgent. Lithium iron phosphate (LFP) cathode materials have received extensive attention and applications due to their high safety, low cost, long cycle life, and other advantages. However, traditional LFP materials have certain limitations in terms of energy density. In order to overcome these limitations of traditional LFP materials, lithium manganese iron phosphate (LMFP), compared with lithium iron phosphate, has a higher voltage and higher energy density, and has become a highly concerned alternative.

[0004] Compared with LFP, LMFP has a lower diffusion coefficient and poor fast charging performance. Therefore, for LMFP, smaller particle sizes are required to reduce the diffusion path of lithium ions inside the cathode active material particles for efficient deintercalation and intercalation, which helps to improve electronic conductivity and thus improve fast charging performance. However, when the particle size of LMFP is small, the reaction surface with the electrolyte is excessive, resulting in serious side reactions of the electrolyte. And for small-sized LMFP particles, the amount of binder used needs to be increased, resulting in a decrease in the areal density of the battery, which limits the improvement of energy density.

[0005] There are reports in the prior art that using LMFP aggregates containing multiple small-sized primary particles can reduce the amount of binder used and improve energy density. However, the use of LMFP aggregates limits the improvement of the compaction density of the electrode sheet. During the processing of higher compaction, the material inside may be broken, and the electrochemical performance deteriorates. Moreover, the aggregates also cause deterioration of the bulk phase transport ability of the material and a decrease in kinetic performance, especially fast charging performance.

[0006] Therefore, it is necessary to develop a positive electrode sheet with both good fast charging performance and energy density. Summary of the Invention

[0007] The object of the present invention is to overcome the deficiencies of the prior art and provide a positive electrode plate, an electrochemical device and an electrical device comprising the same. The positive electrode plate adopts an LMFP material system, and by regulating the particle size distribution of LMFP aggregates and LMFP / LFP nanoparticles, as well as the manganese content of the material, the positive electrode plate has excellent fast charging performance and energy density at the same time.

[0008] To achieve the above object, in the first aspect of the present invention, the present invention provides a positive electrode plate, which includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The positive electrode active material layer contains a positive electrode active material, and 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.

[0009] The first active material includes lithium manganese iron phosphate (LMFP). Based on the total molar number of metal elements other than lithium in the first active material, the molar percentage content of manganese element in the first active material is m%.

[0010] The second active material includes lithium manganese iron phosphate and / or lithium iron phosphate (LFP). Based on the total molar number of metal elements other than lithium in the second active material, the molar percentage content of manganese element in the second active material is n%.

[0011] The m and the n satisfy the following relational expression: 15 ≤ m - n ≤ 85.

[0012] As a preferred embodiment of the present invention, the m and the n satisfy the following relational expression: 40 ≤ m - n ≤ 70.

[0013] As a preferred embodiment of the present invention, the m and the n satisfy the following relational expression: 0.10 ≤ n / m ≤ 0.85.

[0014] As a further preferred embodiment of the present invention, the m and the n satisfy the following relational expression: 0.18 ≤ n / m ≤ 0.45.

[0015] As a preferred embodiment of the present invention, the m% is 70-95%.

[0016] As a preferred embodiment of the present invention, the n% is 0-60%.

[0017] As a preferred embodiment of the present invention, the first active material includes secondary particles formed by primary particles, and the diameter of the primary particles is 20-130 nm.

[0018] As a preferred embodiment of the present invention, the molar ratio of manganese element to iron element (Mn / Fe) in the positive electrode active material is 1-4.

[0019] As a preferred embodiment of the present invention, the positive electrode sheet satisfies the following relational expression: 5 ≤ (a × b) / c ≤ 60;

[0020] Wherein a is the value of m - n;

[0021] Wherein b is the molar ratio of manganese element to iron element in the positive electrode active material;

[0022] Wherein c is the peak intensity ratio of the diffraction peaks of the (101) crystal plane and the (020) crystal plane in the XRD pattern of the positive electrode sheet.

[0023] As a preferred embodiment of the present invention, the range of c is 0.75 to 1.13. In the second aspect of the present invention, the present invention provides an electrochemical device comprising the above-mentioned positive electrode sheet.

[0024] In the third aspect of the present invention, the present invention provides an electrical device comprising the above-mentioned electrochemical device.

[0025] The beneficial effects of the present invention are as follows:

[0026] The present invention provides a positive electrode sheet, an electrochemical device comprising the positive electrode sheet, and an electrical device. The positive electrode sheet of the present invention mainly adopts the LMFP material system. By controlling the particle size distribution of LMFP / LFP aggregates and nano-sized particles in the positive electrode active material, as well as the manganese content relationship of LMFP / LFP, the positive electrode sheet has both excellent fast charging performance and energy density. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is the SEM image of the positive electrode active material of Example 1 at a 5C rate.

[0028] Figure 2 It is the SEM image of the positive electrode active material of Example 19 at a 10C rate.

[0029] Figure 3 It is the XRD pattern of the positive electrode sheet prepared in Example 1.

[0030] Figure 4 It is the XRD pattern of the positive electrode sheet prepared in Example 19. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described clearly and completely below. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0032] In the present invention, among the technically characterized described in an open manner, it includes a closed technical solution composed of the listed features, and also includes an open technical solution containing the listed features.

[0033] In the present invention, regarding the numerical range, unless otherwise specified, the above numerical range is considered continuous, and includes the minimum value and the maximum value of the range, as well as each value between such minimum value and maximum value. Further, when the range refers to an integer, it includes each integer between the minimum value and the maximum value of the range. In addition, when providing multiple ranges to describe features or characteristics, these ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0034] In the present invention, there is no particular limitation on the specific dispersion and stirring treatment methods.

[0035] The reagents or instruments used in the present invention without indicating the manufacturer are all conventional products that can be obtained through commercial purchase.

[0036] An embodiment of the present invention provides a positive electrode sheet, which includes 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 contains a positive electrode active material, and 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;

[0037] The first active material includes lithium manganese iron phosphate (LMFP). Based on the total molar amount of metal elements other than lithium in the first active material, the molar percentage content of manganese element in the first active material is m%;

[0038] The second active material includes lithium manganese iron phosphate and / or lithium iron phosphate (LFP). Based on the total molar amount of metal elements other than lithium in the second active material, the molar percentage content of manganese element in the second active material is n%;

[0039] m and n satisfy the following relationship: 15 ≤ m - n ≤ 85.

[0040] It is found in the research of the present invention that by using LMFP aggregates with a high manganese content in combination with LMFP nanoparticles with a low manganese content and / or LFP nanoparticles without manganese, it is possible to simultaneously improve the fast charging performance and energy density of the positive electrode sheet of the lithium iron manganese phosphate system.

[0041] In the present invention, 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. An aggregate refers to a secondary particle formed by the aggregation of two or more primary particles, presenting an aggregated state. The first active material is in the form of highly aggregated aggregates. Generally speaking, due to the process of high aggregation of primary particles, the particle size of the first active material is relatively large. The particle size of the second active material is relatively small, being nanoparticles. The second active material may be non-aggregated primary particles or secondary particles with a very low degree of aggregation (aggregation of two or three primary particles). By using scanning electron microscope (SEM) images, the aggregated or non-aggregated state of the particles and the number of aggregated particles can be observed. Combining 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.

[0042] In the present invention, the manganese content (m%) in the first active material is relatively high, and the manganese content (n%) in the second active material is relatively low or zero. The form of using high-manganese large-particle aggregates compounded with low-manganese or manganese-free nanoparticles is adopted. The smaller-sized second active material is used to fill the inter-particle voids formed by the large-particle first active material, thereby improving the tap density; a certain amount of aggregates is used as the positive electrode active material, reducing the usage amount of the binder, increasing the coating amount per unit area, and increasing the areal density; the first active material is LMFP aggregates including a high manganese content. By using the positive electrode active material with a high manganese content, the energy density of the battery is further improved. Through the improvement of the tap density and areal density, as well as the specific manganese content, the battery can achieve a higher energy density. In addition, through the compounding of low-manganese or manganese-free nanoparticles, the fast charging performance is greatly improved while maintaining the high energy density of the battery.

[0043] The difference between m and n should be within an appropriate range, and the manganese content gap between the two active materials should not be too large or too small. When 0 ≤ m - n < 15, the difference is too small, meaning the manganese contents of the first active material and the second active material are very close, and the high energy density and excellent fast charging performance brought by the combination of high manganese and low manganese cannot be achieved, and it is difficult to reflect the improvement effect of the combination of high and low manganese content materials; when m - n > 85, the difference is too large, meaning the manganese content in the first active material is too high. Even if the second active material is blended, the improvement of the ion transport rate inside the cathode active material is relatively limited, resulting in a decline 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. Due to its particle size being only nanoscale, it is extremely easy to cause manganese dissolution and aggravation of side reactions in the electrolyte, leading to deterioration of battery performance; while although the first active material has a low manganese content, the particle size of the particles is too large and the degree of aggregation is too high, which also results in the fast charging performance of the battery not being effectively improved.

[0044] Exemplarily, in the present invention, the value of m - n can be 15, 20, 30, 50, 60, 70, 75, 80, 85, or it can also be an interval range formed by any two of the above values.

[0045] In one preferred embodiment, m and n satisfy the following relationship: 40 ≤ m - n ≤ 70.

[0046] When the difference of m - n is within the above preferred range, the energy density and fast charging performance of the battery containing this cathode electrode sheet are more excellent comprehensively.

[0047] In one embodiment, m and n satisfy the following relationship: 0.10 ≤ n / m ≤ 0.85.

[0048] Exemplarily, in the present invention, 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 it can also be an interval range formed by any two of the above values.

[0049] The difference between m and n (m - n) reflects the absolute value difference of the manganese contents in the first and second active materials; different from the difference, the ratio of n to m (n / m) reflects the relative magnitude relationship of the manganese contents in the second active material and the first active material. The present invention studies and finds that when m and n satisfy that the difference is within the range defined by the present invention, and further satisfy 0.10 ≤ n / m ≤ 0.85, the energy density and fast charging performance of the cathode electrode sheet are relatively more balanced.

[0050] In one preferred embodiment, m and n satisfy the following relationship: 0.18 ≤ n / m ≤ 0.45.

[0051] In one embodiment, the m% is 70 to 95%. For example, the m% can be 70%, 75%, 80%, 85%, 90%, or 95%.

[0052] In one preferred embodiment, the m% is 75 to 85%.

[0053] Although LMFP with a higher manganese content has a higher specific capacity, as the manganese content increases, the kinetic performance of the battery further deteriorates, and the fast charging performance is poor. Moreover, when the manganese content is too high, such as exceeding 95%, it is easy to promote the Jahn-Teller effect, resulting in lattice distortion of the material, and the dissolution of manganese and the reaction with the electrolyte may cause a decrease in the stability of the material, excessive heat generation during charge and discharge, affecting the cycle stability and long-term life of the battery. Especially after a certain number of cycles, the energy density of the battery will decrease.

[0054] In one embodiment, the n% is 0 to 60%. For example, the n% can be 0%, 10%, 15%, 20%, 30%, 40%, 50%, 55%, 58%, or 60%.

[0055] In one preferred embodiment, the n% is 15 to 40%.

[0056] The n% of the second active material should not be too low. In the case of being too low (such as less than 15%), it may lead to an insufficiently obvious increase in the platform voltage, affecting the energy density of the overall material. When the n% is greater than 40%, it may cause the overall manganese-iron ratio of the positive electrode active material to be too high, resulting in a decline in the fast charging performance of the battery; and after a certain number of cycles, the material structure with too high a manganese-iron ratio has relatively low stability, and the battery energy density will also decrease.

[0057] When m% and n% are within the above ranges, the high-manganese and low-manganese LMFP materials can be better coordinated to achieve better battery kinetic performance, and the fast charging performance of the battery is greatly improved.

[0058] 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 the n% > 0, the second active material can be either LMFP or a mixture of LMFP and LFP.

[0059] Regarding the detection method of m% and n%, the present invention does not make any limitations. Those skilled in the art can detect the manganese content of the positive electrode active material with a specific particle size according to conventional technical means.

[0060] Exemplarily, m% and n% can be detected by the following method:

[0061] Disassemble the battery to obtain the positive electrode sheet. After treatment, obtain the positive electrode active material powder. Through testing with an electron microscope (SEM) and an energy spectrometer (EDS), obtain m% and n%.

[0062] In one embodiment, the first active material includes secondary particles formed by primary particles, and the average diameter of the primary particles is 20 - 130 nm.

[0063] In one preferred embodiment, the first active material includes secondary particles formed by primary particles, and the average diameter of the primary particles is 40 - 90 nm.

[0064] In the positive electrode active material of the present invention, the average diameter of the primary particles in the first active material is smaller than the particle size of the second active material. For the high - manganese LMFP material, due to the relatively high manganese content, its own lithium - ion diffusion coefficient decreases, resulting in a slowdown in the charge - discharge rate. To compensate for the fast - charging performance defect caused by the high - manganese content, the present invention studies the use of high - manganese primary particles with extremely small particle sizes to form high - manganese aggregates. In particular, it is preferably to use 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 aggregates, which can ensure good fast - charging performance of the battery.

[0065] For the aggregated LMFP, after being coated on the surface of the positive electrode current collector as the positive electrode active material, during the processing of the positive electrode sheet, some aggregates may become somewhat loose, 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 within this particle size range (20 - 130 nm) do not belong to the second active material.

[0066] In one embodiment, the molar ratio (Mn / Fe) of manganese element to iron element 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.

[0067] In one preferred embodiment, the molar ratio of manganese element to iron element in the positive electrode active material is 2.0 - 3.5.

[0068] In one embodiment, the positive electrode sheet satisfies the following relationship: 5 ≤ (a×b) / c ≤ 60;

[0069] a is the value of m - n;

[0070] b is the molar ratio of manganese element to iron element in the positive electrode active material;

[0071] The c is the peak intensity ratio (denoted as I 101 / I 020 ) of the diffraction peaks of the (101) crystal plane and the (020) crystal plane in the XRD pattern of the positive electrode sheet.

[0072] Perform XRD testing on the positive electrode sheet. In the XRD pattern, the diffraction peak at the position of 2θ = 20.7° ± 0.5° (the peak intensity is denoted as I 101 ) corresponds to the (101) crystal plane of the positive electrode active material, and the diffraction peak at the position of 2θ = 29.5° ± 0.5° (the peak intensity is denoted as I 020 ) corresponds to the (020) crystal plane of the positive electrode active material.

[0073] In the positive electrode active material of the present invention, both lithium iron phosphate manganese and lithium iron phosphate are olivine-type materials. For olivine-type materials, the (020) crystal plane corresponding to the I 020 diffraction peak extends along the b-axis direction of the crystal. The diffusion of lithium ions in the b-axis direction is the main path during the charge and discharge process of the battery. Therefore, the good development of the (020) crystal plane is an important factor in improving the fast charging performance of the material. However, the rapid insertion and extraction process of lithium ions may lead to a mutation of the crystal lattice, and the change in the crystal lattice structure may cause a decrease in the energy density of the positive electrode sheet. The present invention studies and finds that the (101) crystal plane corresponding to the I 101 diffraction peak plays an important role in maintaining the integrity of the crystal lattice and suppressing the mutation of the crystal lattice. The (101) crystal plane forms a certain angle with respect to the b-axis and the c-axis in the crystal structure. During the fast charge and discharge process, the (101) crystal plane can provide a relatively stable structural platform, which helps to relieve the lattice stress caused by the rapid migration of lithium ions. The ratio of I 101 and I 020 (i.e., I 101 / I 020 ) can reflect the proportion relationship between the (101) crystal plane and the (020) crystal plane. In the present invention, by controlling I 101 / I 020 , both the structural stability of the material and a good lithium ion diffusion path are maintained during the fast charge and discharge process, so as to achieve a balance between the fast charging of the battery and the maintenance of the energy density.

[0074] The value of I 101 / I 020 is related to the content and distribution of manganese and iron in the positive electrode active material. Therefore, it is necessary to comprehensively limit the values of a, b, and c. The present invention studies and finds that when a, b, and c satisfy 5 ≤ a × b × c ≤ 60, the comprehensive fast charging performance and energy density of the battery are better.

[0075] For the detection method of the c value, the present invention does not make a limitation, and those skilled in the art can perform XRD detection on the positive electrode sheet according to conventional technical means.

[0076] In one preferred embodiment, the positive electrode plate satisfies the following relational expression: 15 ≤ (a × b) / c ≤ 30.

[0077] In one preferred embodiment, the range of c is 0.75 to 1.13.

[0078] In one further preferred embodiment, the range of c is 0.84 to 1.05.

[0079] When the value of c is within the above preferred range, it indicates that the (101) crystal plane and the (020) crystal plane are relatively more balanced, which is helpful for better fast charging performance and energy density of the battery.

[0080] In the present invention, the preparation methods of LMFP and LFP are not limited, and those skilled in the art can prepare LMFP or LFP according to conventional technical means.

[0081] Exemplarily, the preparation method of LMFP may include the following steps:

[0082] Mix a manganese source, an iron source, a phosphorus source, and a lithium source in a certain molar ratio, use deionized water as a dispersant, and perform ball milling;

[0083] Perform spray drying on the wet material after the above ball milling to obtain a dried mixed powder;

[0084] Sinter the above dried powder in an atmosphere with a nitrogen concentration of less than 150 ppm; thus, an LMFP aggregate can be obtained.

[0085] Crush the LMFP aggregate obtained in the previous step, and then perform screening and classification to obtain LMFP nano-sized particles within a specific particle size range.

[0086] The preparation method of LFP is similar to that of LMFP, except that the manganese source is not added.

[0087] The lithium source may include at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxalate, lithium dihydrogen phosphate, lithium citrate, or lithium acetate.

[0088] The phosphorus source may include at least one of diammonium hydrogen phosphate, lithium dihydrogen phosphate, ammonium phosphate, or lithium phosphate.

[0089] The iron source may include at least one of ferrous oxalate, iron hydroxide, ferrous hydroxide, iron phosphate, ferrous phosphate, iron acetate, ferrous acetate, iron carbonate, ferrous carbonate, iron(III) oxide, iron(II,III) oxide, or iron oxalate.

[0090] The manganese source may include at least one of manganese carbonate, manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, or manganese acetate.

[0091] When preparing LMFP and / or LFP, a carbon source can also be mixed with a manganese source (if any), an iron source, a phosphorus source, and a lithium source as needed to obtain LMFP and / or LFP with a carbon coating layer.

[0092] The carbon source can include at least one of glucose, sucrose, polyethylene glycol (PEG), and polyvinyl alcohol.

[0093] When preparing LMFP and / or LFP, a certain amount of a doping element source can also be mixed with a manganese source (if any), an iron source, a phosphorus source, and a lithium source as needed. The doping element source can be, for example, a vanadium source (vanadium pentoxide), a tungsten source (ammonium metatungstate), a titanium source (titanium oxide), a magnesium source (magnesium carbonate), etc., to obtain LMFP and / or LFP containing a certain amount of doping elements.

[0094] Manganese iron phosphate can be selected to act as both a manganese source, an iron source, and a phosphorus source; iron phosphate can be selected to act as both an iron source and a phosphorus source.

[0095] Optionally, the solvent can be at least one of water and ethanol.

[0096] Optionally, zirconia can be used as the ball milling beads for ball milling. The diameter of the ball milling beads can be of conventional sizes in ball milling, such as a diameter of 0.05 - 50 mm. In ball milling, the mass ratio of the abrasive to the ball milling beads (ball-to-material ratio) can be adjusted as needed, for example, a ball-to-material ratio of (2 - 10):1 can be selected. The conditions for the ball milling can be: time 2 - 20 h, rotation speed 200 - 500 rpm.

[0097] Optionally, the sintering conditions can be to sinter at 600 - 1200 °C for 5 - 20 h by heating from room temperature at a heating rate of 5 - 20 °C / min.

[0098] Optionally, the sintering can also adopt gradient sintering conditions.

[0099] By adjusting the addition amounts of the manganese source and the iron source, the proportion of the manganese content in LMFP can be controlled; by adjusting the sintering conditions, the conditions for crushing and screening classification, the particle sizes of LMFP and LFP can be controlled.

[0100] The positive electrode active material can be obtained by directly mixing and homogenizing a first active material and a second active material. The mixing mass ratio of the first active material and the second active material can be (40:60) - (99:1).

[0101] In addition to the above positive electrode active material, the positive electrode active material layer can also contain a conductive agent and a binder.

[0102] The conductive agent only needs to have appropriate electronic conductivity and not cause adverse chemical changes in the battery, and the type of the conductive agent is not particularly limited in the present invention. Specifically, the conductive agent can be at least one of carbon nanotubes, carbon black or graphene.

[0103] 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. In the present invention, the binder can be a conventional choice in the battery field. 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.

[0104] The present invention places no particular limitation on the positive electrode current collector, as long as it has conductivity and will not cause adverse chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, fired carbon can be used; or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc.

[0105] The positive electrode plate of the present invention can be prepared according to the 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, and the positive electrode slurry is coated on the positive electrode current collector, and after processes such as drying and rolling, the positive electrode plate is obtained.

[0106] An embodiment of the present invention provides an electrochemical device including the above-mentioned positive electrode plate.

[0107] In addition to the positive electrode plate, the electrochemical device further includes a negative electrode plate, a separator and an electrolyte.

[0108] The negative electrode plate includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material. For the negative electrode active material, the embodiments of the present invention do not specifically limit the type of the negative electrode active material, and it 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, silicon-carbon composite.

[0109] The separator is located between the positive electrode plate and the negative electrode plate, and is used to separate the positive electrode plate and the negative electrode plate to prevent the positive electrode plate and the negative electrode plate from contacting and short-circuiting. The separator can be various materials suitable for the separator of the electrochemical energy storage device in the art. Specifically, the separator includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, natural fiber.

[0110] The electrolyte of the present invention can be various electrolytes suitable for electrochemical energy storage devices in the art. The electrolyte includes an electrolyte and a solvent, and the electrolyte generally includes a lithium salt.

[0111] Specifically, the lithium salt includes lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluoro(dioxalato)phosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP), etc. The concentration of the electrolyte in the electrolyte can be 0.5 to 5 mol / L.

[0112] Specifically, the solvent includes at least one 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), 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), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE).

[0113] An embodiment of the present invention provides an electrical device including the above-mentioned electrochemical device. The electrochemical device serves as a power supply for the electrical device.

[0114] The electrical device refers to any device that can utilize electrical energy and convert it into other forms of energy such as mechanical energy, thermal energy, and light energy, such as an electric motor, a thermal engine, an electric light source, etc. Specifically, it can be, but is not limited to, mobile devices, electric vehicles, electric trains, ships, satellites, energy storage systems, etc. Mobile devices can be mobile phones, laptops, drones, floor cleaning robots, electronic cigarettes, etc.; electric vehicles can be pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.

[0115] The present invention will be further elaborated with specific embodiments below.

[0116] Examples 1 to 19 and Comparative Examples 1 to 3

[0117] Examples 1 to 19 and Comparative Examples 1 to 3 each provide a lithium-ion battery, and the preparation method is as follows:

[0118] (1) Preparation of the positive electrode sheet

[0119] (1.1) Preparation of the positive electrode active material

[0120] Preparation of the first active material:

[0121] According to the molar ratios of Li, Mn, Fe, and P in the target chemical formula LiMn m / 100 Fe 1-m / 100 PO 4 (the value of m is shown in Table 2), lithium carbonate, manganese carbonate, ferrous oxalate dihydrate, and diammonium hydrogen phosphate are respectively weighed, and then mixed. The mixed material is mixed with glucose and ethanol and subjected to the first ball milling. Zirconia with a diameter of 0.6 mm is used as the ball milling beads, the ball-to-material ratio is 5:1, the rotation speed of the first ball milling is 300 rpm, and the time of the first ball milling is shown in Table 1;

[0122] After filtering the above-ground wet material, it is dried by blowing for 2 h and then spray-dried for 5 h to obtain a dry powder, that is, the precursor;

[0123] The above dry powder is put into a tubular furnace and sintered in an atmosphere with an oxygen concentration of less than 150 ppm. The sintering conditions are shown in Table 1: heating from room temperature to 850 °C at a heating rate of 12 °C / min, holding for 960 min; cooling to room temperature;

[0124] After sintering, the product is classified and screened to select LMFP aggregates with a particle size in the range of 4 - 20 μm, which is the first active material;

[0125] Preparation of the second active material:

[0126] According to the molar ratios of Li, Mn, Fe, and P in the target chemical formula LiMn n / 100 Fe 1-n / 100 PO 4 (the value of n is shown in Table 2), lithium carbonate, manganese carbonate, ferrous oxalate dihydrate, and diammonium hydrogen phosphate are respectively weighed and mixed. The mixed material is mixed with glucose and ethanol and subjected to the second ball milling. Zirconia with a diameter of 0.6 mm is used as the ball milling beads, the ball-to-material ratio is 5:1, the rotation speed of the second ball milling is 200 rpm, and the time of the second ball milling is shown in Table 1;

[0127] Filter, blow-dry, and spray-dry the above-ground wet material after grinding under the same conditions as in the first active material; then sinter it under the following conditions: heat from room temperature to 850 °C at a heating rate of 12 °C / min, hold for 960 min; cool to room temperature;

[0128] Crush the sintered product, then perform classification and screening to select LMFP nanoparticles with a particle size in the range of 200 - 600 nm (when n = 0, it is LFP nanoparticles), which is the second active material;

[0129] (1.2) Mix the above-mentioned first active material and the second active material evenly according to the mass ratio shown in Table 1 to obtain the positive electrode active material;

[0130] Mix the positive electrode active material, conductive agent (SP), and binder (PVDF) evenly in NMP according to a mass ratio of 96:1.5:2.5. Subsequently, evenly coat the mixed positive electrode slurry on an aluminum foil with a thickness of 15 μm, with a coating areal density of 446 m 2 / g and a compaction density of 2.4 m 3 / g; dry it in a vacuum furnace at 100 °C to obtain the positive electrode sheet, cut it into strips, and then roll it to obtain the positive electrode plate.

[0131] (2) Preparation of the negative electrode plate

[0132] Mix the negative electrode active material (artificial graphite), conductive agent (CNT), and binder (carboxymethyl cellulose, CMC) according to a mass ratio of 96:1.5:2.5, disperse them in deionized water, and use a vacuum mixer to make a negative electrode slurry by a wet process. Evenly coat the negative electrode slurry on the negative electrode current collector (copper foil), transfer the negative electrode current collector coated with the negative electrode slurry to a vacuum environment in an oven and dry it at 100 °C for 12 h, and then roll and cut it to obtain the negative electrode plate.

[0133] (3) Preparation of the electrolyte

[0134] Mix ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a weight ratio of 3:7 to obtain an organic solvent. Then dissolve the fully dried lithium salt LiPF 6 in the mixed organic solvent to prepare an electrolyte with a concentration of 1.15 mol / L.

[0135] (4) Preparation of the separator

[0136] Use a polyethylene (PE) separator.

[0137] (5) Preparation of the battery

[0138] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked (40 layers of positive electrode stacking and 41 layers of negative electrode stacking) to obtain an un-injected bare battery cell; the bare battery cell is placed in an outer packaging foil, and the prepared electrolyte is injected into the dried bare battery cell. After processes such as vacuum packaging, standing, forming, shaping, and sorting, a lithium-ion battery with a cell size of 202 mm in length and 90 mm in width is obtained.

[0139] Table 1

[0140]

[0141]

[0142]

[0143] For the m% of the first active material, n% of the second active material, the average primary particle diameter of the first active material, Mn / Fe of the positive electrode active material, and I of the positive electrode sheet in each example and comparative example 101 / I 020 Detection is carried out; the detection methods for the above items are as follows:

[0144] m% of the first active material, n% of the second active material: Disassemble the lithium-ion battery to obtain the positive electrode sheet. Immerse the positive electrode sheet in DMC (dimethyl carbonate) at room temperature for 60 min, take it out, and dry it at room temperature with a humidity ≤ 15% to obtain a pole piece sample;

[0145] First, stick a layer of conductive adhesive on the sample holder, stick the pole piece sample on the sample holder, then coat a layer of conductive film, and then observe it under a scanning electron microscope (SEM). Select a magnification of 5KX for observation. According to the morphology of agglomerates and single particles combined with the particle size, determine the first active material and the second active material, and analyze the molar content of Mn element in the first active material and the second active material respectively through EDS testing to obtain m% and n%.

[0146] Average primary particle diameter of the first active material: As described above, evenly sprinkle the positive electrode active material powder obtained by disassembling the lithium-ion battery on the conductive adhesive, directly put it into the SEM, select an SEM photo with a magnification of 30KN (30KX) and clear image, and measure the particle size distribution of the primary particles in the first active material (measure 400) through particle size measurement software (Nano Measurer) to obtain the average value of the primary particle diameter.

[0147] Mn / Fe of the positive electrode active material:

[0148] As described above, the cathode active material powder obtained by disassembling the lithium-ion battery was accurately weighed at 0.5 g, dispersed in 20 ml of water, and then 10 ml of nitric acid was added. After mixing evenly, heat treatment was carried out. After the cathode active material powder was dissolved, the material was made up to 100 mL with water to obtain the test solution;

[0149] The test solution was subjected to ICP testing. The ICP testing conditions were as follows: The spectral wavelengths for detecting selected elements were determined (Fe wavelengths 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, appropriate ICP instrument working conditions were set, including a gas flow rate of 0.5 L / min and a power of 1150 W;

[0150] By measuring the Mn / Fe content of the elements in it through ICP testing, the overall Mn / Fe of the cathode active material can be calculated.

[0151] I 101 / I 020 : The lithium-ion battery was disassembled to obtain the cathode electrode sheet, and the cathode electrode sheet was subjected to XRD testing. The XRD conditions were as follows: The test was carried out using an X-ray diffractometer; a Cu target, the Start angle was set at 5°, the Stop angle was set at 90°, the SamplingW (step angle) was set at 0.02, the Scan speed was 3° / min, the accelerating voltage was set at 40 KV, and the accelerating current was set at 40 mA.

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

[0153] The SEM images of the cathode active materials of Example 1 and Example 19 are respectively as Figure 1 , Figure 2 shown. Figure 1 Among them, the agglomerates shown in "spectrum Figure 2 " are the first active material, and the particles shown in "spectrum Figure 1 ", "spectrum Figure 3 ", "spectrum Figure 4 " are the second active material.

[0154] The XRD patterns of the cathode electrode sheets of Example 1 and Example 19 are respectively as Figure 3 and Figure 4 shown.

[0155] Table 2

[0156]

[0157]

[0158] Perform performance tests on the fast charging performance and energy density of lithium-ion batteries. The specific methods are as follows:

[0159] (1) Fast charging performance:

[0160] For the stacked three-electrode test method, take out the positive and negative electrode plates of the lithium-ion battery and soak and clean them in DMC solvent for more than 72 hours. Dry the electrode plates in a vacuum oven, and then assemble the positive and negative electrode plates into a stacked three-electrode battery cell, with a copper wire as the reference electrode; use a blue and charge-discharge device for testing;

[0161] At 25°C, charge and discharge two cycles at 0.33C (upper limit voltage 4.25V, lower limit voltage 2.5V), and use the charging capacity of the second cycle as the standard capacity;

[0162] After charging to 10% SOC at 0.33C; start charging at 4C (recorded as time t1 at this time), and perform constant current charging with the upper limit voltage 4.25V or negative reference potential ≤ 0mv as the cut-off condition. After reaching the cut-off condition, step down in steps of 0.2C until the current drops to 0.05C to stop charging, where the time when the charging capacity reaches 80% SOC is recorded as t2;

[0163] The time taken from t1 to t2 (i.e., the time from 10% SOC to 80% SOC) is the fast charging time, with the unit of min.

[0164] (2) Volume energy density:

[0165] In a 25°C constant temperature oven, perform charge and discharge cycle tests on the lithium-ion battery. The charge and discharge regime: charge at a constant current of 0.33C to 4.25V, and then charge at a constant voltage until the current drops to 0.05C. After standing for 5 minutes, discharge the battery at a constant current of 1C to 2.5V. This is 1 cycle; cycle 10 times to obtain the discharge capacity of the lithium-ion battery at the 10th cycle;

[0166] Measure the surface area S and the total thickness T of the positive electrode active material layer in the prepared positive electrode plate;

[0167] The reversible capacity C (Ah / cm 2 ) per unit area of the positive electrode active material layer after cycling = the discharge capacity of the lithium-ion battery at the 10th cycle / the surface area S of the positive electrode active material layer;

[0168] The ratio (C / T) (mAh / cm 3 ) of the reversible capacity per unit area of the positive electrode active material after cycling to the total thickness of the positive electrode active material layer = the reversible capacity C per unit area of the positive electrode active material layer after cycling / the total thickness T of the positive electrode active material layer.

[0169] The volumetric energy density of the lithium-ion battery at 10 cycles is measured by the ratio of the reversible capacity per unit area of the positive electrode active material after cycling to the total thickness of the positive electrode active material layer.

[0170] The test results are shown in Table 3.

[0171] Table 3

[0172]

[0173]

[0174] According to the test results of the examples and comparative examples, it can be seen that the lithium-ion battery using the positive electrode sheets prepared in the examples of the present application has excellent fast charging performance and energy density, where the fast charging time ≤ 25.3 min and the volumetric energy density ≥ 398 mAh / cm 3 .

[0175] According to Examples 1 to 5, it can be seen that when the average primary particle diameter of the first active material is 40 to 90 nm, the comprehensive fast charging performance and energy density of the battery are better; when the primary particle diameter is slightly smaller, although the fast charging performance of the battery is improved, the energy density may decrease and the processing process is more difficult; when the primary particle diameter is slightly larger, the energy density of the battery is higher, but the fast charging time is longer and the fast charging performance decreases.

[0176] According to Examples 6 to 8 and Example 13, it can be seen that when the value of m exceeds 75 to 85, n exceeds 15 to 40, or the value of n / m exceeds 0.18 to 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 worse.

[0177] According to Examples 9 to 12, it can be seen that when the positive electrode sheet further satisfies that the Mn / Fe of the positive electrode active material is 2.0 to 3.5, I 101 / I 020 is 0.84 to 1.05, and (a / b)*c is 15 to 30, the fast charging performance and energy density of the battery are relatively better.

[0178] From Example 19, when the second active material is LFP, as long as m - n is within the scope of the technical solution of the present invention, good fast charging performance and high energy density of the lithium-ion battery can also be achieved.

[0179] It can be seen from Comparative Examples 1-2 that when the value of m-n is too large, it is difficult to effectively match the manganese contents of the first active material and the second active material, resulting in serious deterioration of the fast charging performance of the battery. It can be seen from Comparative Example 3 that when the value of m-n is too small, the manganese contents of the first active material and the second active material are 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.

[0180] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A positive electrode sheet, comprising a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer contains a positive electrode active material, characterized in that: The positive electrode active material includes a first active material with a particle size of 4 to 20 μm and a second active material with a particle size of 200 to 600 nm; The first active material comprises lithium manganese iron phosphate, and the molar percentage of manganese in the first active material is m%, calculated based on the total molar number of metal elements other than lithium in the first active material, and the m% is 70-95%; The second active material comprises lithium manganese iron phosphate and / or lithium iron phosphate, and the molar percentage of manganese element in the second active material is n%, and n% is 0-40%, calculated based on the total molar number of metal elements other than lithium in the second active material; The m and the n satisfy the following relationship: 15≤mn≤85; The peak intensity ratio of the diffraction peaks of the (101) crystal plane and the (020) crystal plane in the XRD spectrum of the positive electrode plate is c, and the range of c is 0.75 to 1.

13.

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

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

85.

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

45.

5. The positive electrode sheet according to claim 1, characterized in that: The first active material includes secondary particles formed of primary particles, and the average diameter of the primary particles is 20 to 130 nm.

6. The positive electrode sheet according to claim 1, characterized in that: The molar ratio of manganese element to iron element in the positive electrode active material is 1-4.

7. The positive electrode sheet according to claim 1, characterized in that: The positive electrode sheet satisfies the following relationship: 5≤(a×b) / c≤60; Said a is the value of mn; b is the molar ratio of manganese to iron in the positive electrode active material; The c is the peak intensity ratio of the diffraction peaks of the (101) crystal plane and the (020) crystal plane in the XRD spectrum of the positive electrode plate.

8. An electrochemical device, characterized in that: A positive electrode sheet comprising the positive electrode sheet according to any one of claims 1 to 7.

9. An electrical device, characterized in that: An electrochemical device comprising the electrochemical device of claim 8.

Images