KR101454372B1 - Silicon Negative Active Material with lithium film, Manufacturing Method thereof And Lithium Secondary Battery Comprising The Same - Google Patents

Abstract

The present invention relates to a silicon-based anode active material electrode having an initial irreversible phase inhibited by inserting a lithium thin film, a method for manufacturing the same, and a lithium secondary battery having the same.
The lithium secondary battery of the present invention comprises a negative electrode comprising a negative electrode active material, a silicon negative electrode active material electrode prepared by mixing a silicone based negative active material with a polyacrylic acid (PAA) high strength binder and a conductive material, A lithium secondary battery to which a metal is added is a technical point.

Description

Technical Field [0001] The present invention relates to a silicon-based anode active material electrode having a lithium thin film inserted therein, a method of manufacturing the same, and a lithium secondary battery having the same.

More particularly, the present invention relates to a method of manufacturing a silicon-based anode active material electrode by inserting a lithium thin film and suppressing initial irreversibility, and a lithium secondary battery having the same. More particularly, The present invention relates to a negative electrode active material electrode in which lithium metal is added to the surface of a negative electrode active material electrode mixed with polyacrylic acid and a conductive material to eliminate an initial irreversible capacity, a method for manufacturing the same, and a lithium secondary battery having the same.

In other words, since the incoincidence of the negative electrode and the positive electrode occurs due to the initial irreversible capacity of the silicon-based negative electrode when manufacturing the lithium secondary battery (full cell) using the silicon-based negative active material, the lithium thin film corresponding to the non- And the inserted lithium battery.

The use of lithium secondary batteries, which are used as power sources for mobile IT devices such as mobile phones and notebook PCs, has recently been expanding its applications as power storage devices. As a means of preventing global warming, development of pollution-free transport vehicles such as electric vehicles is actively under way. In order to further improve the performance of existing electric vehicles, it is necessary to develop a battery having a high energy and an electrode material constituting the battery.

Lithium secondary batteries are not only secondary batteries using lithium metal but also lithium-ion, lithium polymer, and lithium-ion polymer secondary batteries. They have high voltage and high energy density, A gel type polymer battery in which a liquid is mixed with a polymer, and a solid type polymer battery in which only a polymer is used.

The core components of lithium secondary batteries are anodes, cathodes, electrolytes, and separators.

The lithium secondary battery is composed of an anode, a cathode, an electrolyte, a separator, and an exterior material. The anode is constituted by binding a mixture of a cathode active material, a conductive material and a binder to a current collector. As the cathode active material, lithium transition metal compounds such as LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , and LiMnO ₂ are mainly used, and these materials can intercalate / deintercalate lithium ions into the crystal structure.

Lithium metal, carbon or graphite is mainly used for the negative electrode active material. In contrast to the positive electrode active material, the electrochemical reaction potential is low.

The electrolyte is mainly composed of LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ , LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN ((LiPF ₄ ) ₂ ) in a polar organic solvent such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, SO ₂ C ₂ F ₅ ) _2, and the like.

The separator electrically isolates the anode and the cathode and serves as a passage for ions, and polyolefin-based polymers such as porous polyethylene are mainly used.

The exterior material protects the contents of the cell, provides an electrical path to the outside of the cell, and mainly uses a pouch package made of metal can or aluminum and several layers of polymer.

Lithium secondary batteries require a higher performance battery in terms of electronic devices although they are the secondary batteries having the highest performance. Improvement in the performance of lithium secondary batteries plays an important role in improving the properties of the positive electrode and the negative electrode, and development of a high performance negative electrode material is an important task.

The negative electrode material has been progressing dramatically in non-capacity. The current graphite material is a material with a theoretical cost of 372 mAh / g and a density of 2.2 g / ml, but the silicon currently under development has a significantly higher theoretical capacity of 4200 mAh / g and a density of 2.33 g / ml. Silicon exhibits electrochemical reaction potential with lithium as well as characteristics similar to graphite. However, the silicon material has a problem that a volume expansion exceeding 300% (Li ₂₂ Si ₅ ) occurs due to lithium insertion.

The negative electrode active material has a low initial efficiency due to a high irreversible capacity.

In order to solve such a problem, there is a need for research on a method for increasing the initial efficiency by eliminating the irreversible capacity of the lithium secondary battery electrode.

 SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances and provides a negative electrode material composition for a lithium secondary battery as a novel material which can overcome the specific capacity and capacity density of existing graphite materials, And a lithium secondary battery using the same.

In addition, the present invention relates to a method of manufacturing an electrode that maximizes binding capacity while minimizing the binder content by mixing polyacylic acid (PAA), which is a high-strength binder, at a predetermined ratio and applying the same to a lithium secondary battery anode, And to provide a lithium secondary battery capable of improving lifetime characteristics.

The present invention improves the coulomb efficiency by inserting a lithium thin film corresponding to an initial irreversible capacity into a cathode electrode for a high energy lithium secondary battery using a non-carbon material-based negative active material exhibiting a low initial coulombic efficiency but exhibiting a high capacity characteristic, The present invention aims to provide a method of manufacturing an electrode that can be applied to a negative electrode capable of exhibiting both an efficiency characteristic and a high capacity characteristic, and also to an anode, and a lithium secondary battery. That is, an anode active material electrode in which lithium metal is added (inserted) to the surface of a silicon based anode active material electrode to eliminate initial irreversible capacity, a method of manufacturing the same, and a lithium secondary battery having the same.

In order to accomplish the above object, the present invention provides a method of manufacturing a silicon-based anode active material electrode comprising the steps of: (1) mixing a polyacrylic acid (PAA) high strength binder and a conductive material in a nanosilicon- based negative electrode active material to prepare an anode mixture slurry ; (2) applying the negative electrode material mixture slurry to a copper current collector, followed by drying; And (3) adding lithium metal to the surface of the dried negative electrode active material to eliminate the initial irreversible capacity.

Preferably, NMP (N-methyl pyrrolidone) is used as a solvent in the step of preparing the anode mixture slurry, and carbon black (ketylene black, super p. Black) is used as the conductive material.

Preferably, the lithium metal is added in the form of a thin film.

Preferably, the lithium metal is added by pressing the lithium metal thinly, or the lithium metal is added by the vapor deposition method.

The amount and proportion of lithium metal added to the surface of the negative electrode active material can be freely adjusted to eliminate and regulate the irreversible capacity. Preferably, the lithium metal is added to the surface of the negative electrode active material at an initial 95 to 105 parts by weight of the theoretical amount of lithium metal necessary for completely eliminating the irreversible non-capacity is 100 parts by weight.

That is, the amount of lithium metal to be added is preferably 95 to 105 parts by weight (that is, 95 to 105% of the theoretical amount of lithium metal) to 100 parts by weight of the theoretical amount of lithium metal.

A negative electrode active material electrode according to a preferred embodiment of the present invention is characterized by comprising 30 to 50 parts by weight (preferably 40 parts by weight) of a polyacrylic acid (PAA) high strength binder, The lithium secondary battery according to the preferred embodiment of the present invention is manufactured by adding lithium metal to the surface of the negative electrode active material electrode prepared by mixing 50 to 70 (preferably 60 parts by weight) A positive electrode including an active material, and an ion conductor.

 By adding lithium metal to the battery in order to reduce the initial irreversibility of the negative electrode, the lithium metal first reacts in the initial charge reaction to compensate for the irreversible capacity of the negative electrode and prevent lithium ions from being excessively consumed.

In this case, the lithium metal moved from the counter electrode is consumed to compensate for the irreversible capacity of the counter electrode, and the lithium metal added from the outside replaces the counter electrode in the counter electrode. As a result, it contributes to increase the capacity of the battery by increasing the reversible capacity of the counter electrode do.

Table 1 shows the characteristics of a lithium secondary battery anode of a silicon-based negative electrode active material having a lithium metal inserted therein
Fig. 1 shows a change in voltage with respect to initial charging / discharging at a current density of 200 mA / g in a coin cell (Example 1) prepared using a silicon system as a negative electrode active material and without addition of lithium metal.
Fig. 2 shows discharge and charge ratio capacities and efficiencies at a current density of 200 mA / g in a coin cell (Example 1) produced by using a silicon system as a negative electrode active material and without adding lithium metal.
FIG. 3 is a graph showing the results of initial charging and discharging at a current density corresponding to 200 mA / g of a coin cell (Example 2) prepared by adding a lithium metal corresponding to 96.2% efficiency to an anode active material electrode using a silicon system as a negative electrode active material The change in the voltage of the battery is shown.
FIG. 4 is a graph showing the relationship between discharge and charge ratio at a current density of 200 mA / g of a coin cell (Example 2) prepared by adding a lithium metal corresponding to 96.2% efficiency to an anode active material electrode using a silicon- Capacity and efficiency.
5 is a graph showing the results of initial charge and discharge at a current density of 200 mA / g of a coin cell (Example 3) prepared by adding a lithium metal corresponding to 99.8% efficiency to an anode active material electrode using a silicon system as a negative electrode active material The change in the voltage of the battery is shown.
6 is a graph showing the relationship between discharge and charge ratio at a current density corresponding to 200 mA / g of a coin cell (Example 3) prepared by adding a lithium metal corresponding to 99.8% efficiency to an anode active material electrode using a silicon- Capacity and efficiency.
7 is a graph showing the relationship between the initial charge and discharge at a current density of 200 mA / g of the coin cell (Example 4) prepared by adding lithium metal corresponding to 106.4% efficiency to the anode active material electrode using the silicon system as the anode active material The change in the voltage of the battery is shown.
8 is a graph showing the relationship between discharge and charge ratio at a current density corresponding to 200 mA / g of a coin cell (Example 4) produced by adding a lithium metal corresponding to an efficiency of 106.4% to an anode active material electrode using a silicon system as a negative electrode active material Capacity and efficiency.
9 is a graph showing a relationship between a design value and an experimental result for an initial Ah efficiency at a current density of 200 mA / g in a coin cell manufactured by using a silicon system as a negative electrode active material and varying the amount of lithium metal for initial non- .

 The present invention relates to a negative electrode for a high capacity lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery, and more particularly, to a negative electrode active material electrode comprising a silicon system with a lithium iridium interposed therein to suppress initial irreversibility, The secondary battery is disclosed.

In particular, a high capacity anode was prepared using a compound based on a non-carbon anode active material. In order to maximize capacity and energy density, a polyvinylidene fluoride (PVDF) binder, which is a low strength binder used in conventional carbon- A high-efficiency, high-energy lithium secondary battery including a high-capacity cathode using polyacrylic acid (PAA) as a high-strength binder is disclosed.

That is, in the present invention, polyacrylic acid (PAA), which is a high strength binder, is used for a silicon active material cathode, and carbon black (SPB, super p. Black) is used as a conductive material.

Hereinafter, a lithium secondary battery having a silicon based negative active material will be described in detail.

First, a binder and a conductive material are mixed with a silicon-based negative active material (Si) to prepare a negative electrode mixture slurry.

In the present invention, polyacrylic acid (PAA), which is a high-strength binder, is used as the binder, and carbon black (SPB, super p. Black) is used as the conductive material. Preferably, 30 to 50 parts by weight (preferably 40 parts by weight) of a polyacrylic acid (PAA) high-strength binder and 50 to 70 (preferably 60 parts by weight Part) is added.

The negative electrode mixture slurry is preferably applied to a copper current collector (Cu foil), dried at about 100 캜 for about 5 hours, and compressed to produce a negative electrode active material electrode (negative electrode).

The positive electrode, the separator, and the electrolyte are formed together with the negative electrode prepared above to complete the lithium secondary battery.

A celgard separator is used to prevent internal shorting of the lithium electrode and the counter electrode. The separator is a non-electroconductive porous material which is capable of smooth movement of the electrolytic solution, and is not limited to the cell guard shown in this embodiment.

In addition, the ionic conductor is a non-aqueous liquid electrolyte with a LiPF ₆ was dissolved, preferably, the non-aqueous electrolyte than the EC (ethylene carbonate), EMC in LiPF ₆ - contain (ethyl methyl carbonate), VC (vinylene carbonate) . That is, an electrolytic solution in which 2% of vinylene carbonate (VC) is added to a solute in which EC (ethylene carbonate) and EMC (ethyl-methyl carbonate) are dissolved in 1.2M LiPF ₆ in a 1: 1 volume ratio can be used.

In order to solve the irreversible capacity on the surface of the negative electrode active material, Li metal is added in the form of a thin film to produce a battery. The thickness of the Li thin film is a lithium thin film having a thickness of about 65 mu m.

Hereinafter, preferred embodiments of the present invention will be described. However, the following examples are only a preferred embodiment of the present invention, and the present invention is not limited to the following examples.

Example 1

end. Lithium secondary battery assembly using silicon-based anode active material and high-strength binder

 A slurry was prepared to assemble the lithium secondary battery. A carbon black (Super P Black) as a conductive material, and a polyacrylic acid (PAA) as a binder were mixed in a weight ratio of 50:30:20 to prepare a slurry. First, 0.1 g of polyacrylic acid (PAA) was put into a thinky bowl of 9 ml of NMP (N-methyl pyrrolidone), and the mixture was stirred at 2000 rpm for 30 minutes using a thinky mixer (Kurabo AR-250) , 0.15 g of SPB (super p. Black) was added thereto, and the mixture was stirred for 5 minutes in a Sinky mixer. Then, 0.25 g of a silicon-based active material was added and stirred for 20 minutes in a Sinky mixer. The slurry thus prepared was applied to a copper current collector at a thickness of about 100 탆, dried at 100 캜 for 5 hours, and pressed to produce an anode active material electrode.

Here, 16.2 mg (0.0162 g) of a disc-shaped negative electrode active material electrode having a diameter of 1.4 cm (area of 1.5386 cm ² ) was taken to manufacture the battery. That is, 16.2 mg of the negative electrode active material was used. 0.0012 g of the negative electrode active material composite in the negative electrode active material electrode is used.

Lithium metal was used as a counter electrode (anode), and a cell guard separator was sandwiched between the anode and the cathode. Ethylene carbonate (EC) and ethyl-methyl carbonate (EMC) were mixed in 1.2M LiPF ₆ at a volume ratio of 1: 1 A 2032 coin cell was assembled using an electrolytic solution in which 2% of vinylene carbonate (VC) was added to the dissolved solute.

Examples 2-4

After preparing the negative electrode active material electrode in the same manner as in Example 1, lithium metal corresponding to the irreversible capacity was added to the surface of the negative electrode active material electrode in order to solve the irreversibility of the negative electrode in the initial charge reaction.

Let's calculate the amount of lithium to solve the initial irreversible capacity.

The initial irreversible charge amount generated in Example 1 (when lithium metal was not added to the surface) was 1142.3 mAh (one charge capacity-one discharge capacity = 3545.3 - 2403.0 = 1142.3) The negative active material composite was 0.0012 g. Therefore, the irreversible capacity was 1142.3 mAh * 0.0012 g = 1.37 mAhg

However, since the theoretical capacity of lithium metal is 3800 mAh, (1.37 mAhg) / (3800 mAh) = 0.00036 g (about 0.36 mg). That is, theoretically 0.36 mg is expected to solve the initial irreversible capacity.

In Example 3, 0.36 mg of lithium metal required for completely dissolving the initial irreversible capacity was theoretically inserted into a negative electrode active material electrode (0.0012 g of silicon anode active material composite) using a compactor.

In Example 2, 0.34 mg (= 0.95 * 0.36) of lithium metal corresponding to about 95% of the theoretical amount of lithium metal necessary for completely eliminating the initial irreversible capacity was inserted,

In Example 4, 0.38 mg (= 1.05 * 0.36) of lithium metal corresponding to about 105% of the theoretical amount of lithium metal necessary for completely eliminating the initial irreversible capacity was inserted.

That is, a lithium thin film of 0.34 mg (Example 2), 0.36 mg (Example 3), and 0.38 mg (Example 4) was inserted on the electrode of the prepared negative electrode active material to remove irreversible capacity using a compactor.

Lithium metal of 300 mu m thickness was formed at a thickness of 65 mu m using a compactor. When the lithium metal is in the form of a thin film, it is possible to prevent a short circuit inside the cell and perform a smooth electrochemical test.

Next, in the same manner as in Example 1, a battery was produced using a counter electrode, a separator, and an electrolyte.

Experimental Example 1

end. Electrochemical Characterization of Cells

The battery manufactured according to each example was stabilized for 24 hours, and then charge / discharge characteristics and cycle characteristics were evaluated using Toyo's TOSCAT 3100.

Specifically, the device was charged at a current density of 200 mA / g at room temperature to a constant current mode of 0.005 V, charged to a constant current density of 20 mA / g in a constant voltage mode, and discharged at a current density of 200 mA / Completed.

The experimental results are as follows.

 Fig. 1 shows a change in voltage with respect to initial charging and discharging of a lithium secondary battery (Example 1) to which lithium metal was not added, which corresponds to the initial irreversible capacity of the silicon-based active material.

Fig. 2 shows the charge and discharge capacity and efficiency of a lithium secondary battery (Example 1) to which lithium metal was not added, which corresponds to the initial irreversible capacity of the silicon-based active material.

The initial charge capacity was 3545.3 mAh / g, the initial discharge capacity was 2403.0 mAh / g, and the initial Ah efficiency was 67.8%.

As a result of measuring the charging, discharging and efficiency over one to ten times, the 10 times charge capacity was 2368.8 mAh / g, the 10 times discharge capacity was 2274.8 mAh / g, and the 10 times Ah efficiency 96.0%.

Fig. 3 shows the change in voltage with respect to the initial charging and discharging of the lithium secondary battery (Example 2) in which 0.34 mg of the lithium thin film corresponding to the irreversible capacity of the silicon-based active material was inserted.

FIG. 4 shows the charge, discharge capacity and efficiency of a lithium secondary battery (Example 2) in which 0.34 mg of a lithium thin film corresponding to the irreversible capacity of a silicon-based active material was inserted.

The initial charging capacity was 2627.9 mAh / g, the initial discharging capacity was 2529.5 mAh / g, and the initial Ah efficiency was 96.2%.

As a result of measuring the charging, discharging and efficiency over one to ten times, the 10 times charge capacity was 2421.4 mAh / g as shown in FIG. 4, the 10 times discharge capacity was 2342.9 mAh / g, 96.8%.

5 shows changes in voltage with respect to initial charging and discharging of a lithium secondary battery (Example 3) in which 0.36 mg of a lithium thin film corresponding to the irreversible capacity of a silicon-based active material was inserted.

Fig. 6 shows the charge and discharge capacity and efficiency of a lithium secondary battery (Example 3) in which 0.36 mg of a lithium thin film corresponding to the irreversible capacity of the silicon-based active material was inserted.

The initial charge capacity was 2673.9 mAh / g and the initial discharge capacity was 2669.8 mAh / g. The initial Ah efficiency was 99.8%, which was close to 100%.

As a result of measuring the charging, discharging and efficiency over one to ten times, the 10 times charge capacity was 2604.8 mAh / g, the 10 times discharge capacity was 2507.1 mAh / g as shown in FIG. 6, 96.3%.

7 shows changes in voltage with respect to initial charging and discharging of a lithium secondary battery (Example 4) in which 0.38 mg of a lithium thin film corresponding to the irreversible capacity of a silicon-based active material was inserted.

Fig. 8 shows the charging and discharging capacity and efficiency of a lithium secondary battery (Example 4) in which 0.38 mg of a lithium thin film corresponding to the irreversible capacity of the silicon-based active material was inserted.

The initial charge capacity was 2502.6 mAh / g, the initial discharge capacity was 2663.9 mAh / g, and the initial Ah efficiency was 106.4%.

As a result of measuring the charging, discharging and efficiency over one to ten times, the 10 times charge capacity was 2593.9 mAh / g, the 10 times discharge capacity was 2491.3 mAh / g as shown in FIG. 8, 96.0%.

9 shows the difference between the theoretical value and the experimental value of the initial Ah efficiency of the lithium secondary battery in which 0.34 mg, 0.36 mg and 0.38 mg of lithium metal were respectively inserted into the silicon-based active material.

In Fig. 9, 0 represents the case of Example 1, 95 represents the case of Embodiment 2, 100 represents the case of Embodiment 3, and 105 represents the case of Embodiment 4.

Here, the meaning of 95, 100, and 105 means a relative value when the theoretical amount of lithium metal required to completely eliminate the initial irreversible capacity in the case where lithium metal is not used on the surface of the negative electrode active material is taken as 100 .

Table 1 summarizes the negative electrode characteristics of the lithium secondary battery of the silicon based negative active material according to the inserted lithium amount for the initial irreversible capacity dissolution.

Example lithium
content
(mg) 1 time
charge
Non-capacity
(mAh / g) 1 time
Discharge
Non-capacity
(mAh / g) 1 time
Ah
efficiency
(%) 10 times
charge
Non-capacity
(mAh / g) 10 times
Discharge
Non-capacity
(mAh / g) 10 times
Ah
efficiency
(%) One 0 3545.3 2403.0 67.8 2368.8 2274.8 96.0 2 0.34 2627.9 2529.5 96.2 2421.4 2342.9 96.8 3 0.36 2673.8 2669.8 99.8 2604.8 2507.1 96.8 4 0.38 2502.6 2663.7 106.4 2593.9 2491.3 96.0

As can be seen in Table 1 and FIG. 9, it can be confirmed that the efficiency (first) Ah efficiency close to 100% is shown in Example 3 in which 0.36 mg of lithium was added.

As described above, in Examples 2, 3, and 4 corresponding to the case where lithium metal was added to the silicon-based anode active material electrode in comparison with the case where lithium metal was not added to the silicon-based anode active material (Example 1) In the case of Example 4, it was shown that the initial Ah efficiency was excellent, and it was confirmed that the initial irreversible capacity was largely eliminated.

As in the case of Examples 2 to 4, the amount of lithium metal to be added is the theoretical amount of lithium metal required to completely eliminate the initial irreversible capacity in the case where lithium metal is not used on the surface of the negative electrode active material 95 to 105% by weight may be added. The thickness of the thin film is about 65 mu m.

When the amount of lithium to be added is small, the amount of the positive electrode having a relatively high Li source is required to be increased in full cell production, resulting in cost problems and sufficient initial irreversible capacity can not be reduced. And an unnecessary amount of Li is consumed.

Claims (12)

A method for manufacturing a silicon based anode active material electrode,
(1) preparing a negative electrode mixture slurry by mixing a polyacrylic acid (PAA) high-strength binder and a conductive material in a silicon-based negative active material;
(2) applying the negative electrode material mixture slurry to a copper current collector, followed by drying; And
(3) adding lithium metal to the surface of the dried negative electrode active material to eliminate the initial irreversible capacity,
The lithium metal is added to the lithium metal by spreading and pressing the lithium metal thinly. The amount of lithium metal is 95 to 105 wt% of the theoretical amount of lithium metal required to completely eliminate the initial irreversible capacity when the lithium metal is not used on the surface of the negative electrode active material %, Based on the total weight of the negative electrode active material.
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