Positive electrode material for rechargeable lithium-ion batteries

Abstract

The present invention relates to a positive electrode material for rechargeable lithium ion batteries. In particular, the present invention provides a positive electrode active material for a lithium ion battery, said positive electrode active material comprising a lithium transition metal based oxide powder, said powder comprising a compound containing Ni and Co and having the general formula Li 1+a ((Ni z (Ni 1 / 2 Mn 1 / 2 ) y Co x ) 1‑k Ak) 1‑a 02, wherein A is a dopant, -0.02

Description

[0001] This invention patent application is a divisional application of the invention patent application with international application number PCT / EP2018 / 083406, international application date of December 4, 2018, application number 201880083116.2 which entered the Chinese national phase, and invention title "Positive electrode material for rechargeable lithium-ion batteries". Technical Field

[0002] This invention relates to a lithium transition metal oxide material with a single morphology, which can be used as a positive electrode material for rechargeable lithium-ion batteries. More specifically, the material has a cobalt concentration gradient from the surface to the core. This positive electrode material enhances battery performance, such as capacity, cycle stability, and rate performance. Furthermore, due to its unique morphology, the material can be used in solid-state lithium-ion batteries or non-aqueous lithium-ion batteries at high voltages. Background Technology

[0003] Rechargeable lithium-ion batteries (LIBs) are currently used in laptops, mobile phones, cameras, and a variety of other electronic devices due to their high volumetric and gravimetric energy density and long cycle life. Furthermore, to meet the demand for larger batteries used in electric vehicles (EVs) and hybrid electric vehicles (HEVs), batteries with even higher energy density are required. One way to increase battery energy density is to apply higher operating voltages. However, the organic liquid electrolyte used in conventional lithium-ion batteries decomposes and forms byproducts during cycling at high voltages. In addition to stability issues, the electrolyte contains flammable solvents that can cause thermal runaway at high charge levels. Therefore, serious safety problems can occur, such as a high probability of electrolyte leakage, overheating, and combustion. Considering future EV and HEV applications, safety is one of the primary considerations.

[0004] Solid electrolytes have replaced flammable liquid organic electrolytes, opening up the field of solid-state batteries (SSBs). Solid electrolytes not only offer high safety but also promise excellent cycle stability. These properties make solid electrolytes attractive for high-voltage applications as well. Previously, SSB technology was driven by thin-film battery technology for portable applications. Generally, layered oxide materials, especially LiCoO2 (LCO), are preferred as positive electrode materials, for example, in thin-film batteries. LCO possesses sufficiently high theoretical capacity and good thermal stability. However, due to resource scarcity leading to high cobalt (Co) prices and environmental issues, new positive electrode materials with stable 2D layered structures and high theoretical capacity have been developed. Starting with LCO, metal substitution—that is, replacing Co with other transition metals—is used to adjust the three-layer oxide material Li... 1+a M 1- aThe composition of O2 revealed LiNi x Mn y Co Z O2(NMC) and LiNi x Co z Al y O2(NCA), where M is a mixture of nickel (Ni), cobalt (Co), manganese (Mn), or aluminum (Al), and a is typically close to zero. These materials are popular because the combination of Ni, Mn, Co, and Al is advantageous due to the fact that Ni provides high capacity while Mn provides good cycling performance. Furthermore, Co supports the layered crystal structure of NMC, allowing for rapid Li ion transport. Al doping is also known as a way to improve safety.

[0005] In conventional LIBs, polycrystalline NMC with open interconnected pores is preferred because the liquid electrolyte can easily permeate into the porous structure. This is useful because the much higher lithium conductivity of the electrolyte forms "high-speed channels" for rapid diffusion of lithium into and out of the particles. However, porous structures are not beneficial for SSBs because the solid electrolyte cannot enter the pores. Therefore, a non-porous morphology is required. Furthermore, SSBs require good interfacial contact between the solid electrolyte and the positive electrode particles, which can be achieved especially when the particles have, for example, spherical or near-spherical morphologies. This contact is achieved by pressing the solid electrolyte onto the powdered positive electrode material. Therefore, the positive electrode powder needs to be mechanically stable. If polycrystalline (porous) NMC is used in an SSB, the interfacial contact between the solids may be damaged or cracked when the electrodes are compressed as part of the battery manufacturing process. Cracks are also a major concern: during charge-discharge, the particles undergo volume changes due to strain, as described by AL Cuntz et al. in J. Phys. Chem. Lett., 2015, Vol. 6, No. 22. This volume change can cause delamination at the electrode-electrolyte interface, leading to further cracking. Delamination and cracking disrupt lithium-ion pathways, resulting in rapid capacity loss. These problems are less severe in conventional batteries because they contain a liquid electrolyte and electrodes that are somewhat flexible, allowing particles to remain electrically active even after cracking, as the system is more resistant to such deformation. However, this flexibility may be insufficient to withstand repeated volume changes under high-voltage cycling. Similarly, since SSBs lack buffers and binders to withstand such cracking, it becomes a significant problem in such true batteries.

[0006] US2017 / 133668 A1 discloses a polycrystalline positive electrode material having a core and a surface portion, wherein the amount of manganese in the core and the surface portion is higher than 25 mol%, and the amounts of nickel and cobalt in the positive electrode active material vary, resulting in a nickel and cobalt concentration gradient in the positive electrode active material from the core to the surface portion.

[0007] CN107408667 provides a method for preparing a positive electrode active material, the positive electrode active material comprising a core, a shell disposed around the core, and a buffer layer between the core and the shell, the buffer layer comprising pores and a three-dimensional network structure connecting the core and the shell, wherein the core, shell, and three-dimensional network structure of the buffer layer each independently comprise a lithium-nickel-manganese-cobalt composite metal oxide, and at least one metal element selected from nickel, manganese, and cobalt has a concentration gradient that gradually varies in any region of the core, the shell, and the entire positive electrode active material.

[0008] WO2017 / 042654 discloses a method for manufacturing materials with the general formula Li through multiple sintering steps. 1-a' ((Ni z (Ni Mn ) y Co x ) 1-k A k ) 1+a' A method for finding the positive electrode material of O2, wherein x+y+z=1, 0.1≤x≤0.4, 0.25≤z≤0.55, A is a dopant, 0≤k≤0.1, and 0.01≤a'≤0.10.

[0009] The purpose of this invention is to provide a novel positive electrode material that is particularly suitable for SSB or non-aqueous batteries operating at high voltages, without the disadvantages of known single LCO and polycrystalline NMC materials. Specifically, it is mechanically stable and can withstand continuous volume changes and crack formation. Summary of the Invention

[0010] From a first aspect, the present invention provides a positive electrode active material for lithium-ion batteries, the positive electrode active material comprising a lithium transition metal-based oxide powder containing Ni and Co and having the general formula Li 1+a ((Ni z (Ni Mn ) y Co x ) 1-k A k ) 1-aSingle crystal single particles of O2, where A is a dopant, -0.02 < a ≤ 0.06, 0.10 ≤ x ≤ 0.35, 0 ≤ z ≤ 0.90, x + y + z = 1 and k ≤ 0.01, said particles having a cobalt concentration gradient, where the Co content at the particle surface is higher than at the particle center, and where

[0011] - When Mn is present, the ratio between the Co / Mn molar ratio at the particle surface and the Co / Mn molar ratio at a distance d from the surface lies between 1.1 and 1.3, where d = of the distance from the particle surface to the particle center, or

[0012] - When Mn is absent, the ratio between C(4) / C(3) lies between 1.1 and 1.3, where C(4) is the ratio between the molar concentration of Co at the particle surface and the molar concentration of Co at the particle center, and where C(3) is the ratio between a) the molar concentration of Co at a distance from the particle surface to the particle center and b) the molar concentration of Co at the particle center. In one embodiment, Mn is absent and the general formula is Li 1+a' ((Ni z' Co x' ) 1-k' A k' ) 1-a' O2, where A is a dopant, -0.02 < a' ≤ 0.06, 0.10 ≤ x' ≤ 0.35, 0.70 ≤ z' ≤ 0.90, x' + z' = 1 and k' ≤ 0.01. In one embodiment, 0 ≤ y ≤ 0.67, in another embodiment, y > 0 and (z + y / 2) > x. In another embodiment, y > 0 and z > y / 2. In another embodiment, y > 0, z ≥ 0.35 and -0.012 ≤ a ≤ 0.010. The dopant A is one or more of Al, Ca, W, B, Si, Ti, Mg and Zr. The advantages of having a dopant can be an improvement in structural and thermal stability or an enhancement of lithium ion conductivity. The oxygen in the general formula may also be partially replaced by S, F or N.

[0013] The positive electrode active material may be a powder having a particle size distribution with D50 < 10 μm, preferably less than 8 μm, and more preferably between 2 μm and 5 μm. In one embodiment, when Mn is present, the ratio between the Co / Mn molar ratio at the particle surface and the Co / Mn molar ratio at the particle center is between 1.4 and 1.5. In another embodiment, the cobalt concentration gradient varies continuously from the surface to the center of the particle. The powder may consist of particles having a morphology including multiple flat surfaces and an aspect ratio of at least 0.8. Such a morphology is (quasi) spherical or oval. The surface layer of the electrode active material may contain LiCoO2, where Co may also be partially replaced by dopant A. In addition, the particles constituting the powder may be provided with a coating containing either or both of LiNaSCU and Al2O3.

[0014] From a second aspect, the present invention may provide a method for manufacturing the above-mentioned powdery positive electrode material compound, which contains Ni and Co and has the general formula Li 1+a ((Ni z (Ni Mn ) y Co x ) 1- k Ak) 1-a O2, where A is a dopant, -0.02 < a ≤ 0.06, 0.10 ≤ x ≤ 0.35, 0 ≤ z ≤ 0.90, x + y + z = 1 and k ≤ 0.01. The method includes the following steps:

[0015] - Provide a first precursor containing A, Ni, Co, and Mn under conditions present in the powdery positive electrode material, the precursor consisting of particles having a particle size distribution with D50 < 10 μm,

[0016] - Mix the first precursor with any one of LiOH, Li2O, Li2CO3, and LiOH.H2O to obtain a first mixture, whereby the ratio of Li to transition metals in the first mixture, LM1, is between 0.60 and < 1.00,

[0017] - Sinter the first mixture in an oxidizing atmosphere at a temperature between 700 °C and 900 °C for a time between 6 hours and 36 hours to obtain a first intermediate product,

[0018] - Mix the first intermediate product with any one of LiOH, Li2O, Li2CO3, and LiOH.H2O to obtain a second mixture, whereby the ratio of Li to transition metals in the second mixture, LM2 ≥ 0.90,

[0019] - The second mixture was sintered in an oxidizing atmosphere at a temperature between (950 - (155.56*z)) °C and (1050 - (155.56*z)) °C for a time between 6 hours and 36 hours.

[0020] - Grinding and sintering the second mixture, thereby separating the particles of the sintered second mixture into individual primary particles.

[0021] - A Co-based precursor and optionally a Li-based precursor are provided, and the precursors are mixed with a sintered and milled second mixture to obtain a third mixture in which the Li to transition metal ratio LM3 is -0.107*z+1.018≤LM3≤-0.107*z+1.098.

[0022] - The third mixture was sintered in an oxidizing atmosphere at a temperature between 700°C and 800°C for a period of 6 hours and 36 hours.

[0023] In one embodiment, y > 0, z ≥ 0.35 and -0.012 ≤ a ≤ 0.010, and LM1 is between 0.60 and 0.95, LM2 ≥ LM1 or even LM2 > LM1, and LM3 ≥ LM1, and the second sintering temperature can be between 895°C and 995°C. Also in this embodiment, LM3 can be LM2, meaning that the molar content of Co in the Co-based precursor is equal to the molar content of Li in the Li-based precursor, and these two molar contents are expressed relative to the total metal content (excluding Li) in the second mixture. Here, Co between 2 mol% and 10 mol% can also be added to the Co-based precursor. In another embodiment, a grinding step is applied to break the agglomerated powder from the second sintering into individual particles in a ball mill apparatus.

[0024] In another embodiment, the aforementioned method includes the following subsequent steps:

[0025] - Provides inorganic oxidation compounds,

[0026] -Provide chemicals that act as Li acceptors.

[0027] - The sintered third mixture, the oxidized compound, and the Li acceptor are mixed to obtain a fourth mixture, and

[0028] The fourth mixture is heated in an oxygen-containing atmosphere at a temperature between 300°C and 800°C. In this embodiment, both the inorganic oxidizing compound and the Li acceptor chemical can be the same compound, any one of Li₂S₂O₈, H₂S₂O₈, and Na₂S₂O₈, and the heating temperature of the fourth mixture is between 350°C and 450°C. Nanoscale Al₂O₃ powder can also be provided as another Li acceptor chemical.

[0029] In a third aspect, the present invention can provide the use of powdered positive electrode materials in solid-state lithium-ion batteries that are cycled up to a certain voltage or at least 4.35V, or in lithium-ion batteries having a liquid electrolyte. Attached Figure Description

[0030] Figure 1 The relationship between discharge capacity and cycle number for EEX1.1 and EEX1.2.

[0031] Figure 2 Cross-sectional SEM images of EEX1.1 and EEX1.2 before and after the cycle.

[0032] Figure 3 SEM images from .CEX1.1

[0033] Figure 4 SEM images of .EX1.1

[0034] Figure 5 XRD pattern of .EX1.1

[0035] Figure 6.1 EDS linear profiles of Ni, Mn, and Co (mol%) in EX1.1

[0036] Figure 6.2 Cross-sectional SEM images of .EX1.1, with selected locations (D0, D1, D2, D3, and D4) for EDS analysis.

[0037] Figure 6.3 EDS profile of the Co / Mn molar ratio (moles / moles) at the selected location EX1.1.

[0038] Figure 7.1 Full-cell test results for .EX2 and CEX2 at room temperature and 45°C in the range of 3.0V to 4.2V.

[0039] Figure 7.2 Full-cell test results for .EX2 and CEX2 at room temperature and 45°C in the range of 3.0V to 4.35V. Detailed Implementation

[0040] This invention provides NMC or NC(A) powder (also referred to as N(M)C) with a specific single morphology, which can be used as a positive electrode material for SSBs and conventional lithium-ion batteries operating at high voltages. "Single" here refers to a morphology in which the secondary particles ideally contain only one primary particle. Other expressions for the term "single material" include single crystal material and monocrystal material, and monolithic material. The preferred shape of the primary particle can be described as a pebble shape, wherein the aspect ratio of the primary particle is typically close to 1.

[0041] One way to overcome or improve crack formation in battery applications is to avoid using polycrystalline materials. Therefore, replacing polycrystalline materials with N(M)C materials having a single-particle morphology seems interesting because higher energy density can be achieved, and the degradation mechanism associated with more pronounced volume changes and resulting particle cracking is eliminated when the battery is cycled at high voltages (to achieve higher capacity, such as for electric vehicle (EV) applications). Cross-sectional images of the positive electrode before and after cycling show that single N(M)C does not crack after cycling at high voltages, indicating its excellent mechanical strength. Thus, single N(M)C is observed to have significantly better cycle stability than polycrystalline N(M)C at high voltages and temperatures.

[0042] In SSB (Solid State Battery), the monolithic morphology ensures good contact between the solid electrolyte and the positive electrode material during battery packaging and cycling because its quasi-spherical shape, including flat regions, provides face-to-face contact rather than point-to-point contact. Therefore, grain boundary distortion and microcrack formation are avoided during cycling. Furthermore, regarding undesirable side reactions occurring at the interface between the electrolyte and the solid positive electrode, these unwanted reactions are limited due to the small surface area of ​​the monolithic particles. This enhances cycle stability and prevents irreversible capacity loss.

[0043] Individual particles preferably have a particle size distribution with a D50 of less than 10 μm, more preferably less than 8 μm, and even more preferably between 2 μm and 5 μm. When the average particle size is greater than 10 μm, the battery performance may deteriorate, resulting in lower capacity and higher irreversibility. Conversely, if the particle size is too small (i.e., <2 μm), it is difficult to prepare N(M)C powder using existing techniques. For example, the powder cannot be easily sieved due to particle agglomeration. In addition, it is difficult to establish contact with the solid electrolyte in the SSB, resulting in poor performance.

[0044] Typical precursors of single N(M)C are mixed transition metal (N(M)C) hydroxides, hydroxyoxides, carbonates, oxides, etc. The general formula for hydroxides and hydroxyoxides is Ni. x Mny CO z A a O v (OH) w , where 0 ≤ v ≤ 1 and v + w = 2, or Ni x Mn y Co z A a (OH b )2, where 0.5 < b < 1 and A is a dopant. These precursors may already have a single shape. However, usually they are polycrystalline materials. Generally, the synthesis conditions of the powder affect the morphology of the final NMC powder. Preparing a single material from precursors with a polycrystalline structure requires optimizing synthesis parameters such as sintering temperature, sintering time, and the molar ratio of Li to M (hereinafter referred to as Li / M), where M is the sum of Ni, Co, Mn, and Al in Li 1+a M 1-a O2. A high sintering temperature and a large excess of Li (high Li / M) facilitate obtaining a single morphology. However, if the Li / M is too high, the electrochemical performance deteriorates and secondary phases such as lithium carbonate and lithium hydroxide may form, which is undesirable because it causes battery swelling. The Li / M ratio is preferably close to 1.0 or slightly greater than 1.0 to enable the layered cathode material to obtain the desired electrochemical performance, but the optimized Li / M also depends on the composition of M. For example, Li 1+a (Ni 0.6 Mn 0.2 Co 0.2 ) 1-a O2 has an optimized Li / M of about 1.00, while Li 1+a (Ni 0.47 Mn 0.38 Co 0.15 ) 1-a O2 has an optimized Li / M of about 1.07. For Li 1+a (Ni 0.9 Co 0.1 ) 1-a O2, the Li / M ratio is about 0.98. When the Li / M is higher or lower than this optimized Li / M, the electrochemical characteristics of N(M)C deteriorate.

[0045] N(M)C powder can be manufactured using a conventional direct sintering method, which is a solid-state reaction between a lithium source (typically Li₂CO₃ or LiOH-H₂O) and the aforementioned precursor. First, the lithium source and a mixed transition metal source are homogeneously blended and then sintered. In this step, the Li / M ratio in LiMO₂ is the final target composition. To further improve the quality of N(M)C coupled to high throughput, a double sintering method can be performed. First, the mixed transition metal source is blended with a lithium source and then sintered. At this step, the Li / M ratio in the LiMO₂ of the mixture is between 0.60 and <1.00. Then, in a second sintering, the lithium-deficient sintered precursor is blended with the lithium source to correct the Li / M ratio to the final target composition.

[0046] When preparing polycrystalline materials, after (final) sintering, the sintered powder cake is crushed, graded, and sieved to obtain non-agglomerated N(M)C powder. However, for obtaining pure, single-particle materials, a dedicated grinding method for positive electrode materials is more suitable because it separates the final secondary or agglomerated particles into individual primary particles. For single N(M)C powder, ball milling using water is the preferred and scalable method. The degree of grinding can be mainly controlled by the number of balls, the size of the balls, the size of the container, the rotational speed (RPM), and the grinding time.

[0047] Surface modification features, such as coatings on the surface of positive electrode materials, are known strategies for suppressing side reactions between the electrode material and the electrolyte, which can lead to poor electrochemical performance during cycling. Surface coatings can also enhance the structural stability of the positive electrode material, resulting in excellent battery performance. For example, coating materials such as metal oxides (ZrO2, SiO2, ZnO, Al2O3, TiO2, WO3, etc.) can even improve battery characteristics at high voltages or when cycling at high temperatures. A rough surface coating can be formed by mechanically mixing the positive electrode material with a coating precursor and then heat-treating the mixture. However, due to the localized formation of the coating, this can result in many exposed areas on the surface of the electrode material particles. These uncoated areas remain weak points that can be eroded by the electrolyte, potentially leading to side reactions. Alternatively, a core-shell approach can be used by continuously depositing the coating material on the surface of the positive electrode material particles.

[0048] For example, the core-shell positive electrode material can be made of Li(Ni) with high capacity. 0.8 Co 0.1 Mn 0.1 O2 core and Li(Ni) with excellent thermal stability 0.5 Mn 0.5The core-shell structure is as disclosed in J. Am. Chem. Soc., 2005, Vol. 127, No. 38, pp. 13411-13418. Core-shell positive electrode materials thus exhibit excellent cycling and thermal stability.

[0049] Single positive electrode materials can be further improved by applying certain Co-based coatings (which we call "Co-(concentration) gradient" coatings). Providing a concentration gradient for the shell or the entire particle is indeed a good way to improve the electrochemical properties of positive electrode materials. Generally, positive electrode materials with a concentration gradient from the surface to the center can be obtained by using metal precursors with a concentration gradient prepared by a dedicated co-precipitation method. US 2013 / 0202966A1 describes a positive electrode active material with a concentration gradient layer co-precipitated using a batch reactor. The positive electrode material exhibits extended lifetime and improved thermal stability. Heating the surface-coated positive electrode powder is another typical method to obtain a concentration gradient by promoting the decomposition of the coating source and forming a gradient.

[0050] The general coating method can be carried out as follows:

[0051] Step 1) Coating a Co precursor onto a single positive electrode material, wherein the properties of the Co precursor are unrestricted. For example, the Co precursor can be CoSO4, Co(NO3)2, or CoO. x The coating can be any one of Co(OH)2, CoCO3, and LiCoO2. The coating method can be wet or dry. As discussed above, to control the Li / M stoichiometry of the final product, a Li source, such as Li2CO3, LiOH-H2O, or LiNO3, can be added during the coating process.

[0052] Step 2) Heat treatment to allow Co to react with Li and diffuse from the surface into the core, resulting in at least a Co-enriched surface layer. The inventors have observed that the electrochemical properties of a single positive electrode material, such as discharge capacity, rate performance, and cycle stability, can be improved when a specific Co concentration gradient exists within the electrode particles, particularly when the gradient is continuous. The selection of the heat treatment temperature is a key parameter in this invention because it determines the degree of the Co gradient within the particles. This can be analyzed by EDS (or WDS) analysis of the cross-section of the particles, with an EDS scan time of at least 1 minute per analysis point. When Mn is present, the Co / Mn (molar / molar) ratio is considered the standard for defining the degree of gradient.

[0053] Applying further surface treatments to N(M)C materials with a Co gradient coating may be further beneficial. For example, WO2016 / 116862 discloses a surface treatment that provides a surface layer composed of a close mixture of metallic elements of the N(M)C material and one or more compounds selected from the group consisting of Al2O3, TiO2, MgO, WO3, ZrO2, Cr2O3, and V2O5. In one specific embodiment, the surface layer is composed of a close mixture of core elements, LiF, and nanocrystalline Al2O3, which can increase charging voltage without performance degradation, thereby achieving higher energy density. As discussed in WO2015 / 128722, the decomposition of soluble surface alkaline compounds that directly affect battery performance can be further enhanced by applying a surface treatment using Na2S2O8. For example, the Na2S2O8 treatment can be combined with treatments of AIF3 (or Li3AIF6), AlPO4, Al(OH)2, or Al2O3. Fluorides, phosphates, oxides, and hydroxides are all lithium acceptors that can help break down soluble bases and simultaneously form oxide films, such as Al2O3 or LiAlO2.

[0054] This invention provides a positive electrode material that exhibits excellent electrochemical properties due to the synergistic effect between its single morphology and the specific Co gradient in the electrode particles, which is ultimately supplemented by other specialized surface coatings or treatments.

[0055] The following analysis methods are used in the embodiments:

[0056] A) SEM and EDS analysis

[0057] A1) SEM Analysis

[0058] The morphology of the material, the cross-section of the positive electrode, and the cross-section of the positive electrode material were analyzed using scanning electron microscopy (SEM). A JEOL JSM 7100F SEM was used at a resolution of 9.6 x 10⁻⁶. -5 Measurements were performed at 25°C under a high vacuum environment of Pa. Images of the samples were recorded at (at least) 5000x magnification to demonstrate the single structure of the material.

[0059] A2) Cross-section preparation

[0060] Cross sections of positive electrodes or positive electrode materials are prepared using an ion beam cross-section polishing (CP) instrument, namely JEOL (IB-0920CP). This instrument uses argon gas as the beam source.

[0061] Prepare the positive electrode following the procedure described in E1). Cut the electrode before and after cycling as described in method E2). Attach the electrode to an aluminum foil. Then, attach the foil to a sample holder and place it in the instrument. In the standard procedure, set the voltage to 6.5 kV for 3.5 hours. Mix a small amount of positive electrode material powder with resin and hardener, and then heat the mixture on a hot plate for 10 minutes. After heating, place it in an ion beam instrument for cutting, and set the voltage to 6.5 kV for 3 hours in the standard procedure. Analyze the cross-section of the positive electrode material using method A1).

[0062] A3) EDS Analysis

[0063] Using the samples prepared in method A2), the concentration gradient from the surface to the center of the positive electrode material particles was analyzed by SEM and energy-dispersive X-ray spectroscopy (EDS). SEM / EDS was performed using a 50mm SEM camera from Oxford Instruments. 2 X-Max N The EDS sensor was analyzed on a JEOL JSM 7100F SEM. EDS analysis of the positive electrode material particles provided quantitative elemental analysis of the cross-section. In cross-sectional EDS, the particles were assumed to be spherical. A straight line was drawn from the center point of the particle to the surface, with the center point designated as "D0" and the surface point as "D4". Five points were studied by EDS analysis at a 1-minute scan time by setting three additional points between the center (D0) and the surface (D4), namely "D1", "D2", and "D3" (see [link to EDS analysis]). Figure 6.2 ).

[0064] B) PSD Analysis

[0065] After dispersing the powder in an aqueous medium, the PSD was measured using a Malvern Mastersizer 3000 equipped with a Hydro MV wet dispersion attachment. To improve powder dispersibility, sufficient ultrasonic radiation and stirring were applied, and an appropriate surfactant was introduced. D10, D50, and D90 were defined as the particle size at 10%, 50%, and 90% of the cumulative volume % distribution.

[0066] C) X-ray diffraction measurement

[0067] X-ray diffraction of the positive electrode material was measured using a Rigaku X-ray diffractometer (Ultima IV). Measurements were performed using a Cu-Ka radiation source within a diffraction angle range (2θ) from 5 to 90° to collect X-ray diffraction patterns. The scan rate was set to a continuous scan rate of 1° per minute, with a step size of 0.02° per scan.

[0068] Ni can be obtained from the XRD pattern using Rietveld refinement technology. x Mn y CO z A a O v (OH) w The values ​​of v and w are given, where 0 ≤ v ≤ 1 and v + w = ​​2. TOPAS is used as the software for Rietveld refinement. Rietveld refinement provides the space group Ni with space group P-3m1. x Mn y Co z A a O v (OH) w The lattice parameters, such as lattice a and lattice c. With Ni x Mn y Co z A a O v (OH) w As the value v increases from 0 to 1, the lattice a decreases linearly. For example, in Ni... x Mn y Co z A a The lattice a of (OH)₂ (when v = 0 and w = 2) is 3.18 Å, while that of Ni is... x Mn y Co z A a OOH (when v=1 and w=1) Therefore, in this case, the value v can be obtained using the following formula:

[0069] v = -3.03 × lattice a + 9.64

[0070] D) ICP analysis

[0071] The Li, Ni, Mn, and Co contents of the electrode active material were measured using an Agilent ICP 720-ES via inductively coupled plasma (ICP). 2 g of the product powder sample was dissolved in 10 mL of high-purity hydrochloric acid in an Erlenmeyer flask. The flask was covered with glass and heated on a hot plate to completely dissolve the precursor. After cooling to room temperature, the solution was transferred to a 100 mL volumetric flask and rinsed 3 to 4 times with distilled water (DI).

[0072] Next, fill the volumetric flask with deionized water to the 100 mL mark and homogenize completely. Take 5 mL of the solution using a 5 mL pipette and transfer it to a 50 mL volumetric flask for a second dilution. Fill this flask with 10% hydrochloric acid to the 50 mL mark and homogenize. Finally, use this 50 mL solution for ICP measurement.

[0073] E) Button battery test

[0074] E1) Button cell manufacturing

[0075] To prepare the positive electrode, a slurry containing electrochemically active material, conductor (Super P, Timcal), and binder (KF#9305, Kureha) in a solvent (NMP, Mitsubishi) at a weight ratio of 90:5:5 was prepared using a high-speed homogenizer. The homogenized slurry was applied to one side of an aluminum foil using a doctor blade coater with a 230 μm gap. The slurry-coated foil was dried in an oven at 120°C and then pressed using a calendering tool. It was then dried again in a vacuum oven to completely remove any remaining solvent from the electrode film. The coin cell was assembled in an argon-filled glove box. A separator (Celgard 2320) was positioned between the positive electrode and the lithium foil sheet used as the negative electrode. EC / DMC (1:2) containing 1 M LiPF6 was used as the electrolyte and dropped between the separator and the electrode. The coin cell was then completely sealed to prevent electrolyte leakage.

[0076] E2) Test Method 1

[0077] In a Neware computer-controlled constant current cycling station, each cell was cycled to a high voltage (4.7V) at 50°C. The coin cell test program uses a 1C current definition of 160mA / g. Table 1 shows the coin cell test program.

[0078] Table 1. Cyclic Plan for Button Battery Test Method 1

[0079]

[0080] E3) Test Method 2

[0081] Method 2 is the conventional "constant cutoff voltage" test. The conventional button cell battery test in this invention follows the procedure shown in Table 2. Each battery is cycled at 25°C using a Toscat-3100 computer-controlled constant current cycling station (from Toyo). The button cell battery test procedure is defined using a 1C current of 160 mA / g and includes the following two parts:

[0082] Part I evaluates rate performance at 0.1C, 0.2C, 0.5C, 1C, 2C, and 3C within a 4.3V / Li–3.0V / Li metal window. Except for the first cycle, where the initial charge capacity (CQ1) and discharge capacity (DQ1) are measured in constant current mode (CC), all subsequent cycles are characterized by a constant current-constant voltage during charging, with a termination current criterion of 0.05C. A 30-minute rest period is allowed between each charge and discharge cycle for the first cycle and a 10-minute rest period for all subsequent cycles.

[0083] Irreversible capacity Q Irr The following are expressed as %.

[0084]

[0085] Rate performance at 0.2C, 0.5C, 1C, 2C, and 3C is expressed as the ratio between the retained discharge capacities DQn, where n = 2, 3, 4, 5, and 6 for nC = 0.2C, 0.5C, 1C, 2C, and 3C, respectively, as shown below:

[0086]

[0087] For example,

[0088] Part II is the cycle life assessment at 1C. The charge cutoff voltage was set to 4.5V / Li metal. The discharge capacity of the 4.5V / Li metal was measured at 0.1C at 7 and 34 cycles, and at 1C at 8 and 35 cycles. The capacity decay at 1C was calculated as follows and expressed as % / 100 cycles:

[0089]

[0090] Table 2. Cyclic Plan for Button Battery Test Method 2

[0091]

[0092] F) Full Battery Test

[0093] A 200mAh pouch cell was prepared as follows: Super-P (Super-P, Timcal) as the positive electrode material, graphite (KS-6, Timcal) as the positive electrode conductive agent, and polyvinylidene fluoride (PVDF 1710, Kureha) as the positive electrode binder were added to N-methyl-2-pyrrolidone (NMP) as the dispersion medium, such that the mass ratio of the positive electrode active material powder, the positive electrode conductive agent (Super-P and graphite), and the positive electrode binder was set to 92 / 3 / 1 / 4. The mixture was then kneaded to prepare a positive electrode mixture slurry. The resulting positive electrode mixture slurry was applied to both sides of a positive electrode current collector made of 15μm thick aluminum foil. The width of the application area was 26mm, and the length was 190mm. The typical loading weight of the positive electrode active material was approximately 11±1 mg / cm³. 2 The electrodes were then dried and calendered to 3.3 ± 0.5 g / cm³ using a pressure of 100 kgf. 3 The electrode density is determined. Additionally, an aluminum plate, serving as the positive electrode current collector, is arc-welded to the end of the positive electrode. A commercially available negative electrode is used. In short, a mixture of graphite, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) in a 96 / 2 / 2 mass ratio is applied to both sides of a copper foil. A nickel plate, serving as the negative electrode current collector, is arc-welded to the end of the negative electrode. The typical loading weight of the negative electrode active material is 10 ± 1 mg / cm³. 2 A non-aqueous electrolyte was obtained by dissolving a 1.0 mol / L lithium hexafluorophosphate (LiPF6) salt in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 1:2.

[0094] A positive electrode, a negative electrode, and a 20 μm thick microporous polymer membrane inserted between the positive and negative electrode sheets are arranged. The separator (2320, Celgard) was helically wound using a mandrel to obtain a helically wound electrode assembly. This assembly and the electrolyte were then placed in an aluminum laminate bag in a drying chamber at a dew point of -50°C to fabricate a flat pouch-type lithium secondary battery. The secondary battery has a designed capacity of 200mAh when charged to 4.20V.

[0095] Immerse the battery in a non-aqueous electrolyte solution at room temperature for 8 hours. Precharge the battery to 15% of its theoretical capacity and age it at room temperature for one day. Then degas the battery and seal it in an aluminum bag. The battery is prepared for use as follows: In CC mode (constant current), charge the battery with a current of 0.2C (1C = 200mA) to 4.2V or 4.35V, then charge in CV mode (constant voltage) until the cutoff current of C / 20 is reached, and then discharge in CC mode at a rate of 0.5C until the cutoff voltage drops to 3.0V.

[0096] The prepared full cells were subjected to several charge-discharge cycles at 25°C or a high temperature (e.g., 45°C) under the following conditions to determine their charge-discharge cycle performance:

[0097] - Charge in CC mode at a 1C rate until 4.2V or 4.5V, then charge in CV mode until C / 20 is reached.

[0098] -Then let the battery rest for 10 minutes.

[0099] - Discharge at a 1C rate in CC mode, dropping to 3.0V.

[0100] -Then let the battery rest for 10 minutes.

[0101] Perform charge-discharge cycles until the battery reaches approximately 80% of its remaining capacity. Every 100 cycles, discharge once at a 0.2C rate in CC mode, reducing the voltage to 3.0V.

[0102] Example

[0103] The present invention is further illustrated by examples in the following embodiments:

[0104] Explanation of Example 1

[0105] This example illustrates that N(M)C products undergo significant volume changes during charge / discharge cycles at high voltage and high temperature, with consequences.

[0106] The single N(M)C powder labeled EEX1.1 has the formula Li 1+a (Ni 0.47 Mn 0.38 Co 0.15 ) 1-a O2, doped with approximately 0.28% Ba (by weight), where (1+a) / (1-a) represents the Li / M ratio, the powder was prepared by the following procedure:

[0107] 1) Preparation of NMC precursor: A mixed transition metal hydroxide MO was prepared by conventional co-precipitation method using a continuous stirred tank reactor (CSTR) from a mixture of nickel-manganese-cobalt sulfate (MSO4), sodium hydroxide (NaOH), and ammonium hydroxide (NH4OH). 0.71 (OH) 1.29 (where M = Ni) 0.47 Mn 0.38 Co 0.15 ).

[0108] 2) Blending: In a tubular mixer, the mixed transition metal hydroxide was blended with Li2CO3 (obtained from Rockwood) and barium carbonate (BaCO3) (Duksan reagent, 99.9%) as lithium sources by dry mixing for several hours, wherein the target Li / M ratio was 1.07 and the Ba / M ratio was 0.2 mol%.

[0109] 3) Sintering: The mixture from step 2) is sintered in a box furnace at 1020°C for 10 hours in a dry air atmosphere.

[0110] 4) Post-processing: Grind the sintered product to avoid the formation of agglomerates.

[0111] Polycrystalline NMC powder Li was prepared using the same procedure as EEX1.1. 1+a (Ni 0.47 Mn 0.38 Co 0.15 ) 1-a O2, with a Li / M ratio of 1.07, no BaCO3 additive, and a sintering temperature of 925℃. The obtained product is labeled EEX1.2. The D50 of the single NMC powder (EEX1.1) was determined to be 6.96 μm by method B).

[0112] As described in method E1), positive electrodes were prepared using a) single NMC (EEX1.1) and b) polycrystalline NMC (EEX1.2). The freshly prepared electrodes were labeled EEX1.1-FE and EEX1.2-FE, respectively. Cyclic electrodes were prepared according to the procedure in method E2) and labeled EEX1.1-CE and EEX1.2-CE, respectively. The cross-sections of these four electrodes or electrode materials were analyzed as described in methods A2) and A1).

[0113] Figure 1The relationship between discharge capacity (y-axis - mAh / g) and cycle number (x-axis - #) for EEX1.1 and EEX1.2 is shown, where the y-axis represents discharge capacity. Testing method E2 was very difficult due to the high upper cutoff voltage (4.7V), high temperature (50°C), and rapid charge / discharge rate (0.5C charge / 1.0C discharge). It can be confirmed that the single NMC (EEX1.1) exhibits good cycle stability even under these harsh conditions, while the polycrystalline NMC (EEX1.2) begins to show problems from the 26th cycle, resulting in significant capacity decay.

[0114] Figure 2 Cross-sectional images of EEX1.1-FE, EEX1.1-CE, EEX1.2-FE, and EEX1.2-CE are presented. It can be clearly observed that the polycrystalline NMC in the electrode (EEX1.2-CE) exhibits numerous macroscopic and microscopic cracks after cycling at 4.7V, while the cycled mono-NMC shows no microscopic cracks. Therefore, mono-NMC has been demonstrated to withstand volume changes better than polycrystalline NMC, resulting in improved cycling stability.

[0115] Explanation of Example 2

[0116] This example demonstrates the electrochemical properties of a single NMC containing different coating elements. In a 250 ml beaker, single NMC powder EEX1.1 was mixed with 13 ml of 5 mol% Co(NO3)2·6H2O solution (relative to the amount of M) and 2 ml of water and stirred at 180 °C for several hours. The resulting blend was then heated in a box furnace at 850 °C for 5 hours under a dry air atmosphere. The product was a single NMC coated with a Co gradient, exhibiting the formula Li 1+a (Ni 0.448 Mn 0.362 Co 0.190 ) 1-a O2, with a Li / M ratio of 1.02, and labeled EEX2.1. EEX2.2 was prepared using the same method as EEX2.1, except that the coating source was Mn. 0.5 Co 0.5 (NO3)2. EEX2.3 was also prepared according to the same method as in EEX2.1, with Mn(NO3)2·6H2O as the coating source.

[0117] To evaluate the product obtained at the positive electrode of a lithium-ion battery, coin cells were prepared by method E1) and tested by method E3). The initial discharge capacity, irreversibility, rate performance, and capacity decay of EEX1.1, EEX2.1, EEX2.2, and EEX2.3 are shown in Table 3.

[0118] Table 3. Explanation of the electrochemical characteristics of Example 2

[0119] Example ID DQ1 (mAh / g) <![CDATA[Q Irr .(%)]]> 3C(％) 1C Qfad.(%) EEX1.1 156.3 15.1 77.4 57.6 EEX2.1 160.6 10.9 82.6 39.2 EEX2.2 153.2 15.0 77.1 50.6 EEX2.3 135.3 22.7 62.5 64.0

[0120] Compared to EEX1.1, EEX2.2 and EEX2.3, the positive electrode material coated with Co gradient (EEX2.1) has higher initial discharge capacity, lower irreversibility, better rate performance and enhanced cycle stability.

[0121] Example 1 and Comparative Example 1

[0122] Obtaining Li with the target formula via a dual sintering method (such as the example in WO2018 / 158078, but not a single one). 1+a (Ni 0.625 Mn 0.175 Co 0.200 ) 1-a O2 single NMC powder, wherein Li / M is 1.01, the dual sintering method is that the lithium source is usually Li2CO3 or LiOH-H2O and a mixed transition metal source (i.e. Ni). 0.625 Mn 0.175 Co 0.20 O 0.43 (OH) 1.57 (From E&DCo.) Solid-state reactions between. The average particle size of the mixed transition metal sources ranges from 2 μm to 4 μm, which results in a single morphology during the preparation of NMC powder.

[0123] Here, the process includes the following two separate sintering steps:

[0124] 1) First blending: To obtain a lithium-deficient sintering precursor, LiOH-H2O and a mixed transition metal source were blended in Henschel... Mix the mixture uniformly at a Li / M ratio of 0.90 for 30 minutes.

[0125] 2) First sintering: The blend from the first blending step is sintered in a box furnace at 750°C for 10 hours under an oxygen atmosphere. After the first sintering, the sintered powder is crushed, graded, and sieved for the second blending step. The product obtained from this step is a precursor for lithium-deficient sintering, meaning that the Li / M stoichiometry of LiMO2 is less than 1.

[0126] 3) Second blending: The lithium-deficient sintered precursor was blended with LiOH-H2O to correct for Li stoichiometry (Li / M = 1.01). The blending was carried out in Henschel. It will take 30 minutes.

[0127] 4) Second sintering: The blend from the second blending is sintered in a box furnace at 930°C for 12 hours in an oxygen-containing atmosphere.

[0128] 5) Wet ball milling: In a ball mill, water and 10mm ZrO2 balls are used to apply the treatment at 50 RPM for 15 hours to break down the agglomerated NMC powder from the second sintering into individual particles. After the milling process, the wet NMC powder is dried in an oven at 80°C in ambient air for 2 days.

[0129] The single NMC powder prepared by the above steps is designated CEX1.1. In a tubular mixer, CEX1.1 was blended for several hours with 5 mol% powdered Co(NO3)2·6H2O as the coating source and 5 mol% LiOH-H2O as the lithium source (compared to M in CEX1.1). The resulting blend was then heated in a box furnace at 750-800°C for 10 hours under an oxygen atmosphere. This product is designated EX1.1. A single NMC powder with a Co gradient coating was prepared according to the same procedure as EX1.1, designated EX1.2, except that the amount of nitrate powder as the Co coating source was 2 mol% Co(NO3)2·6H2O, and the amount of LiOH-H2O as the Li source was 2 mol%. Sample labeled EX1.3 was prepared according to the same procedure as EX1.1, except that the amount of nitrate powder was 10 mol% Co(NO3)2·6H2O and the amount of LiOH-H2O was 10 mol%.

[0130] The particle size of EX1.1 was determined by method B), and the D50 values ​​are shown in Table 5. The electrochemical performance of EX1.1 to EX1.3 was evaluated by method E3). The initial discharge capacity, irreversibility, rate performance, and capacity decay of EX1.1 to EX1.3 are shown in Table 5.

[0131] To observe its structure as a positive electrode material, CEX1.1 was analyzed using method A1). Figure 3 As shown, CEX1.1 has particles with irregular shapes and flat surfaces. Furthermore, each particle is a single primary particle (without aggregated morphology).

[0132] Therefore, in this invention, "single NMC" refers to a positive electrode material containing a single particle.

[0133] EX1.1 was studied by method C) after a Co gradient coating was applied to a single NMC powder. Figure 4As shown (x-axis: 20, y-axis: logarithmic intensity), EX1.1 exhibits a small (003) peak of LiCoO2 at approximately 19.5°, which is distinct from the (003) peak of NMC at approximately 18.7°. Due to the use of a Co source and a lithium source to achieve a Co gradient concentration, a single powder is coated with LiCoO2 while maintaining the surface morphology of the electrode particles. Figure 5 This indicates that even after the Co gradient coating, EX1.1 still exhibits a single morphology including a flat surface. Individual NMC particles have an aspect ratio of 0.8 or higher; the aspect ratio is the ratio of the particle's minimum diameter to its maximum diameter. Such NMC particles can be considered (quasi-)spherical or elliptical.

[0134] As shown in Table 4 for EX1.1, method D) indicates that the composition of CEX1.1 changed after the Co gradient coating. The molar concentration of Co increased, while the molar concentrations of Ni and Mn decreased, but the Li / M ratio of the total NMC composition remained unchanged. EX1.2 and 1.3 have the formula Li 1+a (Ni 0.613 Mn 0.172 Co 0.216 ) 1-a O2 and Li 1+a (Ni 0.568 Mn 0.159 Co 0.273 ) 1-a O2, where Li / M is 1.01.

[0135] Table 4. ICP results of Example 1.1 and Comparative Example 1.1

[0136] Sample ID Li / M ratio Ni (mol%) Mn (mol%) Co (mol%) EX 1.1 1.01 60.2 16.4 23.4 CEX1.1 1.01 63.0 17.3 19.7

[0137] CEX1.2 was prepared using the same method as EX1.1, except that the heating temperature for forming the Co gradient was 500°C. For CEX1.3, the heating temperature for forming the Co gradient was 900°C. CEX1.4 was prepared using the same method as CEX1.1, except that the second sintering temperature was 950°C. CEX1.4 was also blended with a Co source and a Li source, and then sintered using the same method as EX1.1. This product was designated as EX1.4. CEX1.2, CEX1.3, and EX1.4 have the formula Li 1+a (Ni 0.595 Mn 0.167 Co 0.238 ) 1-aO2, with Li / M of 1.01. The average particle size of EX1.4 and CEX1.4 analyzed by method B) is shown in Table 5. The electrochemical performance of EX1.4 and CEX1.1 to CEX1.4 was evaluated according to method E3). Their initial discharge capacity, irreversibility, rate performance, and capacity decay are shown in Table 5.

[0138] Table 5. Electrochemical characteristics of Example 1 and Comparative Example 1

[0139]

[0140] (*) Heating temperature for drying the coated sample, used to obtain the Co gradient.

[0141] Compared to CEX1.1, CEX1.2, and CEX1.3, EX1.1, EX1.2, and EX1.3 exhibit higher discharge capacity, lower irreversibility, and better rate performance. These superior electrochemical properties of EX1.1, EX1.2, and EX1.3 are assumed to originate from the Co concentration gradient.

[0142] To investigate the formation of the Co concentration gradient on the NMC product based on heating temperature, EX1.1, CEX1.2, and CEX1.3 were analyzed using method A3). Figure 6.1 As shown (x-axis: distance, y-axis: molar percentage), since the EDS line scan analysis of EX1.1 (scan time per detection point: 10 s) indicates a constant Mn molar concentration, the Mn content was set as the calibration value to determine the extent of the Co concentration gradient in the electrode particles. To obtain accurate elemental analysis in the NMC products, Figure 6.2 Cross-sectional SEM images of EX1.1 are shown, where the selected locations (D0, D1, D2, D3, and D4) were used for dedicated EDS analysis. The EDS scan time for each analysis point was increased to 1 minute, resulting in more reliable data. Figure 6.3 The EDS analysis results for the selected locations (x-axis - Dx locations) are shown, where the y-axis represents the normalized Co / Mn molar ratio (CM(x)) obtained by dividing the Co / Mn ratio at each location (D1-D4) by the Co / Mn ratio at location D0. This normalized Co / Mn value can be used to determine the extent of the Co gradient. Therefore, the Co / Mn molar ratios at D0 to D4 are represented as CM(0) to CM(4), respectively. Figure 6.3As shown, the Co / Mn (mol / mol) ratio on the surface of the electrode particles is higher than that in the center. The Co concentration gradient of EX1.1 prepared at 750 °C gradually decreases from D4 to D0, while the composition of CEX1.2 prepared at 500 °C changes drastically. This indicates that a heating temperature of 500 °C is insufficient to allow Co to diffuse into the bulk, resulting in poor electrochemical properties. The CM(x) / CM(0) ratio from D2 to D4 of CEX1.3 prepared at 900 °C has a relatively constant value. This indicates that 900 °C is too high to generate the desired Co gradient, which also leads to poor electrochemical properties.

[0143] Since the NMC sample EX1.1 with a continuous Co concentration gradient exhibits the best electrochemical performance, CM(4) / CM(3) can represent the desired degree of concentration gradient for the purpose of describing this invention. As shown in Table 5, such gradient values ​​for EX1.1, CEX2.2, and CEX2.3 are 1.19, 1.42, and 1.01, respectively. Furthermore, the average particle sizes of EX1.1, EX1.4, and CEX1.4 are 4.83, 6.39, and 6.02 μm, respectively. CEX1.4, with a larger particle size than EX1.1, exhibits a lower discharge capacity and higher irreversibility, but when the Co gradient coating is applied, EX1.4 shows enhanced electrochemical performance relative to CEX1.4. The advantages become less pronounced as the particle size of the individual Co gradient particles increases, as shown in EX1.4, which has DQ1 and Q values ​​comparable to CEX1.1. Irr However, it still has better 3C and Qfad values. Therefore, according to the present invention, NMC products with an average particle size of less than 10 μm, preferably less than 8 μm, and even more preferably between 2 pm and 5 pm, provide preferred electrochemical properties.

[0144] Example 2 and Comparative Example 2

[0145] In Henschel In this process, EX1.1 was blended with 1.2 wt% sodium persulfate (Na2S2O8) and 0.2 wt% alumina (Al2O3) for 30 minutes. The blend was then heated in air at 375°C for 5 hours. As described in WO2015 / 128722 (Example 3), the final product had a coating containing LiNaSO4 and Al2O3 and was named EX2. Polycrystalline NMC powder was prepared using the same method as CEX1.1, except that Ni with an average particle size of 10 μm to 12 μm was used. 0.625 Mn 0.175 Co 0.20 O 0.39 (OH) 1.61The Li / M ratio of the first blend was 0.8. The first and second sintering temperatures were 885°C and 840°C, respectively. Polycrystalline materials were obtained by selecting the precursor particle size and sintering temperature. After the second sintering, the sintered cake powder was crushed, graded, and sieved to obtain non-agglomerated NMC powder. The Li / M ratio of this powder was 1.045. (The last sentence appears to be incomplete and possibly refers to a different process.) The obtained powder was mixed with 1.2 wt% sodium persulfate (Na2S2O8) and 0.2 wt% alumina (Al2O3) for 30 minutes. The blend was heated at 375 °C for 5 hours in air. The final product was named CEX2. The electrochemical properties of EX1.1, EX2, and CEX2 were evaluated by method F). Figure 7.1 and Figure 7.2 The full-cell cycle stability at 4.2V and 4.35V is shown respectively (x-axis: cycle number #; y-axis: relative discharge capacity (in %), i.e., the discharge capacity of cycle # divided by the initial discharge capacity and multiplied by 100).

[0146] like Figure 7.1 As shown in the left figure, during the first 200 cycles at 25°C, CEX2, as a polycrystalline NMC, exhibited better cycle stability than EX2. However, after approximately 1000 cycles, EX1.1, as a single NMC with a concentration gradient, showed less capacity decay than CEX2. EX2, a single NMC with a concentration gradient and an Al / LiNaSO4 coating, also showed significantly less capacity decay than CEX2 after approximately 650 cycles. When testing the battery at 45°C, the cycle stability of EX1.1 and EX2 was significantly better than that of CEX2. Figure 7.2 As shown, when the batteries were tested at a high voltage operating range of 3.0 to 4.35 V, individual NMCs (EX1.1 and EX2) exhibited improved long-term cycle stability at 25 °C.

[0147] A single NMC (EX2) with a superimposed Co concentration and an Al / LiNaSO4 coating exhibits the lowest capacity decay at 45°C. Therefore, a single NMC with a Co concentration gradient, and preferably with a suitable Al / LiNaSO4 coating, is a good choice for SSBs or non-aqueous batteries operating at high voltages. The same Al / LiNaSO4 coating on polycrystalline materials does not provide the same improvement in the cycling behavior of the full cell.

[0148] Example 3 and Comparative Example 3

[0149] EX3.1 was prepared using the same method as EX1.1, except that the mixed transition metal source was Ni. 0.6 Mn 0.2 Co 0.2 O0.52 (OH) 1.48 Furthermore, by adjusting the amounts of Li and Co precursors in the Co gradient coating step, the Li / M ratio of the final product was set to 0.995. Similar to EX3.2 and EX3.3, the Li / M ratios were 1.010 and 1.024, respectively. CEX3.1 was prepared according to the same method as EX3.1, but without the Co gradient coating step. For CEX3.2, the Co gradient coating step was present, and the final Li / M ratio was set to 0.960. The electrochemical performance of EX3.1-3.3 and CEX3.1-3.2 was evaluated using method E3). The initial discharge capacity, irreversibility, rate performance, and capacity decay are shown in Table 6.

[0150] Table 6. Electrochemical characteristics of Example 3 and Comparative Example 3

[0151] Example ID Li / M DQ1 (mAh / g) <![CDATA[Q lrr .(%)]]> 3C(％) 1C Qfad.(%) EX3.1 0.995 175.7 10.0 87.7 15.5 EX3.2 1.010 176.4 9.7 87.9 16.4 EX3.3 1.024 176.5 9.5 88.0 16.0 CEX3.1 - 175.6 11.9 86.9 20.1 CEX3.2 0.960 172.2 11.2 85.9 16.9

[0152] As shown in Table 6, the NMC products with concentration gradients exhibited better electrochemical properties than the NMC materials without the prepared Co gradient coating. Similarly, when the Li / M in the products was >0.96, and even when the Li / M was at least 0.985, the NMC materials showed improved discharge capacity, irreversibility, and cycle stability.

[0153] Example 4

[0154] Using the same method as CEX1.1, but employing Ni precursors with an average particle size of 3-5 μm. 0.9 Co 0.1 O 0.15 (OH) 1.85 Manufacturing with Li 1+a (Ni 0.9 Co 0.1 ) 1-a A single NC powder of O2, with a Li / M ratio of 0.97, was prepared. The first and second sintering temperatures were 700 °C and 860 °C, respectively. The final product was designated EX4.1. EX4.1 was then blended for several hours in a tubular mixer with 5 mol% Co(NO3)2·6H2O as the Co coating source and 5.5 mol% LiOH·H2O as the lithium source (compared to M in EX4.1). The resulting blend was then heated in a box furnace at approximately 800 °C for 10 hours in an oxygen-containing atmosphere. The product was designated EX4.2, having the formula Li... 1+a (Ni 0.857 Co 0.143 ) 1-aO2, with a Li / M ratio of 0.97. EDS analysis of EX4.2, performed using the same method as EX1, showed that the Co concentration gradient decreased from the surface to the center of the NMC particles. Since EX4.2 does not contain Mn, the extent of the Co gradient was determined using the normalized Co molar ratio (C(x)). This extent was obtained by dividing the Co mol% at each position (D1–D4) by the Co mol% at position D0. The gradient value (C(4) / C(3)) for EX4.2 was 1.23.

[0155] The electrochemical performance of EX4.1 and EX4.2 was evaluated using method E3. The initial discharge capacity, irreversibility, rate performance, and capacity decay of EX4.1 and EX4.2 are shown in Table 7.

[0156] Table 7. Electrochemical characteristics of Comparative Example 4

[0157] Example ID DQ1 (mAh / g) <![CDATA[Q lrr. (%)]]> 3C(％) 1C Qfad.(%) EX4.1 196.3 15.6 87.1 17.8 EX4.2 200.8 12.2 86.8 16.8

[0158] Due to the high Ni content in the NC composition, EX4.2 and 4.2 exhibit very high initial discharge capacities. When a Co concentration gradient is applied, the discharge capacity of EX4.2 increases. Therefore, it is demonstrated that single NMCs and NCs with the Co concentration gradient of this invention possess improved electrochemical properties.

Claims

1. A positive electrode active material for a lithium-ion battery, the positive electrode active material comprising a lithium transition metal-based oxide powder, the powder comprising a single crystal single particle containing Ni and Co and having the general formula Li 1+a ((Ni z (Ni 1 / 2 Mn 1 / 2 ) y Co x ) 1- k A k ) 1-a O2, where A is a dopant, -0.02 < a ≤ 0.06, 0.10 ≤ x ≤ 0.35, 0 ≤ z ≤ 0.90, x + y + z = 1 and k ≤ 0.01, the particles having a cobalt concentration gradient, where the Co content on the particle surface is higher than the Co content at the particle center, and where - When Mn is present, the ratio between the Co / Mn molar ratio at the particle surface and the Co / Mn molar ratio at a distance d from the surface is between 1.1 and 1.3, where d = the distance from the particle surface to the particle center. 1 / 4, or - When Mn is absent, the ratio between C(4) / C(3) is between 1.1 and 1.3, where C(4) is the ratio between the molar concentration of Co at the particle surface and the molar concentration of Co at the particle center, and where C(3) is a) the ratio from the particle surface to the particle center. 3 The ratio between the molar concentration of Co at a distance of / 4 and the molar concentration of Co at the center of the particle as described in b).

2. The positive electrode active material according to claim 1, wherein the powder has a particle size distribution with D50 < 10 μm.

3. The positive electrode active material according to claim 1 or 2, wherein when Mn is present, the ratio between the Co / Mn molar ratio at the particle surface and the Co / Mn molar ratio at the particle center is between 1.4 and 1.

5.

4. The positive electrode active material according to claim 1 or 2, wherein the cobalt concentration gradient changes continuously from the surface to the center of the particle.

5. The positive electrode active material according to claim 1 or 2, wherein the particles have a morphology comprising a plurality of flat surfaces and an aspect ratio of at least 0.

8.

6. The positive electrode active material according to claim 1 or 2, wherein the surface layer of the particles comprises LiCoO2.

7. The positive electrode active material according to claim 1 or 2, wherein the particles have a coating comprising any one or both of LiNaSO4 and Al2O3.

8. A method for manufacturing a positive electrode active material according to any one of claims 1 to 7, the positive electrode active material containing Ni and Co and having the general formula Li 1+a ((Ni z (Ni 1 / 2 Mn 1 / 2 ) y Co x ) 1-k A k ) 1-a O2, where A is a dopant, -0.02 < a ≤ 0.06, 0.10 ≤ x ≤ 0.35, 0 ≤ z ≤ 0.90, x + y + z = 1 and k ≤ 0.01, the method comprising the following steps: - A first precursor comprising A, Ni, Co, and Mn is provided under conditions present in the positive electrode active material, the precursor being composed of particles having a particle size distribution of D50 < 10 μm. - The first precursor is mixed with any one of LiOH, Li₂O, Li₂CO₃, and LiOH·H₂O to obtain a first mixture, wherein the ratio of Li to transition metal in the first mixture, LM₁, is greater than or equal to 0.60 and less than 1.

00. - The first mixture was sintered in an oxidizing atmosphere at a temperature between 700°C and 900°C for a time between 6 hours and 36 hours to obtain a first intermediate product. - The first intermediate product is mixed with any one of LiOH, Li₂O, Li₂CO₃, and LiOH·H₂O to obtain a second mixture, wherein the ratio of Li to transition metal in the second mixture is LM₂ ≥ 0.

90. - The second mixture was sintered in an oxidizing atmosphere at a temperature between (950 - (155.56*z)) °C and (1050 - (155.56*z)) °C for a time between 6 hours and 36 hours. - Grinding and sintering the second mixture, thereby separating the particles of the sintered second mixture into individual primary particles. - A Co-based precursor is provided, and the precursor is mixed with a sintered and milled second mixture to obtain a third mixture in which the ratio of Li to transition metal (LM3) is -0.107*z + 1.018 ≤ LM3 ≤ -0.107*z + 1.

098. - The third mixture is sintered in an oxidizing atmosphere at a temperature between 700°C and 800°C for a time between 6 hours and 36 hours.

9. The method of claim 8, wherein in the step of providing a Co-based precursor and mixing the precursor with the sintered and milled second mixture, a Li-based precursor is additionally added.

10. The method according to claim 8 or 9, wherein y>0, z≥0.35 and -0.012≤a≤0.010, LM1 is between 0.60 and 0.95, LM2≥LM1 and LM3≥LM1, and the sintering temperature for the second mixture is between 895°C and 995°C.

11. The method according to claim 8 or 9, wherein LM3 = LM2.

12. The method of claim 10, wherein between 2 mol% and 10 mol% of Co is added to the Co-based precursor, wherein the mol% of Co is expressed relative to the total metal content other than Li in the second mixture.

13. The method of claim 8 or 9, wherein a grinding step is applied to break the agglomerated powder obtained after sintering the second mixture into individual particles in a ball mill apparatus.

14. The method of claim 8 or 9, wherein the method comprises the following subsequent steps: - Provides inorganic oxidation compounds, - Provide a chemical substance as a Li acceptor, wherein the inorganic oxidizing compound and the Li acceptor chemical substance are both the same compound, and are any one of Li₂S₂O₈, H₂S₂O₈, and Na₂S₂O₈. - The sintered third mixture, the oxidized compound, and the Li acceptor are mixed to obtain a fourth mixture, and - The fourth mixture is heated in an oxygen-containing atmosphere at a temperature between 300°C and 800°C.

15. The method of claim 14, wherein the heating temperature of the fourth mixture is between 350°C and 450°C.

16. The method of claim 14, wherein nanoscale Al2O3 powder is provided as another Li acceptor chemical substance.

17. Use of the positive electrode active material according to any one of claims 1 to 7 in a solid-state lithium-ion battery that is cycled to a voltage of at least 4.35V or in a lithium-ion battery having a liquid electrolyte.

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