Rare earth element dual-modified lithium-rich manganese-based positive electrode material and preparation method thereof

Abstract

The invention relates to the field of battery positive electrode materials, in particular to a rare earth element double-modified lithium-rich manganese-based (LRMO) positive electrode material and a preparation method thereof. The preparation method comprises the following steps: preparing a salt solution from lithium, manganese, cobalt, nickel and gadolinium; preparing precursor powder from the uniformly mixed solution through a spray pyrolysis method; placing the precursor powder in a muffle furnace for high-temperature calcination; adding ethanol into the gadolinium-doped lithium-rich manganese-based positive electrode material, and then adding lanthanum phosphate powder to obtain a mixed solution; and drying the mixed solution to obtain mixed powder, and carrying out secondary sintering to obtain the double-modified lithium-rich manganese-based positive electrode material. Release of lattice oxygen is inhibited, so that the structure is more stable, and the overall cycling stability of the battery is improved; the first coulombic efficiency and the specific discharge capacity are improved; the highest initial coulombic efficiency of the lithium-rich manganese-based positive electrode material modified by the double rare earth elements can reach 85.06%, and the capacity retention ratio can reach 99.92% after 400 times of charging and discharging cycles at 1C current.

Description

Technical Field

[0001] The present invention relates to the field of battery positive electrode materials, and in particular to a rare earth element doubly modified lithium-rich manganese-based positive electrode material and a preparation method thereof. Technical Background

[0002] As one of the most widely used and common types of batteries on the market, lithium-ion batteries have the advantages of high energy density, long life, and fast charging speed. At present, the key part that restricts the performance of battery specific capacity and energy density is the positive electrode material. Among them, lithium-rich manganese-based positive electrode materials have become a popular research direction at present because of their obvious advantages such as high specific capacity (above 250mAh / g), wide voltage window (2-4.8V), and energy density of more than 500Wh / kg. Although lithium-rich manganese-based positive electrode materials have broad research prospects, some problems have gradually been found with the deepening of research: such as capacity decay and structural damage are prone to occur during the charging and discharging process, resulting in poor cycle performance. During the first charge, although a higher charging voltage can be achieved and some inert components can be activated, in the subsequent discharge process, lithium ions cannot return to their original positions after deintercalation, resulting in low initial coulombic efficiency. During the cycle, the layered structure is transformed into a spinel structure, resulting in voltage decay. This has greatly affected its performance and limited its development space.

[0003] In the document with application number "CN201910747712.2", a preparation method of a tin-doped lithium-rich manganese-based positive electrode material is disclosed, which uses a mixed salt solution prepared with nickel, cobalt, manganese and tin salts and forms a precursor precipitate by coprecipitation, and then mixes with a lithium source compound and obtains a tin-doped lithium-rich manganese-based positive electrode material by segmented heat treatment. In the document with application number "CN202111179900.3", a magnesium aluminate-coated lithium-rich manganese-based positive electrode material is disclosed, characterized in that the interior of the material is a lithium-rich manganese-based positive electrode, and the outer coating layer is magnesium aluminate. The coating is coated by a secondary sintering method. The previous single or bimetallic modification strategies have not significantly improved the performance of lithium-rich manganese-based positive electrode materials. Experts and scholars have also proposed a solution that combines doping and coating. For example, in the document with application number "CN201910747712.2", a doped and coated lithium-rich manganese-based positive electrode material is disclosed, but the performance improvement after modification is still limited. When discharged at a current of 0.1C, the first discharge specific capacity is only 268.6mAh / g. Summary of the invention

[0004] The present invention provides a rare earth element dual modified lithium-rich manganese-based positive electrode material and a preparation method thereof, so as to overcome the problems of limited performance improvement after modification, low first discharge specific capacity and poor cycle stability existing in the prior art.

[0005] In order to achieve the purpose of the present invention, the technical solution provided by the present invention is: a method for preparing a rare earth element dual modified lithium-rich manganese-based positive electrode material, comprising the following steps:

[0006] Step 1: adding acetates of lithium, manganese, cobalt, nickel and gadolinium into deionized water and mixing them evenly, adding citric acid monohydrate as a complexing agent to the complexing cations to obtain a salt solution, and stirring evenly;

[0007] Step 2, preparing precursor powder by spray pyrolysis of the uniformly mixed solution;

[0008] Step 3, placing the precursor powder in a muffle furnace for high-temperature calcination to obtain a gadolinium-doped lithium-rich manganese-based positive electrode material;

[0009] Step 4: add the gadolinium-doped lithium-rich manganese-based cathode material to an ethanol solution, perform ultrasound for 30 to 60 minutes, add lanthanum phosphate powder, and continue stirring for 4 to 8 hours to obtain a mixed solution;

[0010] Step 5: Place the mixed solution in a blast oven and dry it to obtain a mixed powder. Place the mixed powder in a muffle furnace for secondary sintering. Then, cool it to room temperature with the furnace to obtain a double-modified lithium-rich manganese-based positive electrode material.

[0011] Furthermore, in the salt solution of step 1, the concentration of lithium acetate is 19.12 g / L, the concentration of nickel acetate is 4.85 g / L, the concentration of cobalt acetate is 4.85 g / L, the concentration of manganese acetate is 19.4-19.7 g / L, the concentration of gadolinium acetate is 0.26-0.52 g / L, and the concentration of citric acid is 0.15-0.3 mol / L.

[0012] Furthermore, the stirring rate of the above step 1 is 400-600 R / Min, and the stirring time is 1-3 hours.

[0013] Furthermore, during the spraying process of the above step 2, the temperatures of the inlet and outlet are set to 230° C. and 100-130° C. respectively, and the peristaltic speed is 15-20 rpm.

[0014] Furthermore, the sintering process in the above step three is specifically to increase the temperature to 1000° C. at 3° C. / min and keep the temperature for 20 minutes.

[0015] Cool naturally to room temperature.

[0016] Furthermore, the lanthanum phosphate powder in the above step 4 is 1 to 3 wt % of the mass of the lithium-rich manganese-based positive electrode material, the ultrasonic time is 30 to 60 minutes, and the stirring time is 4 to 8 hours.

[0017] Furthermore, the secondary sintering temperature in the above step 5 is 400-500° C., and the time is 2-4 hours.

[0018] Furthermore, the rare earth element doubly modified lithium-rich manganese-based positive electrode material prepared by the above preparation method.

[0019] Compared with the prior art, the advantages of the present invention are:

[0020] 1. The doping and coating elements gadolinium and lanthanum used in the present invention are both rare earth elements. Rare earth elements have high charge. Gd atoms are doped into the bulk phase and act as a pillar in the structure. The binding energy of Gd-O is higher than that of Mn-O, and the stability is high. It can effectively inhibit the escape of oxygen, thereby improving the initial coulomb efficiency and subsequent structural decay; the Gd ion radius is large, which can reduce the harmful phase transition from layered to spinel during the cycle to stabilize the layered phase. Gd doping also inhibits the migration of Ni2+ into the Li layer, reduces the lithium-nickel mixing in the material, and then inhibits the Jahn-Te l ler effect, stabilizes the layered structure after the cycle, broadens the Li+ transmission channel, and is conducive to ion migration. And doping with rare earth elements will produce special energy levels, which effectively changes the conductivity of the material. During the cycle, due to the doping of gadolinium, the gadolinium-oxygen bond energy is very strong after bonding with oxygen and is not easily destroyed, which inhibits the release of lattice oxygen, makes the structure more stable, and improves the overall cycle stability of the battery.

[0021] 2. The lanthanum phosphate layer coated on the surface of the lithium-rich manganese-based positive electrode material of the present invention can keep the surface of the material stable, reduce the side reaction between the bulk phase of the lithium-rich manganese-based positive electrode material and the electrolyte, and protect it from corrosion by the electrolyte. At the same time, the lanthanum phosphate layer has a strong adhesion ability, so a more uniform coating effect can be obtained, effectively inhibiting the adverse phase change generated from the surface during the cycle, thereby improving the cycle stability. The coating layer can also inhibit the irreversible oxygen release during the first cycle of the lithium-rich manganese-based positive electrode material, thereby improving the first coulomb efficiency and discharge specific capacity.

[0022] 3. The present invention effectively improves the cycle stability and first coulomb efficiency of lithium-rich manganese-based cathode materials by bulk doping with gadolinium and surface coating with lanthanum phosphate. The first coulomb efficiency of lithium-rich manganese-based cathode materials modified with double rare earth elements can reach up to 85.06%, and the capacity retention rate can reach 99.92% after 400 charge and discharge cycles at 1C current. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a comparison chart of the first charge and discharge capacity of Examples 1, 2, 3 and Comparative Example 1;

[0024] Figure 2 1c 400 cycle specific capacity performance diagram of Examples 1, 2, 3 and Comparative Example 1;

[0025] Figure 3 1c 400-cycle discharge median voltage cycle performance diagram of Example 2 and Comparative Example 1;

[0026] Figure 4 1c 400 cycle specific energy performance diagram of Examples 1, 2, 3 and Comparative Example 1;

[0027] Figure 5 It is the rate performance diagram of Example 2 and Comparative Example 1;

[0028] Figure 6 The recovery diagram after discharge at different rates in Example 2;

[0029] Figure 7 It is the CV diagram of Comparative Example 1;

[0030] Figure 8 It is the CV diagram of Example 2;

[0031] Fig. 9 2 are EIS graphs of Example 2 and Comparative Example 1;

[0032] Fig.10 The XRD diagrams of Example 2 and Comparative Example 1 are shown;

[0033] Fig.11 HRTEM image of Example 2;

[0034] Fig.12 This is a scanned image of the mapping surface of Example 2. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0036] Example 1: A method for preparing a rare earth element dual-modified lithium-rich manganese-based positive electrode material Li 1.236Ni0.13Co0.13Mn0.535Gd0.005O2@LaPO4, comprising the following steps:

[0037] Step 1, weighing acetate containing Li, Ni, Co, Mn, and Gd elements according to the molar ratio shown in the chemical formula, dissolving them in deionized water, and preparing a mixed salt solution with a concentration of 0.15 mol / L, wherein the concentration of lithium acetate is 19.12 g / L, the concentration of nickel acetate is 4.85 g / L, the concentration of cobalt acetate is 4.85 g / L, the concentration of manganese acetate is 19.66 g / L, and the concentration of gadolinium acetate is 0.26 g / L; and adding monohydrated citric acid as a complexing agent with a concentration of 0.3 mol / L; placing the mixed solution in a magnetic stirrer, setting the speed to 500 r / min, and stirring for 1 hour.

[0038] Step 2: The mixed solution is granulated through a spray dryer to prepare a precursor powder: the liquid feeding rate is set to 10-15 ml / min, the spray dryer inlet air temperature is 230°C, and the outlet air temperature is maintained between 100 and 120°C.

[0039] Step 3: Load the precursor powder into an alumina crucible, raise the temperature to 1000° C. at a rate of 3° C. / min in a muffle furnace, keep the temperature for 20 minutes, and cool naturally to obtain a gadolinium-doped lithium-rich manganese-based positive electrode material.

[0040] Step 4: Weigh 1 g of gadolinium-doped lithium-rich manganese-based cathode material, add it to 50 ml of ethanol solution, ultrasonicate it for 60 minutes, add 1 wt% (10 mg) of lanthanum phosphate powder, and continue stirring for 4 hours to obtain a mixed solution.

[0041] Step 5. Place the mixed solution in a blast oven, set it to 80°C and continue drying for 8 hours to obtain a mixed powder; place the mixed powder in a muffle furnace, raise the temperature to 400°C at a rate of 3°C / min, keep it warm for 3 hours, and naturally cool it to room temperature in the furnace to obtain a lanthanum phosphate-coated gadolinium-doped dual-modified lithium-rich manganese-based positive electrode material.

[0042] Example 2: Preparation of rare earth element dual modified lithium-rich manganese-based positive electrode material LRMO@LaPO4. The preparation method is basically the same as that of Example 1, except that the LaPO4 added in step 4 is 2 wt% (20 mg).

[0043] Example 3: Preparation of rare earth element dual modified lithium-rich manganese-based positive electrode material LRMO@LaPO4. The preparation method is basically the same as that of Example 1, except that the LaPO4 added in step 4 is 3wt% (30mg).

[0044] Comparative Example: A method for preparing a lithium-rich manganese-based positive electrode material Li 1.236Ni0.13Co0.13Mn0.54O2 comprises the following steps:

[0045] Step 1: weigh acetate containing Li, Ni, Co, and Mn elements according to the molar ratio shown in the chemical formula, dissolve them in deionized water, and prepare a mixed salt solution with a concentration of 0.15 mol / L, wherein the concentration of lithium acetate is 19.12 g / L, the concentration of nickel acetate is 4.85 g / L, the concentration of cobalt acetate is 4.85 g / L, and the concentration of manganese acetate is 19.85 g / L, and the mixed salt solution with a concentration of 0.15 mol / L is prepared; and citric acid is added as a complexing agent with a concentration of 0.3 mol / L; the mixed solution is placed in a magnetic stirrer, the speed is set to 500 r / min, and stirred for 1 hour.

[0046] Step 2: The mixed solution is granulated into a precursor by a spray dryer, the liquid feeding rate is 10-15 ml / min, the spray dryer air inlet temperature is 230°C, and the air outlet temperature is maintained between 100 and 120°C.

[0047] Step 3: The precursor powder obtained by spray pyrolysis of the mixed solution is loaded into an alumina crucible, and the temperature is raised to 1000° C. at a rate of 3° C. / min in a box furnace, kept at that temperature for 20 min, and naturally cooled to obtain a lithium-rich manganese-based positive electrode material.

[0048] Comparative Example 2: A method for preparing a gadolinium-doped modified lithium-rich manganese-based positive electrode material Li 1.236Ni0.13Co0.13Mn0.535Gd0.005O2. The preparation method is basically the same as that of the comparative example, except that in step 1, the concentration of manganese acetate is 19.66 g / L, and the concentration of gadolinium acetate is 0.26 g / L.

[0049] Comparative Example 3: A method for preparing a gadolinium-doped modified lithium-rich manganese-based positive electrode material Li1.236Ni0.13Co0.13Mn0.53Gd0.01O2. The preparation method is basically the same as that of the comparative example, except that in step 1, the concentration of manganese acetate is 19.48 g / L, and the concentration of gadolinium acetate is 0.52 g / L.

[0050] The test results are as follows:

[0051] like Figure 1 As shown, at a voltage of 2 to 4.8 V and a current of 0.1 C, the first discharge specific capacities of the comparative example, example 1, example 2, and example 3 are 275.81 mAh / g, 286.31 mAh / g, 288.41 mAh / g, and 269.81 mAh / g, respectively, and the first coulombic efficiencies are 73.53%, 83.02%, 83.18%, and 82.67%, respectively. The first coulombic efficiencies of examples 1, 2, and 3 are all higher than those of the comparative example, because the gadolinium ions doped in the bulk phase form gadolinium oxygen bonds with oxygen atoms, stabilizing the lattice oxygen, and the lanthanum phosphate layer coated on the surface reduces the negative interface reaction between the positive electrode material and the electrolyte, and inhibits the escape of oxygen during discharge. The first coulombic efficiency of example 2 is the highest, indicating that the optimal coating amount is 2 wt%. The first discharge specific capacity and the first coulombic efficiency of example 3 are lower because the coating amount is too much, resulting in a thicker coating layer, which inhibits the reaction and ion transmission of the positive electrode material and the electrolyte.

[0052] like Figure 2As shown, after 400 charge and discharge cycles at 2-4.8V voltage and 1C current, the discharge specific capacities of the comparative example, example 1, example 2, and example 3 are 113.16, 191.90, 213.24, and 206.30 mAh / g, respectively, and the corresponding capacity retention rates are 53.80%, 87.80%, 97.22%, and 99.92%, respectively. The improvement in capacity retention rate is due to the fact that gadolinium ion doping stabilizes lattice oxygen and the lanthanum phosphate coating layer inhibits harmful side reactions between the positive electrode material and the electrolyte.

[0053] like Figure 3 As shown, the median voltages of Example 2 and the comparative example after 400 cycles at 1C current and 2-4.8V voltage were 2.875 and 2.665V, respectively, and the voltage decay per cycle was 1.70mV and 2.26mV. This shows that gadolinium ion doping plays a supporting role in the material structure, stabilizes the layered structure of the material, and inhibits subsequent undesirable phase changes. The surface lanthanum phosphate coating also inhibits the structural decay of the positive electrode material from the surface to the inside, thereby stabilizing the discharge median voltage.

[0054] like Figure 4 As shown, the discharge specific energies of the comparative example, embodiment 1, embodiment 2, and embodiment 3 after 400 cycles at 1C current and 2-4.8V voltage are 315.70, 565.89, 638.84, and 628.51Wh / Kg, respectively. The embodiments are all higher than the comparative example, mainly because the discharge specific capacity is maintained while the voltage decay is suppressed.

[0055] like Figure 5 As shown, they are rate performance diagrams of the comparative example and embodiment 2, wherein the specific capacities of 0.1C, 0.5C, 1C, 2C, and 5C of the comparative example are 264.07mAh / g, 212.72mAh / g, 184.02mAh / g, 157.69mAh / g, and 120.94mAh / g, respectively, and those of embodiment 2 are 284.56mAh / g, 233.14mAh / g, 206.20mAh / g, 179.74mAh / g, and 147.76mAh / g, respectively. The discharge specific capacity of embodiment 2 at different times is higher than that of the comparative example.

[0056] like Figure 6 As shown in the rate performance diagram of Example 2, after Example 2 is discharged at different currents (0.1C, 0.5C, 1C, 2C, 5C), the 0.1C discharge specific capacity is compared with the initial 0.1C discharge specific capacity, and the recovery rate is 99.6%. And after the next 20 cycles, the retention rate is 99%, which is almost not attenuated, indicating that it has stability under different current charge and discharge environments.

[0057] like Figure 7 , Figure 8As shown, the potential difference (ΔV) between the oxidation peak and the reduction peak of Example 2 is 0.3 V, which is lower than 0.34 V of the comparative example. The double modification of the surface by gadolinium doping and lanthanum phosphate coating can effectively reduce the polarization phenomenon of the electrode material during the charge and discharge process and improve the structural stability of the lithium-rich manganese-based material.

[0058] like Fig. 9 As shown, these are EIS graphs of the comparative example and embodiment 2 after 400 cycles. The radius of the semicircle in the high-frequency region of embodiment 2 is smaller than that of the comparative example. The semicircle in the high-frequency region is related to the charge transfer resistance (Rct), indicating that gadolinium doping improves the migration ability of lithium ions in the lithium-rich manganese-based positive electrode material, and lanthanum phosphate coating inhibits the adverse phase change of the positive electrode material during the cycle, stabilizes the material structure, and maintains the lithium ion transport channel of the material.

[0059] like Fig.10 As shown, the XRD diagrams of the comparative example and Example 2, after double modification of gadolinium doping and lanthanum phosphate surface coating, the main diffraction peaks of Example 2 and the comparative example are basically the same, both showing a-NaFeO2 structure of the R3m space group of the hexagonal layered material (LiMO2 component). It shows that the double modification of rare earth elements will not change the structure of the lithium-rich manganese-based positive electrode material, and a new characteristic peak can be observed in Example 2 at 28-29°. The PFD card is retrieved, indicating that this is the characteristic peak of the LaPO4 phase, indicating that the lanthanum phosphate coating is successful.

[0060] like Fig.11 As shown, it is the HRTEM test image of the comparative example and embodiment 2. From the figure, we can see the obvious bulk layered structure and the apparent lanthanum phosphate coating layer. The surface area is smooth and the coating is uniform. The inverse Fourier transform is performed on the bulk area, and the interlayer spacing is measured to be 0.42nm, corresponding to the (020) plane of the lithium-rich manganese-based positive electrode material.

[0061] like Fig.12 As shown, it is a mapping surface scan of the HRTEM test of Example 2. It can be seen that the elements of lithium, nickel, cobalt, manganese and gadolinium are evenly distributed, while the lanthanum element is mostly in the surface area, indicating that gadolinium doping has been successfully introduced, indicating that the lanthanum phosphate coating effect is complete.

[0062] The cycle performance of the above embodiments and comparative examples is listed in Table 1, and the capacity performance at different rates is listed in Table 2.

[0063] Table 1

[0064]

[0065] Table 2

[0066]

[0067] In summary, embodiment 2 is the best embodiment.

[0068] The above are only specific embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a rare earth element dual modified lithium-rich manganese-based positive electrode material, characterized in that: The following steps are involved: Step 1: adding acetates of lithium, manganese, cobalt, nickel and gadolinium into deionized water and mixing them evenly, adding citric acid monohydrate as a complexing agent to the complexing cations to obtain a salt solution, and stirring evenly; Step 2, preparing precursor powder by spray pyrolysis of the uniformly mixed solution; Step 3, placing the precursor powder in a muffle furnace for high-temperature calcination to obtain a gadolinium-doped lithium-rich manganese-based positive electrode material; Step 4: add the gadolinium-doped lithium-rich manganese-based cathode material to an ethanol solution, perform ultrasound for 30 to 60 minutes, add lanthanum phosphate powder, and continue stirring for 4 to 8 hours to obtain a mixed solution; Step 5: Place the mixed solution in a blast oven and dry it to obtain a mixed powder. Place the mixed powder in a muffle furnace for secondary sintering. Then, cool it to room temperature with the furnace to obtain a double-modified lithium-rich manganese-based positive electrode material.

2. The method for preparing a rare earth element dual modified lithium-rich manganese-based positive electrode material according to claim 1, characterized in that: In the step 1, the concentration of lithium acetate in the salt solution is 19.12 g / L, the concentration of nickel acetate is 4.85 g / L, the concentration of cobalt acetate is 4.85 g / L, the concentration of manganese acetate is 19.4-19.7 g / L, the concentration of gadolinium acetate is 0.26-0.52 g / L; and the concentration of citric acid is 0.15-0.3 mol / L.

3. The method for preparing a rare earth element dual modified lithium-rich manganese-based positive electrode material according to claim 2, characterized in that: In the step 1, the stirring rate is 400-600 R / Min, and the stirring time is 1-3 hours.

4. The method for preparing a rare earth element dual modified lithium-rich manganese-based positive electrode material according to claim 3, characterized in that: In the step 2, the temperatures of the inlet and outlet during the spraying process are set to 230°C and 100-130°C, respectively, and the peristaltic speed is 15-20 rpm.

5. The method for preparing a rare earth element dual modified lithium-rich manganese-based positive electrode material according to claim 4, characterized in that: In the step 3, the sintering process is specifically to heat up to 1000° C. at 3° C. / min and keep the temperature for 20 min; and naturally cool down to room temperature.

6. The method for preparing a rare earth element dual modified lithium-rich manganese-based positive electrode material according to claim 5, characterized in that: In the step 4, the lanthanum phosphate powder is 1-3 wt % of the lithium-rich manganese-based positive electrode material, the ultrasonic time is 30-60 min, and the stirring time is 4-8 hours.

7. The method for preparing a rare earth element dual modified lithium-rich manganese-based positive electrode material according to claim 6, characterized in that: In the step 5, the secondary sintering temperature is 400-500° C. and the time is 2-4 hours.

8. The rare earth element double-modified lithium-rich manganese-based positive electrode material prepared according to the preparation method of claim 1.

Images