KR100838944B1 - Seconday battery - Google Patents

Abstract

In the secondary battery including the positive electrode, the negative electrode, and the electrolyte, when lithium is filled in all active sites of the positive electrode active material after each charge and discharge cycle, lithium ions can be reversibly occluded and released in the active site of the negative electrode active material. It provides a secondary battery characterized by the presence or the presence of excess lithium (excess Li). In addition, according to the present invention, when lithium is filled in all active sites of the positive electrode active material after each charge / discharge cycle of the secondary battery, excess lithium in the active site of the negative electrode active material may be reversibly occluded and released. The present invention provides a method of improving the life characteristics of a secondary battery by allowing or presenting it.

In the present invention, unlike the conventional battery system in which the use of a negative electrode material irreversible than the positive electrode results in a decrease in battery capacity and a decrease in life characteristics due to low charging and discharging efficiency, the present invention spares not only the initial discharge but also after the charge and discharge of each cycle. By constructing a new secondary battery system in which lithium is present in the negative electrode, it is possible to provide an increase in capacity and life characteristics of the secondary battery.

Electrode active material, extra, lithium, electrochemical device, secondary battery

Description

Secondary Battery {SECONDAY BATTERY}

FIG. 1A illustrates a secondary battery system in which excess lithium is present in a negative electrode according to the present invention, and FIG. 1B illustrates a conventional secondary battery system in which excess lithium is not present.

FIG. 2 is a first cycle charge and discharge graph of a coin cell of Reference Example 1 having an electrode including Li ₂ NiO ₂ and a counter electrode of Li-metal.

3 is _{Li (Li 0 .2 Mn 0 .6} Ni 0 .2) O 2 reference the first cycle charge-discharge graph of a coin-type cell of Example 2 including the electrode and Li metal as a counter electrode-containing.

4 is a first cycle charge and discharge graph of a coin-type battery of Reference Example 3 having an electrode including LiCoO ₂ (80 parts by weight) + Li ₂ NiO ₂ (20 parts by weight) and Li-metal as a counter electrode.

5 is a first cycle of a coin-type battery of Reference Example 4 having an electrode comprising LiCoO ₂ (70 parts by weight) + Li (Li _0.2 Mn _0.6 Ni _0.2 ) O ₂ (30 parts by weight) and Li-metal as a counter electrode. Charge and discharge graph.

6 is a first cycle charge / discharge graph of a coin-type battery of Reference Example 5 having an electrode including LiCoO ₂ and a counter electrode having Li-metal.

FIG. 7 is a first cycle charge / discharge graph of a coin-type battery of Reference Example 6 having an electrode including graphite (50 parts by weight) + Si (50 parts by weight) and Li-metal as a counter electrode.

FIG. 8 is a graph showing the life characteristics of a lithium full battery of Comparative Example 1 having a cathode including LiCoO ₂ and a cathode including graphite (50 parts by weight) + Si (50 parts by weight).

FIG. 9 is a graph showing charge and discharge efficiency of a lithium full battery of Comparative Example 1 having a positive electrode including LiCoO ₂ and a negative electrode including graphite (50 parts by weight) + Si (50 parts by weight).

10 is a lithium of Example 1 having a positive electrode comprising LiCoO ₂ (80 parts by weight) + Li ₂ NiO ₂ (20 parts by weight) and a negative electrode comprising graphite (50 parts by weight) + Si (50 parts by weight). It is a graph showing the life characteristics of a secondary battery (full cell).

FIG. 11 shows the lithium of Example 1 having a positive electrode comprising LiCoO ₂ (80 parts by weight) + Li ₂ NiO ₂ (20 parts by weight) and a negative electrode comprising graphite (50 parts by weight) + Si (50 parts by weight). A graph showing charge and discharge efficiency of a full cell.

12 is a lithium full cell of Example 2 having a positive electrode including Li (Li _0.2 Mn _0.6 Ni _0.2 ) O ₂ and a negative electrode including graphite (50 parts by weight) + Si (50 parts by weight) It is a graph showing the lifespan characteristics.

FIG. 13 is a lithium full cell of Example 2 having a positive electrode including Li (Li _0.2 Mn _0.6 Ni _0.2 ) O ₂ and a negative electrode including graphite (50 parts by weight) + Si (50 parts by weight) It is a graph showing charge and discharge efficiency.

The present invention relates to a secondary battery, preferably a lithium secondary battery, which is intended to minimize the capacity reduction of the battery and to improve life characteristics due to improved charge and discharge efficiency for each charge and discharge cycle.

Recently, as miniaturization and light weight of electronic equipment have been realized and the use of portable electronic devices has become common, research on lithium secondary batteries having high energy density has been actively conducted. A lithium secondary battery is prepared by using a material capable of inserting and detaching lithium ions as a negative electrode and a positive electrode, and filling an organic or polymer electrolyte between the positive electrode and the negative electrode, and lithium ions can be inserted and removed from the positive electrode and the negative electrode. Electrical energy is generated by oxidation and reduction reactions.

As a cathode active material of a lithium secondary battery, composite metal oxides such as LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , and LiNi _1/3 Mn _1/3 Co _1/3 are generally used. Most of them are 90 to 97%. It has an initial efficiency of degree. On the other hand, as the negative electrode active material, natural graphite, hard carbon, soft carbon, metal oxide negative electrode active material, metal-based negative electrode active material, and the like, most of them have an initial efficiency of about 30 to 90% depending on the type of active material. As described above, the conventional battery system including the positive electrode active material having a high initial efficiency and the negative electrode active material having a lower initial efficiency than the positive electrode active material has a low capacity and a low charge / discharge efficiency at each charge and discharge cycle due to the negative irreversible negative electrode material. Problems such as reduction in cycle life are caused. That is, the lithium secondary battery forms a solid electrolyte interface (SEI) layer by reacting an electrolyte and a surface of a carbon particle, which is a negative electrode active material, at the negative electrode of the battery during the first charging process. The SEI membrane serves to stabilize the battery by inhibiting decomposition of the electrolyte at the surface of the carbon particles, which are negative electrodes. However, since a certain amount of lithium is consumed when forming the SEI film, the amount of reversible lithium is reduced, thereby reducing the capacity of the battery. . In particular, in the current secondary battery system in which the lithium source is in the positive electrode, when the negative irreversible capacity of the negative electrode is large, a dead volume increase of the positive electrode side occurs through the irreversible negative electrode, so that the capacity of the secondary battery system is less than that available in the actual positive electrode. The capacity is shown, which causes the capacity of the battery to decrease. In addition, the low capacity and low charge and discharge efficiency of each cycle due to the dead volume is also accompanied by a decrease in the life characteristics of the battery.

On the other hand, Si, Sn, Pb, etc., a metal-based active material known as a next-generation high-capacity negative electrode material has a very large capacity to accept 4.4 Li, but problems such as low initial charge and discharge efficiency and decrease in battery performance due to volume expansion It is not commercialized. Active research to solve this problem is being conducted in many research institutes. For example, the method of controlling the structural change or increasing the electrochemical properties through the synthesis of non-reactive alloy with Li, the method of forming the structure of oxide or nitride to prevent the volume expansion, and mixing with the conductive active material such as carbon to increase the conductivity. Method and the like. However, in order to commercialize, electrochemical problems such as capacity reduction due to initial irreversibility and cycle life due to low cycle efficiency are not sufficiently solved.

The inventors of the present invention consider the problems of the conventional battery system in which capacity reduction during initial charge / discharge due to the use of a negative electrode material that is irreversible than the positive electrode and decrease in life characteristics due to low charge / discharge efficiency during each charge / discharge cycle progress. After the discharge and after each cycle charging and discharging, a new battery system for supplying the lithium to the negative electrode in advance so that excess lithium is reversibly present in the negative electrode increases capacity by reducing the dead volume of the positive electrode, It has been found that the cycle efficiency can be improved and the lifespan characteristics of the battery can be increased by improving the electrochemical performance of the negative electrode.

Accordingly, an object of the present invention is to provide a secondary battery with improved overall performance by building a new battery system.

Another object of the present invention is to provide a method of improving the life characteristics of a battery by applying a new battery system in which excess lithium is present in the negative electrode even after the initial discharge and each charge / discharge cycle.

The present invention provides a secondary battery including a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode includes a positive electrode active material including or coated with one or more compounds selected from the group consisting of lithium nickel oxide of Formula 1 and a compound of Formula 2 Wherein the negative electrode includes a negative electrode active material including or coated with one or more metalloids selected from the group consisting of Si, Sn, and Pb, and these are controlled to satisfy the conditions of Equations 1 and 2 below. It is characterized by a secondary battery, preferably a lithium secondary battery.
[Formula 1]
Li _{2 + x} Ni _1-y A _y O _{2 + α} (where −0.5 ≦ x ≦ 0.5, 0 ≦ y <1, 0 ≦ _α <0.3)
[Formula 2]
Solid solution of XLi (Li _1/3 M _2/3 ) O ₂ + YLiM'O ₂ (0 <X <1, 0 <Y <1 and X + Y = 1)
Where
A is at least one element selected from the group consisting of P, B, C, Al, Sc, Sr, Ti, V, Zr, Mn, Fe, Co, Cu, Zn, Cr, Mg, Nb, Mo and Cd,
At least one element of the metal having an oxidation number of M = + 4;
M '= at least one element selected from transition metals;
[Equation 1]
First charge and discharge efficiency of cathode active material <First charge and discharge efficiency of anode active material
[Equation 2]
Irreversible capacity at initial charge and discharge of the positive electrode active material> irreversible capacity at initial charge and discharge of the negative electrode active material, where irreversible capacity = 1-discharge capacity / charge capacity.

In addition, the present invention provides a method of improving the life characteristics of the secondary battery through the above-described configuration.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention is characterized by providing a novel secondary battery system in which excess reversible lithium is present in the negative electrode even after the initial discharge and each charge / discharge cycle.

1) A conventional battery system mainly consists of a positive electrode and a negative electrode having a larger irreversible or lower initial efficiency than the positive electrode. In the current secondary battery system having a lithium source at the positive electrode, if the negative irreversible capacity of the negative electrode is large, the negative electrode is irreversible. Through this, an increase in dead volume of the anode side occurs. Therefore, the capacity of the battery is less than that available in the actual positive electrode, resulting in a reduction in the capacity of the battery. In addition, the use of a negative electrode material having low cycle efficiency characteristics also caused a decrease in the life of the battery.

In contrast, the present invention configures a new secondary battery system including a negative electrode having a higher initial charge / discharge efficiency or a lower irreversible capacity than a positive electrode, thereby minimizing dead volume of the positive electrode generated by initial irreversible. Dose increase can be aimed at.

1A and 1B illustrate the secondary battery system and the conventional secondary battery system of the present invention, respectively. First, in the conventional secondary battery system including a positive electrode having an initial efficiency of 97% and a negative electrode having an initial efficiency of 80%, an irreversible capacity of about 20% occurs when an SEI film is formed on the surface of the negative electrode during initial charging. The irreversible capacity causes the dead volume on the anode side to show a capacity smaller than that available in the actual anode (see FIG. 1B).

In contrast, the novel secondary battery system composed of a positive electrode having an initial efficiency of 70% and a negative electrode having an initial efficiency of 80% has an irreversible amount of about 20%, which is the same irreversible capacity as a conventional secondary battery system when an SEI film is formed on the surface of the negative electrode by initial charging. Capacity is generated. However, when lithium ions are reversibly intercalated in the anode by the first discharge, the amount of reversible lithium exceeds 10% more than the capacity that is actually acceptable in the anode, so that the dead volume of the anode caused by the initial irreversibility ( The dead volume can be minimized so that the capacity reduction of the battery can also be minimized (see FIG. 1A). In addition, the extra reversible lithium (excess Li) of about 10% is present in the active site of the negative electrode active material even after the first discharge, it is possible to improve the cycle performance and life characteristics through the electrochemical performance of the negative electrode material. That is, when the efficiency is not 100% through electrochemical charging and discharging, the consumption of Li always occurs. As in the present invention, when excess Li is present, it is possible to prevent the consumption of Li, thereby improving electrochemical performance. .

2) Also, in the conventional battery system, when the overdischarge is performed while the amount of Li participating in the charge / discharge is reduced as described above, the activated Li sites of the positive electrode are not filled, so that the voltage of the positive electrode does not drop below a certain voltage. It is a phenomenon. Thus, the discharge is terminated by the potential rise of the cathode.

However, in the present invention, the discharge end voltage is regulated by the anode because the potential of the anode is fully filled and thus the potential of the anode falls faster than the potential of the cathode during discharge, thereby increasing the voltage of the cathode at the end voltage of each cycle. In addition to lowering, the SEI film generated at a low voltage can prevent the re-disintegration of the SEI film generated as the voltage of the cathode increases. Therefore, the effect of improving cycle characteristics and lifespan characteristics of the battery can be exhibited.

3) In addition, the conventional (quasi) metal-based negative electrode active material (eg, Si, Sn, Pb, etc.) has a problem in that the long life cycle characteristics are deteriorated due to the volume change generated during the charge and discharge of the battery and the deterioration of the electrode. However, in the present invention, since excess lithium is present in the active site of the negative electrode active material even in a discharged state, a change in volume expansion of the negative electrode active material caused by lithium is occluded or released in the active material, thereby providing a structurally stable battery. can do.

The novel secondary battery system of the present invention provides extra reversible lithium within the active site of the negative electrode active material where lithium ions can be reversibly occluded and released when lithium is filled in all active sites of the positive electrode active material after each charge and discharge cycle as well as the initial discharge. Except for the presence of (excess Li), can be configured in the same manner as conventional batteries known in the art.

The excess lithium is greater than the amount compensating for the irreversible lithium consumption reaction of the anode due to the formation of a solid electrolyte interface (SEI) film on the surface of the cathode during charging, and within each active site of the cathode active material after each charge and discharge cycle. It is preferable that the amount of lithium is greater than or equal to, but not limited thereto. For example, when excess lithium is filled in all active sites of the positive electrode active material after each charge / discharge cycle, the excess lithium present in the active site of the negative electrode active material may allow lithium ions to be reversibly occluded and released. Amount) may range from 0 to 20% relative to 100% of the amount of reversible lithium filled in all active sites of the positive electrode active material at each charge and discharge cycle. If the amount exceeds 20%, the amount of the negative electrode to accommodate the extra Li in the negative electrode must also increase, which may cause a decrease in the overall battery capacity.

In the secondary battery of the present invention, (a) the initial charge and discharge efficiency of the negative electrode active material is controlled to be greater than the initial charge and discharge efficiency of the positive electrode active material; Or (b) adjusting the initial charge / discharge irreversible capacity of the negative electrode active material smaller than the irreversible capacity (1-discharge capacity / charge capacity) at the time of initial charge / discharge of the positive electrode active material, wherein the composition of the battery, components of the component, There is no particular limitation on the content and composition ratio, the manufacturing method of the battery and the like.

The positive electrode, which is one of the elements constituting the secondary battery of the present invention, is lower than the initial charge / discharge efficiency of the negative electrode active material to be used or larger than the irreversible capacity of the negative electrode active material, regardless of its constituents, component ratios, etc. Phosphorus positive electrode active material can be used without limitation. For example, in order to retain excess reversible lithium in the negative electrode after the initial discharge and each charge / discharge cycle, a positive electrode active material having a lower initial charge / discharge efficiency than the negative electrode active material or a larger irreversible capacity at the first charge / discharge than the negative electrode active material is used. As a specific example, the following four embodiments are possible.

That is, the anode comprises (1) at least one selected from the group consisting of lithium nickel oxide of the formula (1) and a compound of the formula (2); (2) at least one selected from the group consisting of lithium nickel oxide of the following formula (1) and a compound of the formula (2) surface-treated with an oxide other than the compound of the following formula (1) and (2); (3) (i) at least one first cathode active material selected from lithium metal composite oxides and chalcogenide compounds capable of occluding and releasing lithium; And (ii) at least one second cathode active material selected from the group consisting of lithium nickel oxide of formula 1 and a compound of formula 2; Or (4) at least one first cathode active material selected from lithium metal composite oxides and chalcogenide compounds capable of occluding and releasing lithium (i) surface treated with oxides other than compounds of Formulas 1 and 2; And (ii) at least one second cathode active material selected from the group consisting of lithium nickel oxide of Formula 1 and a compound of Formula 2.

Li _{2 + x} Ni _{1 - y} A _y O _{2 + α}

Where

A is at least one element selected from the group consisting of P, B, C, Al, Sc, Sr, Ti, V, Zr, Mn, Fe, Co, Cu, Zn, Cr, Mg, Nb, Mo and Cd, -0.5 <x <0.5, 0 <y <1, and 0 <alpha <0.3.

XLi solid solution (solid solution) of _{(Li 1/3 M 2/} 3) O 2 + YLiM'O 2

At least one element of the metal having an oxidation number of M = + 4;

M '= at least one element selected from transition metals;

0 <X <1, 0 <Y <1 and X + Y = 1.

In Chemical Formula 2, M = Mn, Sn, Ti; M '= Ni, Mn, Co, Cr is preferred, but is not limited thereto.

Oxide components other than the compounds of Formulas 1 and 2 are not particularly limited, but Al, Mg, Si, P, Sc, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Mo, Zr, Nb Or one or more of these elements may be oxides or complex oxides. Non-limiting examples thereof include Al ₂ O ₃ , ZrO ₂ , AlPO ₄ , SiO ₂ , TiO ₂ , MgO or mixtures thereof.

In the compound of Formula 1, a space group belongs to Immm, and among them, Ni, M composite oxides form planar quadrangles (Ni, M) O ₄ , It is more preferable that the sides formed of OO share one another and form one-dimensional chains. In the compound of Formula 1, the crystal lattice constant is preferably a = 3.7 ± 0.5 Hz, b = 2.8 ± 0.5 Hz, c = 9.2 ± 0.5 Hz, α = 90 °, β = 90 °, γ = 90 °.

In the structure of the compound of Formula 1, during the initial charging and discharging, there is deintercalation of Li ions, the oxidation number of Ni or M becomes +2 to +4, and Li _{2 + x} Ni _{1 - y} M _y O _{2 +} The structure of _α becomes phase transition to Li _{2 + x- z} Ni _{1 -y} M _y O ₂ (0 ≦ _z <2). For example, LiNiO ₂ has a lattice structure in which the space group is R3-m (trigonal hexagonal), and a = b, a and b are the same, c values are different, and alpha = beta = 90 ^o and gamma = 120 ^o .

The compound of Formula 1 may release more than one mole of lithium ions during the first cycle charging of the battery, and occlude and release less than one mole of lithium ions from the first cycle discharge to subsequent cycles. For example, in the case of Li ₂ NiO _2, unlike the LiNiO _2, basing 1mol or more Li ions during charging into the cathode, at the time of discharge, so that accepts the Li-ion of less than 1mol the anode, Li ₂ NiO ₂ will discharge efficiency of the first cycle ( First discharge capacity / first charge capacity × 100) is approximately 40% or less. In the case of Li _{2 + x} Ni _{1 - y} M _y O _{2 + α} of the compound of Formula 1, there is a slight difference in the discharge efficiency of the first cycle according to the content of another metal M substituted in place of Ni.

Therefore, when lithium nickel oxide of the formula (1) is used for the positive electrode, the positive electrode active material composition of the present invention shows a large difference between the initial charge capacity and the discharge capacity, and thus the irreversible capacity is due to the formation of the SEI film on the negative electrode surface upon initial charge. By providing more than enough lithium ions to compensate for the irreversible lithium consumption of the negative electrode, not only can the large negative irreversible capacity of the negative electrode be compensated for in the first cycle, but also the extra lithium ions remaining in the negative electrode improve the performance of the negative electrode. It becomes possible to plan.

On the other hand, some of the materials used as the electrode active material has a flat level of a certain section above the oxidation / reduction potential exhibited by the oxidation number change of the components in the electrode active material during charge and discharge, the compound of formula 2 is present in the compound Apart from the redox potential section of the transition metal, it is characterized in that it has a flat level of a certain section at a potential higher than the above potential section, for example, 4.4 to 4.6V. That is, when charged at the redox level of M 'or higher, Li of the lithium site is released and deintercalation of oxygen occurs in order to balance the redox balance and has a flat potential section.

The compound of Formula 2 is charged to a flat level section (eg, 4.4 ~ 4.6V) or more of a certain period present in the redox potential section or more of the transition metal constituting the electrode active material during the first charge, and lower the voltage from the second charge In this case, a high capacity can be realized even at a low voltage that does not cause side reaction of the electrolyte, and there is an advantage in that the battery can be configured without causing problems to the battery.

The compounds of Formula 1 and / or Formula 2 may each be used as a positive electrode active material of a single component, or may be used in combination with a conventional positive electrode active material (eg, the first positive electrode active material). In this case, when used in combination with the first positive electrode active material, the content of the compound of Formula 1 and / or Formula 2 (eg, the second positive electrode active material) is not particularly limited, but if possible, 0.1 to 40 parts by weight per 100 parts by weight of the positive electrode active material desirable.

In this case, as the first cathode active material, a conventional cathode active material in the art may be used without limitation, and non-limiting examples thereof include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiCrO ₂ , LiFePO ₄ , LiFeO. ₂ LiCoVO ₄ , LiCr _x Mn _2-x O ₄ , LiNiVO ₄ , LiNi _x Mn _2-x O ₄ , Li _2-x CoMn ₃ O _8, or mixtures thereof.

One of the elements constituting the secondary battery of the present invention, as long as it is higher than the initial charge / discharge efficiency of the positive electrode active material to be used or smaller than the irreversible capacity of the positive electrode active material, the conventionally known in the art regardless of its components, component ratios, etc. Phosphorous negative electrode active material can be used without limitation.

Non-limiting examples of negative electrode active materials include lithium metal or lithium alloys, carbon, petroleum coke, activated carbon, graphite, metals, metal oxides, other carbons, and the aforementioned negative electrode active materials ( Quasi-) metal-based components such as Si, Sn, Pb, or a combination of elements thereof, or conventional surface-treated negative electrode active material in the art. Specific examples thereof include carbon such as hardly graphitized carbon and graphite carbon; Li _x Fe ₂ O ₃ (0 ≦ _x ≦ 1), Li _x WO ₂ (0 ≦ _x ≦ 1), Sn _x Me _{1 - x} Me ' _y O _z (Me: Mn, Fe, Pb, Ge; Me' Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen, 0 <x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , _{Bi 2 O 5, WO 3,} MoO 3, LiCr 3 O 8, LiV 3 O 8, TiS 2, such as Li _4/3 Ti _5/3 O ₅ having a spinel structure _{Li x Ti 5/3-y} L metal oxides such as oxides represented by _y O ₄ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used. In particular, a negative electrode active material to which a (quasi) metal-based component is added is preferable, and the metal component is not particularly limited as long as it can be substituted or doped with the active material.

The secondary battery of the present invention configured as described above is preferably a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, a lithium ion polymer secondary battery, and the like, but is not limited thereto. no.

The secondary battery of the present invention can be prepared by putting a porous separator between the positive electrode and the negative electrode in a conventional manner known in the art and the electrolyte.

The positive electrode and the negative electrode have (i) an initial charge / discharge efficiency of the negative electrode active material greater than the initial charge and discharge efficiency of the positive electrode active material, or (ii) an irreversible capacity (1-discharge capacity / charge capacity) at the time of initial charge and discharge of the positive electrode active material. Except that the initial charge and discharge irreversible capacity of the negative electrode active material is adjusted to be small, can be prepared according to a conventional method known in the art, for example, to prepare an electrode slurry containing a positive electrode active material and a negative electrode active material, respectively, After applying the prepared electrode slurry to each current collector, the solvent or dispersion medium may be removed by drying, and the active material may be bound to the current collector, and the active material may be bound to each other. In this case, a small amount of a conductive agent and / or a binder may be optionally added.

The battery electrolyte includes conventional electrolyte components known in the art, such as electrolyte salts and organic solvents.

Using the electrolyte salts is A ⁺ B ^- A salt of the structure, such as, A ⁺ is Li ^+, Na ^+, K ⁺ comprises an alkaline metal cation or an ion composed of a combination thereof, such as, and 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 ^- is a salt containing an anion ion or a combination thereof, such as. In particular, a lithium salt is preferable.

Organic solvents may be used conventional solvents known in the art, such as cyclic carbonates and / or linear carbonates, non-limiting examples of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl Carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (EMC) Gamma butyrolactone (GBL), fluoroethylene carbonate (FEC), methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, pentyl acetate, methyl propionate, ethyl propionate, ethyl propionate, butyl propionate or these And mixtures thereof. Moreover, the halogen derivative of the said organic solvent can be used, and it can also be used for the battery using water.

The separator is not particularly limited, but a porous separator may be used, for example, a polypropylene-based, polyethylene-based, or polyolefin-based porous separator.

The shape of the secondary battery, preferably the lithium secondary battery, produced by the method presented in the present invention is not particularly limited, but can be cylindrical, coin-shaped, square or pouch (pouch) type of can.

In addition, the present invention (a) to increase the initial charge and discharge efficiency of the negative electrode active material than the initial charge and discharge efficiency of the positive electrode active material; Or (b) controlling the initial charge / discharge irreversible capacity of the negative electrode active material to be smaller than the irreversible capacity (1-discharge / charge capacity) during the initial charge / discharge of the positive electrode active material to provide a method of improving the life characteristics of the secondary battery.

In fact, it was confirmed through the experimental example that the cycle characteristics and the lifespan of the secondary battery can be improved by controlling the factors of the above-described battery, for example, the initial charge / discharge efficiency and / or irreversible capacity of the positive electrode active material and the negative electrode active material.

Hereinafter, preferred examples are provided to help understanding of the present invention, but the following examples are merely to illustrate the present invention, and the scope of the present invention is not limited to the following examples.

[Reference Examples 1 to 6]

Reference Example 1

The electrode slurry obtained by using Li ₂ NiO ₂ as an active material was mixed so that the ratio of active material: conductive agent: binder was 95: 2.5: 2.5, and then dispersed and mixed in NMP solvent in an electrode slurry obtained by using aluminum foil (Al-foil). It coated on and dried to obtain an electrode. Lithium metal (Li-Metal) was used as a counter electrode and an electrolyte solution in which 1 M of LiPF ₆ was dissolved in a carbonate electrolyte as an electrolyte was used to fabricate a coin-type half cell.

Reference Example  2

Li ₂ NiO ₂ as active material instead _{Li (Li 0 .2 Mn 0 .6} Ni 0. 2) and is in the same manner as in Example 1, except that the O ₂ was produced in the cell (half cell).

Reference Example 3

Li ₂ NiO ₂ as active material instead A half cell was manufactured in the same manner as in Example 1, except that LiCoO ₂ (80 parts by weight) and Li ₂ NiO ₂ (20 parts by weight) were mixed and used.

Reference Example  4

Li ₂ NiO ₂ as active material instead LiCoO ₂ (70 weight parts), and _{Li (Li 0 .2 Mn 0 .6} Ni 0. 2) O 2 cell (a half and, the same procedure as in Example 1 except for using a mixture (30 parts by weight) cell).

Reference Example  5

A half cell was manufactured in the same manner as in Example 1, except that LiCoO ₂ was used instead of Li ₂ NiO ₂ .

Reference Example  6

Using graphite (50 parts by weight) and Si (50 parts by weight) instead of Li ₂ NiO ₂ , the active material: conductor: binder ratio was 88: 2: 10, except that copper foil was used instead of aluminum foil. Was prepared in the same manner as in Example 1 (half cell).

[Examples 1 and 2]

Example 1

Graphite (50 parts by weight) and Si (50 parts by weight) are mixed and used as the active material, and the negative electrode composition ratio of the active material: conductive agent: binder is 88: 2: 10 and then coated on copper foil to apply the electrode. Prepared.

Instead of Li-Metal, the prepared electrode was used as a cathode, and the electrode prepared in Reference Example 3 was used as a cathode (LiCoO ₂ (80 parts by weight) and Li ₂ NiO ₂ (20 parts by weight)) as a full cell. Was produced. Charge and discharge efficiency of the negative electrode is as shown in Figure 7, the initial charge and discharge efficiency was about 80%.

Example  2

The electrode ((LiCoO ₂ (80 weight parts prepared in Reference Example 3 as the positive electrode) and Li ₂ NiO ₂ (20 parts by weight)) instead of the electrode manufactured in Reference Example _{2 (Li (Li 0.2 Mn 0.6} Ni 0. 2) O Except for using ₂ ), a battery (full cell) was prepared in the same manner as in Example 1.

Comparative Example 1

The above-described embodiment was used except that the electrode (LiCoO ₂ ) prepared in Reference Example 5 was used as the anode instead of the electrode (LiCoO ₂ (80 parts by weight) and Li ₂ NiO ₂ (20 parts by weight)) prepared in Reference Example 3. A full cell was manufactured in the same manner as in Example 1.

Experimental Example  1. Performance Evaluation of Lithium Secondary Battery

In order to evaluate the performance of the lithium secondary battery according to the present invention, the following experiment was performed.

1-1. Charge and discharge evaluation of half cell

The coin-type batteries of Reference Examples 1 to 6 were used.

After charging 0.1C CC / CV (1 / 100C cut-off) to 4.4V to the battery except for Reference Example 6, the first charge and discharge was performed by discharging to 0.1C at CV up to 3.0V, Reference Example 6 The battery was charged and discharged at 0.1C up to 0.005V with CC / CV (1 / 100C cut off) and 1.5V with CC. The first charge / discharge graph of each cell is shown in FIGS. 1 to 6, respectively.

As a result of the experiment, it can be seen that the batteries of Reference Examples 1 to 4 not only have low discharge efficiency (first discharge capacity / first charge capacity × 100) in the first cycle, but also show a large difference between the initial charge capacity and the discharge capacity. (See FIGS. 2-5). This means that the initial charge and discharge efficiency is low. On the other hand, the battery of Reference Example 5 showed little difference between the initial charge capacity and the discharge capacity, and it was found that the initial charge and discharge efficiency was high (see FIG. 6). On the other hand, the charge and discharge efficiency according to the cycle of the reference example 6 battery is as shown in FIG.

1-2. Evaluation of Cycle Characteristics of Lithium Full Cell

The lithium full battery of Example 1 and Example 2 was used, and the battery of Comparative Example 1 was used as a control thereof.

Each battery was charged to 0.5C with CC / CV (1 / 100C cut-off) up to 4.35V and discharged at 0.5C up to 3V with CC.Fifty cycles were performed. Cycle life was measured. In addition, charge and discharge efficiency for each cycle was obtained.

As a result of the experiment, the battery of Comparative Example 1, which is configured in the same manner as a conventional battery system and does not have excess Li in the negative electrode, showed that the cycle characteristics of the battery were significantly lowered even before 50 cycles were performed (see FIG. 8). In contrast, the batteries of Examples 1 and 2 to which the new secondary battery system was applied showed excellent life characteristics (see FIGS. 10 and 11). In addition, the secondary batteries of Example 1 and Example 2 showed an excellent charge and discharge efficiency improvement effect compared to the battery of Comparative Example 1 (see Fig. 9) the same as the conventional battery system (see Fig. 11 and 13).

In the present invention, by constructing a new secondary battery system in which excess lithium is present in the negative electrode even after the initial discharge, it is possible to provide an increase in capacity and life characteristics of the secondary battery.

Claims (14)

In a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, The cathode includes a cathode active material containing or coated with one or more compounds selected from the group consisting of lithium nickel oxide of Formula 1 and a compound of Formula 2, The negative electrode includes a negative electrode active material containing or coated with one or more metalloids selected from the group consisting of Si, Sn and Pb, Secondary batteries characterized in that they are adjusted to satisfy the conditions of the following equations (1) and (2):  [Formula 1] Li _{2 + x} Ni _1-y A _y O _{2 + α} (where −0.5 ≦ x ≦ 0.5, 0 ≦ y <1, 0 ≦ _α <0.3) [Formula 2] Solid solution of XLi (Li _1/3 M _2/3 ) O ₂ + YLiM'O ₂ (0 <X <1, 0 <Y <1 and X + Y = 1) Where A is at least one element selected from the group consisting of P, B, C, Al, Sc, Sr, Ti, V, Zr, Mn, Fe, Co, Cu, Zn, Cr, Mg, Nb, Mo and Cd, At least one element of the metal having an oxidation number of M = + 4; M '= at least one element selected from transition metals;  [Equation 1] First charge and discharge efficiency of cathode active material <First charge and discharge efficiency of anode active material [Equation 2] Irreversible capacity at initial charge and discharge of the positive electrode active material> irreversible capacity at initial charge and discharge of the negative electrode active material, where irreversible capacity = 1-discharge capacity / charge capacity. delete The secondary battery of claim 1, wherein the charge and discharge efficiency of the anode active material is greater than 0 and less than 20% compared to the charge and discharge efficiency of the cathode active material. The method of claim 1, wherein the anode (a) at least one selected from the group consisting of lithium nickel oxide of formula (1) and a compound of formula (2); (b) at least one selected from the group consisting of lithium nickel oxide of formula (1) and a compound of formula (2) surface treated with an oxide other than the compound of formula (1) and formula (2); (c) (i) at least one first cathode active material selected from lithium metal composite oxides and chalcogenide compounds capable of occluding and releasing lithium; And (ii) at least one second cathode active material selected from the group consisting of lithium nickel oxide of formula 1 and a compound of formula 2; or (d) at least one first cathode active material selected from lithium metal composite oxides and chalcogenide compounds capable of occluding and releasing lithium (i) surface-treated with oxides other than compounds of formulas (1) and (2); And (ii) at least one second cathode active material selected from the group consisting of lithium nickel oxide of formula (1) and a compound of formula (2) Secondary battery characterized in that it comprises: [Formula 1] Li _{2 + x} Ni _{1 - y} A _y O _{2 + α} (where -0.5 ≤ x ≤ 0.5, 0 ≤ y <1, 0 ≤ α <0.3) [Formula 2] _{XLi (Li 1/3 M 2} /3) O 2 + YLiM'O solid solution of _{2 (solid solution) (0 <} X <1, 0 <Y <1 and Im X + Y = 1) Where A is at least one element selected from the group consisting of P, B, C, Al, Sc, Sr, Ti, V, Zr, Mn, Fe, Co, Cu, Zn, Cr, Mg, Nb, Mo and Cd, At least one element of the metal having an oxidation number of M = + 4; M '= at least one element selected from transition metals. The secondary battery of claim 4, wherein M in Formula 2 is at least one element selected from Mn, Sn, and Ti metals, and M ′ is at least one element selected from Ni, Mn, Co, and Cr metals. The method of claim 4, wherein the oxides other than the oxides of Formulas 1 and 2 are Al, Mg, Si, P, Sc, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Mo, Zr, Nb. A secondary battery characterized by being an oxide or a composite oxide containing at least one element selected from the group consisting of. The secondary battery of claim 4, wherein the compound of Formula 1 belongs to Immm. According to claim 7, wherein the compound of formula (1) forms a planar tetragonal (Ni, M) O ₄ and characterized in that the planar quadrupole structure has a structure that shares the sides formed of OO and forms a one-dimensional chain with each other Secondary battery. According to claim 7, wherein the compound of Formula 1 has a crystal lattice constant of a = 3.7 ± 0.5 Å, b = 2.8 ± 0.5 Å, c = 9.2 ± 0.5 Å, α = 90 °, β = 90 °, γ = 90 A secondary battery characterized by having a structure of °. The secondary battery of claim 4, wherein the second positive electrode active material is 0.1 to 40 parts by weight per 100 parts by weight of the positive electrode active material. The method of claim 1, wherein the negative electrode active material component coated with or used with the metalloid component is composed of a carbon material, a metal composite oxide, a lithium metal, a lithium alloy, a metal oxide, a conductive polymer, and a Li-Co-Ni-based material. At least one secondary battery selected from the group. The secondary battery of claim 1, wherein the secondary battery is a lithium secondary battery. (A) a positive electrode comprising a positive electrode active material containing or coated with one or more compounds selected from the group consisting of lithium nickel oxide of Formula 1 and a compound of Formula 2; And (b) a negative electrode comprising a negative electrode active material containing or coated with one or more metalloids selected from the group consisting of Sn and Pb And improving the lifespan characteristics of the secondary battery by adjusting them so as to satisfy the conditions of Equations 1 and 2 below: [Formula 1] Li _{2 + x} Ni _1-y A _y O _{2 + α} (where −0.5 ≦ x ≦ 0.5, 0 ≦ y <1, 0 ≦ α <0.3) [Formula 2] Solid solution of XLi (Li _1/3 M _2/3 ) O ₂ + YLiM'O ₂ (0 <X <1, 0 <Y <1 and X + Y = 1) Where A is at least one element selected from the group consisting of P, B, C, Al, Sc, Sr, Ti, V, Zr, Mn, Fe, Co, Cu, Zn, Cr, Mg, Nb, Mo and Cd, At least one element of the metal having an oxidation number of M = + 4; M '= at least one element selected from transition metals;  [Equation 1] First charge and discharge efficiency of cathode active material <First charge and discharge efficiency of anode active material [Equation 2] Irreversible capacity at initial charge and discharge of the positive electrode active material> irreversible capacity at initial charge and discharge of the negative electrode active material, where irreversible capacity = 1-discharge capacity / charge capacity. delete

Images