Lithium secondary battery and secondary battery module including same

Abstract

A lithium secondary battery (1000) according to an embodiment includes a unit cell including a positive electrode (100) and a negative electrode (200). The positive electrode (100) includes: a positive electrode current collector (110); and a positive electrode mixture layer (120) formed on one surface of the positive electrode current collector, and the negative electrode (200) includes: a negative electrode current collector (210); and a negative electrode mixture layer (220) formed on one surface of the negative electrode current collector, wherein the positive electrode mixture layer (120) and the negative electrode mixture layer (220) are disposed between the positive electrode current collector (110) and the negative electrode current collector (210). The width (WX) of the negative electrode mixture layer is greater than the width (WY) of the positive electrode mixture layer. The positive electrode current collector (110) includes a positive electrode non-coating portion (112) where a positive electrode mixture layer (20) is not formed. The unit cell includes at least one reinforcing layer (130) that is between the positive electrode non-coating portion (112) and the negative electrode mixture layer (220) and includes a binder.

Description

Lithium secondary battery and secondary battery module including the same

[0001] The present disclosure relates to a lithium secondary battery and a secondary battery module including the same.

[0002] Recently, research is actively being conducted on eco-friendly transportation methods such as electric vehicles (EVs) that can replace fossil fuel-based vehicles, one of the main causes of air pollution. Lithium secondary batteries with high discharge voltage and output stability are mainly used as the power source for these eco-friendly transportation methods.

[0003] The lithium secondary battery may include a unit cell having a positive electrode and a negative electrode. When the lithium secondary battery is charged, lithium ions move from the positive electrode to the negative electrode. However, if the negative electrode cannot sufficiently accommodate lithium ions, a lithium plating phenomenon, in which lithium metal is precipitated from the negative electrode, may occur. Accordingly, there is a need for the development of a technology that can prevent the lithium plating phenomenon from occurring on the negative electrode.

[0004] One aspect of the present disclosure is to prevent lithium plating (Li-plating) from occurring on the negative electrode.

[0005] Another aspect of the present disclosure is to improve the safety of lithium secondary batteries.

[0006] Another aspect of the present disclosure is to suppress a large pressure from being applied to the outermost portion of the positive electrode even if an electrode swelling phenomenon occurs during a battery charging / discharging process.

[0007] Another aspect of the present disclosure is to prevent short circuits from occurring inside a battery.

[0008] Another aspect of the present disclosure is to prevent rapid self-discharge from occurring.

[0009] According to one embodiment, a lithium secondary battery includes a unit cell, wherein the unit cell includes a positive electrode and a negative electrode, wherein the positive electrode includes a positive electrode current collector; and a positive electrode mixture layer formed on one surface of the positive electrode current collector, wherein the negative electrode includes a negative electrode current collector; and a negative electrode mixture layer formed on one surface of the negative electrode current collector, wherein the positive electrode mixture layer and the negative electrode mixture layer are disposed between the positive electrode current collector and the negative electrode current collector, and a width of the negative electrode mixture layer is larger than a width of the positive electrode mixture layer, the positive electrode current collector includes a positive electrode non-woven portion on which a positive electrode mixture layer is not formed, and the unit cell includes at least one reinforcing layer including a binder between the positive electrode non-woven portion and the negative electrode mixture layer.

[0010] In the above-described embodiment, the reinforcing layer may be an inactive layer that does not include a positive electrode active material and a negative electrode active material.

[0011] In any of the above-described embodiments, the binder may be at least one selected from polyvinyl fluoride (PVDF), polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), carboxymethyl cellulose (CMC), ethyl cellulose, acrylic resin, styrene-butadiene rubber (SBR), and polytetrafluoroethylene (PTFE).

[0012] In any of the above-described implementation examples, the unit cell may satisfy the condition according to Equation 1 below.

[0013] [Formula 1]

[0014] W A X 0.5 ≤ W X - W Y ≤ W A X 1.5

[0015] In the above equation 1, W A is the sum of the widths of all reinforcement layers, and W X is the width of the cathode composite layer, and W Y is the width of the bipolar composite layer.

[0016] In any of the above-described implementation examples, the unit cell may satisfy the condition according to Equation 2 below.

[0017] [Formula 2]

[0018] W A X 0.67 ≤ W X - W Y ≤ W A X 1.33

[0019] In the above equation 2, W A is the sum of the widths of all reinforcement layers, and W X is the width of the cathode composite layer, and W Y is the width of the bipolar composite layer.

[0020] In any one of the above-described implementation examples, the W X - W Y The value can be from 0.5 to 6.0 mm, and the W A The value can be from 0.1 to 4.0 mm.

[0021] In any of the above-described embodiments, the ratio of the thickness of the reinforcing layer to the thickness of the positive electrode composite layer may be 0.9 to 1.1.

[0022] In any of the above-described embodiments, the positive electrode may further include a positive electrode mixture layer formed on the other surface of the positive electrode current collector, and the negative electrode may further include a negative electrode mixture layer formed on the other surface of the negative electrode current collector.

[0023] In any of the above-described embodiments, the lithium secondary battery may include a plurality of unit cells.

[0024] A secondary battery module according to one embodiment includes a lithium secondary battery according to any one of the above-described embodiments.

[0025] According to one embodiment of the present disclosure, the occurrence of lithium plating (Li-plating) phenomenon can be prevented.

[0026] According to another embodiment of the present disclosure, the gap area between the cathode and the anode can be reduced.

[0027] According to another embodiment of the present disclosure, it is possible to suppress a large pressure from being applied to the outermost portion of the anode.

[0028] According to another embodiment of the present disclosure, even if the electrode expands during the battery charging / discharging process, the occurrence of a short inside the battery can be alleviated.

[0029] According to another embodiment of the present disclosure, even if the electrode expands during the battery charging / discharging process, the self-discharge phenomenon occurring inside the battery can be alleviated.

[0030] Figure 1 is a conceptual drawing showing the form in which the outermost part of the positive electrode is damaged due to the gap between the negative electrode and the positive electrode when the electrode bends in the direction of unit cell stacking in a lithium secondary battery according to a reference example.

[0031] FIGS. 2A to 2H are cross-sectional views each showing the structure of a lithium secondary battery including a unit cell according to implementation examples.

[0032] Figure 3 is a drawing conceptually illustrating a method for manufacturing a lithium secondary battery according to one embodiment.

[0033] According to one embodiment, during the charge / discharge process of a lithium secondary battery, a physical deformation such as swelling of the electrode within the unit cell may occur due to the expansion phenomenon of the active material included in the electrode. In particular, in a module assembly process including a plurality of unit cells, if a thermal adhesive (TA) having a hard property upon curing is coated on the outer surface of the unit cell, the thermal adhesive may cause the electrode to bend in the direction of unit cell stacking when the electrode expands. In this case, if the negative electrode is designed to be larger than the positive electrode, the outermost part of the positive electrode, which is subject to a large pressure due to the gap area between the negative electrode and the positive electrode, may be damaged (see Fig. 1).

[0034] In addition, if the unit cell further includes a separator between the cathode and the anode, the separator located at the outermost part of the cathode may be damaged, causing a short circuit inside the battery, which may cause a rapid self-discharge phenomenon and deteriorate the performance of the battery.

[0035] Hereinafter, implementation examples of the present disclosure will be described with reference to FIGS. 1 to 3, but the embodiments may be modified into various other forms and are not limited to the embodiments described below.

[0036] Figure 1 is a conceptual drawing showing the form in which the outermost part of the positive electrode is damaged due to the gap between the negative electrode and the positive electrode when the electrode bends in the direction of unit cell stacking in a lithium secondary battery according to a reference example.

[0037] FIGS. 2A to 2H are cross-sectional views each showing the structure of a lithium secondary battery including a unit cell according to implementation examples.

[0038] Figure 3 is a drawing conceptually illustrating a method for manufacturing a lithium secondary battery according to one embodiment.

[0039] lithium secondary battery

[0040] A lithium secondary battery (1000) according to one embodiment includes a unit cell including a positive electrode (100) and a negative electrode (200). The positive electrode (100) includes a positive electrode current collector (110); and a positive electrode mixture layer (120) formed on one surface of the positive electrode current collector, and the negative electrode (200) includes a negative electrode current collector (210); and a negative electrode mixture layer (220) formed on one surface of the negative electrode current collector, and the positive electrode mixture layer (120) and the negative electrode mixture layer (220) are disposed between the positive electrode current collector (110) and the negative electrode current collector (210), and the width (W) of the negative electrode mixture layer X ) is the width (W) of the bipolar composite layer Y) is larger than the cathode current collector (110), and the cathode current collector (110) includes a cathode non-coated portion (112) in which a cathode composite layer (20) is not formed, and the unit cell includes at least one reinforcing layer (130) including a binder between the cathode non-coated portion (112) and the cathode composite layer (220).

[0041] The above unit cell is designed such that the negative electrode composite layer (220) is larger than the positive electrode composite layer (120), and includes at least one separate reinforcing layer (130) in the gap region (G) therebetween. Accordingly, in the case of the composite layer participating in the electrochemical reaction of the battery, the negative electrode is designed to be larger than the positive electrode, thereby preventing lithium plating from occurring on the negative electrode, and even if electrode swelling occurs during the battery charge / discharge process, the pressure applied to the outermost portion of the positive electrode is suppressed to prevent short circuit and self-discharge from occurring inside the battery.

[0042] Below, the structure of the unit cell included in the lithium secondary battery is described in detail.

[0043] The above unit cell is the minimum structural unit of a lithium secondary battery (1000) including a positive electrode (100) and a negative electrode (200), wherein the positive electrode (100) and the negative electrode (200) each include a current collector; and a composite layer formed on at least one surface of the current collector.

[0044] The components of the positive electrode current collector (110) are not particularly limited. For example, the positive electrode current collector (110) may be a plate or foil made of one or more of indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), and alloys thereof. In some embodiments, the positive electrode current collector may be aluminum foil (Al-foil).

[0045] The thickness of the positive electrode current collector (110) is not particularly limited. For example, the thickness of the positive electrode current collector (110) may be 0.1 μm to 50 μm.

[0046] The components of the negative electrode current collector (210) are not particularly limited. For example, the negative electrode current collector (210) may be a plate or foil made of one or more of indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), and alloys thereof. In some embodiments, the negative electrode current collector may be a copper foil (Cu-foil).

[0047] The thickness of the negative electrode collector (210) is not particularly limited. For example, the thickness of the negative electrode collector (110) may be 0.1 μm to 50 μm.

[0048] The positive electrode current collector (110) includes a positive electrode non-coated portion (112) on which a positive electrode mixture layer (120) is not formed. Specifically, the positive electrode current collector (110) may include a positive electrode holding portion (111) on which a positive electrode mixture layer (120) is formed on a surface; and a positive electrode non-coated portion (112) on which a positive electrode mixture layer (120) is not formed on a surface. In addition, the negative electrode current collector (210) may include a negative electrode non-coated portion (not shown) on which a negative electrode mixture layer (220) is not formed. Specifically, the negative electrode current collector (210) may include a negative electrode holding portion (not shown) on which a negative electrode mixture layer (220) is formed on a surface; and a negative electrode non-coated portion (not shown) on which a negative electrode mixture layer (220) is not formed on a surface.

[0049] The positive electrode material layer (120) and the negative electrode material layer (220) are active layers that include an active material that substantially participates in the electrochemical reaction of a secondary battery. The positive electrode material layer (120) may include a positive electrode active material, and the negative electrode material layer (220) may include a negative electrode active material.

[0050] The positive electrode active material is not particularly limited. For example, the positive electrode active material may include a compound capable of reversibly intercalating and deintercalating lithium ions. For example, 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).

[0051] 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.

[0052] [Chemical Formula 1]

[0053] Li x Ni a M b O 2+z

[0054] In the above 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.

[0055] The chemical structure represented by the above 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. The above 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.

[0056] In some embodiments, 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 / crystal structure. The auxiliary elements may be incorporated into the layered / 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.

[0057] 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 function as an auxiliary active element that contributes to the capacity / output activity of the positive electrode active material together with Co or Mn, such as Al.

[0058] 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.

[0059] [Chemical Formula 1-1]

[0060] Li x Ni a M1 b1 M2 b2 O 2+z

[0061] In Chemical Formula 1-1, 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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).

[0067] In some embodiments, the positive electrode active material may include a Mn-rich active material, a Li-rich layered oxide (LLO) / over lithiated oxide (OLO) active material, or a Co-less active material having a chemical structure or crystal structure represented by chemical formula 2.

[0068] [Chemical Formula 2]

[0069] p[Li2MnO3]·(1-p)[Li q JO2]

[0070] 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.

[0071] The above negative electrode active material is not particularly limited. For example, the negative electrode active material may be at least one selected from the group consisting of carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers; lithium metal; lithium alloys; silicon-containing materials, and tin-containing materials.

[0072] The above crystalline carbon may be, for example, graphitic carbon such as natural graphite, artificial graphite, graphitized coke, graphitized mesocarbon microbead (MCMB), graphitized mesophase pitch-based carbon fiber (MPCF), etc.

[0073] Examples of the above amorphous carbon may include hard carbon, soft carbon, coke, mesocarbon microbead (MCMB), or mesophase pitch-based carbon fiber (MPCF).

[0074] Elements included in the above lithium alloy may be, for example, aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium or indium.

[0075] The silicon-containing material is not particularly limited as long as it contains silicon, and may be an active material capable of being alloyed with lithium (Li). For example, the silicon-containing material may be silicon (Si), silicon oxide (SiOx; 0 <x<2), 금속 도핑된 실리콘 산화물(SiOx; 0<x<2), 탄소 코팅된 실리콘 산화물(SiOx; 0<x<2), 실리콘-탄소 복합체(Si-C) 및 실리콘 합금으로 이루어진 군으로부터 선택된 1종 이상일 수 있다.

[0076] The above-described positive electrode material layer and negative electrode material layer may each further include a conductive material. The conductive material is not particularly limited, and by way of example, may be at least one selected from graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, and carbon nanotubes (CNT); metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives.

[0077] The positive electrode material layer and the negative electrode material layer may each further include a binder. The binder is not particularly limited. The binder included in the positive electrode material layer may be, for example, at least one selected from polyvinyl fluoride (PVDF), polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), carboxymethyl cellulose (CMC), ethyl cellulose, acrylic resin, styrene-butadiene rubber (SBR), and polytetrafluoroethylene (PTFE). In addition, the binder included in the negative electrode material layer may be, for example, a rubber-based binder such as styrene-butadiene rubber (SBR), fluorine-based rubber, ethylene propylene rubber, butyl acrylate rubber, butadiene rubber, isoprene rubber, acrylonitrile rubber, acrylic rubber, and silane-based rubber; And it may be at least one selected from among cellulose-based binders such as carboxymethylcellulose (CMC), hydroxypropylmethylcellulose, methylcellulose, etc., or alkali metal salts (Na, K, or Li) thereof.

[0078] A unit cell according to one embodiment may not further include a separator (300) interposed between the anode and the cathode (see FIGS. 2a and 2b). On the other hand, a unit cell according to another embodiment may further include a separator (300) interposed between the anode and the cathode (see FIGS. 2c and 2d). A unit cell according to another embodiment may include a solid electrolyte layer (not shown) containing a solid electrolyte instead of a separator between the anode and the cathode. The solid electrolyte is not particularly limited. For example, the solid electrolyte may be an oxide-based solid electrolyte, a sulfide-based solid electrolyte, or a polymer-based solid electrolyte.

[0079] When the above unit cell further includes a separator (300), the separator (300) may be a polyolefin-based polymer separator such as polyethylene or polypropylene, glass fiber, polyester, polytetrafluoroethylene, or a combination thereof, and may be in the form of a non-woven fabric or a woven fabric. In addition, the separator (300) may be coated with a composition including a ceramic component or the like to secure heat resistance or mechanical strength, and may optionally be configured as a single-layer or multi-layer structure. A separator having the above-described compound, structure, etc. may be applied as the separator (300), but is not limited thereto.

[0080] Below, the reinforcing layer (130) included in the unit cell is described in detail.

[0081] The above reinforcing layer (130) refers to a layer that is included in at least one gap region (G) between the positive and negative electrodes, fills the gap region (G), and reinforces the inside of the unit cell. Specifically, the reinforcing layer (130) may be formed in the remaining portion between the negative electrode mixture layer (220) having a larger width than the positive electrode mixture layer (120) and the positive electrode mixture layer (120), and may be formed on one surface of the positive electrode non-coated portion (112) in the direction in which the positive electrode current collector (110) and the negative electrode mixture layer (220) face each other. More specifically, the reinforcing layer (130) may be included in an area surrounded by the positive electrode non-coated portion (112), the positive electrode mixture layer (120), and the negative electrode mixture layer (220).

[0082] The shape of the reinforcing layer (130) is not particularly limited, and can be formed in an appropriate shape considering the shapes of the positive electrode mixture layer (120) and the negative electrode mixture layer (220). For example, when the positive electrode mixture layer (120) and the negative electrode mixture layer (220) are formed in the shape of a rectangular parallelepiped and the gap area therebetween also has the shape of a rectangular parallelepiped, the reinforcing layer (130) can also be formed in the shape of a rectangular parallelepiped.

[0083] When the above unit cell includes the above-described reinforcing layer (130), even if the electrode bends in the direction of unit cell stacking according to the charging / discharging of the battery, damage to the outermost part of the positive electrode can be substantially alleviated.

[0084] The above unit cell includes at least one reinforcing layer (130). For example, the unit cell may include one reinforcing layer (130) on only one side of the positive electrode mixture layer (120) (see FIG. 2a), or may include two reinforcing layers (130), one on each of the two sides of the positive electrode mixture layer (120) (see FIG. 2b). In addition, the unit cell may include a plurality of reinforcing layers on one or both sides of the positive electrode mixture layer (120). That is, a plurality of reinforcing layers (130) may be formed in each section of the area existing between the negative electrode mixture layer (220) and the positive electrode mixture layer (120) to form one reinforcing layer.

[0085] The reinforcing layer (130) may be an inactive layer that does not include a positive electrode active material and a negative electrode active material. That is, according to one embodiment, the reinforcing layer (130) does not include an electrode active material and thus does not substantially participate in the electrochemical reaction of the battery, but may fill the gap region (G) existing between the positive electrode and the negative electrode and perform the function of reinforcing the inside of the unit cell. Accordingly, the reinforcing layer (13) prevents shrinkage / expansion of the electrode active material according to the charging / discharging of the battery, thereby further suppressing the occurrence of a bending phenomenon of the electrode in the direction of stacking of the unit cell, and more effectively preventing damage to the outermost part of the positive electrode, thereby improving the durability of the unit cell and the secondary battery.

[0086] The above reinforcing layer (130) may have excellent adhesion to the positive electrode current collector (110) by including a binder. The type of the binder is not particularly limited. For example, the binder may be at least one selected from polyvinyl fluoride (PVDF), polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), carboxymethyl cellulose (CMC), ethyl cellulose, acrylic resin, styrene-butadiene rubber (SBR), and polytetrafluoroethylene (PTFE). In addition, the content of the binder included in the reinforcing layer (130) may be, for example, 0.1 to 10 wt%.

[0087] The reinforcing layer (130) may further include an insulating material. When the reinforcing layer (130) further includes an insulating material, the electrochemical reaction of the battery may be substantially suppressed through the reinforcing layer (130), thereby further improving the safety of the battery. The insulating material is not particularly limited, and may be, for example, a polyolefin-based polymer such as polyethylene (PE) or polypropylene (PP). When the reinforcing layer (130) further includes an insulating material, the content of the insulating material included in the reinforcing layer (130) may be, for example, 1 to 10 wt%.

[0088] The above unit cell can satisfy the conditions according to Equation 1 below.

[0089] [Formula 1]

[0090] W A X 0.5 ≤ W X - W Y ≤ W A X 1.5

[0091] In the above equation 1, W A is the sum of the widths of all reinforcement layers (130), and W X is the width of the cathode composite layer (220), and W Y is the width of the bipolar composite layer (120).

[0092] The above reinforcing layer (130) can be formed to fill a gap area between the negative electrode mixture layer (220) and the positive electrode mixture layer (120) by a specific ratio. Specifically, the width (W) of the reinforcing layer A ) value vs. the width of the cathode composite layer (W X ) and the width of the bipolar composite layer (W Y ) may be 0.5 to 1.5. If the ratio value is less than 0.5, the reinforcing layer (130) may be formed excessively large and protrude outside the electrode, and if the ratio value is more than 1.5, the reinforcing layer (130) may be formed excessively small, making it difficult to alleviate the phenomenon of the electrode bending in the direction of unit cell stacking according to the charge / discharge of the battery.

[0093] The above unit cell can satisfy the conditions according to Equation 2 below.

[0094] [Formula 2]

[0095] W A X 0.67 ≤ W X - W Y ≤ W A X 1.33

[0096] In the above equation 2, W A is the sum of the widths of all reinforcement layers (130), and W X is the width of the cathode composite layer (220), and W Y is the width of the bipolar composite layer (120).

[0097] The above reinforcing layer (130) may be formed to have substantially the same size as the gap area existing between the negative electrode mixture layer (220) and the positive electrode mixture layer (120) and may be formed to fill the entire gap area. Specifically, the width (W) of the reinforcing layer A ) value vs. the width of the cathode composite layer (W X ) and the width of the bipolar composite layer (W Y) may be 0.67 to 1.33, or 0.9 to 1.1, and may be substantially 1.0. When the ratio value is within the above-described range, the reinforcing layer (130) is formed to correspond to the gap region existing between the negative electrode mixture layer (220) and the positive electrode mixture layer (120), so that the phenomenon of the electrode bending in the unit cell stacking direction according to the charge / discharge of the battery can be effectively alleviated.

[0098] Above W X - W Y The value can be from 0.5 to 6.0 mm, and the W A The value may be 0.1 to 4.0 mm. Specifically, the negative electrode mixture layer (220) and the positive electrode mixture layer (120) may be formed to have a width difference of 0.5 to 6.0 mm, or 1.0 to 4.0 mm, and the reinforcing layer (130) may be formed to have a width of 0.1 to 4.0 mm, or 0.5 to 2.0 mm.

[0099] Above W X - W Y Value and W A The values ​​satisfy the above-described ranges and may also satisfy the conditions according to Equation 1 or Equation 2. In addition, when the reinforcing layer (130) is one (see Fig. 2a), the W A The value may be the width (A) of one reinforcing layer. On the other hand, if there are two reinforcing layers (130) (see Fig. 2b), the W A The value may be the sum of the width (A1) of the first reinforcing layer and the width (A2) of the second reinforcing layer. In addition, when the reinforcing layers (130) are three or more (not shown), the W A The value may be the sum of the width values ​​of all reinforcement layers.

[0100] The width difference (W) between the cathode composite layer (220) and the anode composite layer (120) X - W Y ) and the width (W) of the reinforcing layer (130) A) When the values ​​are as described above, it is possible to design a secondary battery having excellent energy density, safety, etc. by appropriately reducing the gap area between the negative and positive electrode composite layers without affecting each other.

[0101] The thickness of the above bipolar composite layer (T) Y ) thickness of the reinforcement layer (T) A ) ratio may be 0.9 to 1.1. Specifically, the thickness (T) of the positive electrode mixture layer Y ) thickness of the reinforcement layer (T) A ) ratio may be 1.0. That is, the thickness of the reinforcing layer (130) may be substantially the same as the thickness of the positive electrode mixture layer (120). If the thickness of the reinforcing layer (130) is excessively thin compared to the thickness of the positive electrode mixture layer (120), it is difficult to substantially achieve the effect of preventing damage to the outermost part of the positive electrode mixture layer (120) due to swelling of the electrode within the module. In the opposite case, since only a specific part becomes thicker, the thickness of the unit cell and secondary battery including the reinforcing layer (130) may become uneven.

[0102] The positive electrode (100) may further include a positive electrode mixture layer (120) formed on the other surface of the positive electrode current collector (110), and the negative electrode (200) may further include a negative electrode mixture layer (220) formed on the other surface of the negative electrode current collector (210). Specifically, the lithium secondary battery (1000) may include a unit cell in which the positive electrode (100) and the negative electrode (200) each have a mixture layer formed on one surface and the other surface of the current collector (see FIGS. 2e and 2f). At this time, a detailed description of the reinforcing layer (130), etc., is omitted because it overlaps with the above-described content.

[0103] The lithium secondary battery (1000) may include a plurality of unit cells according to any one of the above-described embodiments. For example, the lithium secondary battery (1000) may include a plurality of unit cells in which the positive electrode (100) and the negative electrode (200) each have a composite layer formed on one side and the other side of the current collector, and may include an electrode assembly in which the plurality of unit cells are alternately stacked (see FIGS. 2g and 2h ). The electrode assembly may be a stack type, a lamination / stack type, or a stack / folding type electrode assembly.

[0104] Hereinafter, a method for manufacturing a lithium secondary battery (1000) including the above-described unit cell will be specifically described with reference to FIG. 3.

[0105] The method for manufacturing a unit cell including the positive electrode (100) and negative electrode (200) is not particularly limited. For example, in the case of the positive electrode (100), first, a positive electrode slurry including a positive electrode active material may be applied onto a positive electrode current collector (110) by a method such as bar coating, casting, or spraying, and then a slurry for a reinforcing layer including a binder may be applied to a positive electrode non-coated portion (112) of the positive electrode current collector (110) where the positive electrode slurry is not applied by a method such as bar coating, casting, or spraying. Thereafter, the positive electrode slurry and the slurry for the reinforcing layer may be dried at 80 to 120°C to form a positive electrode mixture layer (120) and a reinforcing layer (130) on the surface of the positive electrode current collector (110).

[0106] In addition, in the case of the negative electrode (200), a negative electrode slurry containing a positive electrode active material may be applied to a negative electrode current collector (210) by a method such as bar coating, casting, or spraying, and the negative electrode slurry may be dried at 80 to 120°C to form a negative electrode mixture layer (220) on the surface of the negative electrode current collector (210).

[0107] At this time, each of the slurries may further include a solvent. Examples of the solvent include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. In addition, the amount of the solvent used is sufficient to dissolve or disperse the components and to have a viscosity that can exhibit excellent thickness uniformity when applied to a current collector, taking into account the coating thickness of the slurry, manufacturing yield, etc.

[0108] Afterwards, a notching process is performed on each structure in which an electrode mixture layer is formed on the surface of the electrode collector, thereby manufacturing a unit negative electrode in which a negative electrode tab is formed and a unit positive electrode in which a positive electrode tab is formed, and a stacking process in which the unit negative electrode and the unit positive electrode are alternately stacked is performed, thereby manufacturing an electrode assembly including a plurality of unit cells.

[0109] The above lithium secondary battery (1000) can be manufactured by inserting an electrode assembly in which a plurality of unit cells are alternately stacked into a battery case and then injecting an electrolyte.

[0110] The battery case may be one commonly used in the relevant field. For example, the battery case may be cylindrical, square, pouch-shaped, or coin-shaped, and preferably pouch-shaped. In addition, the battery case may have a structure in which an insulating layer, an adhesive layer, a metal film, etc. are laminated. The metal film may include aluminum (Al) or the like to secure the mechanical strength of the case and block moisture and oxygen.

[0111] The above electrolyte may include an organic solvent and a lithium salt. The organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move, and examples thereof include carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvents, which may be used singly or in combination of two or more. When two or more types are used in combination, the mixing ratio may be appropriately adjusted depending on the desired battery performance. The lithium salt is a substance that dissolves in an organic solvent and acts as a source of lithium ions in the battery, enables the basic operation of a lithium secondary battery, and promotes the movement of lithium ions between the positive and negative electrodes. Any known substance may be used as the lithium salt at a concentration appropriate for the purpose. The electrolyte may further include a known solvent and a known additive, if necessary, to improve charge / discharge characteristics, flame retardancy characteristics, etc.

[0112] Secondary battery modules and packs

[0113] A secondary battery module according to one embodiment includes a lithium secondary battery (1000) according to any one of the above-described embodiments. Specifically, the secondary battery module may include a plurality of the above-described unit cells and lithium secondary batteries, thereby exhibiting excellent performance, safety, etc.

[0114] A secondary battery pack according to one embodiment includes the secondary battery module. Specifically, the secondary battery pack can be used as a battery pack in which a plurality of secondary battery modules including the above-described lithium secondary batteries are combined and connected, and can be excellently utilized as a power source for medium and large-sized devices such as power tools, electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs).

[0115] [Explanation of symbols]

[0116] 100: positive electrode 110: positive electrode current collector

[0117] 111: Bipolar maintenance section 112: Bipolar non-maintenance section

[0118] 120: Bipolar compound layer 130: Reinforcement layer

[0119] 200: Cathode 210: Cathode current collector

[0120] 220: Cathode composite layer 300: Separator

[0121] 1000: Lithium secondary battery A: Width of the reinforcing layer

[0122] A1: Width of the first reinforcing layer A2: Width of the second reinforcing layer

[0123] W x : Width of the cathode composite layer W Y : Width of the bipolar composite layer

[0124] T Y : Thickness T of the bipolar composite layer A : Thickness of the reinforcing layer

[0125] G: Gap area

[0126] As described above, the features of the present invention can be applied to a lithium secondary battery and a secondary battery module including the same, in whole or in part.

Claims

1. A lithium secondary battery including a unit cell, The above unit cell includes an anode and a cathode, The above positive electrode includes a positive electrode current collector; and a positive electrode mixture layer formed on one surface of the positive electrode current collector, The above negative electrode comprises a negative electrode current collector; and a negative electrode composite layer formed on one surface of the negative electrode current collector, The above positive electrode material layer and negative electrode material layer are disposed between the positive electrode current collector and the negative electrode current collector, The width of the cathode composite layer is larger than the width of the anode composite layer, The above cathode current collector includes a cathode non-conducting portion in which a cathode composite layer is not formed, The above unit cell comprises at least one reinforcing layer including a binder between the positive electrode and negative electrode composite layers. Lithium secondary battery.

2. In paragraph 1, The above reinforcing layer is an inactive layer that does not contain a positive electrode active material and a negative electrode active material. Lithium secondary battery.

3. In paragraph 1, The above binder is at least one selected from polyvinyl fluoride (PVDF), polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), carboxymethyl cellulose (CMC), ethyl cellulose, acrylic resin, styrene-butadiene rubber (SBR), and polytetrafluoroethylene (PTFE). Lithium secondary battery.

4. In paragraph 1, The above unit cell satisfies the condition according to the following equation 1. Lithium secondary battery. [Formula 1] W A X 0.5 ≤ W X - W Y ≤ W A X 1.5 In the above equation 1, W A is the sum of the widths of all reinforcement layers, and W X is the width of the cathode composite layer, and W Y is the width of the bipolar composite layer.

5. In paragraph 4, The above unit cell satisfies the condition according to Equation 2 below. Lithium secondary battery. [Formula 2] W A X 0.67 ≤ W X - W Y ≤ W A X 1.33 In the above equation 2, W A is the sum of the widths of all reinforcement layers, and W X is the width of the cathode composite layer, and W Y is the width of the bipolar composite layer.

6. In paragraph 4, Above W X - W Y The values ​​are 0.5 to 6.0 mm, Above W A The values ​​are 0.1 to 4.0 mm, Lithium secondary battery.

7. In paragraph 1, The ratio of the thickness of the reinforcing layer to the thickness of the above-mentioned bipolar composite layer is 0.9 to 1.1, Lithium secondary battery.

8. In paragraph 1, The above positive electrode further includes a positive electrode composite layer formed on the other surface of the positive electrode collector, The above negative electrode further includes a negative electrode composite layer formed on the other surface of the negative electrode collector. Lithium secondary battery.

9. In any one of paragraphs 1 to 8, Containing multiple of the above unit cells, Lithium secondary battery.

10. Containing a lithium secondary battery according to Article 9, Secondary battery module.

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