KR101302787B1 - High energy density lithium secondary battery and method of preparation of the same - Google Patents

Abstract

The present invention relates to a high energy density lithium secondary battery electrode and a high energy density secondary battery using the same, by inserting a polymer film containing a lithium metal powder on the surface of the negative electrode for additional supply of lithium ions in a lithium ion battery The effect is to increase the dose.
According to the present invention, it is possible to dramatically increase the reversible capacity of lithium after activation by fully utilizing the lithium storage and release capability of the negative electrode and positive electrode materials contained in the battery.

Description

High energy density lithium secondary battery and method of preparation of the same

The present invention relates to a lithium secondary battery having a high energy density, and a lithium secondary battery having a polymer film layer including lithium metal powder as an additional lithium source for negative electrode irreversibility correction and positive electrode capacity reinforcement of a lithium secondary battery and a method of manufacturing the same. It is about.

Recently, miniaturization and weight reduction of portable electronic devices such as mobile phones, PDAs, and laptop computers are being promoted, and researches for high energy density of secondary batteries used as driving power sources thereof continue.

As a secondary battery for achieving high energy density, there is a lithium ion secondary battery using a material capable of occluding and detaching lithium by an electrochemical reaction, such as a carbon material as a negative electrode material. The lithium ion secondary battery is designed assuming that lithium occluded in the negative electrode material is necessarily an ionic state. Therefore, the energy density depends on the number of lithium ions that can be occluded in the negative electrode material. Therefore, in a lithium ion secondary battery, energy density can be improved further by increasing the occlusion amount of lithium ion. However, the lithium ion occlusion amount of graphite, which is currently known as a material capable of occluding and desorbing lithium ions as efficiently as possible, is only 372 mAh in terms of electrical capacity per gram, which has a theoretical limit.

Another example for obtaining a high energy density is a lithium secondary battery using the precipitation and dissolution reaction of lithium metal in the negative electrode reaction by providing a lithium metal in the negative electrode. In this lithium secondary battery, the theoretical electrical chemical equivalent of lithium metal is 2054 mAh / cm ³ , which corresponds to 2.5 times the graphite capacity of the lithium ion secondary battery. However, such a lithium secondary battery has a problem in that aging of the discharge capacity is large when charging and discharging are repeated. This is because the volume of the negative electrode greatly expands during the precipitation of lithium, and conversely greatly shrinks when dissolving lithium.

Recently, a secondary battery has been developed for simultaneously using a capacity component by occlusion and desorption of lithium and a capacity component by precipitation and dissolution of lithium. Here, a graphite material capable of occluding and desorbing lithium is used as the negative electrode material, and lithium is deposited on the surface of the carbon material during filling. However, in such secondary batteries, the precipitated lithium has a high reactivity and is biased, so that the reaction of the precipitated lithium with the electrolyte is likely to occur, and when the precipitated lithium is dissolved, it is physically bent due to the phenomenon of dropping from the negative electrode. Efficiency and charge / discharge cycle characteristics cannot be obtained.

On the other hand, since it is the capacity of the positive electrode to determine the capacity of the battery at the time of initial charge, efforts to improve cycle characteristics by storing more lithium in the negative electrode than the amount of lithium moving between the positive electrode and the negative electrode are also continued. As a method for storing lithium in a negative electrode, a method in which carbon particles or fibers are brought into contact with and reacted with an alkali metal dissolved therein, a method of attaching a lithium metal layer to the negative electrode by a roll transfer method, or a method of attaching lithium metal foil to a negative electrode carbon material , A method of contacting a lithium complex with a negative electrode using an aromatic hydrocarbon forming a complex with a lithium metal, a method of introducing lithium electrochemically, and the like. These methods aim to compensate for the loss of lithium in the negative electrode with large discharge capacity or large initial irreversible capacity.

An object of the present invention is to increase the capacity of a battery by additionally supplying lithium metal to an electrode of a lithium secondary battery. That is, by utilizing the lithium storage release ability of the negative electrode and the positive electrode material contained in the battery to the maximum, it remarkably increases the reversible capacity after activation.

The present invention provides a lithium secondary battery, wherein a polymer film layer including lithium metal powder is provided between an electrode and a separator.

The polymer film layer is prepared by applying and drying a solution in which lithium metal powder is dispersed in a polymer binder solution on an electrode active material.

The polymer binder solution may be a solution of one or more selected from the group consisting of fluorine-based polymers, Acryl-based polymers, SBR-based rubbers, and PAN-based polymers in a non-aqueous solvent.

Preferably, the amount of lithium metal powder included in the polymer film layer is determined by the following [Formula 1]:

[Formula 1]

(Lithium storage capacity of the positive electrode-lithium capacity contained in the initial positive electrode) <amount of lithium metal powder ≤ (Lithium storage capacity of the positive electrode-lithium capacity contained in the initial positive electrode + initial irreversible consumption capacity at the negative electrode)

In particular, the lithium secondary battery of the present invention is characterized by being laminated in the order of a negative electrode, a polymer film layer, a separator and a positive electrode.

The polymer film layer may further include a conductive material.

The present invention provides a lithium metal powder represented by the following [Formula 1] to a polymer binder solution in which at least one selected from the group consisting of a fluorine-based polymer, an acryl-based polymer, an SBR-based rubber, and a PAN-based polymer is dissolved in a non-aqueous solvent. After dispersing, it is applied to the surface of the electrode active material and dried to provide a method for manufacturing a lithium secondary battery, characterized in that to form a polymer film layer containing lithium metal powder on the surface of the electrode.

[Formula 1]

(Lithium storage capacity of the positive electrode-lithium capacity contained in the initial positive electrode) <amount of lithium metal powder ≤ (Lithium storage capacity of the positive electrode-lithium capacity contained in the initial positive electrode + initial irreversible consumption capacity at the negative electrode)

The lithium secondary battery of the present invention can greatly increase the reversible capacity after activation by utilizing the lithium storage release ability of the negative electrode and the positive electrode material contained in the battery to the maximum.

1 is a graph showing charge and discharge capacities of batteries according to Examples and Comparative Examples in comparison with theoretical initial lithium release capacities of positive electrodes.

The present invention relates to a polymer film including lithium metal powder and a lithium secondary battery including the same as an additional lithium source for negative electrode irreversibility correction and positive electrode capacity reinforcement of a lithium secondary battery.

In order to increase the capacity of the battery, it is necessary to additionally supply lithium ions (lithium doping or lithium ion doping) to the existing battery system, and the present invention further includes a polymer film layer including metal lithium powder on the electrode surface. How to do it.

This will be described in detail below.

In the present invention, the positive electrode is composed of a transition metal oxide capable of reversibly occluding and releasing lithium, and is characterized in that the total reversible lithium storage capacity is larger than the initially contained lithium capacity (which can be released while being stored from the beginning). .

The present invention provides a battery having a capacity that is greater than or equal to the difference between the reversible lithium storage capacity of the positive electrode and the containing lithium capacity and equal to or smaller than the sum of the difference and the initial irreversible capacity loss at the negative electrode. It is characterized by including the lithium metal powder in the form of a polymer film, provided on the electrode surface.

For this reason, the capacity | capacitance of a battery can be remarkably increased by fully exhibiting the storage and releasing ability of lithium which the active material contained in a battery has.

As described above, the present invention provides the effect of introducing lithium into a lithium secondary battery and a lithium secondary battery that can dramatically increase the reversible capacity after activation by fully utilizing the lithium storage release ability of the negative electrode and the positive electrode material contained in the battery. Provide a way to maximize.

In the present invention, as a method of supplying lithium of a metal, a method of dispersing particles containing excess metal lithium in a predetermined binder polymer and applying the same to an electrode is used. In particular, the present invention uses a method of forming a polymer film containing metal lithium powder on the electrode surface by applying a composition containing metal lithium to the surface of the electrode active material by a continuous roll process and drying it.

Accordingly, the present invention provides a method for producing a lithium secondary battery electrode, characterized in that to form a polymer film layer containing a metal lithium directly on the electrode surface to which the active material is applied.

The electrode on which the polymer film layer is formed may mean an anode or a cathode, and preferably, a polymer film layer is formed on the surface of the cathode. This is because irreversibility at the negative electrode is generally greater than that of the positive electrode, and in order to compensate for the amount of irreversible lithium at the negative electrode, it is preferable to form a polymer film layer including the lithium metal powder on the surface of the negative electrode. .

As a negative electrode of the lithium secondary battery according to the present invention, a lithium current collector having a high capacity and a large initial irreversible capacity loss as well as a conventional carbon-based material as a negative electrode active material as a negative electrode active material in a metal current collector plate using copper or the like. For example, Si, Sn, Al, and alloys of the active elements, or oxides thereof are used.

The present invention is characterized by utilizing the ability of the positive electrode to reversibly store 100% and fully utilizing the difference between this and the amount of lithium initially contained. As such a positive electrode, a lithium current-containing transition metal oxide, a lithium-containing transition metal oxide capable of reversibly occluding and releasing lithium, or a mixture of these and coated with a metal current collector plate made of aluminum or the like is used as the positive electrode active material.

Non-limiting examples of the lithium-free positive electrode active material is MnO ₂ , MoO ₃ , VO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , Cr ₃ O ₈ , CrO ₂ .

In addition, non-limiting examples of the lithium-containing transition metal oxide, the material of the LiMO ₂ composition having a layer structure (metal M element is Co, Ni, Mn, or a mixture thereof), LiMn ₂ O ₄ of the spinel structure And LiFePO _{4 having an} olivine structure.

The present invention is characterized in that to produce an electrode by forming a metal lithium layer on the electrode surface of the lithium secondary battery. As an example, the metal lithium layer may be formed of a polymer film layer formed by coating a surface of an electrode with a metal lithium powder dispersed on a polymer binder.

This disperse | distributes the particle | grains which contain excessive lithium in a predetermined | prescribed binder solution, it apply | coats continuously to an electrode surface, and it passes through a continuous roll press, and forms a lithium coating film.

At this time, it is possible to use the lithium metal powder in which the stabilization layer was apply | coated to the surface as particle | grains which contain excessive lithium.

The polymer binder solution may be a dispersion of a fluorine-based polymer such as PVDF, an Acryl-based polymer, an SBR-based rubber, and a PAN-based polymer in a non-aqueous solvent. As the non-aqueous solvent, p- Although xylene is used, the type of non-aqueous solvent used in the present invention is not particularly limited, but may be satisfied as long as the organic solvent-based non-aqueous solvent does not contain any moisture.

A lithium metal powder in an amount represented by the following [Formula 1] is dispersed in the polymer binder solution as described above:

[Formula 1]

(Lithium storage capacity of the positive electrode-lithium capacity contained in the initial positive electrode) <amount of lithium metal powder ≤ (Lithium storage capacity of the positive electrode-lithium capacity contained in the initial positive electrode + initial irreversible consumption capacity at the negative electrode)

By including the lithium metal powder of the amount according to [Equation 1] in the electrode, the negative electrode irreversible correction of the lithium and the positive electrode capacity are utilized to the maximum, and even if the amount of the lithium metal powder is excessive, performance deterioration due to precipitation of lithium Can be minimized.

Meanwhile, the polymer binder solution may include a conductive material. The conductive material complements the conductivity deteriorated when the polymer is added to form a film, and serves to form a conductive path so that the lithium metal powder can sufficiently react.

The kind of the conductive material is not particularly limited, and a known conductive carbon-based material such as carbon black can be used. The particle diameter, material, and compounding amount of such conductive material particles are not particularly limited.

As a method of application | coating of the polymeric binder solution containing lithium metal powder, continuous coating methods, such as spray injection, roll coating, dip coating, can be used.

Next, the solvent is evaporated from the applied polymer binder solution, and a polymer film layer is formed by drying while applying heat to cure the polymer resin.

The thickness of the polymer film layer is not particularly limited, but preferably, when the total electrode thickness is about 100 μm, about 30 μm to 40 μm, which corresponds to an amount resulting in an increase in capacity of 0.83 mA / cm ² . do. However, the increase amount of the polymer film layer thickness and current density is only one embodiment and the present invention is not limited thereto.

When the thickness of the polymer film layer is too thin, it is difficult to expect the effect according to the present invention. On the contrary, when the thickness of the polymer film layer containing lithium is too thick, the thickness of the battery becomes thick and the exchange of lithium ions is difficult. Problems may arise.

The present invention provides a lithium secondary battery in which the reversible capacity after activation is dramatically increased by assembling an electrode including the polymer film layer by a conventional lithium secondary battery assembly method.

In addition, the electrode manufacturing method of the present invention is not particularly limited as the current collector of the electrode, and it is possible to use a metal foil current collector which is usually used, and thus the mechanical strength of the electrode is excellent, and the conventional process is also used in the electrode manufacturing process. The present invention can be applied as it is, but it is easy to carry out the invention by adding a step of providing a metal lithium layer on the electrode surface.

Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are only for illustrating the present invention, and the scope of the present invention is not limited only to these examples.

Example

A positive electrode and a negative electrode of a lithium secondary battery were manufactured by the following method.

(1) Preparation of Cathode

As a negative electrode active material on a 20 μm thick copper current collector, the capacity per unit weight is 1950 mAh / g, and the initial irreversible capacity is 520 mAh / g, with 45 wt% SiO / C and a capacity of about 300 mAh / A negative electrode plate having a coating layer having a coating layer of 45 wt% of Soft Carbon having an initial irreversible capacity of 30 mAh / g and 10 wt% of PVDF serving as a binder was prepared. The reversible lithium storage release capacity of the coating layer was adjusted to be 2.5 mAh / cm ² .

Then, after dissolving polyethylene (polystylene) as a curable polymer resin in the non-aqueous solvent p-xylene, the amount of lithium metal powder (capacity 3625 mAh / g) is 0.23 mg / cm ² (calculated according to [Equation 1] above) And a polymer binder solution having a concentration of about 1.9% including lithium metal powder was prepared.

 A polymer film layer containing lithium metal powder was formed on the surface of the negative electrode active material by applying it to the surface of the prepared negative electrode active material by a drop casting method and then drying.

(2) production of anode

In the 20 탆 thick aluminum current collector, 88 wt% of LiMn ₂ O ₄ with an initial emission capacity of 115 mAh / g, reversible lithium storage capacity of 110 mAh / g as a positive electrode active material, and 5.5 wt% of conductive carbon acetylene black , A positive electrode having a coating layer having a PVDF of 6.5% by weight was prepared. The reversible lithium storage, release capacity of the coating layer was adjusted to 1.2mAh / cm ² .

(3) battery assembly

An aluminum laminate package-type small cell having an electrode area of about 12.6 cm ² was assembled by assembling the organic electrolyte solution containing the cathode and the anode, the polyethylene separator, and the EC / EMC / additive containing LiPF ₆ as a salt. Produced.

Comparative Example

A negative electrode and a positive electrode were prepared and combined in the same manner as in the above example, except that the polymer film layer including the lithium metal powder was not applied to the negative electrode composed of the same composition as the negative electrode active material of the above embodiment, and the above-mentioned other implementations Comparative cells were prepared in the same manner as in Example.

Battery capacity evaluation

The batteries produced in the above Examples and Comparative Examples were activated, and then charged and discharged in the range of 4.2 to 1.5V. After that, the charge / discharge cycle characteristics of the battery were investigated, and the results are shown in [Table 1] and [FIG. 1].

As a result, in the capacity evaluation of the battery, as shown in the following [Table 1], the lithium secondary battery having a negative electrode including the polymer film layer containing the lithium metal powder according to the present invention has a charge and discharge capacity and Also in efficiency, the result superior to the battery by a comparative example was shown.

In addition, in the battery of the embodiment according to the present invention as shown in the graph of Figure 1, the irreversible capacity of the negative electrode completely canceled, the excess lithium capacity is low voltage MnO ₂ It can be seen that the material is discharged.

[Table 1]

Claims (10)

A polymer film layer comprising a lithium metal powder is included between the electrode and the separator,
The lithium storage capacity of the positive electrode contains a positive electrode active material larger than the lithium capacity contained in the initial positive electrode,
Lithium secondary battery, characterized in that the amount of the lithium metal powder contained in the polymer film layer is determined by the following [formula 1].
[Formula 1]
(Lithium storage capacity of the positive electrode-lithium capacity contained in the initial positive electrode) <amount of lithium metal powder ≤ (Lithium storage capacity of the positive electrode-lithium capacity contained in the initial positive electrode + initial irreversible consumption capacity at the negative electrode)
The method of claim 1,
The electrode is a lithium secondary battery, characterized in that the negative electrode.
The method of claim 1,
The polymer film layer is a lithium secondary battery, characterized in that produced by applying a solution in which the lithium metal powder dispersed in a polymer binder solution on the electrode active material and dried.
The method of claim 3,
The polymer binder solution is a lithium secondary battery, characterized in that one or more selected from the group consisting of fluorine-based polymer, Acryl-based polymer, SBR-based rubber, and PAN-based polymer in a non-aqueous solvent. delete The method of claim 1,
The lithium secondary battery is a lithium secondary battery, characterized in that laminated in the order of a negative electrode, a polymer film layer, a separator and a positive electrode.
The method of claim 1,
Lithium secondary battery, characterized in that the polymer film layer further comprises a conductive material.
Dispersing lithium metal powder in a polymer binder solution in which at least one selected from the group consisting of a fluorine-based polymer, an acryl-based polymer, an SBR-based rubber, and a PAN-based polymer is dissolved in a non-aqueous solvent;
Forming a polymer film layer containing lithium metal powder on the surface of the electrode by applying the resultant of the above step to the surface of the electrode active material and drying it;
The amount of the lithium metal powder dispersed in the polymer binder solution is determined by the following [formula 2].
[Formula 2]
(Lithium storage capacity of the positive electrode-lithium capacity contained in the initial positive electrode) <amount of lithium metal powder ≤ (Lithium storage capacity of the positive electrode-lithium capacity contained in the initial positive electrode + initial irreversible consumption capacity at the negative electrode)
delete 9. The method of claim 8,
The electrode active material surface is a surface of the negative electrode active material manufacturing method of a lithium secondary battery.

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