KR20170051766A - Rechargeable lithium battery - Google Patents

Abstract

Provided is a lithium secondary battery comprising: a positive electrode including a positive electrode active material; and a negative electrode including a negative electrode active material, wherein the positive electrode active material comprises: lithium nickel cobalt manganese oxide; and activated carbon, the negative electrode active material comprises lithium titanium oxide, and the lithium titanium oxide comprises primary particles and secondary particles where the primary particles are aggregated.

Description

[0002] Lithium secondary batteries {RECHARGEABLE LITHIUM BATTERY}

To a lithium secondary battery.

A lithium secondary battery, which has recently been spotlighted as a power source for portable electronic devices, has a discharge voltage twice as high as that of a conventional battery using an alkaline aqueous solution, resulting in high energy density.

The lithium secondary battery includes a positive electrode including a positive electrode active material capable of intercalating and deintercalating lithium, and a negative electrode active material capable of intercalating and deintercalating lithium An electrolyte is injected into a battery cell including a cathode.

On the other hand, ISG (Idle Stop and Go) or Integrated Starter and Generator (ISG) systems are widely used in the pre-commercialization stage of EVs. ISG automotive lithium secondary batteries require high input / output characteristics. In order to obtain such high input / output characteristics, a low resistance design of the electrode plate has been made.

An additive type additive which improves the characteristics for the low resistance design may be added to the active material. However, the electrode plate composition containing the additive decreases the content of the active material by the content of the additive, leading to a decrease in the capacity and a deterioration in the processability.

In order to reduce the conduction path of the active material, nanoparticles of nanoparticles may be used to improve the conduction characteristics. However, this method is disadvantageous because the large surface energy of the nanoparticles causes agglomeration between the active materials, Loss is the main cause.

One embodiment of the present invention is to provide a lithium secondary battery having excellent high rate charge / discharge characteristics and improved lifetime characteristics as well as improved high rate charge / discharge characteristics at low temperatures.

One embodiment includes a positive electrode comprising a positive electrode active material; And a negative electrode comprising a negative electrode active material, wherein the positive electrode active material includes lithium nickel cobalt manganese oxide and activated carbon, and the negative electrode active material includes lithium titanium oxide, and the lithium titanium oxide includes primary particles and the primary particles The present invention provides a lithium secondary battery comprising secondary particles agglomerated therein.

The lithium titanium oxide may include 1 wt% to 50 wt% of the primary particles and 50 wt% to 99 wt% of the secondary particles.

The particle size (D50) of the primary particles may be 100 nm to 500 nm.

The particle size (D50) of the secondary particles may be from 8 mu m to 35 mu m.

The lithium titanium oxide may include Li ₂ TiO ₃ , LiTiO ₂ , LiTi ₂ O ₄ , Li ₄ Ti ₅ O _12, or a combination thereof.

The lithium nickel cobalt manganese oxide may be represented by the following formula (1).

[Chemical Formula 1]

Li _a Ni _x Co _y Mn _z O ₂

X? 0.9, 0.05? Y? 0.4, 0.05? Z? 0.4 and x + y + z = 1 in the formula (1).

The specific surface area of the activated carbon may be 1000 m ² / g to 2500 m ² / g.

The particle size (D50) of the activated carbon may be from 5 mu m to 30 mu m.

The activated carbon may be included in an amount of 1 wt% to 10 wt% based on the total amount of the lithium nickel cobalt manganese oxide and the activated carbon.

The details of other embodiments are included in the detailed description below.

It is possible to realize a lithium secondary battery having excellent high rate charge / discharge characteristics and improved lifetime characteristics as well as improved high rate charge / discharge characteristics at low temperature.

1 is a schematic view showing a lithium secondary battery according to one embodiment.

Hereinafter, embodiments of the present invention will be described in detail. However, it should be understood that the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

Unless defined otherwise herein, the particle size (D50) of a particle means the diameter of a particle having a cumulative volume of 50 vol% in the particle size distribution.

Hereinafter, a lithium secondary battery according to one embodiment will be described with reference to FIG.

1 is a schematic view showing a lithium secondary battery according to one embodiment.

Referring to FIG. 1, a lithium secondary battery 100 according to an embodiment includes an electrode assembly 110, a battery container 120 containing the electrode assembly 110, and a current generated from the electrode assembly 110 And an electrode tab 130 serving as an electrical path for guiding the electrode tabs to the outside. The two surfaces of the battery container 120 are sealed by overlapping surfaces facing each other. Also, the electrolyte solution is injected into the battery container 120 containing the electrode assembly 110. The electrode assembly 110 includes a positive electrode, a negative electrode facing the positive electrode, and a separator disposed between the positive electrode and the negative electrode.

Of course, the lithium secondary battery according to one embodiment is not limited to the one shown in FIG. 1, and any shape such as a cylindrical shape, a square shape, and a coin shape can be used as long as it can operate as a battery.

The negative electrode includes a current collector and a negative electrode active material layer formed on the current collector.

The current collector may be a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foil, a copper foil, a polymer substrate coated with a conductive metal, or a combination thereof, but is not limited thereto.

The negative electrode active material layer may include a negative electrode active material, and may further include at least one of a binder and a conductive material.

The negative electrode active material may include lithium titanium oxide. The lithium titanium oxide may have the form of primary particles and secondary particles formed by aggregating the primary particles.

The anode active material according to an embodiment may include both the lithium titanium oxide of the primary particles and the lithium titanium oxide of the secondary particles. The interface between the negative electrode active material and the binder is reduced due to the secondary particles, so that the conductivity and the high rate charging / discharging characteristics of the electrode plate can be improved. On the other hand, the active material of the secondary particle type has a relatively small surface energy and may have a deteriorated lifetime due to detachment of the active material due to a decrease in the adhesion of the plate to the current collector. However, in one embodiment, by using lithium titanium oxide as a negative electrode active material in the form of primary particles and secondary particles, it is possible to maintain an excellent high rate charge / discharge characteristic at the same level as that in the case of using only secondary particles, It is possible to realize a lithium secondary battery having improved lifetime characteristics by improving the adhesion of the electrode plate due to the large specific surface area of the primary particles.

The lithium titanium oxide may comprise from 1% to 50% by weight of the primary particles and from 50% to 99% by weight of the secondary particles, for example from 30% to 50% by weight of primary particles and from 2% And from 50% to 70% by weight of the tea particles. When the content ratio of the primary particles and the secondary particles is controlled within the above range, a cathode having an optimal mixture density can be realized. When the formed cathode is applied to a lithium secondary battery, excellent secondary charging / discharging characteristics And at the same time, the binding force of the electrode plate is further strengthened, whereby excellent lifetime characteristics can be secured.

The particle size (D50) of the primary particles may be 100 nm to 500 nm, and may be, for example, 150 nm to 300 nm. When the particle diameter (D50) of the primary particles is within the above range, it is possible to form an electrode plate having better binding force together with the secondary particles, thereby securing a lithium secondary battery having excellent life characteristics.

The particle size (D50) of the secondary particles may be from 8 탆 to 35 탆, for example, from 8 탆 to 12 탆. When the particle diameter (D50) of the secondary particles is within the above range, it is possible to secure a lithium secondary battery having a higher rate of charge / discharge characteristics.

The lithium titanium oxide may include Li ₂ TiO ₃ , LiTiO ₂ , LiTi ₂ O ₄ , Li ₄ Ti ₅ O _12, or a combination thereof.

The binder constituting the negative electrode active material layer functions to adhere the negative electrode active material particles to each other and to adhere the negative electrode active material to the collector well. Typical examples thereof include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, poly Vinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide containing polymer, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene Rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like, but not limited thereto.

The conductive material is used for imparting conductivity to the electrode. Any conductive material can be used without causing any chemical change in the battery. Examples of the conductive material include natural graphite, artificial graphite, carbon black, acetylene black, Carbon-based materials such as black and carbon fiber; Metal powders such as copper, nickel, aluminum, and silver, or metal-based materials such as metal fibers; Conductive polymers such as polyphenylene derivatives; Or a mixture thereof may be used.

The positive electrode includes a current collector and a positive electrode active material layer formed on the current collector.

Al (aluminum) may be used as the current collector, but the present invention is not limited thereto.

The cathode active material layer may include a cathode active material, and may further include at least one of a binder and a conductive material.

The cathode active material may include lithium nickel cobalt manganese oxide and activated carbon. A lithium secondary battery composed of a negative electrode formed by using a mixture of primary particles and secondary particles of lithium titanium oxide as a negative electrode active material and a positive electrode formed by using a mixture of lithium nickel cobalt manganese oxide and activated carbon as a positive electrode active material, The discharge characteristics and the life characteristics are excellent, and the high rate charge / discharge characteristics at low temperature can be improved.

Specifically, the lithium nickel cobalt manganese oxide may be represented by the following formula (1).

[Chemical Formula 1]

Li _a Ni _x Co _y Mn _z O ₂

X? 0.9, 0.05? Y? 0.4, 0.05? Z? 0.4 and x + y + z = 1 in the formula (1).

The specific surface area of the activated carbon may be 1000 m ² / g to 2500 m ² / g, for example, 1600 m ² / g to 2100 m ² / g. When the specific surface area of the activated carbon is within the above range, the dispersibility at the time of forming the cathode active material layer is excellent, and the high rate charge / discharge characteristics and lifetime characteristics can be improved.

The particle diameter (D50) of the activated carbon may be 5 to 30 m, for example, 5 to 20 m and 10 to 20 m. When the particle size (D50) of the activated carbon is within the above range, the aggregation of particles does not occur and the localization of particles to a specific region can be prevented, so that the high rate charge / discharge characteristics can be improved.

The activated carbon may be contained in an amount of 1 wt% to 10 wt%, for example, 3 wt% to 6 wt% based on the total amount of the lithium nickel cobalt manganese oxide and the activated carbon. When the activated carbon is included in the above content range, the high rate charge / discharge characteristics are improved and excellent lifetime characteristics can be secured.

The binder constituting the positive electrode active material layer functions to adhere the positive electrode active material particles to each other and adhere the positive electrode active material to the positive electrode current collector. Specific examples thereof include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, Polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide containing polymer, Butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like.

The conductive material is used for imparting conductivity to the electrode. Any conductive material can be used without causing any chemical change in the battery. Examples of the conductive material include natural graphite, artificial graphite, carbon black, acetylene black, Carbon-based materials such as black and carbon fiber; Metal powders such as copper, nickel, aluminum, and silver, or metal-based materials such as metal fibers; Conductive polymers such as polyphenylene derivatives; Or a mixture thereof may be used.

The positive electrode and the negative electrode are prepared by mixing an active material, a conductive material and a binder in a solvent to prepare an active material composition, and applying the composition to a current collector. As the solvent, N-methylpyrrolidone, water and the like can be used, but it is not limited thereto. The method of manufacturing the electrode is well known in the art, and therefore, a detailed description thereof will be omitted herein.

The electrolytic solution includes an organic solvent and a lithium salt.

The organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move. The organic solvent may be selected from carbonate, ester, ether, ketone, alcohol and aprotic solvents.

Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethyl propyl carbonate ethylpropyl carbonate (EPC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC)

In particular, when a mixture of a chain carbonate compound and a cyclic carbonate compound is used, it can be prepared from a solvent having a high dielectric constant and a low viscosity. In this case, the cyclic carbonate compound and the chain carbonate compound may be mixed in a volume ratio of about 1: 1 to 1: 9.

Examples of the ester solvents include methyl acetate, ethyl acetate, n-propyl acetate, methyl propionate, ethyl propionate,? -Butyrolactone, decanolide, valerolactone, mevalonolactone mevalonolactone, caprolactone, and the like may be used. As the ether solvent, for example, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran and the like can be used. As the ketone solvent, cyclohexanone and the like can be used have. As the alcoholic solvent, ethyl alcohol, isopropyl alcohol, etc. may be used.

The organic solvents may be used singly or in combination of one or more. When one or more of them are mixed, the mixing ratio may be appropriately adjusted according to the performance of the desired cell.

The electrolytic solution may further contain additives such as an overcharge inhibitor such as ethylene carbonate, pyrocarbonate and the like.

The lithium salt is dissolved in an organic solvent to act as a source of lithium ions in the cell to enable operation of a basic lithium secondary battery and to promote the movement of lithium ions between the anode and the cathode.

Specific examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiN (SO ₃ C ₂ F ₅ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO _{2 , LiAlCl 4, LiN (C x} F 2x + 1 SO 2) (C y F 2y + 1 SO 2) ( where, x and y are natural numbers), LiCl, LiI, LiB ( C 2 O 4) 2 ( lithium Lithium bis (oxalato) borate (LiBOB), or a combination thereof.

The concentration of the lithium salt is preferably within the range of about 0.1M to about 2.0M. When the concentration of the lithium salt is within the above range, the electrolytic solution has an appropriate conductivity and viscosity, so that it can exhibit excellent electrolyte performance, and lithium ions can effectively move.

The separator separates the negative electrode and the positive electrode and provides a passage for lithium ion, and any separator can be used as long as it is commonly used in a lithium battery. That is, it is possible to use an electrolyte having a low resistance to ion movement and an excellent ability to impregnate an electrolyte. For example, selected from glass fibers, polyester, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be nonwoven fabric or woven fabric. For example, a polyolefin-based polymer separator such as polyethylene, polypropylene and the like is mainly used for a lithium ion battery, and a coated separator containing a ceramic component or a polymer substance may be used for heat resistance or mechanical strength, Structure.

Hereinafter, specific embodiments of the present invention will be described. However, the embodiments described below are only intended to illustrate or explain the present invention, and thus the present invention should not be limited thereto. In addition, contents not described here can be inferred sufficiently technically if they are skilled in the art, and a description thereof will be omitted.

(Production of lithium secondary battery)

Example  One

The weight ratio of 9: the primary particle of Li ₄ Ti ₅ O ₁₂ having a secondary particle (LTO) and the particle diameter (D50) of 9㎛ Li ₄ Ti ₅ O ₁₂ (LTO) with 150nm of particle size (D50) 1 89% by weight of an anode active material mixed with 5% by weight of carbon black (denka black) and 6% by weight of polyvinylidene fluoride (PVdF) were mixed with N-methylpyrrolidone to prepare a slurry. The prepared slurry was applied to an aluminum foil having a thickness of 15 탆, dried and rolled to produce a negative electrode.

_{LiNi 1/3 Co 1/3} Mn 1/3 O 2 (NCM), and 1600 m ² / g specific surface area and the 10㎛ activated carbon having a particle size (D50) of 94: a cathode active material mixed in a weight ratio of 6 85 , 9 wt% of carbon black (denka black) and 6 wt% of polyvinylidene fluoride (PVdF) were mixed with N-methylpyrrolidone to prepare a slurry. The prepared slurry was applied to an aluminum foil having a thickness of 15 탆, dried and rolled to prepare a positive electrode.

An electrode assembly was formed using the positive and negative electrodes and the separator made of polyethylene prepared above, and then an electrolyte was injected into the electrode assembly to prepare a 50 mAh pouch type lithium secondary battery. The electrolyte solution was prepared by adding 1.15 M LiPF ₆ to a mixed solvent of ethylene carbonate (PC), ethyl methyl carbonate (DMC) and diethyl carbonate (DEC) in a volume ratio of 2: 6: 2 Respectively.

Example  2

Primary particles of the Li ₄ Ti ₅ O _12, and the secondary particles of the Li ₄ Ti ₅ O ₁₂ 3: a and, the lithium secondary battery in the same manner as in Example 1 except for using a cathode active material mixed with 7 weight ratio of Respectively.

Comparative Example  One

A lithium secondary battery was produced in the same manner as in Example 1, except that Li ₄ Ti ₅ O ₁₂ as the primary active material was used alone.

Comparative Example  2

A lithium secondary battery was fabricated in the same manner as in Example 1, except that Li ₄ Ti ₅ O ₁₂ as a secondary active material was used alone as the negative electrode active material.

Comparative Example  3

Used alone, one of the primary particle Li ₄ Ti ₅ O ₁₂ as the negative electrode active material, and is the same as in Example 1, except as a positive electrode active material that exclusively used with the _{LiNi 1/3 Co 1/3} Mn 1/3 O 2 To prepare a lithium secondary battery.

Comparative Example  4

Used alone, the second of the primary particles Li ₄ Ti ₅ O ₁₂ as the negative electrode active material, and is the same as in Example 1, except as a positive electrode active material that exclusively used with the _{LiNi 1/3 Co 1/3} Mn 1/3 O 2 To prepare a lithium secondary battery.

Comparative Example  5

Of the primary particles as the negative electrode active material is Li ₄ Ti ₅ O _12, and the secondary particles Li ₄ Ti ₅ a O ₁₂ 7: using a mixture in a weight ratio of _{3, LiNi 1/3 Co 1} /3 Mn 1 as a positive electrode active material _{/ 3} O ₂ was used alone, a lithium secondary battery was produced in the same manner as in Example 1.

Rating 1: Plate Binding force

In the negative electrode prepared in Examples 1 and 2 and Comparative Examples 1 to 5, a plate having a surface area of 2.5 cm x 2.5 cm was adhered to a glass plate, and the adhesion of the plate was measured using a tensile strength meter. Respectively.

Evaluation 2: High Rate of Lithium Secondary Battery Charging and discharging  characteristic

The discharge capacity and the charge capacity at 50 C of the lithium secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 to 5 were measured at room temperature and low temperature of -20 캜, respectively, and the results are shown in Table 1 below.

In Table 1 below, the 50 C / 1 C discharge rate (%) is obtained as a percentage of the discharge capacity at 50 C-rate versus the discharge capacity at 1 C-rate. The 50C / 1C charge rate (%) is also obtained as a percentage of the charge capacity at 50 C-rate versus the charge capacity at 1 C-rate.

Evaluation 3: Life characteristics of lithium secondary battery

The lithium secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 to 5 were charged at 4C at room temperature and discharged at 4C, and the capacity reduction rate according to the cycle was measured. The results are shown in Table 1 below.

In Table 1, the 2000cy / 1cy capacity retention rate (%) is obtained as a percentage of the discharge capacity in 2000 cycles versus the discharge capacity in one cycle.

LTO
The primary and
Secondary
Particle
Weight ratio NCM and activated carbon weight ratio Binding force
(g / mm) 50C / 1C
Discharge rate (%) 50C / 1C
Charging rate (%) Low temperature 50C / 1C
Discharge rate (%) Low temperature 50C / 1C filling rate (%) 2000cy / 1cy
Volume
Retention rate (%) Example 1 1: 9 94: 6 0.67 78 76 NG NG 90 Example 2 3: 7 94: 6 0.78 73 76 10 22 89 Comparative Example 1 10: 0 94: 6 0.99 61 74 10.2 12.1 88 Comparative Example 2 0:10 94: 6 0.11 79 77 11.1 23.4 85 Comparative Example 3 10: 0 10: 0 0.99 57 74 7 12 87 Comparative Example 4 0:10 10: 0 0.11 77 70 7.2 18.7 85 Comparative Example 5 3: 7 10: 0 0.78 70 75 7 14.7 86

Referring to Table 1, Example 1 in which a lithium secondary battery is constituted by using a mixture of primary particles and secondary particles of lithium titanium oxide as a negative electrode active material, and using a mixture of lithium nickel cobalt manganese oxide and activated carbon as a cathode active material, 2 was superior to Comparative Examples 1 to 4 in which lithium titanium oxide was used as the primary active material in the form of primary particles or secondary particles alone and in Comparative Example 5 in which no activated carbon was used as the positive active material, And the binding force of the electrode plate is improved, so that the lifetime characteristics are improved. It can also be seen that Example 2 has improved charging / discharging characteristics at a lower temperature than Comparative Examples 1 and 3 to 5. From this, it can be confirmed that the lithium secondary battery according to one embodiment is applicable to the ISG automobile.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, And falls within the scope of the invention.

100: Lithium secondary battery
110: electrode assembly
120: Battery container
130: electrode tab

Claims (9)

A cathode comprising a cathode active material; And
A negative electrode comprising a negative electrode active material,
Wherein the cathode active material comprises lithium nickel cobalt manganese oxide and activated carbon,
Wherein the negative electrode active material comprises lithium titanium oxide,
Wherein the lithium titanium oxide comprises primary particles and secondary particles in which the primary particles are aggregated. The method of claim 1,
Wherein the lithium titanium oxide comprises 1 wt% to 50 wt% of the primary particles and 50 wt% to 99 wt% of the secondary particles. The method of claim 1,
And the particle diameter (D50) of the primary particles is 100 nm to 500 nm. The method of claim 1,
Wherein the secondary particles have a particle size (D50) of 8 mu m to 35 mu m. The method of claim 1,
Wherein the lithium titanium oxide comprises Li ₂ TiO ₃ , LiTiO ₂ , LiTi ₂ O ₄ , Li ₄ Ti ₅ O _12, or a combination thereof. The method of claim 1,
Wherein the lithium nickel cobalt manganese oxide is represented by the following formula (1).
[Chemical Formula 1]
Li _a Ni _x Co _y Mn _z O ₂
X? 0.9, 0.05? Y? 0.4, 0.05? Z? 0.4 and x + y + z = 1 in the formula (1). The method of claim 1,
And the specific surface area of the activated carbon is 1000 m ² / g to 2500 m ² / g. The method of claim 1,
Wherein a particle diameter (D50) of the activated carbon is 5 mu m to 30 mu m. The method of claim 1,
Wherein the activated carbon is contained in an amount of 1 wt% to 10 wt% based on the total amount of the lithium nickel cobalt manganese oxide and the activated carbon.

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