KR102292531B1 - Anode Active Materials comprising Si or Si Alloy Systems With MoP Coating For Li Ion Batteries, And Anodes comprising The Same And Manufacturing Methods Thereof - Google Patents

Abstract

Disclosed is a method for preparing a phosphide-based composite anode active material for a lithium secondary battery having improved charge/discharge cycle characteristics. providing a first solution comprising a P source, a second solution comprising a Mo source, and a third solution comprising a Fe source; mixing the first to third solutions; drying and calcining the mixed solution; and synthesizing a composite powder of iron phosphide and molybdenum phosphide by heat-treating the calcined powder in a reducing atmosphere. According to the present invention, it is possible to provide a metal phosphide-based negative active material for a lithium secondary battery capable of improving cycle characteristics by suppressing volume expansion of the metal phosphide-based negative active material.

Description

Anode Active Materials comprising Si or Si Alloy Systems With MoP Coating For Li Ion Batteries, And Anodes comprising The Same And Manufacturing Methods Thereof

The present invention relates to an anode active material for a lithium secondary battery, and more particularly, to a metal phosphide-based anode active material for a lithium secondary battery with improved charge/discharge cycle characteristics.

A lithium secondary battery is largely composed of a positive electrode, an electrolyte, and a negative electrode. A commonly commercialized lithium secondary battery has a structure in which a 20-100 μm thick polymer separator is added to a liquid electrolyte composed of an organic solvent and lithium salt. The charged electrons also move from the cathode to the anode, and vice versa during charging.

For the next-generation high-capacity lithium secondary battery negative electrode material Si, Sn-based metal-based active material is attracting attention as Li _{4 .4} Si, Li _{4 .4} by metal-to-metal, such as Sn based on the compound-forming reaction experimentally, about 3500 ~ 4200mAh / g Although the electrochemical charge/discharge capacity of It faces difficult technical problems.

In order to solve this problem, a layered structure such as _{MoP 2} among MX (M=Si,Sn,Al,V,Mn,Mo, Co.., X=S,P,N,O) type metal materials It has been reported that some compounds having a structure have a partial insertion reaction rather than an existing alloying or conversion reaction when reacting with Li. However, it still has a high Li reaction potential, a slow activation rate that takes more than 20 cycles to reach 100% reversible efficiency close to 100% during the initial cycle, and a conversion reaction when a certain amount of Li is charged, resulting in an electrode lifetime Since it has a fatal effect on the battery, it has a disadvantage that it operates in a limited range of charge and discharge potentials.

Metal phosphide for lithium secondary batteries is mainly synthesized using mechano milling. However, in the case of this method, crystallinity is very low, and long-term heat treatment is required, so that synthesis is difficult.

In addition, the metal phosphide-based negative electrode is inevitably accompanied by volume expansion due to the conversion reaction in the low voltage region during initial charging and discharging. The volume expansion of these electrodes impairs cycle characteristics and is difficult to apply to batteries. In the case of FeP, it also has two reaction mechanisms (insertion and conversion) during charging, and exhibits cycle degradation with volume expansion due to a conversion reaction at a low voltage.

(Prior Literature 1) S. Boyanov et. al., Chemistry of materials, 18, 3531 (2006) (Prior Document 2) S. Boyanov et. al., Chemistry of Materials, 21, 3684 (2009)

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

Another object of the present invention is to provide a metal phosphide active material prepared by the method described above.

Another object of the present invention is to provide an anode comprising a metal phosphide-based active material for a lithium secondary battery including the active material described above.

In order to achieve the above technical problem, the present invention provides a first solution containing a P source, a second solution containing a Mo source, and a third solution containing a Fe source; mixing the first to third solutions; drying and calcining the mixed solution; and synthesizing a composite powder of iron phosphide and molybdenum phosphide by heat-treating the calcined powder in a reducing atmosphere.

In the present invention, the P source may be phosphate, the Mo source may be molybdate, and the Fe source may be iron nitrate.

In addition, the first to third solutions may be aqueous solutions.

The mixing step of the present invention may further include adding a carbon source solution, and the carbon source is polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyaniline, and glucose. ), citric acid and sucrose may include at least one selected from the group consisting of.

In addition, in the present invention, the iron phosphide may include FeP and further include _{Fe 4 P.}

According to another aspect of the present invention, in the phosphide-based active material for a lithium secondary battery, the active material provides a phosphide-based active material for a lithium secondary battery, wherein the active material comprises a composite of iron phosphide and molybdenum phosphide.

In the present invention, the iron phosphide includes FeP and Fe _{4 P, and the content of Fe 4} P in the phosphide of the active material is preferably less than 2% by weight.

In addition, according to another aspect of the present invention, the present invention provides a negative electrode for a lithium secondary battery, comprising: a conductive substrate; and an anode material coated on the conductive substrate and made of a composite of iron phosphide and molybdenum phosphide.

In the present invention, the negative electrode material may further include carbon.

According to the present invention, it is possible to provide a metal phosphide-based negative active material for a lithium secondary battery capable of improving cycle characteristics by suppressing volume expansion of the metal phosphide-based negative active material.

1 is a flowchart illustrating a procedure for preparing a negative active material according to an embodiment of the present invention.
2 is a flowchart illustrating a part of a process of manufacturing an anode active material according to another embodiment of the present invention.
3 is a graph showing the results of XRD analysis of the synthetic powder prepared according to an embodiment of the present invention.
4 is a photograph of a FeP/MoP composite sample synthesized according to an embodiment of the present invention observed with a transmission electron microscope.
5 is a graph showing the charge/discharge capacity of a sample battery prepared according to an embodiment of the present invention.
6 is a graph showing cycle characteristics of a sample battery prepared according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail by describing preferred embodiments of the present invention with reference to the drawings.

The negative active material for a lithium ion battery of the present invention is composed of a composite of at least two kinds of phosphide.

In the present invention, the phosphide includes FeP and MoP. Here, FeP acts as an active material that reacts with lithium, and MoP acts as an inactive material that does not react with lithium. In addition, in the present invention, the phosphide may further include a _{metal-rich composition, such as Fe 4 P.}

The phase fraction (mol fraction) of MoP in the phosphide of the present invention is 5 to 40% It is preferably selected from the range.

It is characterized in that it is produced through a hydrogenation denitrification reaction process using the Fe source, Mo source and P source of the present invention as starting materials.

1 is a flowchart illustrating a procedure for preparing a negative active material according to an embodiment of the present invention.

Referring to FIG. 1 , first, starting materials are prepared. As the starting material, P source, Fe source and Mo source are used (S112, S114, S116). For the production of MoP and FeP in the present invention, the P source and the metal source may be combined so that the mole fraction is 1:1. However, in the present invention, the mole fraction may be formulated differently from the stoichiometric ratio. For example, it is possible to create a new phosphide by adding an excess of P or an excess of metal source as a starting material. _{For example, a phosphide such as Fe 4} P may be generated by adding a metal source in excess.

Phosphate may be used as the P source in the present invention. As the phosphate salt, for example, (NH ₄ ) ₂ HPO ₄ and the like may be used. An iron nitrate salt may be used as the Fe source. For example, Fe(NO ₃ ) ₃ ·9H ₂ O may be used as the Fe source. Molybdate may be used as the Mo source. For example, (NH ₄ ) ₆ Mo ₇ O ₂₄ ·4H ₂ O may be used as the Mo source. In the present invention, it is preferable that the P source, Fe source and Mo source, which are starting materials, are provided in a solution state, preferably in an aqueous solution state.

The P source solution, Fe source solution, and Mo source solution are each stirred for an appropriate time for uniform mixing and dissolution (S122, S124, S126).

Then, the stirred P source solution is mixed with the Fe source solution, and then the Mo source solution is mixed (S130). In the present invention, the mixing order of each solution may be changed. The mixed source solution is stirred for an appropriate time (S140) and dried (S150).

Then, the dried mixed source is calcined at a temperature of about 450 ~ 550 ℃ in the air (S160). Then, the calcined powder is heat-treated in a reducing atmosphere (S170). The reducing atmosphere may be performed while supplying _{H 2} at an appropriate flow rate, for example. In addition, the heat treatment may be performed at an appropriate temperature for the synthesis of MoP, for example, at a temperature of 750 ~ 850 °C.

Through this process, an anode active material made of Fe-Mo-P phosphide can be synthesized.

2 is a flowchart illustrating a part of a process of manufacturing an anode active material according to another embodiment of the present invention.

Referring to Figure 2, Fe source solution, P source solution and C source solution is prepared (S212, S214, S216). The Fe source and C source solutions may be prepared through the same materials and manufacturing process as those described with reference to FIG. 1 . Also, an aqueous solution may be used as the solution. As the C source solution, polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyaniline, glucose, citric acid, and sucrose in distilled water. A dissolved solution may be used.

Each solution is stirred for an appropriate time (S222, S224, S226), and a Fe/P/C source mixed solution is prepared (S230).

Although not shown, a Mo/P/C source mixed solution may also be prepared by the same procedure.

The prepared Fe/P/C source mixed solution and Mo/P/C source mixed solution are mixed, and the cathode made of a composite of Fe-Mo-P phosphide and carbon through drying, calcination and reduction heat treatment described in relation to FIG. 1 . The active material can be synthesized.

The anode active material according to the embodiment described with reference to FIG. 2 contains carbon used as the anode conductive material in the composite structure, thereby making it possible to manufacture an anode material having excellent conductivity.

<Preparation example of Fe-Mo-P negative active material>

An anode active material made of a Fe-Mo-P composite was prepared. As a starting material, ammonium phosphate ((NH ₄ ) ₂ HPO _{4 ; Junsei Chemical) was used as a P source, and ammonium molybdate ((NH 4} ) ₆ Mo ₇ O ₂₄ .4H ₂ O; Junsei Chemical) was used as a Mo source. , As the Fe source, iron nitrate nonhydrate (Fe(NO ₃ ) ₃ ·9H ₂ O; Junsei Chemical) was used.

As a composite powder of FeP phosphide and MoP phosphide, each source is weighed so that the weight ratio of FeP and MoP is 8:2, and 50 ml of distilled water is filled in a 100 ml beaker and then dissolved, and the aqueous solutions are stirred for 2 hours each did.

Table 1 below is a table showing the formulation of each raw material source of this embodiment.

division Content (g) (NH ₄ ) ₂ HPO ₄ 7.20 (NH ₄ ) ₆ Mo ₇ O ₂₄ 4H ₂ O 1.41 Fe(NO ₃ ) ₃ 9H ₂ O 18.99

Then, (NH ₄ ) ₂ HPO ₄ solution was mixed with Fe(NO ₃ ) ₃ ·9H ₂ O solution, and after stirring for 2 hours (NH ₄ ) ₆ Mo ₇ O ₂₄ ·4H ₂ O solution was mixed and for 12 hours After stirring, it was dried in an oven at 100 degrees. The dried mixed sauce was calcined at 500° C. in air for 5 hours.

Then, the calcined powder was heat-treated in a hydrogen atmosphere at 800° C. for 5 hours, and then an anode active material made of a FeP/MoP composite was prepared.

<Preparation example of Fe-Mo-P-C negative active material>

A negative active material made of a Fe-Mo-PC composite was prepared. As a starting material, ammonium phosphate ((NH ₄ ) ₂ HPO _{4 ; Junsei Chemical) was used as a P source, and ammonium molybdate ((NH 4} ) ₆ Mo ₇ O ₂₄ .4H ₂ O; Junsei Chemical) was used as a Mo source. , as the Fe source, iron nitrate nonhydrate (Fe(NO ₃ ) ₃ ·9H ₂ O; Junsei Chemical) was used, and as the carbon source, PVP was used.

First, according to the procedure described in relation to FIG. 2, an aqueous Fe/P/C source solution was prepared. In this process, the Fe source, P source, and PVP source aqueous solution were stirred for 2 hours, respectively, and then PVP source aqueous solution was mixed with P source aqueous solution, and the Fe source aqueous solution was mixed there again. Mo/P/C source aqueous solution was also prepared in the same manner. The content of Fe, Mo, and P sources was such that the weight ratio of FeP:MoP after synthesis was 8:2.

Table 2 below is a table showing the formulation of each raw material source of this embodiment.

division Content (g) (NH ₄ ) ₂ HPO ₄ 7.20 (NH ₄ ) ₆ Mo ₇ O ₂₄ 4H ₂ O 1.41 Fe(NO ₃ ) ₃ 9H ₂ O 18.99 PVP 2.76

The prepared Fe/P/C source aqueous solution and Mo/P/C source aqueous solution were mixed, stirred for 12 hours, and then dried in an oven at 100° C. The dried mixed source was calcined at 500° C. in the air for 5 hours, and the calcined powder was heat-treated at 800° C. in a hydrogen atmosphere for 5 hours to prepare an anode active material made of a FeP/MoP/C composite.

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

3 (a) and (b) are XRD patterns of the FeP/MoP composite sample and the FeP/MoP/C composite sample, respectively.

Referring to FIG. 3 , it can be seen that Fe, Mo, and P contained in the raw material powder were synthesized into an FeP phase and a MoP phase. In addition, it can be seen that a trace amount of Fe _{4 P phase was formed.}

As a result of phase analysis by Rietveld analysis of the PANalytical HoghScore Plus program, _{the weight ratio of FeP:MoP:Fe 4} P was 73:24:3 for the FeP/MoP composite sample, and FeP:MoP for the FeP/MoP/C composite sample: The weight ratio of Fe ₄ P was 81:18:1.

From this, in the case of the sample to which the carbon source was added, it was confirmed that the fraction of _{Fe 4 P was lower.}

4 is a photograph of a FeP/MoP composite sample synthesized according to an embodiment of the present invention observed with a transmission electron microscope.

First, (a) of FIG. 4 is a transmission electron microscope photograph of the synthetic powder, and FIGS. 4 (b) to (e) are photographs showing the results of EDS mapping for particles of the same synthetic powder.

From (b) to (e) of Fig. 4, it can be seen that P is well dispersed as a whole, and Mo and Fe are divided at different positions. Therefore, it can be seen that the sample of this example is formed of a composite of FeP and MoP.

<Battery cell manufacturing example>

Using the FeP/MoP composite sample of FIG. 3 and the FeP/MoP/C active material, respectively, a coating solution obtained by mixing Super P black conductive material and PAI (Poly amideimde) binder in a weight ratio of 75:10:15 in a weight ratio of Cu electrode The electrode was prepared by coating it on a substrate and drying it at a temperature of about 100°C.

_{1M LiPF 6} was dissolved in ethylene carbonate (EC)/diethyl carbonate (DEC)/ethylmethyl carbonate (EMC) (volume 3:5:2) as a solvent, and 10.0 wt% FEC was added to prepare an electrolyte solution.

The electrode prepared above was used, and lithium metal was used as the counter electrode. At this time, in order to prevent contact of each electrode, a P.P (polypropylene) separator was inserted and then impregnated with electrolyte, and then a 2032 coin cell type battery was manufactured.

Using the T-3100 manufactured by Toyo Corporation, charge/discharge capacity and cycle characteristics were measured. At this time, the charging and discharging conditions were 0.1C (initialization, 0.005 to 2 V) -> 0.1C (1 to 100 cycle ~, 0.005 to 2.0 V).

For comparison with the present invention, the FeP active material was prepared in the same manner to prepare a battery cell, and charge/discharge characteristics and cycle characteristics were evaluated under the same conditions.

5 (a) is a graph showing the charge/discharge capacity in the initial formation stage for each sample battery, and (b) is a graph showing the charge/discharge capacity in the first cycle. 6 is a graph showing cycle characteristics for each sample battery.

In the case of the FeP battery sample, a rapid decrease in discharge capacity was observed at the beginning of the cycle and decreased to 100 mAh/g or less after 10 cycles. Also, it can be seen that a sharp decrease in capacity with the progress of the cycle is not observed. In addition, it was confirmed that the FeP/MoP/C battery sample improved the capacity retention rate as the capacity increased and the cycle progressed, compared to the FeP/MoP battery sample.

Table 3 below is a table prepared by comparing the charge-discharge characteristics and cycle characteristics of the sample battery according to the present embodiment and the FeP sample battery.

division Mars stage
(Charging/Discharging Capacity/Efficiency) initial cycle
(Charging/Discharging Capacity/Efficiency) FeP sample cell 1152 mAh/g
514 mAh/g
51.5% 493 mAh/g
372 mAh/g
75.5% FeP/MoP
sample battery 756 mAh/g
576 mAh/g
76.2% 621 mAh/g
601 mAh/g
96.7% FeP/MoP/C
sample battery 905 mAh/g
518 mAh/g
57.3% 736 mAh/g
650mAh/g
88.2%

Claims (13)

providing a first solution comprising a P source, a second solution comprising a Mo source, and a third solution comprising a Fe source;
mixing the first to third solutions;
drying and calcining the mixed solution; and
and synthesizing a composite powder of iron phosphide and molybdenum phosphide by heat-treating the calcined powder in a reducing atmosphere. According to claim 1,
The P source is a method of manufacturing an anode active material of a lithium secondary battery, characterized in that the phosphate. According to claim 1,
The Mo source is a method of manufacturing a negative active material of a lithium secondary battery, characterized in that the molybdate. According to claim 1,
The Fe source is an anode active material manufacturing method of a lithium secondary battery, characterized in that the iron nitrate salt. According to claim 1,
The first to third solutions are a method of manufacturing a negative active material for a lithium secondary battery, characterized in that the aqueous solution. According to claim 1,
The method of manufacturing a negative active material of a lithium secondary battery, characterized in that it further comprises the step of adding a carbon source solution in the mixing step. 7. The method of claim 6,
The carbon source of the carbon source solution is made of polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyaniline, glucose, citric acid, and sucrose. A method of manufacturing a negative active material for a lithium secondary battery, comprising at least one selected from the group. According to claim 1,
The iron phosphide is a method of manufacturing a negative active material, characterized in that it comprises FeP. According to claim 1,
The iron phosphide is an anode active material manufacturing method, characterized in that it further _{comprises Fe 4 P.} In the phosphide-based active material for a lithium secondary battery,
The active material includes a composite of iron phosphide and molybdenum phosphide,
The iron phosphide includes FeP and Fe ₄ P,
Phosphide-based active material for a lithium secondary battery, characterized in that the content _{of Fe 4} P in the phosphide of the active material is less than 2% by weight.
delete In the negative electrode for a lithium secondary battery,
conductive substrate; and
It is applied on the conductive substrate and includes an anode material made of a composite of iron phosphide and molybdenum phosphide,
The iron phosphide includes FeP and Fe ₄ P,
A negative electrode for a lithium secondary battery, characterized in that the content of Fe _{4 P in the phosphide is less than 2% by weight.} 13. The method of claim 12,
The negative electrode material for a lithium secondary battery, characterized in that it further comprises carbon.

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