CN103326016A - Preparation method of layered lithium (Li)-rich manganese (Mn)-based anode material having multiple core-shell structures - Google Patents

Abstract

The invention discloses a preparation method of a layered lithium-rich manganese-based positive electrode material with a multiple core-shell structure, that is, LiNi _x Co _y Mn _1-xy O ₂ is used as the core (0≤x, y≤1), and the concentration is gradient The changed Li ₂ MnO ₃ is the shell, and the layered (1-t)LiNi _x Co _y Mn _1-xy O ₂ tLi ₂ MnO ₃ with multiple core-shell structure is prepared. The invention applies the core-shell structure to lithium-rich layered materials, proposes the concept of multiple core-shell structures, and overcomes the shortcomings of poor performance of simple core-shell structure materials and complex operation and difficult realization of concentration gradient materials reported in literature. The concentration of the core and the shell shows an anti-gradient change according to a certain arithmetic sequence, that is, from the core to the shell, the concentration of the core material is distributed in a decreasing arithmetic sequence, and the concentration of the shell material is distributed in an increasing arithmetic sequence. During the design, the concentration of transition metal ions in each layer is guaranteed to be the same, so as to reduce the phase boundary resistance between materials as much as possible and improve the performance of materials.

Description

Preparation method of a layered lithium-rich manganese-based positive electrode material with multiple core-shell structure

technical field

The invention relates to a preparation method of a layered lithium-rich manganese-based positive electrode material with multiple core-shell structures.

Background technique

Since it can exhibit unusual electrochemical properties, such as high specific capacity (discharge specific capacity exceeding 230mAh/g, up to 300mAh/g), high specific power (up to 300Wh/kg), and a new electrochemical charge-discharge mechanism, the layer Li _1+X+ M _1-x O ₂ -like lithium-rich material (M is one or more transition metal elements) has become one of the research hotspots in the field of cathode materials for lithium-ion batteries worldwide, making it a next-generation The most likely cathode material candidate for high-performance lithium-ion battery technology. After nearly 20 years of research, researchers have proposed many improvement measures (such as bulk phase doping, surface coating, etc.) to address the defects of this type of material, which has greatly promoted the practical application of layered lithium-rich materials. However, this type of material still has some shortcomings, such as large irreversible capacity, unsatisfactory cycle performance, poor thermal stability of delithiation materials, unsatisfactory rate performance, and poor low temperature performance. Therefore, how to carry out innovative structural design of this type of material and optimize its preparation process is still very necessary to promote the practical application of this type of material.

For the research on cathode materials for lithium-ion batteries, in addition to research on surface coating, bulk phase doping and other modification methods for existing material systems, some new technologies and methods for material preparation have also appeared from time to time. Among them, designing materials into a core-shell structure (to give full play to the advantages of core materials and shell materials and overcome their respective shortcomings) is a promising method . Su and Yoshio et al. first used the co-precipitation method to prepare the core-shell structure precursor, and then formed the core-shell structure to improve the performance of layered LiNi _1-x Co _x Mn _y O ₂ . The core material they used is a nickel-rich layered material with high capacity, low cycle and safety, and the shell material is a manganese-rich layered material with high safety, stable structure and good cycle performance, and finally obtained capacity and cycle performance. Materials with excellent comprehensive properties such as magnification performance and safety performance. Subsequently, Sun et al. further designed and prepared a core-shell material with a concentration gradient, that is, by adding a quantitative pump to continuously change the composition of the salt solution to achieve a continuous change in the feed composition of the salt, so as to reduce the composition difference between the core and the shell material and reduce the material The phase boundary resistance between them further optimizes the performance of the material. However, due to the difficult control of experimental conditions, precise instruments and strict control conditions are required. Zhang Lianqi et al. found in their research that the layered lithium-rich material Li _1.2 Co _0.4 Mn _0.4 O ₂ - Li _1.2 Ni _0.2 Mn _0.6 O ₂ -Li _1.2 Ni _0.4 Mn _0.4 O ₂ can be formed in a full range, and the composition is different charge and discharge Mechanisms may be different, resulting in a large difference in electrochemical performance. In 2011, Argonne Laboratory in the United States successfully applied the concept of concentration gradient core-shell structure design materials to the synthesis of layered lithium-rich materials, and observed excellent electrochemical performance. These studies enlighten us that it is feasible to control the composition gradient core-shell structure of precursors by co-precipitation method, so as to prepare layered lithium-rich materials with composition gradient core-shell structure. However, the first core-shell structure material proposed by Sun is simple to prepare and has strong controllability, but its performance is worse than the second core-shell structure material proposed by them; while the second core-shell structure material has excellent performance, but it is difficult to prepare. Poor controllability, difficult industrial production, resulting in poor product consistency. From the perspective of material essence, the former has a structural mutation between the core material and the shell material, while the latter has a continuous change in composition between the core material and the shell material, and there is no structural mutation, so the material performance is excellent. Then, is there a structure between the two, which not only takes into account the advantages of simple preparation and strong controllability of the former, but also takes advantage of the high performance of the material? Under this idea, we proposed a core-shell structure with "one core and multiple shells", that is, a multiple core-shell structure. In this structure, the composition gradient changes stepwise. Theoretically, the number of steps (this study called "multiplicity"), the larger the material structure is, the closer to the concentration gradient core-shell structure (the second type), and the material performance is better, but within the limited multiplicity, this structure is more reliable than the concentration gradient core-shell structure. operability.

Contents of the invention

The purpose of the present invention is to provide a preparation method of a layered lithium-rich manganese-based positive electrode material with multiple core-shell structures, so as to realize the perfect balance between high capacity, cycle performance, safety performance, and rate performance of the material.

The object of the present invention is achieved in the following manner: with LiNi _x Co _y Mn _1-xy O ₂ as the core (0≤x, y≤1) and Li ₂ MnO ₃ with a gradient concentration as the shell, multiple Core-shell structure layered (1-t)LiNi _x Co _y Mn _1-xy O ₂ tLi ₂ MnO ₃ .

One of the preparation steps of the multiple core-shell structure layered (1-t)LiNi _x Co _y Mn _1-xy O ₂ tLi ₂ MnO ₃ is the preparation of the core and shell precursor solution: nickel source, cobalt source and manganese According to the metal ion n(Ni ²⁺ ):n(Co ²⁺ ):n(Mn ²⁺ )=x:y:(1-xy), a uniform mixed salt solution with a certain concentration is prepared as the precursor solution of the nuclear material; at the same time The manganese source is formulated into a certain concentration of Mn ²⁺ as the precursor solution of the shell material.

The second preparation step of the layered (1-t)LiNi _x Co _y Mn _1-xy O ₂ tLi ₂ MnO ₃ with multiple core-shell structures is the uniform mixing of the core and shell precursor solutions: from the core material and the shell material The solutions with the same volume fraction as the total volume of the respective solutions are taken out from the precursor solutions. Divide the taken-out nuclear solution into several parts according to the volume in a certain arithmetic sequence (decreasing): A1, A2, ... An; also divide the taken-out shell solution into the same number according to the volume in a reverse arithmetic series (increasing): B1 , B2, ... Bn. Then the corresponding salt solutions are uniformly mixed to form salt solutions A1B1, A2B2, . . . AnBn.

The third preparation step of the layered (1-t) LiNi _x Co _y Mn _1-xy O ₂ tLi ₂ MnO ₃ with multiple core-shell structure is the formation of the core precursor: stirring in the reactor according to a certain dropping rate Add the above remaining nuclear solution, add a certain concentration of alkali solution to adjust the pH value of the solution to a certain value, and co-precipitate at a certain temperature to obtain a suspension of the nuclear material precursor, and its solid is the precursor of the nuclear material (Ni _x Co _y Mn _1-xy )(OH) ₂ .

The fourth preparation step of the layered (1-t)LiNi _x Co _y Mn _1-xy O ₂ tLi ₂ MnO ₃ with multiple core-shell structure is the formation of multiple shell precursors: in the suspension of the above-mentioned core material precursor Stir and add salt solutions A1B1, A2B2, ... AnBn in sequence, and finally add the remaining shell solution in the claim to realize multiple co-precipitation.

The fifth preparation step of the layered (1-t)LiNi _x Co _y Mn _1-xy O ₂ tLi ₂ MnO ₃ with multiple core-shell structure is the formation of the precursor of the layered lithium-rich manganese-based material with multiple core-shell structure: when All the salt solution was added to the reactor to stop the reaction, and after solid-liquid separation and washing, it was dried in a vacuum oven at 105°C for 12-24 hours to obtain the precursor (1-t)[Ni _x Co _y Mn _1-xy (OH) ₂ ]t [Mn(OH) ₂ ].

The sixth preparation step of the layered (1-t)LiNi _x Co _y Mn _1-xy O ₂ tLi ₂ MnO ₃ with a multiple core-shell structure is the formation of a layered lithium-rich manganese-based material with a multiple core-shell structure: the multiple core Layered lithium-rich manganese-based material precursor with shell structure and lithium source are evenly mixed according to a certain ratio, roasted in a muffle furnace according to a certain roasting system, cooled and ground to obtain multiple core-shell structure layered (1-t)LiNi _x Co _y Mn _1-xy O ₂ tLi ₂ MnO ₃ .

The metal source may be one or more of the metal's nitrate, sulfate, oxalate, halide or other organic metal salts.

The alkali may be one or more of sodium hydroxide, ammonia water, sodium carbonate, sodium bicarbonate or other alkaline substances.

The lithium source can be one or both of lithium carbonate and lithium hydroxide.

The calcination system refers to multi-step calcination including low-temperature pre-calcination and high-temperature sintering, and the calcination time can vary from 0.5h to 48h.

The value of t in the layered (1-t)LiNi _x Co _y Mn _1-xy O ₂ tLi ₂ MnO ₃ with multiple core-shell structure is in the range of 0≤t≤0.5, especially 0≤t≤0.3.

The invention applies the core-shell structure to lithium-rich layered materials, proposes the concept of multiple core-shell structures, and overcomes the shortcomings of poor performance of simple core-shell structure materials and complex operation and difficult realization of concentration gradient materials reported in literature. The concentration of the core and the shell shows an anti-gradient change according to a certain arithmetic sequence, that is, from the core to the shell, the concentration of the core material is distributed in a decreasing arithmetic sequence, and the concentration of the shell material is distributed in an increasing arithmetic sequence. During the design, the concentration of transition metal ions in each layer is guaranteed to be the same, so as to reduce the phase boundary resistance between materials as much as possible and improve the performance of materials.

The lithium-ion battery adopting the layered (1-t) LiNi _x Co _y Mn _1-xy O ₂ tLi ₂ MnO ₃ with multiple core-shell structure prepared by the invention as the positive electrode material is suitable for various mobile electronic devices or mobile energy-driven Devices such as mobile phones, laptops, camcorders, electric bicycles, electric vehicles, hybrid electric vehicles, and energy storage devices.

Detailed ways:

Example 1 (preparation of triple core-shell structure material)

a. Preparation of core material and shell material precursor solution: prepare a certain amount and concentration of core material salt solution A with a material ratio of Ni:Co:Mn=5:2:3; prepare a certain concentration of manganese salt solution as the shell Materials Salt solution B. Control the ratio of metal ions in A and B solutions to be 9:1;

b. Take out 70% of the total solution volume from the salt solution A and the salt solution B respectively, divide the A solution and B solution into two parts respectively, and record them as A1 (40%), A2 (30%) and B1 ( 30%), B2 (40%); mix the corresponding A solution and B solution evenly to form salt solutions A1B1, A2B2;

c. Stir and add the remaining 30% salt solution A into the reaction kettle according to a certain dropping rate, add a certain concentration of sodium hydroxide to adjust the pH value of the solution to a certain value of 10-11, and co-precipitate at 60°C to obtain nuclei The suspension of the material precursor, the solid is the precursor of the nuclear material ( Ni _0.5 Co _0.2 Mn _0.3 )(OH) ₂ ;

d. Keeping the conditions unchanged, add the salt solutions A1B1 and A2B2 to the above suspension in turn, and finally add the remaining 30% of the salt solution B to achieve multiple co-precipitation;

e. After all the salt solution was added to the reaction kettle, the reaction was stopped. After solid-liquid separation and washing, it was dried in a vacuum oven at 105°C for 18 hours to obtain a layered lithium-rich manganese-based material precursor with multiple core-shell structures 0.9[Ni _0.5 Co _0.2 Mn _0.3 (OH) ₂ ]0.1[Mn(OH) ₂ ];

f. Mix 0.9[Ni _0.5 Co _0.2 Mn _0.3 (OH) ₂ ]0.1[Mn(OH) ₂ ] obtained in e with lithium hydroxide at a ratio of 1:1.2 (in order to prevent the volatilization of lithium, lithium hydroxide is in excess) Mixed in a muffle furnace for two-step calcination (pre-calcination at 400°C for 3 hours, then high-temperature sintering at 950°C for 16 hours), cooling and grinding to obtain a layered 0.9LiNi _0.5 Co _0.2 Mn _0.3 O ₂ 0.1Li ₂ MnO ₃ with multiple core-shell structures .

The electrochemical performance of gained sample is determined by the following method: the mass fraction is 80% sample, 10% acetylene black and 10% polyvinylidene fluoride (PVDF), make electrode sheet and assemble into battery according to embodiment 1 . The cycle test of the electrode material uses a charge-discharge rate of 0.2C at room temperature to charge to 4.2V and discharge to 3.0V. The discharge curve of the sample showed a stable discharge voltage platform around 3.6V, the first reversible specific capacity was about 192 mAh/g, and the capacity retention rate after 50 cycles at 0.2C rate reached 94.5%; the capacity after 50 cycles at 5C rate reached The retention rate reached 89.9%.

Claims (12)

1. the preparation method of a multi-kernel shell structure stratiform lithium-rich manganese-based anode material, it is characterized in that: this material is with LiNi _xco _ymn _1-x-yo ₂for core (0≤x, y≤1), the Li that changes with concentration in gradient ₂mnO ₃for shell.

2. the preparation method of a kind of multi-kernel shell structure stratiform lithium-rich manganese-based anode material according to claim 1 is characterized in that: by He Meng source, ,Gu source, nickel source according to metal ion n (Ni ²⁺): n (Co ²⁺): n (Mn ²⁺)=x:y:(1-x-y) the precursor solution that the even mixing salt solution of preparation finite concentration is nuclear material; The manganese source is mixed with to certain density Mn simultaneously ²⁺precursor solution as shell material.

3. the preparation method of a kind of multi-kernel shell structure stratiform lithium-rich manganese-based anode material according to claim 1 is characterized in that: the solution that takes out respectively the volume that the volume fraction that accounts for overall solution volume separately is identical from the precursor solution of nuclear material and shell material; The core solution of taking-up is to certain arithmetic progression (successively decreasing) according to volume and is divided into some parts: A1, A2 ... An; Equally by the shell solution of taking-up according to volume be reverse arithmetic progression (increasing progressively) be divided into same umber: B1, B2 ... Bn; Then corresponding salting liquid is uniformly mixed to form salting liquid A1B1, A2B2 ... AnBn.

4. the preparation method of a kind of multi-kernel shell structure stratiform lithium-rich manganese-based anode material according to claim 1, it is characterized in that: according to certain drop rate to stirring and add the described remaining core solution of claim 3 in reactor, add the pH value of certain density aqueous slkali regulator solution to certain value, coprecipitation reaction obtains the suspension of nuclear material presoma at a certain temperature, and its solid is the presoma (Ni of nuclear material _xco _ymn _1-x-y) (OH) ₂.

5. the preparation method of a kind of multi-kernel shell structure stratiform lithium-rich manganese-based anode material according to claim 1, it is characterized in that: in the described suspension of claim 4, stir successively add salting liquid A1B1, A2B2 ... AnBn, finally add the described remaining shell solution of claim 3, realize repeatedly co-precipitation.

6. the preparation method of a kind of multi-kernel shell structure stratiform lithium-rich manganese-based anode material according to claim 1, it is characterized in that: stop reaction after all salting liquids all add reactor, dry 12-24h after Separation of Solid and Liquid, washing in 105 ℃ of vacuum drying ovens, obtain the lithium-rich manganese-based material presoma of multi-kernel shell structure stratiform (1-t) [Ni _xco _ymn _1-x-y(OH) ₂]@t[Mn (OH) ₂].

7. the preparation method of a kind of multi-kernel shell structure stratiform lithium-rich manganese-based anode material according to claim 1 is characterized in that: by the presoma of gained in claim 6 and lithium source evenly be blended according to a certain percentage in Muffle furnace according to cooling after certain roasting system roasting, grind and obtain multi-kernel shell structure stratiform (1-t) LiNi _xco _ymn _1-x-yo ₂@tLi ₂mnO ₃.

8. the preparation method of a kind of multi-kernel shell structure stratiform lithium-rich manganese-based anode material according to claim 1 is characterized in that: the source metal described in claim 2 can be one or more in nitrate, sulfate, oxalates, halide or other organic metal salt of this metal.

9. the preparation method of a kind of multi-kernel shell structure stratiform lithium-rich manganese-based anode material according to claim 1, it is characterized in that: the alkali described in claim 4 can be one or more in NaOH, ammoniacal liquor, sodium carbonate, sodium acid carbonate or other alkaline matter.

10. the preparation method of a kind of multi-kernel shell structure stratiform lithium-rich manganese-based anode material according to claim 1, it is characterized in that: the lithium source described in claim 7 can be one or both in lithium carbonate, lithium hydroxide.

11. the preparation method of a kind of multi-kernel shell structure stratiform lithium-rich manganese-based anode material according to claim 1, it is characterized in that: the roasting system described in claim 7 refers to the multistep roasting of steps such as comprising low temperature presintering and high temperature sintering, and roasting time can change from 0.5h to 48h.

12. the preparation method of a kind of multi-kernel shell structure stratiform lithium-rich manganese-based anode material according to claim 1 is characterized in that: the scope of the t value in claim 6 and claim 7 is 0≤t≤0.5, particularly 0≤t≤0.3.