CN108172820A - A kind of preparation method of surface layer doped Y3+ NCM ternary cathode material - Google Patents

Abstract

The present invention relates to a kind of surface layers to adulterate Y³⁺NCM tertiary cathode materials preparation method, belong to field of chemical energy storage battery.The method of the invention is to carry out Y during nickel cobalt manganese hydroxide precursor is mixed with lithium salts³⁺Doping, the Y of doping³⁺It enters in the transition metal layer on surface layer, occupies Ni²⁺Position, can play braced frame, inhibit surface structure phase transformation and inhibit Li⁺/Ni²⁺The effect of mixing；In addition, Y³⁺Ionic radius it is bigger, doping enter transition metal layer after, help to widen Li⁺It is embedded it is embedding go out channel, help to improve Li⁺Transmission rate, chemical property of the NCM tertiary cathode materials under high voltage high magnification (4.5V, >=1C) can be significantly improved.

Description

A kind of preparation method of surface layer doped Y3+ NCM ternary cathode material

technical field

The invention relates to a preparation method of an NCM ternary positive electrode material whose surface layer is doped with Y3 ⁺ , and belongs to the field of chemical energy storage batteries.

Background technique

At present, fossil energy sources such as coal, oil, and natural gas are increasingly depleted. In addition, the problem of environmental pollution has gradually become the focus of attention of all countries. The development of pure electric vehicles and gasoline-gas hybrid vehicles has attracted more and more attention. This requires the rapid development of lithium secondary batteries to meet people's urgent needs for practical applications of new energy batteries. In the family of lithium secondary batteries, lithium cobalt oxide, lithium iron phosphate and ternary materials play an important role in the market in turn. Lithium cobalt oxide is mostly used in small portable electronic devices, while lithium iron phosphate is gradually being replaced by ternary materials due to its low mass specific capacity and its role in power electric vehicles. After Tesla released the electric vehicle Model S using NCA (Li[Ni _0.85 Co _0.1 Al _0.05 ]O ₂ ) ternary cathode material as the power battery in 2012, research on ternary cathode materials (including NCM and NCA) has been carried out around the world. The tide kept rising. China is also sparing no effort to develop high-voltage, high-nickel cathode ternary materials (NCM, NCA) to meet the requirements of a new generation of high-capacity electrode materials.

NCM (Li[Ni _x Co _y Mn _1-xy ]O ₂ , x>0.5) ternary cathode material has a high discharge specific capacity (>200 mAh/g), which is mentioned in the key project of new energy vehicles in China By 2020, the energy density of industrialized lithium-ion batteries will reach more than 300Wh/Kg, and the cost will be reduced to less than 0.8 yuan/Wh. The most potential cathode battery material. However, at present, NCM ternary cathode materials have not been widely used commercially, and one of the main reasons is that their cycle stability and rate performance are relatively poor. This is because Ni elements will segregate and enrich on the surface during the synthesis of NCM ternary cathode materials, and the ionic radii of Li ⁺ and Ni ²⁺ are similar, so Li ⁺ is easy to occur during the electrochemical charge-discharge cycle. /Ni ²⁺ mixes the structure of the NCM ternary cathode material, thereby affecting the electrochemical stability and electrochemical cycle performance of the NCM ternary cathode material (Nickel‐Rich and Lithium‐Rich Layered Oxide Cathodes: Progress and Perspectives, Arumugam Manthiram, James C. Knight, Seung-Taek Myung, Seung-MinOh, and Yang-Kook Su, Adv. Energy Mater. 2016, 6, 1501010).

Because in the delithiated state, Ni ions are reduced to Ni ⁴⁺ ions, and the Ni ⁴⁺ on the surface of the NCM ternary positive electrode material is extremely unstable; at the same time, the high pressure makes the electrolyte prone to oxidative decomposition, and the decomposition products are deposited on the NCM ternary On the surface of the positive electrode material, the acidic substances in the electrolyte are likely to further corrode the surface layer of the NCM ternary positive electrode material. For these reasons, the surface layer of the NCM ternary cathode material will undergo a transformation from a layered structure to a spinel structure. And it is generally believed that the phase change process of NCM ternary cathode materials gradually diffuses from the surface layer to the inside, so it is very important to strengthen the stability of the surface layer of NCM ternary cathode materials. After research, it is found that doping NCM ternary cathode materials with other metal elements can improve its electrochemical performance, but there is no report on Y ³⁺ doping NCM ternary cathode materials.

Contents of the invention

Aiming at the problem that the surface layer structure of NCM ternary positive electrode material is unstable during cycling and the rate performance is poor, the purpose of the present invention is to provide a preparation method of NCM ternary positive electrode material whose surface layer is doped with Y ³⁺ . In the process of mixing the precursor of NCM ternary cathode material with lithium salt, Y ³⁺ is doped, and the doped Y ³⁺ enters the transition metal layer on the surface and occupies the position of Ni ²⁺ , which can stabilize the Structural framework, inhibition of surface structure phase transition and inhibition of Li ⁺ /Ni ²⁺ mixing; in addition, doping Y ³⁺ with a larger ion radius can increase the transmission rate of Li ⁺ , thereby improving the performance of NCM ternary cathode materials. Rate performance, especially the electrochemical performance of high voltage and high rate.

The purpose of the present invention is achieved through the following technical solutions.

A method for preparing an NCM ternary positive electrode material doped with Y ³⁺ on the surface, the chemical formula of the NCM ternary positive electrode material doped with Y ³⁺ is Li[Ni _0.8-x Co _0.1 Mn _0.1 Y _x ]O ₂ , where 0.005≤x≤0.03;

The method steps are as follows,

Mix nickel-cobalt-manganese hydroxide precursor powder (Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ ), yttrium nitrate powder and lithium hydroxide powder evenly, and then place them in an oxygen atmosphere for calcination; wherein, first Insulate at 450°C-550°C for 4h-6h, then raise the temperature to 750°C-850°C and hold for 12h-20h, then cool with the furnace to obtain the NCM ternary cathode material doped with Y ³⁺ on the surface, which is abbreviated as Y-NCM811 .

Wherein, the molar ratio of lithium hydroxide to the nickel-cobalt-manganese hydroxide precursor powder is 0.98 to 1.05:1, and the molar ratio of yttrium nitrate to the nickel ion in the nickel-cobalt-manganese hydroxide precursor powder is The molar ratio is 1:(25.6～159).

Further, first add lithium hydroxide into the mortar and dry grind for 10 to 15 minutes. Grinding lithium hydroxide particles into powder helps Li ⁺ to be uniformly mixed in the nickel-cobalt-manganese strong oxide precursor, and then mixed with yttrium nitrate Ultrasound the powder and nickel-cobalt-manganese hydroxide precursor in ethanol for 1h~2h, then transfer the ultrasonicated mixture to a mortar, first dry grind for 20min~30min, then add ethanol for wet grinding for 20min~30min, and then place Calcination is carried out under an oxygen atmosphere.

Beneficial effect:

(1) The method of the present invention is to add the yttrium source in the process of mixing the nickel-cobalt-manganese hydroxide precursor powder and the lithium salt, so as to realize the doping of Y ³⁺ in the surface transition metal layer, and the doped Y ³⁺ Occupying the position of Ni ²⁺ , Y ³⁺ can play a role in stabilizing the structural framework during the process of a large amount of Li ⁺ intercalation, and can also inhibit the surface structure from changing from layered structure to spinel during electrochemical cycling. The phase change of structural transformation, while inhibiting the effect of Li ⁺ /Ni ²⁺ mixing, retaining more lithium sites, so as to achieve better intercalation/intercalation reversibility of Li ⁺ , so the NCM ternary cathode material is improved in Structural stability and reversible discharge capacity during electrochemical charge-discharge cycles.

(2) The binding energy between YO is greater than that between other MOs (M=Ni, Co or Mn), so Y ³⁺ doped in the surface transition metal layer helps to stabilize the lattice structure, especially the stable The lattice structure under high-voltage conditions alleviates the serious problem of high-nickel materials releasing oxygen at high cut-off voltages, and significantly improves the electrochemical performance of NCM ternary cathode materials at high voltages and high rates (4.5V, ≥1C); in addition , the ionic radius of Y ³⁺ is relatively large, after doping into the transition metal layer, it helps to widen the channel for Li ⁺ intercalation and intercalation, and helps to increase the transport rate of Li ⁺ , thereby improving the electrochemical performance of NCM ternary cathode materials. cycle performance.

(3) The source of raw materials used in the present invention is wide, the price is low, and the operation process of the method is simple, the process and technology are easy to realize, and can be used in large-scale commercial applications. At the same time, the method can be used for other ternary positive electrode materials or lithium-rich positive electrodes The surface of the material is doped with Y ³⁺ .

Description of drawings

Fig. 1 is the comparative figure of the X-ray diffraction (XRD) spectrogram of the Y-NCM811 that embodiment 1 prepares and the NCM811 that comparative example 1 prepares.

Fig. 2 adopts the Y-NCM811 that embodiment 1 prepares as the CR2025 button battery of positive electrode material assembly Cycling 1 week and the alternating current impedance (EIS) test figure after 10 weeks of cycling.

Fig. 3 is the cyclic voltammetry (CV) curve graph that adopts Y-NCM811 prepared by embodiment 1 as the CR2025 button cell of positive electrode material assembly cycle 1 week and cycle 10 weeks.

Fig. 4 adopts the Y-NCM811 prepared by embodiment 1 as the X-ray diffraction figure of the CR2025 button battery of positive electrode material assembly before cycle, cycle 1 week and cycle 10 weeks.

Fig. 5 is the AC impedance test figure after 1 cycle and 10 cycles of the CR2025 button battery assembled by using the NCM811 prepared in Comparative Example 1 as the positive electrode material.

Fig. 6 adopts the NCM811 prepared by comparative example 1 as the cyclic voltammetry curve of the CR2025 button battery assembled by the positive electrode material after 1 week and 10 weeks of circulation.

Fig. 7 is the X-ray diffraction pattern of the CR2025 button battery assembled by using NCM811 prepared in Comparative Example 1 as the positive electrode material before cycle, cycle 1 week and cycle 10 weeks.

Fig. 8 is a graph showing cycle performance curves of the CR2025 button battery assembled in Example 1 and the CR2025 button battery assembled in Comparative Example 1 at a voltage range of 2.75V to 4.35V and at a rate of 1C (1C=200mAh/g).

Fig. 9 is a cycle performance curve of the CR2025 button battery assembled in Example 1 and the CR2025 button battery assembled in Comparative Example 1 in the voltage range of 2.75V to 4.5V and at a rate of 1C (1C=200mAh/g).

Figure 10 is the rate performance diagram obtained by cycling the CR2025 button battery assembled in Example 1 and the CR2025 button battery assembled in Comparative Example 1 at the rates of 0.1C, 0.2C, 1C, 2C, 5C, and 10C respectively for 5 weeks.

Figure 11 is a graph showing the cycle performance curves of the CR2025 button battery assembled in Example 1 and the CR2025 button battery assembled in Comparative Example 1 at a voltage range of 2.75V to 4.35V and at a rate of 0.1C.

Detailed ways

In order to better understand the present invention, the present invention will be further described in detail below in conjunction with specific examples. It should be understood that the specific embodiments described here are only used to illustrate and explain the present invention, not to limit the present invention. Additionally, the endpoints and any values disclosed herein are not limited to such precise ranges or values, and these ranges or values are understood to include values approaching these ranges or values. For numerical ranges, between the endpoints of each range, between the endpoints of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, these values Ranges should be considered as specifically disclosed herein.

In the following examples:

X-ray diffractometer: the instrument model is Rigaku Ultima IV, Japan;

AC impedance test: CHI604c electrochemical workstation, China; the test voltage is 4.5V, the frequency range is 0.01Hz-0.1MHz, the amplitude of the sine wave AC voltage disturbance signal is 5m, and the counter electrode is used as the reference electrode;

Cyclic voltammetry test: CHI660e electrochemical workstation, China; the test voltage range is 2V to 4.8V, and the scan rate is 0.1mV/s;

Assembly and testing of CR2025 button cell: the positive electrode material (Y-NCM811 prepared in Examples 1-6 or NCM811 prepared in Comparative Example 1), acetylene black, PVDF (polyvinylidene fluoride) according to the quality of 8:1:1 Slurry is made and coated on aluminum foil, and the dried aluminum foil loaded with slurry is cut into small discs with a diameter of about 1 cm with a cutting machine to be used as positive electrodes, lithium metal sheets are used as negative electrodes, and Celgard2300 is used as separators , 1M carbonate solution is the electrolyte (wherein, the solvent is a mixed solution of ethylene carbonate and dimethyl carbonate with a volume ratio of 1:1, and the solute is LiPF ₆ ), assembled into a CR2025 button battery in an argon glove box ; Use CT2001A Alnd battery tester to conduct constant current charge and discharge tests on the assembled CR2025 button batteries at different current densities, define 1C current density as 200mA/g, and charge and discharge voltage ranges as 2.75V～4.35V and 2.75V～ 4.5V, the test temperature is 30°C; when the rate performance test is performed, the constant current charge and discharge test is carried out at different current densities of 0.1C, 0.2C, 1C, 2C, 5C, 10C, and 0.1C for 5 weeks. , after 2C, 5C, 10C high-rate constant current charging, then constant voltage charging for 1 hour or constant voltage charging until the current density is less than 0.05C.

The Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ used in Examples 1-6 were all prepared according to the method described in Comparative Example 1.

Example 1

First add LiOH·H ₂ O into the mortar, dry mill for 15 min, then ultrasonicate with Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ and Y(NO ₃ ) ₃ ·6H ₂ O in ethanol for 1.5 h, and then The final mixture was transferred to a mortar, firstly dry-milled for 25 minutes, then added ethanol and continued to grind for 25 minutes, then placed the wet-milled mixture in an oxygen atmosphere, first heated to 450°C and kept for 6h, then raised to 750°C and Keeping it warm for 12 hours and cooling with the furnace, the NCM ternary positive electrode material Li[Ni _0.79 Co _0.1 Mn _0.1 Y _0.01 ]O ₂ doped with Y ³⁺ on the surface layer was obtained, which is abbreviated as Y-NCM811; among them, LiOH·H ₂ O and Ni The molar ratio of _0.8 Co _0.1 Mn _0.1 (OH) ₂ is 1.05:1, and the molar ratio of nickel ions in Y(NO ₃ ) ₃ ·6H ₂ O to Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ is 1:79.

The Y-NCM811 prepared in Example 1 was used as the positive electrode material to assemble a CR2025 button battery, and the corresponding electrochemical performance tests were carried out.

It can be seen from the XRD spectrum in Figure 1 that the Y-NCM811 prepared in this example did not change the main crystal structure of the original high-nickel ternary cathode material NCM811, both of which are typical α-NaFeO ₂ structures, belonging to R-3m space group. The bottom vertical line in Figure 1 is PDF#09-0063, which represents the characteristic peak position of LiNiO ₂ with a perfect layered structure, indicating that the high-nickel ternary material NCM811 before and after doping the surface layer with Y ³⁺ has a perfect layered structure. However, from the partially enlarged XRD patterns at θ=18.5°～19.5° and θ=44°～45°, it can be seen that the (003) peak and (104) peak of Y-NCM811 are slightly shifted to low angles relative to NCM811 , indicating that after Y ³⁺ enters the surface transition metal layer, since the ionic radius of Y ³⁺ (r=0.090nm) is greater than that of Ni ²⁺ (r=0.069nm), the positive electrode material after the surface layer is doped with Y ³⁺ The interlayer spacing is increased, which will facilitate the intercalation and extraction of Li ⁺ . From the changes of the unit cell parameters before and after the surface layer doping Y ³⁺ listed in Table 1, it can be seen that the values of the unit cell parameters a and c after Y ³⁺ doping increase, and the value of c/a also increases The ratio of the (003) peak to the (104) peak of Y-NCM811 is significantly increased, which proves that the surface doping ^{Y 3+} contributes to Inhibit Li ⁺ /Ni ²⁺ mixing. In addition, because the binding force between YO bonds is much greater than that between other MO (M=Ni, Co or Mn) bonds, the Gibbs free energy of formation of Y ₂ O ₃ (-1816.65KJ/mol) is greater than The Gibbs formation free energy of MnO ₂ and NiO (-465.1KJ/mol, -211.7KJ/mol), Y ³⁺ doped in the surface transition metal layer can stabilize the oxygen in the lattice and stabilize the structure.

The CR2025 button battery assembled using Y-NCM811 prepared in this example as the positive electrode material was subjected to EIS tests after cycling for 1 week and 10 weeks at a voltage range of 2.75V to 4.5V and a rate of 0.1C. The test results are shown in Figure 2. ; The CR2025 button battery assembled using NCM811 prepared in Comparative Example 1 as the positive electrode material was subjected to EIS tests after cycling for 1 week and 10 weeks at a voltage range of 2.75V to 4.5V and a rate of 0.1C. The test results are shown in Figure 5. The arc in the low frequency area in Figure 2 and Figure 5 represents _the charge transfer resistance R _ct of the positive electrode material. It can be seen that after the first cycle and 10 cycles, the charge transfer resistance R _ct of Y-NCM811 is smaller than that of NCM811, indicating that the surface layer The surface lattice structure of the positive electrode material doped with Y ³⁺ is more stable during the electrochemical cycle.

The CR2025 button battery assembled with Y-NCM811 prepared in this example as the positive electrode material was cycled for 1 week and 10 weeks at a voltage range of 2.75V to 4.5V and at a rate of 0.1C. The CV test was carried out respectively. The test results are shown in Figure 3 ; The CR2025 button battery assembled using NCM811 prepared in Comparative Example 1 as the positive electrode material was subjected to CV tests after cycling for 1 week and 10 weeks at a voltage range of 2.75V to 4.5V and a rate of 0.1C. The test results are shown in Figure 6. According to the test results in Figure 3 and Figure 6, after the first cycle and 10 cycles, the positions of the CV peaks of the two cathode materials are almost not shifted, but the peak intensity of NCM811 after 10 cycles is significantly higher than that in the first cycle. After 10 weeks of cycling, the peak intensity decreased, while the peak intensity of Y-NCM811 remained almost unchanged after 10 weeks of cycling, indicating that the capacity retention rate of NCM811 was lower after 10 weeks of cycling, that is, the substances that contributed to the redox capacity decreased.

XRD tests were carried out on Y-NCM811 after 1 week and 10 weeks of cycling in the voltage range of 2.75V-4.5V and 0.1C magnification, and the results are shown in Figure 4; NCM811 was tested by XRD after 1 week and 10 weeks of down cycle, and the results are shown in Figure 7, where the vertical line at the bottom of Figure 7 is PDF#09-0063. According to the test results in Figure 4 and Figure 7, it can be seen that the layered structure of the positive electrode material is still well maintained after cycling, but according to the local enlarged diagram at 18.5°-19.5°, the position of the (003) peak is shifted, However, the peak position of NCM811 shifts more seriously to high angles, indicating that the structure lattice of NCM811 decreases more significantly with the progress of the electrochemical cycle process, that is to say, the structural instability of NCM811 occurs during the process of intercalation and release of Li ⁺ Structural changes such as lattice collapse reduce the value of the unit cell parameter c, while the lattice change of Y-NCM811 is not significant during cycling, which proves that the Y ³⁺ doped on the surface inhibits the process of intercalation and release of Li ⁺ The change of the lattice structure of the positive electrode material is prevented, and the structural stability is significantly improved, that is, the cycle performance of the positive electrode material is improved.

The CR2025 button battery assembled using Y-NCM811 prepared in this example as the positive electrode material and the CR2025 button battery assembled using NCM811 prepared in Comparative Example 1 as the positive electrode material, in the voltage range of 2.75V to 4.35V, 1C rate and 30 The constant current charge and discharge test was carried out at ℃, and the test results are shown in Figure 8; the constant current charge and discharge test was carried out at 2.75V to 4.5V voltage range, 1C rate and 30°C, and the test results are shown in Figure 9. According to the test results in Figure 8, in the voltage range of 2.75V to 4.35V, the discharge capacity of NCM811 in the first cycle of the cycle is 170.8mAh/g, the discharge capacity after 500 cycles is 111.9 mAh/g, and the capacity retention rate is 65.5%; The discharge capacity of Y-NCM811 is 179.2mAh/g in the first cycle, and 122.7mAh/g after 500 cycles, and the capacity retention rate is 68.5%. At this time, the cycle performance of Y-NCM811 is slightly better than that of NCM811. According to the test results in Figure 9, in the voltage range of 2.75V to 4.5 V, the discharge capacity of NCM811 in the first cycle is 194mAh/g, and the discharge capacity after 500 cycles is 44.2mAh/g, with a capacity retention rate of 22.8%; Y- The discharge capacity of NCM811 in the first cycle is 180mAh/g, the discharge capacity after 500 cycles is 110.9mAh/g, and the capacity retention rate is 61.6%. In the state of high cut-off voltage, Y-NCM811 can maintain the stability of the material. obvious advantage.

The CR2025 button battery assembled with Y-NCM811 prepared in this example as the positive electrode material and the CR2025 button battery assembled with NCM811 prepared in Comparative Example 1 as the positive electrode material were tested at voltages of 2.75V to 4.35V and 2.75V to 4.5V In the interval and at 30°C, cycle at 0.1C, 0.2C, 1C, 2C, 5C and 10C for 5 weeks respectively. The test results are shown in Figure 10. According to the test results in Figure 10, in the voltage range of 2.75V to 4.35V, the discharge capacity of NCM811 at 10C rate is 151.1mAh/g, and the discharge capacity of Y-NCM811 at 10C rate is 163.1mAh/g; at 2.75 V In the ~4.5V voltage range, the discharge capacity of NCM811 at 10C rate is 157.5mAh/g, and the discharge capacity of Y-NCM811 at 10C rate is 170.5mAh/g, which further shows that the structure of Y-NCM811 is more stable and can be used at high voltage and high The electrochemical performance at higher rates is even better.

For the CR2025 button battery assembled with Y-NCM811 prepared in this example as the positive electrode material and the CR2025 button battery assembled with NCM811 prepared in Comparative Example 1 as the positive electrode material, the voltage range of 2.75V to 4.35V, the rate of 0.1C and the 30 The constant current charge and discharge test was carried out at ℃. According to the test results in Figure 11, it can be seen that the discharge capacity of NCM811 is 192.8mAh/g in the first week, and the discharge capacity after 20 cycles is 192.2mAh/g; the discharge capacity of Y-NCM811 is 202.7mAh/g in the first week, and the discharge capacity after 20 cycles It is 202.2mAh/g.

Table 1

Example 2

First add LiOH·H ₂ O into the mortar, dry mill for 15 min, then sonicate with Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ and Y(NO ₃ ) ₃ ·6H ₂ O in ethanol for 2 h, and then Transfer the mixture to a mortar, dry grind for 25 minutes, then add ethanol and continue grinding for 25 minutes, then place the wet-ground mixture in an oxygen atmosphere, first heat to 450°C and keep it for 6 hours, then raise the temperature to 750°C and keep it 12h, cooled with the furnace, and obtained NCM ternary cathode material Li[Ni _0.795 Co _0.1 Mn _0.1 Y _0.005 ]O ₂ doped with Y ³⁺ on the surface layer, which is abbreviated as Y-NCM811; among them, LiOH·H ₂ O and Ni _0.8 The molar ratio of Co _0.1 Mn _0.1 (OH) ₂ is 1.05:1, and the molar ratio of Y(NO ₃ ) ₃ to Ni ions in Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ is 1:159.

Y-NCM811 prepared by embodiment 2 is assembled into CR2025 button cell as positive electrode material and carries out electrochemical performance test. The constant current charge and discharge test was carried out under the voltage range of 2.75V to 4.35V, 30°C and 0.1C rate. The discharge capacity in the first week was 177.5mAh/g, and the discharge capacity after 500 cycles was 118.6mAh/g. The capacity retention rate was 66.8%. The constant current charge and discharge test was carried out in the voltage range of 2.75V to 4.5V, 30°C and 1C rate. The discharge capacity in the first week was 188mAh/g, and the discharge capacity after 500 cycles was 112.4mAh/g, with a capacity retention rate of 59.8%. .

Example 3

First add LiOH·H ₂ O into the mortar, dry mill for 15 min, then sonicate with Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ and Y(NO ₃ ) ₃ ·6H ₂ O in ethanol for 2 h, and then Transfer the mixture to a mortar, dry grind for 25 minutes, then add ethanol and continue grinding for 25 minutes, then place the wet-ground mixture in an oxygen atmosphere, first heat to 450°C and keep it for 6 hours, then raise the temperature to 750°C and keep it 12h, cooling with the furnace, the NCM ternary cathode material Li[Ni _0.785 Co _0.1 Mn _0.1 Y _0.015 ]O ₂ doped with Y ³⁺ on the surface was obtained, abbreviated as Y-NCM811; among them, LiOH·H ₂ O and Ni _0.8 The molar ratio of Co _0.1 Mn _0.1 (OH) ₂ is 1.05:1, and the molar ratio of nickel ions in Y(NO ₃ ) ₃ ·6H ₂ O to Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ is 1:52.3.

Y-NCM811 prepared by embodiment 3 is assembled into CR2025 button cell as positive electrode material and carries out electrochemical performance test. The constant current charge and discharge test was carried out under the voltage range of 2.75V to 4.35V, 30°C and 0.1C rate. The discharge capacity in the first week was 175.6mAh/g, and the discharge capacity after 500 cycles was 119.8 mAh/g. The capacity retention rate was 68.2%. The constant current charge and discharge test was carried out under the voltage range of 2.75V to 4.5V, 30°C and 1C rate. The discharge capacity in the first week was 188.4mAh/g, the discharge capacity after 500 cycles was 108.6mAh/g, and the capacity retention rate was 57.6 %.

Example 4

First add LiOH·H ₂ O into the mortar, dry mill for 15 min, then sonicate with Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ and Y(NO ₃ ) ₃ ·6H ₂ O in ethanol for 2 h, and then Transfer the mixture to a mortar, dry grind for 25 minutes, then add ethanol and continue grinding for 25 minutes, then place the wet-ground mixture in an oxygen atmosphere, first heat to 450°C and keep it for 6 hours, then raise the temperature to 750°C and keep it 12h, cooled with the furnace to obtain the NCM ternary cathode material Li[Ni _0.77 Co _0.1 Mn _0.1 Y _0.03 ]O ₂ doped with Y ³⁺ on the surface layer, which is abbreviated as Y-NCM811; among them, LiOH·H ₂ O and Ni _0.8 The molar ratio of Co _0.1 Mn _0.1 (OH) ₂ is 1.05:1, and the molar ratio of nickel ions in Y(NO ₃ ) ₃ ·6H ₂ O to Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ is 1:25.7.

Y-NCM811 prepared by embodiment 4 is assembled into CR2025 button cell as positive electrode material and carries out electrochemical performance test. The constant current charge and discharge test was carried out under the voltage range of 2.75V to 4.35V, 30°C and 0.1C rate. The discharge capacity in the first week was 172.1mAh/g, and the discharge capacity after 500 cycles was 113.8 mAh/g. The capacity retention rate was 66.1%. The constant current charge and discharge test was carried out under the voltage range of 2.75V to 4.5V, 30°C and 1C rate. The discharge capacity in the first week was 182mAh/g, and the discharge capacity after 500 cycles was 103.3mAh/g, and the capacity retention rate was 56.8%. .

Example 5

First add LiOH·H ₂ O into the mortar, dry grind for 10 min, then ultrasonicate with Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ and Y(NO ₃ ) ₃ ·6H ₂ O in ethanol for 1.5 h, then The final mixture was transferred to a mortar, firstly dry-milled for 30 minutes, then added ethanol and continued to grind for 30 minutes, then the wet-milled mixture was placed in an oxygen atmosphere, first heated to 500 °C and kept for 5 h, then heated to 800 °C and Keeping it warm for 15 hours, and cooling with the furnace, the NCM ternary cathode material Li[Ni _0.79 Co _0.1 Mn _0.1 Y _0.01 ]O ₂ doped with Y ³⁺ on the surface layer was obtained, which is abbreviated as Y-NCM811; among them, LiOH·H ₂ O and Ni The molar ratio of _0.8 Co _0.1 Mn _0.1 (OH) ₂ is 1.02:1, and the molar ratio of nickel ions in Y(NO ₃ ) ₃ ·6H ₂ O to Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ is 1:79.

Y-NCM811 prepared by embodiment 5 is assembled into CR2025 button cell as positive electrode material and carries out electrochemical performance test. The constant current charge and discharge test was carried out under the voltage range of 2.75V to 4.35V, 30°C and 0.1C rate. The discharge capacity in the first week was 175.4mAh/g, and the discharge capacity after 500 cycles was 116.8 mAh/g. The capacity retention rate was 66.6%. The constant current charge and discharge test was carried out under the voltage range of 2.75V to 4.5V, 30°C and 1C rate. The discharge capacity in the first week was 190.7mAh/g, the discharge capacity after 500 cycles was 110.4mAh/g, and the capacity retention rate was 57.9. %.

Example 6

First add LiOH·H ₂ O into the mortar, dry mill for 15 min, then sonicate with Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ and Y(NO ₃ ) ₃ ·6H ₂ O in ethanol for 1 h, and then Transfer the mixture to a mortar, dry grind for 30 minutes, then add ethanol and continue grinding for 20 minutes, then place the wet-ground mixture in an oxygen atmosphere, first heat to 550°C and keep it for 4 hours, then raise the temperature to 850°C and keep it 18h, cooled with the furnace to obtain the NCM ternary cathode material Li[Ni _0.79 Co _0.1 Mn _0.1 Y _0.01 ]O ₂ doped with Y ³⁺ on the surface layer, which is abbreviated as Y-NCM811; among them, LiOH·H ₂ O and Ni _0.8 The molar ratio of Co _0.1 Mn _0.1 (OH) ₂ is 0.98:1, and the molar ratio of nickel ions in Y(NO ₃ ) ₃ ·6H ₂ O to Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ is 1:79.

Y-NCM811 prepared by embodiment 6 is assembled into CR2025 button cell as positive electrode material and carries out electrochemical performance test. The constant current charge and discharge test was carried out under the voltage range of 2.75V to 4.35V, 30°C and 0.1C rate. The discharge capacity in the first week was 171.8mAh/g, and the discharge capacity after 500 cycles was 114.2 mAh/g. The capacity retention rate was 66.5%. The constant current charge and discharge test was carried out under the voltage range of 2.75V ~ 4.5V, 30°C and 1C rate. The discharge capacity in the first week was 187.8mAh/g, the discharge capacity after 500 cycles was 106.2mAh/g, and the capacity retention rate was 56.5 %.

Comparative example 1

The preparation steps of the original ternary cathode material NCM811 without Y doping are as follows:

(1) Manganese sulfate, nickel sulfate and cobalt sulfate are dissolved in deionized water according to the mol ratio of Mn:Ni:Co=8:1:1, to obtain the sulfate solution of 2mol/L;

(2) configuration contains the alkaline aqueous solution of 2mol/L sodium carbonate and 2mol/L ammoniacal liquor;

(3) The prepared sulfate solution and alkaline solution are continuously added to the reaction kettle with agitator and nitrogen gas respectively with a peristaltic pump, and the pH value is controlled by adjusting the addition rate of sulfate solution or alkaline solution, Stabilize the pH to 11, control the reaction temperature to 55°C, the stirring speed to 650r/min, and adjust the injection speed to 0.25mL/min; Filter, wash, and dry to obtain Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ ;

(4) Mix Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ and LiOH powder at a molar ratio of 1:1.05, dry-grind in a mortar for 25 minutes, then add ethanol and continue to grind for 25 minutes, then mix the mixture of the two Placed in an oxygen atmosphere, first heated to 450°C and held for 6 hours, then raised to 750°C and held for 12 hours, then cooled with the furnace to obtain NCM ternary cathode material, abbreviated as NCM811.

The NCM811 prepared in Comparative Example 1 was assembled into a CR2025 button battery as the positive electrode material, and carried out corresponding electrochemical performance tests. The analysis of the test results is detailed in Example 1.

Through the test results of the above-mentioned examples and comparative examples, ^it can be seen that the method of doping Y in the surface transition metal layer of the NCM ternary positive electrode material provided by the present invention can significantly improve the rate performance and the first cycle of the NCM ternary positive electrode material. Efficiency, especially the improvement of electrochemical performance under high voltage and high rate is better and more significant, and the cost of raw materials used is low, non-toxic and environmentally friendly, the entire process is simple, efficient, and environmentally friendly, with wide experimental conditions and high reliability Industrial application prospects.

Claims (2)

1. A preparation method of the NCM ternary positive electrode material doped with Y ³⁺ on the surface, characterized in that: the chemical formula of the NCM ternary positive electrode material doped with Y ³⁺ is Li[Ni _0.8-x Co _0.1 Mn _0.1 Y _x ]O ₂ , where 0.005≤x≤0.03; The method steps are as follows, Mix the nickel-cobalt-manganese hydroxide precursor powder, yttrium nitrate powder and lithium hydroxide powder evenly, and then place it in an oxygen atmosphere for calcination, first keep it warm at 450°C-550°C for 4h-6h, and then heat up to 750°C-850°C and keep it warm for 12h-20h, then cool down with the furnace to obtain the NCM ternary cathode material whose surface layer is doped with Y ³⁺ ; Wherein, the molar ratio of lithium hydroxide to the nickel-cobalt-manganese hydroxide precursor powder is 0.98 to 1.05:1, and the molar ratio of yttrium nitrate to the nickel ion in the nickel-cobalt-manganese hydroxide precursor powder is The molar ratio is 1:(25.6～159). 2. a kind of surface layer doping Y according to claim 1 The preparation method of the NCM ternary cathode material of Y ³⁺ is characterized in that: Lithium hydroxide is added in the mortar earlier, dry grinding 10min～15min, then with nitric acid Sonicate the yttrium powder and nickel-cobalt-manganese hydroxide precursor in ethanol for 1h to 2h, then transfer the ultrasonicated mixture to a mortar, first dry grind for 20min to 30min, then add ethanol to wet mill for 20min to 30min, and then Placed in an oxygen atmosphere for calcination.