Method for improving capacity of modified NCM811 based on sodium lignin sulfonate interface activation

Abstract

The invention discloses a method for improving capacity of modified NCM811 based on sodium lignin sulfonate interface activation, which is characterized by comprising the steps of complexing-coprecipitation and sintering-oxidation, and specifically comprising the following steps: adding deionized water as a base solution into a reaction kettle, adding sodium lignin sulfonate, controlling the temperature to be 40-60 DEG C in a nitrogen atmosphere, and reacting for 1-2 hours; adding a sodium hydroxide solution to adjust the pH value to 11-12, synchronously adding a transition metal salt solution and an ammonia solution to react, and after the reaction is finished, filtering, washing and drying to obtain precursor powder; and adding LiOH.H2O into the precursor powder, mixing, grinding, and sintering in an air or oxygen atmosphere to obtain the NCM811 positive electrode material.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy and chemical industry, and particularly relates to a method for improving the capacity of modified NCM811 based on the interfacial activation of sodium lignin sulfonate. Background Art

[0002] The rapid popularization of electric vehicles and hybrid electric vehicles has promoted the development of lithium-ion batteries, making it one of the most critical energy storage technologies today. Among them, lithium nickel cobalt manganese oxide positive electrode material, that is, a mixture of three transition metals Ni / Co / Mn, as one of the mainstream positive electrode solutions, has the advantages of high energy density, long cycle life, low cost and good safety. By increasing the proportion of nickel in NCM ternary materials, the capacity of the battery can be significantly improved and the production cost can be reduced. For example, LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811) can provide about 200 mAh g at 4.3 V cutoff voltage -1 However, this is still about 20% lower than the theoretical discharge capacity of NCM811 at this cut-off voltage (assuming Ni 2+ / Ni 3+ All converted to Ni 4+ And Co 3+ Maintain unchanged). Traditional modification strategies such as element doping can increase the interlayer spacing of NMC811 through the support of doped ions, thereby improving the material capacity. However, the non-bulk elements introduced by ion doping increase the complexity of the material structure, which may have an adverse effect on the structural order and stability. Therefore, it is very necessary to develop a method to solve the above technical problems. Summary of the invention

[0003] The object of the present invention is to provide a method for improving the capacity of modified NCM811 based on the interfacial activation of sodium lignin sulfonate.

[0004] The object of the present invention is achieved by comprising the steps of complexation-coprecipitation and sintering-oxidation, specifically comprising: A. Complexation-coprecipitation: deionized water is added as the base liquid in the reactor, sodium lignin sulfonate is added, the temperature is controlled at 40-60°C under a nitrogen atmosphere, sodium hydroxide solution is added to adjust the pH value to 11-12, and transition metal salt solution and ammonia solution are added simultaneously to react. After the reaction is completed, the precursor powder is obtained after filtration, washing and drying; B. Sintering-oxidation: Add LiOH·H2O to the precursor powder, mix and grind, and then sinter in air or oxygen atmosphere to obtain NCM811 positive electrode material.

[0005] The specific operations are as follows: 1) Complexation-coprecipitation stage: Add deionized water as the base liquid to the reactor, add 0.1-2 mol% sodium lignin sulfonate, stir until dissolved, and then introduce N2 to purge the air in the reactor. Then raise the temperature to 40-60 ℃, and pump in 6-10 M NaOH solution to adjust the pH value in the reactor to a constant range of 11--12. After the temperature and pH value are stable, add 1--2 mol L -1 The transition metal salt solution was stirred at a rate of 0.5-5 ml min -1 The feed rate is pumped into the kettle, and the ammonia solution as a complexing agent is pumped into the kettle at a rate of 0.05-1 ml min according to the concentration of the salt solution and the feed rate. -1 The feed rate of the NaOH solution is synchronously pumped in, and the pH total dynamic control system automatically adjusts the feed rate of the NaOH solution to maintain the pH fluctuation in the kettle below ±0.1. After the feed liquid is pumped in, the reaction is continued for 4-12 hours to mature the precursor particles. The precursor powder is obtained after filtration, washing and drying.

[0006] The reaction principle of the complexation-coprecipitation stage: The coprecipitation reaction of the precursor is completed in two main steps using transition metal salt solution as raw material, NaOH as precipitant, NH4OH as complexing agent, and sodium lignin sulfonate as interfacial activator. In the first step, the transition metal ions (TM refers to Ni 2+ 、Co 2+ , Mn 2+ ) forms an ammonia complex with NH3 in the solution (Formula 1). Then, in the second step, the hydroxide ion (OH - ) replaces the ammonium ion in the complex, reacts and forms a transition metal hydroxide precipitation core (Formula 2): TM 2+ + nNH3 → [TM(NH3) n ] 2+ (1) [TM(NH3) n ] 2+ + 2OH - → TM(OH)2+ nNH3(2) As the reaction proceeds, the precipitates aggregate around the core and gradually form primary particles. When their particle size exceeds a certain threshold, the growth of these primary particles stagnates and they begin to gradually aggregate to form secondary particles. The size of the particles begins to increase until they reach a critical value and stop growing.

[0007] In this process, the lignin sulfonate (surfactant) in the solution precisely modifies the interface properties of the precursor (001) crystal plane through the same complexing effect on transition metal ions. The stacking process is disturbed and the spacing in the c-axis direction is regulated by adjusting the stacking interface activity. After the lattice arrangement is fixed, the complexed lignin sulfonate and ammonium ions are hydrated by OH - It can be replaced, but its local lattice expansion effect can be retained.

[0008] 2) Sintering-oxidation stage: The precursor powder is mixed with LiOH·H2O (molar ratio Li:TM = 1--1.1:1) and ground, and then placed in a vacuum box atmosphere furnace for sintering in air or O2 atmosphere. The heating rate is set to 2-10 ℃ min -1 The first stage of sintering is kept at a constant temperature of 500-600 °C for 4-10 h, and the second stage of sintering is kept at a constant temperature of 700-800 °C for 8-16 h, followed by cooling in the furnace to obtain NCM811 positive electrode material.

[0009] Principle of sintering-oxidation stage: The components in the mixture are evenly distributed in the first constant temperature process. As the temperature rises further, lithium ions gradually embed into the oxygen-oxygen layer gap, and the nickel cobalt manganese hydroxide precursor gradually transforms into lithium nickel cobalt manganese oxide with a hexagonal layered α-NaFeO2 structure. The reactions in the whole process are as follows (TM in the formula refers to the transition metal Ni / Co / Mn): TM(OH)2+ LiOH·H2O + O2→ LiTMO2+ H2O The present invention forms a technology to expand the precursor lattice interlayer spacing in a residue-free manner during the coprecipitation stage, which promotes the increase of lithium ion embedding and the reduction of "dead lithium" during the sintering process, and achieves a significant increase in the capacity of NCM811. It is worth noting that since the optimization effect of this technology depends on the regulation of material structure parameters rather than the introduction of other substances or structures, the modified NCM811 using this technology can be further modified by other strategies without hindrance to achieve further improvement of electrochemical performance.

[0010] The process flow adopted by the present invention is specifically as follows: NiSO4·6H2O, CoSO4·7H2O and MnSO4·H2O were dissolved in deionized water to obtain a transition metal salt solution, and the molar ratio of Ni:Co:Mn was controlled to be 8:1:1.

[0011] Prepare NaOH solution as precipitant and NH3·H2O as complexing agent for later use.

[0012] A pH meter was used to control the pH value of the entire process in the reactor to be constant.

[0013] Before the experiment, deionized water was added to the continuous stirred reactor (CSTR), N2 was used to purge the air in the reactor, and an appropriate amount of sodium lignin sulfonate (C 20 H 24 Na2O 10 S2) stirring until dissolved, heating to reaction temperature, and pumping in NaOH solution to adjust pH value to designed value.

[0014] After the pH value and temperature are stabilized, the prepared transition metal salt solution and ammonia solution are gradually pumped into the kettle at a constant rate, and NaOH solution is used to maintain the pH value of the liquid in the kettle constant.

[0015] The reactor is operated under stirring for a period of time and then allowed to stand to allow the precursor particles to mature.

[0016] The kettle liquid was filtered and washed alternately with deionized water and ethanol for more than three times. The filter cake was dried in a blast drying oven to obtain Ni 0.8 Co 0.1 Mn 0.1 (OH)2 precursor precipitation.

[0017] Then, the precursor was mixed with LiOH·H2O (prepared in a certain molar ratio) and ground, and then placed in a vacuum box atmosphere furnace for sintering.

[0018] The two-stage calcination method is used to maintain the temperature at two temperatures for a period of time, and then the furnace is naturally cooled to obtain Li(Ni 0.8 Co 0.1 Mn 0.1 )O2 positive electrode material.

[0019] Our previous study showed that the electrochemical performance of NCM811 active materials can be traced back to the lattice characteristics of the precursors. Therefore, we proposed a novel modification strategy to expand the Ni 0.8 Co 0.1 Mn 0.1 The (OH)2 lattice spacing was used to increase the discharge capacity of NMC811 from 200 mAh g -1 Increased to nearly 210 mAh g -1 . BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the process flow of the present invention; Figure 2 Schematic diagram of the comparison of XRD patterns of the interface activated modified NCM811 precursor (M-pre) and the control sample (S-pre); Figure 3Schematic diagram of SEM image comparison of interface activated modified NCM811 precursor (M-pre) and control sample (S-pre); Among them, a is the interface activated modified NCM811 precursor (M-pre); b is the control sample (S-pre); Figure 4 Schematic diagram of the comparison of XRD patterns of interface activated modified NCM811 (M) and control sample (S); Figure 5 Schematic diagram of SEM image comparison of interface activated modified NCM811 (M) and control sample (S); Figure 6 Schematic diagram of the charge-discharge curve comparison between the interface activated modified NCM811 (M) and the control sample (S); Figure 7 Schematic diagram of the comparison of cyclic stability tests of interface activated modified NCM811 (M) and control sample (S). DETAILED DESCRIPTION

[0021] The present invention is further described below in conjunction with the embodiments, but the present invention is not limited in any way. Any changes or substitutions made based on the teachings of the present invention belong to the protection scope of the present invention.

[0022] The method for improving the capacity of modified NCM811 based on the interfacial activation of sodium lignin sulfonate of the present invention comprises the steps of complexation-coprecipitation and sintering-oxidation, specifically comprising: A. Complexation-coprecipitation: deionized water is added as the base liquid in the reactor, sodium lignin sulfonate is added, the temperature is controlled at 40-60°C under a nitrogen atmosphere, sodium hydroxide solution is added to adjust the pH value to 11-12, and transition metal salt solution and ammonia solution are added simultaneously to react. After the reaction is completed, the precursor powder is obtained after filtration, washing and drying; B. Sintering-oxidation: Add LiOH·H2O to the precursor powder, mix and grind, and then sinter in air or oxygen atmosphere to obtain NCM811 positive electrode material.

[0023] The transition metal salt solution described in step A is a nickel-cobalt-manganese salt solution.

[0024] The molar ratio of nickel, cobalt and manganese in the nickel-cobalt-manganese salt solution is (6-10): (0.5-1.5): (0.5-1.5).

[0025] The molar ratio of nickel, cobalt and manganese in the nickel-cobalt-manganese salt solution is 8:1:1.

[0026] The reaction time in step A is 4 to 12 hours.

[0027] During the reaction process of step A, the feed rate of NaOH solution is automatically adjusted by the pH control system to maintain the pH value at 11-12 with a fluctuation less than ±0.1.

[0028] The sintering described in step B is to set the heating rate to 2~10℃ / min; the first stage of sintering is to maintain a constant temperature of 500~600℃ for 4~10h; the second stage of sintering is to maintain a constant temperature of 700~800℃ for 8~16h, and then cool in the furnace to obtain the target NCM811 positive electrode material.

[0029] The present invention is further described below with specific implementation cases: Example 1 Complexation-coprecipitation stage: AR-grade NiSO4·6H2O, CoSO4·7H2O and MnSO4·H2O were dissolved in deionized water to prepare 1.5L transition metal salt solution with a transition metal ion concentration of 2 mol L -1 ; Prepare 10 mol L -1 NaOH solution was used as a precipitant; 250 ml of commercial ammonia water was added to 50 ml of deionized water as a complexing agent; 1 mol% of sodium lignin sulfonate was weighed as a surfactant. 1.5 L of deionized water was added to a 5 L reactor as a base liquid, and all the sodium lignin sulfonate was added to the base liquid. The stirring and N2 purge of the reactor were turned on. After the sodium lignin sulfonate was completely dissolved, the reactor was heated to 55 °C, and NaOH solution was pumped in to adjust the pH of the base liquid to 11.8. After the temperature and pH value were stable, the reaction mixture was stirred at 1 ml min -1 and 0.2 ml min -1 The transition metal salt solution and the complexing agent were pumped in synchronously at a feed rate of , and the feed rate of the precipitant was controlled by a pH meter. After all the feed solutions were pumped in, the reaction continued for 8 hours. It was then filtered and washed, and dried at 120 °C for 12 hours to obtain a modified precursor, which was labeled M-pre (the control experimental group without the addition of surfactant was labeled S-pre). The XRD, SEM, and ICP-MS characterization comparison results of the precursor are shown in Figure 2. Figure 2 , Figure 3 shown.

[0030] Content of non-main phase residual elements in precursor samples (ICP-MS) .

[0031] Sintering-oxidation stage: 10 g of the precursor and 4.73 g of LiOH·H2O were weighed, ground and mixed evenly, and then placed in a vacuum box atmosphere furnace and heated at 5 °C min -1The temperature was raised to 500 °C at a heating rate and kept constant for 6 h, then continued to rise to 750 °C and kept constant for 12 h, and then cooled in the furnace to obtain the active material NCM811. The interface activation modification group and the control group are marked as M and S, respectively. The structural morphology characterization comparison results of the active materials are shown in Figure 4 , Figure 5 shown.

[0032] Comparison of the content ratio of main phase elements (ICP-OES) .

[0033] The electrochemical performance test was carried out using a CR2032 half-cell. The positive electrode slurry was prepared by dissolving and mixing 10 wt% polyvinylidene fluoride (PVDF), 10 wt% Super P and 80 wt% active material in N-methylpyrrolidone (NMP) to prepare a slurry. After the slurry was stirred evenly, it was coated on an aluminum foil (28±1 μm) with a thickness of 300 μm, and then dried at 80 °C for 1 h. After the NMP on the surface of the electrode was volatilized, it was moved to a vacuum drying oven and dried at 120 °C for 24 h. The dried electrode was rolled to a thickness of 70 μm, and the electrode sheet with a diameter of 14 mm obtained by slicing was transferred to a glove box filled with argon to ensure that the concentrations of H2O and O2 were maintained below 0.1 ppm. Metal lithium sheet was used as the counter electrode, Celgard 2400 as the separator, EC:DEC solution (volume ratio of 1:1) containing 1M LiPF6 as the electrolyte, CR2032 half-cell was assembled and sealed in the glove box. To ensure data accuracy, the active material loading in all batteries was kept at 18.0±0.4 mg. The electrochemical performance was evaluated using the Blue Battery Test System in the voltage range of 2.8 V to 4.3 V. Before the test, it was first allowed to stand at room temperature for 12 h to ensure that the electrolyte fully wetted the electrode, and the current density was set to 1C=200 mA g -1 (vs. Li / Li+).

[0034] like Figure 6 and Figure 7 As shown in Figure 2, at a charge and discharge rate of 0.1C, the discharge capacity of the interface activated modified sample can reach 209.8 mAh g -1 , which is about 11 mAh g higher than the control sample -1 . The results of 300 charge-discharge cycles at 1C rate showed that the improvement of NCM811 capacity by the interface activation modification method did not sacrifice the material's cyclic stability.

Claims

1. A method for improving the capacity of modified NCM811 based on the interfacial activation of sodium lignin sulfonate, characterized in that: The method comprises the steps of complexation-coprecipitation and sintering-oxidation, specifically comprising: A. Complexation-coprecipitation: deionized water is added as the base liquid in the reactor, sodium lignin sulfonate is added, the temperature is controlled at 40-60°C under a nitrogen atmosphere, sodium hydroxide solution is added to adjust the pH value to 11-12, and transition metal salt solution and ammonia solution are added simultaneously to react. After the reaction is completed, the precursor powder is obtained after filtration, washing and drying; B. Sintering-oxidation: Add LiOH·H2O to the precursor powder, mix and grind, and then sinter in air or oxygen atmosphere to obtain NCM811 positive electrode material.

2. The method for improving the capacity of modified NCM811 based on the interfacial activation of sodium lignin sulfonate according to claim 1, characterized in that: The transition metal salt solution described in step A is a nickel-cobalt-manganese salt solution.

3. The method for improving the capacity of modified NCM811 based on the interfacial activation of sodium lignin sulfonate according to claim 2, characterized in that: The molar ratio of nickel, cobalt and manganese in the nickel-cobalt-manganese salt solution is (6-10): (0.5-1.5): (0.5-1.5).

4. The method for improving the capacity of modified NCM811 based on the interfacial activation of sodium lignin sulfonate according to claim 2 or 3, characterized in that: The molar ratio of nickel, cobalt and manganese in the nickel-cobalt-manganese salt solution is 8:1:

1.

5. The method for improving the capacity of modified NCM811 based on the interfacial activation of sodium lignin sulfonate according to claim 1, characterized in that: The reaction time in step A is 4 to 12 hours.

6. The method for improving the capacity of modified NCM811 based on the interfacial activation of sodium lignin sulfonate according to claim 1, characterized in that: During the reaction process of step A, the feed rate of NaOH solution is automatically adjusted by the pH control system to maintain the pH value at 11-12 with a fluctuation less than ±0.

1.

7. The method for improving the capacity of modified NCM811 based on the interfacial activation of sodium lignin sulfonate according to claim 1, characterized in that: The sintering described in step B is to set the heating rate to 2~10℃ / min; The first stage of sintering is to maintain a constant temperature of 500-600°C for 4-10 hours; The second stage of sintering is to maintain a constant temperature of 700~800℃ for 8~16h, and then cool the furnace to obtain the target NCM811 positive electrode material.

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