KR101999146B1 - Lithium-iron-manganese phosphate cathode active material composition, method for preparing the same and lithium secondary thin film battery using the same - Google Patents

Abstract

Disclosed are an olivine-based lithium-iron-manganese phosphate compound positive electrode active material composition for a lithium thin film secondary battery, which is represented by LiFe_1-xMn_xPO_4 (0<x<0.5), a method for manufacturing the same, and a lithium thin film secondary battery using the same. Accordingly, a positive electrode active material having a high transmittance, a high operating voltage, a high capacity, and suitable for a transparent lithium thin film secondary battery can be provided.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a lithium-iron-manganese phosphate compound, a lithium-iron-manganese phosphate compound, and a lithium secondary battery using the same.

TECHNICAL FIELD The present invention relates to a lithium-iron-manganese phosphate compound cathode active material composition, a method for producing the same, and a lithium secondary battery, particularly, a lithium thin film secondary battery using the same.

Lithium secondary batteries are widely used as portable power supplies for small-sized devices such as mobile phones, tablet computers, notebooks, and cameras. In addition, with the recent rapid development of electric vehicles and energy storage devices, demands for high energy density, high output, and high stability electrode materials are increasing.

At present, LiCoO ₂ and LiFePO ₄ anode are used as cathode active materials for lithium secondary batteries, and LiCoO ₂ is restricted due to high cost of Co, toxicity to human body and explosion risk.

In addition, LiFePO ₄ is a cheap raw material and environmentally friendly material, but it has disadvantages such as low operating voltage. Nonetheless, LiFePO ₄ with an olivine structure has excellent stability and high capacity as a conventional LiCoO ₂ It is attracting much attention as a substitute material for cathode materials.

Recently LiMnPO ₄ having an olivine structure of LiFePO _4, as it is not only has a high stability and high capacity benefits of LiFePO ₄ has a high energy density and a high operating voltage (4.1V), for a lithium secondary battery positive electrode material to the next generation are actively Research.

However, since LiMnPO ₄ has low electric conductivity and ion conductivity, there is a problem in expressing the theoretical capacity.

Therefore, in order to overcome the low electrical conductivity and ionic conductivity of LiMnPO ₄ , several studies have been carried out in order to overcome the problems of nanoparticle formation and carbon coating on particles. Some of the Li _- Fe _{- 1 - x} Mn _x PO Research on ₄ / C materials is underway.

However, in the case of the existing technology, it is difficult to synthesize it as a method for applying to a thick film on the premise of using a conductive material such as carbon, and it is difficult to apply it as a thin film.

Therefore, it is required to develop a lithium secondary battery cathode active material capable of satisfying high stability and high capacity required in wearable devices and micro micro devices.

Korean Patent Application Publication No. 10-2016-0060856

 J. Mater. Chem., Vol 21, pp. 15813-15818 (2011)

Exemplary embodiments of the present invention provide, in one aspect, a lithium-iron-manganese battery having a high operating voltage and high capacity, which is simple to synthesize and can be applied as a thin film secondary battery, Phosphate compound, a process for producing the same, and a lithium thin film secondary battery using the same.

In an exemplary embodiment of the present invention, there is provided an olivine lithium-iron-manganese phosphate compound cathode active material composition for a lithium thin film secondary battery in which a conductive material is not coated, wherein the cathode active material composition of lithium- to provide.

[Chemical Formula 1]

LiFe _{1 - X} Mn _X PO ₄

(Wherein x is in the range of 0 < x < 0.5).

Exemplary embodiments of the present invention also provide a method for preparing the lithium-iron-manganese phosphate compound cathode active material composition, comprising: searching for a composition of LiFe _{1 - X} Mn _x PO ₄ through a continuous diffusion method; - iron-manganese phosphate compound cathode active material composition.

Exemplary embodiments of the present invention also provide a positive electrode comprising the lithium-iron-manganese phosphate compound cathode active material composition and a lithium thin film secondary battery comprising the same.

When a thin film of a lithium-iron-manganese phosphate compound cathode active material composition according to an exemplary embodiment of the present invention is applied to a cathode material of a lithium thin film secondary battery, a higher operating voltage is provided than a conventional LiFePO ₄ composition, A thin film secondary battery can be obtained. In addition, the olivine crystal structure is highly stable. In addition, since there is no use of a conductive material such as carbon, it can be formed into a thin film by a simple method. Therefore, it is very useful as a cathode active material of a lithium thin film secondary battery which can satisfy high stability and high capacity required in wearable devices and micro micro devices in recent years.

FIG. 1 is a schematic view showing a thin film manufacturing process using a continuous composition diffusion method according to an embodiment of the present invention.
FIG. 2 is a graph showing a characteristic analysis result of a single thin film of LiFePO ₄ and LiMnPO ₄ for a continuous composition diffusion method according to an embodiment of the present invention.
3 shows the XRD results of the olivine-based lithium-iron-manganese phosphate compound cathode active material thin film deposited by the continuous diffusion method according to the embodiment of the present invention.
FIG. 4 shows charge / discharge characteristics of the olivine-based lithium-iron-manganese phosphate compound cathode active material thin film deposited through the continuous diffusion method according to an embodiment of the present invention.
FIG. 5 is a graph showing the compositional analysis results of a cathode active material layer of an olivine-based lithium-iron-manganese phosphate compound deposited by a continuous diffusion method according to an embodiment of the present invention.
6 shows the XRD results of an olivine-based lithium-iron-manganese phosphate compound cathode active material powder synthesized for coin cell fabrication, according to an embodiment of the present invention.
FIG. 7 shows charge / discharge characteristics of a coin cell fabricated using the LiFe _0.77 Mn _0.23 PO ₄ composition and the conventional LiFePO ₄ composition powder, which were searched through the continuous diffusion method, according to an embodiment of the present invention.

Exemplary implementations of the present invention will now be described in detail with reference to the accompanying drawings.

The term &quot; continuous compositional diffusion method &quot; as used herein refers to a method of continuously depositing a thin film having different compositions continuously on a substrate by simultaneously sputtering the composition to be sought using, for example, a 90 DEG vertically opposed independent gun, Is a method capable of searching for the composition of the compound having a small amount of hydrogen in a short time.

In the present specification, the thin film secondary battery is a secondary battery in which all components of the anode / electrolyte / cathode are in a solid state. It can be manufactured to a thickness of several microns (탆) on a thin substrate through a CVD or PVD deposition method.

In the exemplary embodiments of the present invention, the optimum composition of LiFePO ₄ according to the substitution amount of Mn was investigated in applications such as thin film secondary batteries which can not use a conductive material such as carbon.

Specifically, after the substitution of Mn for the Fe sites of the LiFePO ₄ cathode without a conductive material such as carbon by the continuous diffusion method, electrochemical characterization of the whole composition was carried out. Of these, conductive materials such as carbon Without coating, a composition with high operating voltage and high capacity was identified.

In this way, it was found that the optimal composition of the cathode active material thin film exhibiting the high voltage and high capacity characteristics in the composition different from the known composition by replacing Mn in Fe in the LiFePO ₄ cathode active material thin film by the continuous composition diffusion method.

Specifically, in exemplary embodiments of the present invention, an olivine lithium-iron-manganese phosphate compound cathode active material composition for a lithium thin film secondary battery in which a conductive material is not coated is characterized by comprising a lithium-iron-manganese phosphate compound anode An active material composition and a lithium thin film secondary battery using the same are provided.

[Chemical Formula 1]

LiFe _{1 - X} Mn _X PO ₄

(Wherein x is in the range of 0 < x < 0.5 or 0.01 < x &lt; 0.5, preferably 0.01 &

The substitution with Mn starts to increase the voltage and capacity. As can be seen from FIG. 4b below, the Mn addition exhibits a higher capacity and operating voltage than LiFePO _{4 with} x = 0 and an optimal composition at position 2 (x = 0.23). However, in the range exceeding x = 0.5, the capacity decrease remarkably occurs, so x should be less than 0.5.

In an exemplary embodiment, the thickness of the cathode active material film is 0.5 to 10 占 퐉. If the thickness is less than 0.5 탆, the capacity is too small. If the thickness is more than 10 탆, the charge / discharge capacity may be decreased due to the reduction in the efficiency of lithium insertion and extraction due to the increase in thickness.
In an exemplary embodiment, the anode thin film may be a transparent anode thin film.

The LiFe _{1 - x} Mn _x PO ₄ (0 < x < 0.5) cathode active material composition thin film described above provides a higher operating voltage than that of the conventional LiFePO ₄ composition, so that a lithium thin film secondary battery having a higher energy density can be obtained.

Therefore, the olivine-based lithium-iron-manganese phosphate compound composition of the exemplary embodiments of the present invention is particularly useful as a cathode active material of a lithium thin film secondary battery, and can be suitably used for a wearable device or a microelectronic device.

The following illustrative embodiments of the invention are described in further detail by way of example. The embodiments of the present invention are illustrated for illustrative purposes only and the embodiments of the present invention can be implemented in various forms and the present invention should not be construed as being limited to the embodiments.

<Examples>

In order to evaluate the electrochemical properties of LiFePO ₄ thin films substituted with Mn without using a conductive material such as carbon, the continuous composition diffusion method was used to continuously deposit the entire composition according to the ratio of Mn: Fe on one substrate, Respectively.

1 is a view illustrating a thin film manufacturing process using a continuous diffusion method according to an embodiment of the present invention.

As shown in FIG. 1, first, an RF-magnetron gun was charged with an olivine-based LiFePO ₄ target and a LiFePO ₄ target by an off-axis continuous composition diffusion method in which the direction of the sputter gun was arranged at 90 ° to the substrate LiMnPO ₄ target was used for the composition search.

FIG. 2 is a graph showing a characteristic analysis result of a single thin film of LiFePO ₄ and LiMnPO ₄ for a continuous composition diffusion method according to an embodiment of the present invention.

In order to proceed with the composition search using the continuous diffusion method, it is important to optimize the conditions of the two independent targets. Therefore, the preceding experiment was carried out with each independent single composition. As shown in FIG. 2, the characteristics of the thin films deposited on both targets were analyzed.

In the case of LiFePO ₄ , optimal deposition conditions were established through X-ray diffraction analysis and charge / discharge experiments, and the experiment was conducted using the LiMnPO ₄ target in the same manner.

As can be seen from FIG. 2, the X-ray diffraction analysis of the LiMnPO ₄ single thin film showed a single phase consistent with the peak of LiMnPO ₄ found in the JCPDS, and it was confirmed that the charging and discharging had a discharge of 5 hh / cm 2 there was. This value is similar to that of the existing research literature of LiMnPO ₄ not coated with carbon (Non-Patent Document 1).

LiFePO ₄ Target and LiMnPO ₄ A thin film was deposited on the substrate at room temperature for 1 hour by sputtering with a power of 160 W and 120 W applied to the target, respectively.

As for the deposition conditions, deposition was performed at a partial pressure of 5 mTorr of the chamber using argon gas as in the optimum deposition conditions found in the preceding experiments. For crystallization of the thin film, crystallization was carried out by keeping in a reducing atmosphere of 500 캜 for 2 hours using an atmosphere furnace after the deposition.

FIG. 3 shows XRD results of an olivine-based lithium-iron-manganese phosphate compound cathode active material thin film deposited by a continuous diffusion method according to an embodiment of the present invention.

As can be seen from FIG. 3, X-ray diffraction analysis was performed to confirm the crystallinity of the thin film crystallized through the post-heat treatment, and the X-ray diffraction pattern of the olivine structure was confirmed.

This was consistent with the LiMnPO ₄ peak found in JCPDS and confirmed that no secondary phase was present. Also, LiMnPO ₄ As the amount of iron to manganese substitution increased, the main peaks shifted to low angle.

X - ray diffraction analysis confirmed the crystallinity of the thin films.

FIG. 4 is a graph showing the charge-discharge characteristics (FIG. 4A) and the capacity characteristics (FIG. 4B) of the lithium-iron-manganese phosphate compound cathode active material deposited by the continuous diffusion method according to the present invention, .

As shown in FIG. 4, charging and discharging characteristics were evaluated for each deposited position. As a result, as the amount of manganese increased, the discharge capacity increased and the capacity decreased after Positon 2 . In addition, the capacity decrease after position 5 was remarkable.

The x value for each position is x = 0.11 for position 1, x = 0.23 for position 2, x = 0.38 for position 3, x = 0.49 for position 4, x = 0.57 for position 5 and x = 0.65 for position 6.

Therefore, in LiFe _{1 - x} Mn _x PO ₄ , x is in the range of 0 < x < 0.5 or 0.01 < x &lt; 0.5, preferably 0.01 &

This shows that manganese improves the operating voltage by increasing the potential difference, but when it is replaced by more than a certain amount, the capacity decrease is caused by the low ion conductivity of manganese.

Therefore, it was confirmed that the composition deposited at the position (Position 2) had the best electrochemical characteristics among the various compositions determined by the continuous diffusion method, and it was confirmed that the LiFePO ₄ had higher discharge capacity than the LiFePO ₄ .

It was confirmed that the cathode active material deposited at the position 2 had a discharge capacity of 27.8 hh / cm 2 when the thickness was 1 탆, and it was confirmed that the operation voltage was higher than LiFePO ₄ due to the effect of manganese .

Using Rutherford backscattering spectrometry, the composition of Position 2 showing the best electrochemical properties was confirmed.

FIG. 5 is a graph showing the compositional analysis (FIG. 5A) and the respective positions of the lithium-iron-manganese phosphate compound cathode active material thin films deposited through the continuous diffusion diffusion method according to the embodiment of the present invention (Fig. 5B).

As shown in Fig. 5A, the position (Position 2) is LiFe _{0 . 77} Mn _{0 . 23} PO ₄ .

Also, as shown in Fig. 5B, the position 1 is LiFe _{0 . 89} Mn _{0 . 11} PO ₄ , position 3 is LiFe _0.62 Mn _0.38 PO ₄ , and position 4 is LiFe _{0 . 51} Mn _{0 . 49} PO ₄ , and position 5 is LiFe _{0 . 43} Mn _{0 . 57} PO ₄ , and position 6 is LiFe _{0 . 35} Mn _{0 . 65} PO ₄ composition.

On the other hand, LiFe _{0 . 77} Mn _{0 . 23} PO ₄ composition showed better characteristics than LiFePO ₄ .

The synthesis of the anode powder was carried out using Li ₂ CO ₃ (Aldrich Co), FeC ₂ O ₄ .2H ₂ O (Aldrich Co.), MnCO ₃ (Aldrich. Co.) and NH ₄ H ₂ PO ₄ (Aldrich Co.) Lt; / RTI &gt; as starting materials.

The anode materials LiFePO ₄ and LiFe _{0 . 77} Mn _{0 . 23} PO ₄ was prepared by ball milling the starting materials for 24 hours at a constant rate and then calcining at 350 ° C for 12 hours. The calcined powder was pressed and sintered with a pellet. The sintering was carried out at 650 ° C. for 12 hours in a nitrogen atmosphere. After the sintering, the hard pellet type material was pulverized and sieved to 400 mesh.

The positive electrode used in the coin cell was prepared by mixing 80 wt.% Of positive electrode powder, 15 wt.% Of conductive material (Supar P) and 5 wt.% Of PVdF (polyvinylidene fluoride) binder in NMP (Nmethylpyrrolidene) Uniformly applied to a foil, and then dried at 80 DEG C for 3 hours. The dried positive electrode was pressed with a rotary press and vacuum dried at 80 ° C for 24 hours. A coin cell was fabricated using a LiPF ₆ liquid electrolyte and a porous separator.

FIGS. 6A and 6B show XRD results of an olivine-based lithium-iron-manganese phosphate compound cathode active material powder synthesized for coin cell fabrication, according to an embodiment of the present invention.

As can be seen from FIGS. 6A and 6B, X-ray diffraction analysis was performed to confirm the crystallinity of the synthesized powder, and it was confirmed that the X-ray diffraction pattern of the olivine structure was confirmed. This was consistent with the LiFePO ₄ peak found in JCPDS and confirmed that no secondary phase was present. LiFe ₀ substituted with manganese _{. 77} Mn _{0 . 23} PO ₄ composition, it was confirmed that the main peaks were shifted to low angle.

The prepared coin cell was subjected to electrochemical characterization using a WBCS3000 charge / discharge device.

FIG. 7 is a graph showing the relationship between the composition of LiFe _0.77 Mn _0.23 PO ₄ (LFMP) and the composition of LiFePO ₄ Discharge characteristics of a coin cell fabricated using a coarse powder (LFP) composition powder.

As shown in FIG. 7A, LiFe _{0 . 77} Mn _{0 . 23} PO ₄ composition (3.5 V, 121.8 mAh / g) showed higher operating voltage and discharge capacity than conventional LiFePO ₄ (3.4 V, 112.3 mAh / g).

FIG. 7B shows the average discharge capacity according to the current density of six samples _{. In} this result, LiFe _{0 . 77} Mn _{0 . 23} PO ₄ It was confirmed that the composition had a discharge capacity higher than that of LiFePO ₄ and showed high reproducibility and reliability.

As can be seen from the results of FIG. 7, it can be seen that even when applied as a thick film instead of a thin film, excellent characteristics are exhibited.

Claims (9)

An olivine-based lithium-iron-manganese phosphate compound cathode active material composition for a lithium thin film secondary battery,
Conductive material is not coated,
A lithium-iron-manganese phosphate compound according to claim 1, wherein the lithium-iron-manganese phosphate compound is represented by the following formula.
[Chemical Formula 1]
LiFe _{1 - X} Mn _X PO ₄
(Where x is in the range of 0 < x < 0.38).
The method according to claim 1,
Wherein x is 0.01 < x &lt; 0.38. &Lt; / RTI &gt;
The method according to claim 1,
The lithium-iron-manganese phosphate compound according to claim 1, wherein x is 0.01? X? 0.23.
The method according to claim 1,
The lithium-iron-manganese phosphate compound according to claim 1, wherein x is 0.23.
As a positive electrode thin film for a lithium thin film secondary battery,
A positive electrode thin film for a lithium thin film secondary battery, comprising the lithium-iron-manganese phosphate compound cathode active material composition according to any one of claims 1 to 4.
6. The method of claim 5,
Wherein the positive electrode thin film is a transparent positive electrode thin film.
6. The method of claim 5,
Wherein the thickness of the positive electrode thin film is 0.5 to 10 mu m.
As a lithium thin film secondary battery,
The lithium thin film secondary battery according to any one of claims 1 to 4, comprising a cathode thin film made of a lithium-iron-manganese phosphate compound cathode active material composition.
A process for producing a lithium-iron-manganese phosphate compound cathode active material composition according to any one of claims 1 to 4,
Through continuous diffusion method, LiFe _{1 - X} Mn _X PO ₄ The method comprising the steps of: preparing a lithium-iron-manganese phosphate compound;

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