CN117154086A - Fe/Mg doping regulated layered lithium-rich cathode material, preparation method and lithium ion battery - Google Patents

Fe/Mg doping regulated layered lithium-rich cathode material, preparation method and lithium ion battery Download PDF

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CN117154086A
CN117154086A CN202310947431.8A CN202310947431A CN117154086A CN 117154086 A CN117154086 A CN 117154086A CN 202310947431 A CN202310947431 A CN 202310947431A CN 117154086 A CN117154086 A CN 117154086A
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lithium
lnmo
element doped
rich layered
cathode material
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郭少华
褚世勇
柯冰钰
许成荣
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Nanjing Research Institute Of Nanjing University
Nanjing University
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Nanjing Research Institute Of Nanjing University
Nanjing University
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Abstract

The invention relates to the technical field of preparation of lithium battery materials, in particular to a layered lithium-rich cathode material regulated and controlled by Fe/Mg doping, a preparation method and a lithium ion battery. In the anode material prepared by the method, the covalent nature between transition metal and oxygen can be reduced by doping Fe element, so that the first-circle irreversible oxygen loss can be restrained, li/Ni mixed emission can be reduced by substituting Mg element for lithium, a layered structure can be supported, the structure of the material is stabilized by introducing Fe and Mg, the cycle performance and the multiplying power performance of the material are improved, the voltage drop of LNMO is obviously relieved, and the overall electrochemical performance of the material is improved.

Description

Fe/Mg doping regulated layered lithium-rich cathode material, preparation method and lithium ion battery
Technical Field
The invention relates to the technical field of preparation of lithium battery materials, in particular to a layered lithium-rich anode material regulated and controlled by Fe/Mg doping, a preparation method and a lithium ion battery.
Background
With the increase of application of lithium ion batteries, the application fields of the lithium ion batteries range from consumer electronics to electric automobiles and to smart grids, the demands of the lithium ion batteries with high energy density are increasingly urgent, and as an important component of the lithium ion batteries, a great deal of researches are carried out on positive electrode materials with good development prospects.
Layered lithium-rich oxides (LLROs) have emerged as candidate positive electrode materials for next generation lithium ion batteries in combination with anionic and cationic redox reactions, but currently commercialized positive electrode materials provide lithium-rich layered positive electrode materials Li with lower capacity, without cobalt 1.2 Ni x Mn 0.8-x O 2 The lithium-rich layered anode material (LNMO) has the advantages of high theoretical specific capacity, environmental friendliness and lower cost, but similar to the lithium-rich layered anode material containing cobalt, the problems of irreversible oxygen release, low initial coulombic efficiency, poor cycle rate performance, quicker voltage decay and the like still exist.
Disclosure of Invention
The technical problems to be solved by the invention are as follows: the existing LNMO material has the problems of low initial coulomb efficiency and capacity, low discharge average voltage attenuation and poor multiplying power performance.
According to the invention, fe and Mg are doped together on the basis of a cobalt-free lithium-rich layered anode material (LNMO) with an R-3m space group structure to replace Mn and Li in a transition metal layer respectively, so that a multi-element doped lithium-rich layered anode material (MF-LNMO) is prepared, and the problems are solved.
In order to achieve the above purpose, the present invention provides the following technical solutions:
a multi-element doped lithium-rich layered anode material has a molecular formula of: li (Li) 1.2-x Mg x Fe y Ni 0.2 Mn 0.6-y O 2 ，0<x<0.02，0<y<0.02。
Preferably, the molecular formula is specifically: li (Li) 1.19 Mg 0.01 Fe 0.01 Ni 0.2 Mn 0.59 O 2 。
Preferably, the preparation method of the multi-element doped lithium-rich layered anode material comprises the following steps:
(1) Preparing a metal salt solution: weighing lithium oxalate, manganese oxalate, nickel oxalate, iron acetate and magnesium oxalate according to a molecular formula metering ratio, and mixing and dissolving in water to obtain a metal salt solution;
(2) Preparation of aqueous citric acid solution: weighing citric acid, dissolving in water, and stirring until the citric acid is completely dissolved to obtain a citric acid aqueous solution;
(3) Preparing sol: dropwise adding the metal salt solution into the citric acid aqueous solution for chelation, and continuously stirring the mixed solution until sol is formed;
(4) And drying the sol, and then calcining to obtain the multi-element doped lithium-rich layered anode material.
Preferably, the purified water in the step (1) and the step (2) is 15ml, and the mass excess of the lithium oxalate in the step (1) is weighed to be 5% -15%.
Preferably, the stirring temperature in the step (3) is 70-90 ℃ and the stirring time is 4-5h.
Preferably, the drying treatment in the step (4) is carried out at 100-130 ℃ for 10-15 hours.
Preferably, the calcination treatment in the step (4) is two times of calcination, wherein the temperature of the first calcination is 800-1000 ℃ and the calcination time is 9-12 h; the temperature of the second calcination is 900-1200 ℃, the calcination time is 14-18 h, and the temperature rising rate of the two times of calcination is 3-7 ℃/min.
Preferably, the storage conditions of the multi-element doped lithium-rich layered cathode material obtained in the step (4) are as follows: vacuum storage or storage in an argon glove box.
The positive electrode of the lithium ion battery comprises the multi-element doped lithium-rich layered positive electrode material.
The lithium ion battery comprises a battery shell, an electrode group and electrolyte, wherein the electrode group and the electrolyte are sealed in the battery shell, the electrode group comprises a positive electrode, a diaphragm and a negative electrode, and the lithium ion battery comprises the positive electrode of the lithium ion battery.
Compared with the prior art, the invention has the beneficial effects that:
the invention selects two elements of Fe and Mg to carry out co-doping regulation and control material components, fe 3+ With Mn 4+ The ion radius and electronegativity are similar, and the doping of Fe element can reduce the covalent property between transition metal and oxygen so as to inhibit the irreversible oxygen loss of the first circle; mg of 2+ The radius is close to that of lithium ions, so that Mg can replace lithium of a lithium layer and a transition metal layer simultaneously, and the Li/Ni mixed arrangement can be reduced by replacing lithium with Mg element, and the layered structure can be supported.
The introduction of the two elements of Fe and Mg stabilizes the structure of the material, improves the multiplying power performance of the material, obviously relieves the voltage drop of LNMO and improves the overall electrochemical performance of the material.
Drawings
FIG. 1 is an XRD refinement of (a) MF-LNMO and (b) LNMO;
FIG. 2 is a scanning electron microscope image of materials (a) MF-LNMO and (b) LNMO;
FIG. 3 is a graph showing the distribution of element Ni, mn, mg, fe in the sample MF-LNMO; (b) profile of Ni and Mn elements in the control LNMO;
FIG. 4 is a cyclic voltammogram of (a) MF-LNMO and (b) LNMO at a voltage window of 2-4.8V, and a sweep rate of 0.1 mV/s;
FIG. 5 is a voltage-specific capacity plot of (a) MF-LNMO and (b) LNMO materials at a rate of 0.1C for first-pass charge and discharge;
FIG. 6 is a graph of (a) average voltage-cycle number of 150 cycles and (b) specific discharge capacity-cycle number of 160 cycles of the voltage range of 2-4.8V for MF-LNMO and LNMO positive electrode materials at 1C;
FIG. 7 is a graph of specific capacity versus number of cycles for (a) MF-LNMO and (b) LNMO positive electrode materials cycled five cycles at each of 0.1C, 0.2C, 0.5C, 1C, 2C; a first-round charge-discharge curve of (c) MF-LNMO and (d) LNMO at each magnification current density;
FIG. 8 is an EIS test pattern and a fitting pattern of (a) MF-LNMO and (b) LNMO anodes.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1
Preparation of MF-LNMO (Li) using sol gel method 1.19 Mg 0.01 Fe 0.01 Ni 0.2 Mn 0.59 O 2 ): weighing lithium oxalate, manganese oxalate tetrahydrate, nickel oxalate tetrahydrate, ferric acetate and magnesium oxalate dihydrate according to a molecular mass ratio, mixing and dissolving in 15ml of purified water, adding magnetons, heating and stirring until the solution is clear, wherein the excess of the lithium oxalate is 10%, and compensating lithium loss caused by subsequent reaction; citric acid monohydrate was also dissolved in 15ml of purified water and stirred until dissolved. After both are stirred uniformly, the metal salt solution is added dropwise into the citric acid aqueous solution for chelation to form a green mixed solution, and the mixed solution is stirred for 4 hours at the temperature of 80 ℃. After sol is formed, placing the material into a constant temperature oven, preserving heat at 120 ℃ for 12 hours, transferring the material into a muffle furnace, calcining at 850 ℃ for 10 hours, grinding, calcining at 950 ℃ for 15 hours again, heating at a temperature rate of 5 ℃ per minute, cooling along with the furnace, and taking out the synthesized materialAnd grinding the material by using a mortar to obtain the multi-element doped lithium-rich layered anode material.
Comparative example 1
Preparation of LNMO (Li) using sol gel method 1.2 Ni 0.2 Mn 0.6 O 2 ): weighing lithium oxalate, manganese oxalate tetrahydrate, nickel oxalate tetrahydrate, ferric acetate and magnesium oxalate dihydrate according to a molecular mass ratio, mixing and dissolving in 15ml of purified water, adding magnetons, heating and stirring until the solution is clear, wherein the excess of the lithium oxalate is 10%, and compensating lithium loss caused by subsequent reaction; citric acid monohydrate was also dissolved in 15ml of purified water and stirred until dissolved. After both are stirred uniformly, the metal salt solution is added dropwise into the citric acid aqueous solution for chelation to form a green mixed solution, and the mixed solution is stirred for 4 hours at the temperature of 80 ℃. After sol is formed, placing the material into a constant temperature oven, preserving heat for 12 hours at 120 ℃, transferring the material into a muffle furnace, calcining for 10 hours at 950 ℃, wherein the temperature rising rate is 5 ℃ per minute, cooling along with the furnace, taking out the synthesized material, and grinding by using a mortar to obtain the lithium-rich layered anode material.
Test example 1: characterization of materials
(a) The structures of the MF-LNMO of the example material and the LNMO of the comparative example material are mainly characterized by XRD, the model of the XRD is a German Bruker D8X-ray powder diffractometer, the result is shown in figure 1, and the analysis of diffraction peaks shows that the material has a R-3m space group structure; the morphology and size of the material were mainly characterized by SEM, which is a TOPCN DS-720 instrument in japan, and TEM, and as a result, as shown in fig. 2, it was observed that both materials exhibited irregular shapes, and that there were some primary particle agglomeration. The particle size of MF-LNMO is slightly smaller than that of LNMO, the particle size of the MF-LNMO is 200-400nm, the particle size of the MF-LNMO is 300-500nm, and the small positive electrode material particles are beneficial to stabilizing the cycle performance and the rate performance in electrochemical tests.
(b) The result of the energy spectrometer test is shown in fig. 3, the Ni and Mn in the MF-LNMO and four transition metal elements of doping elements Mg and Fe are uniformly distributed in the material, and the elements in the comparative example are also uniformly distributed.
In conclusion, the MF-LNMO sample with smaller particle size and uniform distribution of each element can be synthesized by using the synthesis method of sol-gel-high temperature solid phase sintering combination.
Test example 2: electrochemical performance test
The battery case used for electrochemical performance testing of MF-LNMO and LNMO materials was a button battery case set of CR2032, comprising a positive electrode and a lithium metal negative electrode. Wherein the positive electrode is composed of 80% of positive electrode active material, 10% of conductive agent acetylene black and 10% of binder PVdF. Then uniformly coating the mixture on a current collector aluminum foil, and putting the current collector aluminum foil into a vacuum oven for drying at 120 ℃ for 5 hours to ensure complete removal of water and other organic liquids, wherein the loading amount of active substances in an electrode is 1-2mg/cm 2 . The cell assembly was carried out in an anhydrous oxygen-free argon glove box, in which 1mol/L LiPF6 as electrolyte was dissolved in an anhydrous EC: DEC: EMC solvent, 100 μl of electrolyte was added dropwise to each cell, and a glass fiber film was used as a cell separator. The charge and discharge test of the battery is carried out on a Land BT2000 battery test system of Wuhan blue electric Co., ltd., china, wherein the test temperature is room temperature, the voltage test window is 2-4.8V, and the battery needs to stand for more than 8 hours before the test. The cyclic voltammetry of the cells was tested on the CHI 660E system from Shanghai Chenhua instruments Co.
(1) In order to study the influence of the Mg element and the Fe element on the electrochemical performance of the original sample after regulating and controlling the LNMO component, the modified sample MF-LNMO and the reference sample LNMO are assembled and subjected to electrochemical test, and the redox behaviors of the two materials in the electrochemical behaviors are explored by adopting a cyclic voltammetry.
As shown in FIG. 4, during the first charge, two small peaks appear at about 4.0V for both materials, corresponding mainly to Ni 2+/3+ And Ni 3+/4+ Oxidation-reduction of (2) and extraction of lithium ions; when the voltage exceeds 4.5V, both also exhibit a higher peak corresponding to anion redox. On discharge, the first cycle only showed a reduction peak of about 3.75V, here Ni 4+ Reduction to Ni 2+ . During the discharge of the subsequent cycle, a reduction peak starts to appear near 3.25V, which is Mn after the end of the first turn 4+ Start to go outThe reduction reaction is now performed. For MF-LNMO, the reversibility of the subsequent two circles is superior to that of LNMO, the oxidation-reduction potential difference is lower than that of the comparative LNMO during charge and discharge, and the polarization is smaller. The MF-LNMO has higher capacity in the first charge and discharge process, and shall be Fe here 3+/3+δ There is a redox reaction and this variable valence gives additional capacity to the material. The peak intensity above 4.5V for MF-LNMO is less than the control, indicating that double doping inhibits oxygen release in the structure due to less oxygen loss during activation as a result of metal-oxygen covalent decrease.
(2) The LNMO material can be subjected to lithium ion removal when the first ring is charged to high voltage, and the irreversible release phenomenon of oxygen is followed, so that the first ring coulomb efficiency of the material is lower. It can be seen from fig. 5 that the introduction of Mg and Fe increases the initial coulombic efficiency of the material during electrochemical cycling from 75.01% to 82.78% and increases the specific discharge capacity. This indicates that the transition metal bonding with oxygen in MF-LNMO is enhanced, the irreversible oxidation-reduction of oxygen is suppressed, and the capacity utilization is improved.
(3) In order to explore the influence of Mg and Fe on the recycling performance of raw materials after regulating LNMO components, constant current charge and discharge tests were carried out on MF-LNMO and LNMO under the current density of 1C (250 mA/g) and the voltage range of 2-4.8V. The initial discharge specific capacity of MF-LNMO can reach 197.9mAh/g, the capacity retention rate can reach 85.79% after 160 circles, and the capacity of LNMO sample only remains 71.29% after the same circle. The LNMO material gradually has spinel structure when it is circulated, so that the material tends to exhibit a larger voltage decay (i.e., a decrease in average cell voltage) when it is electrochemically tested as a positive electrode active material. To investigate the effect of Mg, fe introduction on voltage decay of the LNMO starting material, the present work was tested for cycle performance at 1C, as shown in fig. 6, after 150 cycles the MF-LNMO showed an average voltage drop of 0.813 mV/cycle, whereas the control LNMO showed a more severe voltage decay, about 2.054 mV/cycle. Mg of 2+ The doping of the lithium/nickel cations can reduce the mixing degree of the Li/Ni cations and has stable pillar effect; fe (Fe) 3+ The doping of (2) enhances the TM-O bond energy and stabilizes part of lattice oxygen reaction.
In summary, the irreversible phase of the MF-LNMO structure is suppressed, the capacity retention is improved, and the voltage decay is alleviated.
(4) The rate capability of the MF-LNMO and the LNMO is shown in FIG. 7, the initial discharge specific capacities of the MF-LNMO are 253.8, 238.8, 214, 193.8 and 173.9mAh/g when the MF-LNMO circulates for five circles under the rates of 0.1C, 0.2C, 0.5C, 1C and 2C, and the discharge specific capacities can still reach 250mAh/g when the current density returns to 0.1C; the comparative LNMO material has higher specific discharge capacity at low magnification, but the capacity is rapidly reduced to 147.7mAh/g after charge-discharge cycle at each current density, which indicates that the tolerance of MF-LNMO to strong current density is superior to LNMO. Fig. 7 also shows charge and discharge curves for the two materials at each magnification.
In conclusion, the multiplying power performance of the MF-LNMO is superior to that of the LNMO, so that the MF-LNMO has a more stable structure after component regulation, and lithium ions can be rapidly deintercalated in the whole structure, so that the migration rate is accelerated, and the application potential is better.
(5) To further explore the impedance of the cell when MF-LNMO and comparative LNMO were used as positive electrode materials to study its electrochemical mechanism, we performed EIS characterization of both, as fig. 8 shows the original spectra, fitted impedance spectra, and equivalent circuit of MF-LNMO and LNMO. The charge transfer resistance illustrated in the figure represents the resistance encountered by lithium ions in a lithium ion battery as they migrate through the material. The spectrum comprises a semicircle in the middle frequency region and a slant line in the low frequency region, wherein the former refers to the charge transfer impedance (Rct), and the latter refers to the Warburg impedance of the whole material to reflect the diffusion process. The MF-LNMO electrode had an Rct of 188.2 Ω and the original sample LNMO had a resistance of 337.3 Ω. The electrode material after Mg and Fe are introduced is smaller than the charge transfer resistance of the original LNMO electrode material, which shows that the migration rate of lithium ions in MF-LNMO is faster, and the resistance is smaller.
Taken together, MF-LNMO exhibits superior kinetic performance, higher conductivity, and electrochemical activity than LNMO.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.

Claims (9)

1. The multi-element doped lithium-rich layered anode material is characterized by comprising the following molecular formula: li (Li) 1.2- x Mg x Fe y Ni 0.2 Mn 0.6-y O 2 ，0<x<0.02，0<y<0.02。
2. The multi-element doped lithium-rich layered cathode material of claim 1, wherein the molecular formula is: li (Li) 1.19 Mg 0.01 Fe 0.01 Ni 0.2 Mn 0.59 O 2 。
3. The method for preparing the multi-element doped lithium-rich layered cathode material according to claim 1, comprising the steps of:
(1) Preparing a metal salt solution: weighing lithium oxalate, manganese oxalate, nickel oxalate, iron acetate and magnesium oxalate according to a molecular formula metering ratio, and mixing and dissolving in water to obtain a metal salt solution;
(2) Preparation of aqueous citric acid solution: weighing citric acid, dissolving in water, and stirring until the citric acid is completely dissolved to obtain a citric acid aqueous solution;
(3) Preparing sol: dropwise adding the metal salt solution into the citric acid aqueous solution for chelation, and continuously stirring the mixed solution until sol is formed;
(4) And drying the sol, and then calcining to obtain the multi-element doped lithium-rich layered anode material.
4. The method for preparing a multi-element doped lithium-rich layered cathode material according to claim 3, wherein the mass excess of lithium oxalate in the step (1) is 5% -15%.
5. The method for preparing a multi-element doped lithium-rich layered cathode material according to claim 3, wherein the stirring temperature in the step (3) is 70 ℃ to 90 ℃ and the stirring time is 4 to 5 hours.
6. The method for preparing a multi-element doped lithium-rich layered cathode material according to claim 3, wherein the drying treatment temperature in the step (4) is 100-130 ℃, and the heat preservation time is 10-15h.
7. The method for preparing a multi-element doped lithium-rich layered cathode material according to claim 3, wherein the calcination treatment in the step (4) is two times of calcination, wherein the temperature of the first calcination is 800-1000 ℃ and the calcination time is 9-12 h; the temperature of the second calcination is 900-1200 ℃, the calcination time is 14-18 h, and the temperature rising rate of the two times of calcination is 3-7 ℃/min.
8. A lithium ion battery positive electrode, characterized in that the positive electrode comprises the multi-element doped lithium-rich layered positive electrode material of claim 1.
9. A lithium ion battery comprising a battery housing, an electrode assembly and an electrolyte, the electrode assembly and the electrolyte being sealed within the battery housing, the electrode assembly comprising a positive electrode, a separator and a negative electrode, wherein the lithium ion battery comprises a lithium ion battery positive electrode as defined in claim 8.
CN202310947431.8A 2023-07-28 2023-07-28 Fe/Mg doping regulated layered lithium-rich cathode material, preparation method and lithium ion battery Pending CN117154086A (en)

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CN103682322A (en) * 2013-12-26 2014-03-26 昆明理工大学 Li-rich Fe-Mn based cathode material for lithium ion battery and preparation method of Li-rich Fe-Mn based cathode material
CN107768639A (en) * 2017-10-19 2018-03-06 深圳市比克动力电池有限公司 Anode material of lithium battery and preparation method thereof, the lithium battery using the positive electrode
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WO2022272139A1 (en) * 2021-06-25 2022-12-29 The Regents Of The University Of California A new doping strategy for layered oxide electrode materials used in lithium-ion batteries
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CN103441238A (en) * 2013-08-27 2013-12-11 上海电力学院 Mg-doped Li-rich anode material and preparation method for same
CN103682322A (en) * 2013-12-26 2014-03-26 昆明理工大学 Li-rich Fe-Mn based cathode material for lithium ion battery and preparation method of Li-rich Fe-Mn based cathode material
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