KR101573421B1 - Positive active material for rechargeable lithium battery, method prepareing the same, and rechargeable lithium battery including the same - Google Patents

Abstract

A lithium manganese composite metal oxide particle, and a phosphorus (P) coating layer formed on the surface of the lithium manganese composite metal oxide particle, wherein the lithium manganese composite metal oxide particle has a P element A concentration gradient in which the atomic% concentration of the lithium secondary battery is reduced, a method for producing the same, and a lithium secondary battery comprising the same.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a positive active material for a lithium secondary battery, a method for producing the positive active material, and a lithium secondary battery including the lithium secondary battery.

The present invention relates to a cathode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery comprising the same.

Currently, lithium secondary batteries are mainly used as power sources for mobile IT devices such as mobile phones, but their use is expanded to electric vehicles (plug-in vehicles (also called xEVs) and energy storage systems (ESS) Therefore, there is an increasing need for high performance and high capacity of active materials, which are one of the key raw materials for power supply and storage devices of these devices.

In a lithium secondary battery, a lithium ion (Li ⁺ ) existing in an ion state moves from a cathode to an anode at the time of discharging and from the cathode to an anode at the time of charging, Like electrons, electrons move to generate electrons.

Currently, the capacity of the cathode active material used in lithium secondary batteries is 145 mAh / g based on LiCoO ₂ , mainly using LiCoO ₂ as the anode and carbon as the cathode. However, cobalt is required to develop alternative cathode materials because of its low storage capacity, high cost, toxicity to human body and environmental pollution problem. For example, various metal oxides such as LiMn ₂ O ₄ , LiNiO ₂ , LiNi _{1 -xy} Co _x Mn _y O ₂ (0 <x <1, 0 <y <1) and LiFePO ₄ are used. 4V Spinel LiMn ₂ O ₄ , a cathode active material, is environmentally friendly, has a higher potential difference (4V) than lithium, has excellent thermal stability, is rich in deposits, and is inexpensive. And is attracting attention as a cathode active material. However, rapid capacity deterioration due to the elution of manganese ions during high temperature (60 ° C) charge and discharge and rapid capacity reduction during high charge / discharge cycles due to low electron conductivity and low ionic conductivity have been overcome have.

In recent years, researches on active material composition change, particle size control, surface treatment, and the like have been variously carried out in order to improve the electrochemical characteristics of a cathode active material for a lithium secondary battery.

An embodiment of the present invention is to provide a cathode active material for a lithium secondary battery which has a capacity gradient and a high-rate characteristic change due to a surface concentration gradient of phosphorus.

Another embodiment of the present invention is to provide a method for producing the cathode active material.

Another embodiment of the present invention provides a lithium secondary battery comprising the cathode active material.

In one embodiment of the present invention, lithium manganese composite metal oxide particles; And a phosphorus (P) coating layer formed on the surface of the lithium manganese composite metal oxide particle, wherein the lithium manganese composite metal oxide particle has an atomic% concentration of the phosphorus (P) element depending on the depth toward the center of the particle at the surface of the particle Of the positive electrode active material for a lithium secondary battery.

The phosphorous (P) coating layer may further comprise a coating element selected from the group consisting of Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, .

Wherein the lithium manganese composite metal oxide particle comprises a coating element selected from the group consisting of Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, , And the coating element may have a concentration gradient such that the atomic% concentration of the coating element decreases according to the depth toward the center of the particle at the surface of the particle.

The lithium manganese composite metal oxide may further include a metal element selected from the group consisting of a transition metal, a rare earth metal, and combinations thereof.

The lithium-manganese composite metal oxide may be LiMn ₂ O ₄ , Li _a Mn _{1 - b} X _b O ₂ wherein X is Li, Al, Ni, Co, Cr, Fe, Mg, Sr, V, And 0.5? A? 1 and 0? B? 0.25), and mixtures thereof.

In another embodiment of the present invention, there is included a step of mixing a lithium manganese complex metal oxide with a phosphorus source and then drying to produce a dried powder, and calcining the dried powder at a temperature of about 400 ° C to about 850 ° C The present invention also provides a method for producing a positive electrode active material for a lithium secondary battery.

The lithium manganese composite metal oxide and the phosphorus source may be mixed at a molar ratio of about 1: 0.003 to about 1: 0.03.

The lithium manganese composite metal oxide may be prepared by mixing lithium source and manganese source and reacting at a temperature of about 400 ° C to about 900 ° C.

The lithium source and the manganese source may be mixed in a molar ratio of 1: 2 to 2: 1.

The phosphorus source may be an oxide, hydroxide, oxyhydroxide, alkoxide, nitrate, halide, A carbonate salt, an acetate salt, a oxalate salt, a citric acid salt, and a mixture thereof, and specifically may be selected from the group consisting of diammonium phosphate, Li ₂ PO ₄ , AlPO ₄ , MgPO ₄ , .

The firing process may be conducted at a temperature of about 400 [deg.] C to about 800 [deg.] C for about 1 hour to about 5 hours.

In still another embodiment of the present invention, there is provided a lithium secondary battery comprising a positive electrode containing the positive electrode active material, a negative electrode including the negative electrode active material, and a nonaqueous electrolyte.

Other details of the embodiments of the present invention are included in the following detailed description.

The cathode active material for a lithium secondary battery has a surface concentration gradient of phosphorus (P) relative to a lithium manganese composite metal oxide, thereby protecting the surface of the lithium manganese oxide during a high-temperature cycle, thereby preventing capacity deterioration due to elution of manganese ions, It is possible to suppress a decrease in the capacity of the battery and a change in the high-rate characteristics.

1 is a schematic view schematically showing a structure of a lithium secondary battery according to an embodiment of the present invention.
FIG. 2A is a photograph of a lithium manganese composite metal oxide before forming a phosphorous coating layer in Example 1 by a scanning electron microscope (SEM). FIG. 2B is a SEM photograph showing the cathode active material prepared in Example 1 to be.
FIG. 3 is a graph showing the results of observing the lithium manganese composite metal oxide before the formation of the phosphorous coating layer and the finally prepared cathode active material in Example 1 using an X-ray diffractometer (XRD).
4 is a mapping photograph using the energy-dispersive X-ray spectroscopy (EDX) of the cathode active material prepared in Example 1. FIG.
FIG. 5 is a photograph of a cathode active material prepared in Example 1, which is cut by a focused ion beam (FIB) for elemental analysis and mapped with an energy dispersive X-ray spectroscope (EDX).
6 shows the results of evaluating the performance of a 1 ^st cell at 25 ° C for the cathode active material of Example 1 and Comparative Example 1. FIG.
7 is a graph showing the results of observing the cycle characteristics of the cathode active material of Example 1 and Comparative Example 1 at 60 ° C.

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

The cathode active material for a lithium secondary battery according to an embodiment of the present invention includes lithium manganese composite metal oxide particles; And a phosphorus (P) coating layer formed on the surface of the lithium manganese composite metal oxide particle, wherein the lithium manganese composite metal oxide particle has a composition in which the atomic% concentration of the P element decreases with the depth toward the center of the particle at the surface of the particle Concentration gradient.

The cathode active material may be prepared by mixing lithium manganese composite metal oxide particles with a phosphorus source such as diammonium phosphate, followed by drying and firing at a high temperature of about 400 ° C or higher. As a result of the calcination, a phosphorous coating layer is formed on the surface of the lithium manganese composite metal oxide particle, and phosphorus contained in the phosphorus coating layer penetrates into the lithium manganese composite metal oxide particle. As a result, the lithium manganese composite metal oxide particles (hereinafter, simply referred to as "final lithium manganese composite metal oxide") in the finally produced cathode active material had a high concentration of P element on the particle surface due to the phosphor coating layer formed on the surface, And the concentration gradient is gradually decreased.

The P coating layer may contain Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr and mixtures thereof And a coating element selected from the group consisting of: Specifically, the P coating layer may contain the coating element at about 100 atom% to about 10000 atom% with respect to the P element content.

In addition, the coating element may penetrate into the lithium manganese composite metal oxide particle like phosphorus and form a concentration gradient in which the atomic% concentration of the coating element decreases from the surface to the center. As a result, the final lithium manganese composite metal oxide particles are coated with a coating selected from the group consisting of Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, And the coating element may have a concentration gradient in which the atomic% concentration of the coating element is reduced depending on the depth from the surface of the particle toward the center of the particle.

The lithium-manganese composite metal oxide can be reversibly intercalated and deintercalated by lithium, and can be used without limitation as long as it is a composite metal oxide (lithium intercalation compound) including lithium and manganese. The lithium manganese composite metal oxide may further include a metal element selected from the group consisting of transition metals such as aluminum, nickel, and cobalt, rare earth metals, and combinations thereof.

Specifically, the lithium-manganese composite metal oxide may be LiMn ₂ O ₄ , Li _a Mn _{1 -b} X _b O ₂ (where X is Li, Al, Ni, Co, Cr, Fe, Mg, Sr, V, And 0.5? A? 1 and 0? B? 0.25), and a mixture thereof.

The lithium manganese composite metal oxide particle may have a specific surface area of about 0.1 m 2 / g to about 10 m 2 / g.

The lithium manganese composite metal oxide particles may have an average particle diameter of about 0.1 占 퐉 to about 100 占 퐉. In other embodiments, the lithium manganese composite metal oxide particles may have an average particle diameter of from about 0.5 占 퐉 to about 100 占 퐉.

The positive electrode active material protects the surface of the lithium manganese composite metal oxide particle and the surface of the lithium manganese composite metal oxide contained in the particles to thereby prevent deterioration in capacity due to elution of manganese ions during the high temperature cycle, It is possible to suppress the capacity decrease and the change in the high-rate characteristics of the battery. In addition, lithium manganese composite metal oxide particles have a high potential difference relative to lithium and can exhibit excellent thermal stability.

Specifically, the cathode active material includes P in a total amount of about 0.05 wt% to about 0.5 wt%, including P contained in the coating layer and the lithium manganese composite metal oxide.

In another embodiment of the present invention, there is included a step of mixing a lithium manganese complex metal oxide with a phosphorus source and then drying to produce a dried powder, and calcining the dried powder at a temperature of about 400 ° C to about 850 ° C The present invention also provides a method for producing a positive electrode active material for a lithium secondary battery.

Each step will be described in detail below.

First, in step 1, a lithium manganese complex metal oxide is mixed with a phosphorus source and then dried to prepare a dry powder.

As the lithium manganese composite metal oxide, the same materials as described above can be used. The lithium manganese complex metal oxide may be prepared directly or commercially available by a conventional method. In the case of direct preparation, lithium manganese complex metal oxides can be prepared, for example, by mixing a lithium source and a manganese source and then reacting at a temperature of about 400 ° C to about 900 ° C.

The lithium source is used as a lithium source of the lithium manganese composite metal oxide to be produced. The lithium source includes lithium hydroxide, oxyhydroxide, nitrate, halide, carbonate, acetate, oxalate, citrate and mixtures thereof Can be used. Specifically, lithium hydroxide, lithium nitrate, lithium acetate, lithium carbonate, and mixtures thereof may be used.

The manganese source is a material used as a manganese source for the lithium manganese composite metal oxide to be produced. The manganese source is an oxide, a hydroxide, an oxyhydroxide, a nitrate, a halide, A carbonate, an acetate, a oxalate, a citrate, and a mixture thereof. Specific examples thereof include manganese hydroxide, manganese nitrate, manganese carbonate, manganese acetate, Mn ₂ O ₃ , Mn ₃ O _4, and mixtures thereof. May be used.

The lithium source and the manganese source may be used in a suitable chemical equivalent ratio taking into consideration the content of lithium and manganese in the lithium manganese composite metal oxide to be produced. Specifically, the lithium source and the manganese source may be used at a molar ratio of about 1: 2 to about 2: .

The lithium manganese composite metal oxide can be obtained by reacting a mixture of the lithium source and the manganese source mixed at the above-mentioned molar ratio at a temperature of about 400 ° C to about 900 ° C.

When the lithium manganese composite metal oxide further contains a metal element such as a transition metal such as aluminum, nickel, cobalt or a rare earth metal in addition to the lithium metal element and the manganese metal element, the lithium manganese composite metal oxide is added to the mixture of the lithium source and the manganese source A source of the metallic element, for example aluminum hydroxide, may be used. Here, the source of the additional metal element may be used in an appropriate chemical equivalent ratio in consideration of the content of the added metal element in the finally produced lithium manganese composite metal oxide.

Further, a boronic acid may be further added to the mixture of the lithium source and the manganese source for reasons of reaction promotion, shape and size of the particles, and the like.

The boronic acid may be used in an amount of about 1% by weight or less based on the manganese source.

Then, the prepared lithium manganese composite metal oxide is mixed at a suitable chemical equivalent ratio in consideration of the phosphorus content of the cathode active material to be finally produced. Specifically, the lithium manganese complex metal oxide and the phosphorus source may be mixed at a molar ratio of about 1: 0.003 to about 1: 0.03.

The phosphorus source is used as a phosphorus-supplying source material for the cathode active material to be produced, and includes oxides, hydroxides, oxyhydroxides, alkoxides, nitrates, halides, A carbonate, an acetate, a oxalate, a citrate, and a mixture thereof. Specifically, diammonium phosphate or the like can be used.

The phosphorus coating layer formed on the surface of the lithium manganese composite metal oxide may contain Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, When the lithium manganese oxide and the phosphorus source are mixed, the source of these coating elements may be mixed together. At this time, the source of the coating element may also be used in a suitable chemical equivalent ratio, taking into account the content of the coating element in the final coating layer.

Examples of the source of the coating element include oxides, hydroxides, oxyhydroxides, alkoxides, nitrates, halides, Carbonates, acetic acid salts, oxalic acid salts, citric acid salts and mixtures thereof may be further added and mixed together. Specifically, aluminum isopropoxide may be used as a source of aluminum. Also, phosphorus compounds simultaneously containing the coating element and phosphorus such as Li ₂ PO ₄ , AlPO ₄ and MgPO ₄ may be used as the source of the coating element.

The phosphorus source and the coating element source may be mixed with the lithium manganese composite metal oxide particles in the form of a solution dissolved in a solvent such as water, alcohol or the like. As the solvent, water, ethanol, etc. may be used.

The concentration of the phosphorus source in the solution can be appropriately determined in consideration of the phosphorus content in the finally produced cathode active material. For example, the phosphorus source may be included at a concentration of from about 0.5 moles to about 2 moles.

As a reaction solvent, a conventional organic solvent such as alcohol may be used in the reaction of the lithium manganese complex metal oxide and the phosphorus source. When considering the shortening of the drying process time, boiling point of 100 ° C or less such as ethanol, acetone, isopropyl alcohol, Is more preferably used.

The solvent may be added in an amount of about 1/10 to about 200 parts by weight based on 100 parts by weight of the lithium manganese composite metal oxide.

After mixing the lithium manganese composite metal oxide with the phosphorus source, the resulting mixture is dried.

Preferably, the drying step is carried out at a temperature of about 90 DEG C to about 100 DEG C for about 20 minutes to about 2 hours to increase the firing efficiency together with the removal of the solvent component and to form a uniform coating layer.

Subsequently, in step 2, the dried powder obtained after drying is subjected to a sintering process.

The firing step is preferably performed at a temperature of about 400 ° C to about 800 ° C for about 1 hour to about 5 hours. The P coating layer is formed on the surface of the lithium manganese composite metal oxide particles by the firing process, and at the same time, P penetrates into the lithium manganese composite metal oxide particles to form a concentration gradient decreasing from the surface.

Wherein the firing step comprises a first firing step of firing at a temperature of from about 700 [deg.] C to about 800 [deg.] C for about 5 hours to about 18 hours; And a second firing step in which the first firing step is followed by the firing at about 400 ° C. to about 800 ° C. for about 1 hour to about 5 hours.

The cathode active material prepared according to the above-described preparation method protects the surface of lithium manganese oxide during the high-temperature cycle through the phosphorous concentration gradient inside the phosphor coating layer formed on the surface of the lithium manganese composite metal oxide particle, The capacity deterioration can be prevented, and as a result, it is possible to prevent a decrease in the capacity of the battery and a change in the high-rate characteristics.

In another embodiment of the present invention, the positive electrode comprising the positive electrode active material; A negative electrode comprising a negative electrode active material; And a non-aqueous electrolyte.

The lithium secondary battery can be classified into a lithium ion battery, a lithium ion polymer battery, and a lithium polymer battery depending on the type of the separator and electrolyte used. The lithium secondary battery can be classified into a cylindrical shape, a square shape, a coin shape, Depending on the size, it can be divided into bulk type and thin type. The structure and the manufacturing method of these cells are well known in the art, and detailed description thereof will be omitted.

1 is an exploded perspective view of a lithium secondary battery according to one embodiment. 1, the lithium secondary battery 100 includes a positive electrode 112, a negative electrode 114, a separator 113 disposed between the positive electrode 112 and the negative electrode 114, a positive electrode 112, (Not shown), a battery container 120 and a sealing member 140 for sealing the battery container 120 impregnated into the separator 114 and the separator 113 as main parts. The lithium secondary battery 100 is constructed by laminating an anode 112, a cathode 114 and a separator 113 in this order, and then winding the lithium secondary battery 100 in a spiral wound state.

The anode 112 includes a current collector and a cathode active material layer formed on the current collector.

The cathode active material layer includes the above-mentioned cathode active material.

The cathode active material layer may further include a compound capable of reversibly intercalating and deintercalating lithium (a lithium intercalation compound) together with the cathode active material. As the compound, at least one of complex oxides of metal and lithium of cobalt, manganese, nickel or a combination thereof may be used. As a specific example thereof, compounds represented by any one of the following formulas may be used: Li _a A _{1 - b} R _b D ₂ wherein, in the formula, 0.90? a? 1.8 and 0? b? 0.5; Li _a E _{1 -b} R _b O _{2 -c} D _c wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, and 0? C? 0.05; LiE (in the above formula, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05) 2-b R b O 4-c D c; Li _a Ni _{1 -b- c} Co _b R _c D _{α where} 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, and 0 <α ≦ 2; Li _a Ni _{1 - b - c} Co _b R _c O _{2 - ?} Z _{? Wherein} 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05 and 0 <? Li _a Ni _{1 -b- c} Co _b R _c O _{2 - ?} Z ₂ wherein 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, and 0 <? Li _a Ni _{1 -b- c} Mn _b R _c D _? Wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, and 0 <? Li _a Ni _{1 -bc} Mn _b R _c O _{2 -?} Z _{? Where} 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05 and 0 <? Li _a Ni _{1 -b- c} Mn _b R _c O _{2 - ?} Z ₂ wherein 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05 and 0 <? Li _a Ni _b E _c G _d O ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, and 0.001 ≤ d ≤ 0.1; Li _a Ni _b Co _c Mn _d GeO ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, and 0.001 ≤ e ≤ 0.1; Li _a NiG _b O ₂ (in the above formula, 0.90? A? 1.8 and 0.001? B? 0.1); Li _a CoG _b O ₂ (in the above formula, 0.90? A? 1.8 and 0.001? B? 0.1); Li _a MnG _b O ₂ (in the above formula, 0.90? A? 1.8 and 0.001? B? 0.1); Li _a Mn ₂ G _b O ₄ (in the above formula, 0.90? A? 1.8 and 0.001? B? 0.1); QO _2; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiTO ₂ ; LiNiVO _4; Li _(3-f) J ₂ (PO ₄ ) ₃ (0? F? 2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0? F? 2); And LiFePO _4.

In the above formula, A is Ni, Co, Mn or a combination thereof; R is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is O, F, S, P or a combination thereof; E is Co, Mn or a combination thereof; Z is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; T is Cr, V, Fe, Sc, Y or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu or a combination thereof.

Of course, a compound having a coating layer on the surface of the compound may be used, or a compound having a coating layer may be mixed with the compound. The coating layer may comprise, as a coating element compound, an oxide, a hydroxide of a coating element, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, or a hydroxycarbonate of a coating element. The compound constituting these coating layers may be amorphous or crystalline. The coating layer may contain Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr or a mixture thereof. The coating layer forming step may be carried out by any of coating methods such as spray coating, dipping, and the like without adversely affecting the physical properties of the cathode active material by using these elements in the above compound. It is a content that can be well understood by people engaged in the field, so detailed explanation will be omitted.

The cathode active material layer may also include a binder and a conductive material.

The binder functions to adhere the positive electrode active material particles to each other and to adhere the positive electrode active material to the current collector. Examples of the binder include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, poly Polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene, polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, vinyl chloride, carboxylated polyvinyl chloride, Butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like can be used, 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, Metal powders such as black, carbon fiber, copper, nickel, aluminum, and silver, metal fibers, and the like, and conductive materials such as polyphenylene derivatives may be used alone or in combination.

The current collector may be an aluminum foil, 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. An aluminum foil can be used.

The cathode 114 includes a current collector and an anode active material layer formed on the current collector and including a negative electrode active material.

The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, a lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

As a material capable of reversibly intercalating / deintercalating lithium ions, any carbonaceous anode active material commonly used in lithium ion secondary batteries can be used as the carbonaceous material. Typical examples thereof include crystalline carbon , Amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite in the form of amorphous, plate-like, flake, spherical or fibrous type. Examples of the amorphous carbon include soft carbon (soft carbon) Or hard carbon, mesophase pitch carbide, fired coke, and the like.

Examples of the lithium metal alloy include lithium and a metal such as Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Alloys may be used.

As the material capable of doping and dedoping lithium, Si, SiO _x (0 <x <2), Si-X ₁ alloy (X ₁ is an alkali metal, an alkali earth metal, a group 13 to 16 group element, , A rare earth element or a combination thereof and not Si), Sn, SnO ₂ and Sn-X ₂ alloy (X ₂ is an alkali metal, an alkali earth metal, a Group 13 to 16 Group element, a transition metal, And Sn is not used), and at least one of them may be mixed with SiO ₂ . The specific elements of X ₁ and X ₂ include Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, As, Sb, Bi, S, Se, Te, Po, or a combination thereof.

Examples of the transition metal oxide include vanadium oxide, lithium vanadium oxide, and the like.

The negative electrode active material layer also includes a binder, and may optionally further include a conductive material.

The binder serves to adhere the anode active material particles to each other and to adhere the anode active material to the current collector. Typical examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, Such as polyvinyl chloride, polyvinyl fluoride, polymers comprising ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, Styrene-butadiene rubber, epoxy resin, nylon, and the like may be used, but the present invention is not limited thereto.

The conductive material is used for imparting conductivity to the electrode. Any material can be used as long as it does not cause 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 carbon fibers; 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 current collector of the negative electrode 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. Copper foil can be used.

The positive electrode and the negative electrode are prepared by mixing each active material with a binder and optionally a conductive material and other additives in a solvent such as N-methylpyrrolidone or water to prepare a positive electrode or negative electrode slurry, And rolling.

A separator 113 is disposed between the anode 112 and the cathode 114.

The separator 113 includes a support and a fluorinated polymer layer positioned on both sides of the support.

The separator 113 separates the cathode 112 and the anode 114 and provides a passage for lithium ions. Any separator 113 may 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 fiber, polyester, Teflon, 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.

The anode 112, the cathode 114 and the separator 113 are impregnated with an electrolyte (not shown).

As the electrolyte, a liquid electrolyte including a lithium salt and a non-aqueous organic solvent may be used. By including the liquid electrolyte in this way, a high-density anode can be used.

The lithium salt is dissolved in the non-aqueous organic solvent to act as a source of lithium ions in the battery to enable operation of a basic lithium secondary battery, and a material capable of promoting the movement of lithium ions between the positive electrode and the negative electrode as its typical examples include _{LiPF 6, LiBF 4, LiSbF 6} , LiAsF 6, 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 bis oxalate reyito borate (lithium bis (oxalato) borate; LiBOB) , or a mixture thereof In the present invention, these are included as supporting electrolyte salts.

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

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move. Typical examples thereof include carbonate, ester, ether, ketone, alcohol or aprotic solvents. .

Examples of the carbonate-based solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate Ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) and the like can be used. As the ester solvent, γ-butyrolactone, decanolide, valerolactone, mevalono Mevalonolactone, caprolactone, and the like may be used. Examples of the ether solvent include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran. As the ketone solvent, cyclohexanone may be used have. As the alcoholic solvent, ethyl alcohol, isopropyl alcohol and the like can be used. As the aprotic solvent, R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, An amide such as nitriles such as dimethylformamide, and dioxolanes such as 1,3-dioxolane, sulfolanes, and the like can be used.

The non-aqueous organic solvent may be used alone or in admixture of one or more. If the non-aqueous organic solvent is used in combination, the mixing ratio may be appropriately adjusted according to the desired cell performance. .

The non-aqueous organic solvent preferably contains 20% by volume or more of the cyclic carbonate with respect to the total volume of the electrolyte. By including the cyclic carbonate in an amount of 20% by volume or more, the lifetime characteristics of the battery can be further improved.

The non-aqueous organic solvent may further include an aromatic hydrocarbon-based organic solvent together with a carbonate-based solvent. At this time, the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent may be mixed in a volume ratio of about 1: 1 to about 30: 1.

The aromatic hydrocarbon-based organic solvent may be an aromatic hydrocarbon-based compound represented by the following formula (1).

[Chemical Formula 1]

In Formula 1, R ₁ to R ₆ are each independently hydrogen, halogen, a C1 to C10 alkyl group, a C1 to C10 haloalkyl group, or a combination thereof.

The aromatic hydrocarbon-based organic solvent is selected from the group consisting of benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3- , 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4 - triiodobenzene, toluene, fluorotoluene, 1,2-difluorotoluene, 1,3-difluorotoluene, 1,4-difluorotoluene, 1,2,3-trifluorotoluene, 1,2,4-trifluorotoluene, chlorotoluene, 1,2-dichlorotoluene, 1,3-dichlorotoluene, 1,4-dichlorotoluene, 1,2,3-trichlorotoluene, 1,2,4 - trichlorotoluene, iodotoluene, 1,2-diiodotoluene, 1,3-diiodotoluene, 1,4-diiodotol Ene, 1,2,3-tree-iodo toluene, 1,2,4-iodo toluene, xylene, or may be a combination thereof.

The lithium secondary battery having the above-described configuration can be manufactured according to a conventional method for manufacturing a lithium secondary battery, and specifically, it comprises the steps of: preparing a positive electrode and a negative electrode; Forming a battery assembly by interposing a separator between the positive electrode and the negative electrode; And impregnating the battery assembly with an electrolytic solution.

Hereinafter, examples and comparative examples of the present invention will be described. The following embodiments are only examples of the present invention, and the present invention is not limited to the following embodiments.

(Example 1)

24.4 g of lithium carbonate, 95 g of manganese dioxide, 4.4 g of aluminum hydroxide, and 0.3 g of boronic acid were mixed and stirred for about 15 minutes. The resulting mixture was calcined at 800 ° C. for about 11 hours to obtain a lithium manganese composite oxide LiMn ₂ O ₄ ).

Separately, 0.5 g of aluminum isopropoxide (AIP) and 0.32 g of diammonium phosphate (DAP) were added to a mixed solvent of 35 ml of ethanol and 15 ml of pure water, followed by addition of 20 Min to prepare a mixed solution.

The lithium manganese composite metal oxide g prepared above was added to the mixed solution, followed by mixing for 30 minutes and drying at 90 ° C for 2 hours to obtain a powder. The obtained dry powder was fired at 700 ° C for 2 hours to prepare a cathode active material.

( Comparative Example  One)

The lithium manganese composite metal oxide (bare LiMn ₂ O ₄ ) prepared in Example 1 was used as a cathode active material.

The lithium manganese composite metal oxide before the formation of the phosphorus coating layer prepared in Example 1 and the finally prepared cathode active material were observed with a scanning electron microscope (SEM). The results are shown in Figs. 2A and 2B.

2A is a SEM photograph of a lithium manganese composite metal oxide before forming a phosphorus coating layer in Example 1, and FIG. 2B is a SEM photograph of the cathode active material prepared in Example 1. FIG.

It can be seen from FIGS. 2A and 2B that there is no change in morphology after the formation of the phosphor coating layer.

In Example 1, the lithium manganese composite metal oxide and the finally prepared cathode active material were observed using an X-ray diffractometer (XRD) before forming the phosphorous coating layer. The results are shown in Fig. In FIG. 3, the red line shows the result of the measurement of the finally prepared cathode active material, and the black line shows the result of measurement of the lithium manganese composite metal oxide before the formation of the phosphorus coating layer.

It can be seen from Fig. 3 that the spinel structure is well maintained without impurities even after the phosphorus coating layer is formed.

The cathode active material prepared in Example 1 was subjected to elemental analysis using Energy-dispersive X-ray spectroscopy (EDX). The results are shown in Fig.

As shown in FIG. 4, it can be seen that the P element is evenly distributed over the entire region.

For the elemental analysis of the cross-section of the cathode active material prepared in Example 1, elemental analysis was performed with an energy dispersive X-ray spectroscope (EDX) using a focused ion beam (FIB). The results are shown in Fig.

As shown in FIG. 5, phosphorus is concentrated on the surface of the lithium manganese composite metal oxide particle, and the phosphorus content decreases from the surface to the center. On the other hand, in the case of aluminum, it can be seen that the lithium metal manganese composite metal oxide is uniformly distributed throughout the entire lithium manganese composite metal oxide by being used both in the formation of the phosphorus coating layer and in the production of the lithium manganese composite metal oxide. , When a phosphorus compound containing a metal coating element different from the metallic element additionally contained in the lithium manganese composite metal oxide particle is used, the concentration of the gold coating element decreases from the surface to the center of the lithium manganese composite metal oxide particle similarly to phosphorus Is expected to do.

Test Example

In order to evaluate the battery performance improvement effect of the cathode active material according to the present invention, the lithium secondary battery including the cathode active material prepared in the above example was manufactured, and the battery performance was evaluated.

Specifically, a 2016 coin-type half cell was prepared using the cathode active materials prepared in Example 1 and Comparative Example 1, respectively. The electrode plate was made of carbon black as a conductive material and polyimide (PI) as a binder. The solvent was NMP (N-methyl-2-pyrrolidone) Money) was used to make an electrode plate. Lithium metal was used as a counter electrode, a separator was inserted in the middle, and an electrolyte was injected and sealed to complete a battery. EC (ethylene carbonate) / EMC (ethylmethyl carbonate) / DMC (dimethyl carbonate) = 3/3/4 (volume ratio) was used as the electrolytic solution.

The lithium secondary battery was charged / discharged at a current density of 0.1 C at a temperature ranging from 3.0 to 4.3 V at 25 캜, and the voltage profile according to one charge / discharge cycle was shown in FIG.

As shown in FIG. 6, the lithium secondary battery including the cathode active material prepared in Example 1 exhibited almost the same initial charging and discharging characteristics as the lithium secondary battery including the cathode active material of Comparative Example 1.

The lithium secondary battery including the cathode active material of Example 1 and Comparative Example 1 was charged and discharged at a current density of 1.0 C discharge at 0.5 C and 3.0 C to 4.3 V at 60 캜. As a result, the capacity change according to the number of cycles obtained by carrying out charge and discharge 300 times is shown in Fig.

8, the capacity retention rate of the lithium secondary battery including the cathode active material of Example 1 after 81 cycles was 81.7%, and the capacity retention rate of the lithium secondary battery including the cathode active material of Comparative Example 1 was 76.2% Compared with Comparative Example 1, the lithium secondary battery including the cathode active material of Example 1 had a small decrease in discharge capacity as the cycle number increased even at a high temperature.

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
112: cathode
113: Separator
114: anode
120: Battery container
140: sealing member

Claims (16)

Lithium manganese composite metal oxide particles; And
(P) coating layer formed on the surface of the lithium manganese composite metal oxide particle,
The lithium manganese composite metal oxide particle has a concentration gradient in which the concentration of the phosphorus (P) element decreases along the depth from the surface of the particle toward the center of the particle,
Wherein the lithium manganese composite metal oxide is LiMn ₂ O ₄ , Li _a Mn _1-b X _b O ₂ wherein X is selected from the group consisting of Li, Al, Mg, Sr, and combinations thereof, Lt; = 1 and 0 &lt; = b &lt; = 0.25), and mixtures thereof,
Wherein a part of the phosphorus coating layer formed on the surface of the lithium manganese composite metal oxide particle is substituted in a spinel structure of the lithium manganese composite metal oxide particle in a doped form. delete The method according to claim 1,
Wherein the phosphorus (P) coating layer comprises a coating element selected from the group consisting of Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, And a cathode active material for a lithium secondary battery. The method according to claim 1,
Wherein the lithium manganese composite metal oxide particle comprises a coating element selected from the group consisting of Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, Wherein the coating element has a concentration gradient in which the atomic% concentration of the coating element is decreased according to a depth from the surface of the particle toward the center of the particle. The method according to claim 1,
Wherein the lithium manganese composite metal oxide is LiMn ₂ O ₄ . Mixing the lithium manganese composite metal oxide with a phosphorus (P) source and then drying to produce a dried powder; and calcining the dried powder at a temperature of 400 to 850 ° C,
The positive electrode active material produced by the above-
The lithium manganese composite metal oxide particles; And
(P) coating layer formed on the surface of the lithium manganese composite metal oxide particle,
The lithium manganese composite metal oxide particle has a concentration gradient in which the concentration of the phosphorus (P) element decreases along the depth from the surface of the particle toward the center of the particle,
Wherein the lithium manganese composite metal oxide is LiMn ₂ O ₄ , Li _a Mn _1-b X _b O ₂ wherein X is selected from the group consisting of Li, Al, Mg, Sr, and combinations thereof, Lt; = 1 and 0 &lt; = b &lt; = 0.25), and mixtures thereof,
Wherein a part of the phosphorous coating layer formed on the surface is substituted in a spinel structure of the lithium manganese composite metal oxide particle in a doped form. The method according to claim 6,
Wherein the lithium manganese composite metal oxide and the phosphorus (P) source are mixed in a molar ratio of 1: 0.003 to 1: 0.03. The method according to claim 6,
Wherein the lithium manganese composite metal oxide is prepared by mixing a lithium source and a manganese source and then reacting at a temperature of 400 to 900 ° C. 9. The method of claim 8,
Wherein the lithium source and the manganese source are mixed in a molar ratio of 1: 2 to 2: 1. The method according to claim 6,
Wherein said phosphorus (P) source is selected from the group consisting of oxides, hydroxides, oxyhydroxides, alkoxides, nitrates, halides, Wherein the cathode active material is selected from the group consisting of carbonate, acetate, oxalate, citrate, and mixtures thereof. The method according to claim 6,
The phosphorus (P) source is diammonium _{phosphate, Li 2 PO 4, AlPO 4} , MgPO 4 and a method of producing a cathode active material for a lithium secondary battery is selected from the group consisting of a mixture thereof. The method according to claim 6,
Wherein the firing step is performed at a temperature of 400 ° C to 800 ° C for 1 to 5 hours. The method according to claim 6,
Wherein the lithium manganese composite metal oxide is LiMn ₂ O ₄ . A cathode comprising a cathode active material;
A negative electrode comprising a negative electrode active material; And
A non-aqueous electrolyte,
The cathode active material may include lithium manganese composite metal oxide particles; And a phosphorus (P) coating layer formed on a surface of the lithium manganese composite metal oxide particle,
The lithium manganese composite metal oxide particle has a concentration gradient in which the atomic% concentration of the phosphorus (P) element decreases along the depth toward the center of the particle at the surface of the particle,
Wherein the lithium manganese composite metal oxide is LiMn ₂ O ₄ , Li _a Mn _1-b X _b O ₂ wherein X is selected from the group consisting of Li, Al, Mg, Sr, and combinations thereof, Lt; = 1 and 0 &lt; = b &lt; = 0.25), and mixtures thereof,
Wherein a part of the phosphorus coating layer formed on the surface of the lithium manganese composite metal oxide particle is doped in a spinel structure of the lithium manganese composite metal oxide particle. delete 15. The method of claim 14,
Wherein the lithium manganese composite metal oxide is LiMn ₂ O ₄ .

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