Lithium secondary battery containing amorphous positive electrode active material

Abstract

The present invention provides a secondary battery having excellent electrochemical stability and excellent reversibility of lithium ion insertion and conversion reactions. According to one aspect of the present invention, there is provided a secondary battery including a positive electrode containing a transition metal-based lithium compound, wherein a differential capacity (dQ / dV)-voltage (V) graph of the secondary battery does not show a peak value between 3.8 and 4.0 V.

Description

[Technical Field]

[0001] The present invention relates to a lithium secondary battery including an amorphous positive electrode active material, and more particularly to a high-capacity lithium secondary battery having excellent reversibility of lithium ion insertion reaction-conversion reaction. [Background technology]

[0002] Recently, as electronic devices have become increasingly portable, there has been a growing demand for small, lightweight, and high-energy-density secondary batteries as power sources for these devices. Furthermore, with the recent development and commercialization of electric and hybrid vehicles in an effort to protect the global environment, there has been a growing demand for lithium secondary batteries with excellent storage characteristics for large-scale applications. In this context, lithium secondary batteries, which have the advantage of having a large charge / discharge capacity, have been attracting attention.

[0003] Conventionally, commonly known cathode active materials useful for high-energy lithium secondary batteries with a voltage of 4V or higher include spinel-type LiMn2O4, zigzag-layered LiMnO2, and layered rock-salt-type LiCOO2 and LiNiO2. Among these, lithium secondary batteries using LiNiO2 have attracted attention for their high charge / discharge capacity. However, these materials have poor thermal stability and cycle characteristics during charging, so further improvements in their properties are required. Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a lithium secondary battery including an amorphous positive electrode active material capable of stably performing reversible lithium ion insertion and conversion reactions.

[0005] Another object of the present invention is to provide a lithium secondary battery having excellent electrochemical stability.

[0006] It is still another object of the present invention to provide a lithium secondary battery having excellent long-term cycle stability.

[0007] It is yet another object of the present invention to provide a lithium secondary battery including a high capacity electrode.

[0008] The objects and advantages of the present invention are not limited to those mentioned above, but may be understood from the following description and may be more clearly understood from the examples of the present invention. Furthermore, it should be easily understood that the objects and advantages of the present invention can be realized by the means and combinations thereof set forth in the claims. [Means for solving the problem]

[0009] To achieve the above object, the present invention provides a secondary battery including a positive electrode containing a transition metal-based lithium compound, wherein a peak value between 3.8 and 4.0 V does not exist in a differential capacity dQ / dV-voltage V graph of the secondary battery.

[0010] In an embodiment of the present invention, the transition metal-based lithium compound may include an amorphous phase.

[0011] In an embodiment of the present invention, the differential capacity dQ / dV-voltage V graph of the secondary battery may be obtained after 1 to 5 cycles at a 0.01 C-rate to 0.5 C-rate and at 25°C.

[0012] In an embodiment of the present invention, the transition metal-based lithium compound may include a compound represented by the following Formula 1: [Formula 1] Li x M 2-x SO4A In the general formula 1, M is one or more elements selected from the group consisting of Fe, Mg, Ni, Co, Cr, Ti, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, and Bi, A is a halogen atom, and 0.5≦x≦1.5.

[0013] In an embodiment of the present invention, the transition metal-based lithium compound may include LiFeSO4F.

[0014] In an embodiment of the present invention, the particle size D of the transition metal-based lithium compound 50 can be 0.5 to 3.0 μm.

[0015] In an embodiment of the present invention, the transition metal-based lithium compound may include an amorphous matrix and crystalline grains.

[0016] In an embodiment of the present invention, the crystal grain may include a plurality of grains, and each of the grains may have an average size of 4 to 8 nm.

[0017] In an embodiment of the present invention, a differential capacity dQ / dV-voltage V graph of the secondary battery may have a first peak at 2.5 to 2.7V.

[0018] In an embodiment of the present invention, a differential capacity dQ / dV-voltage V graph of the secondary battery may have a second peak at 2.1 to 2.3V.

[0019] In an embodiment of the present invention, a secondary battery may be provided, further including a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

[0020] The above summary of the invention is not an exhaustive list of the features of the invention, and the various features and advantages thereof will be more fully understood with reference to the following specific examples. [Effects of the Invention]

[0021] According to one aspect of the present invention, it is possible to achieve excellent cycle performance with excellent electrochemical stability without any additional treatment process.

[0022] According to another aspect of the present invention, a secondary battery having stable reversibility can be provided by embodying an effect in which the lithium ion insertion reaction of an electrode is stably maintained without significant performance degradation despite the considerable bond rearrangement that is expected to occur during the conversion reaction.

[0023] The above-mentioned effects and specific effects of the present invention will be described together with the details of the embodiments of the present invention below. [Brief explanation of the drawings]

[0024] [Figure 1] 1 shows XRD (X-ray diffraction) patterns of LiFeSO4F in Synthesis Example 1 after ball milling, LiF-FeSO4 in Synthesis Example 1 before ball milling, LiF, and FeSO4. [Figure 2] 1 shows Fe K-edge Hard X-ray absorption spectroscopy (XAS) spectra of LiFeSO4F and FeSO4 of Synthesis Example 1 after ball milling. [Figure 3] 1 shows the radial distribution of LiFeSO4F and FeSO4 around Fe in Synthesis Example 1 after ball milling. [Figure 4] The F K-edge and Fe L3 edge of LiFeSO4F obtained in Synthesis Example 1 were analyzed by SXAS (Soft X-ray absorption spectroscopy). [Figure 5] 1 shows electron diffraction patterns of LiFeSO4F according to Synthesis Example 1 and various reference materials (Ref). [Figure 6] 1 is a TEM photograph of LiFeSO4F according to Synthesis Example 1. [Figure 7] 1 shows a charge / discharge profile of a half-cell according to Production Example 2. [Figure 8] 1 shows the charge-discharge profile of a half-cell according to Comparative Example 1 at 60° C. [Figure 9]1 shows the charge-discharge profile of a half-cell according to Comparative Example 2 at 60° C. [Figure 10] 1 is a differential capacity curve of a half cell according to Preparation Example 2. [Figure 11a] 1 shows charge / discharge profiles of the half-cell of Example 1 over time in the high voltage region (2.2 to 4.7 V) and the low voltage region (1.5 to 2.2 V). [Figure 11b] 1 shows Fe K-edge XANES spectra for the charging process of the half-cell according to Example 1 in the high voltage region. [Figure 11c] 1 shows Fe K-edge XANES spectra for the discharge process of the half-cell according to Example 1 in the high voltage region. [Figure 11d] 1 shows Fe K-edge XANES spectra for the charging process of the half-cell according to Example 1 in the low voltage region. [Figure 11e] 1 shows Fe K-edge XANES spectra for the discharge process of the half-cell according to Example 1 in the low voltage region. [Figure 11f] 1 shows Fe K-edge EXAFS (Extended X-ray absorption fine structure) spectra for Fe metal (Ref), pristine, and the half-cell according to Example 1 when discharged to 1.5 V and charged to 2.2 V, respectively. [Figure 11g] TEM photograph of Fe metal contained within a discharged lithium compound matrix. [Figure 11h] 1 shows the F K-edge spectra of the half-cell according to Example 1 in a fully charged, half-discharged, or fully discharged state. [Figure 11i] 1 shows IR (Infrared spectroscopy) spectra of a half-cell according to Example 1 in a fully charged, half-discharged, or fully discharged state. [Figure 12] 1 is a charge-discharge profile for the two-step reaction (insertion and conversion reaction) of a-LiFeSO4F in a half-cell according to Example 1. [Figure 13]1 shows the results of evaluation of electrochemical stability of the half cell according to Example 1 against long-term charge-discharge cycles. [Figure 14a] 1 shows the charge-discharge profiles of the half-cell according to Example 1 at current densities of 0.02 A / g, 0.05 A / g, 0.1 A / g, 0.2 A / g, 0.5 A / g, 1 A / g, and 2 A / g. [Figure 14b] The discharge capacity of the half cell of Example 1 according to the number of cycles when the temperature is 60°C and the current density is 0.02 A / g, 0.05 A / g, 0.1 A / g, 0.2 A / g, 0.5 A / g, 1 A / g, and 2 A / g. DETAILED DESCRIPTION OF THE INVENTION

[0025] In this specification, the singular expression includes the plural expression unless the context clearly indicates otherwise.

[0026] In this specification, a range of values ​​indicated using the term "to" refers to a range of values ​​that includes the values ​​before and after the term as the lower and upper limits, respectively. If multiple values ​​are disclosed as the upper and lower limits of a given range, the range of values ​​disclosed in this specification can be understood as any range of values ​​having any one value among the multiple lower limits and any one value among the multiple upper limits as the lower and upper limits, respectively.

[0027] In this specification, the meaning of "no peak" in a differential capacitance dQ / dV-voltage V graph can be understood as common knowledge in the art and can mean that no peak is observed in the corresponding voltage range.

[0028] According to one aspect of the present invention, there is provided a secondary battery including a positive electrode containing a transition metal-based lithium compound, wherein the differential capacity dQ / dV-voltage V graph of the secondary battery does not exhibit a peak between 3.8 and 4.0 V. If the differential capacity dQ / dV-voltage V graph of the secondary battery exhibits a peak between 3.8 and 4.0 V, the overall capacity of the recharged secondary battery may be poorly electrochemically active in the low voltage range. Furthermore, conventional electrodes based solely on conversion reactions have had problems maintaining stable capacity due to side effects such as significant volume change during the conversion reaction, compositional non-uniformity, dissolution of transition metals, and formation of a cathode passive layer (CEI) due to electrolyte decomposition. While solutions to these problems have been successful in improving reversibility by alleviating some of these side effects, they have required additional processes such as a surface protection layer, a three-dimensional positive electrode structure, or the use of a high-grade electrolyte system. According to one aspect of the present invention, a secondary battery having excellent electrochemical stability and cycle performance can be achieved by using a cathode active material having an amorphous phase with a layered structure without the need for additional treatment. According to another aspect of the present invention, a secondary battery having stable reversibility can be provided by stably maintaining the lithium ion insertion reaction of the electrode without significant performance degradation despite the considerable bond rearrangement that is expected to occur during the conversion reaction.

[0029] The configuration of the present invention will be described in more detail below.

[0030] Positive electrode and secondary battery including same The secondary battery according to the present invention includes a positive electrode, which includes a transition metal-based lithium compound.

[0031] The differential capacity dQ / dV-voltage V graph is a graph showing dQ / dV, which is the differential value of capacity with respect to voltage, versus voltage V based on the time and voltage results of a constant current test. Various factors can affect this differential capacity dQ / dV-voltage V graph, including the composition of the positive electrode active material, temperature, discharge rate, charging method, charging time, and magnitude of charging current.

[0032] In the differential capacitance dQ / dV-voltage V graph according to the present invention, there is no peak value between 3.8 and 4.0 V, specifically 3.9 V.

[0033] Meanwhile, the differential capacity dQ / dV-voltage V graph of the secondary battery may be obtained after 1 to 5 cycles under conditions of 0.01 C-rate to 0.5 C-rate and 25°C.

[0034] The transition metal-based lithium compound according to the present invention is a compound in which the constituent elements of the positive electrode active material are positioned in a layered structure, and the layered structure may have a structure in which lithium ions are inserted or extracted during charge and discharge. Specifically, the lithium ions may be deintercalated from the lattice during charging of the secondary battery, and may be intercalated into the lattice during discharging of the secondary battery.

[0035] According to one embodiment of the present invention, the transition metal-based lithium compound may include an amorphous phase. Meanwhile, an amorphous phase refers to a phase without a crystallized structure. Specifically, since the transition metal-based lithium compound includes an amorphous phase, it can realize excellent cycle performance with electrochemical stability and can realize an effect of stably maintaining the lithium ion insertion reaction of the electrode without a significant performance degradation despite considerable bond rearrangement that is expected to occur during the conversion reaction. Specifically, the amorphous characteristics of the transition metal-based lithium compound can contribute to maintaining the lithium insertion reaction well even after repeated conversion reactions of the secondary battery. If the transition metal-based lithium compound includes LiFeSO4F, Fe 2+ The substitution / diffusion of e can be carried out much more easily than in the crystalline phase due to the amorphous character. 2+ This influences the electrode kinetics by facilitating the substitution / diffusion of , resulting in an effective reversible lithium ion insertion-conversion reaction.

[0036] For example, XRD analysis or XAS analysis can be used to analyze the crystal structure of the transition metal-based lithium compound.

[0037] In another embodiment of the present invention, the transition metal-based lithium compound may include a compound represented by the following general formula 1: [Formula 1] Li x M 2-x SO4A In the general formula 1, M is one or more elements selected from the group consisting of Fe, Mg, Ni, Co, Cr, Ti, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, and Bi, and A is a halogen atom, and x may be 0.5≦x≦1.5. Specifically, A may be a halogen atom capable of bonding with a lithium ion to form a salt structure.

[0038] For example, the transition metal-based lithium compound may include LiFeSO4F. When LiFeSO4F is used as the transition metal-based lithium compound, high reversibility and stability can be achieved so that the lithium ion insertion reaction can be well maintained even after repeated conversion reactions of the secondary battery. For example, the lithium ion insertion reaction and conversion reaction can occur as shown in Reaction Schemes 1 and 2 below. [Reaction Scheme 1] a-FeSO4F+Li + +e - → a-LiFeSO4F (lithium ion insertion reaction) [Reaction Scheme 2] a-LiFeSO4F+2Li + +2e - →Fe+LiSO3F+Li2O (conversion reaction) According to another embodiment of the present invention, the particle size D of the transition metal-based lithium compound 50 When the particle size of the transition metal-based lithium compound is within the above range, the dispersion of the positive electrode active material in the positive electrode slurry may be excellent.

[0039] According to another embodiment of the present invention, the transition metal-based lithium compound may include an amorphous matrix and crystalline grains. Specifically, the amorphous matrix may mean that a phase without a crystalline structure is formed within the structure of the transition metal-based lithium compound, and the crystalline grains may include grains in which a crystalline structure is formed.

[0040] According to another embodiment of the present invention, the crystal grain may include a plurality of grains, and the average size of each grain may be 8 nm or less, 4 to 8 nm, 5 to 7 nm, or 6 to 7 nm. Specifically, when the average size of each grain satisfies the above numerical range, a reversible lithium ion insertion reaction and conversion reaction may be effectively carried out.

[0041] According to still another embodiment of the present invention, the differential capacity dQ / dV-voltage V graph of the secondary battery may have a first peak at 2.5 to 2.7 V, and more particularly, at 2.6 V. Here, the first peak may refer to a peak in a charging curve of the differential capacity dQ / dV-voltage V graph.

[0042] According to still another embodiment of the present invention, the differential capacity dQ / dV-voltage V graph of the secondary battery may have a second peak at 2.1 to 2.3 V, more specifically, at 2.2 V. Here, the second peak may refer to a peak in the discharge curve of the differential capacity dQ / dV-voltage V graph.

[0043] According to another embodiment of the present invention, the reversible capacity of the secondary battery may be 360 ​​mAh / g or more. Specifically, the reversible capacity may refer to a value obtained by subtracting the irreversible capacity from the charge amount of the positive electrode active material.

[0044] According to still another embodiment of the present invention, the capacity retention rate of the secondary battery may be 90% or more at 25° C. or 98% or more at 60° C. even after 200 cycles. Meanwhile, the capacity retention rate of the secondary battery may refer to a value indicating a ratio of the maximum capacity to the design capacity of the secondary battery.

[0045] According to yet another embodiment of the present invention, there is provided a method for manufacturing the positive electrode active material.

[0046] A method for producing a positive electrode active material according to the present invention may include (S1) preparing a precursor containing a lithium salt and an anhydrous transition metal sulfate, and (S2) pulverizing the precursor and then heat-treating it.

[0047] If a transition metal sulfate containing water is used instead of an anhydrous transition metal sulfate in step S1, the phase of the final cathode active material may not be amorphous. As a result, the reversible stability of the lithium ion insertion / conversion reaction may not be sufficiently improved. According to another aspect of the present invention, an amorphous cathode active material may be effectively formed by preparing an anhydrous transition metal sulfate as a precursor.

[0048] For example, the lithium salt may include any one selected from the group consisting of LiF, LiCl, and combinations thereof, and more particularly, LiF.

[0049] For example, in the anhydrous transition metal sulfate, the transition metal may include any one or more of Fe, Mg, Ni, Co, Cr, Ti, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, and Bi.

[0050] Optionally, the precursor may further comprise graphite.

[0051] In step S2, various grinders commonly used in the art, particularly a ball mill, may be used as a means for grinding the precursor, and step S2 may include grinding the precursor at a rotation speed of 300 to 500 rpm for 30 to 50 hours.

[0052] In step S2, the heat-treating step may include heating the pulverized material at 200 to 400°C for 60 to 80 hours at a heating rate of 1 to 3°C / min. Specifically, when the combination of the anhydrous transition metal sulfate and the conditions of the heat-treating step is satisfied, an amorphous phase positive electrode active material may be produced.

[0053] Separation membrane Separation membranes according to the present invention may comprise porous substrates or glass fiber filter paper.

[0054] The separator according to the present invention can electrically insulate the anode and cathode to prevent short circuits while providing a path for lithium ions to move, and can have a porous structure with high resistance to the electrolyte and fine pore diameters.

[0055] The porous substrate may be made of any electrically insulating organic or inorganic material. The porous substrate may include, for example, at least one selected from the group consisting of polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene, and more particularly, may include polyolefin. Polyolefins not only have excellent coating properties, but can also reduce the thickness of the separator, thereby increasing the proportion of electrode active material in the battery and increasing capacity per volume. Specifically, the weight-average molecular weight M of the polyolefin may be 0.015 to 0.015. w The weight average molecular weight of the polyolefin may be 100,000 to 500,000 g / mol. If the weight average molecular weight of the polyolefin is below this range, it may be difficult to ensure sufficient mechanical properties, and if it exceeds this range, it may be difficult to realize the shutdown function or to mold the material. The shutdown function refers to the function of preventing thermal runaway of the battery by blocking the movement of ions when the temperature of the secondary battery rises due to the thermoplastic resin dissolving and closing the pores of the porous substrate.

[0056] The thickness of the porous substrate may be, for example, 3 to 50 μm or 4 to 15 μm. If the thickness of the porous substrate is below this range, the conductive barrier function may be insufficient, and if the thickness exceeds this range, the resistance of the separator may increase excessively.

[0057] The average diameter of the pores in the porous substrate may be, for example, 10 to 100 nm. The pores in the porous substrate are interconnected, allowing gas or liquid to pass from one side of the porous substrate to the other side.

[0058] The separation membrane according to the present invention may further include a coating layer disposed on at least one surface of the porous substrate.

[0059] The coating layer according to the present invention can improve the mechanical strength and heat resistance of the separator for a secondary battery and increase the ionic conductivity within the secondary battery.

[0060] The coating layer according to the present invention may include a binder polymer and inorganic particles.

[0061] The binder polymer according to the present invention can link and stably fix inorganic particles. Examples of the binder polymer include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene-vinyl acetate copolymer (Poly(ethylene-co-vinyl acetate)), polyethylene oxide, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. One or a mixture of two or more selected from the group consisting of acrylonitrile-styrene butadiene copolymer, polyimide, and styrene-butadiene rubber may be used.

[0062] The inorganic particles according to the present invention can contribute to improving the mechanical strength and heat resistance of the separator membrane for secondary batteries. Specifically, the inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are those in which oxidation and / or reduction reactions do not occur within the operating voltage range of the secondary battery to which they are applied (for example, 0 to 5 V based on Li / Li + and there is no particular limitation as long as they do not undergo oxidation and / or reduction reactions within the operating voltage range of the secondary battery to which they are applied (for example, 0 to 5 V based on Li / Li).

[0063] As an example, when using inorganic particles with a high dielectric constant as the inorganic particles, it can contribute to an increase in the dissociation degree of the electrolyte salt in the liquid electrolyte, for example, a lithium salt, and improve the ionic conductivity of the electrolyte. Due to the reasons described above, the inorganic particles can be inorganic particles with a dielectric constant of 5 or more, inorganic particles having the ability to transfer lithium ions, or a mixture thereof.

[0064] The inorganic particles with a dielectric constant of 5 or more are one or more mixtures selected from the group consisting of Al2O3, SiO2, ZrO2, AlO(OH), Al(OH)3, Mg(OH)2, BaSO4, TiO2, BaTiO3, Pb(Zr x Ti 1-x )O3 (PZT, where 0 < x < 1), Pb 1-x La x Zr 1-y Ti y O3 (PLZT, where 0 < x < 1, 0 < y < 1), (1 - x)Pb(Mg 1 / 3 Nb 2 / 3 )O 3-x PbTiO3 (PMN - PT, where 0 < x < 1), HfO2, SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, and SiC.

[0065] The inorganic particles having the ability to transfer lithium ions are lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z(PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3, (LiAlTiP) x O y Series of glass (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride (Li x N y , 0 < x < 4, 0 < y < 2), SiS2 series of glass (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4), and P2S5 series of glass (Li x P y S z It may be one or more mixtures selected from the group consisting of 0 < x < 3, 0 < y < 3, 0 < z < 7).

[0066] For example, the average particle size D 50 of the inorganic particles can be from 1 nm to 10 μm for the formation of a coating layer of uniform thickness and appropriate porosity, specifically from 10 nm to 2 μm, and more specifically from 50 nm to 1 μm. The "average particle size D 50 " means the particle size at the 50% point of the cumulative distribution of the number of particles by particle size. The average particle size can be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac S3500), and the difference in the diffraction pattern due to the particle size when the particles pass through the laser beam is measured to calculate the particle size distribution.

[0067] According to another embodiment of the present invention, the weight ratio of the inorganic particles to the binder polymer (inorganic particles:binder polymer) may be 50:50 to 99:1, and more specifically, 70:30 to 95:5. If the ratio of the inorganic particles to the binder polymer is less than this range, the binder polymer content may be too high, which may reduce the performance of improving the thermal stability of the separator, and the void space formed between the inorganic particles may be reduced, which may reduce the pore size and porosity, resulting in a decrease in the performance of the final battery. If the ratio exceeds this range, the binder polymer content may be too low, which may weaken the peel resistance of the coating layer.

[0068] For example, the thickness of the coating layer may be 0.1 to 10 μm, specifically 1 to 3 μm, and more specifically 1.4 to 1.6 μm. When the thickness of the coating layer is within this range, the insulating properties and thermal stability of the separator can be improved, and the energy density of the battery can be improved.

[0069] For example, the packing density of the coating layer is 0.1 to 20 g / cm 3 and more particularly 0.5 to 12 g / cm 3 , more specifically 1 to 3 g / cm 3 When the packing density of the coating layer satisfies the numerical range, the permeability of lithium ions may be favorable and the heat resistance of the separator may be maintained at an appropriate level. Meanwhile, the packing density is determined by the unit area (m 2 ) is the density of the coating layer loaded at a height of 1 μm.

[0070] negative electrode The negative electrode according to an embodiment of the present invention may include lithium metal.

[0071] A negative electrode according to another embodiment of the present invention may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer may include a negative electrode active material, a conductive material, and a negative electrode binder.

[0072] The negative electrode current collector can play a role of transmitting electrons from the outside so that an electrochemical reaction occurs with the negative electrode active material, or receiving electrons from the negative electrode active material and sending them to the outside. For example, as the negative electrode current collector, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel can be used. Specifically, a transition metal that can adsorb carbon well, such as copper or nickel, may be used as the current collector. For example, the thickness of the negative electrode current collector can be 6 μm to 20 μm, but the thickness of the negative electrode current collector is not limited thereto.

[0073] The negative electrode active material can play a role of generating electricity while storing or releasing lithium ions. For example, the negative electrode active material may include at least one of silicon-based active material particles and graphite-based active material particles.

[0074] The silicon-based active material particles may be selected from one or more kinds selected from the group consisting of Si, SiOx (0 < x < 2), Si-C composite, and Si-Y alloy (Y is any one element selected from the group consisting of alkali metals, alkaline earth metals, transition metals, group 13 elements, group 14 elements, and rare earth elements).

[0075] The graphite-based active material particles may be selected from one or more kinds selected from the group consisting of artificial graphite, natural graphite, graphitized carbon fibers, and graphitized mesocarbon microbeads.

[0076] The content of the negative electrode active material can be 80 to 97% by weight based on the total solid content contained in the negative electrode active material layer.

[0077] The conductive material can improve conductivity between active material particles or between the active material and the metal current collector in the electrode and prevent the binder from acting as a non-conductor. The conductive material can be, for example, a mixture of one or more conductive materials selected from the group consisting of graphite, carbon black, carbon fiber, metal fiber, metal powder, conductive whiskers, conductive metal oxides, activated carbon, and polyphenylene derivatives. More specifically, the conductive material can be a mixture of one or more conductive materials selected from the group consisting of natural graphite, artificial graphite, Super-P, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, Denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide.

[0078] The negative electrode binder may suppress separation between negative electrode active material particles or between the negative electrode and the current collector. The negative electrode binder may be a polymer commonly used in electrodes in the relevant technical field. Examples of such negative electrode binders include, but are not limited to, poly(vinylidene fluoride co-hexafluoropropylene), poly(vinylidene fluoride-co-trichloroethylene), poly(methylmethacrylate), poly(ethylhexylacrylate), poly(butylacrylate), poly(acrylonitrile), poly(vinylpyrrolidone), poly(vinyl acetate), poly(ethylene-co-vinyl acetate), poly(ethylene oxide), polyacrylate, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. The polymer may include, but is not limited to, cyanoethyl propionate, cyano ethyl pullulan, cyano ethyl poly(vinylalcohol), cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose.

[0079] electrolyte The electrolyte according to the present invention may include a solvent and a lithium salt.

[0080] The solvent according to the present invention may be, for example, one or a mixture of two or more selected from the group consisting 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), ethyl methyl 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, and butyl propionate.

[0081] The lithium salt according to the present invention may be, for example, NO 3- , F - , Cl - , Br - , I - , PF6 - The negative ions may include:

[0082] The electrolyte solution according to the present invention may further contain an additive, specifically a compound containing a fluorine atom. For example, the additive may be one or more selected from the group consisting of LiBF, LiTFSI, and LiFSI. Here, LiTFSI and LiFSI form a lithium fluoride (LiF)-rich passive film on the surface of lithium metal through corrosion, thereby increasing the conductivity of lithium ions.

[0083] application According to another embodiment of the present invention, there may be provided any one of a battery module including the secondary battery as a unit battery, a battery pack including the battery module, and a device including the battery pack as a power source. Specific examples of the device include, but are not limited to, a power tool powered by a battery-powered motor, electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters, electric golf carts, and power storage systems.

[0084] Hereinafter, the embodiments of the present invention will be described in detail so that a person having ordinary skill in the art to which the present invention pertains can easily implement the present invention. However, this is merely an example, and the scope of the present invention is not limited by the following content.

[0085] [Synthesis example: synthesis of positive electrode active material] <Synthesis Example 1: Synthesis of a-LiFeSO4F> FeSO4·7H2O (Sigma-Aldrich) was dehydrated at 300°C for 12 hours under an argon atmosphere to produce FeSO4. Next, a 1:1 molar mixture of LiF and FeSO4 and 20 wt% graphite (Bay Carbon Inc.) was placed in the bowl of a ball mill (Pulverisette 5; Fritsch) and sealed in an argon-filled glove box (H2O, O2 <1 ppm). To prevent side reactions due to high temperature, the ball milled powder was ball milled at 400 rpm for 48 hours with a 5-minute break every 30 minutes. The ball-milled pellets were then heated at 300°C for 72 hours at a heating rate of 2°C / min to finally synthesize amorphous LiFeSO4F (a-LiFeSO4F).

[0086] <Comparative Synthesis Example 1: Synthesis of Tavorite Phase LiFeSO4F> For the tavorite phase LiFeSO4F, FeSO4·H2O was prepared by dehydrating FeSO4·7H2O (Sigma-Aldrich) with EMI-TFSI (1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) ionic liquid at 110°C for 2-3 hours. The FeSO4·H2O and LiF were ball-milled in a 1:1 molar ratio for 11 minutes, and the ball-milled sample (pellet) was then heated at 300°C for 72 hours at a heating rate of 2°C / min to finally synthesize the tavorite phase LiFeSO4F.

[0087] <Comparative Synthesis Example 2: Synthesis of triplite phase LiFeSO4F> For triplite phase LiFeSO4F, LiF and the prepared FeSO4·H2O mixed at a molar ratio of 1.05:1 were ball milled in ethanol (anhydrous conditions) for 2 hours and then dried in vacuum at 60°C for 12 hours. The dried sample (pellet) was heated at 450°C for 45 minutes and then heated for an additional 90 minutes to finally synthesize triplite phase LiFeSO4F.

[0088] [Experimental Example 1: Analysis of XRD Patterns] Figure 1 shows the XRD patterns of LiFeSO4F in Synthesis Example 1 after ball milling, LiF-FeSO4 before ball milling, LiF, and FeSO4 in Synthesis Example 1. The XRD patterns of the samples were collected at a scan rate of 0.15° / min over the 2θ range of 15° to 70° with a step size of 0.005° using a D8 ADVANCE 2020 (Bruker) equipped with Cu Kα radiation (λ = 1.54178 Å).

[0089] Referring to FIG. 1, it can be seen that the mixture containing crystalline LiF and FeSO4 precursors is converted to amorphous after ball milling.

[0090] [Manufacturing Example 1: Manufacturing of Positive Electrode] Example 1: Positive electrode containing the positive electrode active material of Synthesis Example 1 Cathode slurry production A mixture of the positive electrode active material (α-LiFeSO4F) of Synthesis Example 1, polyacrylonitrile (PAN), and conductive carbon (Super P; Timcal, Bodio, Switzerland) in a weight ratio of 7:2:1 was added to N-methyl-2-pyrrolidone (NMP, 99.5%; Sigma-Aldrich) to prepare a positive electrode slurry.

[0091] The cathode is manufactured by coating the cathode slurry onto the current collector. The prepared positive electrode slurry was applied to one side of an aluminum foil at a thickness of 2.7 to 3.0 mg / cm. 2 After casting with a loading amount of 1000, the mixture was dried in vacuum at 60°C to prepare a positive electrode having a total thickness of 32 µm.

[0092] <Comparative Example 1: Positive electrode containing the positive electrode active material (Tavorite phase) of Comparative Synthesis Example 1> A positive electrode was produced in the same manner as in Example 1, except that the positive electrode active material of Comparative Synthesis Example 1 was used in place of the positive electrode active material of Synthesis Example 1.

[0093] <Comparative Example 2: Positive electrode containing the positive electrode active material (Triplite phase) of Comparative Synthesis Example 2> A positive electrode was produced in the same manner as in Example 1, except that the positive electrode active material of Comparative Synthesis Example 2 was used in place of the positive electrode active material of Synthesis Example 1.

[0094] [Manufacturing Example 2: Manufacturing of half-cell] Coin cells (CR2032, Hohsen Corp.) were fabricated using lithium metal as the negative electrode, glass fiber filter paper (GF / F filter) as the separator, the electrodes of Example 1 and Comparative Examples 1 and 2 as the positive electrode, and an electrolyte solution of 1M LiPF6 dissolved in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1 (v / v) as the electrolyte. Specifically, a separator was interposed between the positive and negative electrodes, and the resulting assembly was placed in an argon-filled glove box (HO, O<1 ppm) before the electrolyte was poured into the coin cells.

[0095] [Experimental Example 2: Analysis of XAS Spectra] Figure 2 shows the Fe K-edge Hard XAS spectra of LiFeSO4F and FeSO4 from Synthesis Example 1 after ball milling. For Fe K-edge XAS analysis, coin cells (CR2032) were charged or discharged to a constant SOC (state of charge) and then disassembled in an Ar-filled glove box. The disassembled cells' cathodes were then washed with DMC (dimethyl carbonate) and sealed with Kapton film. Fe K-edge XAS analysis was performed at the 7D XAFS, 8C nano-XAFS, and 10C wide-XAFS beamlines at the Pohang Light Source-II (PLS-II). All Fe K-edge XAS spectra were measured in transmission mode, and the Fe spectra were simultaneously referenced and energy-corrected. The storage ring was operated in top-up mode at 3.0 GeV with a ring current of 300 mA.

[0096] Referring to FIG. 2, it can be seen that each of a-LiFeSO4F and FeSO4 exhibits a clearly distinguishable Fe K-edge spectrum at about 7127-7200 eV, which indicates the Fe structure.

[0097] FIG. 3 shows the radial distribution of LiFeSO4F and FeSO4 around Fe in Synthesis Example 1 after ball milling.

[0098] 3, it can be seen that LiFeSO4F of Synthesis Example 1 exhibits a radial distribution different from that of the initial FeSO4 phase. The change in adjacent bonds is clearly observed, along with additional shoulder peaks at approximately 3.01 and 3.60 Å, and it can be seen that the second-neighbor bond distance of a-LiFeSO4F (~2.6 Å) is slightly shorter than that of the initial pure FeSO4 phase (~2.7 Å).

[0099] Figure 4 shows the F K-edge and Fe L3-edge measured by SXAS analysis of LiFeSO4F prepared in Synthesis Example 1. To analyze the F K-edge and Fe L3-edge, the coin cell (CR2032) prepared in Preparation Example 2 was charged or discharged to a constant SOC and then disassembled in an Ar-filled glove box. The cathode of the disassembled cell was washed with DMC, and the cathode was carefully scraped to collect the cathode powder. The collected cathode powder was sonicated with DMC, and the sonicated cathode powder was then dropped onto a TEM sample grid. For STXM analysis, PLS-II was operated at the 10A2 HR-PES beamline, with the storage ring operating in top-up mode at 3.0 GeV with a ring current of 300 mA.

[0100] Referring to FIG. 4, it can be seen that the new fluorine bond peak of LiFeSO4F according to Synthesis Example 1 is detected by the SXAS spectrum. That is, the spectrum shows the presence of a pre-edge peak at 683.5 eV that appears after the ball milling process. 1s Considering that this is a characteristic that starts from the -TM 3d g hybrid orbital, it can be inferred that a new Fe-F bond is formed from LiFeSO4F of Synthesis Example 1.

[0101] [Experimental Example 3: STXM analysis and TEM photographs] FIG. 5 shows electron diffraction patterns of LiFeSO4F according to Synthesis Example 1 and various reference materials.

[0102] Referring to FIG. 5, LiFeSO4F according to Synthesis Example 1 exhibited an electron diffraction pattern distinct from that of LiFeSO4F in the triplite and taborite phases, and exhibited peaks distinct from that of positive electrode active materials of other compositions.

[0103] FIG. 6 is a TEM photograph of LiFeSO4F obtained in Synthesis Example 1.

[0104] 6, it can be seen that LiFeSO4F prepared in Synthesis Example 1 is composed of 0.5 to 3.0 μm particles consisting of randomly distributed 4 to 8 nm grains. Here, LiFeSO4F prepared in Synthesis Example 1 may include an amorphous matrix and some grains forming crystalline particles.

[0105] [Experimental Example 4-1: Evaluation of Electrochemical Performance of Half-Cells - Charge / Discharge Profiles] 7 shows the charge / discharge profile of the half cell according to Preparation Example 2. Specifically, the electrochemical characteristics of the half cell according to Preparation Example 2 were measured at 25°C and 60°C, a current density (40 mA / g), and a voltage of 1.5 to 4.7V.

[0106] Referring to FIG. 7, the half-cell according to Example 1 exhibited a capacity of 145 mAh / g during the first charging process. In the case of the half-cell according to Example 1, the first discharge reaction started from about 3.9 V and reached about 3.59 V (vs. Li + In this voltage range, the reversible reaction occurs during the desorption / insertion of lithium ions in a-LiFeSO4F. 2+ / 3+ It can be assumed that this is due to the oxidation / reduction reaction of

[0107] It can be seen that the discharge voltage of the half-cell according to Example 1 is slightly lower than that of the half-cell according to Comparative Example 1 containing taboritic LiFeSO4F (up to 3.60 V) and that of Comparative Example 2 containing triplitic LiFeSO4F (up to 3.90 V).

[0108] Furthermore, the half-cell of Example 1 exhibited a substantially more sloped voltage profile due to the amorphous structural characteristics of the positive electrode active material compared to the half-cells of Comparative Examples 1 and 2. Specifically, oxidation / reduction peaks were observed at approximately 3.60 V and 3.90 V in the half-cells of Comparative Examples 1 and 2, respectively, while no clear oxidation / reduction peaks were observed in the half-cell of Example 1 in a similar voltage range.

[0109] The half-cells of Example 1, Comparative Examples 1 and 2 each had a voltage of 1.5 V (vs. Li + When discharged to a voltage of 2.2 V (or 2.6 V in the case of charging), the half-cell of Example 1, unlike Comparative Examples 1 and 2, exhibited a capacity at a discharge voltage of 2.2 V (or 2.6 V in the case of charging) and demonstrated a cumulative discharge capacity of 360 mAh / g (or an energy density of 906 Wh / kg) due to the inclusion of an amorphous cathode active material, unlike Comparative Examples 1 and 2. In contrast, the half-cells of Comparative Examples 1 and 2 exhibited almost no capacity below 3 V, demonstrating very low cumulative discharge capacities.

[0110] FIG. 8 shows the charge-discharge profile of the half cell according to Comparative Example 1 at 60°C.

[0111] FIG. 9 shows the charge-discharge profile of the half cell according to Comparative Example 2 at 60°C.

[0112] Referring to Figures 8 and 9, it can be seen that even when the cutoff voltage of the half-cells according to Comparative Examples 1 and 2 was lowered from 1.5 V to 1.2 V to induce the conversion reaction, neither of them exhibited significant capacity at voltages below 3 V.

[0113] [Experimental Example 4-2: Evaluation of Electrochemical Performance of Half-Cells - Differential Capacity Curve] 10 is a differential capacity curve of the half cell of Production Example 2. On the other hand, the differential capacity curve is a curve showing the differential value dQ / dV of capacity with respect to voltage based on the results of time and voltage under constant current conditions.

[0114] Referring to FIG. 10 and Table 1 below, it can be seen that the half-cell according to Example 1, unlike the half-cells according to Comparative Examples 1 and 2, exhibits a differential capacity dQ / dV peak below 3 V, but shows an almost constant differential capacity dQ / dV at 4.5 V, with no peak corresponding to 4.5 V.

[0115] [Table 1]

[0116] In addition, oxidation / reduction peaks were observed at 3.60 V and 3.90 V in the half-cells of Comparative Examples 1 and 2, respectively, but no clear peaks were observed in the half-cell of Example 1 in a similar voltage range.

[0117] [Experimental Example 5: Ex-situ hard XAS] FIG. 11a shows the charge / discharge profile of the half-cell according to Example 1 over time in the high voltage region (2.2 to 4.7 V) and the low voltage region (1.5 to 2.2 V).

[0118] FIG. 11b shows Fe K-edge XANES spectra for the charging process of the half-cell according to Example 1 in the high voltage region.

[0119] FIG. 11c shows Fe K-edge XANES spectra for the discharge process of the half-cell according to Example 1 in the high voltage region.

[0120] FIG. 11d shows Fe K-edge XANES spectra for the charging process of the half-cell according to Example 1 in the low voltage region.

[0121] FIG. 11e shows the Fe K-edge XANES spectrum for the discharge process of the half-cell according to Example 1 in the low voltage region.

[0122] The measurement method of Experimental Example 5 was the same as that of Example 2.

[0123] Referring to FIGS. 11a to 11c, the Fe K-edge line is easily shifted to higher and lower energy values ​​by the charge and discharge processes, respectively, which indicates that the electrochemical activity in this region is higher than that of Fe during the general lithium ion insertion / extraction process. 2+ / 3+ This may suggest that the reaction began with an oxidation / reduction reaction of

[0124] 11a, 11d, and 11e, when the half-cell according to Example 1 is further discharged to the low voltage region, the XAS spectrum of a-LiFeSO4F shows a changed profile, and Fe 0 It can be seen that the properties of the metallic phase are exhibited.

[0125] As shown in Figure 11e, a reversible reaction was observed during subsequent charging. During the electrochemical reaction in this region, an isosbestic point at 7121.2 eV was clearly observed, which coincides with the Fe metal reference spectrum. Meanwhile, isosbestic points can appear in XANES (X-ray absorption near-edge structure) when the fractions of reactants and products change reversibly while maintaining their respective chemical compositions in a two- or more-phase reaction.

[0126] FIG. 11f shows the Fe K-edge EXAFS spectra relative to the Fe metal reference (Ref), pristine, and the half-cell according to Example 1 when discharged to 1.5 V and charged to 2.2 V, respectively.

[0127] Referring to Figure 11f, EXAFS analysis confirmed the reversible conversion reaction of the pristine a-LiFeSO4F electrode. Specifically, the Fe-Fe bond peak at 2.2 Å may indicate the appearance of an Fe metal phase upon discharge (approximately 1.5 V) of the a-LiFeSO4F electrode, and it decreased upon recharge (approximately 2.2 V). In the pristine a-LiFeSO4F electrode, the partial residual intensity at 1.7 Å may be attributed to partially unreacted a-LiFeSO4F after discharge.

[0128] FIG. 11g is a TEM image of Fe metal contained within the discharged lithium compound matrix.

[0129] Referring to FIG. 11g, it can be seen that the Fe metal segments contained in the lithium compound matrix in the discharged state have particle sizes of 5 to 8 nm and form a body-centered cubic (BCC) crystal lattice along the <0111> axis.

[0130] FIG. 11h shows the F K-edge spectra of the half-cell according to Example 1 in a fully charged, half-discharged, or fully discharged state.

[0131] Referring to Figure 11h, to clarify the conversion reaction occurring in the low-voltage region, we investigated changes in fluorine local bonding. The results showed that the pre-edge, which indicates an F-Fe bond at the pristine electrode (triangle symbol), remained unchanged in the high-voltage region (>2.2 V), but significantly decreased to 1.5 V upon discharge, which is consistent with the dissociation of the F-Fe bond during the conversion reaction. In particular, although LiF is a common discharge product in the conversion reaction of fluorine-based compounds, the characteristic LiF signal (~700 eV) was not observed in the fully discharged state.

[0132] FIG. 11i shows the IR spectra of the half-cell according to Example 1 in a fully charged, half-discharged, and fully discharged state.

[0133] Referring to Figure 11i, the IR analysis results show that the discharge product is SO3F - -It can be confirmed that the compound is a polyanion-containing compound. Specifically, when the a-LiFeSO4F electrode is discharged to 1.5 V, the -1 , 831cm -1 , and 1,311 cm -1 A new peak appears at (triangle symbol), and it can be seen that the corresponding peak reversibly decreases upon recharging. This peak is a common SO3F - -OSO deformation vibrations of polyanion-containing compounds (550-590cm)-1 ), SF stretching vibration (~800cm -1 ), and SO3 stretching vibration (~1300cm -1 ) mode. These results suggest that the lithium-containing discharge product of the conversion reaction is LiSO3F, and considering the formation of Fe metal and the stoichiometry of LiFeSO4F, the residual reaction product after discharge can be estimated to be Li2O.

[0134] Experimental Example 6: Evaluation of electrochemical performance of half-cell according to Example 1 12 shows the charge-discharge profile for the two-step reaction (insertion and conversion reaction) of a-LiFeSO4F in the half cell according to Example 1. Specifically, the same measurement method as that of Experimental Example 6 was used as that of Experimental Example 4-1.

[0135] Referring to FIG. 12, the lithium ion insertion reaction may occur as shown in the following reaction scheme 1, and the conversion reaction may occur as shown in the following reaction scheme 2. [Reaction Scheme 1] a-FeSO4F+Li + +e - → a-LiFeSO4F (lithium ion insertion reaction at 3.59V) [Reaction Scheme 2] a-LiFeSO4F+2Li + +2e - →Fe + LiSO3F + Li2O (conversion reaction at 2.18V) In detail, the first oxidation-reduction reaction is a-LiFe 2+ SO4F and Fe 3+ Fe between SO4F 2+ / 3+ The initial reaction is an insertion reaction involving redox reactions, and the subsequent redox reactions are 0 , LiSO3F, Li2O, and a-LiFe 2+ Fe with reversible formation of SO4F 0 / 2+ It can be seen that this is achieved by a conversion reaction involving an oxidation-reduction reaction.

[0136] 13 shows the results of evaluating the electrochemical stability of the half-cell according to Example 1 against the long-term charge-discharge cycle. Specifically, the results of the electrochemical stability evaluation are the capacity retention and coulombic efficiency versus the number of cycles measured under conditions of 0.01 C-rate to 0.5 C-rate and temperature (25°C or 60°C).

[0137] 13, the half-cell according to Example 1 exhibited a capacity of 300 mAh / g or more for both reactions at room temperature, demonstrating a 90% capacity retention rate over 200 cycles, confirming that stable lithium ion insertion and conversion reactions were induced for a long period of time. Meanwhile, in contrast to the conventional cathode materials FeF2 and FeF3, which exhibit significant cycle degradation, the electrochemical profile and average voltage of a-LiFeSO4F were well maintained over 200 cycles without any noticeable degradation.

[0138] In addition, the half-cell according to Example 1, which contains a-LiFeSO4F positive electrode, exhibits a higher capacity of approximately 360 mAh / g at 60°C, and maintains approximately 98.6% of the initial capacity even after 200 cycles.

[0139] On the other hand, conventional electrodes based solely on the conversion reaction have had problems maintaining stable capacity due to various undesirable side effects of the conversion reaction (e.g., significant volume change, non-uniform composition, dissolution of transition metals, and cathode passive layer (CEI) formation due to electrolyte decomposition). While some of these side effects could be alleviated to improve reversibility (e.g., the use of a surface protection layer, a three-dimensional cathode structure, or a high-grade electrolyte system), additional processing steps were required. According to one aspect of the present invention, the amorphous structure of a-LiFeSO4F exhibits excellent electrochemical stability and cycling performance without the need for additional processing steps. It has been confirmed that the lithium ion insertion reaction of the a-LiFeSO4F electrode is stably maintained without significant performance degradation, despite the considerable bond rearrangement that is expected to occur during the conversion reaction.

[0140] FIG. 14a is the charge-discharge profile of the half-cell according to Example 1 at current densities of 0.02 A / g, 0.05 A / g, 0.1 A / g, 0.2 A / g, 0.5 A / g, 1 A / g, and 2 A / g.

[0141] FIG. 14b shows the discharge capacity of the half-cell according to Example 1 according to the number of cycles when the temperature is 60° C. and the current densities are 0.02 A / g, 0.05 A / g, 0.1 A / g, 0.2 A / g, 0.5 A / g, 1 A / g, and 2 A / g.

[0142] 14a and 14b, the specific capacity of the half-cell according to Example 1 tends to decrease as the applied current density increases from 0.02 A / g to 5 mA / g. However, the half-cell according to Example 1 can maintain a specific capacity of 250 mAh / g or more even at a current density of 1 A / g, which can be inferred to be an appropriate rate performance.

[0143] Moreover, since repeated conversion reactions induce morphological changes that lead to the reorganization of the electrode structure, the sudden increase in discharge capacity at the last 0.02 A / g can be assumed to be due to the activation of the initially deactivated stage.

[0144] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited to these, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims also fall within the scope of the present invention.

[0145] This research was supported by the Samsung Future Technology Development Program (Project Number: SRFC-TA1403-53).

Claims

1. A secondary battery including a positive electrode containing a transition metal-based lithium compound, In the differential capacity dQ / dV-voltage V graph of the secondary battery, There is no peak value between 3.8 and 4.0 V, A first peak is present at 2.5 to 2.7 V and a second peak is present at 2.1 to 2.3 V. Secondary battery.

2. The transition metal-based lithium compound includes an amorphous phase. The secondary battery according to claim 1 .

3. The differential capacity dQ / dV-voltage V graph of the secondary battery was obtained after 1 to 5 cycles at 0.01 C-rate to 0.5 C-rate and 25°C. The secondary battery according to claim 1 .

4. The transition metal-based lithium compound includes a compound represented by the following general formula 1: The secondary battery according to claim 1: [Formula 1] Li ｘ M ２－ｘ SO ４ A In the general formula 1, M is one or more elements selected from the group consisting of Fe, Mg, Ni, Co, Cr, Ti, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, and Bi; A is a halogen atom; 0.5≦x≦1.

5.

5. The transition metal-based lithium compound is LiFeSO ４ Including F. The secondary battery according to claim 1 .

6. The particle size D of the transition metal-based lithium compound ５０ is 0.5 to 3.0 μm, The secondary battery according to claim 1 .

7. The transition metal-based lithium compound is It comprises an amorphous matrix and crystalline grains. The secondary battery according to claim 1 .

8. The crystal grain includes a plurality of grains, The average size of each of the grains is 4 to 8 nm. The secondary battery according to claim 7 .

9. a negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte solution, The secondary battery according to claim 1 .

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