Novel lithium-rich nickel-based layered positive electrode material and preparation method thereof

Abstract

The chemical formula of the novel lithium-rich nickel-based layered positive electrode material is Li < 1 + x > (NiyM < 1-y >) < 1-x > O2, x is more than or equal to 0.05 and less than or equal to 0.5, and y is more than or equal to 0.5 and less than or equal to 0.99; m is a transition metal element with the oxyphilicity larger than that of Ni, and when M contains one or more of Ti, Cr, V and Cu, the proportion of Ti, Cr, V and Cu in the total molar weight of the transition metal is not larger than 20%; when M contains one or more of Mn, Fe and Co, the M accounts for not more than 50% of the total molar weight of the transition metal; the material crystal has monoclinic symmetry, the transition metal layer has a LiNi6-zMz (0 < = z < = 3) superlattice structure along the crystal face (001), and an XRD pattern has a superlattice structure diffraction peak at 20-25 degrees. The material is a brand new material which breaks through the theoretical capacity and energy density upper limit of an existing nickel-based layered positive electrode material, the electrochemical activity of anions is changed by constructing a novel Li-Ni-TM-Li superstructure, lattice oxygen is effectively activated to participate in the reaction, the activation potential of the anions is reduced, the suitability with an electrolyte is improved, and the performance of the material is improved. And meanwhile, the voltage window, the discharge capacity and the energy density of the material are improved.

Description

Technical Field

[0001] The present invention relates to a cathode material for lithium-ion batteries, and particularly to a novel lithium-rich nickel-based layered cathode material and a preparation method thereof, belonging to the field of electrochemistry technology. Background Art

[0002] As one of the key devices in the construction of modern new energy systems, lithium-ion batteries have developed rapidly and received much attention in the past few decades since the birth of lithium cobalt oxide cathode material (LCO). In the early stage, under the concept of "rocking chair" battery with insertion and extraction, spinel-type LiMn 2 O 4 , polyanion-type LiFePO 4 , and layered cathode materials constitute the three main structural materials of lithium-ion battery cathode materials. Although these three battery systems all have good electrochemical performance in different energy conversion fields, the insufficient energy density is a common challenge faced by traditional cathode materials.

[0003] Traditional nickel-based cathode materials can be represented by LiNi x Co y Mn z O 2 (x + y + z = 1), where the molar ratio of lithium to transition metal is 1:1, which is a typical layered structure material and belongs to space group. Among them, Ni provides capacity, Co improves the layered characteristics, and Mn, an inert element, improves the cycle stability. The synergistic effect of the three enhances the physical and chemical properties of the material. Therefore, in order to pursue higher capacity and energy density to meet the requirements of the power and energy storage markets for energy density, the Ni content in nickel-based cathode materials has gradually increased, from NCM333 (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 ), NCM523 (LiNi 0.5 Co 0.2 Mn 0.3 O 2 ), NCM622 (LiNi 0.6 Co 0.2 Mn 0.2 O 2 ) to NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 O 2 ) and even cathode materials with a higher Ni content of Ni > 0.9 (molar ratio). However, when the molar ratio of Li:TM (TM represents transition metal) is 1:1, the comprehensive gain effect that traditional nickel-based cathode materials can achieve only by increasing the Ni content is decreasing. That is to say, traditional The capacity and energy density of the layered cathode materials of the space group have an upper limit (the theoretical capacity is about 280 mAh / g). Although strategies such as coating and doping can effectively improve the cycling stability of the materials, they cannot change the relative ratio between Li and transition metals, and thus cannot fundamentally solve the problem of the upper limit of the energy density of nickel-based layered cathode materials. Summary of the Invention

[0004] The object of the present invention is to provide a new strategy to break through the theoretical capacity and energy density upper limits of the current nickel-based layered cathode materials. On the one hand, it can improve the energy density of nickel-based cathode materials, and on the other hand, the new lithium-rich nickel-based cathode materials have great innovation both conceptually and structurally. This system not only has scientific research value but also has great application potential in the power battery market.

[0005] Essentially, the more Li content in the structural unit, the higher the potential for the material to have a reversible capacity. Considering that in lithium-rich manganese-based cathode materials, due to the existence of extra Li in the transition metal layer, it not only changes the symmetry (C2 / m) but also changes the coordination species around the local oxygen, from the original 3 lithium and 3 transition metals to 4 lithium and 2 transition metals. Therefore, there is a Li-O-Li coordination configuration in the local environment. A covalent bond cannot be formed between Li and O, so there are unpaired isolated electrons (non-bonding oxygen) around the local oxygen, which in turn increases the energy level position of the oxygen. The non-bonding oxygen close to the Fermi level is oxidized to peroxide (from O 2- oxidized to O (2-n)- ) or even superoxide. The activated lattice oxygen participating in charge compensation provides the possibility for the design of high-energy density cathode materials.

[0006] The first problem studied in the present invention is: Does anion charge compensation exist in conventional nickel-based layered cathode materials? From the crystal structure, the layered nickel-based cathode materials have a layered structure with space symmetry. Lithium ions occupy the 3a position of the (111) plane of the rock salt structure, transition metal nickel, cobalt, manganese ions, etc. occupy the 3b position, and oxygen ions occupy the 3c position. Using conventional synthesis methods, although there is a certain degree of Li / Ni mixing in the materials (the chemical formula can be expressed as {(Li 1-x Ni x )} 3a {(Li x Ni y-x M 1-y )} 3b {O 2} 3c, where M represents other transition metal elements such as Mn other than Ni), but the overall nickel-based layered cathode material obtained still has a stoichiometric ratio of Li:TM = 1:1 (TM represents transition metal elements). Therefore, the elemental species coordinated with oxygen in the local structure can be summarized as three lithiums and three transition metals, which has nothing to do with whether Li / Ni is mixed ( Figure 1 ). The capacity contribution mainly provides energy through the redox reaction of transition metals during the process of lithium deintercalation and intercalation, and cannot effectively activate the participation of anion ligands in the redox reaction.

[0007] The second problem studied in this invention is: Can the promotion strategy of "lithium enrichment" be migrated to nickel-based materials?

[0008] We notice that there are two possible compositional paths A and B in the case where the Li / Ni stoichiometric ratio is greater than 1. Among them, path A is expressed as Li 2 NiO 3 -LiNiO 2 , and path B is expressed as Li 2 NiO 2 -LiNiO 2 . Among them, the end component Li 2 NiO 2 is structurally different from LiNiO 2 : In LiNiO 2 , there is only 1 unit of lithium ion in the lithium layer. In Li 2 NiO 2 , 2 units of lithium in the lithium layer occupy two tetrahedral sites in the lithium layer, which leads to the structure changing from symmetry to orthorhombic phase (Immm). Although the structural symmetry has changed, there is no Li in the transition metal layer. Therefore, the local coordination species of oxygen are still three Li and three transition metals. And Li 2 NiO 2 is not only difficult to synthesize but also its capacity is not reversible, and it is generally used as a lithium supplement agent.

[0009] The compositional path A is different. Among them, the end component Li 2 NiO 3 can be written as Li[Li 1 / 3 Ni 2 / 3 O 2 . The ratio of Li:TM in the transition metal layer is 1:2, resulting in the so-called lithium-rich layered structure. However, Li 2 NiO 3The synthesis is extremely difficult and requires synthesis under a pressure of 3 - 4 GPa. Obviously, this synthesis method does not have practical benefits for large-scale production. In addition, we notice that such lithium-rich materials not only have a higher Li / TM ratio but also a higher O / TM ratio. That is to say, the effective synthesis of the material depends not only on the amount of lithium during the sintering process but also on the relative chemical potential of oxygen during the sintering process, and neither of them can be absent. For example, in the synthesis of NCM single-crystal high-nickel cathode materials, a lithium source with a far-excessive Li / TM ratio is usually added, and then a molten salt system is formed during the high-temperature sintering process to facilitate crystal growth. However, the material obtained under high-temperature conditions by simply increasing the Li / TM stoichiometric ratio is still a conventional layered cathode material with the space group (Journal of The Electrochemical Society, 164(7) A1534 - A1544(2017)), and it cannot produce lithium-rich characteristics. The key lies in: at high temperatures, the formation and loss of lattice oxygen in traditional nickel-based cathode materials reach chemical equilibrium, and the excess lithium source combines with oxygen to form Li 2 O, so it cannot effectively enter the transition metal layer. This mechanism is verified in the examples of the present invention.

[0010] Therefore, the key to the synthesis of lithium-rich nickel-based cathode materials lies in the regulation of the key oxygen chemical potential. The chemical potential of oxygen can be simply described by the following formula (Chem. Mater. 2008, 20, 5, 1798–1807):

[0011]

[0012] The chemical potential is a function of the oxygen partial pressure and the temperature T. In the formula, p 0 represents the standard partial pressure, k represents the Boltzmann constant, represents the enthalpy change per mole of oxygen at temperature T and standard partial pressure p 0 , and represents the entropy change per mole of oxygen at temperature T and standard partial pressure p 0 . The synthesis pressure of 3 - 4 GPa at high temperatures increases the chemical potential of oxygen by increasing the oxygen partial pressure to synthesize lithium-rich high-nickel materials. However, the high-pressure synthesis method is difficult and it is hard to be applied in batches. In addition, the decrease in temperature also helps to increase the chemical potential of oxygen. That is to say, we expect to synthesize lithium-rich nickel-based materials under normal pressure and low temperature. In fact, simply by reducing the sintering temperature, lithium-rich Li 2 NiO 3 materials cannot be obtained, which is due to the relatively poor affinity of nickel for oxygen.

[0013] Among them, the oxygen affinity is a competitive concept relative to the oxygen phobicity. Therefore, the relative oxygen affinity can be used to characterize the binding tendency of the system to oxygen. Research shows that the oxygen affinity is not related to the chemical hardness of the Lewis acid, but is related to the electronegativity and the effective nuclear charge number. The general trend is that the left side of the d-group elements has a stronger oxygen affinity. Since it is a competitive concept, the relative oxygen-philic or -phobic ability can be quantitatively calculated by the binding ability with elements other than oxygen, such as sulfur. The dissociation energy of M-O can be obtained from the database and can be directly used for related calculations.

[0014] If the energy difference between the phile and phobe can be expressed by the following formula (1):

[0015] Δ (M-O) = D (M-O) - D (M-S) Formula (1)

[0016] In formula (1), D (M-O) represents the dissociation energy between M-O, and D (M-S) represents the dissociation energy between M-S, where M represents any metal element. If Δ (Ni-O) is used as a scale, the relative magnitude between Δ (M-O) and Δ (Ni-O) is a reference element for the increase in the proportion of lattice oxygen in the system. The relative oxygen affinity R can be calculated using the following formula (2):

[0017] R = [Δ (M-O) - Δ (Ni-O) / Δ (Ni-O) Formula (2)

[0018] The relative oxygen affinity R of each element calculated according to formula (2) is shown in the following table.

[0019] M <![CDATA[D (Ni-O) > <![CDATA[D (Ni-S) > <![CDATA[Δ (Ni-O) > <![CDATA[D (M-O) > <![CDATA[D (M-S) > <![CDATA[Δ (M-O) > R Li 366.00 356.00 10.00 340.5 312.5 28.00 1.80 Ti 366.00 356.00 10.00 666.5 418 248.50 23.85 V 366.00 356.00 10.00 629.7 449.4 180.30 17.03 Cr 366.00 356.00 10.00 461 331 130.00 12.00 Mn 366.00 356.00 10.00 362 301 61.00 5.10 Fe 366.00 356.00 10.00 407.0 328.9 78.10 6.81 Co 366.00 356.00 10.00 397.4 331 66.40 5.64 Ni 366.00 356.00 10.00 366 356 10.00 0.00 Cu 366.00 356.00 10.00 287.4 274.5 12.90 0.29

[0020] When R>0, it indicates that M has a greater oxygen affinity than Ni, and theoretically can effectively increase the oxygen chemical potential of the system (importantly, the transition metal layer). In addition, the differences in charge and ionic radius should also be considered to avoid the formation of a disordered rock salt phase. The degrees of increase in the oxygen affinity of Fe, Mn, and Co are quite similar, so all three of these elements can improve the layered characteristics to a certain extent. Elements such as Ti, V, and Cr on the left side of the 3d period can significantly increase the oxygen affinity, but V and Cr with high valence and small ionic radius are more likely to migrate to the tetrahedral interstitial sites during the electrochemical process, having an adverse effect on the electrochemical performance. Ti with a +4 valence has obvious advantages in valence state and oxygen affinity, but the Li-Ti-Ni-O system is more likely to form a lithium-rich rock salt phase structure. Therefore, when selecting Cr, Ti, V, Fe metal elements, the doping content of the elements should be considered. In the present invention, the doping amounts of Cr, V, and Ti are controlled within 0.2. Fe, Co, etc. are difficult to be oxidized to +4 valence and only exist as stabilizers for the layered characteristics. Mn can not only increase the oxygen affinity of the transition metal layer but also is beneficial to the formation of the layered property. The doping content of Mn is not strictly controlled, but considering the effective distinction from lithium-rich manganese-based materials, the element content of Mn in the present invention is set below 0.5.

[0021] Based on the above research, the present invention proposes a lithium-rich nickel-based layered cathode material with a honeycomb superlattice structure of LiNi 6-z M z (along the (001) crystal plane; 0 ≤ z ≤ 3, and z is an integer), and its chemical formula is Li 1+x (Ni y M 1-y ) 1- x O 2 , where 0.05 ≤ x ≤ 0.5, 0.5 ≤ y ≤ 0.99; M is an element with a greater oxygen affinity than Ni, including one or more of Ti, V, Cr, Mn, Fe, Co, Cu elements, but not limited to 3d group elements. The content of M is 0.01 ≤ 1 - y ≤ 0.5; and when M contains one or more of Ti, Cr, V, Cu, the total content of one or more of Ti, Cr, V, Cu accounts for no more than 20% of the total molar amount of TM (transition metal, including Ni and M); when M contains one or more of Mn, Fe, Co, the total content of one or more of Mn, Fe, Co accounts for no more than 50% of the total molar amount of TM (transition metal). This lithium-rich nickel-based layered cathode material has the following obvious crystal structure characteristics:

[0022] (a) It has monoclinic symmetry;

[0023] (b) The X-ray diffraction pattern has a superlattice structure diffraction peak at 20 - 25°, which is different from that of traditional nickel-based cathode materials (without

[0024] diffraction peak) and lithium-rich manganese-based cathode materials (the main peak angles are different);

[0025] (c) The diffraction peak intensity of the superlattice structure is temperature-dependent. A low sintering temperature makes it difficult to balance the crystallinity and layered nature of the superstructure. A high sintering temperature makes it difficult for Li to enter the transition metal layer, making it difficult to effectively synthesize the superlattice structure.

[0026] More inclined to generate Li 2 O mixed phase;

[0027] (d) The transition metal layer exhibits an orderly arrangement of Li-Ni-TM-Li (TM represents one of the transition metal elements including Ni and M) on the (100) crystal plane.

[0028] (e) The atomic spacing between Ni and M atoms in the transition metal layer of the superlattice region is 0.12 nm, which is significantly smaller than that of Li 2 MnO 3 The Mn-Mn spacing in .

[0029] The present invention also provides a method for preparing the above-mentioned lithium-rich nickel-based layered positive electrode material, comprising: uniformly mixing a lithium source and a transition metal precursor, first heating to 200-500°C for pre-sintering for 1-20 hours, and then heating to 510-830°C for sintering for 2-24 hours to obtain the lithium-rich nickel-based layered positive electrode material.

[0030] The lithium-rich nickel-based positive electrode material of the present invention is synthesized at low temperature and for a long time. The lithium source can be selected from one or more of lithium oxalate, lithium acetate, lithium hydroxide, anhydrous lithium hydroxide, lithium carbonate, lithium sulfate, lithium molybdate, lithium nitrate, lithium chloride, lithium oxide, and lithium iodide; the transition metal precursor is selected from one or more of Ni and M carbonates, hydroxides, oxides, and chlorides. The ratio of Ni and M in the transition metal precursor is related to the chemical formula of the material Li 1+x (Ni y M 1-y ) 1-x O 2 Chinese Ni y M 1-y The content ratio indicated remains consistent. The sintering temperature, as a key parameter, requires precise control of the heating rate and sintering time, wherein the heating rate is preferably 0.1-5°C / min; preferably, the sintering temperature is 550-730°C, and the sintering time is 5-15h. The sintering atmosphere can be one or more of air, oxygen, nitrogen and oxygen (50% vs 50%), and argon.

[0031] The conventional synthesis method for high-nickel layered cathode materials is high-temperature solid-state sintering, and the ratio of Li to transition metals usually does not exceed 1.05. However, the lithium-rich nickel-based layered cathode material of the present invention requires a lower synthesis temperature, generally 100-200 °C lower than that of the layered materials with a conventional structure. For example, LiNi 0.9 Mn 0.1 O 2 The most suitable synthesis temperature for the conventional high-nickel layered material of the component is 750-800 °C, while the optimal synthesis temperature of the lithium-rich Li 1.2 (Ni 0.9 Mn 0.1 ) 0.8 O 2 material of the present invention is between 600 and 700 °C.

[0032] Judging from the electrochemical curve, the first cycle and the subsequent charge-discharge curves of the lithium-rich nickel-based layered cathode material of the present invention have significant differences. Among them, the first-cycle charge curve shows an obvious charge plateau, the voltage plateau is 4.4 ± 0.05 V, and the voltage plateau is 50-120 mV lower than that of the lithium-rich manganese-based cathode material. The capacity contributed by the plateau is related to the composition and sintering temperature, and the plateau capacity is between 20 and 300 mAh / g (4.4 V). After the first cycle, it shows a solid-solution type charge-discharge curve.

[0033] Compared with the prior art, the lithium-rich nickel-based layered cathode material of the present invention has the following technical advantages:

[0034] 1. By constructing a new Li-Ni-TM-Li superstructure, the electrochemical activity of the anion is changed, effectively activating the lattice oxygen to participate in the reaction. The activation potential of the anion is reduced by about 100 mV, improving the compatibility with the electrolyte;

[0035] 2. The theoretical capacity of the nickel-based cathode material is improved: from the original 280 mAh / g to 370 mAh / g;

[0036] 3. The voltage window of the nickel-based cathode material is expanded: from 3.0-4.3 V of the traditional layered nickel-based cathode material to 2.0-4.8 V.

[0037] 4. The actual discharge capacity is increased by 20% and the energy density is increased by 20% compared with the traditional nickel-based layered material. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 . Schematic diagram of the coordination species around O in the lithium-rich nickel-based layered cathode material with and without Li / Ni mixing.

[0039] Figure 2 . Li synthesized in Example 1 2 NiO 3XRD pattern of the material.

[0040] Figure 3 . Li synthesized in Example 2 1.2 (Ni 0.9 Mn 0.1 ) 0.8 O 2 XRD pattern of the material.

[0041] Figure 4 . Li synthesized in Example 2 1.2 (Ni 0.9 Mn 0.1 ) 0.8 O 2 Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy atomic phase of the material.

[0042] Figure 5 . Li synthesized in Example 2 1.2 (Ni 0.9 Mn 0.1 ) 0.8 O 2 First 5 charge-discharge curves (a) of the lithium-rich nickel-based cathode material and comparison chart (b) of the first charge curve with that of the lithium-rich manganese-based cathode material.

[0043] Figure 6 . Lithium-rich nickel-based material Li synthesized in Example 2 1.2 (Ni 0.9 Mn 0.1 ) 0.8 O 2 Comparison chart (a) of the first charge-discharge curve with that of the traditional high-nickel layered cathode material LiNi 0.9 Mn 0.1 O 2 and energy density retention chart (b) during cycling.

[0044] Figure 7 . XRD pattern of the lithium-rich nickel-based cathode material synthesized at different sintering temperatures in Example 3 1.2 (Ni 0.9 Mn 0.1 ) 0.8 O 2 .

[0045] Figure 8 . XRD pattern of the lithium-rich nickel-based cathode material with different lithium doping amounts synthesized in Example 4

[0046] Figure 9 . Lithium-rich nickel-based cathode material Li synthesized in Example 4 1.1 (Ni 0.9 Mn 0.1 ) 0.9 O 2Spherical aberration electron microscope high-angle annular dark-field scanning transmission electron microscope atomic phase.

[0047] Figure 10 . The Li-rich nickel-based cathode material Li synthesized in Example 5 1.2 (Ni 0.5 Co 0.2 Mn 0.3 ) 0.8 O 2 XRD pattern. Detailed implementation manners

[0048] The present invention will be further described in detail below through examples. However, those skilled in the art should understand that the scope of the present invention is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention shall be covered by the protection of the present invention.

[0049] Example 1: Synthesis of Li 2 NiO 3 cathode material

[0050] Ni(OH) 2 and anhydrous LiOH are uniformly mixed in a molar ratio of 1:2, heated to 400 °C at a heating rate of 0.5 °C / min and kept warm for 4 h, and then kept warm at 550 °C for 20 h to obtain the target product. The structure and electrochemical performance are tested. Structurally, there is no superlattice diffraction peak at 20-25 degrees ( Figure 2 ), and the peak intensity ratio of (003) / (104) is significantly less than 1, indicating a large degree of Li / Ni mixing. The layered splitting peak characteristics near 38 degrees and 65 degrees disappear, indicating that the layered phase characteristics of the material are not obvious. In addition, there is no obvious first-cycle charging platform in the electrochemical curve, and the discharge capacity at 0.1C is only 140 mAh / g, and the capacity retention rate after 50 cycles is about 50%.

[0051] Example 2: Synthesis of Li-rich nickel-based cathode material Li 1.2 (Ni 0.9 Mn 0.1 ) 0.8 O 2

[0052] Ni 0.9 Mn 0.1 (OH) 2 and anhydrous LiOH are uniformly mixed in a molar ratio of 1:1.5, heated to 400 °C at a heating rate of 0.5 °C / min and kept warm for 4 h, and then kept warm at 620 °C for 20 h to obtain the target product. There are obvious differences in the crystal structure from traditional high-nickel layered materials. This Li-rich nickel-based cathode material has obvious superlattice diffraction peaks at 20-25 degrees ( Figure 3)。The aberration-corrected electron microscope image with atomic resolution taken along the

[100] zone axis shows a superlattice structure with an ordered arrangement of "two bright and one dark" in the transition metal layer ( Figure 4 ), which corresponds to the results of XRD. Due to the presence of Li ions in the transition metal layer, the crystal structure symmetry changes to a monoclinic system with the C2 / c space group. The electrochemical curve shows obvious characteristics of the first-cycle charging plateau, mainly from the activation of oxygen in the superlattice structure, where the plateau capacity is about 200 mAh / g. Due to the difference from Li 2 MnO 3 For different superlattice structures and compositions, the anion activation voltage decreases by 100 mV compared to the lithium-rich manganese-based cathode material, and the voltage plateau is 4.45 V ( Figure 5 ). The results of physical and chemical tests mutually confirm that the superlattice in the transition metal layer is a Li-Ni-M-Li superlattice. Compared with traditional layered high-nickel cathode materials (there is no 4.4 V anion activation plateau in the first cycle), the capacity of the lithium-rich nickel-based cathode material of the present invention has increased significantly by 20%, and the energy density has increased by 20% ( Figure 6 ). The energy retention rate reaches 80% after 100 cycles. The results prove the unique advantages of the lithium-rich strategy.

[0053] Example 3: Synthesis of lithium-rich nickel-based cathode material Li 1.2 (Ni 0.9 Mn 0.1 ) 0.8 O 2

[0054] Ni 0.9 Mn 0.1 (OH) 2 is uniformly mixed with anhydrous LiOH in a molar ratio of 1:1.5, heated to 400 °C at a heating rate of 0.5 °C / min and held for 4 h, and then held for 20 h at 600, 625, 640, 650, 675, 700 °C respectively to obtain the target product. There are obvious superlattice diffraction peaks at 20 - 25 degrees in the structure, and the diffraction peaks of the superlattice structure have temperature-dependent characteristics ( Figure 7 ). The intensity of the superlattice diffraction peak is closely related to the sintering temperature. The appearance of the Li 2 O impurity phase during sintering at 700 °C indicates that the lattice oxygen loss in the transition metal layer increases at too high temperatures, and the excess Li is difficult to effectively enter the transition metal layer, thus generating an obvious Li 2 O impurity phase. At the same time, the intensity of the superlattice peak becomes weak, and this result also shows that the conventional high-nickel synthesis method is difficult to effectively form a superlattice structure. At low temperatures, there is no Li 2O. The intensity of the superlattice diffraction peak is mainly related to the temperature-driven crystallinity of the particles. This result indicates that the optimal synthesis temperature range of the lithium-rich nickel-based cathode material with a superlattice structure at M = Mn and 1 - y = 0.1 is between 600 - 700 °C.

[0055] Example 4: Synthesis of lithium-rich nickel-based cathode materials Li 1+x (Ni 0.9 Mn 0.1 ) 1-x O 2

[0056] Ni 0.9 Mn 0.1 (OH) 2 and anhydrous LiOH were uniformly mixed in molar ratios of 1:1.11, 1:1.22, and 1:1.35 respectively, heated to 400 °C at a heating rate of 0.1 °C / min and held for 4 h, then heated to 620 °C and held for 20 h to obtain the target product. There is an obvious superlattice diffraction peak at 20 - 25 degrees in the structure ( Figure 8 ), but the peak intensity is significantly weakened, mainly related to the content of the lithium source. However, there is also an obvious Li-Ni-M-Li superlattice structure in the transition metal layer. Different from that, there is an obvious stacking fault structure in the material ( Figure 9 ).

[0057] Example 5: Synthesis of lithium-rich nickel-based cathode material Li 1.2 (Ni 0.5 Co 0.2 Mn 0.3 ) 0.8 O 2

[0058] Ni 0.5 Co 0.2 Mn 0.3 (OH) 2 and anhydrous LiOH were uniformly mixed in a molar ratio of 1:1.5, heated to 400 °C at a heating rate of 1 °C / min and held for 4 h, then heated to 720 °C and held for 20 h to obtain the target product. There is an obvious superlattice diffraction peak at 20 - 25 degrees in the structure ( Figure 10 ), and the peak intensity ratio of (003) / (104) is significantly increased, indicating that the layered characteristics of the material are significantly improved. However, the intensity of the superlattice decreases, which may be related to the fact that Co can make the superlattice distribution more disordered. In addition, there is an obvious first-cycle charge plateau in the electrochemical curve, the plateau capacity is about 250 mAh / g, the voltage plateau is 4.40 V, and the retention rate after 50 cycles at 0.1C is 85%.

[0059] Example 6: Synthesis of lithium-rich nickel-based cathode material Li 1.2 (Ni 0.9 Ti 0.02 V 0.02 Cr 0.02 Mn 0.02 Fe 0.02 ) 0.8 O 2

[0060] Ni 0.9 Ti 0.02 V 0.02 Cr 0.02 Mn 0.02 Fe 0.02 (OH) 2 is uniformly mixed with anhydrous LiOH in a molar ratio of 1:1.5, heated to 400 °C at a heating rate of 0.5 °C / min and held for 4 h, and then held at 800 °C for 20 h to obtain the target product. There are obvious superlattice diffraction peaks at 20 - 25 degrees in terms of structure, the symmetry is the C2 / m space group, the electrochemical curve has an obvious first-cycle charging plateau, the plateau capacity is about 180 mAh / g, the voltage plateau is 4.42 V, and the capacity retention rate after 100 cycles at 0.5 C is 77%.

[0061] Example 7: Synthesis of lithium-rich nickel-based cathode material Li 1.2 (Ni 0.8 Ti 0.2 ) 0.8 O 2

[0062] Ni(OH) 2 is uniformly mixed with nano-titanium dioxide in a molar ratio of 4:1, and then the mixture is uniformly mixed with anhydrous LiOH in a molar ratio of 1:1.5. It is pressed into a sphere with a diameter of 14 mm using a hydraulic press at a pressure of 30 - 50 MPa. It is heated to 400 °C at a heating rate of 0.5 °C / min and held for 4 h, and then held at 800 °C for 20 h to obtain the target product. There are obvious superlattice diffraction peaks at 20 - 25 degrees in terms of structure, without other impurity phases, and the symmetry is the C2 / m space group. The electrochemical curve has an obvious first-cycle charging plateau, the plateau capacity is about 180 mAh / g, the voltage plateau is 4.4 V, and the capacity retention rate after 100 cycles at 0.5 C is 90%.

[0063] Example 8: Synthesis of lithium-rich nickel-based cathode material Li 1.2 (Ni 0.8 Ti 0.1 V 0.1 ) 0.8 O 2

[0064] Ni0.9 Ti 0.1 V 0.1 O(OH) 2 is uniformly mixed with anhydrous LiOH in a molar ratio of 1:1.35, heated to 400 °C at a heating rate of 0.5 °C / min and held for 4 h, and then held at 730 °C for 20 h to obtain the target product. Structurally, there are obvious superlattice diffraction peaks at 20 - 25 degrees, the symmetry is the C2 / c space group, the electrochemical curve has an obvious first-cycle charging plateau, the plateau capacity is about 200 mAh / g, the voltage plateau is 4.45 V, and the capacity retention rate after 100 cycles at 0.5 C is 85%.

[0065] Example 9: Synthesis of lithium-rich nickel-based cathode material Li 1.2 (Ni 0.9 Fe 0.1 ) 0.8 O 2

[0066] Ni 0.9 Fe 0.1 (OH) 2 is uniformly mixed with anhydrous LiOH in a molar ratio of 1:1.5, heated to 400 °C at a heating rate of 0.5 °C / min and held for 4 h, and then held at 600 °C for 20 h to obtain the target product. Structurally, there are obvious superlattice diffraction peaks at 20 - 25 degrees, and the intensity of the superlattice peaks is weak. The material has a C2 / m space group structure. The electrochemical curve has an obvious first-cycle charging plateau, the plateau capacity is about 270 mAh / g, the voltage plateau is 4.38 V, and the capacity retention rate after 100 cycles at 0.5 C is 66%.

[0067] Example 10: Synthesis of lithium-rich nickel-based cathode material Li 1.18 (Ni 0.9 Cr 0.1 ) 0.82 O 2

[0068] Ni 0.9 Cr 0.1 (OH) 2.1 is uniformly mixed with anhydrous LiOH in a molar ratio of 1:1.44, heated to 400 °C at a heating rate of 0.5 °C / min and held for 4 h, and then held at 710 °C for 20 h to obtain the target product. Structurally, there are obvious superlattice diffraction peaks at 20 - 25 degrees, the symmetry is the C2 / m space group, the electrochemical curve has an obvious first-cycle charging plateau, the plateau capacity is about 100 mAh / g, the voltage plateau is 4.42 V, and the capacity retention rate after 100 cycles at 0.5 C is 88%.

[0069] Example 11: Synthesis of lithium-rich nickel-based cathode material Li1.2 (Ni 0.9 Cu 0.1 ) 0.8 O 2

[0070] Ni 0.9 Cu 0.1 (OH) 2 is uniformly mixed with anhydrous LiOH in a molar ratio of 1:1.5, heated to 400 °C at a heating rate of 0.5 °C / min and held for 4 h, and then held at 800 °C for 20 h to obtain the target product. There are obvious superlattice diffraction peaks at 20-25 degrees in terms of structure, the symmetry is the C2 / c space group, the electrochemical curve has an obvious first-cycle charging plateau, the plateau capacity is about 230 mAh / g, the voltage plateau is 4.45 V, and the capacity retention rate after 100 cycles at 0.5 C is 55%.

Claims

1. A lithium-rich nickel-based layered cathode material, characterized in that, Its chemical formula is Li 1+x (Ni y M 1-y ) 1-x O 2 , where 0.05 ≤ x ≤ 0.5, 0.5 ≤ y ≤ 0.99; M is an element with a greater oxygen affinity than Ni, selected from one or more of the elements Ti, V, Cr, Mn, Fe, Co, Cu, and moreover, when M contains one or more of Ti, Cr, V, Cu, the total content of one or more of Ti, Cr, V, Cu accounts for no more than 20% of the total molar amount of transition metals; when M contains one or more of Mn, Fe, Co, the total content of one or more of Mn, Fe, Co accounts for no more than 50% of the total molar amount of transition metals; the crystal of this lithium-rich nickel-based layered cathode material has monoclinic symmetry, and the transition metal layer has a LiNi 6-z M z honeycomb-like superlattice structure, and its X-ray diffraction pattern has a superlattice structure diffraction peak at 20 - 25°, where z is an integer from 0 to 3; the transition metal layer shows an ordered arrangement of Li-Ni-TM-Li on the (100) crystal plane, where TM represents one of the transition metal elements including Ni and M.

2. The lithium-rich nickel-based layered cathode material according to claim 1, characterized in that, the Ni-M atomic spacing in the transition metal layer of the superlattice region is 0.12 nm.

3. The lithium-rich nickel-based layered cathode material according to claim 1, characterized in that, The lithium-rich nickel-based positive electrode material is selected from one of the following chemical compositions: Li 1.2 (Ni 0.9 Mn 0.1 ) 0.8 O 2 , Li 1.05 (Ni 0.9 Mn 0.1 ) 0.95 O 2 , Li 1.1 (Ni 0.9 Mn 0.1 ) 0.9 O 2 , Li 1.15 (Ni 0.9 Mn 0.1 ) 0.85 O 2 , Li 1.2 (Ni 0.5 Co 0.2 Mn 0.3 ) 0.8 O 2 , Li 1.2 (Ni 0.9 Ti 0.02 V 0.02 Cr 0.02 Mn 0.02 Fe 0.02 ) 0.8 O 2 , Li 1.2 (Ni 0.8 Ti 0.2 ) 0.8 O 2 , Li 1.2 (Ni 0.8 Ti 0.1 V 0.1 ) 0.8 O 2 , Li 1.2 (Ni 0.9 Fe 0.1 ) 0.8 O 2 , Li 1.18 (Ni 0.9 Cr 0.1 ) 0.82 O 2 and Li 1.2 (Ni 0.9 Cu 0.1 ) 0.8 O 2 .

4. A method for preparing the lithium-rich nickel-based layered cathode material according to any one of claims 1 to 3, comprising: uniformly mixing a lithium source and a transition metal precursor, first heating to 200-500 °C for pre-sintering for 1-20 h, and then heating to 510-830 °C for sintering for 2-24 h to obtain the lithium-rich nickel-based layered cathode material.

5. The preparation method according to claim 4, characterized in that, the lithium source is selected from one or more of lithium oxalate, lithium acetate, lithium hydroxide, anhydrous lithium hydroxide, lithium carbonate, lithium sulfate, lithium molybdate, lithium nitrate, lithium chloride, lithium oxide, and lithium iodide.

6. The preparation method according to claim 4, characterized in that, The transition metal precursor is selected from one or more of carbonates, hydroxides, oxides, and chlorides of Ni and M, and the component ratio of Ni and M in the transition metal precursor is the same as the content ratio shown in the chemical formula Li 1+x (Ni y M 1-y ) 1-x O 2 The content ratio of Ni y M 1-y is the same as the content ratio shown 7. The preparation method according to claim 4, characterized in that, the heating rate is 0.1-5 °C / min.

8. The preparation method according to claim 4, characterized in that, the sintering temperature is 550-730 °C and the sintering time is 5-15 h.

9. The preparation method according to claim 4, characterized in that, the sintering atmosphere is one or more of air, oxygen, nitrogen-oxygen, and argon.

Images