Pouch-type secondary battery, operating method thereof, and manufacturing method thereof

Abstract

A method for manufacturing a pouch-type secondary battery according to one embodiment comprises the steps of: accommodating an electrode assembly including a positive electrode and a lithium metal negative electrode in an inner space of a pouch-type case; injecting a composition for a polymer electrolyte into the pouch-type case; curing the composition for a polymer electrolyte; and degassing, wherein the curing step may involve curing the polymer electrolyte without pressurizing the pouch-type case.

Description

Pouch-type secondary battery, its operating method and its manufacturing method

[0001] The present disclosure relates to a pouch-type secondary battery, a method for operating the same, and a method for manufacturing the same.

[0002] Lithium secondary batteries, which boast high energy density and are easy to carry, are primarily used as power sources for mobile information terminals such as mobile phones, laptops, and smartphones. Furthermore, research is actively underway to utilize lithium secondary batteries, leveraging their high energy density, as power sources for hybrid and battery-powered vehicles, or as power storage devices. When used in these medium- to large-sized devices, numerous secondary batteries are electrically connected to increase capacity and output.

[0003] Among these, lithium polymer batteries have improved safety and flexibility because they use solid polymer electrolytes.

[0004] Among these lithium polymer batteries, the development of lithium metal batteries using lithium metal is attracting significant attention. Lithium metal batteries utilize lithium metal (Li-metal) or lithium alloy (Li-alloy) as the negative active material, and theoretically offer the advantage of very high energy capacity.

[0005] At this time, during the manufacturing process of lithium polymer batteries, a squeeze-out phenomenon may occur, in which the electrolyte leaks out of the pouch-shaped case, hardens, and does not return to its original state during charging. A squeeze-out battery may exhibit reduced cycle characteristics and efficiency due to an increase in the electrolyte resistance (Rs) caused by a lack of electrolyte within the electrode assembly.

[0006] According to one aspect of the present disclosure, a method for operating a pouch-type secondary battery having excellent cycle characteristics and efficiency by pressurizing during charging and discharging can be provided.

[0007] According to another aspect of the present disclosure, a pouch-type secondary battery and a method for manufacturing the same are provided that suppress an interface peeling phenomenon due to dendrite formation in the battery.

[0008] A method for manufacturing a pouch-type secondary battery according to the present disclosure includes the steps of: housing an electrode assembly including a positive electrode and a lithium metal negative electrode in a pouch-type case; injecting a polymer electrolyte composition into the pouch-type case; and curing the polymer electrolyte composition without pressurizing the pouch-type case.

[0009] A degassing step may be further included after the above-mentioned hardening step.

[0010] The composition for the polymer electrolyte may include a lithium salt, a polymerizable monomer, and a polymerization initiator.

[0011] The above lithium salt is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN -and (CF3CF2SO2)2N - It may include at least one selected from the group consisting of as an anion.

[0012] The above polymer electrolyte composition may further include an organic solvent.

[0013] The above organic solvent may be a linear carbonate solvent, a cyclic carbonate solvent, or a mixed solvent thereof.

[0014] The linear carbonate solvent may be at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC), and methyl propyl carbonate (MPC); and the cyclic carbonate solvent may be at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate (BC), 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate (VC), and fluoroethylene carbonate (FEC).

[0015] The above polymerizable monomers are tetraethylene glycol diacrylate, polyethylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6-hexandioldiacrylate, trimethylolpropane triacrylate, trimethylolpropane ethoxylate triacrylate, trimethylolpropane propoxylate triacrylate, ditrimethylolpropane tetraacrylate, pentaerythritol tetraacrylate, pentaerythritol ethoxylate Pentaerythritol ethoxylate tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, poly(ethylene glycol) diglycidylether, 1,5-hexadiene diepoxide, glycerol propoxylate triglycidyl ether, vinylcyclohexene dioxide, 1,2,7,8-diepoxyoctane, 4-vinylcyclohexene dioxide, butyl glycidyl ether,It may be at least one selected from the group consisting of diglycidyl 1,2-cyclohexanedicarboxylate, ethylene glycol diglycidyl ether, glycerol triglycidyl ether, and glycidyl methacrylate.

[0016] A pouch-type secondary battery according to the present disclosure comprises: an electrode assembly including a positive electrode and a lithium metal negative electrode; a polymer electrolyte; a pouch-type case in which the electrode assembly and the polymer electrolyte are stored; and a pressurizing unit for pressurizing the pouch-type case.

[0017] The polymer electrolyte may include a lithium salt.

[0018] The above lithium salt is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 -, SCN - and (CF3CF2SO2)2N - It may include at least one selected from the group consisting of as an anion.

[0019] The above polymer electrolyte may include an organic solvent.

[0020] The above organic solvent may be a linear carbonate solvent, a cyclic carbonate solvent, or a mixed solvent thereof.

[0021] The linear carbonate solvent may be at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC), and methyl propyl carbonate (MPC); and the cyclic carbonate solvent may be at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate (BC), 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate (VC), and fluoroethylene carbonate (FEC).

[0022] The polymer electrolyte is tetraethylene glycol diacrylate, polyethylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6-hexandioldiacrylate, trimethylolpropane triacrylate, trimethylolpropane ethoxylate triacrylate, trimethylolpropane propoxylate triacrylate, ditrimethylolpropane tetraacrylate, pentaerythritol tetraacrylate, pentaerythritol ethoxylate Pentaerythritol ethoxylate tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, poly(ethylene glycol) diglycidylether, 1,5-hexadiene diepoxide, glycerol propoxylate triglycidyl ether, vinylcyclohexene dioxide, 1,2,7,8-diepoxyoctane, 4-vinylcyclohexene dioxide, butyl glycidyl ether,It may include a structural unit derived from at least one selected from the group consisting of diglycidyl 1,2-cyclohexanedicarboxylate, ethylene glycol diglycidyl ether, glycerol triglycidyl ether, and glycidyl methacrylate.

[0023] The pressure applied by the above pressurizing unit may be 0.5 to 15 Mpa.

[0024] A buffer pad may further be included between the pouch-shaped case and the pressurized portion.

[0025] The above pouch-type secondary battery may further include a separator interposed between the positive electrode and the lithium metal negative electrode.

[0026] A pouch-type secondary battery according to the present disclosure includes a pressurizing unit that pressurizes the pouch-type case in a pouch-type secondary battery manufactured by the above-described method.

[0027] The method for operating a pouch-type secondary battery according to the present disclosure is to charge and discharge a pouch-type secondary battery manufactured by the above-described method by pressurizing it at a pressure of 0.5 to 15 Mpa.

[0028] According to one embodiment of the present disclosure, a method for operating a pouch-type secondary battery having excellent cycle characteristics and efficiency can be provided by pressurizing the pouch-type secondary battery during charging and discharging.

[0029] According to another embodiment of the present disclosure, a pouch-type secondary battery and a method for manufacturing the same can be provided that suppresses an interfacial peeling phenomenon due to dendrite formation between an electrode and an electrolyte.

[0030] Figure 1 is a photograph comparing the presence or absence of squeeze out of a polymer electrolyte depending on the presence or absence of pressure during thermal curing in a method for manufacturing a pouch-type secondary battery according to one embodiment.

[0031] Figure 2 is a photograph comparing the difference in the degree to which a polymer electrolyte is deposited on a lithium metal negative electrode depending on whether or not the pouch-type case is pressurized during charging and discharging.

[0032] Figure 3 is a graph showing the capacity retention rate of Example 1 and Comparative Examples 1 to 3.

[0033] Figure 4 is a graph showing the Coulomb efficiency of Example 1 and Comparative Examples 1 to 3.

[0034] Figure 5 is a graph showing the capacity retention rates of Examples 1 to 3 and Comparative Example 3.

[0035] Figure 6 is a graph showing the Coulomb efficiency of Examples 1 to 3 and Comparative Example 3.

[0036] Figure 7 is a graph showing the EIS analysis results of Examples 1 to 3 and Comparative Example 3 and their enlarged views.

[0037] 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.

[0038] Manufacturing method of pouch-type secondary battery

[0039] A method for manufacturing a pouch-type secondary battery according to one embodiment may include: a step of housing an electrode assembly including a positive electrode and a lithium metal negative electrode in an internal space of a pouch-type case; a step of injecting a polymer electrolyte composition into the pouch-type case; and a step of curing the polymer electrolyte composition, wherein the curing step may cure the polymer electrolyte without pressurizing the pouch-type case.

[0040] Additionally, a degassing step may be further included after the above-mentioned hardening step.

[0041] A step of housing an electrode assembly of one embodiment in a pouch-type case is included, and the electrode assembly can be manufactured according to a conventional method known in the art.

[0042] The above electrode assembly can be manufactured by sequentially stacking a positive electrode and a lithium metal negative electrode to form an electrode assembly, and then storing the electrode assembly in a pouch-shaped case.

[0043] The positive electrode may include a positive electrode current collector and a positive electrode composite layer disposed on at least one surface of the positive electrode current collector.

[0044] The positive electrode current collector may comprise stainless steel, nickel, aluminum, titanium, or an alloy thereof. The positive electrode current collector may also comprise aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. The positive electrode current collector may have a thickness of, but is not limited to, 10 to 50 μm, for example.

[0045] The positive electrode active material layer may include a positive electrode active material. The positive electrode active material may include a compound capable of reversibly intercalating and deintercalating lithium ions.

[0046] According to exemplary embodiments, the positive electrode active material may include a lithium-nickel metal oxide. The lithium-nickel metal oxide may further include at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0047] In some embodiments, the positive electrode active material or the lithium-nickel metal oxide may include a layered structure or crystal structure represented by the following chemical formula 1.

[0048] [Chemical Formula 1]

[0049] Li x Ni a M b O 2+z

[0050] In Chemical Formula 1, 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b≤0.4, -0.5≤z≤0.1 may be satisfied. As described above, M may include Co, Mn, and / or Al.

[0051] The chemical structure represented by Chemical Formula 1 represents the bonding relationship included in the layered structure or crystal structure of the positive electrode active material and does not exclude other additional elements. For example, M includes Co and / or Mn, and Co and / or Mn can serve as the main active element of the positive electrode active material together with Ni. Chemical Formula 1 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.

[0052] In one embodiment, auxiliary elements may be further included in addition to the main active element 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 1.

[0053] The auxiliary element may include, for example, at least one of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, or Zr. The auxiliary element may also act as an auxiliary active element that contributes to the capacity / output activity of the positive electrode active material together with Co or Mn, for example, Al.

[0054] For example, the positive electrode active material or the lithium-nickel metal oxide may include a layered structure or crystal structure represented by the following chemical formula 1-1.

[0055] [Chemical Formula 1-1]

[0056] Li x Ni a M1 b1 M2 b2 O 2+z

[0057] In Chemical Formula 1, M1 may include Co, Mn, and / or Al. M2 may include the auxiliary elements described above. In Chemical Formula 1-1, 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b1+b2≤0.4, -0.5≤z≤0.1 may be satisfied.

[0058] The above-described positive electrode active material may further include a coating element or doping element. For example, elements substantially identical to or similar to the above-described auxiliary elements may be used as the coating element or doping element. For example, the above-described elements may be used singly or in combination of two or more.

[0059] The above coating element or doping element may be present on the surface of the lithium-nickel metal oxide particle, or may penetrate through the surface of the lithium-nickel metal composite oxide particle and be included in the bonding structure represented by the above chemical formula 1 or chemical formula 1-1.

[0060] The above positive electrode active material may include a nickel-cobalt-manganese (NCM) lithium oxide. In this case, an NCM lithium oxide with an increased nickel content may be used.

[0061] Ni can be provided as a transition metal associated with the output and capacity of a lithium secondary battery. Therefore, by employing a high-content (High-Ni) composition as described above in the positive electrode active material, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.

[0062] However, as the Ni content increases, the long-term storage stability and lifespan stability of the cathode or secondary battery may relatively deteriorate, and side reactions with the electrolyte may also increase. However, according to exemplary embodiments, the inclusion of Co can maintain electrical conductivity, while improving lifespan stability and capacity retention characteristics through Mn.

[0063] The content of Ni (e.g., the mole fraction of nickel among the total moles of nickel, cobalt, and manganese) in the NCM-based lithium oxide may be 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the content of Ni may be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95.

[0064] In some embodiments, the positive electrode active material may include a lithium cobalt oxide-based active material, a lithium manganese oxide-based active material, a lithium nickel oxide-based active material, or a lithium iron phosphate (LFP)-based active material (e.g., LiFePO4).

[0065] In some embodiments, the positive electrode active material may include, for example, a Mn-rich active material, an LLO (Li rich layered oxide) / OLO (Over Lithiated Oxide) active material, or a Co-less active material having a chemical structure or crystal structure represented by Chemical Formula 2.

[0066] [Chemical Formula 2]

[0067] p[Li2MnO3]·(1-p)[Li q JO2]

[0068] In chemical formula 2, 0 <p<1이고, 0.9≤q≤1.2이며, J는 Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg 및 B 중 적어도 하나의 원소를 포함할 수 있다.

[0069] The above lithium metal negative electrode may include a lithium metal layer and a lithium metal protective layer. The lithium metal protective layer may be formed on at least one surface of the lithium metal layer.

[0070] The lithium metal layer includes lithium metal or an alloy thereof, and may be a metal layer substantially composed only of lithium metal. The thickness of the lithium metal layer is not particularly limited, and may be, for example, 1 to 200 μm.

[0071] The above lithium metal protective layer is formed on at least one surface of the lithium metal layer to induce uniform lithium deposition behavior, thereby effectively suppressing the growth of lithium dendrites.

[0072] The lithium metal protective layer may include lithium-affinity inorganic particles capable of suppressing dendrite growth in the lithium metal layer. The lithium-affinity inorganic particles refer to particles containing lithium-affinity (lithio-philic) inorganic materials such as silver (Ag), gold (Au), zinc (Zn), and magnesium (Mg), and may be substantially composed only of lithium-affinity inorganic materials. Such lithium-affinity inorganic materials can electrochemically react with lithium and induce uniform electrodeposition behavior of lithium ions. Accordingly, when a lithium metal protective layer including the lithium-affinity inorganic particles is formed on at least one surface of the lithium metal layer, the growth of lithium dendrites can be suppressed during the battery charge / discharge process, thereby effectively preventing problems such as a decrease in irreversible capacity and an internal short circuit in the battery.

[0073] A separator may be interposed between the anode and cathode. The separator may be configured to prevent electrical short-circuiting between the anode and cathode and to allow ion flow. Depending on the embodiment, the thickness of the separator may be 10 μm to 20 μm, but the present disclosure is not limited thereto.

[0074] For example, the separator may include a porous polymer film or a porous nonwoven fabric. The porous polymer film may include a polyolefin polymer such as an ethylene polymer, a propylene polymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer. The porous nonwoven fabric may include high-melting-point glass fibers, polyethylene terephthalate fibers, and the like. The separator may also include a ceramic material. For example, inorganic particles may be coated on the polymer film or dispersed within the polymer film to improve heat resistance.

[0075] The separator may have a single-layer or multi-layer structure including the above-described polymer film and / or non-woven fabric.

[0076] A method for manufacturing a pouch-type secondary battery according to one embodiment may include a step of injecting a polymer electrolyte composition into a pouch-type case containing the electrode assembly.

[0077] Since the polymer electrolyte has superior electrochemical stability compared to a liquid electrolyte, it is possible to maintain a constant thickness of a secondary battery and to manufacture a lithium secondary battery with improved stability by preventing electrolyte leakage.

[0078] The composition for the polymer electrolyte may include a lithium salt, a polymerizable monomer, and a polymerization initiator.

[0079] The above lithium salt is expressed as, for example, Li+X-, and F is used as the anion (X-) of the lithium salt. - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 -, ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - Examples include:

[0080] The lithium salt may be appropriately varied within a commonly usable range to achieve an optimal anti-corrosion film-forming effect on the electrode surface. The content of the lithium salt included in the polymer electrolyte may be 0.01 to 5 mol%. If it is less than the above-mentioned range, there may be a disadvantage of low ionic conductivity, and if it exceeds the above-mentioned range, the impregnation property of the polymer electrolyte composition may be reduced as the viscosity increases.

[0081] The above polymerizable monomer has at least one polymerizable functional group selected from the group consisting of a vinyl group, an epoxy group, an allyl group, and a (meth)acrylic group capable of undergoing a polymerization reaction within its structure, and is a compound capable of being changed into a gel phase by polymerization or crosslinking, and is not particularly limited as long as it is a polymerizable monomer, oligomer, or copolymer used for producing a conventional polymer electrolyte.

[0082] The polymerizable monomers include, for example, tetraethylene glycol diacrylate, polyethylene glycol diacrylate (molecular weight 50 to 20,000), 1,4-butanediol diacrylate, 1,6-hexandioldiacrylate, trimethylolpropane triacrylate, trimethylolpropane ethoxylate triacrylate, trimethylolpropane propoxylate triacrylate, ditrimethylolpropane tetraacrylate, and pentaerythritol tetraacrylate. tetraacrylate), pentaerythritol ethoxylate tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, poly(ethylene glycol) diglycidylether, 1,5-hexadiene diepoxide, glycerol propoxylate triglycidyl ether, vinylcyclohexene dioxide, 1,2,7,8-diepoxyoctane, 4-vinylcyclohexene dioxide,Examples thereof include, but are not limited to, butyl glycidyl ether, diglycidyl 1,2-cyclohexanedicarboxylate, ethylene glycol diglycidyl ether, glycerol triglycidyl ether, and glycidyl methacrylate, and these compounds may be used alone or in combination of two or more.

[0083] The polymerization initiator may be a conventional thermal or photopolymerization initiator known in the art. For example, the polymerization initiator may be thermally decomposed to form radicals, which may react with a polymerizable monomer through free radical polymerization to form a polymer electrolyte.

[0084] The polymerization initiator may be, for example, organic peroxides or hydroperoxides such as benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di-tert-butylperoxide, t-butyl peroxy-2-ethyl-hexanoate, cumyl hydroperoxide, and hydrogen peroxide, and 2,2'-azobis(2-cyanobutane), 2,2'-azobis(methylbutyronitrile), 2,2'-azobis(isobutyronitrile) (AIBN; 2,2'-Azobis(iso-butyronitrile)). One or more azo compounds selected from the group consisting of 2,2'-azobisdimethyl-valeronitrile (AMVN), but is not limited thereto.

[0085] The polymer electrolyte composition may include an organic solvent. The organic solvent is not limited as long as it minimizes decomposition due to oxidation reactions during the charge / discharge process of a secondary battery and, together with additives, exhibits the desired properties. For example, the organic solvent may be a carbonate-based organic solvent.

[0086] The above carbonate-based organic solvent may include a linear carbonate-based organic solvent, a cyclic carbonate-based organic solvent, or a mixed solvent thereof.

[0087] Specifically, the linear carbonate-based organic solvent is a solvent having low viscosity and low dielectric constant, and may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC), and methyl propyl carbonate (MPC), and more specifically, may include dimethyl carbonate.

[0088] In addition, the cyclic carbonate-based organic solvent may include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate (BC), 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate (VC), and fluoroethylene carbonate (FEC).

[0089] A method for manufacturing a pouch-type secondary battery according to one embodiment may include a heat curing step of injecting a polymer electrolyte composition in a liquid state into a pouch-type case containing an electrode assembly and then applying heat. In a method for manufacturing a pouch-type secondary battery according to one embodiment, the pouch-type secondary battery may be manufactured without pressurizing the pouch-type case during the heat curing step, thereby preventing a squeeze-out phenomenon of the pouch-type secondary battery.

[0090] The above thermal curing step can be performed at a temperature and for a time according to a conventional method known in the art for secondary batteries containing polymer electrolytes, and for example, thermal curing can be performed at a temperature of 70 to 80°C for 1 to 2 hours.

[0091] A method for manufacturing a pouch-type secondary battery according to one embodiment may further include a step of degassing after curing a polyethylene electrolyte composition. The degassing step may discharge gases generated during the manufacturing process of the pouch-type secondary battery to the outside of the secondary battery.

[0092] Pouch-type secondary battery and its operating method

[0093] A pouch-type secondary battery of one embodiment may include an electrode assembly including a positive electrode and a lithium metal negative electrode; a polymer electrolyte; a pouch-type case in which the electrode assembly and the polymer electrolyte are stored; and a pressurizing unit for pressurizing the pouch-type case. In addition, the pouch-type secondary battery may further include a separator interposed between the positive electrode and the lithium metal negative electrode. The positive electrode, the lithium metal negative electrode, the pouch-type case, the polymer electrolyte, and the separator may be the same as those described in the method for manufacturing the pouch-type secondary battery described above.

[0094] For example, the polymer electrolyte may comprise a lithium salt and optionally an organic solvent, wherein the lithium salt and the organic solvent may be as described above.

[0095] For example, the polymer electrolyte may include a structural unit derived from the above-mentioned polymerizable monomer, specifically, tetraethylene glycol diacrylate, polyethylene glycol diacrylate (molecular weight 50 to 20,000), 1,4-butanediol diacrylate, 1,6-hexandioldiacrylate, trimethylolpropane triacrylate, trimethylolpropane ethoxylate triacrylate, trimethylolpropane propoxylate triacrylate, ditrimethylolpropane tetraacrylate, Pentaerythritol tetraacrylate, pentaerythritol ethoxylate tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, poly(ethylene glycol) diglycidylether, 1,5-hexadiene diepoxide, glycerol propoxylate triglycidyl ether, vinylcyclohexene dioxide, 1,2,7,8-diepoxyoctane,It may include a structural unit derived from one or more selected from the group consisting of 4-vinylcyclohexene dioxide, butyl glycidyl ether, diglycidyl 1,2-cyclohexanedicarboxylate, ethylene glycol diglycidyl ether, glycerol triglycidyl ether, and glycidyl methacrylate.

[0096] In addition, the pouch-type secondary battery may be, for example, a pouch-type secondary battery manufactured according to the above-described pouch-type secondary battery manufacturing method.

[0097] The above-mentioned pressurizing unit may be in a shape facing one side and the other side of the pouch-type case, and its shape is not limited as long as it is a device for pressurizing a pouch-type secondary battery. For example, the above-mentioned pressurizing unit may be a pressurizing jig. The shape of the pressurizing jig may be configured as a bolt-tightening unit and may be a shape for pressurizing a pouch-type secondary battery, but is not particularly limited.

[0098] Additionally, a buffer pad may be further included between the pressurizing portion and the pouch-shaped case. The buffer pad may enable the pressurizing portion to evenly press the surface of the pouch-shaped case. The material of the buffer pad is not particularly limited, but may be, for example, a silicone material.

[0099] The area of ​​the above-mentioned buffer pad is not particularly limited, but may be, for example, 2 to 4% of the area of ​​one side of the pouch-type secondary battery. A pressurizing portion including a buffer pad within the above-mentioned range can evenly pressurize the surface of the pouch-type case.

[0100] The thickness of the above-described buffer pad is not particularly limited, but may be, for example, 2 to 3 mm. A pressurizing portion including a buffer pad having the above-described thickness can evenly pressurize the surface of a pouch-shaped case.

[0101] The pressure applied by the above pressurizing unit may be 0.5 to 15 MPa, specifically 0.5 to 7 MPa. When the pouch-type case is pressurized within the above range, the delamination phenomenon at the interface between the electrode and the electrolyte can be suppressed, and the electrolyte resistance (Rs) and charge transfer resistance (Rct) caused by electrolyte deficiency can be prevented from increasing, so that the capacity retention rate and coulombic efficiency can be excellent.

[0102] A method for operating a pouch-type secondary battery according to an embodiment may be to pressurize the above-described pouch-type secondary battery during charging and discharging.

[0103] The pressure applied when the above pouch-type secondary battery is operated may be 0.5 to 15 MPa, and specifically, 0.5 to 7 MPa. When the pouch-type secondary battery is pressurized within the above range, the delamination phenomenon at the interface between the electrode and the electrolyte is suppressed, and an increase in the electrolyte resistance (Rs) and charge transfer resistance (Rct) caused by electrolyte insufficiency can be prevented, so that the capacity retention rate and coulombic efficiency can be excellent.

[0104] 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 changes and modifications to the examples are possible within the scope and technical idea of ​​the present disclosure, and it is natural that such changes and modifications fall within the scope of the appended claims.

[0105] Manufacturing example

[0106] LiNi as a cathode active material 0.6 Co0.2 Mn 0.2 A cathode slurry was prepared with a weight ratio of 95:2.5:2.5 consisting of O2, carbon black as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder. This was then coated, dried, and pressed onto an aluminum substrate to produce a cathode. Lithium metal with a thickness of 100 μm from Honzo was used as the anode. The above-mentioned cathodes and anodes were laminated with a polyethylene (PE) separator (7 μm) in between, and wound to produce an electrode assembly.

[0107] The above-described electrode assembly was placed in a pouch-type case, and then a curable polymer electrolyte solution containing a t-BPP initiator mixed in an amount of 1 wt% based on the monomer weight was injected into a solution containing (LiTFSi 0.8 M and LiDFOB in FEC / EMC (4:6 v / v%) 0.2 M) : TMPETA monomer in a weight ratio of 95 : 5, sealed, and cured in an oven at 70°C for 1 hour to manufacture a lithium secondary battery. At this time, the pouch-type secondary battery was not pressurized during the thermal curing step.

[0108] Comparative manufacturing example

[0109] The electrode assembly manufactured in the above-described manufacturing example was placed in a pouch-type case, and then a curable polymer electrolyte solution containing a t-BPP initiator mixed in an amount of 1 wt% based on the monomer weight was injected into a solution mixed in a weight ratio of (LiTFSi 0.8 M and LiDFOB in FEC / EMC (4:6 v / v%) 0.2 M): TMPETA monomer = 95: 5, sealed, and cured in a 70°C oven for 1 hour to manufacture a lithium secondary battery. At this time, the pouch-type secondary battery was pressurized to 1.96 MPa in the thermal curing step.

[0110] Evaluation example

[0111] The pouch-type secondary batteries manufactured in the above manufacturing examples and comparative manufacturing examples were operated according to the conditions in Table 1 below, and their performance was evaluated.

[0112] At this time, pressurization during charging and discharging means that a pouch-type secondary battery is inserted between a pressurizing jig consisting of six bolt-fastening parts and the bolt-fastening parts are fastened to a certain pressure, and a silicone pad is used as a buffer pad.

[0113] Type of pouch-type secondary batteryPressure applied during charging / discharging (MPa)Presence or absence of buffer padExample 1 Manufacturing example 1.96OExample 2 Manufacturing example 0.98OExample 3 Manufacturing example 2.45OComparative example 1 Manufacturing example-XComparative example 2 Comparative Manufacturing example 1.96OComparative example 3 Comparative Manufacturing example-X

[0114] 1. Evaluation of secondary battery performance according to pressurization

[0115] Using a battery cycler from Wonik PNE, the performance of the secondary battery was evaluated by measuring the cycle retention and Coulomb efficiency based on 30 cycles of the pouch-type secondary battery operated in Example 1 and Comparative Examples 1 to 3 described above.

[0116] The results of the above experiment are shown in Fig. 3, Fig. 4 and Table 2. In addition, the differences between the manufacturing example and the comparative manufacturing example are shown in Fig. 1, and the differences between Example 1 and Comparative Example 1 are shown in Fig. 2.

[0117] 30 cycle standard Cycle Retention(%)30 cycle average Coulomb Efficiency(%)Example 110099.88Comparative example 16398.76Comparative example 28599.43Comparative example 31594.23

[0118] Referring to FIGS. 3, 4, and Table 2, it can be confirmed that the pouch-type secondary battery of Example 1, which was manufactured using the pouch-type secondary battery of the manufacturing example manufactured without pressurizing in the electrolyte curing step and operated under pressurization during charge and discharge, has high Cycle Retention and Coulomb Efficiency. This may mean that the cycle performance of the pouch-type secondary battery is excellent. However, even if it is manufactured using the pouch-type secondary battery of the manufacturing example manufactured without pressurizing in the electrolyte curing step, it can be confirmed that the pouch-type secondary battery (Comparative Example 1) that is not pressurized during charge and discharge has inferior cycle performance.

[0119] In addition, referring to FIG. 2, it can be confirmed that in the secondary battery of Comparative Example 1, when lithium metal is electrodeposited without pressurization, it is unevenly deposited on the copper foil used as the current collector.

[0120] Furthermore, it can be confirmed that the cycle performance of the pouch-type secondary battery of the comparative manufacturing example manufactured by pressurizing during the electrolyte curing step is inferior even when operated under pressure during charge and discharge. Referring to Fig. 1 (a), it can be confirmed that the pouch-type secondary battery of the comparative manufacturing example that was pressurized during thermal curing expanded because the electrolyte was squeezed out, and referring to Fig. 1 (b), it can be confirmed that the pouch-type secondary battery of the manufacturing example that was not pressurized during thermal curing did not have an expanded portion because the electrolyte was not squeezed out. Due to the above difference, it can be confirmed that there is a difference in performance from Example 1 even when operated under pressure during charge and discharge.

[0121] It can be confirmed that the pouch-type secondary battery of the comparative manufacturing example manufactured by pressurizing in the electrolyte hardening step has a significantly lower cycle retention and thus a lower performance than the pouch-type secondary battery (Comparative Example 3) that is not pressurized during charging and discharging.

[0122] 2. Evaluation of secondary battery performance according to pressure level

[0123] Using a battery cycler from Wonik PNE, the pouch-type secondary batteries of Examples 1 to 3 and Comparative Example 3 were evaluated for secondary battery performance by measuring the Cycle Retention and Coulomb Efficiency based on 20 cycles, and the experimental results are shown in Figures 5 and 6 and Table 2 below.

[0124] In addition, the electrolyte resistance (Rs) and charge transfer resistance (Rct) of the pouch-type secondary batteries of Examples 1 to 3 and Comparative Example 3 described above were measured using electrochemical impedance spectroscopy (EIS), and the results are shown in FIG. 7 and Table 3 below.

[0125] 20 cycle standard Cycle Retention(%)20 cycle average Coulomb Efficiency(%)Rs (Ohm)Rct (Ohm)Example 110099.880.1080.518Example 29999.820.0910.618Example 38699.360.1130.783Comparative example 34796.510.1020.822

[0126] Referring to FIGS. 5 to 7 and Table 3, the pouch-type secondary batteries (Examples 1 to 3) manufactured without pressurizing in the electrolyte curing step and operated under pressure during charge and discharge not only have excellent cycle performance, but also show a small difference in the Rs value, indicating that the squeeze-out phenomenon of the electrolyte is reduced. At this time, it can be confirmed that the secondary battery of Example 1 has the best cycle performance. However, the pouch-type secondary battery (Comparative Example 3) manufactured without pressurizing in the electrolyte curing step and operated under pressure during charge and discharge has inferior cycle performance, and judging from the large difference in the Rs value, it can be determined that the squeeze-out phenomenon of the electrolyte still occurs.

[0127] 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 step of storing an electrode assembly including a positive electrode and a lithium metal negative electrode inside a pouch-type case; A step of injecting a polymer electrolyte composition into the pouch-shaped case; and A method for manufacturing a pouch-type secondary battery, comprising a step of curing the polymer electrolyte composition without pressurizing the pouch-type case.

2. In paragraph 1, A method for manufacturing a pouch-type secondary battery, further comprising a degassing step after the above-mentioned curing step.

3. In paragraph 1, A method for manufacturing a pouch-type secondary battery, wherein the polymer electrolyte composition comprises a lithium salt, a polymerizable monomer, and a polymerization initiator.

4. In paragraph 3, The above lithium salt is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - A method for manufacturing a pouch-type secondary battery comprising at least one anion selected from a group consisting of:

5. In paragraph 3, A method for manufacturing a pouch-type secondary battery, wherein the polymer electrolyte composition further comprises an organic solvent.

6. In paragraph 5, A method for manufacturing a pouch-type secondary battery, wherein the organic solvent is a linear carbonate solvent, a cyclic carbonate solvent, or a mixed solvent thereof.

7. In paragraph 6, The linear carbonate solvent is selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC), and methyl propyl carbonate (MPC). A method for manufacturing a pouch-type secondary battery, wherein the cyclic carbonate solvent is at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate (BC), 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate (VC), and fluoroethylene carbonate (FEC).

8. In paragraph 3, The above polymerizable monomers are tetraethylene glycol diacrylate, polyethylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6-hexandioldiacrylate, trimethylolpropane triacrylate, trimethylolpropane ethoxylate triacrylate, trimethylolpropane propoxylate triacrylate, ditrimethylolpropane tetraacrylate, pentaerythritol tetraacrylate, pentaerythritol ethoxylate Pentaerythritol ethoxylate tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, poly(ethylene glycol) diglycidylether, 1,5-hexadiene diepoxide, glycerol propoxylate triglycidyl ether, vinylcyclohexene dioxide, 1,2,7,8-diepoxyoctane, 4-vinylcyclohexene dioxide, butyl glycidyl ether,A method for manufacturing a pouch-type secondary battery, wherein the secondary battery comprises at least one selected from the group consisting of diglycidyl 1,2-cyclohexanedicarboxylate, ethylene glycol diglycidyl ether, glycerol triglycidyl ether, and glycidyl methacrylate.

9. Electrode assembly including a positive electrode and a lithium metal negative electrode; polymer electrolyte; A pouch-shaped case in which the electrode assembly and polymer electrolyte are stored; and A pouch-type secondary battery including a pressurizing unit for pressurizing the above pouch-type case.

10. In paragraph 9, The above polymer electrolyte is a pouch-type secondary battery containing a lithium salt.

11. In paragraph 10, The above lithium salt is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - A pouch-type secondary battery comprising at least one anion selected from the group consisting of:

12. In paragraph 9, A pouch-type secondary battery, wherein the polymer electrolyte contains an organic solvent.

13. In paragraph 12, A pouch-type secondary battery in which the organic solvent is a linear carbonate solvent, a cyclic carbonate solvent, or a mixed solvent thereof.

14. In paragraph 13, The linear carbonate solvent is at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC), and methyl propyl carbonate (MPC). A pouch-type secondary battery, wherein the above cyclic carbonate solvent is at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate (BC), 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate (VC), and fluoroethylene carbonate (FEC).

15. In paragraph 9, The polymer electrolyte is tetraethylene glycol diacrylate, polyethylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6-hexandioldiacrylate, trimethylolpropane triacrylate, trimethylolpropane ethoxylate triacrylate, trimethylolpropane propoxylate triacrylate, ditrimethylolpropane tetraacrylate, pentaerythritol tetraacrylate, pentaerythritol ethoxylate Pentaerythritol ethoxylate tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, poly(ethylene glycol) diglycidylether, 1,5-hexadiene diepoxide, glycerol propoxylate triglycidyl ether, vinylcyclohexene dioxide, 1,2,7,8-diepoxyoctane, 4-vinylcyclohexene dioxide, butyl glycidyl ether,A pouch-type secondary battery comprising a structural unit derived from at least one selected from the group consisting of diglycidyl 1,2-cyclohexanedicarboxylate, ethylene glycol diglycidyl ether, glycerol triglycidyl ether, and glycidyl methacrylate.

16. In paragraph 9, A pouch-type secondary battery, wherein the pressure applied by the above pressurizing unit is 0.5 to 15 Mpa.

17. In paragraph 9, A pouch-type secondary battery further comprising a buffer pad between the pouch-type case and the pressurized portion.

18. In paragraph 9, The above pouch-type secondary battery further includes a separator interposed between the positive electrode and the lithium metal negative electrode.

19. A pouch-type secondary battery comprising a pressurizing unit for pressurizing a pouch-type case in a pouch-type secondary battery manufactured by the method of any one of claims 1 to 8.

20. A method for operating a pouch-type secondary battery, comprising charging and discharging a pouch-type secondary battery manufactured by any one of the methods of clauses 1 to 8 by pressurizing the battery at a pressure of 0.5 to 15 Mpa.

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