Sulfide-based solid electrolyte and lithium secondary battery comprising same

Abstract

According to the present disclosure, provided are: a sulfide-based solid electrolyte comprising a Li-P-S-based compound including an anion lattice structure represented by P1-bMbS4-aSea 3- (0<a≤1.5, 0<b<1, M being at least one element selected from the group consisting of Si, Ge, Sn, and Al); and a lithium secondary battery in which an electrolyte layer comprising the sulfide-based solid electrolyte is disposed on a positive electrode.

Description

Sulfide-based solid electrolyte and lithium secondary battery containing the same

[0001] The present disclosure provides a sulfide-based solid electrolyte and a lithium secondary battery including the same.

[0002]

[0003] Secondary batteries, which can be repeatedly charged and discharged, are widely used as power sources for portable electronic communication devices such as camcorders, mobile phones, and laptops, thanks to the advancements in the information and communication and display industries. Furthermore, battery packs containing secondary batteries are being developed and applied as power sources for eco-friendly vehicles such as hybrid vehicles.

[0004] Examples of secondary batteries include lithium secondary batteries, nickel-cadmium batteries, and nickel-hydrogen batteries. Among these, lithium secondary batteries are actively being researched and developed due to their high operating voltage and energy density per unit weight, as well as their advantages in charging speed and weight reduction.

[0005] A lithium secondary battery may include an electrode assembly including a positive electrode, a negative electrode, and a separator, and an electrolyte that impregnates the electrode assembly. The lithium secondary battery may further include an outer packaging material, for example, in the form of a pouch, that accommodates the electrode assembly and the electrolyte.

[0006] Additionally, there are all-solid-state batteries that use solid electrolytes instead of liquid electrolytes, and all-solid-state batteries can include inorganic solid electrolytes (sulfide, oxide) and organic solid electrolytes (polymer). For example, sulfide-based solid electrolytes have high ionic conductivity and formability, and can have improved ionic conductivity by including additional elements in addition to the basic elements Li, P, and S.

[0007] All-solid-state batteries do not use flammable organic solvents, preventing fire and explosion even in the event of a short circuit. Therefore, all-solid-state batteries can offer improved safety compared to lithium-ion batteries that use electrolytes.

[0008]

[0009] One object of the present disclosure is to provide a sulfide-based solid electrolyte with improved electrochemical properties.

[0010] An object of the present disclosure is to provide a lithium secondary battery with improved electrochemical characteristics.

[0011]

[0012] A sulfide-based solid electrolyte according to the present disclosure comprises a Li-PS compound. The Li-PS compound comprises an anion lattice structure represented by the following chemical formula 1.

[0013] [Chemical Formula 1]

[0014] P 1-b M b S 4-a Se a 3-

[0015] In chemical formula 1, 0 <a≤1.5, 0<b<1이고, M은 Si, Ge, Sn 및 Al로 구성된 그룹으로부터 선택된 적어도 하나의 원소이다.

[0016] In exemplary embodiments, the P-Si peak area ratio represented by the following formula 1 of the Li-PS compound may be 0.03 to 0.3.

[0017] [Formula 1]

[0018] P-Si peak area ratio = A / B

[0019] In Equation 1, A is the integral area of ​​the Si 2p peak appearing at 98 eV to 105 eV in the XPS spectrum obtained by analyzing the Li-PS compound using X-ray photoelectron spectroscopy (XPS), and B is the integral area of ​​the P 2p peak appearing at 130 eV to 135 eV.

[0020] In exemplary embodiments, the S-Si peak area ratio represented by the following formula 2 of the Li-PS compound may be 0.009 to 0.06.

[0021] [Formula 2]

[0022] S-Si peak area ratio = A / C

[0023] (In Equation 2, A is the integral area of ​​the peak of Si 2p appearing at 98 eV to 105 eV in the XPS spectrum obtained by analyzing the Li-PS compound using X-ray photoelectron spectroscopy (XPS), and C is the integral area of ​​the peak of S 2p appearing at 159 eV to 164 eV).

[0024] In exemplary embodiments, the P-Se peak area ratio represented by the following formula 3 of the Li-PS compound may be 1 to 2.

[0025] [Formula 3]

[0026] P-Se peak area ratio = D / B

[0027] In the above formula 3, B is the integral area of ​​the P 2p peak appearing at 130 eV to 135 eV in the XPS spectrum obtained by analyzing the Li-PS compound by X-ray photoelectron spectroscopy (XPS), and D is the integral area of ​​the Se KLM peak appearing at 135 eV to 140 eV.

[0028] In exemplary embodiments, the anion lattice structure may satisfy the following equation 4.

[0029] [Formula 4]

[0030] 0.3≤E / F≤0.95

[0031] In Equation 4, E is the Raman spectrum obtained by analyzing the Li-PS compound using Raman spectroscopy at 410 cm -1 430 cm inland -1 is the intensity of the peak appearing in , and F is Li 5.5 PS 4.5 Cl 1.5 The Raman spectrum obtained by analyzing the compound indicated by Raman spectroscopy is 410 cm -1 430 cm inland -1 is the intensity of the peak that appears in .

[0032] In exemplary embodiments, 0.01≤a≤0.8 and 0.01≤b≤0.2 may be satisfied.

[0033] In exemplary embodiments, the Li-PS compound may be an argyrodite structured compound, a thio-lithicon structured compound, a glass ceramic structured compound, or a glass structured compound.

[0034] In exemplary embodiments, the lattice constant of the Li-PS compound may be 9.86 Å to 10 Å.

[0035] In exemplary embodiments, the lithium ion conduction activation energy of the Li-PS compound may be 0.15 eV to 0.3 eV.

[0036] In exemplary embodiments, the Li-PS compound may be represented by the following chemical formula 2.

[0037] [Chemical Formula 2]

[0038] Li 6+b-c P 1-b M b S 5-a-c Se a X1+c

[0039] In the above chemical formula 2, a is 0 <a≤1.5, 0<b<1, 0<c≤1이고, X는 F, Cl, Br 및 I로 구성된 그룹으로부터 선택된 적어도 하나의 원소이고, M은 Si, Ge, Sn 및 Al로 구성된 그룹으로부터 선택된 적어도 하나의 원소이다.

[0040] A lithium secondary battery according to the present disclosure comprises: a positive electrode; and an electrolyte layer disposed on the positive electrode, wherein the electrolyte layer includes the sulfide-based solid electrolyte.

[0041] In exemplary embodiments, the lithium secondary battery includes a cathode opposite the cathode, and the electrolyte layer may be disposed between the cathode and the cathode.

[0042] In exemplary embodiments, the positive electrode or the negative electrode may include the sulfide-based solid electrolyte.

[0043]

[0044] The sulfide-based solid electrolyte according to the present disclosure can have improved ionic conductivity by including ion migration paths with increased stability and diameter. Accordingly, the movement speed of lithium ions can be increased, and an electrolyte layer with improved high-speed charge / discharge characteristics can be realized.

[0045] A lithium secondary battery according to the present disclosure can have a shortened charging time and improved coulombic efficiency by including the sulfide-based solid electrolyte.

[0046]

[0047] Figures 1 to 8 are XPS spectra of Li-PS compounds of Examples 1 to 4 and Comparative Examples 1 to 4.

[0048] Figures 9 and 10 are Raman spectra of the Li-PS compounds of Example 1 and Comparative Example 1.

[0049]

[0050] The sulfide-based solid electrolyte according to the present disclosure is P 1-b M b S 4-a Se a 3- A Li-PS compound including an anion lattice structure is included. In addition, a lithium secondary battery according to the present disclosure includes an electrolyte layer including the sulfide-based solid electrolyte.

[0051] Hereinafter, the present disclosure will be described in detail with reference to the attached drawings. However, these are merely exemplary and the present disclosure is not limited to the specific embodiments described as examples.

[0052] When the terms "above," "on," or "between" a component are used in this disclosure, this may include not only cases where a component is directly disposed, but also cases where one or more other components are present in between.

[0053] According to exemplary embodiments, the sulfide-based solid electrolyte includes a Li-PS-based compound. The Li-PS-based compound includes an anion lattice structure represented by the following chemical formula 1.

[0054] [Chemical Formula 1]

[0055] P 1-b M b S 4-a Se a 3-

[0056] In chemical formula 1, 0 <a≤1.5, 0<b<1이고, M은 Si, Ge, Sn 및 Al로 구성된 그룹으로부터 선택된 적어도 하나의 원소이다.

[0057] In the present disclosure, the term "anionic lattice structure" may refer to a portion of a lattice structure corresponding to an anion among structures present in a compound. The anionic lattice structure may include a single lattice structure, or may be a mixture of two or more lattice structures.

[0058] Solid electrolytes do not contain a separate solvent, and lithium ions can move through ion channels within the solid electrolyte without the need for a solvent or other medium. Therefore, securing ion channels within the solid electrolyte can increase lithium ion conductivity, thereby enabling the realization of a battery with improved high-rate characteristics.

[0059] According to exemplary embodiments, M including Si, Ge, Sn, Al, etc. may be substituted at the P site of the Li-PS compound, and Se may be substituted at the S site. M such as Si may have a larger ionic radius than the P atom, and Se may have a larger ionic radius than the S atom. Accordingly, the lattice spacing may increase, and the diameter of the ion migration path may become larger. The Li-PS compound may have an ion migration path through which lithium ions can smoothly move, thereby having improved lithium ion conductivity.

[0060] In exemplary embodiments, a in Chemical Formula 1 may be 0.01 or more and 1.5 or less, 0.01 to 1, 0.01 to 0.8, or 0.1 to 0.75. Furthermore, b in Chemical Formula 1 may be 0.01 or more and less than 1, 0.01 to 0.5, 0.01 to 0.2, or 0.05 to 0.15.

[0061] Within the above range, the lattice spacing of the Li-PS compound can be increased sufficiently to secure an ion movement path for lithium ions, and the electrochemical stability of the solid electrolyte can be maintained during battery charging and discharging.

[0062] In chemical formula 1, if a exceeds 1.5, there may be a problem in which some Se atoms cannot enter the lattice structure and form an impurity phase.

[0063] The Li-PS compound may include a halogen element. The halogen element may include F, Cl, Br, I, etc., and for example, the electrochemical stability and lithium ion conductivity of the Li-PS compound in which the halogen element includes Cl or Br may both be improved. For example, the halogen element may be substituted at the S site of the Li-PS compound, and a pore may be formed at the Li site. Accordingly, the crystal structure of the Li-PS compound may be stabilized, and the lithium ion conductivity may be improved.

[0064] In exemplary embodiments, the Li-PS compound may be represented by the following chemical formula 2.

[0065] [Chemical Formula 2]

[0066] Li 6+b-c P 1-b M b S 5-a-c Se a X 1+c

[0067] In the above chemical formula 2, 0 <a≤1.5, 0<b<1, 0<c≤1일 수 있다.

[0068] In some embodiments, in the above chemical formula 2, 0.01≤a≤1.5, 0.01≤a≤1, 0.01≤a≤0.8, or 0.01≤a≤0.75 may be satisfied.

[0069] In some embodiments, in the above chemical formula 2, 0.01≤b<1, 0.01≤b≤0.5, 0.01≤b≤0.2, or 0.05≤b≤0.15 may be satisfied.

[0070] In some embodiments, in the above chemical formula 2, 0.01≤c≤1, 0.01≤c≤0.9, 0.1≤b≤0.8, or 0.2≤b≤0.7 may be satisfied.

[0071] In the above chemical formula 2, X is a halogen element, and may be at least one element selected from the group consisting of F, Cl, Br, and I.

[0072] In the above chemical formula 2, M may be at least one element selected from the group consisting of Si, Ge, Sn, and Al.

[0073] In exemplary embodiments, the Li-PS compound may be an argyrodite structured compound, a thio-lithicon (e.g., LGPS), a glass ceramic structured compound, or a glass structured compound. In some embodiments, the Li-PS compound may be an argyrodite structured compound.

[0074] The above argyrodite structure may mean a crystal structure similar to or substantially identical to the ore Ag8GeS6. For example, the Li-PS compound may have a cubic phase at low temperatures and an orthorhombic phase at high temperatures.

[0075] In exemplary embodiments, the lattice constant of the Li-PS compound may be 9.86 Å to 10 Å. In some embodiments, the lattice constant of the Li-PS compound may be 9.87 Å to 9.95 Å or 9.88 Å to 9.93 Å.

[0076] Within the above range, a path through which lithium ions can move is secured, thereby increasing the linearity of the lithium ion movement path. Accordingly, a battery with improved high-speed charge / discharge characteristics can be realized.

[0077] In exemplary embodiments, the P-Si peak area ratio represented by the following formula 1 of the Li-PS compound may be 0.03 to 0.3.

[0078] [Formula 1]

[0079] P-Si peak area ratio = A / B

[0080] In Equation 1, A is the integral area of ​​the Si 2p peak appearing at 98 eV to 105 eV in the XPS spectrum obtained by analyzing the Li-PS compound using X-ray photoelectron spectroscopy (XPS), and B is the integral area of ​​the P 2p peak appearing at 130 eV to 135 eV.

[0081] Within the above P-Si peak area ratio range, the amount of P sites substituted with M elements is appropriate, and thus the lithium ion conductivity and electrochemical stability of the Li-PS compound can be improved.

[0082] In exemplary embodiments, the S-Si peak area ratio represented by the following formula 2 of the Li-PS compound may be 0.009 to 0.06.

[0083] [Formula 2]

[0084] S-Si peak area ratio = A / C

[0085] In Equation 2, A is the integral area of ​​the Si 2p peak appearing at 98 eV to 105 eV in the XPS spectrum obtained by analyzing the Li-PS compound using X-ray photoelectron spectroscopy (XPS), and C is the integral area of ​​the S 2p peak appearing at 159 eV to 164 eV.

[0086] Within the above S-Si peak area ratio range, the interaction between S and Si is appropriate, so that the crystal structure stability of the Li-PS compound can be improved.

[0087] In exemplary embodiments, the P-Se peak area ratio represented by the following formula 3 of the Li-PS compound may be 1 to 2.

[0088] [Formula 3]

[0089] P-Se peak area ratio = D / B

[0090] In the above formula 3, B is the integral area of ​​the P 2p peak appearing at 130 eV to 135 eV in the XPS spectrum obtained by analyzing the Li-PS compound by X-ray photoelectron spectroscopy (XPS), and D is the integral area of ​​the Se KLM peak appearing at 135 eV to 140 eV.

[0091] Typically, XPS analysis of Li-PS compounds reveals that the Se peak appears at 52 eV to 58 eV as Se 3d, but overlaps with the Li 1s peak, making it difficult to separate and distinguish them. However, in the XPS spectrum of the Li-PS compounds of the present disclosure, a Se peak is observed within a range of approximately 135 eV to 140 eV, which appears to be due to electron emission from the inner shell (K, L, M electron shell) of Se atoms in this region, and can be referred to as the Se KLM peak.

[0092] Within the above range, the amount of S sites substituted with Se is appropriate, and thus the lithium ion conductivity and electrochemical stability of the Li-PS compound can be improved.

[0093] In exemplary embodiments, the XPS analysis may be performed using a method known in the art, and is not particularly limited. For example, the XPS analysis may be performed using a 250Xi instrument from Thermo Fisher Scientific. The analysis may be performed under conditions of an Al k alpha source (1486.68 eV, 900 μm beam size).

[0094] In exemplary embodiments, the anion lattice structure in the Li-PS compound may satisfy Equation 4 below. In some embodiments, the anion lattice structure in the Li-PS compound may satisfy Equation 5 below.

[0095] [Formula 4]

[0096] 0.3≤E / F≤0.95

[0097] [Formula 5]

[0098] 0.5≤E / F≤0.9

[0099] In Equations 4 and 5, E is the Raman spectrum obtained by analyzing the Li-PS compound using Raman spectroscopy at 410 cm -1 430 cm inland -1 is the intensity of the peak appearing in , and F is Li 5.5 PS 4.5 Cl 1.5 The Raman spectrum obtained by analyzing the compound indicated by Raman spectroscopy is 410 cm -1 430 cm inland -1 is the intensity of the peak that appears in .

[0100] Among the Raman spectra obtained by analyzing the above Li-PS compound by Raman spectroscopy, 410 cm -1 430 cm inland -1 The peak appearing in may be derived from the anion lattice structure represented by the above chemical formula 1. The above Li 5.5 PS 4.5 Cl 1.5 The Raman spectrum obtained by analyzing the compound indicated by Raman spectroscopy is 410 cm -1 430 cm inland -1 The peaks appearing in PS4 3- It may be derived from the anion lattice structure.

[0101] Among the Raman spectra of the above Li-PS compounds, 410 cm -1 430 cm inland -1 The intensity of the peaks appearing in is the reference compound Li not substituted with M and Se. 5.5 PS 4.5 Cl 1.5The peak intensity may be lower than that observed at a similar position in the Raman spectrum of the compound represented by .

[0102] Raman spectroscopy analysis can be performed using any method known in the art, with no particular limitations. For example, Raman analysis can be performed using Renishaw's inVia instrument. The analysis can be performed under conditions of a wavelength of approximately 532 nm.

[0103] In some embodiments, the ionic conductivity of the Li-PS compound may be 1 mS / cm or more, or 6 mS / cm to 10 mS / cm. Accordingly, the internal resistance of the battery may be reduced, and the capacity characteristics and output characteristics may be further improved.

[0104] The above ionic conductivity can be measured by a method known in the art and is not particularly limited.

[0105] For example, it can be measured using the VMP-300 equipment of Biologics. The measurement can be performed under the condition of AC impedance with an amplitude of about 10 mV in the frequency range of 7 MHz to 100 mHz.

[0106] In exemplary embodiments, the lithium ion conduction activation energy of the Li-PS compound may be 0.1 eV to 0.3 eV. In some embodiments, the lithium ion conduction activation energy of the Li-PS compound may be 0.15 eV to 0.25 eV. Within this range, the activation energy for initiating lithium ion conduction may be low, and lithium ions may move more quickly when an external power source is applied. Accordingly, a battery having a fast charging speed may be implemented.

[0107] The above lithium ion conduction activation energy can be measured using a method known in the art and is not particularly limited. For example, the ionic conductivity can be measured as a function of temperature and calculated using the Arrhenius relationship in Equation 6 below.

[0108] [Formula 6]

[0109] σ = A * exp(-Ea / kT)

[0110] In the above equation 6, σ is ionic conductivity, A is a frequency factor, k is Boltzmann constant, T is absolute temperature, and Ea is activation energy. In some embodiments, the sulfide-based solid electrolyte may further include another sulfide-based compound in addition to the Li-PS-based compound. For example, the sulfide-based solid electrolyte may include a sulfide-based compound different from the Li-PS-based compound, such as Li2S-P2S5, Li 10 GeP2S 12 , Li 10 SnP2S 12 , Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 , Li 10 (Si 0.5 Ge 0.5 )P2S 12 , Li 10 (Ge 0.5 Sn 0.5 )P2S 12 , Li 10 (Si 0.5 Sn 0.5 )P2S 12 , Li 10 GeP2S 11.7 O 0.3 , Li 9.6 P3S 12 , Li9P3S9O3, Li 10.35 Ge 1.35 P 1.65 S 12 , Li 10.35 Si 1.35 P 1.65 S 12 , Li9.81 Sn 0.81 P 2.19 S 12 , Li 9.42 Si 1.02 P 2.1 S 9.96 O 2.04 , Li6PS5Cl, etc. may be further included.

[0111] A lithium secondary battery according to the present disclosure comprises: a positive electrode; and an electrolyte layer disposed on the positive electrode and including the sulfide-based solid electrolyte.

[0112] In some embodiments, the positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. For example, the positive electrode active material layer may include a positive electrode active material, a solid electrolyte, a binder, and / or a conductive material. For example, the positive electrode slurry may be prepared by mixing and stirring the positive electrode active material with the sulfide-based electrolyte, a conductive material, and / or a binder, and the positive electrode slurry may be applied to the positive electrode current collector, dried, and pressed to prepare the positive electrode.

[0113] The positive electrode collector may include stainless steel, nickel, aluminum, titanium, copper or an alloy thereof, for example, aluminum or an aluminum alloy.

[0114] The above positive electrode active material may include a compound represented by the following chemical formula 3.

[0115] [Chemical Formula 3]

[0116] Li x Ni y Me 1-y O2

[0117] In the above chemical formula 3, 0.95≤x≤1.08, 0.5≤y<1, and Me may be Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Ba, Zr, or a combination thereof.

[0118] In one embodiment, the positive electrode active material comprises nickel (Ni) and may further comprise at least one of cobalt (Co) and manganese (Mn). For example, a nickel-cobalt-manganese (NCM) lithium oxide may be used as the positive electrode active material particles.

[0119] For example, nickel (Ni) can be provided as a metal associated with the capacity of lithium secondary batteries. While a higher nickel content can improve the capacity and output of a lithium secondary battery, excessive nickel content can shorten its lifespan and compromise mechanical and electrical stability.

[0120] In one embodiment, the conductivity or resistance of a lithium secondary battery can be improved by cobalt (Co), and the mechanical and electrical stability of a lithium secondary battery can be improved by manganese (Mn).

[0121] The chemical structure represented by Chemical Formula 3 represents the bonding relationship included in the layered structure or crystal structure of the positive electrode active material particles and does not exclude other additional elements. For example, Me includes Co and / or Mn, and Co and Mn can serve as the main active element of the positive electrode active material together with Ni. Chemical Formula 2 is provided to express the bonding relationship of the above main active elements and should be understood as a formula encompassing the introduction and substitution of additional elements.

[0122] In one embodiment, in addition to the main active element, auxiliary elements may be further included to enhance the chemical stability of the positive electrode active material or the layered structure / crystal structure. The auxiliary elements may be incorporated into the layered structure / crystal structure to form bonds, and in this case, it should be understood that they are also included within the chemical structure range represented by Chemical Formula 3.

[0123] In one embodiment, the solid electrolyte included in the positive electrode may include the above-described sulfide-based solid electrolyte.

[0124] The conductive material may be included to promote electron transfer between the positive electrode active material particles. For example, the conductive material may include a carbon-based conductive material such as graphite, carbon black, graphene, carbon nanotubes, and / or a metal-based conductive material including a perovskite material such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0125] In some embodiments, the positive electrode active material layer may further include a binder. For example, the binder may include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, nitrile butadiene rubber, or the like.

[0126] In some embodiments, the lithium secondary battery may include an anode facing the cathode, and the electrolyte layer may be disposed between the anode and the anode. The anode may include an anode current collector, and in some embodiments, may include an anode current collector and an anode active material layer disposed on the anode current collector. For example, the anode active material layer may include an anode active material, a solid electrolyte, a binder, and / or a conductive material. For example, an anode slurry may be prepared by mixing and stirring an anode active material with a solid electrolyte, a conductive material, and / or a binder, and the anode slurry may be applied to an anode current collector, dried, and pressed to prepare an anode.

[0127] The negative electrode current collector may include gold, stainless steel, nickel, aluminum, titanium, copper or an alloy thereof, for example, copper or a copper alloy.

[0128] The negative electrode active material may be a material capable of absorbing and desorbing lithium ions. Examples thereof include carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers; lithium alloys; and silicon or tin. Examples of the amorphous carbon include hard carbon, coke, mesocarbon microbeads (MCMB) calcined at 1500°C or lower, and mesophase pitch-based carbon fibers (MPCF). Examples of the crystalline carbon include graphite-based carbons such as natural graphite, graphitized coke, graphitized MCMB, and graphitized MPCF. Elements included in the lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, and indium.

[0129] The above-described negative electrode active material layer may further include a negative electrode binder and / or a negative electrode conductive material. The negative electrode binder and conductive material may be materials substantially the same as or similar to the positive electrode binder and conductive material described above. For example, the negative electrode binder may be an aqueous binder such as styrene-butadiene rubber (SBR). In addition, for example, the negative electrode binder may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0130] In one embodiment, the solid electrolyte included in the cathode may include the above-described sulfide-based solid electrolyte.

[0131] According to exemplary embodiments, an electrolyte layer is interposed between the positive electrode and the negative electrode. The electrolyte layer includes the sulfide-based solid electrolyte, and may further include a polymer electrolyte, an oxide-based solid electrolyte, or the like. For example, the lithium secondary battery may be provided as an all-solid-state battery.

[0132] In some embodiments, the oxide-based solid electrolyte may include a metal oxide or an ion-conducting compound containing oxygen. For example, examples of the oxide-based solid electrolyte include Al2O3, ZnO2, Ce2O3, TiO2, ZrO2, HfO2, MnO2, MgO, WO 2, Metal oxides such as V2O5, LLTO compounds, Li6La2CaTa2O 12 , Li6La2ANb2O 12 (A is Ca or Sr), Li2Nd3TeSbO 12 , Li3BO 2.5 N 0.5 , Li9SiAlO8, LAGP compounds, LATP compounds, Li 1+x Ti 2-x Al x Si y (PO4) 3-y (0≤x≤1, 0≤y≤1), LiAl x Zr 2-x (PO4)3(0≤x≤1, 0≤y≤1), LiTi x Zr 2-x (PO4)3 (wherein, 0≤x≤1, 0≤y≤1), LISICON compounds, LIPON compounds, perovskite compounds, NASICON compounds, and LLZO compounds can be mentioned.

[0133] In one embodiment, one of the positive electrode and the negative electrode may be lithium metal or a lithium alloy.

[0134] For example, if the positive or negative electrode is a lithium electrode, the solid electrolyte layer may decompose upon contact with lithium metal. Furthermore, operating the secondary battery at relatively high voltages may accelerate the breakdown and structural changes of the solid electrolyte.

[0135] According to one embodiment, the electrochemical stability of the solid electrolyte layer can be further enhanced by including the aforementioned sulfide-based solid electrolyte. Accordingly, even when operated at high voltage or in contact with a lithium electrode, the internal structure of the solid electrolyte can be maintained stably, thereby improving the lifespan characteristics and stability of the secondary battery.

[0136] According to exemplary embodiments, an electrode cell is defined by an anode, a cathode, and a solid electrolyte layer, and a plurality of the electrode cells may be stacked to form an electrode assembly. For example, the electrode assembly may be formed through winding, lamination, folding, or the like.

[0137] The above electrode assembly may be housed within a case to define a lithium secondary battery. The lithium secondary battery may be manufactured in a cylindrical, square, pouch, or coin shape using, for example, a can.

[0138] Electrode tabs (positive electrode tab and negative electrode tab) may protrude from the positive electrode current collector and the negative electrode current collector, respectively, and may extend to one side of the case of the secondary battery. The electrode tabs may be fused together with the one side of the case to form electrode leads (positive electrode lead and negative electrode lead) that extend or are exposed to the outside of the case.

[0139] The embodiments of the present disclosure described above include the following aspects and can be implemented through at least one of the following aspects.

[0140] A sulfide-based solid electrolyte according to the first aspect of the present disclosure comprises a Li-PS-based compound. The Li-PS-based compound comprises an anion lattice structure represented by the following chemical formula 1.

[0141] [Chemical Formula 1]

[0142] P 1-b M b S 4-a Se a 3-

[0143] In chemical formula 1, 0 <a≤1.5, 0<b<1이고, M은 Si, Ge, Sn 및 Al로 구성된 그룹으로부터 선택된 적어도 하나의 원소이다.

[0144] In the first aspect, according to the second aspect, the P-Si peak area ratio of the Li-PS compound represented by the following formula 1 may be 0.03 to 0.3.

[0145] [Formula 1]

[0146] P-Si peak area ratio = A / B

[0147] In Equation 1, A is the integral area of ​​the Si 2p peak appearing at 98 eV to 105 eV in the XPS spectrum obtained by analyzing the Li-PS compound using X-ray photoelectron spectroscopy (XPS), and B is the integral area of ​​the P 2p peak appearing at 130 eV to 135 eV.

[0148] In the first or second aspect, according to the third aspect, the S-Si peak area ratio of the Li-PS compound represented by the following formula 2 may be 0.009 to 0.06.

[0149] [Formula 2]

[0150] S-Si peak area ratio = A / C

[0151] (In Equation 2, A is the integral area of ​​the peak of Si 2p appearing at 98 eV to 105 eV in the XPS spectrum obtained by analyzing the Li-PS compound using X-ray photoelectron spectroscopy (XPS), and C is the integral area of ​​the peak of S 2p appearing at 159 eV to 164 eV).

[0152] In any one of the first to third aspects, according to the fourth aspect, the P-Se peak area ratio of the Li-PS compound represented by the following formula 3 may be 1 to 2.

[0153] [Formula 3]

[0154] P-Se peak area ratio = D / B

[0155] In the above formula 3, B is the integral area of ​​the P 2p peak appearing at 130 eV to 135 eV in the XPS spectrum obtained by analyzing the Li-PS compound by X-ray photoelectron spectroscopy (XPS), and D is the integral area of ​​the Se KLM peak appearing at 135 eV to 140 eV.

[0156] In any one of the first to fourth aspects, according to the fifth aspect, the anion lattice structure can satisfy the following equation 4.

[0157] [Formula 4]

[0158] 0.3≤E / F≤0.95

[0159] In Equation 4, E is the Raman spectrum obtained by analyzing the Li-PS compound using Raman spectroscopy at 410 cm -1 430 cm inland -1 is the intensity of the peak appearing in , and F is Li 5.5 PS 4.5 Cl 1.5The Raman spectrum obtained by analyzing the compound indicated by Raman spectroscopy is 410 cm -1 430 cm inland -1 is the intensity of the peak that appears in .

[0160] In any one of the first to fifth aspects, according to the sixth aspect, 0.01≤a≤0.8 and 0.01≤b≤0.2 may be satisfied.

[0161] In any one of the first to sixth aspects, according to the seventh aspect, the Li-PS compound may be an azirodite structure compound, a thio-lisicon structure compound, a glass ceramic structure compound, or a glass structure compound.

[0162] In any one of the first to seventh aspects, according to the eighth aspect, the lattice constant of the Li-PS compound may be 9.86 Å to 10 Å.

[0163] In any one of the first to eighth aspects, according to the ninth aspect, the lithium ion conduction activation energy of the Li-PS compound may be 0.15 eV to 0.3 eV.

[0164] In any one of the first to ninth aspects, according to the tenth aspect, the Li-PS compound may be represented by the following chemical formula 2.

[0165] [Chemical Formula 2]

[0166] Li 6+b-c P 1-b M b S 5-a-c Se a X 1+c

[0167] In the above chemical formula 2, a is 0 <a≤1.5, 0<b<1, 0<c≤1이고, X는 F, Cl, Br 및 I로 구성된 그룹으로부터 선택된 적어도 하나의 원소이고, M은 Si, Ge, Sn 및 Al로 구성된 그룹으로부터 선택된 적어도 하나의 원소이다.

[0168] A lithium secondary battery according to an eleventh aspect of the present disclosure comprises: a positive electrode; and an electrolyte layer disposed on the positive electrode, wherein the electrolyte layer comprises the sulfide-based solid electrolyte according to any one of the first to tenth aspects.

[0169] In the eleventh aspect, according to the twelfth aspect, the lithium secondary battery includes a negative electrode facing the positive electrode, and the electrolyte layer can be disposed between the positive electrode and the negative electrode.

[0170] In the 12th aspect, according to the 13th aspect, the positive electrode or the negative electrode may include the sulfide-based solid electrolyte.

[0171] Hereinafter, embodiments of the present invention will be further described with reference to specific experimental examples. The examples and comparative examples included in the experimental examples are merely illustrative of the present invention and do not limit the scope of the appended claims. It will be apparent to those skilled in the art that various modifications and variations of the examples are possible within the scope and technical spirit of the present invention, and it is also natural that such modifications and variations fall within the scope of the appended claims.

[0172]

[0173] Example 1

[0174] Manufacturing of sulfide-based solid electrolytes and electrolyte layers

[0175] Li2S, P2S5, LiCl, Li2Se and SiS2 were milled in a molar ratio of 1.265:0.485:1.5:0.75:0.03 using a Fritsch TMThe mixture was prepared by putting it into a P-6 model and milling it for 10 hours with an energy of 24 to 30 G.

[0176] The above mixture was heat treated at 550°C in an argon atmosphere for 6 hours to obtain Li 5.53 P 0.97 Si 0.03 S 3.75 Se 0.75 Cl 1.5 A Li-PS compound having the composition was prepared.

[0177] Manufacturing of lithium secondary batteries

[0178] A secondary battery was manufactured using the Li-PS compound manufactured above. Specifically, the Li-PS compound, cathode active material (NCM811), binder (NBR), and conductive material (Super P) were mixed in a mass ratio of 68:28:2:2, respectively, to manufacture a cathode slurry.

[0179] The above positive electrode slurry was uniformly applied onto an aluminum foil (15 μm thick) and dried to manufacture a positive electrode.

[0180] Li-PS compound was placed in a SUS circular mold with a diameter of Φ13 and molded using a uniaxial cold isostatic pressing (CIP) at 80 MPa to obtain a density of 10 mg / cm. 2 Solid electrolyte pellets were manufactured.

[0181] The positive electrode is placed on one side of the solid electrolyte pellet at 10 mg / cm 2 After being placed on one side and pressed at 350 MPa to pelletize, an In foil was placed on the other side and pressed at 50 MPa to manufacture an electrode cell having a structure of a cathode composite-solid electrolyte-In cathode. The electrode cell was assembled into a coin cell outer case with a diameter of Φ20.

[0182]

[0183] Examples 2 to 4 and Comparative Examples 1 to 4

[0184] A Li-PS compound and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the molar ratios of Li2S, P2S5, LiCl, Li2Se, and SiS2 and the composition of the Li-PS compound were adjusted as shown in Table 1 below. In the composition, the values ​​corresponding to a, b, and c in Chemical Formula 2 are written in parentheses.

[0185] Composition Mixing Molar RatioLi2SP2S5LiClLi2SeSiS2Example 1Li 5.53 P 0.97 Si 0.03 S 3.75 Se 0.75 Cl 1.5 (a=0.75, b=0.03, c=0.5)1.2650.4851.50.750.03Example 2Li 5.56 P 0.94 Si 0.06 S 3.75 Se 0.75 Cl 1.5 (a=0.75, b=0.06, c=0.5)1.280.471.50.750.06Example 3Li 5.62 P 0.88 Si 0.12 S 3.75 Se 0.75 Cl 1.5 (a=0.75, b=0.12, c=0.5)1.310.441.50.750.12Example 4Li 5.75 P 0.75 Si 0.25 S 3.75 Se 0.75 Cl 1.5 (a=0.75, b=0.25, c=0.5)1.3750.3751.50.750.25Comparative example 1Li 5.5 P1S 4.5 Cl 1.5 (a=0, b=0, c=0.5)20.51.500Comparative example 2Li 5.56 P 0.94 Si 0.06 S 4.5 Cl 1.5 (a=0, b=0.06, c=0.5)2.030.471.500.06Comparative example 3Li 5.5 P1S3.75 Se 0.75 Cl 1.5 (a=0.75, b=0, c=0.5)1.250.51.50.750Comparative example 4Li 5.6 P 0.9 Si 0.1 S 2.5 Se2Cl 1.5 (a=2, b=0.1, c=0.5)0.050.451.520.1

[0186]

[0187] Experimental Example 1: Spectroscopic Analysis of Li-PS Compounds

[0188] (1) XPS analysis

[0189] Analysis was performed on the Li-PS compounds of the examples and comparative examples using X-ray photoelectron spectroscopy (XPS). Specifically, XPS analysis was performed on the Li-PS compounds of the examples and comparative examples using a 250Xi device from Thermo Fisher Scientific under the conditions of an Al k alpha source (1486.68 eV, 900 μm beam size), and spectra were obtained for P, Si, S, and Se.

[0190] From the XPS spectrum, the Si 2p peak appearing at 98 eV to 105 eV, the P 2p peak appearing at 130 eV to 135 eV, the Se KLM peak appearing at 135 eV to 140 eV, and the S 2p peak appearing at 159 eV to 164 eV were confirmed. The integrated area of ​​each peak was calculated to calculate the P-Si peak area ratio according to Equation 1, the S-Si peak area ratio according to Equation 2, and the P-Se peak area ratio according to Equation 3, which are shown in Table 2 below.

[0191] XPS spectra of the Li-PS compounds of Examples 1 to 4 and Comparative Examples 1 to 4 are shown in FIGS. 1 to 8, respectively.

[0192] (2) Raman analysis

[0193] The Li-PS compounds of the Examples and Comparative Examples were analyzed by Raman spectroscopy. Specifically, Raman analysis was performed on the Li-PS compounds of the Examples and Comparative Examples in the 532 nm wavelength range using Renishaw's inVia equipment, and spectra were obtained.

[0194] 410 cm of all Raman spectra -1 430 cm inland -1 Peaks were observed in the range of . Accordingly, the peak intensities of the examples and comparative examples were calculated as a ratio to the peak intensity of comparative example 1 and are shown in Table 2 below.

[0195] The Raman spectra of the Li-PS compounds of Example 1 and Comparative Example 1 are shown in FIG. 9 and FIG. 10, respectively.

[0196] (3) Ionic conductivity measurement

[0197] The ionic conductivity of the Li-PS compounds used in the above-described examples and comparative examples was measured using electrochemical impedance spectroscopy (EIS).

[0198] Specifically, the solid electrolyte powders of the examples and comparative examples were placed in a PET circular mold with a diameter of Φ13 and a density of 100 mg / cm. 2 A solid electrolyte pellet was manufactured by adding a solid electrolyte and molding it using a uniaxial cold isostatic pressing (CIP) at 380 MPa. The ionic conductivity was measured by applying an AC voltage to the solid electrolyte pellet using a VMP-300 device from Biologics, and the results are shown in Table 3 below. The measurement was performed under AC impedance conditions with an amplitude of approximately 10 mV in the frequency range of 7 MHz to 100 mHz.

[0199] (4) Lithium ion conduction activation energy

[0200] For the Li-PS compounds of the examples and comparative examples, the ionic conductivity according to temperature was measured in the same manner as in (3) above, and the lithium ion conduction activation energy was calculated using the Arrhenius relationship of Equation 6 described above. The calculated values ​​are shown in Table 3 below.

[0201] XPS analysisRaman peak integral area formula 1 formula 2 formula 3 4S 2pSe KLMP 2pSi 2pExample 118336657546031780.03860.00971.430.59Example 215041571335074010.11430.02661.520.42Example 313427492528357390.26060.05511.670.31Example 482395015280210250.36580.12441.790.21Comparative example 110029-1952-0001Comparative example 215745-33863980.11720.025200.36Comparative example 3859131312193-001.420.63Comparative example 411051940532564250.13050.38455.960.11

[0202]

[0203] Lithium ion conduction activation energy (eV) Ion conductivity (mS / cm) Example 10.28.11 Example 20.159.52 Example 30.198.25 Example 40.246.88 Comparative Example 10.285.54 Comparative Example 20.275.89 Comparative Example 30.266.45 Comparative Example 40.420.8

[0204]

[0205] Referring to Tables 2 and 3 above, the Li-PS compounds of the examples had low lithium ion conduction activation energy by including an anion lattice structure represented by Chemical Formula 1, and thus the ion conductivity was improved compared to the comparative examples.

[0206] In particular, the Li-PS compounds of Examples 1 to 3 had a P-Si peak area ratio of 0.03 to 0.3 according to Equation 1, and a S-Si peak area ratio of 0.009 to 0.06 according to Equation 2. In addition, the Li-PS compounds of the Examples had a Raman spectrum of 410 cm compared to Comparative Example 1. -1 430 cm inland -1 The intensity of the peaks observed within the range was reduced, and the lithium ion conduction activation energy was lowered, resulting in a particularly improved ionic conductivity.

[0207] On the other hand, in the Li-PS compounds of the comparative examples, a was 0 or b was 0 in chemical formula 1. Alternatively, the P-Si peak area ratio according to chemical formula 1 of the Li-PS compounds of the comparative examples was too large or the S peak area ratio according to chemical formula 2 was too large, and thus the ionic conductivity was lower than that of the Li-PS compounds of the examples.

[0208]

[0209] Experimental Example 2: Battery Characteristics Evaluation

[0210] (1) Evaluation of high-speed charging characteristics

[0211] The fabricated coin cell was charged and discharged at 0.1C for the first three cycles at a temperature of 30℃ with a cut-off charge of 4.3V and a discharge of 2.5V, and the discharge capacity (B1) in the first cycle was measured. Thereafter, two cycles of charge and discharge were performed at a rate of 0.2C, and two cycles of charge and discharge were performed at a rate of 0.5C. Thereafter, charge and discharge were performed at 1C, and the discharge capacity (B2) was measured.

[0212] The high-rate capacity characteristics were calculated according to Equation 7 below as a percentage of the discharge capacity (B2) at high rate (1C) to the discharge capacity (B1) at low rate (0.1C), and are shown in Table 4 below.

[0213] [Formula 7]

[0214] High-rate capacity characteristic (%) = B2 / B1 × 100%

[0215]

[0216] (2) Coulomb efficiency evaluation

[0217] The above-mentioned manufactured coin cell was charged (CC-CV 0.1C, 4.3V, 0.01C cut-off) and discharged (CC 0.1C, 2.5V cut-off) at 30°C to measure the initial charge and discharge capacities. The initial efficiency was calculated according to Equation 8 below as a percentage of the initial discharge capacity (A2) to the initial charge capacity (A1), as shown in Equation 2 below, and is shown in Table 4 below.

[0218] [Formula 8]

[0219] Initial efficiency (%) = A2 / A1 × 100%

[0220] High-rate capacity characteristics (%) Initial Coulombic efficiency (%) Example 168.181.6 Example 273.482.8 Example 368.481.7 Example 467.480.9 Comparative example 160.777.5 Comparative example 262.778.1 Comparative example 365.980.5 Comparative example 441.070.8

[0221] Referring to Table 4 above, the lithium secondary batteries of the examples exhibited a fast lithium ion movement rate during rapid charging, resulting in a small difference in capacity during high-rate charging compared to low-rate charging. In addition, the lithium secondary batteries of the examples exhibited high coulombic efficiency during initial charge and discharge, resulting in high energy efficiency.

[0222] On the other hand, the lithium secondary batteries of the comparative examples had significantly lower capacities at high rates of charging compared to those at low rates, and their coulombic efficiency also decreased.

[0223] The above description is merely an example of applying the principles of the present disclosure, and other configurations may be included without departing from the scope of the present invention.

Claims

1. A sulfide-based solid electrolyte comprising a Li-PS compound, wherein the Li-PS compound comprises an anion lattice structure represented by the following chemical formula 1: [Chemical Formula 1] P 1-b M b WITH 4-a With a 3- (In chemical formula 1, 0 <a≤1.5, 0<b<1이고, M은 Si, Ge, Sn 및 Al로 구성된 그룹으로부터 선택된 적어도 하나의 원소임).

2. In the first paragraph, a sulfide-based solid electrolyte in which the P-Si peak area ratio represented by the following formula 1 of the Li-PS-based compound is 0.03 to 0.3: [Formula 1] P-Si peak area ratio = A / B (In Equation 1, A is the integrated area of ​​the Si 2p peak appearing at 98 eV to 105 eV in the XPS spectrum obtained by analyzing the Li-PS compound using X-ray photoelectron spectroscopy (XPS), and B is the integrated area of ​​the P 2p peak appearing at 130 eV to 135 eV).

3. In the first paragraph, a sulfide-based solid electrolyte in which the S-Si peak area ratio represented by the following formula 2 of the Li-PS-based compound is 0.009 to 0.06: [Formula 2] S-Si peak area ratio = A / C (In Equation 2, A is the integral area of ​​the peak of Si 2p appearing at 98 eV to 105 eV in the XPS spectrum obtained by analyzing the Li-PS compound using X-ray photoelectron spectroscopy (XPS), and C is the integral area of ​​the peak of S 2p appearing at 159 eV to 164 eV).

4. In the first paragraph, a sulfide-based solid electrolyte in which the P-Se peak area ratio represented by the following formula 3 of the Li-PS-based compound is 1 to 2: [Formula 3] P-Se peak area ratio = D / B (In the above formula 3, B is the integral area of ​​the P 2p peak appearing at 130 eV to 135 eV in the XPS spectrum obtained by analyzing the Li-PS compound by X-ray photoelectron spectroscopy (XPS), and D is the integral area of ​​the Se KLM peak appearing at 135 eV to 140 eV).

5. In the first paragraph, the anion lattice structure is a sulfide-based solid electrolyte that satisfies the following equation 4: [Formula 4] 0.3≤E / F≤0.95 (In Equation 4, E is the Raman spectrum obtained by analyzing the Li-PS compound using Raman spectroscopy at 410 cm -1 430 cm inland -1 is the intensity of the peak appearing in , and F is Li 5.5 PS 4.5 Cl 1.5 The Raman spectrum obtained by analyzing the compound indicated by Raman spectroscopy is 410 cm -1 430 cm inland -1 (is the intensity of the peak that appears in ).

6. A sulfide-based solid electrolyte in the first paragraph, wherein 0.01≤a≤0.8 and 0.01≤b≤0.

2.

7. A sulfide-based solid electrolyte according to claim 1, wherein the Li-PS compound is an argyrodite structure compound, a thio-lithicon structure compound, a glass ceramic structure compound, or a glass structure compound.

8. A sulfide-based solid electrolyte according to claim 1, wherein the lattice constant of the Li-PS-based compound is 9.86 Å to 10 Å.

9. A sulfide-based solid electrolyte in the first paragraph, wherein the lithium ion conduction activation energy of the Li-PS-based compound is 0.15 eV to 0.3 eV.

10. In the first paragraph, the Li-PS compound is a Li-PS sulfide solid electrolyte represented by the following chemical formula 2: [Chemical Formula 2] Li 6+b-c P 1-b M b S 5-a-c Se a X 1+c (In the above chemical formula 2, 0 <a≤1.5, 0<b<1, 0<c≤1이고, X is at least one element selected from the group consisting of F, Cl, Br and I, M is at least one element selected from the group consisting of Si, Ge, Sn and Al).

11. Bipolar; and Including an electrolyte layer disposed on the above anode, A lithium secondary battery, wherein the electrolyte layer comprises a sulfide-based solid electrolyte according to claim 1.

12. A lithium secondary battery according to claim 11, further comprising a cathode facing the cathode, and wherein the electrolyte layer is disposed between the cathode and the anode.

13. A lithium secondary battery according to claim 12, wherein the positive electrode or the negative electrode includes the sulfide-based solid electrolyte.

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