Patent Publication Number: US-2022231326-A1

Title: All-solid-state batteries comprising composite electrode

Description:
TECHNICAL FIELD 
     This application claims the benefit of priority to Korean Patent Application No. 2019-0053694 filed on May 8, 2019, the disclosure of which is hereby incorporated by reference herein its entirety. 
     The present invention relates to an all-solid-state battery comprising a composite electrode capable of complementing the low electrochemical performance of all-solid-state batteries by disposing an electrode generating a large amount of heat in the center of the electrode assembly. 
     BACKGROUND ART 
     As mobile electronic devices including mobile phones are required to have multiple functions, the demand for lithium secondary batteries with high energy density has been increased. 
     In addition, in order to use lithium secondary batteries in power storage devices and electric vehicles requiring high capacity and high output energy sources, research on safety improvement and high voltage of lithium secondary batteries has been actively conducted. 
     A lithium ion secondary battery, which is a kind of the lithium secondary batteries, has advantages of high energy density, low self-discharge rate, and long lifespan compared to a nickel manganese battery or a nickel cadmium battery. However, the stability problem against overheating with the lithium ion secondary battery has been pointed out as a disadvantage. 
     In order to overcome the problems of the lithium ion secondary battery, an all-solid-state battery has been proposed as an alternative. The all-solid-state battery may comprise an electrolyte layer including a solid electrolyte, and a positive electrode layer and a negative electrode layer including a solid electrolyte formed on both sides of the electrolyte layer, and may be configured to have a structure in which a current collector may be coupled to each of the positive electrode layer and the negative electrode layer. 
     When compared to a conventional lithium-ion secondary battery, the all-solid-state battery has superior safety than the conventional lithium-ion secondary battery. However, since the solid electrolyte has low ion conductivity, the all-solid-state battery has a problem of poor performance such as capacity and output. 
     In order to solve the problems described above, a technology using the characteristics of an all-solid-state battery in which the ion conductivity is greatly improved when the temperature is increased has been proposed as an alternative. 
     In particular, Patent Document 1 discloses a secondary battery in which a heat generation unit insulated from electrodes is disposed on a current collector, the secondary battery provided with a temperature control unit and a current-carrying control unit for detecting the temperature of the inside of the battery and controlling a current into the heat generation unit. 
     When a separate heat generation unit is provided as in Patent Document 1, there are problems in that energy density is lowered due to the increase of the overall size of the battery and energy is wasted when a separate power is required for an external heat generation unit. 
     Patent Document 2 discloses a non-aqueous electrolyte secondary battery capable of suppressing heat generation of the battery, the nonaqueous electrolyte secondary battery providing a PTC layer between a positive electrode active material layer and a positive electrode current collector, wherein the PTC layer is composed of a collection of conductive particles, thereby blocking the flow of current under heating conditions due to overcharging of the battery. 
     Patent Document 3 discloses a non-aqueous secondary battery having a structure in which a conductive layer covers an electrode current collector, the conductive layer including a crystalline thermoplastic resin having a function of a constant temperature coefficient resistor whose resistance value increases when the temperature rises, a conductive material, and a binder. 
     Patent Document 2 and Patent Document 3 only disclose a technology for preventing heat generation by blocking current when the battery temperature rises, but fail to provide a method for maintaining the heat generation state of the battery. 
     Patent Document 4 relates to a battery cell in which a heating element that emits resistance heat by interaction inside the battery is disposed at one or both interfaces of a unit cell located in the center of an electrode assembly. 
     Patent Document 4 discloses the battery cell comprising the heating element that increases the internal temperature of the battery. However, since the thickness of the battery cell comprising the heating element increases or the thickness of the electrode assembly decreases relatively, there is a problem in that energy density decreases. 
     Therefore, there is a high need for a technology capable of improving the function of a battery by increasing the battery temperature in an all-solid-state battery, and at the same time, capable of preventing energy density from being lowered in an all-solid-state battery without increasing the volume of a battery cell and without adding a separate external power. 
     PRIOR ART DOCUMENT 
     
         
         (Patent Document 1) Japanese Patent No. 5314872 (2013 Jul. 12) 
         (Patent Document 2) Japanese Patent Application Publication No. 2009-176599 (2009 Aug. 6) 
         (Patent Document 3) Japanese Patent Application Publication No. 2001-357854 (2001 Dec. 26) 
         (Patent Document 4) Korean Patent No. 1760647 (2017 Jul. 18) 
       
    
     DISCLOSURE 
     Technical Problem 
     The present invention has been made in view of the above problems, and it is an object of the present invention to provide an all-solid-state battery having characteristics of high capacity and high energy density by raising the battery temperature itself by heat generated in a normal operating environment of the battery by applying an electrode having a large amount of heat generation to a part of electrodes of an electrode assembly. 
     Technical Solution 
     In order to accomplish the above objects, the present invention provides an all-solid-state battery comprising an electrode assembly and a solid electrolyte, wherein the electrode assembly includes a structure in which plate-shaped electrodes are stacked; and the electrodes include a relatively high heat-generating first electrode and a relatively low heat-generating second electrode, wherein the first electrode is disposed in a center of the electrode assembly. 
     In a concrete example, the electrode assembly may be a stacked type electrode assembly; and the first electrode and the second electrode may have the same composition of an active material, wherein an amount ratio of the solid electrolyte in the first electrode may be higher than an amount ratio of the solid electrolyte in the second electrode. 
     Alternatively, the electrode assembly may be a laminated/stacked type electrode assembly or a stacked/folded type electrode assembly comprising a plurality of unit cells, wherein the plurality of unit cells are configured to have a first unit cell including the first electrode and a second unit cell including the second electrode. The first electrode and the second electrode may have the same composition of an active material, wherein an amount ratio of the solid electrolyte in the first electrode may be higher than an amount ratio of the solid electrolyte in the second electrode. 
     In another concrete example, the electrode assembly may be a stacked type electrode assembly; and an active material of the first electrode and an active material of the second electrode may be a relatively high heat-generating negative electrode active material and a relatively low heat-generating negative electrode active material selected from among hard carbon, soft carbon, artificial graphite, natural graphite coated with artificial graphite, natural graphite, and silicon oxide. 
     Alternatively, the electrode assembly may be a laminated/stacked type electrode assembly or a stacked/folded type electrode assembly comprising a plurality of unit cells; the plurality of unit cells may be configured to have a first unit cell including the first electrode and a second unit cell including the second electrode; and an active material of the first electrode and an active material of the second electrode may be a relatively high heat-generating negative electrode active material and a relatively low heat-generating negative electrode active material selected from among hard carbon, soft carbon, artificial graphite, natural graphite coated with artificial graphite, natural graphite, and silicon oxide. 
     In addition, each of the first unit cell and the second unit cell may include a uniform active material. 
     The electrode may be a positive electrode or a negative electrode, or a positive electrode and a negative electrode. 
     The solid electrolyte may be a sulfide-based solid electrolyte, an oxide-based solid electrolyte or a polymer-based solid electrolyte. 
     A temperature of the first electrode may be transferred to the second electrode to increase an internal temperature of the battery. 
     The all-solid-state battery may have a larger capacity at subzero temperatures compared to an all-solid-state battery composed of a single electrode and having the same capacity at room temperature. 
     The present invention provides a battery pack comprising the all-solid-state battery, and a device comprising the battery pack. The device may be any one selected from a group consisting of mobile electronic devices, wearable electronic devices, tablet computers, laptop computers, electric vehicles, and power storage devices. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is side views showing stacked type electrode assemblies including a plurality of positive electrodes and negative electrodes. 
         FIG. 2  is a side view showing a stacked/folded type electrode assembly according to the present invention. 
         FIG. 3  is a side view showing a laminated/folded type electrode assembly according to the present invention. 
         FIG. 4  is a graph showing results according to Experimental Example 1. 
         FIG. 5  is a graph showing results according to Experimental Example 2. 
         FIG. 6  is a graph showing results according to Experimental Example 3. 
     
    
    
     BEST MODE 
     Now, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings such that the preferred embodiments of the present invention can be easily implemented by a person having ordinary skill in the art to which the present invention pertains. In describing the principle of operation of the preferred embodiments of the present invention in detail, however, a detailed description of known functions and configurations incorporated herein will be omitted when the same may obscure the subject matter of the present invention. 
     In addition, the same reference numbers will be used throughout the drawings to refer to parts that perform similar functions or operations. In the case in which one part is said to be connected to another part in the specification, not only may the one part be directly connected to the other part, but also, the one part may be indirectly connected to the other part via a further part. In addition, that a certain element is included does not mean that other elements are excluded, but means that such elements may be further included unless mentioned otherwise. 
     The present invention relates to an all-solid-state battery comprising an electrode assembly and a solid electrolyte, wherein the electrode assembly has a structure in which plate-shaped electrodes are stacked. 
     In general, the electrode assembly may be divided into a structure in which plate-shaped electrodes are stacked such as a stacked type electrode assembly, a stacked/folded type electrode assembly, and a laminated/stacked electrode assembly, or a jelly-roll type electrode assembly structure in which a long sheet-type electrode is wound. 
     Since the jelly-roll type electrode assembly includes one positive electrode and one negative electrode, the jelly-roll type electrode assembly has a structure in which it is difficult to diversify the configuration of the electrode. On the other hand, since the stacked type, stacked/folded type and laminated/stacked type electrode assemblies are configured such that a plurality of plate-shaped electrodes are stacked, various types of positive electrodes and negative electrodes can be applied. 
     Accordingly, an electrode assembly of an all-solid-state battery according to the present invention includes a relatively high heat-generating first electrode and a relatively low heat-generating second electrode, wherein the first electrode may be disposed in a center of the electrode assembly. 
     The relatively high heat-generating first electrode used in the present specification is an electrode having a relatively large amount of heat generated, and may be an electrode using a high heat-generating electrode active material or an electrode having an amount ratio of solid electrolyte higher than that of the second electrode. The relatively low heat-generating second electrode used in the present specification is a relatively low heat-generating electrode compared to the first electrode, and may be an electrode using a low heat-generating electrode active material or an electrode having an amount ratio of solid electrolyte lower than that of the first electrode. 
     The first electrode may be located in the center of the electrode assembly, and thus, the first electrode may be disposed in the center of the electrode assembly composed of a plurality of electrodes. Alternatively, a unit cell including the first electrode or composed of the first electrode may be disposed in the center of the electrode assembly. By placing the first electrode having a high exothermic property in the center of the electrode assembly, the temperature of the first electrode can be transferred to the second electrode, thereby increasing the internal temperature of the battery. 
     In general, the high heat-generating first electrode may damage the electrode active material or the internal structure of the electrode due to a high rate, thereby deteriorating a lifespan characteristic. However, the low heat-generating second electrode, which exhibits a relatively stable rate, may exhibit a relatively excellent lifespan characteristic due to less damage to the electrode active material or the internal structure of the electrode. 
     Therefore, in order to increase the overall temperature of the electrode assembly, when the electrode assembly includes both the high heat-generating first electrode and the second electrode having a stable lifespan characteristic, the first electrode and the second electrode may complement their inferior characteristics to each other. 
     In this regard,  FIG. 1  is side views showing stacked type electrode assemblies including a plurality of positive electrodes and negative electrodes. 
     Referring to  FIG. 1 , an electrode assembly  100  of  FIG. 1( a )  is a stacked type electrode assembly having a structure in which a plurality of positive electrodes  101  and  101 ′ and a plurality of negative electrodes  102  are stacked with a solid electrolyte layer  103  interposed therebetween. 
     The positive electrode  101 ′ disposed at the center of the electrode assembly  100  is a high heat-generating first electrode, and the positive electrode  101  disposed at an outer side of the electrode assembly  100  is a low heat-generating second electrode. In addition, in consideration of the performance of the battery, the two negative electrodes  102  may be applied simultaneously or selectively as a high heat-generating first negative electrode or as a low heat-generating second negative electrode. As described above, by disposing the high heat-generating positive electrode at the center of the electrode assembly, thermal energy may be transferred in opposite directions based on a stacking direction of the electrodes, thereby uniformly raising the internal temperature of the battery. 
     An electrode assembly  110  of  FIG. 1( b )  is a stacked type electrode assembly having a structure in which a plurality of positive electrodes  111  and a plurality of negative electrodes  112  and  112 ′ are stacked with a solid electrolyte layer  113  interposed therebetween. 
     The negative electrode  112 ′ disposed at the center of the electrode assembly  110  may be a high heat-generating first negative electrode, and the negative electrode  112  disposed at an outer side of the electrode assembly may be a low heat-generating second negative electrode. 
     In addition, in consideration of the performance of the battery, the two positive electrodes  111  may be applied simultaneously or selectively as a high heat-generating first positive electrode or as a low heat-generating second positive electrode. As described above, by disposing the high heat-generating negative electrode at the center of the electrode assembly, thermal energy may be transferred in opposite directions based on a stacking direction of the electrodes, thereby uniformly raising the internal temperature of the battery. 
     In a concrete example, each of the positive electrode  101 , the positive electrode  101 ′, the negative electrode  112 , and the negative electrode  112 ′ has a difference in the amount ratio of the solid electrolyte, while the composition of the electrode active material may be the same. 
     For example, the negative electrode  112  and the negative electrode  112 ′ may be artificial graphite, natural graphite, natural graphite coated with artificial graphite, silicon oxide, hard carbon, or soft carbon. 
     In addition, the positive electrode  101  and the positive electrode  101 ′ may be Ni—Co—Mn oxide (LiNCMO 2 (LiNCM)), lithium nickel oxide (LiNiO 2 (LNO)), oxide of olivine structure (LFP(LiFePO 4 ) or LiMnPO 4 (LMP)), lithium cobalt oxide (LiCoO 2 (LCO)) or lithium manganese oxide (LiMn 2 O 4 (LMO)). 
     In another concrete example, the positive electrode  101 ′ and the negative electrode  112 ′ may have a form in which a high heat-generating electrode active material is applied, and the positive electrode  101  and the negative electrode  112  may have a form in which a low heat-generating electrode active material is applied. 
     When the heat generation of negative electrode active materials are listed in order from high to low, it is in the order of hard carbon&gt;soft carbon&gt;artificial graphite&gt;natural graphite coated with artificial graphite&gt;natural graphite&gt;silicon oxide. When the heat generation of positive electrode active materials are listed in order from high to low, it is in the order of LMO&gt;LCO&gt;LiNCM&gt;LNO&gt;LMP, LFP. 
     The positive electrode  101 ′ and the negative electrode  112 ′ have relatively higher heat generation than the positive electrode  101  and the negative electrode  112 . Thus, in consideration of the magnitude of heat generation described above, the relatively high heat-generating positive electrode and negative electrode, and the relatively low heat-generating positive electrode and negative electrode may be selectively applied. 
     Alternatively, the positive electrode active material and the negative electrode active material may be selected and applied from the electrode active materials divided into a high heat-generating group and a low heat-generating group. 
     For example, the negative electrode  112  may be one or more selected from the group consisting of artificial graphite, natural graphite, natural graphite coated with artificial graphite, and silicon oxide, and the negative electrode  112 ′ may be one or more selected from the group consisting of hard carbon and soft carbon. 
     The positive electrode  101  may be one or more selected from the group consisting of Ni—Co—Mn oxide (LiNCMO 2 , Ni&gt;60%) with Ni of more than 60%, lithium nickel oxide (LiNiO 2 (LNO)), and olivine-structured oxide (LFP (LiFePO 4 ) or LiMnPO 4 (LMP)). The positive electrode  101 ′ may be one or more selected from the group consisting of lithium cobalt oxide (LiCoO 2 (LCO)), lithium manganese oxide (LiMn 2 O 4 (LMO)), and Ni—Co—Mn oxide (LiNCMO 2 , Ni&lt;60%) with Ni of 60% or less. 
       FIG. 2  is a side view showing a stacked/folded type electrode assembly according to the present invention. 
     Referring to  FIG. 2 , the electrode assembly  200  is a stacked/folded type electrode assembly in which a solid electrolyte layer  290  is compressed while being positioned bi-cell type unit cells  210 ,  220 ,  230 ,  240 ,  250 ,  260 ,  270 , and  280  on one side of the solid electrolyte layer  290 , the unit cells configured to have a structure of positive electrode/solid electrolyte layer/negative electrode/solid electrolyte layer/positive electrode or a negative electrode/solid electrolyte layer/positive electrode/solid electrolyte layer/negative electrode. The electrode assembly  200  prevents the solid electrolyte layer  290  from loosening by attaching a fixing tape  291  to an end of the solid electrolyte layer  290 . 
     The electrode assembly  200  is composed of eight unit cells. The unit cells  210 ,  220 ,  230 , and  240  disposed in the center of the electrode assembly are first unit cells including a first electrode having a high exothermic property that includes an electrode active material having a high amount ratio of solid electrolyte or a large amount of heat generated when compared to the unit cells  250 ,  260 ,  270 , and  280  disposed at outer sides of the electrode assembly. The unit cells  250 ,  260 ,  270 , and  280  are second unit cells including a low heat-generating second electrode. 
     In particular, both of the positive electrode and the negative electrode constituting the first unit cells may be a high heat-generating first positive electrode and a high heat-generating first negative electrode. Alternatively, the high heat-generating first positive electrode or the high heat-generating first negative electrode may be applied to only one of the positive electrode or the negative electrode in the first unit cells. 
     However, both the positive electrode and the negative electrode constituting the second unit cells may be a low heat-generating second positive electrode and a low heat-generating second negative electrode. 
     The first positive electrode and the first negative electrode, and the second positive electrode and the second negative electrode may be applied in the same manner as described in the description of  FIG. 1 , respectively, in the case in which (i) the amount ratio of solid electrolyte is applied differently and the same kind of electrode active material is applied, or (ii) a relatively high heat-generating electrode active material and a relatively low heat-generating electrode active material are applied. 
     Unlike the unit cells shown in  FIG. 2 , only two of the first unit cells may be applied to the center, and the second unit cells may be applied to six unit cells excluding the first unit cells. Alternatively, the second unit cells may be applied to the unit cells  270  and  280  located at the outermost part of the electrode assembly, and the first unit cells may be applied to the remaining six unit cells. 
     In the electrode assembly  200  of  FIG. 2 , the positive electrode and the negative electrode constituting the first unit cells  210 ,  220 ,  230 , and  240  may be designed to have the same electrode constituent materials, such as an electrode active material, a conductive agent, and a solid electrolyte. Alternatively, the positive electrode and the negative electrode constituting the first unit cells  210 ,  220 ,  230 , and  240  may be designed to be selectively different in the type and/or composition ratio of the electrode constituent materials in a state in which the amount of heat generated is higher than that of the second unit cells. 
     In addition, the positive electrode and the negative electrode constituting the second unit cells  250 ,  260 ,  270 , and  280  may be designed to have the same electrode constituent materials, such as an active material, a conductive agent, and a solid electrolyte. Alternatively, the positive electrode and the negative electrode constituting the second unit cells  250 ,  260 ,  270 , and  280  may be designed to be selectively different in the type and/or composition ratio of the electrode constituent materials in a state in which the amount of heat generated is lower than that of the first unit cells. 
       FIG. 3  is a side view showing a laminated/folded type electrode assembly according to the present invention. 
     Referring to  FIG. 3 , the electrode assembly  300  is a laminated/stacked type electrode assembly in which bi-cell type unit cells  310 ,  320 ,  330 ,  340 ,  350 ,  360 ,  370 , and  380  having a structure of positive electrode/solid electrolyte layer/negative electrode/solid electrolyte layer/positive electrode or a negative electrode/solid electrolyte layer/positive electrode/solid electrolyte layer/negative electrode are stacked with a solid electrolyte layer  390  interposed therebetween and are heat-sealed. 
     The unit cells  330 ,  340 ,  350 , and  360  located in the center of the electrode assembly  300  are high exothermic unit cells having properties corresponding to the unit cells  210 ,  220 ,  230 , and  240 , which are the first unit cells of  FIG. 2 . The unit cells  310 ,  320 ,  370 , and  380  located on the outer periphery of the electrode assembly  300  are low exothermic unit cells having properties corresponding to the unit cells  250 ,  260 ,  270 , and  280 , which are the second unit cells of  FIG. 2 . 
     Therefore, the description of the unit cells  330 ,  340 ,  350 , and  360  and the unit cells  310 ,  320 ,  370 , and  380  of the electrode assembly  300  may be applied in the same manner as the description of the unit cells  210 ,  220 ,  230 , and  240  and the unit cells  250 ,  260 ,  270 , and  280  of the electrode assembly  200 . 
     The solid electrolyte may be a sulfide-based solid electrolyte, an oxide-based solid electrolyte or a polymer-based solid electrolyte. 
     It is preferable for the sulfide-based solid electrolyte to contain a sulfur atom (S), to exhibit ion conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and to exhibit electronic insulation properties. Although it is preferable that the sulfide-based solid electrolyte contains at least Li, S and P as elements, and has lithium ion conductivity, the sulfide-based solid electrolyte may contain elements other than Li, S and P depending on the purpose or case. 
     Specifically, examples of the sulfide-based solid electrolyte are as follows. For example, Li 2 S—P 2 S 5 , Li 2 S—P 2 S 5 —LiCl, Li 2 S—P 2 S 5 —H 2 S, Li 2 S—P 2 S 5 —H 2 S—LiCl, Li 2 S—LiI—P 2 S 5 , Li 2 S—LiI—Li 2 O—P 2 S 5 , Li 2 S—LiBr—P 2 S 5 , Li 2 SLi 2 O—P 2 S 5 , Li 2 S—Li 3 PO 4 —P 2 S 5 , Li 2 S—P 2 S 5 —P 2 O 5 , Li 2 S—P 2 S 5 —SiS 2 , Li 2 S—P 2 S 5 —SiS 2 —LiCl, Li 2 S—P 2 S 5 —SnS, Li 2 S—P 2 S 5 —Al 2 S 3 , Li 2 S—GeS 2 , Li 2 S—GeS 2 —ZnS, Li 2 S—Ga 2 S 3 , Li 2 S—GeS 2 —Ga 2 S 3 , Li 2 S—GeS 2 —P 2 S 5 , Li 2 S—GeS 2 —Sb 2 S 5 , Li 2 S—GeS 2 —Al 2 S 3 , Li 2 S—SiS 2 , Li 2 S—Al 2 S 3 , Li 2 S—SiS 2 —Al 2 S 3 , Li 2 S—SiS 2 —P 2 S 5 , Li 2 S—SiS 2 —P 2 S 5 —LiI, Li 2 S—SiS 2 —LiI, Li 2 S—SiS 2 —Li 4 SiO 4 , Li 2 SSiS 2 —Li 3 PO 4 , or Li 10 GeP 2 S 12  may be used. 
     An example of a method of synthesizing the sulfide-based solid electrolyte material is an amorphization method. Examples of the amorphization method include a mechanical milling method, a solution method, and a melting and rapid cooling method. Among them, the mechanical milling method is preferable because it is possible to process at room temperature (25° C.) and it has the advantage of simplifying the manufacturing process. 
     It is preferable for the oxide-based solid electrolyte to contain an oxygen atom (O), to exhibit ion conductivity of a metal belonging to Group 1 or 2 of the periodic table, and to exhibit electrical insulation. 
     As the oxide-based solid electrolyte, for example, there may be used Li xa La ya TiO 3  (xa=0.3 to 0.7 and ya=0.3 to 0.7) (LLT), Li xb La yb Zr zb M bb   mb O nb  (M bb  is at least one of Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, or Sn, xb satisfies 5≤xb≤10, yb satisfies 1≤yb≤4, zb satisfies 1≤zb≤4, mb satisfies 0≤mb≤2, and nb satisfies 5≤nb≤20), Li xc B yc M cc   zc O nc  (M cc  is at least one of C, S, Al, Si, Ga, Ge, In, or Sn, xc satisfies 0≤xc≤5, yc satisfies 0≤yc≤1, zc satisfies 0≤zc≤1, and nc satisfies 0≤nc≤6), Li xd (Al, Ga) yd (Ti, Ge) zd Si ad P md O nd  (here, 1≤xd≤3, 0≤yd≤1, 0≤zd≤2, 0≤ad≤1, 1≤md≤7, and 3≤nd≤13), Li (3−2xe) M ee   xe D ee O (xe satisfies 0≤xe≤0.1, M ee  is a two-valent metal atom, and D ee  indicates a halogen atom or a combination of two or more kinds of halogen atoms), Li xf Si yf O zf  (1≤xf≤5, 0≤yf≤3, and 1≤zf≤10), Li xg S yg O zg  (1≤xg≤3, 0≤yg≤2, and 1≤zg≤10), Li 3 BO 3 —Li 2 SO 4 , Li 2 O—B 2 O 3 —P 2 O 5 , Li 2 O—SiO 2 , Li 6 BaLa 2 Ta 2 O 12 , Li 3 PO (4−3/2w) N w  (w&lt;1), Li 3.5 Zn 0.25 GeO 4  having a lithium super ionic conductor (LISICON) type crystalline structure, La 0.55 Li 0.35 TiO 3  having a perovskite type crystalline structure, LiTi 2 P 3 O 12  having a natrium super ionic conductor (NASICON) type crystalline structure, Li 1+xh+yh (Al, Ga) xh (Ti, Ge) 2−xh Si yh P 3−yh O 12  (here, 0≤xh≤1 and 0≤yh≤1), or Li 7 La 3 Zr 2 O 12 (LLZ) having a garnet type crystalline structure. In addition, a phosphorus compound including Li, P, and O is preferably used. For example, lithium phosphate (Li 3 PO 4 ), LiPON in which a portion of oxygen in lithium phosphate is replaced by nitrogen, or LiPOD 1  (D 1  being at least one selected from among Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, and Au) may be used. In addition, LiA 1 ON (A 1  being at least one selected from among Si, B, Ge, Al, C, and Ga) is preferably used. 
     The polymer-based solid electrolyte may be a solid polymer electrolyte formed by adding a polymer resin to a lithium salt that is independently solvated or a polymer gel electrolyte formed by impregnating a polymer resin with an organic electrolytic solution containing an organic solvent and lithium salt. 
     The solid polymer electrolyte is not particularly restricted as long as the solid polymer electrolyte is made of, for example, a polymer material that is ion conductive and is generally used as a solid electrolyte material of the all-solid-state battery. As examples of the solid polymer electrolyte, mention may be made of a polyether-based polymer, a polycarbonate-based polymer, an acrylate-based polymer, a polysiloxane-based polymer, a phosphazene-based polymer, a polyethylene derivative, an alkylene oxide derivative, a phosphoric acid ester polymer, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and a polymer containing an ionic dissociation group. In a concrete embodiment of the present invention, the solid polymer electrolyte may include: a branch-like copolymer formed by copolymerizing an amorphous polymer, such as poly methyl methacrylate (PMMA), polycarbonate, polysiloxane, and/or phosphazene, which is a comonomer, in the main chain of a polyethylene oxide (PEO), which is a polymer resin; a comb-like polymer resin; and a crosslinking polymer resin. 
     The polymer gel electrolyte includes an organic electrolytic solution including lithium salt and a polymer resin, wherein the organic electrolytic solution is included in an amount of 60 parts by weight to 400 parts by weight based on weight of the polymer resin. Although the polymer resin applied to the polymer gel electrolyte is not limited to specific components, a PVC-based resin, a poly methyl methacrylate (PMMA)-based resin, polyacrylonitrile (PAN), polyvinylidene fluoride (PVdF), and polyvinylidene fluoride hexafluoropropylene (PVdF-HFP) may be included. 
     The lithium salt is a lithium salt that can be ionized and may be represented by Li + X − . Although a negative ion of the lithium salt is not particularly restricted, F − , Cl − , Br − , I − , NO 3   − , N(CN) 2   − , BF 4   − , ClO 4   − , PF 6   − , (CF 3 ) 2 PF 4   − , (CF 3 ) 3 PF 3   − , (CF 3 ) 4 PF 2   − , (CF 3 ) 5 PF − , (CF 3 ) 6 P − , CF 3 SO 3   − , CF 3 CF 2 SO 3   − , (CF 3 SO 2 ) 2 N − , (FSO 2 ) 2 N − , CF 3 CF 2 (CF 3 ) 2 CO − , (CH 3 SO 2 ) 2 CH − , (SF 5 ) 3 C − , (CF 3 SO 2 ) 3 C − , CF 3 (CF 2 ) 7 SO 3   − , CF 3 CO 2   − , CH 3 CO 2   − , SCN − , or (CF 3 CF 2  SO 2 ) 2 N −  may be illustrated. 
     Hereinafter, the present invention will be described with reference to the following examples. These examples are provided only for easier understanding of the present invention and should not be construed as limiting the scope of the present invention. 
     Example 1 
     As shown in  FIG. 3 , a laminated/stacked type electrode assembly including eight unit cells was manufactured. 
     Among the unit cells, one high heat-generating unit cell was disposed at the center of the electrode assembly, and seven low heat-generating unit cells were disposed on both sides of the high heat-generating unit cell, thereby completing an electrode assembly including all eight unit cells. 
     The high heat-generating unit cell includes a positive electrode prepared using 75 weight % of LiNi 0.8 Co 0.1 Mn 0.1 O 2  as a positive electrode active material, 5 weight % of Super P as a conductive agent, 15 weight % of polyethylene oxide (PEO) as a solid electrolyte, 5 weight % of polyvinylidene fluoride (PVDF) as a binder; and a negative electrode prepared using 71 weight % of artificial graphite as a negative electrode active material, 2 weight % of Super C as a conductive agent, 23 weight % of polyethylene oxide (PEO) as a solid electrolyte, and 4 weight % of styrene-butylene rubber (SBR)+carboxymethyl cellulose (CMC) as a binder. 
     The low heat-generating unit cell includes a positive electrode prepared using 85 weight % of LiNi 0.8 Co 0.1 Mn 0.1 O 2  as a positive electrode active material, 3 weight % of Super C as a conductive agent, 8 weight % of polyethylene oxide (PEO) as a solid electrolyte, 4 weight % of polyvinylidene fluoride (PVDF) as a binder; and a negative electrode prepared using 83 weight % of artificial graphite as a negative electrode active material, 1 weight % of Super C as a conductive agent, 13 weight % of polyethylene oxide (PEO) as a solid electrolyte, and 3 weight % of styrene-butylene rubber (SBR)+carboxymethyl cellulose (CMC) as a binder. 
     A solid electrolyte layer interposed between the positive electrode and the negative electrode was prepared and used by dissolving polyethylene oxide and LiFSI in acetonitrile at a ratio of 20 mol % and 1 mol % and casting them thinly on a glass plate, followed by vacuum-drying to a thickness of 100 μm. 
     Example 2 
     An electrode assembly was manufactured using the same method as Example 1, except that the number of high heat-generating unit cells was two and the number of low heat-generating unit cells was six. 
     Example 3 
     An electrode assembly was manufactured using the same method as Example 1, except that the number of high heat-generating unit cells was three and the number of low heat-generating unit cells was five. 
     Example 4 
     An electrode assembly was manufactured using the same method as Example 1, except that the number of high heat-generating unit cells was four and the number of low heat-generating unit cells was four. 
     Comparative Example 1 
     As shown in  FIG. 3 , a laminated/stacked type electrode assembly including eight unit cells was manufactured. 
     The unit cells all include electrodes having the same heat generation property. 
     In particular, the unit cell includes a positive electrode prepared using 80 weight % of LiNi 0.8 Co 0.1 Mn 0.1 O 2  as a positive electrode active material, 4 weight % of Super C as a conductive agent, 10 weight % of polyethylene oxide (PEO) as a solid electrolyte, 6 weight % of polyvinylidene fluoride (PVDF) as a binder; and a negative electrode prepared using 77 weight % of artificial graphite as a negative electrode active material, 1.5 weight % of Super C as a conductive agent, weight % of polyethylene oxide (PEO) as a solid electrolyte, and 3.5 weight % of styrene-butylene rubber (SBR)+carboxymethyl cellulose (CMC) as a binder. 
     The electrode assembly of Comparative Example 1 was designed to have the same capacity as the electrode assemblies of Examples 1 to 4 at room temperature. 
     Experimental Example 1 
     In order to confirm the improved level of low-temperature capacity of the electrode assembly including the high heat-generating electrode, secondary batteries including the electrode assemblies manufactured in Examples 1 to 4 and Comparative Example 1 were fully charged and fully discharged at −10° C.  FIG. 4  shows a graph showing the ratio of the improved capacity based on the capacity of Comparative Example 1. 
     Referring to  FIG. 4 , it can be seen that the capacity of the battery increases as the number of high heat-generating unit cells increases. 
     Since the experiment was conducted under low temperature conditions, it can be confirmed that the capacity improvement effect at low temperature is excellent in the case of the present invention. 
     Example 5 
     As shown in  FIG. 3 , a laminated/stacked type electrode assembly including eight unit cells was manufactured. 
     Among the unit cells, four high heat-generating unit cells were disposed at the center of the electrode assembly, and two low heat-generating unit cells were disposed each side of the high heat-generating unit cell, thereby completing an electrode assembly including all eight unit cells. 
     The high heat-generating unit cell includes a negative electrode prepared using 80 weight % of natural graphite as a negative electrode active material, 2 weight % of Super C as a conductive agent, 13 weight % of polyethylene oxide (PEO) as a solid electrolyte, and 5 weight % of styrene-butylene rubber (SBR)+carboxymethyl cellulose (CMC) as a binder; and a positive electrode prepared using 80 weight % of LiNi 0.8 Co 0.1 Mn 0.1 O 2  as a positive electrode active material, 4 weight % of Super C as a conductive agent, 10 weight % of polyethylene oxide (PEO) as a solid electrolyte, 6 weight % of polyvinylidene fluoride (PVDF) as a binder. 
     The low heat-generating unit cell was manufactured using the same method as the high heat-generating unit cell, except that artificial graphite was used instead of natural graphite, which was the negative electrode active material used for the high heat generating unit cell. 
     A solid electrolyte layer interposed between the positive electrode and the negative electrode was prepared and used by dissolving polyethylene oxide and LiFSI in acetonitrile at a ratio of 20 mol % and 1 mol % and casting them thinly on a glass plate, followed by vacuum-drying to a thickness of 100 μm. 
     Example 6 
     An electrode assembly was manufactured using the same method as Example 5, except that soft carbon was used instead of natural graphite used for the high heat-generating negative electrode in Example 5. 
     Example 7 
     An electrode assembly was manufactured using the same method as Example 5, except that hard carbon was used instead of natural graphite used for the high heat-generating negative electrode in Example 5. 
     Comparative Example 2 
     As shown in  FIG. 3 , a laminated/stacked type electrode assembly including eight unit cells was manufactured. 
     The unit cells all include electrodes having the same heat generation property. 
     In particular, the electrode assembly was manufactured using the same positive electrode and solid electrolyte as in Example 5, except that a negative electrode including artificial graphite as the negative electrode active material was applied to the unit cell. 
     The electrode assembly of Comparative Example 2 was designed to have the same capacity as the electrode assemblies of Examples 5 to 7 at room temperature. 
     Experimental Example 2 
     In order to confirm the improved level of low-temperature capacity by applying a negative electrode active material with different heat generating properties, secondary batteries including the electrode assemblies manufactured in Examples 5 to 7 and Comparative Example 2 were fully charged and fully discharged at −10° C.  FIG. 5  shows a graph showing the ratio of the improved capacity based on the capacity of Comparative Example 2. 
     Referring to  FIG. 5 , it can be seen that there is an effect of increasing the capacity of the battery according to the type of the negative electrode active material. In particular, it is confirmed that the capacity of the battery increases in the order of natural graphite, soft carbon and hard carbon. 
     Since the experiment was conducted under low temperature conditions, it can be confirmed that the capacity improvement effect at low temperature is excellent in the case of the present invention. 
     Comparative Example 3 
     An electrode assembly was manufactured using the same method as Example 1, except that two high heat-generating unit cells manufactured in Example 1 were disposed at both ends of the electrode assembly and six low heat-generating unit cells manufactured in Example 1 were disposed at the center of the electrode assembly so as to have a laminated/stacked electrode assembly including eight unit cells as shown in  FIG. 3 . 
     Experimental Example 3 
     In order to confirm the improved level of battery capacity according to the location of high heat-generating electrode, secondary batteries including the electrode assemblies manufactured in Example 2 and Comparative Example 3 were fully charged and fully discharged at −10° C.  FIG. 6  shows a graph showing the ratio of the improved capacity based on the capacity of Comparative Example 1. 
     Referring to  FIG. 6 , it can be seen that the secondary battery including the electrode assembly of Example 2 has a capacity improvement effect of about 3.5% compared to the secondary battery including the electrode assembly composed of only the electrodes of Comparative Example 1 with uniform heat generation. 
     However, the secondary battery including the electrode assembly of Comparative Example 3, in which the high heat-generating unit cells were disposed only at both ends of the electrode assembly, appears to have a lower battery capacity than the secondary battery including the electrode assembly of Comparative Example 1. 
     Therefore, it can be seen that when the number of high heat-generating electrodes is the same, a capacity-increasing effect is remarkably increased when the high heat-generating electrodes are disposed at the center of the electrode assembly rather than disposed at both ends of the electrode assembly. 
     A person having ordinary skill in the art to which the present invention pertains will appreciate that various applications and modifications are possible based on the above description without departing from the scope of the present invention. 
     DESCRIPTION OF REFERENCE NUMERALS 
     100, 110, 200, 300: Electrode assemblies 
     101, 101′,  111 : Positive electrodes 
     102, 112, 112′: Negative electrodes 
     103, 113, 290, 390: Solid electrolyte layers 
     210, 220, 230, 240, 250, 260, 270, 280, 310, 320, 330, 340, 350, 360, 370, 380: Unit cells 
     291: Fixing tape 
     INDUSTRIAL APPLICABILITY 
     As is apparent from the above description, an all-solid-state secondary battery including a composite electrode according to the present invention partially includes an electrode generating a large amount of heat, and thus, the overall temperature increase effect can be obtained due to the thermal energy generated during normal use of the battery. 
     In addition, by applying an electrode assembly including both a high heat-generating electrode and a low heat-generating electrode, it is possible to maintain not only the temperature increase effect by the high heat-generating electrode, but also the lifespan improvement effect by the low heat-generating electrode. 
     In addition, since a separate heat generation member is not added for heat generation, an additional external power source is not required, so that the volume of the battery can be prevented from increasing to provide the external power source.