阅读说明：本技术 可再充电锂电池 (Rechargeable lithium battery ) 是由 河在焕 金基俊 刘喜恩 尹延曦 李圭曙 于 2019-07-03 设计创作，主要内容包括：公开了一种可再充电锂电池,所述可再充电锂电池包括正电极和负电极,所述正电极包括正极活性物质层,所述负电极包括负极活性物质层和设置在负极活性物质层上的负极功能层,其中所述正极活性物质层包括第一正极活性物质和第二正极活性物质,所述第一正极活性物质包括选自钴、锰、镍及其组合中的金属与锂的一种或多种复合氧化物,所述第二正极活性物质包括由化学式1表示的化合物,并且负极功能层包括薄片状聚乙烯颗粒。[化学式1]Li<Sub>a</Sub>Fe<Sub>1-x</Sub>M<Sub>x</Sub>PO<Sub>4</Sub>在化学式1中,0.90≤a≤1.8,0≤x≤0.7,并且M为Mg、Co、Ni或其组合。(A rechargeable lithium battery is disclosedA battery including a positive electrode active material layer, and a negative electrode including a negative electrode active material layer and a negative electrode functional layer disposed on the negative electrode active material layer, wherein the positive electrode active material layer includes a first positive electrode active material including one or more complex oxides of a metal selected from cobalt, manganese, nickel, and a combination thereof and lithium, and a second positive electrode active material including a compound represented by chemical formula 1, and the negative electrode functional layer includes flake-shaped polyethylene particles. [ chemical formula 1]Li a Fe 1‑x M x PO 4 In chemical formula 1, a is 0.90-1.8, x is 0-0.7, and M is Mg, Co, Ni, or a combination thereof.)

1. A rechargeable lithium battery, comprising:

a negative electrode including a negative electrode current collector, a negative electrode active material layer disposed on the negative electrode current collector, and a negative electrode functional layer disposed on the negative electrode active material layer; and

a positive electrode including a positive electrode collector and a positive electrode active material layer disposed on the positive electrode collector,

wherein the negative electrode functional layer includes flaky polyethylene particles, and

the positive electrode active material layer includes a first positive electrode active material including one or more complex oxides of lithium and a metal selected from cobalt, manganese, nickel, and a combination thereof, and a second positive electrode active material including a compound represented by chemical formula 1:

[ chemical formula 1]

Li_aFe_1-xM_xPO₄

Wherein, in chemical formula 1, a is 0.90-1.8, x is 0-0.7, and M is Mg, Co, Ni or their combination.

2. A rechargeable lithium battery according to claim 1, wherein said flaky polyethylene particles have an average particle diameter D50 of 1 to 8 μm.

3. A rechargeable lithium battery according to claim 1, wherein said flaky polyethylene particles have a ratio of a major axis length to a minor axis length of 1 to 5.

4. A rechargeable lithium battery according to claim 1, wherein said flaky polyethylene particles have a thickness of 0.2 to 4 μm.

5. A rechargeable lithium battery according to claim 1, wherein the negative electrode functional layer further comprises inorganic particles and a binder.

6. A rechargeable lithium battery as claimed in claim 5, wherein the weight ratio of the sum of said flaked polyethylene particles and said inorganic particles to said binder is comprised between 80:20 and 99: 1.

7. A rechargeable lithium battery according to claim 5, wherein said flaky polyethylene particles and said inorganic particles are included in a weight ratio of 95:5 to 10: 90.

8. A rechargeable lithium battery according to claim 1, wherein the negative electrode functional layer has a thickness of 1 μ ι η to 10 μ ι η.

9. The rechargeable lithium battery according to claim 1, wherein a ratio of a thickness of the negative electrode active material layer to a thickness of the negative electrode functional layer is 50:1 to 10: 1.

10. The rechargeable lithium battery according to claim 1, wherein the first positive active material is contained in an amount of 70 wt% to 99 wt% based on the total weight of the positive active material layer.

11. The rechargeable lithium battery according to claim 1, wherein the content of the second positive active material is 1 wt% to 15 wt% based on the total weight of the positive active material layer.

12. A rechargeable lithium battery as claimed in claim 1, wherein said positive electrode further comprises a positive electrode functional layer disposed on said positive electrode active material layer.

13. A rechargeable lithium battery according to claim 12, wherein the second positive active material is included in the positive electrode functional layer.

14. A rechargeable lithium battery as claimed in claim 1, wherein said second positive active material comprises LiFePO₄。

Technical Field

The present disclosure relates to a rechargeable lithium battery.

Background

Portable information devices, such as mobile phones, notebook computers, smart phones, etc., or electric vehicles, have used rechargeable lithium batteries having high energy density and being conveniently carried as driving power sources. In addition, recently, active research into rechargeable lithium batteries as power sources for hybrid or electric vehicles or power storage has been conducted using high energy density characteristics.

One of the main research tasks of such rechargeable lithium batteries is to improve the safety of the rechargeable batteries. For example, if a rechargeable lithium battery generates heat due to internal short circuit, overcharge, overdischarge, etc., and an electrolyte decomposition reaction and a thermal runaway phenomenon occur, the internal pressure inside the battery may rapidly rise, resulting in explosion of the battery. Among them, when an internal short circuit occurs in a rechargeable lithium battery, there is a high risk of explosion because high electric energy stored in each electrode is electrically conducted in the short-circuited positive and negative electrodes.

In addition to damage to the rechargeable lithium battery, explosion may cause fatal damage to users. Therefore, it is urgently required to develop a technology capable of improving the stability of a rechargeable lithium battery.

Disclosure of Invention

A rechargeable lithium battery having improved stability is provided.

According to an embodiment, a rechargeable lithium battery includes a negative electrode including a negative electrode current collector, a negative electrode active material layer disposed on the negative electrode current collector, and a negative electrode functional layer disposed on the negative electrode active material layer; the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, wherein the negative electrode functional layer includes flake-shaped polyethylene particles, and the positive electrode active material layer includes a first positive electrode active material including one or more complex oxides of lithium and a metal selected from cobalt, manganese, nickel, and a combination thereof, and a second positive electrode active material including a compound represented by chemical formula 1.

[ chemical formula 1]

Li_aFe_1-xM_xPO₄

In chemical formula 1, a is more than or equal to 0.90 and less than or equal to 1.8, x is more than or equal to 0 and less than or equal to 0.7, and M is Mg, Co, Ni or the combination thereof.

The flaky polyethylene particles may have an average particle diameter (D50) of about 1 μm to about 8 μm.

The flaky polyethylene particles may have a ratio of major axis length to minor axis length of about 1 to about 5.

The flaky polyethylene particles may have a thickness of about 0.2 μm to about 4 μm.

The anode functional layer may further include inorganic particles and a binder.

The binder weight ratio of the sum of the flaky polyethylene particles and inorganic particles may be included in a range of about 80:20 to about 99: 1.

The flaked polyethylene particles and inorganic particles may be included in a weight ratio of about 95:5 to about 10: 90.

The negative electrode functional layer may have a thickness of about 1 μm to about 10 μm.

The ratio of the thickness of the anode active material layer to the thickness of the anode functional layer may be about 50:1 to about 10: 1.

The content of the first cathode active material may be about 70 wt% to about 99 wt% based on the total weight of the cathode active material layer.

The content of the second positive electrode active material may be about 1 wt% to about 15 wt% based on the total weight of the positive electrode active material layer.

The positive electrode may further include a positive electrode functional layer disposed on the positive electrode active material layer.

The first positive electrode active material may be included in the positive electrode active material layer, and the second positive electrode active material may be included in the positive electrode functional layer.

The first positive electrode active material may be one or more complex oxides of lithium and a metal selected from cobalt, manganese, nickel, and a combination thereof.

The second positive active material may include LiFePO₄。

With the increase of the reaction rate following the temperature, the function of self-closing (shutdown) in advance can be realized and the stability of the rechargeable lithium battery can be ensured.

Drawings

Fig. 1 schematically illustrates a structure of a rechargeable lithium battery according to an embodiment of the present disclosure.

Fig. 2 is an SEM image of spherical particles of polyethylene in the state of an aqueous dispersion.

Fig. 3 is an SEM image of polyethylene particles according to an embodiment.

Fig. 4 is an SEM image of the negative electrode functional layer composition according to an embodiment.

Fig. 5 is a graph showing particle distributions of the flaky polyethylene particles included in the negative electrode functional layers according to examples 1 to 3.

Fig. 6 is a graph showing the rate of increase in resistance of the electrode plate with temperature.

Fig. 7 is a graph showing capacity retention rates for 150 cycles of a rechargeable lithium battery cell (cell) according to an embodiment.

Fig. 8 is a schematic diagram of a coin symmetrical cell fabricated to evaluate the rate of increase in resistance of the electrode plates.

Fig. 9 is an SEM image showing a cross-section of a surface of a negative electrode during self-closing of a rechargeable lithium battery cell not including the positive electrode according to an embodiment.

Fig. 10 is an SEM image showing a cross-section of a surface of a negative electrode during self-closing of a rechargeable lithium battery cell including both the negative electrode including a negative electrode functional layer and a positive electrode according to an embodiment.

< description of symbols >

100: rechargeable lithium battery

112: negative electrode

113: partition board

114: positive electrode

120: battery case

140: sealing member

200: coin symmetrical single cell

210: spring

212: negative electrode

214: positive electrode

216: first spacer

218: partition board

220: bottom shell

222: second spacer

224: top shell

Detailed Description

Hereinafter, embodiments of the present invention are described in detail with reference to the accompanying drawings. In the following description of the present disclosure, well-known functions or constructions will not be described in detail in order to make the present disclosure clear.

For clarity of explanation of the present disclosure, descriptions and relationships are omitted, and the same or similar configuration elements are denoted by the same reference numerals throughout the present disclosure. Also, since the size and thickness of each configuration shown in the drawings are arbitrarily shown for better understanding and ease of description, the present disclosure is not necessarily limited thereto.

The rechargeable lithium battery may be classified into a lithium ion battery, a lithium ion polymer battery, and a lithium polymer battery according to the kinds of a separator and an electrolyte. It can also be classified into a cylindrical shape, a prismatic shape, a coin shape, a pouch shape, etc. according to the shape. In addition, it may be a bulk (bulk) type and a thin film type according to size. The structure and fabrication methods of lithium ion batteries pertaining to the present disclosure are well known in the art.

Herein, as an example of the rechargeable lithium battery, for example, a cylindrical rechargeable lithium battery is described. Fig. 1 is a schematic view of a structure of a rechargeable lithium battery according to an embodiment. Referring to fig. 1, a rechargeable lithium battery 100 according to an embodiment includes a battery cell including a negative electrode 112, a positive electrode 114 facing the negative electrode 112, a separator 113 interposed between the negative electrode 112 and the positive electrode 114, and an electrolyte (not shown) for a rechargeable lithium battery impregnating the negative electrode 112, the positive electrode 114, and the separator 113; a battery case 120 that houses battery cells; and a sealing member 140 sealing the battery case 120.

Hereinafter, a more detailed configuration of the rechargeable lithium battery 100 according to an embodiment of the present invention will be described.

A rechargeable lithium battery according to an embodiment of the present invention includes a negative electrode including a negative electrode current collector, a negative electrode active material layer disposed on the negative electrode current collector, and a negative electrode functional layer disposed on the negative electrode active material layer; and a positive electrode including a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, wherein the negative electrode functional layer includes flake-like polyethylene particles, and the positive electrode active material layer includes a first positive electrode active material including one or more complex oxides of a metal selected from cobalt, manganese, nickel, and a combination thereof, and lithium; and a second positive electrode active material including the compound represented by chemical formula 1.

A negative electrode for a rechargeable lithium battery according to an embodiment of the present invention may include a negative electrode functional layer including flake-shaped polyethylene particles.

In the case where the negative electrode functional layer includes the flake-shaped polyethylene particles, the reaction rate following the temperature increases under the same reaction conditions as compared to the case where the spherical polyethylene particles are included, and thus the stability-improving effect of the rechargeable lithium battery may be further improved. In the case of the flake polyethylene particles before melting, the area covering the pores is thinner and wider than the area covering the pores for the spherical polyethylene particles before melting. If the polyethylene particles are melted at a temperature exceeding a certain temperature and the ion channels are closed, the electrode plate area where the flaky polyethylene particles are melted and closed is larger than the electrode plate area where the spherical polyethylene particles are melted and closed, and a rapid reaction rate can be achieved.

That is, during thermal runaway of the battery, polyethylene particles included in the anode functional layer are melted and ion channels are closed, thereby restricting movement of ions and exhibiting a self-closing function, and thus additional electrochemical reactions may be prevented.

For example, as shown in fig. 4, the flake-like polyethylene particles according to the embodiment are disposed on the pores in the negative electrode functional layer composition in a thin and wide shape, and thus they are more rapidly melted at the time of thermal runaway due to thermal/physical influence, thereby inhibiting ion channels.

In general, the polyethylene can be classified according to density into High Density Polyethylene (HDPE) having a density of about 0.94g/cc to about 0.965g/cc, Medium Density Polyethylene (MDPE) having a density of about 0.925g/cc to about 0.94g/cc, Low Density Polyethylene (LDPE) having a density of about 0.91g/cc to about 0.925g/cc, and Very Low Density Polyethylene (VLDPE) having a density of about 0.85g/cc to about 0.91 g/cc. The laminar polyethylene particles may comprise, for example, a polyethylene polymer such as HDPE, MDPE or LDPE alone, or a mixture of two or more.

The flaky polyethylene particles included in the anode functional layer disposed on the anode active material layer may have an average particle diameter (D50) of about 1 μm to about 8 μm, and particularly about 2 μm to about 6 μm.

As used herein, when a definition is not otherwise provided, the average particle diameter (D50) can be measured by methods well known to those of ordinary skill in the art, for example, using a particle size analyzer, or from TEM or SEM photographs. Optionally, data analysis is performed using a dynamic light scattering measurement device and the number of particles per particle size range is counted. Thus, the D50 value can be easily obtained by calculation.

In another aspect, the ratio of the length of the major axis to the length of the minor axis of the flaky polyethylene particles may be from about 1 to about 5, and particularly from about 1.1 to about 4.5 or from about 1.2 to about 3.5.

In addition, the flaky polyethylene particles may have a thickness of about 0.2 μm to about 4 μm, and particularly about 0.3 μm to about 2.5 μm or about 0.3 μm to about 1.5 μm.

The polyethylene particles according to the present invention have a flake shape as shown in fig. 3 and have a shape different from the spherical polyethylene particles in the state of aqueous dispersion of the typical polyethylene particles as shown in fig. 2, and the average particle diameter of the flake-shaped polyethylene particles can be defined as D50.

When the flaky polyethylene particles have a size and a thickness within this range, the ion channel can be effectively closed in a small amount.

The anode functional layer may further include inorganic particles and a binder.

The weight ratio of the sum of the flaky polyethylene particles and inorganic particles to the binder may be from about 80:20 to about 99:1, and particularly from about 85:15 to about 97: 3.

The weight ratio of the flaked polyethylene particles and inorganic particles included may be from about 95:5 to about 10:90, and particularly from about 30:70 to about 70: 30.

When the amounts of the flaky polyethylene particles and the inorganic particles are within this range, the cycle-life characteristics and output characteristics of the battery can be secured.

The inorganic particles may include, for example, Al₂O₃、SiO₂、TiO₂、SnO₂、CeO₂、MgO、NiO、CaO、GaO、ZnO、ZrO₂、Y₂O₃、SrTiO₃、BaTiO₃、Mg(OH)₂Boehmite, or a combination thereof, but is not limited thereto. In addition to the inorganic particles, organic particles such as an acrylic compound, an imide compound, an amide compound, or a combination thereof may be further included, but not limited thereto.

The inorganic particles may be spherical, lamellar, cubic, or amorphous. The inorganic particles may have an average particle diameter of from about 1nm to about 2500nm, for example from about 100nm to about 2000nm, or from about 200nm to about 1000nm, or from about 300nm to about 800 nm. The average particle diameter of the inorganic particles may be a particle diameter at which a cumulative volume proportion in a size-distribution curve is 50% (D50).

The thickness of the negative electrode functional layer may be about 1 μm to about 10 μm, and particularly about 3 μm to about 10 μm.

The ratio of the thickness of the anode active material layer to the thickness of the anode functional layer may be about 50:1 to about 10:1, and particularly about 30:1 to about 10: 1.

When the thickness of the anode functional layer is within this range, thermal stability may be significantly improved while maintaining excellent cycle-life characteristics.

In particular, when the ratio of the thickness of the included anode functional layer is within this range, thermal safety may be improved while minimizing energy density deterioration.

The negative electrode current collector may include one selected from the group consisting of a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with a conductive metal, and a combination thereof.

The negative active material may include a material capable of reversibly intercalating/deintercalating lithium ions, lithium metal, a lithium metal alloy, a material capable of doping/dedoping lithium, or a transition metal oxide.

The material that reversibly intercalates/deintercalates lithium ions may include a carbon material, which is a carbon-based negative active material commonly used in rechargeable lithium batteries. Examples of the carbon-based negative active material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon is amorphous, or plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite. The amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbonization products, coke, and the like.

The lithium metal alloy includes an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn.

The material capable of doping/dedoping lithium may be a silicon-based material, e.g., Si, SiO_x(0<x<2) Si-Q alloy (wherein Q is selected from alkali metals)Alkaline earth metals, group 13 elements, group 14 elements, group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, and not being Si), Si-C composites, Sn, SnO₂Sn-R alloys (where R is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), Sn-C composites, and the like. At least one of these materials may be mixed with SiO₂And (4) mixing. The elements Q and R may be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po and combinations thereof, wherein R is not Sn.

The transition metal oxide includes lithium titanium oxide.

In the anode active material layer, the content of the anode active material may be about 95 wt% to about 99 wt% based on the total weight of the anode active material layer.

The negative electrode active material layer may further include an optional negative electrode conductive material and a negative electrode binder.

The respective amounts of the negative electrode conductive material and the negative electrode binder may be about 1 wt% to about 5 wt%, based on the total weight of the negative electrode active material layer.

A negative electrode conductive material is included to provide electrical conductivity to the negative electrode. Any conductive material may be used as the conductive material unless it causes a chemical change in the battery. Examples thereof may be carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, and the like; metal-based materials including metal powders or metal fibers of copper, nickel, aluminum, silver, or the like; conductive polymers such as polyparaphenylene derivatives; or mixtures thereof.

The negative electrode binder serves to adhere the negative electrode active material particles to each other and the negative electrode active material to the current collector. The negative electrode binder may be a non-aqueous binder, an amphiphilic binder (aqueous/non-aqueous binder), or a combination thereof.

The non-aqueous binder may be polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

The aqueous binder may be styrene-butadiene rubber, acrylated styrene-butadiene rubber, polyvinyl alcohol, sodium polyacrylate, copolymers of polypropylene and C2 to C8 olefins, copolymers of (meth) acrylic acid and alkyl (meth) acrylates, or combinations thereof.

The amphiphilic binder may be an acrylated styrenic rubber or the like.

When the negative electrode binder is an aqueous binder, a cellulose-based compound may be further used as a thickener to provide viscosity. The cellulose-based compound includes one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose and alkali metal salts thereof. The alkali metal may be Na, K or Li. The thickener may be included in an amount of about 0.1 parts by weight to about 3 parts by weight, based on 100 parts by weight of the anode active material.

A positive electrode of a rechargeable lithium battery according to an embodiment of the present invention includes a positive active material layer including a first positive active material including one or more complex oxides of lithium and a metal selected from cobalt, manganese, nickel, and a combination thereof, and a second positive active material including a compound represented by chemical formula 1.

A rechargeable lithium battery according to an embodiment of the present invention includes a negative electrode functional layer disposed on a negative electrode and a positive electrode active material layer including both a first positive electrode active material and a second positive electrode active material, and thus may reduce a heat increase rate by heat/physical influence and may melt flake-shaped polyethylene particles, thereby helping an ion channel to be effectively shut down.

The positive electrode active material layer may further include a positive electrode functional layer disposed on the positive electrode active material layer.

The first positive electrode active material may be included in the positive electrode active material layer, and the second positive electrode active material may be included in at least one of the positive electrode active material layer and the positive electrode functional layer.

The first cathode active material may include one or more complex oxides of lithium and a metal selected from cobalt, manganese, nickel, and a combination thereof.

A specific example of the first positive electrode active material may be a compound represented by one of the following chemical formulas.

Li_aA_1-bX_bD₂(0.90≤a≤1.8，0≤b≤0.5)；Li_aA_1-bX_bO_2-cD_c(0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05)；Li_aE_1-bX_bO_2-cD_c(0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05)；Li_aE_2-bX_bO_4-cD_c(0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05)；Li_aNi_1-b-cCo_bX_cD_α(0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.5，0<α≤2)；Li_aNi_1-b-cCo_bX_cO_2-αT_α(0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05，0<α<2)；Li_aNi_1-b-cCo_bX_cO_2-αT₂(0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05，0<α<2)；Li_aNi_1-b-cMn_bX_cD_α(0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05，0<α≤2)；Li_aNi_1-b-cMn_bX_cO_2-αT_α(0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05，0<α<2)；Li_aNi_1-b-cMn_bX_cO_2-αT₂(0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05，0<α<2)；Li_aNi_bE_cG_dO₂(0.90≤a≤1.8，0≤b≤0.9，0≤c≤0.5，0.001≤d≤0.1)；Li_aNi_bCo_cMn_dG_eO₂(0.90≤a≤1.8，0≤b≤0.9，0≤c≤0.5，0≤d≤0.5，0.001≤e≤0.1)；Li_aNiG_bO₂(0.90≤a≤1.8，0.001≤b≤0.1)；Li_aCoG_bO₂(0.90≤a≤1.8，0.001≤b≤0.1)；Li_aMn_1-bG_bO₂(0.90≤a≤1.8，0.001≤b≤0.1)；Li_aMn₂G_bO₄(0.90≤a≤1.8，0.001≤b≤0.1)；Li_aMn_1-gG_gPO₄(0.90≤a≤1.8，0≤g≤0.5)；QO₂；QS₂；LiQS₂；V₂O₅；LiV₂O₅；LiZO₂；LiNiVO₄；Li_(3-f)J₂(PO₄)₃(0≤f≤2)；Li_(3-f)Fe₂(PO₄)₃(0≤f≤2)；Li_aFePO₄(0.90≤a≤1.8)。

In the above formula, A is selected from the group consisting of Ni, Co, Mn, and combinations thereof; x is selected from Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements and combinations thereof; d is selected from O, F, S, P and combinations thereof; e is selected from Co, Mn and combinations thereof; t is selected from F, S, P and combinations thereof; g is selected from Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V and combinations thereof; q is selected from Ti, Mo, Mn and combinations thereof; z is selected from Cr, V, Fe, Sc, Y and combinations thereof; and J is selected from V, Cr, Mn, Co, Ni, Cu, and combinations thereof.

These compounds may have a coating on the surface, or may be mixed with another compound having a coating. The coating may comprise at least one coating element compound selected from the group consisting of: oxides of the coating elements, hydroxides of the coating elements, oxyhydroxides of the coating elements, oxycarbonates of the coating elements and hydroxycarbonates of the coating elements. The compounds used for the coating may be amorphous or crystalline. The coating elements included in the coating may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The coating layer can be provided by using these elements in the compound in a method that does not adversely affect the performance of the positive electrode active material. For example, the method may include any coating method (e.g., spraying, dipping, etc.), but is not described in more detail as it is well known to those skilled in the relevant art.

The content of the first cathode active material may be about 70 wt% to about 99 wt%, more particularly about 85 wt% to about 99 wt%, about 87 wt% to about 95 wt%, or about 90 wt% to about 98 wt%, based on the total weight of the cathode active material layer. When the amount of the first positive electrode active material satisfies this range, safety can be improved without deteriorating capacity.

The second positive active material may include, for example, LiFePO₄。

The content of the second cathode active material may be about 1 wt% to about 15 wt%, and more particularly about 2 wt% to about 15 wt%, about 2 wt% to about 12 wt%, or about 2 wt% to about 10 wt%, based on the total weight of the cathode active material layer. When the amount of the second positive electrode active material satisfies this range, safety can be improved without deteriorating capacity.

The positive electrode collector may be aluminum or nickel, but is not limited thereto.

The positive electrode active material layer may further include an optional positive electrode conductive material and a positive electrode binder.

The respective amounts of the positive electrode conductive material and the positive electrode binder may be about 1 wt% to about 5 wt%, based on the total weight of the positive electrode active material layer.

The positive electrode conductive material is used to provide conductivity to the positive electrode. The type of positive electrode conductive material is the same as the type of negative electrode conductive material described previously.

The positive electrode binder improves the binding property of the positive electrode active material particles to each other and the binding property of the positive electrode active material particles to the current collector. Examples thereof may be polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like, but are not limited thereto.

The electrolyte contains a nonaqueous organic solvent and a lithium salt.

The non-aqueous organic solvent serves as a medium for transporting ions participating in the electrochemical reaction of the battery.

The non-aqueous organic solvent may be a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent or an aprotic solvent. The carbonate-based solvent may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), Ethylene Carbonate (EC), Propylene Carbonate (PC), Butylene Carbonate (BC), etc., and the ester-based solvent may include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, γ -butyrolactone, decalactone, valerolactone, mevalonolactone, caprolactone, and the like. The ether solvent may include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc., and the ketone solvent may be cyclohexanone, etc. The alcoholic solvent may include ethanol, isopropanol, etc., and the aprotic solvent may include nitriles such as R — CN (where R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, and R may include a double bond, an aromatic ring, or an ether bond), etc., amides such as dimethylformamide, etc., dioxolanes such as 1, 3-dioxolane, etc., sulfolane, etc.

The non-aqueous organic solvents may be used alone or in a mixture. When the organic solvent is used in a mixture, the mixing ratio may be controlled according to desired battery performance, which is known to those of ordinary skill in the art.

In addition, the carbonate-based solvent may include a mixture of cyclic carbonates and chain carbonates. In this case, when the cyclic carbonate and the chain carbonate are mixed together in a volume ratio of about 1:1 to about 1:9, electrolyte performance can be enhanced.

The non-aqueous organic solvent of the present disclosure may further include an aromatic hydrocarbon organic solvent in addition to the carbonate-based solvent. Herein, 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 organic solvent may be an aromatic hydrocarbon compound of chemical formula 2.

[ chemical formula 2]

In chemical formula 2, R₁To R₆The same or different and selected from hydrogen, halogen, C1 to C10 alkyl, haloalkyl, and combinations thereof.

Specific examples of the aromatic hydrocarbon organic solvent may be selected from benzene, fluorobenzene, 1, 2-difluorobenzene, 1, 3-difluorobenzene, 1, 4-difluorobenzene, 1,2, 3-trifluorobenzene, 1,2, 4-trifluorobenzene, chlorobenzene, 1, 2-dichlorobenzene, 1, 3-dichlorobenzene, 1, 4-dichlorobenzene, 1,2, 3-trichlorobenzene, 1,2, 4-trichlorobenzene, iodobenzene, 1, 2-diiodobenzene, 1, 3-diiodobenzene, 1, 4-diiodobenzene, 1,2, 3-triiodobenzene, 1,2, 4-triiodobenzene, toluene, fluorotoluene, 2, 3-difluorotoluene, 2, 4-difluorotoluene, 2, 5-difluorotoluene, 2,3, 4-trifluorotoluene, 2,3, 5-trifluorotoluene, chlorotoluene, and the like, 2, 3-dichlorotoluene, 2, 4-dichlorotoluene, 2, 5-dichlorotoluene, 2,3, 4-trichlorotoluene, 2,3, 5-trichlorotoluene, iodotoluene, 2, 3-diiodotoluene, 2, 4-diiodotoluene, 2, 5-diiodotoluene, 2,3, 4-triiodotoluene, 2,3, 5-triiodotoluene, xylene, and combinations thereof.

In order to improve the cycle life of the battery, the non-aqueous electrolyte may further include an additive of vinylene carbonate or an ethylene carbonate-based compound of chemical formula 3.

[ chemical formula 3]

In chemical formula 3, R₇And R₈Identical or different and selected from hydrogen, halogen, Cyano (CN), Nitro (NO)₂) And a fluorinated C1 to C5 alkyl group, provided that R₇And R₈At least one of them is selected from halogen, Cyano (CN), Nitro (NO)₂) And fluorinated C1 to C5 alkyl, and R₇And R₈Not hydrogen at the same time.

Examples of the ethylene carbonate-based compound may be difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate or fluoroethylene carbonate. The amount of the additive for improving cycle life may be used within an appropriate range.

The lithium salt dissolved in the organic solvent supplies lithium ions to the battery, basically operates the rechargeable lithium battery, and improves the transport of lithium ions between the positive electrode and the negative electrode. Examples of the lithium salt include at least one supporting salt selected from the following: LiPF₆、LiBF₄、LiSbF₆、LiAsF₆、LiN(SO₂C₂F₅)₂、Li(CF₃SO₂)₂N、LiN(SO₃C₂F₅)₂、LiC₄F₉SO₃、LiClO₄、LiAlO₂、LiAlCl₄、LiN(C_xF_2x+1SO₂)(C_yF_2y+1SO₂) (wherein x and y are natural numbers), LiCl, LiI and LiB (C)₂O₄)₂(lithium bis (oxalato) borate; LiBOB). The concentration of the lithium salt may be in the range of about 0.1M to about 2.0M. When the salt is included within the above concentration range, the electrolyte may have excellent properties and lithium ion mobility due to optimal electrolyte conductivity and viscosity.

Meanwhile, as described above, the separator 113 may be disposed between the positive electrode 114 and the negative electrode 112. The separator 113 may, for example, be selected from fiberglass, polyester, polyethylene, polypropylene, polytetrafluoroethylene, or combinations thereof. It may have the form of a non-woven fabric or a woven fabric. For example, in a rechargeable lithium battery, polyolefin-based polymer separators such as polyethylene and polypropylene may be mainly used. In order to secure heat resistance or mechanical strength, a coated separator including a ceramic component or a polymer material may be used. Optionally, it may have a single-layer structure or a multi-layer structure.

Hereinafter, the above-described aspects of the present disclosure will be explained in more detail with reference to examples. However, these embodiments are exemplary, and the present disclosure is not limited thereto.

(manufacture of rechargeable lithium Battery cell)