KR101248108B1 - Negative electrode for lithium ion secondary battery, production method thereof and lithium ion secondary battery comprising the same - Google Patents

Abstract

Amorphous silicon according to the present invention Oxide (SiO _x 0.3 ≤ x ≤ 1.5) thin-film anode shows improved charge / discharge characteristics due to less structural change stress than crystalline and silicon with wide Si: O ratio An oxide thin film can be produced.
In addition, the charge / discharge performance of the lithium ion secondary battery including the non-aqueous carbonate electrolyte and the room temperature ionic liquid electrolyte employing an amorphous silicon oxide thin film anode and adding a silane compound is stabilized.

Description

 A negative electrode for a lithium ion secondary battery, a manufacturing method thereof, and a lithium ion secondary battery employing the same {Negative electrode for lithium ion secondary battery, production method etc. and lithium ion secondary battery comprising the same}

The present invention relates to a lithium ion secondary battery, and more particularly, to a method for manufacturing a negative electrode, a negative electrode of a lithium ion secondary battery, and a lithium ion secondary battery using the same.

Recently, the secondary battery has attracted attention as a battery for driving a portable device because of its light weight and high energy density, and research and development of the secondary battery has been actively progressed.

 In particular, the lithium ion secondary battery has a high energy density and is widely used as a power source for mobile phones, notebook computers, and digital cameras.

The lithium ion secondary battery currently used is composed of a positive electrode composed of lithium-cobalt oxide-based powder, a negative electrode made of carbon, an organic electrolyte, a separator and the like.

When a graphite material is used as a negative electrode for a lithium ion secondary battery, the average potential at the time of releasing lithium is about 0.2 V (vs. Li / Li +), and the potential at this time is kept relatively flat. Therefore, as a power source for equipment requiring high voltage and voltage flatness, a lithium ion secondary battery having a negative electrode made of graphite material is suitably used. However, the graphite material has a small capacity per unit mass of 372 mAh / g, and it is difficult to expect a further increase in capacity.

As an example of a negative electrode material exhibiting a high capacity for solving such a problem, silicon, tin, and such an oxide may be mentioned as a material for forming an intermetallic compound with lithium. However, this material has a disadvantage in that the cycle characteristics are deteriorated since particles gradually fall off due to expansion due to volume change in the process of lithium ion entering and exiting the anode material by repeated charging and discharging. If the volume change of the active material is large, cracking of the active material particles, poor contact between the active material and the current collector, and the like cause a problem that the charge and discharge cycle life is shortened. In particular, when the active material particles are cracked, the surface area of the active material particles increases, so that the reaction between the active material particles and the nonaqueous electrolyte is increased. As a result, the film which consists of decomposition products of a nonaqueous electrolyte becomes easy to form on the surface of an active material. When such a film is formed, the interfacial resistance between the active material and the nonaqueous electrolyte increases, which is a great cause of shortening the charge / discharge cycle life.

Therefore, research on a cathode material exhibiting high capacity and a method of increasing the charge / discharge cycle life are required.

The present invention is easy to manufacture and less stress on the structural change amorphous silicon having improved charge and discharge characteristics Provided are an oxide thin film cathode and a method of manufacturing the same.

The present invention also provides a lithium ion secondary battery employing the amorphous silicon oxide thin film anode.

The present invention is amorphous Provided are a silicon oxide thin film cathode and a method of manufacturing the same.

A method of manufacturing an amorphous silicon oxide thin film anode includes forming a thin film of amorphous silicon oxide (SiO _x 0.3 ≦ x ≦ 1.5).

Forming the thin film of amorphous silicon oxide may use a mixture of Si and any one selected from SiO and SiO ₂ .

Preferably, Si in the step of forming a thin film of amorphous silicon oxide may be crystalline or amorphous, and SiO and SiO ₂ are amorphous.

Preferably, the mixture of Si and SiO may have a molar ratio of 1 to 4 mol of SiO per 1 mol of Si, and 1 to 4 mol of SiO ₂ per 1 mol of Si.

In addition, the amorphous silicon oxide thin film may be prepared by deposition.

Forming a thin film of amorphous silicon oxide may be performed under an argon or oxygen atmosphere and may be performed at a temperature of 20 ~ 600 ℃.

In another aspect, the present invention provides a negative electrode for a lithium ion secondary battery comprising a thin film of amorphous silicon oxide (SiO _x 0.3 ≤ x ≤ 1.5).

Preferably, the thin film of amorphous silicon oxide may have a thickness of 0.001 to 5 μm and may be deposited on one substrate selected from copper, stainless steel, graphene, graphene oxide, nickel, titanium, or graphite.

The present invention also provides a lithium ion secondary battery comprising an amorphous silicon oxide thin film.

Preferably, the lithium ion secondary battery including the amorphous silicon oxide thin film may include an electrolyte containing an silane compound represented by the following formula as an additive.

Si- (R) _y (OR ') _4-y

[In the formula, R is an alkyl group or a vinyl group, R 'is an alkyl group substituted with an alkyl group or an alkoxy group, y is an integer selected from 1 to 3.]

 The electrolyte may include 2 to 10 wt% of a silane compound.

In addition, the electrolyte is lithium salt, which is selected from lithium bis (trifluoromethylsulfonyl) imide (LiTFSI), lithium hexafluorophosphate (LiPF ₆ ), and lithium fluoromethylsulfonylimide (LiFSI), and a water-insoluble carbonate solvent or imidazolium-based, blood It may include a room temperature ionic liquid solvent of pyrrolididinum and piperidinium.

It may be a mixed solvent including 5 to 70 parts by weight of the non-aqueous carbonate solvent based on 100 parts by weight of the room temperature ionic solvent.

More preferably, the carbonate solvent may be one or more mixtures selected from dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC).

The amorphous silicon oxide cathode thin film according to the present invention can be produced simply and exhibits improved charge and discharge characteristics as being amorphous.

Therefore, the lithium secondary battery employing the amorphous silicon oxide anode thin film according to the present invention also exhibits improved charge and discharge characteristics, and further improves battery performance by stabilizing the interfacial structure between the anode and the electrolyte by further adding a silane additive.

1 is a SEM surface photograph of a SiO _0.85 thin film anode prepared in Example 1. FIG.
Figure 2 shows the X- ray diffraction pattern of the SiO _{0 .85} thin film negative electrode prepared in Example 1.
Figure 3 shows the Raman spectrum of the SiO _{0 .85} thin film cathode prepared in Example 1.
Figure 4 is an embodiment 1 of the SEM elemental mapping of SiO _{0 .85} thin film cathode (elemental mapping) picture.
FIG. 5 illustrates a siloxane having a three-dimensional structure in which a silane additive is included in an electrolyte and self-formed on a silicon oxide thin film (SiO _x ) surface.
Figure 6 shows the charge and discharge performance of the lithium ion secondary battery prepared in Example 1 and Examples 4 to 6.
7 is a charge and discharge of the lithium ion secondary battery of Example 3 employing a SiO _0.85 thin film negative electrode of Example 1, including a room temperature ionic liquid electrolyte (1M LiTFSI / (N-methyl-N-propylpyrrolidinium + TFSI) Cycle characteristics are shown.
And Figure 8 is adopted SiO _{1 .3} thin film negative electrode of Example 6 contains a room temperature ionic liquid electrolyte (1M LiTFSI / (N-methyl -N-propylpyrrolidinium + TFSI) 50wt% and ethylmethyl carbonate (EMC) 50wt% It shows the charge and discharge cycle characteristics of the lithium ion secondary battery of Example 7 prepared.

The present invention provides an amorphous silicon oxide thin film cathode and a method of manufacturing the same.

A method of manufacturing an amorphous silicon oxide thin film anode includes forming a thin film of amorphous silicon oxide (SiO _x 0.3 ≦ x ≦ 1.5).

In the step of forming the thin film of amorphous silicon oxide of the present invention, a mixture of Si and any one selected from SiO and SiO ₂ may be used. The Si, SiO and SiO ₂ is preferably a powder.

Preferably, in the step of forming a thin film of amorphous silicon oxide, the target material may be Si or crystalline or amorphous. SiO and SiO ₂ are amorphous.

In this case, in the case of the mixture of Si and SiO, the composition is controlled so that SiO is 1 to 4 mol per 1 mol of Si, and in the case of the mixture of Si and SiO ₂ , it is 1 to 4 mol of SiO ₂ per 1 mol of Si. And stabilizing electrochemical charge and discharge performance.

In addition, the amorphous silicon oxide thin film may be prepared by deposition.

In the step of forming the amorphous silicon oxide thin film, the formation method is not particularly limited, but pulse laser method, sputtering, chemical vapor deposition method can be used, and preferably pulse laser method can be used.

Since a precipitate or sintered powder of SiO or Si-SiO ₂ mixture powder was conventionally used as a material for forming a silicon oxide SiO _x thin film cathode, such a material preparation process was further required, and the manufactured SiO _x was crystalline.

Meanwhile, the amorphous silicon oxide thin film according to the present invention does not need a conventional material preparation process, and thus can be easily manufactured. Since the amorphous silicon oxide thin film according to the present invention has a low stress due to the structural change, the lithium ion secondary battery has improved charge and discharge. Performance can be seen.

In addition, according to the present invention, the step of forming a thin film of amorphous silicon oxide may be performed in an argon or oxygen atmosphere. Since the amorphous silicon oxide thin film formation of the present invention can be performed under an argon or oxygen atmosphere rather than in a conventional vacuum or inert atmosphere, the silicon oxide thin film can have a large ratio of Si: O. As the oxygen (O) content of the silicon oxide thin film increases, the capacity decreases, but the capacity retention is greatly improved. The ratio of Si: O in this wide area is appropriate for the secondary battery according to the oxygen content in the silicon oxide thin film. There is an advantage that can be adjusted to show capacity and capacity retention.

Forming the thin film of amorphous silicon oxide of the present invention is preferably carried out at a temperature of 20 ~ 600 ℃ in terms of preventing crystal growth from amorphous to crystalline.

In another aspect, the present invention provides a negative electrode for a lithium ion secondary battery comprising a thin film of amorphous silicon oxide (SiO _x 0.3 ≤ x ≤ 1.5).

In order to facilitate contact with the electrolyte and facilitate lithium diffusion, the thin film of amorphous silicon oxide preferably has a thickness of 0.001 to 5 µm, more preferably 0.01 to 2 µm.

Although not particularly limited, the amorphous silicon oxide thin film may be deposited on one substrate selected from copper, stainless steel, graphene, graphene oxide, nickel, titanium, or graphite.

In another aspect, the present invention provides a lithium ion secondary battery comprising an amorphous silicon oxide thin film. In the lithium ion secondary battery including the amorphous silicon oxide thin film according to the present invention, since the silicon oxide thin film is amorphous, there is little structural change stress, thereby showing improved charge and discharge characteristics.

The electrolyte of the lithium ion secondary battery including the amorphous silicon oxide thin film according to the present invention is not particularly limited, but may include a conventional lithium salt and a solvent.

More preferably, the lithium ion secondary battery including the amorphous silicon oxide thin film may include an electrolyte containing a silane-based compound of the following formula as an additive.

Si- (R) _y (OR ') _4-y

[In the formula, R is an alkyl group or a vinyl group, R 'is an alkyl group substituted with an alkyl group or an alkoxy group, y is an integer selected from 1 to 3.]

In the above formula, the alkyl group is C ₁ -C ₃₀ alkyl group and the vinyl group is C ₂ -C ₂₀ vinyl group. This is preferably a silane-based compounds but are also limited in the Si- (R) ₁ (OR ') _3, and can be exemplified by but are not limited in this specific example, trimethoxy (methyl) silane (SiCH ₃ (OCH _{3) 3} ), tris (2-methoxyethoxy) vinylsilane (CH ₂ = CHSi (OCH ₂ CH ₂ OCH ₂ ) ₃ ).

When the electrolyte contains a silane additive, a condensation reaction between the -OH group on the surface and the alkoxide group (-OR ') of the silane additive occurs on the surface of SiO _x , which is a silicon oxide thin film, and thus a three-dimensional structure of siloxane on the SiO _x surface. ) Can be self-forming. An example of the reaction scheme may be as follows, which is as shown in FIG.

R-Si- (OR ') ₃ + HO-SiO _x → R-Si-O-SiO _x + 3R'OH

The self-forming siloxane may serve as a silicon oxide thin film (SiO _x ) surface protection layer because chemically stable -Si-O-Si molecular bonds are formed in the horizontal and vertical directions to surround the SiO _x surface. Silicon oxide thin film having a siloxane formed on the surface not only improves the charge / discharge cycle life characteristics when used in a lithium ion secondary battery, but also a PF _x O _y compound derived from LiPF ₆ even when the battery is stored at a high temperature or charge / discharge proceeds. Electrolyte decomposition reaction due to the interfacial reaction between the HF component and SiO _x is suppressed, thereby improving the life characteristics of the battery.

The electrolyte including the silane-based compound in the electrolyte may include 2 to 10 wt% of the silane-based compound. The content of 2 to 10 wt% of the electrolyte may be more advantageous because it can effectively induce the formation of a protective layer on the silicon oxide surface while maintaining the performance of the electrolyte.

On the other hand, the electrolyte is a lithium salt which is one selected from LiTFSI, LiPF ₆ and LiFSI and a non-aqueous carbonate solvent or a lithium salt which is one selected from LiTFSI, LiPF ₆ and LiFSI and an imidazolium-based, pyrrolidinium-based and piperidinium-based It may include an electrolyte consisting of a room temperature ionic liquid solvent which is one selected from.

In other words, the electrolyte is more preferably a room temperature ionic solvent containing no lithium salt of LiPF ₆ . The room temperature ionic solvent not containing LiPF ₆ lithium salt does not have an interfacial reaction between the silicon oxide thin film anode and the LiPF ₆ derivative, and the room temperature ionic solvent has a solid electrolyte interphase (SEI) layer which is stable during the initial charge and discharge process. This is because the charge and discharge cycle performance can be stabilized by forming on the surface of the silicon oxide thin film to suppress interfacial reaction with the electrolyte later.

On the other hand, the solvent may include a water-insoluble carbonate solvent in addition to the room temperature ionic solvent, the content of the non-water-soluble carbonate solvent is 5 to 70 parts by weight based on 100 parts by weight of the room temperature ionic solvent flame retardancy of the ionic liquid solvent It can be advantageous to obtain a fat or oil or a fire suppression effect.

The water-insoluble carbonate solvent is not limited thereto, but may be, for example, one or two or more mixtures selected from dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC).

In addition to the amorphous silicon oxide thin film anode and the electrolyte described above, the lithium ion battery secondary battery may include, but is not limited to, a conventional positive electrode and a separator.

Hereinafter, the present invention will be described in detail with reference to Examples. However, the following examples do not limit the present invention.

Example 1

Amorphous SiO _0.85  Thin film cathode manufacturing

Amorphous SiO _0.85 thin film cathode was prepared by pulsed laser deposition. After grinding the mixture of amorphous Si powder and amorphous SiO ₂ powder (molar ratio 50:50) by ball mill, pressurized for 20 seconds at 30 kg pressure, and then using a target manufactured under isotatic press for 20 minutes at 200 Mpa pressure. In an argon atmosphere using a KrF excimer laser (wavelength: 248 nm) at a deposition temperature of 400 ° C, a laser frequency of 10 Hz, and an energy of ~ 3-4 mJ / cm ² . Amorphous SiO _0.85 thin films were deposited on stainless steel. The prepared amorphous SiO _0.85 thin film cathode has a thickness of 65 nm.

An example of the results observed using the X-ray diffraction pattern and the Raman spectroscopic spectrum is shown in FIG. 1. As shown in FIG. 1, the SEM surface image of the amorphous SiO _0.85 thin film cathode prepared from Example 1 shows that the surface of the thin film is very smooth. In addition, as shown in FIG. 2, only the current collector-based peaks were observed in the X-ray diffraction pattern and the silicon oxide thin film (SiO _x ) was observed. Since no peak is observed, it can be seen that the prepared silicon oxide thin film (SiO _x ) is amorphous. As shown in FIG. 3, it was confirmed that the silicon oxide thin film (SiO _x ) was amorphous even in the Raman spectral spectrum.

[Example 2]

Fabrication of Lithium Ion Secondary Battery

A lithium metal is used as a counter electrode, and a cathode prepared in Example 1 is used as a working electrode. A mixture of 50 wt% of ethylene carbonate (EC) and 50 wt% of diethyl carbonate (DEC) in which 1M LiPF ₆ is dissolved as an electrolyte is used. Tris (2-methoxyethoxy) vinylsilane as silane additive in solution 5 wt% of (CH ₂ = CHSi (OCH ₂ CH ₂ OCH ₂ ) ₃ ) was added to manufacture a lithium secondary battery.

The cycle characteristics of the lithium ion secondary battery prepared above were 0.1 -1.5 V vs. lithium at 35 mA / cm 2 current density. Charging and discharging were performed by the constant current method in the Li / Li ⁺ section.

As shown in Figure 6 it can be seen that the capacity retention of 72% compared to the maximum discharge capacity at 200 cycles, showing a capacity of 1658-1194 mAh / g.

[Example 3]

Fabrication of Lithium Ion Secondary Battery

In Example 1, except for using a room temperature ionic liquid electrolyte of N-methyl-N-propylpyrrolidinium containing 1M LiTFSI and TFSI as the electrolyte solution It manufactured by the same method as a lithium ion secondary battery.

In addition, the electrochemical characteristics of the lithium ion secondary battery prepared in Example 3 were measured in the same manner as in Example 1, and the results are shown in FIG. 7.

As a result of Figure 7 it can be seen that the SiO _x thin film cathode of the present invention shows a very stable charge and discharge performance in a pyrrolidinium-based room temperature ionic liquid electrolyte. At 200 cycles, it has 88% capacity retention compared to the maximum discharge capacity and 1058-930 mAh / g capacity.

Example 4

 Amorphous SiO _0.4  Thin film cathode manufacturing

The amorphous silicon of Example 1 was used in Example 1 except that a mixture of Si powder and amorphous SiO powder (molar ratio 50:50) was used instead of the target prepared from the mixture of amorphous Si powder and amorphous SiO ₂ powder (molar ratio 50:50). It was prepared in the same manner as the oxide thin film cathode.

Fabrication of Lithium Ion Secondary Battery

Example 2 Amorphous SiO _{0 .85} to manufacture a thin film instead of the cathode the same manner as that of the lithium ion secondary battery of Example 1, except that the amorphous SiO _0.4 negative electrode with a thin film prepared in Example 4 in the same manner of Example 1 Battery performance was evaluated.

The results are shown in FIG. 6, and as shown in FIG. 6, the capacity retention was 53% compared to the maximum discharge capacity at 200 cycles, and the capacity was 1863-997 mAh / g.

[Example 5]

Amorphous SiO _One Thin film cathode manufacturing

In Example 1 A deposition was performed in the same manner as the amorphous silicon oxide thin film cathode of Example 1, except that an oxygen atmosphere was used instead of an argon atmosphere.

Fabrication of Lithium Ion Secondary Battery

Example 1 with the amorphous SiO _{0 .85} thin film instead of the negative electrode in Example 5 by the same procedure of Example 1 is prepared in the same manner as the lithium ion secondary battery of Example 1, except for using the amorphous SiO thin film ₁ produced in the cathode Battery performance was evaluated.

The results are shown in FIG. 6 and show 84% capacity retention compared to the maximum discharge capacity at 200 cycles and 1206-1017 mAh / g capacity as shown in FIG. 6.

[Example 6]

Amorphous SiO _1.3 Thin film cathode manufacturing

Instead of a target made of a mixture of amorphous Si powder and amorphous SiO ₂ powder (molar ratio 50:50), a target made of a mixture of amorphous Si powder and amorphous SiO ₂ powder (molar ratio 33:67) and an oxygen atmosphere during deposition It was prepared in the same manner as the amorphous silicon oxide thin film cathode of Example 1 except that it was used.

Fabrication of Lithium Ion Secondary Battery

It was prepared in the same manner as in the lithium ion secondary battery of Example 1 except for using the amorphous SiO _1.3 thin film anode prepared in Example 6 instead of the amorphous SiO _0.85 thin film anode of Example 1. In addition, the battery performance was evaluated in the same manner as in Example 1, and the results are shown in FIG. 6.

As shown in FIG. 6, it can be seen that the capacity retention of 78% compared to the maximum discharge capacity at 200 cycles and a capacity of 1069-847 mAh / g is shown.

[Example 7]

Fabrication of Lithium Ion Secondary Battery

50 wt% of the room temperature ionic liquid solvent N-methyl-N-propylpyrrolidinium containing 1M LiTFSI and TFSI as the amorphous SiO _1.3 thin film anode and electrolyte prepared in Example 6 A lithium ion secondary battery of Example 1 was prepared in the same manner as in Example 1, except that an electrolyte of 50 wt% of a water-soluble ethyl methyl carbonate (EMC) solvent was used.

In addition, the electrochemical characteristics of the lithium ion secondary battery prepared in Example 7 were measured in the same manner as in Example 1, and the results are shown in FIG. 8.

As a result of FIG. 8, the SiO _x anode thin film of the present invention has a slightly reduced charge / discharge performance in the mixed electrolyte of a pyrrolidinium-based room temperature ionic liquid solvent and a carbonate solvent than in an ionic liquid solvent electrolyte. The cycle maintains 48% of the maximum discharge capacity and 913-440 mAh / g capacity.

Claims (17)

delete delete delete delete delete delete delete delete delete delete delete A cathode comprising an amorphous silicon oxide thin film,
The amorphous silicon oxide thin film is SiO _x (0.3 ≦ x ≦ 1.5) formed from a mixture of amorphous Si and any one selected from amorphous SiO or SiO ₂ ;
Lithium ion secondary battery comprising an electrolyte containing a silane-based compound of the formula.
Si- (R) _y (OR ') _4-y
[In the formula, R is a vinyl group, R 'is an alkyl group substituted with an alkyl group or an alkoxy group, y is an integer selected from 1 to 3.] delete 13. The method of claim 12,
The silane-based compound is a lithium ion secondary battery containing 2 to 10 wt% of the electrolyte. 13. The method of claim 12,
The electrolyte includes an electrolyte comprising a lithium salt which is one selected from LiTFSI, LiPF ₆ and LiFSI and a non-aqueous carbonate solvent or a room temperature ionic liquid solvent which is one selected from imidazolium based, pyrrolidinium based and piperidinium based Lithium-ion secondary battery. 16. The method of claim 15,
Lithium ion secondary battery which is a mixed solvent containing 5 to 70 parts by weight of a non-aqueous carbonate solvent based on 100 parts by weight of the room temperature ionic liquid solvent. 17. The method of claim 16,
The water-insoluble carbonate-based solvent is a lithium ion secondary battery which is one or more mixtures selected from dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

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