KR20170048047A - Anode Active CoP Composite Materials System Comprising MoP For Li Ion Batteries, And Anodes comprising The Same And Manufacturing Methods Thereof - Google Patents

Abstract

Disclosed is a method for producing a phosphide-based composite anode active material of a lithium secondary battery having improved charging and discharging cycle properties. The present invention provides a method for producing an anode active material of a lithium secondary battery, wherein the method comprises the steps of: producing a mixed solution including a Co source, an Mo source, and a P source, wherein the Co source and the Mo source are combined to have a weight ratio of CoP:MoP at 1-x:x (herein, x>=0.05) on the basis of synthesized CoP and MoP; calcining the mixed solution in atmospheric air; and synthesizing CoP-phase and MoP-phase composite powder by heating the calcined powder in a reduction atmosphere. According to the present invention, a solution-type source is used, and a reduction process is applied, so a CoP composite active material can be produced through a simple scheme.

Description

[0001] The present invention relates to a CoP-based composite anode active material including MoP, an anode including the same, and a method for manufacturing the same. [0002]

The present invention relates to a negative electrode active material of a lithium secondary battery, and more particularly, to a metal phosphide negative electrode active material of a lithium secondary battery having improved charge-discharge cycle characteristics.

Lithium secondary batteries are largely composed of an anode, an electrolyte and a cathode. A commercially available lithium secondary battery has a structure in which a polymer separator having a thickness of 20 to 100 탆 is added in a liquid electrolyte composed of an organic solvent and a lithium salt, and Li + ions migrate from the cathode to the anode during discharging, The electrons move from the cathode to the anode when they are charged, and vice versa when charged.

Based on the intermetallic compound formation reaction of Li _{4 .4} Si and Li _{4 .4} Sn in the case of Si and Sn based metal-based active materials, which are attracting attention as a high-capacity cathode material for next generation lithium secondary batteries, about 3500 to 4200 mAh / g (300-400%) due to a new intermetallic compound phase generated as the reaction with Li proceeds, the deterioration of the life of the electrode is overcome It has difficult technical problems.

In order to solve such a problem, a layered structure of MoP ₂ or the like among metallic materials of MX (M = Si, Sn, Al, V, Mn, Mo, Co. Some compounds with a structure have been reported to undergo a partial insertion reaction rather than an alloying or conversion reaction upon reaction with Li. However, when the Li reaction potential is still high and the reversible efficiency approaches 100% while the initial cycle proceeds, a slow activation rate takes more than 20 cycles, and when a certain amount of Li is charged, it is converted into a conversion reaction, And it has a disadvantage in that it operates at a limited charge / discharge potential range because it has a critical influence on the electrode life. The volumetric expansion of the electrodes hinders cycle characteristics.

In the case of CoP, which is a metal phosphide, it is known that it has two reaction mechanisms of charging and inserting at the same time of charging. It exhibits a cycle degradation characteristic accompanied by volume expansion due to conversion reaction at a low voltage.

On the other hand, the metal phosphide is synthesized mainly by using a ball-milling method. In this case, the produced metal phosphide has a disadvantage in that it is difficult to synthesize such as low crystallinity and heat treatment for a long time .

(Prior Art 1) Z. Zhang et. al., Solid state Ionics 2005, 176, 693 (Prior Art 2) R. Khatib et al., J. Phys. Chem. C 2013, 117, 837 (Prior Art 3) Journal of Catalysis 2001, 202, 187

In order to solve the problems of the prior art described above, it is an object of the present invention to provide a CoP-based active material for a lithium secondary battery capable of suppressing electrode deterioration due to volume expansion.

It is another object of the present invention to provide a method for producing a CoP-based active material having a high crystallinity.

It is another object of the present invention to provide a CoP-based active material produced by the above-described method.

It is another object of the present invention to provide a negative electrode for a lithium secondary battery comprising the aforementioned CoP-based active material.

According to an aspect of the present invention, there is provided a mixed solution including a Co source, a Mo source, and a P source, wherein the Co source and the Mo source have a CoP: MoP weight ratio of 1- x: x (where x? 0.05); Calcining the mixed solution in an atmospheric environment; And heat-treating the calcined powder in a reducing atmosphere to synthesize a composite powder of a CoP phase and an MoP phase. The present invention also provides a method of manufacturing a negative active material for a lithium secondary battery.

In the present invention, the P source may be phosphate. Also, the Mo source may be molybdate. In addition, the Co source may be a cobalt nitrate salt.

In one embodiment of the present invention, the mixed solution may be an aqueous solution.

In one embodiment of the present invention, x is preferably in the range of 0.1? X? 0.2.

Further, in one embodiment of the present invention, the reducing atmosphere may be a hydrogen atmosphere.

Also, according to an embodiment of the present invention, the composite powder of the synthesis step does not contain cobalt oxide.

According to another aspect of the present invention, there is provided an anode for a lithium secondary battery comprising: a conductive substrate; And a CoP phase and an MoP phase, wherein the MoP phase is contained in an amount of 10 to 20% by weight based on the weight of the composite.

According to the present invention, it is possible to provide a CoP composite active material capable of suppressing the volume expansion of a CoP-based negative electrode active material and improving cycle characteristics.

The Mo source added for the production of the CoP complex active material in the present invention acts as a catalyst for reducing the cobalt oxide formed by calcination and also acts as a buffer for the volume expansion of CoP.

Further, according to the present invention, the CoP composite active material can be produced in a simple manner by using a source in the form of a solution and applying a reduction process.

FIG. 1 is a flow chart illustrating a procedure for manufacturing a negative electrode active material according to an embodiment of the present invention.
FIG. 2 is a graph showing XRD analysis results of a synthetic powder prepared according to an embodiment of the present invention. FIG.
3 is an electron micrograph of the active material powder synthesized according to this embodiment.
4 is a graph showing a charge / discharge capacity of a sample cell manufactured according to an embodiment of the present invention.
5 is a graph showing the cycle characteristics of a sample cell manufactured according to an embodiment of the present invention.
FIG. 6 is a graph showing electrode thickness measurement results of a sample cell manufactured according to an embodiment of the present invention before and after charging / discharging. FIG.
FIG. 7 is a graph showing the results of an Ex-situ XRD analysis of a sample manufactured in an embodiment of the present invention. FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to the preferred embodiments of the present invention with reference to the drawings.

The negative electrode active material composite for a lithium ion battery of the present invention comprises a CoP as a main phase and a MoP phase as a part thereof.

In the present invention, the CoP phase has an orthorhombic crystal structure, and the MoP phase has a hexagonal crystal structure. In the present invention, the active material may further include at least one third phase other than the CoP and MoP phases. For example, the third phase is preferably a phosphide.

In one embodiment, the complex active of the present invention can be prepared via a hydrogenation denitrification process.

FIG. 1 is a flow chart illustrating a procedure for manufacturing a negative electrode active material according to an embodiment of the present invention.

Referring to FIG. 1, the starting material is prepared first. As the starting material, a P source, a Co source, and a Mo source are used (S112, S114, S116). In the present invention, the Co source and the Mo source are blended so that CoP: MoP becomes (1-x): x in terms of the synthesized composite. According to an embodiment of the present invention, x is preferably 0.05 or more, more preferably 0.1 or more. According to the embodiment of the present invention, it is preferable that x is in a range of 0.2 or less.

In the present invention, the P source is prepared in an appropriate ratio to the molar amount of Co and Mo. For example, in the present invention, for the production of CoP and MoP, the P source and the metal source can be compounded so that the molar fraction is 1: 1. However, in the present invention, the molar fraction may be different from the stoichiometric ratio. For example, it is also possible to produce a new phosphite by adding excess P or excess metal source as a starting material. For example, a P source may be added in excess to include a phosphite such as MoP ₂ .

Phosphate may be used as the P source in the present invention. As the phosphate, for example, (NH ₄ ) ₂ HPO ₄ can be used. As the Co source, a cobalt nitrate salt may be used. For example, Co (NO ₃ ) ₃ .6H ₂ O (cobalt nitrate hexahydrate) may be used as the Co source. As the MoP source, a molybdate such as (NH ₄ ) 6 Mo ₇ O ₂₄ .4H ₂ O (ammonium molybdate) may be used.

In the present invention, it is preferable that the P source, Co source and Mo source, which are starting materials, are provided in a solution state, preferably in an aqueous solution state. The P source solution, the Co source solution and the Mo source solution are stirred for an appropriate time for uniform mixing and dissolution respectively.

Subsequently, a Co source solution is mixed with the stirred P source solution, and then the Mo source solution is mixed (S118). In the present invention, the mixing order of each solution may be changed. The mixed source solution is stirred for an appropriate time and dried (S120).

Subsequently, the dried mixed source is calcined at a temperature of about 450 to 550 DEG C in the atmosphere (S122). Subsequently, the calcined powder is heat-treated in a reducing atmosphere (S124). The reducing atmosphere can be carried out, for example, while supplying H ₂ at an appropriate flow rate. Of course, in the present invention, the reducing atmosphere may also be performed in a mixed gas atmosphere including a hydrogen gas, for example, an H ₂ + H ₂ O atmosphere. In addition, the heat treatment may be performed at a suitable temperature for the synthesis of CoP, for example, at a temperature of 600 to 800 ° C.

Through such a process, a negative electrode active material composed of CoP and MoP can be synthesized.

As described later, the Mo source added for the production of the CoP complex active material in the present invention promotes the reduction of the cobalt oxide formed by calcination. In the present invention, MoP in the complex active material is also expected to act as an active material for insertion and desorption, and can act as a buffer for volume expansion upon insertion of CoP.

<Production example of CoP / MoP negative electrode composite active material>

CoP / MoP composite was prepared. Ammonium phosphate ((NH ₄ ) ₂ HPO ₄ ; Junsei Chemical Co., Ltd.) was used as a P source and ammonium molybdate ((NH ₄ ) ₆ Mo ₇ O ₂₄ .4H ₂ O, Junsei Chemical Co., Ltd.) , And cobalt nitrate hexahydrate (Co (NO ₃ ) ₃ .6H ₂ O; Aldrich) was used as the Co source.

(# 1), 0.95: 0.5 (# 2), 0.9: 0.1 (# 3), and 0.8: 0.2 (# 4) in terms of the weight ratio of CoP: MoP as a synthesized conversion equivalent of CoP phosphide and MoP phosphide Each of the sources was weighed, dissolved in 50 ml of distilled water in a 100 ml beaker, and the source aqueous solutions were each stirred for 2 hours.

Table 1 below is a table showing the composition of each raw material in this embodiment.

division #One #2 # 3 #4 Co (NO ₃ ) ₃ .6H ₂ O 16.52 g 15.69 g 14.86 g 13.21 g (NH ₄ ) ₆ Mo ₇ O ₂₄ .4H ₂ O - 0.35 g 0.70 g 1.40 g (NH _{4) 2} HPO ₄ 7.42 g 7.31 g 7.20 g 6.98 g

Then, an appropriate amount of Co (NO ₃ ) ₃ .6H ₂ O was added to the (NH ₄ ) ₂ HPO ₄ solution, followed by stirring for 2 hours. (NH ₄ ) ₆ Mo ₇ O ₂₄ .4H ₂ O was added, Were also dried in an oven.

The dried precursor powder was calcined in an air atmosphere at 500 캜 for 5 hours. Subsequently, a CoP / MoP composite was synthesized after reduction heat treatment at 650 ° C. and hydrogen atmosphere for 5 hours.

FIG. 2 is a graph showing XRD analysis results of a synthetic powder prepared according to an embodiment of the present invention. FIG.

Referring to FIG. 2, in the case of a sample to which no Mo source is added, it corresponds to a CoP peak (ICSD code: 43401) and a small amount of Co ₂ P ₂ O ₇ (Monoclinic P121 / c1, ICSD code: 2830) A second order phase peak is present.

The second phase (Co ₂ P ₂ O ₇ ) peak is reduced as Mo content increases as the raw material is added, and the second phase (Co ₂ P ₂ O ₇ ) peak is extinguished when 10 wt% And only a peak of CoP and MoP is observed for a sample added with a Mo content of 10 wt% or more based on MoP conversion.

Phosphorus such as Co ₂ P ₂ O ₇ reacts with lithium during initial charge and discharge and decomposes, which can adversely affect charge-discharge stability. It can be seen that the MoP added in the present invention promotes the reaction of converting the phosphate to the phosphide.

Table 2 is a graph showing the results of calculating the content of each phase from the XRD pattern.

Sample CoP MoP CoP ₂ O ₇ # 1 (CoP) 86 - 14 # 2 (0.95CoP-0.05MoP) 92 4 4 # 3 (0.9CoP-0.1MoP) 90 10 - # 4 (0.8CoP-0.2MoP) 80 20 -

As shown in Table 2, as the amount of MoP increases, CoP ₂ O ₇ disappears in the synthesized composite, and only peaks of CoP and MoP are present. This result shows that the addition of an appropriate amount of Mo source to the hydrogen denitrification reactor enables the production of the CoP / MoP composite phase without the generation of the secondary phase. It can be seen that the added Mo source functions as a catalyst promoting the CoP production reaction in the reduction process.

3 is an electron micrograph of the active material powder synthesized according to this embodiment. 3 (a) is a photograph of # 1 sample, and (b) is a photograph of # 2 sample.

&Lt; Example of battery cell production &

The CoP / MoP composite active material prepared above was mixed with a Super P black conductive material and a PAI (poly amideimde) binder at a weight ratio of 75:10:15. Lt; / RTI &gt; to produce a negative electrode.

1M LiPF ₆ was dissolved in ethylene carbonate (EC) / diethyl carbonate / EMC (ethylmethyl carbonate) (bipiper 3: 5: 2) as a solvent, and 10.0 wt% FEC was added thereto to prepare an electrolytic solution.

A 2032 coin cell type cell with a cathode, a polypropylene (P) separator and a lithium anode was fabricated.

The charge / discharge capacity and cycle characteristics of the battery cell were measured using T-3100 manufactured by TOYO. At this time, the charge and discharge conditions were 0.1 C (initialization, 0.005 to 2 V) -> 0.1 C (1 to 100 cycles to 0.005 to 2.0 V).

FIG. 4 is a graph showing the charge / discharge capacity in the initial cycle for each sample cell in this embodiment. FIG. 5 (a) and 5 (b) are graphs showing the cycle characteristics for each sample cell.

As can be seen from the charge and discharge curves in FIG. 4, the CoP and CoP / MoP negative active materials exhibit a flat region due to a CoP decomposition reaction by lithium insertion at 0.1 V at the initial charging.

In the case of CoP and CoP-MoP (9.5: 1.5), a flat region of 1.0 V and 0.9 V due to the reaction of Co ₂ P ₂ O ₇ was observed. The voltage drop is linear from 0.7 V to 0.1 V, presumably due to the SEI film formation due to the reaction between the electrolyte and the electrode. In the discharging process, it was confirmed that a linear curve shape was observed in a region of about 0.75 and 0.1 V after a sharp voltage rise from 0.005 to 0.7 V due to lithium desorption.

In the case of the CoP-MoP compound, a charge-discharge curve similar to that of the CoP compound is observed except for a flat voltage of about 1 V. However, the capacity expression in the voltage drop period up to 0.1 V during the charge reaction was higher than that of the CoP compound, which is presumed to be due to the capacity of the MoP formed in the complex form. It is also confirmed that the reaction amount of lithium is decreased in the flat region at 0.1 V as compared with the CoP compound.

In the second charging process, both materials showed a different shape from the initial charging process, and they were found to be flat at about 0.6 and 0.1 V, respectively. This is presumably due to the structural decomposition of the CoP compound generated in the initial charging process of lithium. Charge-discharge capacity and cycle characteristics are shown in Table 3. &lt; tb &gt; &lt; TABLE &gt;

division Initial cycle
(Charge / discharge capacity / efficiency) After 100 cycles
Capacity retention rate (%) CoP 1014 mAh / g
755 mAh / g
74.5% 49.6 CoP / MoP (9.5: 1.5) 958 mAh / g
548 mAh / g
57.2% 81.8 CoP / MoP (9: 1) 765 mAh / g
358 mAh / g
46.8% 100 CoP / MoP (8: 2) 884 mAh / g
361 mAh / g
40.8% 100

6 is a graph showing the electrode thickness measured before and after charging / discharging.

After the lithiation and delithiation were performed to each potential, the coin cell was disassembled and the thickness of each electrode was measured using a micrometer.

Referring to FIG. 6, it was confirmed that the thickness of the CoP sample increased by about 120% after lithium insertion, and decreased to 22% after lithium removal,

CoP / MoP (8: 2) samples were increased by about 28% and decreased by 6% after lithium removal. Also in the second cycle, it was confirmed that the volume expansion / shrinkage of the electrode was gentle as compared with the CoP-MoO 2 CoP. From these results, it was confirmed that the cycle characteristics due to the volume expansion inhibition were improved in the case of the CoP-MoP composite by introducing MoP which is excellent in mechanical properties and reversibly reacted with lithium in the CoP compound.

FIG. 7 is a graph showing the results of an Ex-situ XRD analysis of a sample manufactured in an embodiment of the present invention. FIG.

The analysis was performed by lithiation and delithiation to each potential, and then the coin cell was disassembled and XRD analysis of each electrode was performed.

Referring to FIG. 7 (a), it can be seen that most of the CoP peaks existing in the initial stage of lithium insertion / desorption disappear in the case of the CoP sample. This is because the Li-P compound and the CoP remain in Co form by the insertion of lithium, and no special phase is observed after the lithium is desorbed.

7 (b), peaks of MoP and CoP were observed in the CoP-MoP (8: 2) sample even after insertion and desorption of lithium, and it was confirmed that the Li-P compound was reversibly formed and decomposed there was.

From this, it can be seen that the CoP / MoP composite having MoP, which has excellent mechanical properties to the CoP compound and reversibly reacted with lithium, has a better structural stability than the CoP even in the case of lithium insertion and desorption, Can be confirmed.

Claims (9)

Wherein the Co source and the Mo source are prepared so that the weight ratio of CoP: MoP is 1-x: x (where x? 0.05) based on the synthesized CoP and MoP, Blending; And
Calcining the mixed solution in an atmospheric environment; And
And heat-treating the calcined powder in a reducing atmosphere to synthesize a composite powder of a CoP phase and an MoP phase. The method according to claim 1,
Wherein the P source is phosphate. &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt; The method according to claim 1,
Wherein the Mo source is molybdate. &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt; The method according to claim 1,
Wherein the Co source is a cobalt nitrate salt. The method according to claim 1,
Wherein the mixed solution is an aqueous solution. The method according to claim 1,
Wherein x is 0.1? X? 0.2. The method according to claim 1,
Wherein the reducing atmosphere is a hydrogen atmosphere. The method according to claim 1,
Wherein the composite powder in the synthesis step contains no cobalt oxide. In a negative electrode for a lithium secondary battery,
Conductive substrates; And
As a composite of a CoP phase and an MoP phase coated on the conductive base,
Wherein the MoP phase is contained in an amount of 10 to 20% by weight in the composite.

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