Cobalt-free lithium-rich ultra-high nickel positive electrode material with composite crystal domain structure and preparation method thereof

Abstract

The invention discloses a cobalt-free lithium-rich ultrahigh-nickel positive electrode material with a composite crystal domain structure and a preparation method, and belongs to the field of lithium battery positive electrode materials. The positive electrode material with the composite crystal domain structure is composed of LiNiaMbMn (1-a-b) O2 with an R-3m space group and Li2MnO3 with a C2 / m space group, the Li2MnO3 crystal domain can effectively inhibit the aggravation of the lithium-nickel mixing degree of the cobalt-free ultrahigh nickel positive electrode material caused by cobalt removal, and the conversion of the positive electrode material structure from a layered phase to a disordered rock salt phase is slowed down; meanwhile, the Li2MnO3 crystal domain with a stable structure inhibits severe unit cell volume change caused by phase structure transformation in the electrochemical cycle process of the cobalt-free ultra-high nickel positive electrode material, stress and strain accumulation is reduced, microcracks in the material are further effectively inhibited, and the cycle stability and thermal stability of the cobalt-free ultra-high nickel positive electrode material are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion battery materials, and particularly relates to a composite domain structure cobalt-free lithium-rich ultra-high nickel positive electrode material design and regulation and preparation method. BACKGROUND

[0002] The positive electrode material of a lithium ion battery is one of the key factors determining the performance of the battery, directly affecting the energy density, cycle life and safety. Common positive electrode materials include lithium cobalt oxide (LiCoO2) with a layered structure, lithium manganese oxide (LiMn2O4) with a spinel structure and lithium iron phosphate (LiFePO4) with an olivine structure. Lithium cobalt oxide has high energy density, but is high in cost and poor in safety; lithium manganese oxide is low in cost and good in safety, but is insufficient in cycle performance; lithium iron phosphate is excellent in safety and long in life, but is low in energy density.

[0003] Ternary positive electrode materials are currently the mainstream materials applied in the power battery market, and high-nickel ternary positive electrode materials (LiNi a Co b Mn (1-a-b) O2, a≥0.6) are one of the best choices for realizing high-energy-density lithium ion batteries due to their high specific capacity (>200 mAh / g) and high energy density (>800 Wh / kg), however, cobalt, which is one of the important components of high-nickel ternary materials, has problems such as strong toxicity, difficult purification, high cost and uneven distribution, especially the cobalt resources with mining significance in China are extremely rare, and are extremely dependent on imports, which has brought great hidden dangers to China's energy security. Therefore, from the perspective of national energy strategy and industrial layout, designing and developing cobalt-free high-nickel positive electrode materials (such as: LiNi 0.9 Mn 0.1 O2 or LiNi 0.9 Mn 0.05 Al 0.05 O2, etc.) with high specific energy, low cost and long cycle life is the only way to develop high-performance lithium ion batteries.

[0004] However, after the cobalt-free high-nickel positive electrode material is decobaltized, a series of problems restrict its further development and application. On the one hand, Co 3+ ions have no magnetic moment, which inhibits the "magnetic frustration" effect in the transition metal layer, and Co 3+The presence of ions increases the formation energy of Li / Ni exchange, and to some extent inhibits Li / Ni mixing. When cobalt is removed, the degree of Li / Ni mixing increases, which promotes the transformation of the material from a layered structure to a spinel structure and / or a rock salt phase structure (NiO-like phase), resulting in a loss of irreversible capacity. On the other hand, in high-nickel cathode materials, when charged to a higher voltage (>4.2V), a H2-H3 phase structure transition occurs, which in turn causes a sharp contraction of the c-axis lattice parameter, resulting in distortion and stress accumulation in the material, leading to the formation of micro-cracks. Electrolyte gradually penetrates into the interior of the particles along the cracks, attacks the fresh surface exposed in the interior of the particles and undergoes side reactions, accelerates the phase structure transition of the material at the interface and the pulverization of the electrode material, and finally causes the sharp decline of the electrochemical performance and thermal stability of the material.

[0005] Li2MnO3 material has a stable crystal structure during charging and discharging at low voltage (≤4.4V), and oxygen does not participate in electrochemical reaction, and manganese does not undergo reduction and oxidation reaction, so it has good electrochemical and thermal stability. In previous studies, it has been proved that Li2MnO3 crystal domains in lithium-rich layered oxides (LLOs) play a role in stabilizing the crystal structure during low-voltage (≤4.4V) charging and discharging cycles, thereby realizing the long cycle stability of low-voltage LLOs. Introducing Li2MnO3 crystal domains into high-nickel cathode materials can effectively inhibit Li / Ni mixing, thereby slowing down the transformation of the material from a layered structure to a spinel and / or rock salt phase structure during electrochemical cycling, reducing the loss of irreversible capacity. In addition, during low-voltage charging and discharging, the introduction of electrochemically stable Li2MnO3 crystal domains inhibits the sharp change of the lattice parameter during charging and discharging, slows down the accumulation of stress and strain caused by the change of the lattice parameter, inhibits the formation of micro-cracks in high-nickel cathode materials, and reduces the decline of electrochemical performance. Therefore, by introducing Li2MnO3 crystal domains into cobalt-free high-nickel cathode materials, constructing a composite crystal domain structure cathode material is the key to realizing high-energy-density long-cycle-life lithium-ion batteries. SUMMARY

[0006] The present application aims to provide a composite crystal domain structure cobalt-free lithium-rich ultra-high nickel cathode material and its design and preparation method, which has a chemical formula of xLi2MnO3·(1-x)LiNi a M b Mn (1-a-b)O2, 0 < x < 0.2, 0.8 < a < 1, 0 < b < 0.03, by optimizing the ratio of nickel and manganese content in the precursor, the energy barrier of lithium migration to the transition metal layer in the process of thermal sintering is reduced, thereby realizing the introduction of Li2MnO3 crystal domains in the super-high nickel (Ni > 80%) positive electrode material. M is selected from one or more of Mg, Al, Ca, Ti, Zn, Y, Zr, Nb, Mo, Sb, La, Ta, W.

[0007] The Li2MnO3 crystal domain matches the lattice structure of the layered structure, and the introduction of the Li2MnO3 crystal domain realizes the combination of the two at the atomic level, which not only effectively suppresses the dramatic change of the unit cell parameter of the super-high nickel positive electrode material due to the H2-H3 phase transition when charged to 4.2V, slows down the accumulation of local stress and strain caused by the change of the unit cell parameter, and suppresses the generation of micro-cracks, thereby improving the electrochemical cycle stability and thermal stability of the electrode material; at the same time, the introduction of the Li2MnO3 crystal domain reduces the Li / Ni mixing degree of the super-high nickel positive electrode material, suppresses the transformation of the layered structure to the electrochemically inert rock salt phase structure, and improves the cycle stability.

[0008] In addition, the application utilizes a high-temperature solid-phase sintering one-step method for introduction, which avoids additional processing, thereby reducing production cost and process difficulty.

[0009] In order to achieve the above-mentioned purpose, the technical scheme adopted by the application is:

[0010] The obtained composite crystal domain structure positive electrode material is composed of LiNi a M b Mn (1-a-b) O2 phase and Li2MnO3 crystal domain with C2 / m space group, and the proportion and distribution of the Li2MnO3 crystal domain are controllable, and the preparation method thereof comprises the following steps:

[0011] (1) configuring a certain concentration of soluble nickel-manganese mixed salt solution, alkali solution and ammonia water complexing agent solution;

[0012] (2) adding a certain volume of deionized water and ammonia water as a reaction bottom liquid into a reaction kettle, and controlling the temperature of the co-precipitation reaction kettle by using a constant-temperature water bath; the mixed salt solution, ammonia solution and alkali solution are simultaneously flowed into the reaction kettle in a parallel flow manner to carry out a co-precipitation reaction, the stirring speed and pH of the reaction kettle are controlled, and a cobalt-free super-high nickel precursor mixed solution is obtained after a certain period of reaction;

[0013] (3) after aging for a certain period of time, the cobalt-free super-high nickel precursor mixed solution obtained in step (2) is filtered and vacuum dried to obtain the designed cobalt-free super-high nickel precursor;

[0014] (4) The precursor powder obtained in step (3) is mixed evenly with a certain proportion of lithium source in a three-dimensional mixer and then placed in a high-temperature sintering furnace. Under an oxygen atmosphere, it is sintered in three stages according to a certain procedure. After sintering, it is cooled down to a certain temperature by air cooling and then taken out of the high-temperature furnace to obtain a cobalt-free lithium-rich high-nickel cathode material with a composite crystal domain structure.

[0015] M is selected from one or more of Mg, Al, Ca, Ti, Zn, Y, Zr, Nb, Mo, Sb, La, Ta, and W. The doping element can be introduced during the co-precipitation process or the lithium sintering process, that is, the precursor of the desired doping element is added to the nickel-manganese mixed salt or alkaline solution in step (1), or added during the lithium preparation in step (4) and then sintered together.

[0016] A further technical solution is that the molar ratio of nickel and manganese in the nickel-manganese mixed salt solution in step (1) is 0.8-0.95:0.05-0.2, and the sum of the two is 1.

[0017] A further technical solution is that, in step (1), the soluble nickel salt used can be one or more of nickel acetate, nickel nitrate, nickel chloride, nickel sulfate, and nickel oxalate; the soluble manganese salt used can be one or more of manganese acetate, manganese nitrate, manganese chloride, manganese sulfate, and manganese oxalate; the alkaline solution used can be one or more of potassium hydroxide, potassium carbonate, sodium carbonate, and sodium hydroxide; and the lithium source used can be one or more of lithium hydroxide, lithium carbonate, lithium oxalate, lithium nitrate, and lithium sulfate.

[0018] A further technical solution is that the total concentration of nickel and manganese in the mixed salt solution in step (1) is 2-6 mol / L.

[0019] A further technical solution is that the concentration of alkali in step (1) is 2-10 mol / L and the concentration of complexing agent ammonia is 2-8 mol / L.

[0020] A further technical solution is that, in step (2), the pH of the co-precipitation reaction system is 8-12, the temperature of the reaction vessel is 40-70℃, the speed of the stirring paddle is 500-1000 rpm, the co-precipitation reaction time is 5-40 h, the aging time is 1-24 h, and the speed of the stirring paddle during the aging process is 200-500 rpm.

[0021] A further technical solution is that the constant temperature vacuum drying temperature in step (3) is 60-120℃.

[0022] A further technical solution is that the molar ratio of the precursor to the lithium source in step (4) is 1:(1.1~1.40).

[0023] A further technical solution is that the sintering method in step (4) is a three-step segmented sintering process. The first step sintering temperature is 500-600℃, the heating rate is 1-7℃ / min, and the holding time is 3-8h; the second step sintering temperature is 700-1000℃, the heating rate is 1-7℃ / min, and the holding time is 10-25h; the third step sintering is carried out at 750-1050℃ for 1-5h, with a heating rate of 1-3℃ / min. Preferably, during the high-temperature sintering process, the second step sintering temperature is adjusted according to the different nickel-manganese compositions of the precursor, so that the lithium source migrates to the transition metal layer of the cathode material. Generally, the sintering temperature decreases accordingly with the increase of nickel content, thereby forming Li2MnO3 crystal domains and achieving control over the proportion and distribution of Li2MnO3 crystal domains.

[0024] A further technical solution is that, in step (4), the air cooling is used to accelerate the cooling down to a certain temperature of 300-600℃. The air cooling is achieved by using a wind-blown calcination device to cool the device down to 300-600℃, thereby cooling the product down to 300-600℃. This rapid cooling reduces material stress and also reduces residual lithium on the surface of the cathode material, preventing surface reconstruction due to residual lithium. On the other hand, it enables the control of the proportion and distribution of Li2MnO3 crystal domains.

[0025] The cobalt-free, lithium-rich, ultra-high nickel cathode material with a composite domain structure obtained in this invention has a charging voltage of less than or equal to 4.4V, preferably 4.3-4.4V. It is subjected to cyclic charge-discharge cycles at rates of 0.1C-3C.

[0026] This invention, from the perspective of composite domain structure design and control, achieves improved comprehensive electrochemical performance and thermal stability of cobalt-free ultra-high nickel cathode materials. It achieves this by controlling the ratio of the co-precipitated nickel-manganese mixed solution, key parameters of the co-precipitation reaction (reaction temperature, time, stirring speed, complexing agent concentration, precipitant concentration, pH value, etc.), and key sintering process parameters (lithium ratio, sintering temperature, atmosphere, heating rate, holding time, cooling method, cooling rate, etc.). This allows lithium ions to migrate to the transition metal layer of the ultra-high nickel cathode material during sintering, forming Li2MnO3 domains. On the one hand, this invention suppresses the Li / Ni mixing degree of the ultra-high nickel cathode material, slowing down the irreversible transformation of the layered structure to the rock salt phase structure during electrochemical cycling. On the other hand, the introduction of Li2MnO3 crystal domains suppresses the H2-H3 phase transition when the material is charged to 4.2V during cycling, reducing the drastic changes in cell parameters. This effectively avoids microcracks caused by rapid changes in cell parameters, ultimately improving the cycling stability of the cathode material. In addition, the material obtained by this invention is completely cobalt-free, reducing the cost of the material and being environmentally friendly. It is expected to achieve industrial mass production and has broad application prospects.

[0027] In summary, compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The cathode material prepared by this invention does not contain cobalt, which significantly reduces the material production cost, effectively solves the problem of domestic cobalt resource scarcity and reliance on imports, and removes highly toxic cobalt, which is in line with the concepts of green environmental protection and carbon neutrality.

[0029] (2) By designing and controlling the ratio of nickel and manganese elements in the precursor, combined with the lithium source ratio and sintering process, this invention realizes the introduction of controllable Li2MnO3 crystal domains in cobalt-free high-nickel layered oxides, thus realizing the preparation of lithium-rich high-nickel cathode materials. This method avoids complex post-processing, reduces production costs, and is expected to be applied in large-scale production.

[0030] (3) The cathode material prepared in this invention has a composite structure of Li2MnO3 crystal domains and layered structure. Compared with lithium-rich manganese-based cathode materials, the cobalt-free lithium-rich ultra-high nickel cathode material has a higher discharge voltage plateau and lower cycle voltage decay. Compared with layered cobalt-free high nickel cathode materials, the introduction of Li2MnO3 crystal domains suppresses the severe lithium-nickel mixing in the cathode material and slows down the irreversible phase structure transformation from layered structure to rock salt structure during cycling. At the same time, Li2MnO3 crystal domains exhibit electrochemical inertness at 4.5V, thereby suppressing the H2-H3 phase transition when charged to 4.2V during high nickel cycling, reducing the drastic changes in cell parameters, thus effectively avoiding microcracks caused by rapid changes in cell parameters, and ultimately improving the cycle stability of the cathode material. Attached Figure Description

[0031] Figure 1 SEM images of the materials prepared in Example 1 of this invention.

[0032] Figure 2 The XRD patterns of the materials prepared in Comparative Example 1, Example 1, and Example 2 of this invention are shown below.

[0033] Figure 3 The charge-discharge curves of the products of Comparative Example 1, Example 1, and Example 2 of this invention were tested under conditions of 0.1C (1C = 180mAh / g) and 2.0-4.8V.

[0034] Figure 4 The dQ / dV curves of the products of Comparative Example 1, Example 1, and Example 2 of this invention were tested at 0.1C (1C = 180 mAh / g) and 2.0-4.8V.

[0035] Figure 5 The charge-discharge curves of the products of Comparative Example 1, Example 1, and Example 2 of this invention were tested under conditions of 0.1C (1C = 180 mAh / g) and 2.7-4.4V.

[0036] Figure 6 This is a comparison chart showing the electrochemical cycling performance of the products of Comparative Example 1, Example 1, and Example 2 of this invention under 1C (1C = 180 mAh / g) and 2.7-4.4V conditions.

[0037] Figure 7 This is a schematic diagram of the material preparation process of the present invention; Detailed Implementation

[0038] The present invention will be further described in detail below with reference to specific embodiments, comparative examples, and accompanying drawings. These embodiments are merely for further understanding of the invention and should not be construed as limiting the scope of protection of the invention. The scope of protection of the invention is not limited to the following embodiments. xLi2MnO3·(1-x)LiNi a M b Mn (1-a-b) O2, whose total average chemical formula corresponding to its metallic elements can be expressed as Li e( Ni f Mn g M h)i O2 form.

[0039] Comparative Example 1

[0040] A 2 mol / L salt solution containing nickel and manganese in a Ni:Mn ratio of 0.8:0.2, a 4.0 mol / L NaOH solution, and a 4 mol / L ammonia solution were prepared. The coprecipitation reaction was carried out at 55℃. To prevent the transition metal cations from being oxidized during the reaction, the reaction was conducted under a nitrogen atmosphere. A certain volume of deionized water and ammonia water were added to the reaction vessel as the reaction base solution.

[0041] A salt solution, ammonia solution, and alkali solution were simultaneously fed into a reactor in a co-current flow to carry out a co-precipitation reaction. The stirring speed was controlled at 600 rpm, and the pump speed of NaOH solution entering the reactor was adjusted to stabilize the pH at 11.5 during the reaction. After 20 hours of reaction, the stirring speed was reduced to 300 rpm, and the liquid feeding was stopped. The solution was aged for 4 hours, centrifuged, and filtered to obtain the precipitate. The precipitate was washed multiple times with deionized water until neutral, and then dried in a constant temperature vacuum drying oven at 80℃ to obtain a Ni-containing product. 0.8 Mn 0.2 (OH)2 precursor.

[0042] The dried precursor was mixed with LiOH·H2O at a molar ratio of 1:1.05 and then sintered in a high-temperature furnace under an O2 atmosphere. The specific sintering procedure was as follows: the temperature was increased from room temperature to 550℃ at a rate of 3℃ / min and held for 5 hours; then increased to 900℃ at a rate of 3℃ / min and held for 15 hours; then increased to 925℃ at a rate of 3℃ / min and held for 2 hours; finally, air cooling was turned on, and the mixture was removed and ground at 600℃ to obtain LiNi. 0.8 Mn 0.2 O2-free cobalt-rich lithium-nickel cathode material.

[0043] Example 1

[0044] A 2 mol / L salt solution containing nickel and manganese in a Ni:Mn ratio of 0.8:0.2, a 4.0 mol / L NaOH solution, and a 4 mol / L ammonia solution were prepared. The reactor temperature was set at 55℃. To prevent the metal cations from being oxidized during the reaction, pure nitrogen gas was continuously introduced into the reactor throughout the process. A certain volume of deionized water and ammonia water were added to the reactor as the reaction base solution.

[0045] A salt solution, ammonia solution, and alkali solution were simultaneously fed into a reactor in a co-precipitation process. The stirring speed of the reactor was controlled at 600 rpm, and the pump speed of the NaOH solution entering the reactor was adjusted to stabilize the pH of the solution in the reactor at 11.5. After 20 hours of reaction, the stirring speed was reduced to 300 rpm, and the liquid feeding was stopped. The reaction solution was aged for 4 hours, centrifuged, and filtered to obtain the precipitate. The precipitate was washed multiple times with deionized water until neutral, and then dried in a constant temperature vacuum drying oven at 80℃ to obtain a Ni-containing product. 0.8 Mn 0.2 (OH)2 precursor.

[0046] The dried precursor was mixed with LiOH·H2O at a molar ratio of 1:1.15 and then sintered in a high-temperature furnace under an O2 atmosphere. The specific sintering procedure was as follows: the temperature was increased from room temperature to 550℃ at a rate of 3℃ / min and held for 5 hours; then increased to 900℃ at a rate of 3℃ / min and held for 15 hours; then increased to 925℃ at a rate of 3℃ / min and held for 2 hours; finally, air cooling was turned on, and the mixture was removed and ground at 600℃ to obtain the product with an average chemical formula of Li. 1.05 (Ni 0.8 Mn 0.2 ) 0.95 O2-free cobalt-rich lithium-nickel layered oxide cathode material.

[0047] The morphology of the cathode material obtained in Example 1 was observed using SEM, and the results are as follows: Figure 1 As shown. ByFigure 1 It can be seen that the prepared material is a quasi-single crystal with a particle size between 200-400nm. Figure 2 The XRD pattern of the prepared cathode material is shown. It can be seen that the synthesized material conforms to the corresponding crystal structure, and the cathode material has good peak separation and low lithium-nickel mixing, indicating that the introduction of Li2MnO3 crystal domains effectively suppressed the lithium-nickel mixing caused by the removal of cobalt.

[0048] Example 2

[0049] A 2 mol / L salt solution containing nickel and manganese in a Ni:Mn ratio of 0.8:0.2, a 4.0 mol / L NaOH solution, and a 4 mol / L ammonia solution were prepared. The reactor temperature was set at 55℃. To prevent the metal cations from being oxidized during the reaction, pure nitrogen gas was continuously introduced into the reactor throughout the process. A certain volume of deionized water and ammonia water were added to the reactor as the reaction base solution.

[0050] A salt solution, ammonia solution, and alkali solution were simultaneously fed into a reactor in a co-precipitation process. The stirring speed of the reactor was controlled at 600 rpm, and the pump speed of the NaOH solution entering the reactor was adjusted to stabilize the pH of the solution in the reactor at 11.5. After 20 hours of reaction, the stirring speed was reduced to 300 rpm, and the liquid feeding was stopped. The reaction solution was aged for 4 hours, centrifuged, and filtered to obtain the precipitate. The precipitate was washed multiple times with deionized water until neutral, and then dried in a constant temperature vacuum drying oven at 80℃ to obtain a Ni-containing product. 0.8 Mn 0.2 (OH)2 precursor.

[0051] The dried precursor was mixed with LiOH·H2O at a molar ratio of 1:1.25 and then sintered in a high-temperature furnace under an O2 atmosphere. The specific sintering procedure was as follows: the temperature was increased from room temperature to 550℃ at a rate of 3℃ / min and held for 5 hours; then increased to 900℃ at a rate of 3℃ / min and held for 15 hours; then increased to 925℃ at a rate of 3℃ / min and held for 2 hours; finally, air cooling was turned on, and the mixture was removed and ground at 600℃ to obtain the product with an average chemical formula of Li. 1.1 (Ni 0.8 Mn 0.2 ) 0.9 O2-free cobalt-rich lithium-nickel layered oxide cathode material.

[0052] The cathode materials obtained in Comparative Example 1, Example 1, and Example 2 were mixed with acetylene black and PVDF in a ratio of 8:1:1, coated onto aluminum foil, and assembled into 2032 coin cells. Electrochemical performance was then tested. The electrolyte composition was 1M LiPF6 dissolved in ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (volume ratio 1:1:1). Performance graphs were obtained under a voltage window of 2.0-4.8V. Figure 3 As shown. By Figure 3 It can be seen that Examples 1 and 2 have higher charge specific capacity compared to Comparative Example 1. This is due to the fact that the introduced Li2MnO3 crystal domains are activated when charged to around 4.5V, and the oxygen anions participate in the reaction, contributing additional capacity. In addition, the... Figure 4 As shown in the dQ / dV curves, both Examples 1 and 2 exhibit a significant Li2MnO3 oxygen anion oxidation peak at around 4.5V, further confirming that the cathode material is a composite structure composed of Li2MnO3 crystal domains and a high-nickel layered phase. Figure 5 As shown, charge-discharge tests were conducted at room temperature (25°C), 2.7-4.4V, and a 0.1C rate. Compared to Comparative Example 1, the discharge capacity of Examples 1 and 2 was slightly lower, but after constant current charge-discharge cycles at a 1C rate, the discharge capacity increased. Figure 6 As shown, after 50 cycles, the capacity retention rates of Examples 1 and 2 were 81.06% and 93.45%, respectively, which were much higher than the 63.31% of Comparative Example 1. This is because the introduced Li2MnO3 crystal domains stabilized the crystal structure under low voltage (<4.4V) conditions when they were not activated, thus improving the cycle stability of the cathode material.

[0053] Example 3

[0054] A salt solution containing nickel, manganese, aluminum, and magnesium in a ratio of Ni:Mn:Al:Mg = 0.85:0.14:0.005:0.005 with a total concentration of 2 mol / L, a 4.0 mol / L NaOH solution, and a 4 mol / L ammonia solution were prepared. The reaction vessel temperature was set at 55℃. To prevent the metal cations from being oxidized during the reaction, pure nitrogen gas was continuously introduced into the reaction vessel throughout the process. A certain volume of deionized water and ammonia water were added to the reaction vessel as the reaction base solution.

[0055] A salt solution, ammonia solution, and alkali solution were simultaneously fed into a reactor in a co-precipitation process. The stirring speed of the reactor was controlled at 600 rpm, and the pump speed of the NaOH solution entering the reactor was adjusted to stabilize the pH of the solution in the reactor at 11.5. After 20 hours of reaction, the stirring speed was reduced to 300 rpm, and the liquid feeding was stopped. The reaction solution was aged for 4 hours, centrifuged, and filtered to obtain the precipitate. The precipitate was washed multiple times with deionized water until neutral, and then dried in a constant temperature vacuum drying oven at 80℃ to obtain a Ni-containing product. 0.85 Mn 0.14 Al 0.005 Mg 0.005 (OH)2 precursor.

[0056] The dried precursor was mixed with LiOH·H2O at a molar ratio of 1:1.2 and then sintered in a high-temperature furnace under an O2 atmosphere. The specific sintering procedure was as follows: the temperature was increased from room temperature to 550℃ at a rate of 3℃ / min and held for 5 hours; then increased to 850℃ at a rate of 3℃ / min and held for 15 hours; then increased to 875℃ at a rate of 3℃ / min and held for 2 hours; finally, air cooling was turned on, and the mixture was removed and ground at 400℃ to obtain the product with an average chemical formula of Li. 1.05 (Ni 0.85 Mn 0.14 Al 0.005 Mg 0.005 ) 0.95 O2-free cobalt-rich lithium-nickel layered oxide cathode material.

[0057] Example 4

[0058] A 2 mol / L salt solution containing nickel and manganese in a Ni:Mn ratio of 0.9:0.1, a 4.0 mol / L NaOH solution, and a 4 mol / L ammonia solution were prepared. The reactor temperature was set at 55℃. To prevent the metal cations from being oxidized during the reaction, pure nitrogen gas was continuously introduced into the reactor throughout the process. A certain volume of deionized water and ammonia water were added to the reactor as the reaction base solution.

[0059] A salt solution, ammonia solution, and alkali solution were simultaneously fed into a reactor in a co-precipitation process. The stirring speed of the reactor was controlled at 600 rpm, and the pump speed of the NaOH solution entering the reactor was adjusted to stabilize the pH of the solution in the reactor at 11.5. After 20 hours of reaction, the stirring speed was reduced to 300 rpm, and the liquid feeding was stopped. The reaction solution was aged for 4 hours, centrifuged, and filtered to obtain the precipitate. The precipitate was washed multiple times with deionized water until neutral, and then dried in a constant temperature vacuum drying oven at 80℃ to obtain a Ni-containing product. 0.9 Mn 0.1 (OH)2 precursor.

[0060] The dried precursor, LiOH·H2O, nano-WO3, and nano-TiO2 were mixed evenly in a molar ratio of 1:1.25:0.005:0.005 and then sintered in a high-temperature furnace under an O2 atmosphere. The specific sintering procedure was as follows: the temperature was increased from room temperature to 550℃ at a rate of 3℃ / min and held for 5 hours; then increased to 800℃ at a rate of 3℃ / min and held for 15 hours; then increased to 825℃ at a rate of 3℃ / min and held for 2 hours; finally, air cooling was turned on, and the mixture was removed and ground at 400℃ to obtain a product with an average chemical formula of Li. 1.05 (Ni 0.9 Mn 0.09 W 0.005 Ti 0.005 ) 0.95 O2-free cobalt-rich lithium-nickel layered oxide cathode material.

[0061] Example 5

[0062] A salt solution with a total concentration of 6 mol / L (Ni:Mn = 0.95:0.05), a 10.0 mol / L NaOH solution, and an 8 mol / L ammonia solution were prepared. The reactor temperature was set at 55℃. To prevent the metal cations from being oxidized during the reaction, pure nitrogen gas was continuously introduced into the reactor throughout the process. A certain volume of deionized water and ammonia water were added to the reactor as the reaction base solution.

[0063] A salt solution, ammonia solution, and alkali solution were simultaneously fed into a reactor in a co-precipitation process. The stirring speed of the reactor was controlled at 1000 rpm, and the pump speed of the NaOH solution entering the reactor was adjusted to stabilize the pH of the solution at 12. After 40 hours of reaction, the stirring speed was reduced to 500 rpm, and the liquid feeding was stopped. The reacted solution was aged for 24 hours, centrifuged, and filtered to obtain the precipitate. The precipitate was washed multiple times with deionized water until neutral, and then dried in a constant temperature vacuum drying oven at 120℃ to obtain a Ni-containing product. 0.95 Mn 0.05 (OH)2 precursor.

[0064] The dried precursor, LiOH·H2O, nano-Y2O3, nano-La2O3, and nano-Sb2O5 were mixed evenly in a molar ratio of 1:1.1:0.002:0.004:0.004 and then sintered in a high-temperature furnace under an O2 atmosphere. The specific sintering procedure was as follows: the temperature was increased from room temperature to 600℃ at a rate of 5℃ / min and held for 3 hours; then increased to 700℃ at a rate of 5℃ / min and held for 25 hours; then increased to 725℃ at a rate of 5℃ / min and held for 5 hours; finally, air cooling was turned on, and the mixture was removed and ground at 300℃ to obtain the product with an average chemical formula of Li. 1.02 (Ni 0.95 Mn 0.04 Y 0.002 La 0.004 Sb 0.004 ) 0.98 O2-free cobalt-rich lithium-nickel layered oxide cathode material.

[0065] Example 6

[0066] A 2 mol / L salt solution containing nickel and manganese in a Ni:Mn ratio of 0.82:0.18, a 2 mol / L Na₂CO₃ solution, and a 2 mol / L ammonia solution were prepared. The reactor temperature was set at 40°C. To prevent oxidation of the metal cations during the reaction, pure argon gas was continuously introduced into the reactor throughout the process. A certain volume of deionized water and ammonia water were added to the reactor as the reaction base solution.

[0067] A salt solution, ammonia solution, and alkali solution were simultaneously fed into a reactor in a co-precipitation process. The stirring speed of the reactor was controlled at 500 rpm, and the pump speed of the NaOH solution entering the reactor was adjusted to stabilize the pH of the solution in the reactor at 8. After 5 hours of reaction, the stirring speed was reduced to 200 rpm, and the liquid feeding was stopped. The solution was aged for 1 hour, centrifuged, and filtered to obtain the precipitate. The precipitate was washed multiple times with deionized water until neutral, and then dried in a constant temperature vacuum drying oven at 60℃ to obtain a Ni-containing product. 0.82 Mn 0.18 (OH)2 precursor.

[0068] The dried precursor was mixed with LiOH·H2O at a molar ratio of 1:1.2 and then sintered in a high-temperature furnace under an O2 atmosphere. The specific sintering procedure was as follows: the temperature was increased from room temperature to 500℃ at a rate of 7℃ / min and held for 8 hours; then increased to 1000℃ at a rate of 7℃ / min and held for 10 hours; then increased to 1050℃ at a rate of 7℃ / min and held for 1 hour; air cooling was then turned on, and the mixture was removed and ground at 600℃ to obtain the product with an average chemical formula of Li. 1.1 (Ni 0.82 Mn0.18 ) 0.9 O2-free cobalt-rich lithium-nickel layered oxide cathode material.

[0069] Example 7

[0070] A salt solution with a total concentration of 2 mol / L (Ni:Mn = 0.83:0.17), a 4.0 mol / L NaOH solution, and a 4 mol / L ammonia solution were prepared. C₂H₅NNbO₄ with a molar fraction of 0.005 was dissolved in the salt solution. The reactor temperature was set at 55℃. To prevent oxidation of the metal cations during the reaction, pure nitrogen gas was continuously introduced into the reactor throughout the process. A certain volume of deionized water and ammonia water were added to the reactor as the reaction base solution.

[0071] A salt solution, ammonia solution, and alkali solution were simultaneously fed into a reactor in a co-precipitation process. The stirring speed of the reactor was controlled at 600 rpm, and the pump speed of the NaOH solution entering the reactor was adjusted to stabilize the pH of the solution in the reactor at 11.2. After 20 hours of reaction, the stirring speed was reduced to 300 rpm, and the liquid feeding was stopped. The reaction solution was aged for 4 hours, centrifuged, and filtered to obtain the precipitate. The precipitate was washed multiple times with deionized water until neutral, and then dried in a constant temperature vacuum drying oven at 80℃ to obtain a Ni-containing product. 0.83 Mn 0.165 Nb 0.005 (OH)2 precursor.

[0072] The dried precursor was mixed with LiOH·H2O at a molar ratio of 1:1.15 and then sintered in a high-temperature furnace under an O2 atmosphere. The specific sintering procedure was as follows: the temperature was increased from room temperature to 550℃ at a rate of 3℃ / min and held for 5 hours; then increased to 850℃ at a rate of 3℃ / min and held for 15 hours; then increased to 875℃ at a rate of 3℃ / min and held for 2 hours; finally, air cooling was turned on, and the mixture was removed and ground at 400℃ to obtain the product with an average chemical formula of Li. 1.05 (Ni 0.83 Mn 0.165 Nb 0.005 ) 0.95 O2-free cobalt-rich lithium-nickel layered oxide cathode material.

[0073] Example 8

[0074] A salt solution with a total concentration of 2 mol / L (Ni:Mn = 0.81:0.19), a 4.0 mol / L NaOH solution, and a 4 mol / L ammonia solution were prepared. Zr(SO4)2·4H2O with a molar fraction of 0.01 was dissolved in the salt solution. The reaction vessel temperature was set at 55℃. To prevent the metal cations from being oxidized during the reaction, pure nitrogen gas was continuously introduced into the reaction vessel throughout the process. A certain volume of deionized water and ammonia water were added to the reaction vessel as the reaction base solution.

[0075] A salt solution, ammonia solution, and alkali solution were simultaneously fed into a reactor in a co-precipitation process. The stirring speed of the reactor was controlled at 600 rpm, and the pump speed of the NaOH solution entering the reactor was adjusted to stabilize the pH of the solution in the reactor at 11.2. After 20 hours of reaction, the stirring speed was reduced to 300 rpm, and the liquid feeding was stopped. The reaction solution was aged for 4 hours, centrifuged, and filtered to obtain the precipitate. The precipitate was washed multiple times with deionized water until neutral, and then dried in a constant temperature vacuum drying oven at 80℃ to obtain a Ni-containing product. 0.81 Mn 0.18 Zr 0.01 (OH)2 precursor.

[0076] The dried precursor was mixed with LiOH·H2O at a molar ratio of 1:1.2 and then sintered in a high-temperature furnace under an O2 atmosphere. The specific sintering procedure was as follows: the temperature was increased from room temperature to 550℃ at a rate of 3℃ / min and held for 5 hours; then increased to 800℃ at a rate of 3℃ / min and held for 15 hours; then increased to 825℃ at a rate of 3℃ / min and held for 2 hours; finally, air cooling was turned on, and the mixture was removed and ground at 500℃ to obtain the product with an average chemical formula of Li. 1.08 (Ni 0.81 Mn 0.18 Zr 0.01 ) 0.92 O2-free cobalt-rich lithium-nickel layered oxide cathode material.

[0077] Example 9

[0078] A 2 mol / L salt solution containing nickel and manganese in a Ni:Mn ratio of 0.82:0.18, a 4.0 mol / L NaOH solution, and a 4 mol / L ammonia solution were prepared. WO3 with a molar fraction of 0.001 was dissolved in the alkaline solution. The reactor temperature was set at 55°C. To prevent oxidation of the metal cations during the reaction, pure nitrogen gas was continuously introduced into the reactor throughout the process. A certain volume of deionized water and ammonia water were added to the reactor as the reaction base solution.

[0079] A salt solution, ammonia solution, and alkali solution were simultaneously fed into a reactor in a co-precipitation process. The stirring speed of the reactor was controlled at 600 rpm, and the pump speed of the NaOH solution entering the reactor was adjusted to stabilize the pH of the solution in the reactor at 11.5. After 30 hours of reaction, the stirring speed was reduced to 300 rpm, and the liquid feeding was stopped. The reaction solution was aged for 4 hours, centrifuged, and filtered to obtain the precipitate. The precipitate was washed multiple times with deionized water until neutral, and then dried in a constant temperature vacuum drying oven at 80℃ to obtain a Ni-containing product. 0.80 Mn 0.199 W 0.001 (OH)2 precursor.

[0080] The dried precursor was mixed with LiOH·H2O at a molar ratio of 1:1.15 and then sintered in a high-temperature furnace under an O2 atmosphere. The specific sintering procedure was as follows: the temperature was increased from room temperature to 550℃ at a rate of 3℃ / min and held for 5 hours; then increased to 720℃ at a rate of 3℃ / min and held for 15 hours; then increased to 755℃ at a rate of 3℃ / min and held for 2 hours; finally, air cooling was turned on, and the mixture was removed and ground at 400℃ to obtain the product with an average chemical formula of Li. 1.05 (Ni 0.80 Mn 0.199 W 0.001 ) 0.95 O2-free cobalt-rich lithium-nickel layered oxide cathode material.

[0081] Table 1. Comparison of half-cell performance of assembled coin cells with different modified samples based on commercial electrolytes, at voltages of 2.7–4.4 V, initial activation at 0.1 C, and cycling at 1 C (1C = 180 mAh / g).

[0082]

Claims

1. A cobalt-free, lithium-rich, ultra-high nickel cathode material with a composite domain structure, characterized in that, The cathode material is LiNi with the R-3m space group. a M b Mn (1-a-b) It is composed of O2 and Li2MnO3 with C2 / m space group, and its general chemical formula is xLi2MnO3·(1-x)LiNi. a M b Mn (1-a-b) O2, 0 < x ≤ 0.2, 0.8 ≤ a < 1, 0 ≤ b ≤ 0.03; M is selected from one or more of Mg, Al, Ca, Ti, Zn, Y, Zr, Nb, Mo, Sb, La, Ta, and W.

2. The method for preparing a cobalt-free, lithium-rich, ultra-high nickel cathode material with a composite domain structure as described in claim 1, characterized in that, Includes the following steps: (1) Prepare a soluble nickel-manganese mixed salt solution, an alkaline solution, and an ammonia complexing agent solution of a certain concentration; (2) Add a certain volume of deionized water and ammonia water to the reactor as the reaction base liquid, and use a constant temperature water bath to control the temperature of the co-precipitation reactor; the mixed salt solution, ammonia solution and alkaline solution are simultaneously flowed into the reactor in a co-flow manner to carry out the co-precipitation reaction, and the stirring speed and pH of the reactor are controlled. After a certain reaction time, a cobalt-free ultra-high nickel precursor mixed solution is obtained. (3) After aging the cobalt-free ultra-high nickel precursor mixture obtained in step (2) for a certain period of time, filter and vacuum dry it to obtain the designed cobalt-free ultra-high nickel precursor. (4) The precursor powder obtained in step (3) is mixed evenly with a certain proportion of lithium source in a three-dimensional mixer and then placed in a high-temperature sintering furnace. Under an oxygen atmosphere, it is sintered in three stages according to a certain procedure. After sintering, it is cooled down to a certain temperature by air cooling and then taken out of the high-temperature furnace to obtain a cobalt-free lithium-rich high-nickel cathode material with a composite crystal domain structure. M is selected from one or more of Mg, Al, Ca, Ti, Zn, Y, Zr, Nb, Mo, Sb, La, Ta, and W. The doping element can be introduced during the co-precipitation process or the lithium sintering process, that is, the required doping element is added to the nickel-manganese mixed salt or alkaline solution in step (1), or added during the lithium preparation in step (4) and then sintered together.

3. The method according to claim 2, characterized in that, In step (1), the molar ratio of nickel and manganese in the nickel-manganese mixed salt solution is 0.8-0.95:0.05-0.2, and the sum of the two is 1.

4. The method according to claim 2, characterized in that, In step (1), the soluble nickel salt used can be one or more of nickel acetate, nickel nitrate, nickel chloride, nickel sulfate, and nickel oxalate; the soluble manganese salt used can be one or more of manganese acetate, manganese nitrate, manganese chloride, manganese sulfate, and manganese oxalate; the alkaline solution used can be one or more of potassium hydroxide, potassium carbonate, sodium carbonate, and sodium hydroxide; and the lithium source used can be one or more of lithium hydroxide, lithium carbonate, lithium oxalate, lithium nitrate, and lithium sulfate.

5. The method according to claim 2, characterized in that, The total concentration of nickel and manganese in the mixed salt solution in step (1) is 2-6 mol / L; the concentration of alkali is 2-10 mol / L; and the concentration of complexing agent ammonia is 2-8 mol / L.

6. The method according to claim 2, characterized in that, In step (2), the pH of the co-precipitation reaction system is 8-12, the temperature of the reaction vessel is 40-70℃, the speed of the stirring paddle is 500-1000 rpm, the co-precipitation reaction time is 5-40h, the aging time is 1-24h, the stirring paddle speed during the aging process is 200-500 rpm, and the constant temperature vacuum drying temperature in step (3) is 60-120℃.

7. The method according to claim 2, characterized in that, In step (4), the molar ratio of the precursor to the lithium source is 1:(1.1~1.40); the sintering method described in step (4) is a three-step segmented sintering process. The first step sintering temperature is 500-600℃, the heating rate is 1-7℃ / min, and the holding time is 3-8h; the second step sintering temperature is 700-1000℃, the heating rate is 1-7℃ / min, and the holding time is 10-25h; the third step sintering is carried out at 750-1050℃ for 1-5h, and the heating rate is 1-3℃ / min. Preferably, during the high-temperature sintering process, the second step sintering temperature is adjusted according to the different nickel-manganese composition of the precursor so that the lithium source migrates to the transition metal layer of the cathode material. Generally, the sintering temperature decreases accordingly as the nickel content increases.

8. The method according to claim 7, characterized in that, In step (4), the air cooling is used to accelerate the cooling down to a certain temperature of 300-600℃ (the air cooling is achieved by using a wind-blown calcination device to cool the device down to 300-600℃, thereby cooling the product down to 300-600℃). This rapid cooling reduces material stress and residual lithium on the surface of the cathode material, preventing surface reconstruction due to residual lithium. On the other hand, it enables the control of the proportion and distribution of Li2MnO3 crystal domains.

9. The cobalt-free, lithium-rich, ultra-high nickel cathode material with a composite domain structure prepared by the method according to any one of claims 1-8.

10. The application of the composite domain structure cobalt-free lithium-rich ultra-high nickel cathode material prepared according to any one of claims 1-8 as a cathode material for lithium-ion batteries.

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