KR100965710B1 - Secondary battery comprising lithium titanium oxide - Google Patents

Abstract

In the present invention, a secondary battery including a positive electrode, a negative electrode, and an electrolyte solution, the negative electrode includes a lithium titanium oxide having _a composition formula Li _a Ti _3-a O ₄ (0 <a <3) as a current collector and a negative electrode active material. Is a metal or an alloy thereof in which an alloying reaction occurs with lithium at a lower potential than the lithium titanium oxide, and provides a secondary battery having a capacity ratio of the negative electrode active material to the positive electrode active material of 1.5 or more. In the secondary battery of the present invention, since the negative electrode and the unreacted lithium are alloyed with the current collector, the battery voltage at the end of charging can be increased, and the energy density of the battery is improved.

Secondary battery, energy density improvement, lithium titanium oxide, capacity ratio

Description

Secondary battery containing lithium titanium oxide {SECONDARY BATTERY COMPRISING LITHIUM TITANIUM OXIDE}

1 is a charge and discharge graph of the battery prepared in Example 1 of the present invention.

2 is a graph showing the life characteristics of the battery prepared in Example 1 of the present invention.

Figure 3 is a charge and discharge graph of the battery prepared in Comparative Example 1 of the present invention.

4 is a discharge graph of the battery prepared in Example 2 and Comparative Example 2 of the present invention.

The present invention relates to a secondary battery containing lithium titanium oxide.

Although a lithium secondary battery using lithium metal was used as a negative electrode active material of a lithium secondary battery in the 1970s, when lithium metal was used as a negative electrode, dendrite was formed on the surface of the lithium metal during the charge and discharge of the battery. There is a risk of short circuit and battery explosion.

In order to solve this problem, since the 1990s, the operating voltage is similar to that of lithium metal, and it is structurally stable and can reversibly accept or supply lithium ions. However, it is still insufficient to secure the safety of the battery.

Recently, attempts to use lithium titanium oxide as a negative electrode active material as a method of improving the safety of lithium ions have been announced. When the battery is manufactured using lithium titanium oxide, since the occlusion and discharge voltage of lithium is about 1.5V, the degree of freedom of selecting an electrolyte is increased, and there is an advantage that the precipitation of lithium is small during high-speed charging and discharging. In addition, since there is no reaction between lithium- occluded carbon and PVDF used as a binder, which are commonly present in a carbon-based active material used as a negative electrode active material, there is an advantage of excellent thermal safety.

Therefore, researches have been made to develop a battery by applying lithium titanium oxide as a negative electrode active material, but there are no studies to solve the accompanying decrease in energy density, and the driving voltage of the battery is increased to 4V or higher. There is no example. In the existing published data, Japanese Patent Laid-Open No. 2001-243952 describes 2.7V, Japanese Patent Laid-Open No. 2005-100771 is 3V and Japanese Patent Laid-Open No. 2005-142047 is limited to 2.8V. There is a situation. In addition, when the lithium titanium oxide is used as the negative electrode active material, the energy density of the battery is lower than that of the carbon used as the negative electrode active material, which is shown in Table 1 below.

Using carbon
Conventional Lithium Secondary Battery With Li _4/3 Ti _5/3 O ₄
Conventional Lithium Secondary Battery Average voltage (V) 3.6 2.3 Energy Density (Wh / ℓ) 340 160

The present invention uses a metal or an alloy current collector thereof and a negative electrode including lithium titanium oxide as a negative electrode active material, in which an alloying reaction occurs at a lower potential than lithium titanium oxide, and a capacity ratio of the negative electrode active material to the positive electrode active material used in a conventional battery. Taken in reverse, the negative electrode active material and the unreacted lithium are to be alloyed with the current collector contained in the negative electrode to improve the battery voltage at the end of the charge, to provide a secondary battery improved the energy density of the battery.

In the present invention, a secondary battery including a positive electrode, a negative electrode, and an electrolyte solution, the negative electrode includes a lithium titanium oxide having _a composition formula Li _a Ti _3-a O ₄ (0 <a <3) as a current collector and a negative electrode active material. Is a metal or an alloy thereof in which an alloying reaction occurs with lithium at a lower potential than the lithium titanium oxide, and provides a secondary battery having a capacity ratio of the negative electrode active material to the positive electrode active material of 1.5 or more.

Hereinafter, the present invention will be described in detail.

Lithium titanium oxide used as the negative electrode active material has a high potential of 1.5V for the desorption and insertion reaction of lithium. Thus, when a battery is constructed using a commercially available positive electrode active material, the potential of the lithium inserted into the negative electrode active material is 2.3 to 2.4V. It has a flat potential of has a disadvantage of reducing the energy density.

When the battery is manufactured with the capacity ratio of the negative electrode active material to the positive electrode active material being 1.5 or more, the excess lithium that is not inserted into the negative electrode active material during charging may cause an alloying reaction with the current collector, Since desorption may occur, the charge / discharge voltage of the battery is changed by the alloying reaction, and as a result, the energy density of the battery can be improved. For example, when aluminum is used as the metal foil current collector of the negative electrode and the capacity ratio of the negative electrode active material to the positive electrode active material is 1.5 or more, the unreacted lithium with the negative electrode active material is alloyed at around 0.2 ± 0.05 V with the current collector aluminum. This can happen, thereby raising the battery voltage at the end of charging.

However, when the capacity ratio of the negative electrode active material to the positive electrode active material is less than 1.5, due to the irreversible alloying reaction between lithium and the current collector, the alloying reaction between lithium and the current collector appearing at around 0.2 ± 0.05 V cannot be effectively used. Cannot effectively improve energy density. Therefore, the capacity ratio of the electrode must be at least 1.5 or higher to enable a battery of high energy density using an alloying reaction of lithium and aluminum.

In addition, the driving voltage of the secondary battery according to the present invention may exceed 3.0V. When the high voltage life characteristic of the positive electrode active material that determines the charging voltage of the battery is good, the battery voltage can be realized up to 4.2 V. Otherwise, the driving voltage can be controlled by adjusting the active material capacity ratio.

The negative electrode constituting the secondary battery of the present invention may include a lithium titanium oxide and a current collector as a negative electrode active material.

The current collector may use a metal or an alloy thereof in which the alloying reaction occurs with lithium at a lower voltage than the lithium titanium oxide, and preferred examples thereof include aluminum or an alloy thereof.

In addition, the lithium titanium oxide may be a lithium titanium oxide represented by the composition formula Li _a Ti _3-a O ₄ (0 <a <3) as the negative electrode active material. Non-limiting examples thereof include Li _4/3 Ti _5/3 O ₄ , LiTi ₂ O ₄ , Li _4/5 Ti _11/5 O ₄ , and the like, and one or more of these lithium titanium oxides may be used.

On the other hand, the positive electrode may be made of a positive electrode active material capable of storing and releasing lithium.

In general, the positive electrode active material may be an oxide containing a transition metal having a structure in which lithium is intercalated. Non-limiting examples include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (0 <a <1, 0 <b <1, 0 <c <1, a + b + c = 1), LiNi _1-Y Co _Y O ₂ , LiCo _1-Y Mn _Y O ₂ , LiNi _1-Y Mn _Y O ₂ (where 0 <Y <1), Li (Ni _a Co _b Mn _c ) O ₄ (0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), LiMn _2-z Ni _z O ₄ , LiMn _2-z Co _z O ₄ (here, 0 <z <2), lithium manganese composite oxides such as LiCoPO ₄ , LiFePO ₄ , lithium nickel oxide, lithium cobalt oxide and a part of manganese, nickel, cobalt oxides of these oxides are substituted with other transition metals Vanadium oxide containing lithium or the like can be used.

Electrodes in the present invention can be prepared by conventional methods known in the art. For example, after applying a negative electrode slurry prepared by mixing a negative electrode active material with a binder to a current collector, the solvent or dispersion medium is removed by drying, and the active material is bound to the current collector, and the active materials can be bound together. have.

Examples of binders that can be used include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and the like.

Examples of the solvent include organic solvents such as NMP (N-methyl pyrrolidone), DMF (dimethyl formamide), acetone, and dimethyl acetamide or water, and these solvents may be used alone or in combination of two or more thereof. . The amount of the solvent is sufficient to dissolve and disperse the electrode active material, the core-shell binder, and the conductive material in consideration of the coating thickness of the slurry and the production yield.

The method of applying the slurry to the current collector is also not particularly limited. For example, it can be applied by a method such as doctor blade, dipping, brushing, and the like, but the coating amount is not particularly limited, but the thickness of the active material layer formed after removing the solvent or the dispersion medium is usually 0.005 to 5 mm, preferably 0.05 to 2 mm. The amount of the range which becomes a range is preferable. The method of removing the solvent or the dispersion medium is not particularly limited, but the solvent or the dispersion medium may be used as quickly as possible within the speed range in which stress concentration occurs and cracks occur in the active material layer or the active material layer does not peel off from the current collector. It is preferable to use a method of adjusting to remove to volatilize.

The secondary battery of the present invention may be prepared by inserting a porous separator between the positive electrode and the negative electrode by a conventional method known in the art and adding an electrolyte solution. Secondary batteries include lithium ion secondary batteries, lithium polymer secondary batteries or lithium ion polymer secondary batteries.

The electrolyte may include a nonaqueous solvent and an electrolyte salt.

The nonaqueous solvent is not particularly limited as long as it is normally used as a nonaqueous solvent for nonaqueous electrolyte, and cyclic carbonate, linear carbonate, lactone, ether, ester or ketone can be used.

Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and the like. Examples of the linear carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC) and dipropyl carbonate. (DPC), ethylmethyl carbonate (EMC), methyl propyl carbonate (MPC), and the like. Examples of the lactone include gamma butyrolactone (GBL), and examples of the ether include dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, and the like. There is this. In addition, examples of the ester include n-methyl acetate, n-ethyl acetate, methyl propionate, methyl pivalate, and the like. The ketone includes polymethylvinyl ketone. These nonaqueous solvents can be used individually or in mixture of 2 or more types.

The electrolyte salt is not particularly limited as long as it is usually used as an electrolyte salt for nonaqueous electrolyte. Electrolytic salt, non-limiting example, A ⁺ B ^- A salt of the structure, such as, A ⁺ comprises a Li ^+, Na ^+, an alkali metal cation or an ion composed of a combination thereof, such as K ⁺ B ^- is PF ₆ ^{- _{, BF 4 -, Cl -,}} Br -, I -, ClO 4 -, ASF 6 -, CH 3 CO 2 -, CF 3 SO 3 -, N (CF 3 SO 2) 2 -, C (CF 2 SO 2 ) ₃ ^- and a salt containing the same anion ion or a combination thereof. In particular, lithium salts are preferred. These electrolyte salts can be used individually or in mixture of 2 or more types.

The secondary battery of the present invention may include a separator. The separator can be used is not particularly limited, it is preferable to use a porous separator, non-limiting examples include a polypropylene-based, polyethylene, or polyolefin-based porous separator.

The lithium secondary battery of the present invention is not limited in appearance, but may be cylindrical, square, pouch type, or coin type using a can.

Hereinafter, the present invention will be described in detail with reference to the following Examples. However, the following examples are merely to illustrate the present invention and the present invention is not limited by the following examples.

(Example 1)

92 parts by weight of the active material (Li _4/3 Ti _5/3 O ₄ ), 2 parts by weight of a superconducting agent (Super P carbon black) and 6 parts by weight of a binder (PVdF) are uniformly mixed, and N-methylpyrrolidone ( NMP) was added to prepare a slurry in a uniform state, which was applied to one surface of an aluminum foil as a current collector and dried at 100 ° C. in a vacuum oven to remove the solvent, thereby preparing an electrode.

The prepared electrode was used as a positive electrode, the negative electrode was lithium metal, the separator was a porous polyethylene membrane, and the electrolyte was a coin-type half cell using an EC / DMC (1: 1) -based liquid electrolyte in which 1M LiPF ₆ was dissolved. Was prepared.

Each operating voltage was tested under normal conditions between 3.5V and 1.0V and between 3.5V and 0V to determine the reaction voltage and reversibility of aluminum foil and lithium. The results of charging and discharging the half cell at different operating voltages are shown in FIG. 1.

(A) and (b) of FIG. 1 respectively show the capacity according to the operating voltage, and when the operating voltage is 0V, an alloy reaction of aluminum and lithium is shown at 0.2 ± 0.05V, Tally was confirmed to appear.

In addition, it was confirmed through the life test results that the reaction has a reversible. Confirmation of the life characteristics is shown in FIG.

(Comparative Example 1)

A half cell test was conducted in the same manner as in Example 1 except that copper foil was used as the current collector, and the charge and discharge results are shown in FIG. 3.

In the case of using copper foil as the current collector, it was confirmed that the alloying reaction as in Example 1 did not occur, and as a current collector, lithium and lithium at a lower voltage than lithium titanium oxide (Li _4/3 Ti _5/3 O ₄ ) In the case of using a metal foil in which the alloying reaction does not occur, it was confirmed that the energy density of the battery using lithium titanium oxide (Li _4/3 Ti _5/3 O ₄ ) as the active material could not be increased.

(Example 2)

The electrode prepared in Example 1 was used as the cathode.

LiCoO ₂ was used as anode, membrane was porous polyethylene membrane, and electrolyte was EC / DMC (1: 1) -based non-aqueous electrolyte in which 1M LiPF ₆ was dissolved. A secondary battery was prepared.

The cells were subjected to electrochemical experiments at 1.5V and 4.2V conditions. Experimental results are shown in FIG.

Lithium ions that exceed the theoretical capacity of the negative electrode active material provided from the anode during charging are alloyed with aluminum, and when discharged, a voltage curve with an average voltage of about 3.7 V appears and occludes Li _4/3 Ti _5/3 O ₄ . As the voltage at which lithium was released, a curve having an average voltage of 2.3 V was shown.

Through the above results, in the case of manufacturing a battery using lithium titanium oxide (Li _4/3 Ti _5/3 O ₄ ) as the active material, by adjusting the capacity ratio of the negative electrode and the positive electrode and the current collector of the negative electrode and the aluminum or aluminum alloy As described above, it can be seen that the energy density of the battery can be improved when using a metal or an alloy thereof in which an alloying reaction occurs with lithium at a lower voltage than lithium titanium oxide (Li _4/3 Ti _5/3 O ₄ ).

(Comparative Example 2)

Except that the capacity ratio of the negative electrode active material to the positive electrode active material was 0.9, a secondary battery was prepared under the same conditions as in Example 2, and electrochemical experiments were performed under 1.5 V and 2.7 V conditions. The reason for setting the charge voltage limit to 2.7 V is due to the structural instability of LiCoO ₂ . The discharge curves under the above conditions are shown in FIG. 4.

In the secondary battery of the present invention, since the negative electrode and the unreacted lithium are alloyed with the current collector, the battery voltage at the end of charging can be increased, and the energy density of the battery is improved.

Claims (4)

In a secondary battery including a positive electrode, a negative electrode and an electrolyte solution, The negative electrode includes _a lithium titanium oxide having _a composition formula Li _a Ti _3-a O ₄ (0 <a <3) as a current collector and a negative electrode active material, The lithium titanium oxide is at least one selected from the group consisting of Li _4/3 Ti _5/3 O ₄ , LiTi ₂ O ₄ and Li _4/5 Ti _11/5 O ₄ , The current collector is a metal or an alloy thereof in which an alloying reaction occurs with lithium at a lower potential than the lithium titanium oxide. The capacity ratio of the negative electrode active material to the positive electrode active material is 1.5 or more, The secondary battery is characterized in that the drive voltage of the secondary battery is more than 3.0V. delete The secondary battery of claim 1, wherein the current collector is aluminum or an aluminum alloy. delete

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