Active material of the positive electrode, positive pole piece and electrochemical energy storage device

Abstract

Active material of the positive electrode, comprising a lithium metal composite oxide with a layered structure, characterized in that the chemical formula of the lithium metal composite oxide is LiNi x Co y M z O2 is where 0.7≤x≤0.9,0.05≤y≤0.2, 0.05≤z≤0.2 and x+y+z=1, and where M is at least one of Mn and Al or includes Mn and Al; and wherein, according to the weight fraction, the active material of the positive electrode is divided into three distribution intervals A, B and C: interval A: consisting of lithium metal composite oxide particles with a particle size of 300 nm-1000 nm, wherein the percentage of the total weight of the lithium metal composite oxide particles is 0.1%-8%; the interval B: consisting of lithium metal composite oxide particles with a particle size of 1300 nm-3550 nm, where the percentage of the total weight of the lithium metal composite oxide particles is 30%-75%; the interval C: consisting of lithium metal composite oxide particles with a particle size of 4500 nm-8800 nm, where the percentage of the total weight of the lithium metal composite oxide particles is 10%-35%.

Description

Technical area

[0001] The present invention relates to a positive electrode active material for lithium-ion batteries and a lithium-ion battery containing the positive electrode active material. State of the art

[0002] Lithium-ion batteries are widely used in electronic products, vehicles, aerospace, and other related fields due to their high energy density, high energy efficiency, lack of memory effect, and low self-discharge. With the rapid development of new energy vehicles, the requirements for lithium-ion batteries are becoming increasingly stringent. The performance of lithium-ion batteries depends largely on the performance of the positive electrode material. Ternary positive electrode materials are increasingly used in power batteries due to their high discharge capacity and long cycle life.However, gas production in battery cells made of ternary positive electrode materials is more serious, especially in ternary materials with high nickel content. As the nickel content increases, the material structure becomes unstable, increasing the likelihood of extreme safety events such as oxygen loss, fire, and explosion under high-temperature and long-cycle conditions. Especially in today's era of global warming and the occurrence of extreme high-temperature weather events, lithium-ion batteries are subject to stricter requirements regarding high-temperature storage and high-temperature cycle life.

[0003] Therefore, positive electrode active materials must be developed to increase the energy density of batteries and improve high-temperature performance. By developing lithium-transition metal composite oxides such as NCM and NCA, and designing an appropriate ratio, the stability of the materials can be improved to a certain extent, allowing the materials to exhibit higher capacity while maintaining better stability and safety. However, this places more demanding requirements on synthesis, storage, homogenization, coating, and other process conditions. Non-standardized process conditions are likely to cause the materials to experience problems with gas production and capacity degradation during application. Content of the invention(1) Technical problems

[0004] In order to overcome the deficiencies and inadequacies of the existing technology, the purpose of the present invention is to provide a positive electrode active material, a positive pole piece and an electrochemical energy storage device to solve the problems of high temperature storage and poor cycle life of the existing positive electrode active materials. (2) Technical solution

[0005] After conducting a large number of experiments, the inventor surprisingly discovered that by adjusting the particle size range and particle content in the positive electrode active material, it is possible to achieve a hierarchical distribution of the positive electrode active substance content with different particle sizes, so that the lithium-ion battery exhibits better high-temperature storage performance and cycle life, thus further realizing the stability and safety of the battery. The invention is defined by the features of the independent claims. Advantageous embodiments are the subject of the dependent claims.

[0006] According to one aspect of the present invention, there is provided a positive electrode active material, wherein the positive electrode active material comprises a lithium metal composite oxide having a layered structure, and wherein the chemical formula of the lithium metal composite oxide is LiNi x Co y M z O2, and where 0.7≤x≤0.9, 0.05≤y≤0.2, 0.05≤z≤0.2 and x+y+z=1, and where M is one of Mn and Al;

[0007] According to the weight fraction, the active material of the positive electrode is divided into three intervals of particle size distribution: A, B and C: (1) Interval A: consisting of lithium metal composite oxide particles with a particle size of 300 nm-1000 nm, the percentage of the total weight of the lithium metal composite oxide particles being 0.1%-8%; (2) Interval B: consisting of lithium metal composite oxide particles with a particle size of 1300 nm-3550 nm, the percentage of the total weight of the lithium metal composite oxide particles being 30%-75%; (3) Interval C: consisting of lithium metal composite oxide particles with a particle size of 4500 nm-8800 nm, where the percentage of the total weight of the lithium metal composite oxide particles is 10%-35%.

[0008] Preferably, the percentage of particles of interval A in the total weight of the lithium metal composite oxide particles is 4%-7%.

[0009] Preferably, the percentage of particles of interval B in the total weight of the lithium metal composite oxide particles is 50%-70%.

[0010] Preferably, the percentage of particles of interval C in the total weight of the lithium metal composite oxide particles is 14%-25%.

[0011] Preferably, the lithium metal composite oxide particles are primary particles and / or secondary particles composed of the primary particles, wherein the primary particles and / or the secondary particles composed of the primary particles have a Dv10 of 1100 nm-1400 nm and a Dv90 of 4500 nm-5200 nm, and wherein Dv10 and Dv90 each represent the particle size corresponding to the time at which the cumulative volume distribution percentage reaches 10% and 90%, respectively.

[0012] Preferably, the lithium metal composite oxide particles are primary particles and / or secondary particles composed of the primary particles, wherein the primary particles and / or the secondary particles composed of the primary particles have a Dv50 of 2400-3000 nm, and wherein Dv50 represents the particle size corresponding to the time at which the cumulative volume distribution percentage reaches 50%.

[0013] Preferably, the specific surface area Sw of the lithium metal composite oxide particles is 0.1 m 2 / g-1 m 2 / G.

[0014] Preferably, the specific surface area Sw of the lithium metal composite oxide particles is 0.25 m 2 / g-0.6 m 2 / G.

[0015] Preferably, the porosity P of the positive electrode active material satisfies 25%≤P≤40%.

[0016] Preferably, the weight fraction of the lithium metal composite oxide particles in the distribution intervals A and C satisfies 0.1≤A / C≤0.8.

[0017] Preferably, the weight fraction of the lithium metal composite oxide particles in the distribution intervals A and C satisfies 0.2≤A / C≤0.6.

[0018] Preferably, the weight fraction of the lithium metal composite oxide particles in the distribution intervals A, B and C satisfies 1.3≤B / (A+C)≤4.4.

[0019] Preferably, the porosity P of the positive electrode active material satisfies the relationship: k=P*(B / (A+C)); where K satisfies the range 0.6≤K≤1.1.

[0020] Preferably, the lithium metal composite oxide particles further satisfy: 1.9≤3 / (Sw×(Dv90-Dv10))≤2.5.

[0021] Preferably, according to a further aspect of the present invention, there is provided a positive pole piece comprising a positive electrode active material according to the present invention.

[0022] According to a third aspect of the present invention, there is provided an electrochemical energy storage device comprising a positive electrode active material according to the present invention. (3) Advantages

[0023] By reasonably controlling the distribution of the content of particles of different sizes in the positive electrode active material, the present application effectively reduces the side reaction between the positive electrode active material and the electrolyte, reduces the amount of gas generated by the electrochemical energy storage device, and the present application is capable of improving the storage performance of the electrochemical energy storage device without deteriorating the energy density, cycle performance, and multiplicity performance of the electrochemical energy storage device.

[0024] At the same time, by regulating the particle size distribution of the positive electrode material, the proportion of large-size particles and small-size particles is controlled, and the gradation distribution of particle size is realized to control the specific surface area and porosity of the material, improve the effective contact area between the positive electrode active material and the electrolyte, optimize the ion transport, electron transport and diffusion rate of the electrolyte, and improve the power performance of the battery, especially the cycle life and high-temperature storage life. Example

[0025] The present invention is described in more detail below. Obviously, the described embodiments do not represent all embodiments, but only a portion of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments in the present application without creative effort should be considered to be covered by the scope of the present application.

[0026] It is to be understood that the words or terms used in the specification and claims are not to be interpreted as defined in commonly used dictionaries, and it is further understood that the said words or terms are to be interpreted to have a meaning consistent with their meaning in the context of the relevant field and technical ideas of the present invention, based on the principle that the inventor can correctly define the meaning of the said words or terms in order to best interpret the present invention.

[0027] In this description, "Dv10, Dv50, Dv90" can be defined as the particle size at 10%, 50%, and 90% of the cumulative volume in the particle size distribution curve, which can be measured using laser diffraction. Laser diffraction can generally measure particle sizes in the range of a few nanometers to a few millimeters, and results with high repeatability and high resolution can be achieved. [Positive active material]

[0028] A first aspect of the present application provides a positive electrode active material, wherein the positive electrode active material comprises a lithium metal composite oxide having a layered structure, and the positive electrode active material is divided into three particle size distributions A, B, and C according to the weight fraction; Particle size distribution interval A consists of lithium metal composite oxide particles with a particle size of 300 nm–1000 nm, wherein the percentage of the total weight of the lithium metal composite oxide particles is 0.1%–8%; Particle size distribution interval B consists of lithium metal composite oxide particles with a particle size of 1300 nm–3550 nm, wherein the percentage of the total weight of the lithium metal composite oxide particles is 30%–75%;The particle size distribution interval C consists of lithium metal composite oxide particles with a particle size of 4500 nm-8800 nm, with the percentage of the total weight of the lithium metal composite oxide particles being 10%-35%.;

[0029] The methods for improving the energy density of a lithium-ion battery mainly include increasing the nickel content in the ternary material, increasing the upper voltage limit, and other methods. When the nickel content in the lithium metal oxide is high, a high-capacity secondary battery can be achieved. However, for lithium metal oxides with high nickel content, the thermal stability subsequently decreases, and capacity loss occurs due to cyclic charging and discharging, as well as accelerated capacity decay in high-temperature environments. While increasing the upper voltage limit can increase the working voltage of the lithium-ion battery, it also causes the electrolyte to be easily oxidized and decomposed under high potential, leading to serious deterioration of battery performance and even safety issues.

[0030] The present inventor has found through a large number of experiments that particles with different particle sizes can be optimally graded by adjusting their weight ratio distribution within a certain range and controlling the specific surface area and porosity of the material, thereby suppressing particle fragmentation in the roll pressing process, improving the effective contact area between the positive electrode active material and the electrolyte, and achieving a balance between the specific surface area of ​​the positive electrode active material and the electron conductivity, which can significantly improve the electrochemical performance of the battery and, in particular, prolong the cycle life at high temperatures.

[0031] In some embodiments of the present application, the cumulative mass fraction in the particle size distribution interval A may be 0.1%-8%, such as 7.65%, 5.39%, 6.29%, 5.23%, 4.89%, 6.45%, 7.69%, 4.76%, preferably 4%-7%; the cumulative mass fraction in the particle size distribution interval B is 30%-75%, such as 62.77%, 72.45%, 60.92%, 58.91%, 63.47%, 56.23%, 42.78%, 73.5%, preferably 50%-70%; the cumulative mass fraction of the particle size distribution interval C is 10%-35%, such as 17.13%, 13.26%, 19.85%, 22.38%, 20.57%, 27.79%, 17.11%, 12.04% 4 and the like, preferably 14%-25%.

[0032] In some embodiments of the present application, the weight fraction of the lithium metal composite oxide particles in the distribution intervals A and C satisfies 0.1≤A / C≤0.8, preferably 0.2≤A / C≤0.6, which may be, for example, 0.45, 0.41, 0.32, 0.23, 0.24, 0.23, 0.45, 0.40.

[0033] In some embodiments of the present application, the weight fraction of the lithium metal composite oxide particles in the distribution intervals A, B and C further satisfies 1.3≤B / (A+C)≤4.4, e.g., 2.53, 3.88, 2.33, 2.13, 2.49, 1.64, 1.73, 4.38.

[0034] When the positive electrode active material is controlled to be in different particle size distribution intervals and the cumulative mass fraction value is within this range, the particle morphology, particle size, particle size distribution and specific surface area of ​​the positive electrode active material are in a better state, which can further improve the high-temperature power performance of the battery and increase the volumetric energy density of the battery.

[0035] In some embodiments of the present application, 1100 nm≤Dv10≤1400 nm; for example, it may be 1336 nm, 1152 nm, 1254 nm, 1288 nm, 1312 nm, 1291 nm, 1387 nm, 1305 nm, or a range consisting of any two of these values. In some embodiments of the present application, 4500 nm≤Dv90≤5200 nm may be, for example, 4730 nm, 4772 nm, 5023 nm, 4650 nm, 5118 nm, 5150 nm, 5120 nm, 4633 nm, or a range consisting of any two of these values.

[0036] In some embodiments of the present application, 2400 nm≤Dv50≤3000 nm may be, for example, 2830 nm, 2431 nm, 2650 nm, 2547 nm, 2530 nm, 2876 nm, 2980 nm, 2520 nm, or a range consisting of any two of these values.

[0037] It is well known that the particle size of the positive electrode active material has a direct impact on the preparation of the battery slurry and the pole piece. The larger the particle size, the lower the viscosity and the better the flowability of the positive electrode slurry; the smaller the particle size, the larger the specific surface area of ​​the active material and the better the electrochemical reaction, but the particles are easily agglomerated, resulting in a decrease in the solid-phase diffusion coefficient and electron conductivity, thereby increasing the internal resistance of the lithium-ion battery.

[0038] However, if the positive electrode active substance has a particle size distribution that satisfies the above range, the fragmentation of particles during rolling can be suppressed, the side reaction between the positive electrode active material and the electrolyte is reduced, and even if there is a high nickel content, secondary batteries with excellent high-temperature life characteristics and high-temperature storage performance can be achieved.

[0039] In some embodiments of the present application, the lithium metal composite oxide particles have a specific surface area Sw of 0.1 m 2 / g-1 m 2 / g, furthermore 0.25 m 2 / g-0.6 m 2 / g, for example 0.430 m 2 / g, 0.410 m 2 / g, 0.350 m 2 / g, 0.420 m 2 / g, 0.343 m 2 / g, 0.332 m 2 / g, 0.325 m 2 / g, 0.461 m 2 / g or a range consisting of any two of these values. By controlling the specific surface area of ​​the positive electrode active material, the effective contact area between the positive electrode active material and the electrolyte can be better controlled, the side reaction between the positive electrode active material and the electrolyte can be controlled, and the power performance of the battery can be improved.

[0040] The specific surface area is measured using a well-known BET device for measuring the specific surface area of ​​powders. Specifically, nitrogen is used as the adsorption gas and helium as the carrier gas, and the BET single point is measured using the continuous flow method. First, the powder sample is heated to 450°C or lower and degassed with a mixed gas, and then cooled to liquid nitrogen temperature to adsorb the mixed gas. It is heated to room temperature with water to desorb the adsorbed nitrogen, and the amount is detected with a thermal conductivity detector, from which the specific surface area of ​​the sample is calculated.

[0041] In some embodiments of the present application, the porosity P of the positive electrode active material satisfies 25%≤P≤40%. If the porosity is too large, the diffusion resistance of the electrolyte is low, but the electrode also contains fewer active components, so the energy density is low. If the porosity is too small, the active component contained in the electrode increases, but the pores are too narrow and are not conducive to electrolyte transfer, so the energy density still cannot be improved. The inventor found that by adjusting the particle size gradation and adjusting the porosity within the above range, better electrolyte conductivity can be achieved, which in turn increases the energy density and improves battery performance.

[0042] Porosity is measured using the mercury pressure method.

[0043] In some embodiments of the present application, the porosity of the positive electrode active material further satisfies the relationship equation: k=P*(B / (A+C)); where K satisfies the range 0.6≤K≤1.1, and K is preferably 0.7-0.9.

[0044] The particle size and distribution of the positive electrode active material also affect the porosity. Reducing the particle size leads to a reduction in the pores between the particles, which increases the resistance to the diffusion of lithium ions in the electrolyte between the particles. A particle size distribution that is too wide and a large difference in the surface current densities of particles of different sizes results in the battery being polarized and impairs discharge performance, especially at high temperatures. Therefore, the present invention adjusts the porosity according to the appropriate particle size distribution, improves lithium ion diffusion within the electrolyte without causing excessive polarization, and ultimately achieves the purpose of improving battery performance.

[0045] In some embodiments of the present application, the specific surface area Sw of the positive electrode active material with respect to Dv10, Dv90 is preferably 1.9≤3 / (Sw×(Dv90-Dv10))≤2.5. It may be, for example, 2.06, 2.02, 2.27, 2.12, 2.30, 2.34, 2.47, 1.96, or a range consisting of any two of these values. When the above range between Sw and Dv10, Dv90 is maintained, the size and particle size distribution of the positive electrode active material are controlled in a more reasonable range, which effectively alleviates the problem of particle fragmentation and improves the interfacial side reaction of the battery, increases the compaction density of the positive pole piece, improves the compaction capacity of the positive pole piece, and achieves the effect of increasing the volumetric energy density of the battery and improving the long-term cycle life.

[0046] In some embodiments of the present application, the positive electrode active material comprises a lithium metal composite oxide having the chemical formula LiNi x Co y M z O2. Where 0.7≤x≤0.9, 0.05≤y≤0.2, 0.05≤z≤0.2, x+y+z=1, and M can be at least one of manganese (Mn) or aluminum (Al), and preferably comprises both manganese (Mn) and aluminum (Al).

[0047] The ternary material is a material with superior overall performance, and the nickel element can improve the material's activity and increase energy density. The cobalt element is also an active substance, which can not only stabilize the layered structure of the material but also reduce cation mixing and discharge, thus facilitating the material's deep discharge and improving its discharge capacity. The manganese element, which plays a supporting role in the material, ensures stability in the charging and discharging process. However, the gas production of the battery cell is more serious for ternary materials, the safety issues are more pronounced, and the performance in high-temperature storage and high-temperature cycling needs to be improved.

[0048] Controlling the content of nickel (Ni), cobalt (Co), manganese and / or aluminum (M) within the above range can further improve the stability of the structure of the ternary positive electrode active material, so that the battery has better ion transport and electron transport, and it can improve the thermal stability, alleviate the problems of increased side reaction with the electrolyte and the increase in gas production, so that the battery has better high-temperature performance.

[0049] Accordingly, the present application also discloses a method for producing the positive electrode active material in the following steps:

[0050] Step 1: Prepare an aqueous solution of a metal precursor in which a manganese source or an aluminum source is mixed with a nickel source and a cobalt source in a certain molar ratio, and add distilled water to the coprecipitation reactor and remove the internal dissolved oxygen by blowing nitrogen.

[0051] Step 2: A precipitant and a complexing agent are added to the aqueous solution of the metal precursor, and the coprecipitation reaction is carried out under stirring at a speed of 500 rpm.

[0052] The precipitant comprises a sodium hydroxide solution, and the complexing agent is one or a mixture of several of ammonia, ammonium sulfate, sodium citrate, and iminodiacetic acid. The pH can be controlled between 10 and 13 and further between 11 and 12. The stirring speed can be between 350 and 600 rpm and further between 450 and 550 rpm.

[0053] Step 3: At the end of the coprecipitation reaction, the sediment is filtered and dried at 130°C for 10 hours to obtain a metal hydroxide. The metal hydroxide and the lithium source are mixed and sintered. The sintering temperature can be 500-1100°C, then 650-950°C, and then 780-900°C, and the temperature is increased to these temperatures at a rate of 10-40°C / min. The sintering time can be 4-15 hours, then 5-12 hours, and then 7-10 hours.

[0054] Step 4: After calcination, the calcined product is naturally cooled to room temperature, then ground and crushed, and the particle size of the positive electrode active material is adjusted by a sorting device. The sorting device includes, but is not limited to, a sorter, a sieve, or a built-in crusher of a classifier, etc. After sorting by the sorting device, a lithium metal composite oxide is obtained.

[0055] The present invention optimizes the nucleation rate and growth rate by changing process parameters such as pH, complexing agent concentration, and synthesis atmosphere during precursor production. The present application also controls the sintering temperature, sintering time, and crushing intensity, and achieves precise regulation of particle size on the weight distribution scale using a sorting device.

[0056] In some embodiments of the present invention, the nickel source comprises at least one of the following elements: nickel sulfate, nickel acetate, or nickel nitrate; and / or the cobalt source comprises at least one of the following elements: cobalt sulfate, cobalt acetate, or cobalt nitrate; and / or the manganese source comprises at least one of the following elements: manganese sulfate, manganese acetate, or manganese nitrate; and / or the aluminum source comprises at least one of the following elements: aluminum sulfate, aluminum acetate, or aluminum nitrate; and / or the cover element source comprises at least one of aluminum nitrate, titanium nitrate, cobalt nitrate, tungsten nitrate, yttrium nitrate, silicon oxide, boron oxide, phosphorus pentoxide, or aluminum oxide.

[0057] In addition, a capping process may be performed on the positive electrode active material. Specifically, the capping material on the surface of the positive electrode active material is capped by dry capping (high-temperature solid phase method), and the surface of the positive electrode active material is partially or completely covered with the capping layer formed by the capping material. The capping layer includes at least one element (hereinafter referred to as "capping element") selected from the following elements: aluminum (Al), titanium (Ti), tungsten (W), boron (B), phosphorus (P), cobalt (Co), yttrium (Y), and silicon (Si).In the case where the coating described above is included, since the contact between the lithium metal composite oxide and the electrolyte is blocked, the gas generation and leaching of transition metals due to side reactions with the electrolyte can be effectively suppressed, and the structural stability of the positive electrode active material is improved, thereby further improving the high-temperature performance of the battery. [Positive pole piece]

[0058] Furthermore, the present invention provides a positive pole piece for lithium secondary batteries, wherein the positive pole piece for lithium secondary batteries comprises a positive material produced by the method described above.

[0059] In particular, the positive pole piece comprises a positive electrode collector and a positive electrode active material layer, wherein the positive electrode active material layer is provided on at least one surface of the positive electrode collector and comprises the positive electrode active material.

[0060] There are no special restrictions on the positive electrode collector as long as it is conductive without causing adverse chemical changes in the battery, and it is possible to use, for example, stainless steel, aluminum, nickel, titanium, burnt carbon, or aluminum or stainless steel that has been subjected to a surface treatment with any of carbon, nickel, titanium, silver, and the like.

[0061] In addition to the above-mentioned positive electrode material according to the present invention, the positive electrode active material layer may further comprise a conductive material and an adhesive.

[0062] The conductive material is used to impart electrical conductivity to the electrode. Any electrically conductive material can be used without particular limitation as long as it has suitable electron conductivity without causing adverse chemical changes in the battery. Carbon fibers such as carbon nanofibers, carbon black such as acetylene black and cochineal black, carbon materials such as activated carbon, graphite, mesoporous carbon, fullerenes, carbon nanotubes, and the like are preferred. Preferably, the weight of the conductive material is 2%-4% of the weight of the positive electrode active material layer, within which the conductive path in the positive electrode active material layer can be ensured even if the positive electrode active material layer deforms due to expansion or contraction.

[0063] The adhesive improves the adhesion between the particles of the positive electrode active material and the adhesion between the positive electrode active material and the collector. Therefore, suitable adhesives in this embodiment are synthetic rubber such as SBR, BR, CR, IR, or NBR, or polysaccharides such as CMC. Preferably, the weight percentage of the adhesive, based on the total weight of the positive electrode active material layer, can be between 1% and 20% to reduce the deformation of the positive electrode active material and improve the durability of the positive electrode active material layer.

[0064] In addition to using the positive electrode material according to the present invention, the positive electrode can be manufactured according to a typical method for manufacturing a positive electrode. Specifically, the positive electrode can be manufactured by coating a positive electrode collector with a positive material mixture prepared by dissolving or dispersing the above-described positive electrode material, a selective adhesive, and a conductive material in a solvent, and then drying and calendering the coated positive electrode collector; or the positive electrode can be manufactured by casting the positive material mixture onto a separate support and then laminating a film separate from the support onto the positive electrode collector.

[0065] The solvent can be a common solvent in this field. The solvent can be dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, or water; any of these solvents or mixtures of two or more of them can be used. The amount of solvent used can be sufficient if the solvent dissolves or disperses the positive electrode material, the conductive material, and the adhesive, and enables a viscosity that ensures excellent thickness uniformity during the subsequent coating to produce the positive electrode, taking into account the coating thickness of the slurry and the manufacturing yield. [Lithium-ion secondary battery]

[0066] Furthermore, the present invention may provide an electrochemical device for the active material of the positive electrode. The electrochemical device may, in particular, be a battery or a capacitor, e.g., a lithium secondary battery.

[0067] Specifically, the lithium secondary battery includes a positive electrode, a negative electrode opposite the positive electrode, a diaphragm disposed between the positive electrode and the negative electrode, and an electrolyte. Since the positive electrode is the same as the one described above, a detailed description is omitted, and only the remaining structures are described in detail below.

[0068] In addition, the lithium secondary battery may optionally include a battery container in which the electrode assembly consisting of the positive electrode, the negative electrode and the diaphragm is housed, and a sealing member that seals the battery container.

[0069] In the lithium secondary battery, the negative electrode includes a negative electrode collector and a negative electrode active material layer provided on the negative electrode collector.

[0070] The negative electrode active material layer is formed by applying or rolling and drying a mixture of a negative electrode active material, an adhesive, and a conductive additive used as required onto a negative electrode collector, e.g., a metal foil.

[0071] When using the negative electrode with the negative electrode active substance layer formed by coating or rolling and drying a mixture of a negative electrode active material, an adhesive, and a conductive additive as needed on a negative electrode collector, a carbon material is preferably used as the negative electrode active substance. The carbon material preferably adopts graphite. In particular, when the graphite is included in the negative electrode active substance layer, there is an advantage in that the battery performance can be improved even when the remaining capacity (SOC) of the battery is low.

[0072] There are no specific restrictions on the negative electrode collector, as long as it has high electrical conductivity without causing adverse chemical changes in the battery. It is possible to use materials such as copper, stainless steel, aluminum, nickel, titanium, burnt carbon, and copper or stainless steel that has undergone a surface treatment with carbon, nickel, titanium, silver, and the like, as well as aluminum-cadmium alloy. Furthermore, the negative electrode collector typically has a thickness of 3 μm to 500 μm and, similar to the positive electrode collector, can have microscopic pits on the collector surface to enhance the adhesion of the negative electrode active material.For example, the negative electrode collector can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foamed body, a nonwoven body, and the like.

[0073] In addition to the negative electrode active material, the negative electrode active material layer optionally comprises an adhesive and a conductive material.

[0074] The adhesive serves to bond particles of the carbon material, the negative electrode active material, together and to bond the negative electrode active material layer to the metal foil. For example, when PVDF is used as an adhesive, N-methylpyrrolidone (NMP) can be used as a solvent, eliminating the need for water. This prevents gas formation caused by residual water.

[0075] The negative electrode active material layer may optionally contain a conductive material. The conductive material may preferably be carbon fibers such as carbon nanofibers, carbon black such as acetylene black and cochineal black, carbon materials such as activated carbon, mesoporous carbon, fullerenes, and carbon nanotubes.

[0076] Based on the total weight of the negative electrode active material layer, the weight percentage of the negative electrode active material can be 70%-95%.

[0077] In the lithium secondary battery, the diaphragm is a membrane-like battery component by which the positive electrode is isolated from the negative electrode to ensure the conductivity of lithium ions between the negative electrode and the positive electrode. Any diaphragm can be used as the diaphragm without particular limitation, as long as it is commonly used in lithium secondary batteries, and in particular, a diaphragm that is resistant to high temperatures of the electrolyte and has low resistance to the transfer of ions from the electrolyte can be used. In the embodiment of the present invention, it is preferable that the olefin-based resin layer is a layer having a structure including pores that are closed when the temperature of the battery rises, that is,The olefin-based resin layer is a layer of polyolefin comprising a porous mass or a microporous mass. Because the olefin resin layer has such a structure, the diaphragm can be closed (shut down) and the ion flow can be interrupted even when the battery temperature rises. A porous polyethylene membrane is preferably used to achieve the sealing effect. Depending on the case, the diaphragm can also be coated with a heat-resistant microparticle layer in the olefin-based resin layer. The heat-resistant microparticle layer with a heat resistance of 150°C or more can be composed of inorganic oxides such as silicon dioxide, alumina (α-alumina, β-alumina, and θ-alumina), iron oxide, titanium oxide, barium titanate, and zirconium dioxide, as well as minerals such as boehmite, zeolite, apatite, kaolin, spinel, mica, and mullite.In this way, a ceramic diaphragm with a heat-resistant resin layer can also be used.

[0078] Furthermore, the electrolyte used in the present invention may include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a melt-type inorganic electrolyte that can be used in the manufacture of the lithium secondary battery, but the present invention is not limited thereto.

[0079] In particular, the electrolyte may contain an organic solvent and a lithium salt. Any organic solvent may be used as the organic solvent without any particular restrictions, as long as it can serve as a medium through which the ions involved in the battery's electrochemical reaction can move.In particular, the following substances can be used as organic solvents: ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic solvents such as benzene and fluorobenzene; or carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylidene carbonate (EC) and propylene carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitrile such as R-CN (where R is a linear, branched or cyclic C2-C20 hydrocarbon group and may comprise a double bond, an aryl ring or an ether bond); amide such as dimethylformamide; dioxolane such as 1,3-dioxolane; or cyclobutanesulfone. Among these solvents, carbonate solvents can also be used, e.g. mixtures of cyclic carbonates (e.g.Ethylidene carbonate or propylidene carbonate) with high ionic conductivity and high dielectric constant, which can improve the charge / discharge performance of batteries, and linear carbonates with low viscosity (e.g. ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate).

[0080] A lithium salt can be used without any particular restrictions as long as it is a compound capable of supplying the lithium ions used in lithium secondary batteries. Specifically, the following substances can be used as the lithium salt: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. A lithium salt can be used in a concentration range of 0.1M-2.0M. In the case where the concentration of the lithium salt is within the above range, excellent electrolyte performance can be achieved and lithium ions can be moved effectively because the electrolyte can have appropriate conductivity and viscosity.

[0081] To improve the battery life characteristics, suppress the decrease in battery capacity, and improve the discharge capacity of the battery, at least one additive may be added to the electrolyte in addition to the electrolyte component described above, e.g., halogenated alkylidene carbonate compounds such as difluoroethylidene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, (condensed) glycol dimethyl ether analogues, hexamethylphosphorotriamine, nitrobenzene derivatives, sulfur, quinone imine dyes, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum trichloride. In this case, the additive content may be between 0.1 wt% and 5 wt% based on a total weight of 100 wt% electrolyte.

[0082] As described above, since the lithium secondary battery comprising the positive electrode material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention, the lithium secondary battery is suitable for portable devices such as mobile phones, notebook computers, and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs). [Examples of implementation]

[0083] The present application is described in more detail below in conjunction with exemplary embodiments. It should be understood that these exemplary embodiments are used only to illustrate the present application and are not intended to limit the scope of the present application.

[0084] The preparation of the positive electrode active material in the embodiments comprises the following steps: (1) Weighing nickel sulfate, cobalt sulfate, and manganese sulfate according to the elemental molar ratio and dissolving them in deionized water, supplying each metal solution to a reactor through a pipeline to form a mixed metal solution and introducing nitrogen as a protective gas, adding an aqueous NaOH solution as a precipitant and ammonia as a complexing agent to the mixed metal solution, gradually adjusting the ammonia concentration of the solution and the pH of the solution, and reacting for 10 hours to obtain the precursor. (2) uniformly mixing precursor and lithium carbonate, and controlling the ratio of lithium to 1.1:1. (3) Transferring the mixed material into the sintering process, which consists of two stages: the first stage of sintering at 600°C for 6 hours; the second stage of sintering at 880°C for 9 hours. (4) Grinding and crushing the material after sintering and then uniformly mixing the crushed material with alumina, the weight proportion of alumina and crushed material being 0.5 wt%. (5) Transfer the mixed material into the sintering process with a sintering temperature of 450°C and a sintering time of 8 hours to obtain the positive electrode active material. (6) Sort the positive electrode active material using four sieves (mesh size: 1250 mesh, 2500 mesh, 3250 mesh and 12500 mesh), and the weight proportion of different particle level intervals is determined by weighing and adjusting.

[0085] The molar element ratio of nickel sulfate, cobalt sulfate, and manganese sulfate in Working Examples 1 / 2 / 5 / 6 / 7 and Comparative Examples 1 / 3 is 8:1:1; and the molar element ratio of nickel sulfate, cobalt sulfate, and manganese sulfate in Working Examples 3 / 4 / 8 and Comparative Example 2 is 7:2:1.

[0086] The weight fraction of the different particle size ranges is varied by the classifying sieve in each embodiment and comparative example, whereby the particle size of the positive electrode active material, the cumulative weight gradation of the different particle size ranges, and the specific surface area can be controlled, and the positive electrode active material with predetermined parameter properties is obtained. Comparative Examples 1 to 3 list the cases where the cumulative weight gradation of the different particle size ranges does not fall within the scope of the present application.

[0087] Method for manufacturing the positive pole piece using the above positive electrode active material in the working examples and comparative examples: the positive electrode active material, the conductive agent and the adhesive are mixed in the mass ratio of 97:2:1, after which they are stirred and mixed homogeneously with a solvent, and then the positive pole piece is manufactured by the process of screening, coating, rolling, slitting and cutting the plate.

[0088] The lithium-ion secondary battery is manufactured using the positive electrode prepared in the working examples and the comparative examples, the negative electrode using graphite as the active material, the polyethylene diaphragm, and the LiPF6 electrolytic solution with EC:EMC = 1:1.

[0089] The specific parameters are listed in Tables 1 and 2. Table 1 A(%) B(%) C(%) A / C B / (A+C) Example 1 7,65 62,77 17,13 0,45 2,53 Example 2 5,39 72,45 13,26 0,41 3,88 Example 3 6,29 60,92 19,85 0,32 2,33 Example 4 5,23 58,91 22,38 0,23 2,13 Example 5 4,89 63,47 20,57 0,24 2,49 Example 6 6,45 56,23 27,79 0,23 1,64 Example 7 7,69 42,78 17,11 0,45 1,73 Example 8 4,76 73,5 12,04 0,40 4,38 Comparison example 1 0,35 50,84 37,21 0,01 1,35 Comparison example 2 11,23 72,95 4,82 2,33 4,55 Comparison example 3 1,61 78,44 10,95 0,15 6,25 Table 2 Dv10 (nm) Dv50 (nm) Dv90 (nm) Sw (m 2 / g) P K=P* (B / (A+C) 3 / (Sw ×(Dv90-Dv10)) Execution 1,336 2,830 4,730 0,430 35,5 3% 0,90 2,06 -example 1 Implementation example 2 1,152 2,431 4,772 0,410 25,7 4% 1,00 2,02 Implementation example 3 1,254 2,650 5,023 0,350 38,6 2% 0,90 2,27 Implementation example 4 1,288 2,547 4,650 0,420 42,1 8% 0,90 2,12 Implementation example 5 1,312 2,530 5,118 0,343 24,0 7% 0,60 2,30 Implementation example 6 1,291 2,876 5,150 0,332 36,4 5% 0,60 2,34 Implementation example 7 1,387 2,980 5,120 0,325 36,0 0% 0,62 2,47 Execution 1,305 2,520 4,633 0,461 25,1 4% 1,10 1,96 -example 8 Comparison example 1 1,302 3,439 6,227 0,227 31,0 4% 0,42 2,68 Comparison example 2 0,882 3,077 4,665 0,482 27,2 0% 1,24 1,65 Comparison example 3 1,310 2,780 4,983 0,451 20,4 2% 1,28 1,81 Performance Evaluation1) High-temperature cycle test (cycle life) of lithium-ion batteries

[0090] The lithium-ion battery is charged at 45°C with a current of 0.5C to 4.2V and then discharged with a current of 0.5C to 2.0V, and the initial discharge capacity is recorded. The battery is then charged / discharged 500 times at 0.5C / 0.5C, and the discharge capacity of the 500th time is recorded. The discharge capacity of the 500th time is divided by the discharge capacity of the first time to obtain the battery's capacity retention rate after 500 charge / discharge cycles. 2) Capacity retention rate of the lithium-ion battery after storage at high temperatures (storage life)

[0091] The lithium-ion secondary battery obtained in each embodiment is subjected to a high-temperature storage test in which the battery is first charged at room temperature with a constant current of 1 C to 4.2 V, then charged with a constant current and constant voltage until the current drops to 0.05 C, and then discharged with a constant current of 1 C to 3.0 V, and the initial discharge capacity of the battery is measured, and then after charging to full capacity and storing the battery for 60 days in an environment of 55 ° C and 70 ° C, the battery is discharged with a constant current of 1 C to 3 V, the discharge capacity of the battery is measured, and the capacity retention rate is determined by the following equation. Capacity retention rate = (discharge capacity after the high-temperature storage test) / (initial discharge capacity) 3. High-temperature safety test of the lithium-ion battery

[0092] The lithium-ion battery is subjected to a HOT box test, specifically in Working Example 1, Working Example 5 and Comparative Example 1 and Comparative Example 2, SOC 100% fully charged and heated to 120°C at a heating rate of 5°C / minute and left for 5 hours to check whether a fire occurred in the experiment or not, which is an evaluation index to confirm the high temperature resistance.

[0093] The results of the individual assessments are shown in Table 3. Table 3 Capacity retention rate in % after 500 cycles at 45°C Capacity retention rate in % after high temperature storage at 55°C Capacity retention rate in % after high temperature storage at 70°C High temperature safety test Fire or not Fire start time Example 1 84,43 92,08 81,58 no - Example 2 85,2 87,64 78,09 no - Example 3 89,77 90,31 80,05 no - Example 4 83,09 85,276 80,97 no - Example 5 87,31 89,2 76,11 no - Example 6 83,75 88,39 79,5 no - Example 7 81,57 85,07 74,26 no - Example 8 79,11 84,66 77,15 no - Comparison example 1 67,24 73,92 59,54 no - Comparison example 2 72,15 70,96 66,35 Yes 8 minutes Comparison example 3 69,98 68,23 63,21 Yes 15 minutes

Claims

[1] A positive electrode active material comprising a lithium metal composite oxide having a layered structure, characterized by that the chemical formula of the lithium metal composite oxide LiNi x Co y M z O2, where 0.7≤x≤0.9, 0.05≤y≤0.2, 0.05≤z≤0.2 and x+y+z=1, and where M is at least one of Mn and Al or comprises Mn and Al; and wherein, according to the weight fraction, the positive electrode active material is divided into three distribution intervals A, B and C: the interval A: consisting of lithium metal composite oxide particles with a particle size of 300 nm-1000 nm, the percentage of the total weight of the lithium metal composite oxide particles being 0.1%-8%; the interval B: consisting of lithium metal composite oxide particles with a particle size of 1300 nm-3550 nm, the percentage of the total weight of the lithium metal composite oxide particles being 30%-75%; the interval C: consisting of lithium metal composite oxide particles with a particle size of 4500 nm-8800 nm, where the percentage of the total weight of the lithium metal composite oxide particles is 10%-35%. [2] The positive electrode active material according to claim 1, characterized by , where the percentage of particles of interval A in the total weight of the lithium metal composite oxide particles is 4%-7%. [3] Positive electrode active material according to any one of the preceding claims, characterized by that the percentage of particles of interval B in the total weight of the lithium metal composite oxide particles is 50-70%. [4] Positive electrode active material according to any one of the preceding claims, characterized by that the percentage of particles of interval C in the total weight of the lithium metal composite oxide particles is 14%-25%. [5] Positive electrode active material according to any one of the preceding claims, characterized by that the lithium metal composite oxide particles are primary particles and / or secondary particles composed of the primary particles, wherein the primary particles and / or the secondary particles composed of the primary particles have a Dv10 of 1100 nm-1400 nm and a Dv90 of 4500 nm-5200 nm, and wherein Dv10 and Dv90 each represent the particle size corresponding to the time at which the cumulative volume distribution percentage reaches 10% and 90%, respectively. [6] Positive electrode active material according to any one of the preceding claims, characterized bythat the lithium metal composite oxide particles are primary particles and / or secondary particles composed of the primary particles, wherein the primary particles and / or the secondary particles composed of the primary particles have a Dv50 of 2400-3000 nm, and wherein Dv50 represents the particle size corresponding to the time at which the cumulative volume distribution percentage reaches 50%. [7] Positive electrode active material according to any one of the preceding claims, characterized by that the specific surface area Sw of the lithium metal composite oxide particles is 0.1 m 2 / g-1 m 2 / g. [8] Positive electrode active material according to any one of the preceding claims, characterized by that the specific surface area Sw of the lithium metal composite oxide particles is 0.25 m 2 / g-0.6 m 2 / g. [9] Positive electrode active material according to any one of the preceding claims, characterized by that the porosity P of the positive electrode active material satisfies 25%≤P≤40%. [10] Positive electrode active material according to any one of the preceding claims, characterized by that the weight fraction of the lithium metal composite oxide particles in the intervals A and C satisfies 0.1≤A / C≤0.

8. [11] Positive electrode active material according to any one of the preceding claims, characterized by that the weight fraction of the lithium metal composite oxide particles in the intervals A and C satisfies 0.2≤A / C≤0.

6. [12] Positive electrode active material according to any one of the preceding claims, characterized by that the weight fraction of the lithium metal composite oxide particles in the intervals A, B and C satisfies 1.3≤B / (A+C) ≤4.

4. [13] Positive electrode active material according to any one of the preceding claims, characterized bythat the porosity P of the positive electrode active material satisfies the relationship equation: k=P*(B / (A+C)); where K satisfies the range 0.6≤K≤1.

1. [14] Positive electrode active material according to any one of the preceding claims, characterized by that the lithium metal composite oxide particles continue to: 1.9≤3 / (Sw×(Dv90-Dv10))) ≤2.5 is met. [15] A positive electrode active material according to any one of the preceding claims, comprising at least one of the following compounds or materials: Li(Ni 0,8 Mn 0,1 Co 0,1 )O2, Li(Ni 0,8 Co 0,15 Al 0,05 )O2 and Li(Ni 0,86 Mn 0,07 Co 0,05 Al 0,02 )O2. [16] A positive electrode active material according to any one of the preceding claims, comprising at least the following compound or material Li(Ni 0,9 Mn 0,05 Co 0,05 )O2. [17] Positive pole piece, in particular for lithium secondary batteries or lithium-ion batteries, characterized by that it comprises a positive electrode active material according to any one of claims 1 to 16. [18] A positive pole piece according to claim 17, comprising a positive electrode collector and a positive electrode active material layer, wherein the positive electrode active material layer is provided on at least one surface of the positive electrode collector and comprises the positive electrode active material. [19] A positive pole piece according to claim 18, wherein the positive electrode collector is made of aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel. [20] A positive pole piece according to claim 18 or 19, the positive electrode active material layer comprising a conductive material and an adhesive. [21] A positive pole piece according to claim 20, wherein the conductive material comprises carbon fibers, carbon black, or carbon material. [22] A positive pole piece according to claim 20 or 21, wherein the weight of the conductive material is 2%-4% of the weight of the positive electrode active material layer. [23] A positive pole piece according to any one of claims 20 to 22, wherein the adhesive comprises synthetic rubber or polysaccharides, [24] A positive pole piece according to any one of claims 22 to 23, wherein the percentage by weight of the adhesive, based on the total weight of the positive electrode active material layer, is between 1% and 20%. [25] Electrochemical energy storage device, in particular lithium-ion battery, characterized by that it comprises a positive electrode active material according to any one of claims 1 to 14 or a positive pole piece according to any one of claims 17 to 24. [26] An electrochemical energy storage device according to claim 25, comprising a positive electrode or the positive pole piece with the positive electrode active material, a negative electrode or a negative pole piece opposite to the positive electrode, a diaphragm arranged between the positive electrode and the negative electrode, and an electrolyte or an electrolyte solution. [27] An electrochemical energy storage device according to claim 25 or 26, comprising a battery container in which the electrode assembly comprising the positive electrode, the negative electrode and the diaphragm is housed, and a sealing member which seals the battery container. [28] An electrochemical energy storage device according to any one of claims 25 to 27, wherein the negative electrode comprises a negative electrode collector and a negative electrode active material layer provided on the negative electrode collector. [29] An electrochemical energy storage device according to any one of claims 25 to 28, wherein the negative electrode collector is made of or used for aluminum, nickel, titanium, calcined carbon, copper, stainless steel or an aluminum-cadmium alloy. [30] An electrochemical energy storage device according to any one of claims 25 to 29, wherein the negative electrode collector has a thickness of 3 µm to 500 µm and microscopic depressions on the surface of the collector to improve the adhesion of the negative electrode active material. [31] An electrochemical energy storage device according to any one of claims 25 to 30, wherein the negative electrode collector is provided in the form of a film, a sheet, a foil, a net, a porous body, a foamed body or a nonwoven body. [32] An electrochemical energy storage device according to any one of claims 26 to 31, wherein the electrolyte contains an organic solvent and a lithium salt. [33] The electrochemical energy storage device of claim 32, wherein the lithium salt is selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, and LiB(C2O4)2. [34] An electrochemical energy storage device according to claim 32 or 33, wherein a concentration range of 0.1 M-2.0 M of the lithium salt is provided. [35] Electrochemical energy storage device according to one of claims 26 to 34, wherein at least one additive is added to the electrolyte or the electrolyte solution, e.g. halogenated alkylidene carbonate compounds such as difluoroethylidene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, (condensed) glycol dimethyl ether analogues, hexamethylphosphorotriamine, nitrobenzene derivatives, sulphur, quinone imine dyes, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol or aluminium trichloride. [36] An electrochemical energy storage device according to any one of claims 25 to 35 for use in a portable device such as a mobile phone, a notebook computer and a digital camera, or an electric vehicle such as a hybrid electric vehicle. [37] A portable device, namely a mobile phone, notebook computer or digital camera, comprising an electrochemical energy storage device according to any one of claims 25 to 36. [38] An electric vehicle comprising an electrochemical energy storage device according to any one of claims 25 to 36. [39] A hybrid electric vehicle comprising an electrochemical energy storage device according to any one of claims 25 to 36.