Battery

Abstract

To provide a battery capable of suppressing peeling of a negative electrode current collector.SOLUTION: A battery according to the present disclosure includes, in this order, a positive electrode layer, an electrolyte layer containing an electrolytic solution, and a negative electrode layer, and the negative electrode layer includes, from the electrolyte layer side, a negative electrode active material layer and a negative electrode current collector, the negative electrode active material layer includes granulated particles containing Si particles having pores, the average particle size (D50) of the granulated particles is 5.5 μm or more and 7.2 μm or less, and the electrolytic solution includes an ionic liquid.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to batteries. [Background technology]

[0002] In recent years, it has been expected that lithium-ion secondary batteries will use Si-based materials as negative electrode active materials in order to further increase the capacity. Patent Document 1 discloses an electrode system including an active material containing nanosilicon, a polyacrylonitrile polymer that binds the active material to conduct electricity and lithium ions, and an electrolyte in contact with the active material, the electrolyte containing LiFSI salt and an ionic liquid having a bis(fluorosulfonyl)imide (FSF) anion. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2016-070120 Summary of the Invention [Problem to be solved by the invention]

[0004] Negative electrode active materials containing Si-based materials (hereinafter referred to as Si-based negative electrode active materials) have a high theoretical capacity density, but their volume changes significantly during charge and discharge. In liquid-based batteries, a solid electrolyte interphase (SEI) film is formed at the interface between the negative electrode and the electrolyte, mainly during charging, due to the reductive decomposition of the electrolyte. In liquid-based batteries using Si-based negative electrode active materials, the SEI film partially collapses due to volume changes during charging and discharging of the Si-based negative electrode active material, and is repeatedly reformed. This increases the battery resistance during charging and discharging, and causes a decrease in capacity due to Li depletion.

[0005] To reduce the expansion and contraction of Si-based negative electrode active materials, it is conceivable to use Si particles with fine pores (porous Si particles (p-Si particles)). However, because p-Si particles have a high specific surface area, they have poor interfacial adhesion, and expansion and contraction can cause the negative electrode current collector to peel off from the negative electrode active material layer. Peeling of the negative electrode current collector deteriorates cycle characteristics.

[0006] The present disclosure has been made in view of the above circumstances, and has as its main object to provide a battery capable of suppressing peeling of the negative electrode current collector. [Means for solving the problem]

[0007] [1] A battery having a positive electrode layer, an electrolyte layer containing an electrolytic solution, and a negative electrode layer in this order, the negative electrode layer includes, from the electrolyte layer side, a negative electrode active material layer and a negative electrode current collector, the negative electrode active material layer contains granulated particles containing Si particles having pores, The average particle size of the granulated particles (D 50 ) is 5.5 μm or more and 7.2 μm or less, The battery, wherein the electrolyte comprises an ionic liquid.

[0008] [2] the electrolyte solution further contains lithium bis(fluorosulfonyl)imide (LiFSI) as a Li salt; The ionic liquid contains a bis(fluorosulfonyl)imide anion (FSI) as an anion moiety, The battery according to [1], wherein the molar ratio of the Li salt to the ionic liquid (number of moles of the Li salt / number of moles of the ionic liquid) is 2 / 3 or more.

[0009] [3] The average particle size of the above Si particles (D 50 ) is 0.5 μm or more and 0.6 μm or less.

[0010] [4] The battery according to any one of [1] to [3], wherein the granulated particles contain a polyvinylidene fluoride-hexafluoropropylene copolymer. [Effects of the Invention]

[0011] The battery according to the present disclosure has an effect of being able to suppress peeling of the negative electrode current collector. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view illustrating a battery according to the present disclosure. [Figure 2] 1 shows SEM images of granulated particles 1 and granulated particles 2 used in Examples 1 and 2. [Figure 3] 1 shows charge / discharge curves of Comparative Example 1 and Comparative Example 2. [Figure 4] 1 shows charge / discharge curves, coulombic efficiency measurement results, and impedance measurement results of Example 1. [Figure 5] 1 shows charge / discharge curves, coulombic efficiency measurement results, and impedance measurement results of Example 2. [Figure 6] 1 is an observation diagram of the batteries of Reference Example and Comparative Example 1 at the time of the first discharge and after the cycle. DETAILED DESCRIPTION OF THE INVENTION

[0013] The battery of the present disclosure will be described in detail below with reference to the drawings. The following drawings are schematic illustrations, and the size and shape of each part are appropriately exaggerated for ease of understanding. Furthermore, in this specification, when describing an arrangement of another member relative to a certain member, the term "above" or "below" refers to both an arrangement of another member directly above or below the certain member, in contact with the certain member, and an arrangement of another member above or below the certain member via another member, unless otherwise specified.

[0014] 1 is a schematic cross-sectional view illustrating a battery according to the present disclosure. The battery 10 shown in FIG. 1 includes a negative electrode current collector 1, a negative electrode active material layer 2, an electrolyte layer 3, a positive electrode active material layer 4, and a positive electrode current collector 5 arranged in a thickness direction D T The negative electrode layer AN has, from the electrolyte layer 3 side, a negative electrode active material layer 2 and a negative electrode current collector 1. The positive electrode layer CA has a positive electrode active material layer 4 and a positive electrode current collector 5. In the present disclosure, the negative electrode active material layer 2 contains granulated particles containing Si particles having pores (hereinafter also referred to as p-Si particles), and the average particle size of the granulated particles is within a predetermined range. Also, in the present disclosure, the electrolyte solution contained in the electrolyte layer has an ionic liquid.

[0015] Because p-Si particles have a large specific surface area, they have poor interfacial adhesion with the negative electrode current collector, and expansion and contraction of the particles can easily cause peeling between the negative electrode current collector and the negative electrode active material layer. According to the present disclosure, the negative electrode active material layer 2 contains granulated particles obtained by granulating p-Si particles, and the average particle size of the granulated particles is within a predetermined range. Therefore, the specific surface area is reduced by granulation, which can prevent peeling of the negative electrode current collector 1. Furthermore, although there is concern that an increase in the average particle size due to granulation may reduce ionic conductivity, in the present disclosure, the electrolyte solution penetrates between the granulated particles, thereby preventing a decrease in ionic conductivity.

[0016] 1. Negative electrode layer The negative electrode layer in the present disclosure includes a negative electrode active material layer and a negative electrode current collector.

[0017] (1) Negative electrode active material layer The negative electrode active material layer contains at least granulated particles containing Si particles having pores. The negative electrode active material layer may further contain at least one of a conductive material and a binder.

[0018] (a) Granulated particles The granulated particles are granulated particles obtained by granulating Si particles having pores using, for example, a binder. The average particle size of the granulated particles (D 50 ) is 5.5 μm or more and 7.2 μm or less. 50) refers to the particle size (median diameter) at cumulative 50% of the cumulative particle size distribution, and is calculated, for example, from measurements using a laser diffraction particle size distribution analyzer or a scanning electron microscope (SEM). The granulated particles preferably contain a binder (granulation binder). The granulated particles do not necessarily need to contain a conductive material.

[0019] The p-Si particles have pores inside the primary particles. The presence of pores can suppress volume changes during charge and discharge. The porosity of the Si particles is not particularly limited, but is, for example, 5% or more and 50% or less. The porosity can be calculated, for example, by observing a scanning electron microscope (SEM) image of the cross section of the p-Si particle and using the following formula: Porosity (%) = 100 × (pore area) / (particle area)

[0020] The p-Si particles preferably have many pores with a pore diameter of 100 nm or less. The pore volume P1 of pores with a pore diameter of 100 nm or less is, for example, 0.1 cc / g or more, and may be 0.2 cc / g or more. On the other hand, the pore volume P1 is, for example, 0.5 cc / g or less, and may be 0.45 cc / g or less. In the present disclosure, the pore volume refers to the cumulative pore volume, and can be determined, for example, by BET measurement.

[0021] The p-Si particles preferably have many pores with a pore diameter of 10 nm or less. The pore volume P2 of the pores with a pore diameter of 10 nm or less is, for example, 0.03 cc / g or more, and may be 0.035 cc / g or more. On the other hand, the pore volume P2 is, for example, 0.08 cc / g or less, and may be 0.07 cc / g or less.

[0022] The p-Si particles may have a silicon clathrate crystal phase. The silicon clathrate crystal phase may be a silicon clathrate I crystal phase or a silicon clathrate II crystal phase. The p-Si particles may or may not have a diamond-type Si crystal phase.

[0023] The p-Si particles are not particularly limited in terms of particle size, etc., as long as they are granular. 50 ) is, for example, 0.3 μm or more, may be 0.4 μm or more, or may be 0.5 μm or more. 50 ) is, for example, 1.0 μm or less, may be 0.8 μm or less, or may be 0.6 μm or less.

[0024] The p-Si particles may have a predetermined BET specific surface area. The BET specific surface area of the p-Si particles may be, for example, 20.0 m 2 / g or more, and 25.0m 2 / g or more, and 2 / g or more, and 2 On the other hand, the BET specific surface area of the p-Si particles may be, for example, 60.0 m 2 / g or less, and 55.0m 2 / g or less, and 2 / g or less, and 2 / g or less, and 2 The BET specific surface area can be calculated, for example, by the BET method using a pore size distribution analyzer.

[0025] Examples of methods for producing p-Si particles include producing an alloy of Mg and Si (Mg—Si alloy) and then removing Mg from the Mg—Si alloy. The Mg—Si alloy can be obtained, for example, by heating a mixture of Mg and Si. The ratio of Mg to Si (Mg / Si) is, for example, 1.0 or more, or may be 1.5 or more, or even 2.0 or more. On the other hand, Mg / Si is, for example, 6.0 or less. Examples of methods for removing Mg from an Mg—Si alloy include heating the Mg—Si alloy in an oxygen-containing inert gas atmosphere to convert the Mg in the Mg—Si alloy to MgO, and then removing the MgO with an acid solution. Examples of acid solutions include aqueous solutions containing hydrochloric acid (HCl) and hydrogen fluoride (HF).

[0026] Furthermore, examples of methods for producing p-Si particles include producing an alloy of Li and Si (Li-Si alloy) and then removing Li from the Li-Si alloy. The Li-Si alloy can be obtained, for example, by mixing Li and Si. The ratio of Li to Si (Li / Si) is, for example, 1.0 or more, or may be 2.0 or more, 3.0 or more, or even 4.0 or more. On the other hand, Li / Si is, for example, 8.0 or less. Examples of methods for removing Li from a Li-Si alloy include reacting the Li-Si alloy with a Li extractant. Examples of Li extractants include alcohols such as methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, and 1-hexanol; and acids such as acetic acid, formic acid, propionic acid, and oxalic acid.

[0027] In addition, examples of methods for producing p-Si particles include producing an alloy of Mg and Si (Mg-Si alloy), then removing Mg from the Mg-Si alloy, then producing an alloy of Si and Li (Li-Si alloy) from which the Mg has been removed, and then removing Li from the Li-Si alloy.

[0028] The binder contained in the granulated particles (hereinafter also referred to as a granulation binder) can be appropriately selected from known binders used in lithium-ion secondary batteries. Examples include butadiene rubber (BR), butylene rubber (IIR), acrylate butadiene rubber (ABR), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVdF), and polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP). Among these, PVdF-HFP is preferred, and PVdF-HFP containing 50 mol % to 95 mol % of VDF is more preferred. PVdF-HFP may be a block copolymer or a random copolymer.

[0029] The proportion of p-Si particles and granulation binder in the granulated particles is not particularly limited, but the proportion of the granulation binder is, for example, 1 part by weight or more, 5 parts by weight or more, or even 10 parts by weight or more per 100 parts by weight of p-Si particles. On the other hand, the proportion of the granulation binder is, for example, 30 parts by weight or less, 20 parts by weight or less, or even 15 parts by weight or less per 100 parts by weight of p-Si particles. If the proportion of the granulation binder is too high, the proportion of the Si-based active material will be relatively low, which may result in a decrease in volumetric energy density.

[0030] Granulated particles can be produced, for example, by mixing (granulating) p-Si particles, a granulation binder, a solvent, and the like. The granulation method is not particularly limited, and examples thereof include tumbling granulation, fluidized bed granulation, stirring granulation, compression granulation, extrusion granulation, crushing granulation, and spray drying (atomization granulation). In the present disclosure, a mixture (suspension) obtained by mixing p-Si particles and a granulation binder in a solvent is preferably granulated by spray drying. In the spray drying method, the mixture is sprayed into a dry atmosphere. At this time, the particles contained in the sprayed droplets are granulated into roughly a single mass. Therefore, the amount of solids contained in the granulated particles varies depending on the size of the droplets, and the size and mass of the granulated particles vary. The sprayed droplets contain, for example, p-Si particles and a granulation binder. The sprayed droplets may also contain, for example, a conductive material or a thickener.

[0031] The proportion of granulated particles contained in the negative electrode active material layer is, for example, 40% by weight or more, or alternatively, 50% by weight or more, or even 60% by weight or more, while the proportion of granulated particles contained in the negative electrode layer is, for example, 95% by weight or less.

[0032] The negative electrode active material layer has a plurality of granulated particles, and an electrolyte solution, which will be described later, usually permeates and exists between the plurality of granulated particles.

[0033] The negative electrode active material layer may contain a conductive material. Examples of the conductive material include carbon materials, metal particles, and conductive polymers. Examples of the carbon material include particulate carbon materials such as acetylene black (AB) and ketjen black (KB), and fibrous carbon materials such as carbon fibers, carbon nanotubes (CNT), and carbon nanofibers (CNF).

[0034] The negative electrode active material layer may contain a binder. Examples of binders include fluoride-based binders, polyimide-based binders, and rubber-based binders. The binder contained in the negative electrode active material layer may be the same as or different from the granulation binder described above.

[0035] The thickness of the negative electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less.

[0036] An example of a method for forming the negative electrode active material layer includes first preparing a negative electrode active material layer-forming slurry containing at least granulated particles, and then applying the negative electrode active material layer-forming slurry to a negative electrode current collector and drying it. In the present disclosure, it is preferable not to perform a pressing process in which the negative electrode active material layer is pressed in the thickness direction when forming the negative electrode active material layer. Examples of pressing processes include a roller press and a flat plate press. By not performing a pressing process, the packing rate of the negative electrode active material layer can be reduced, and when a high-concentration electrolyte solution described below is used, reaction irregularities can be suppressed, resulting in further improved cycle characteristics. In the present disclosure, even without performing a pressing process, peeling of the negative electrode current collector can be suppressed by using the above-described granulated particles.

[0037] (2) Negative electrode current collector The negative electrode current collector is a layer that collects current from the negative electrode active material layer. Examples of the negative electrode current collector include metal current collectors. Examples of the metal current collector include current collectors containing metals such as Cu and Ni. The metal current collector may be a simple substance of the above metal or an alloy of the above metals. Examples of the shape of the negative electrode current collector include a foil shape.

[0038] 2. Electrolyte layer The electrolyte layer contains an electrolytic solution containing an ionic liquid. The ionic liquid has a cation moiety and an anion moiety. Examples of the cation moiety include organic nitrogen-based compounds (imidazolium salts, ammonium salts, pyridinium salts, piperidinium salts, etc.), organic phosphorus-based compounds (phosphonium salts, etc.), and organic sulfur-based compounds (sulfonium salts, etc.). On the other hand, examples of the anion moiety include AlCl4 - , NO2 - , NO3 - , I - , BF4 - , PF6 - , SbF6 - , NbF6 - , F(HF) 2.3 - , CH3CO2 - ,CH3SO3 - , CF3SO3 - , (CF3SO2)2N - , (FSO2)2N - (bis(fluorosulfonyl)imide anion (FSI)). Of these, the ionic liquid preferably contains FSI as the anion moiety.

[0039] The electrolyte preferably contains a Li salt, such as lithium bis(fluorosulfonyl)imide (LiFSI) or lithium bis(trifluoromethane)sulfonimide (LiTFSI), with LiFSI being preferred.

[0040] When the electrolyte solution of the present disclosure contains bis(fluorosulfonyl)imide anion (FSI) as the anion portion of the ionic liquid and lithium bis(fluorosulfonyl)imide (LiFSI) as the Li salt, the molar ratio of the Li salt to the ionic liquid (moles of Li salt / moles of ionic liquid) is preferably 2 / 3 or more. Such ionic liquid-containing electrolyte solutions with high lithium ion concentrations tend to achieve high average Coulombic efficiency when combined with a negative electrode containing Si. On the other hand, such high-concentration electrolyte solutions have high viscosity, which can easily cause reaction irregularities when the filling rate of the negative electrode active material layer is high. In the present disclosure, the use of the above-described granulated particles eliminates the need for a press process to suppress peeling of the current collector, allowing the formation of a negative electrode active material layer with a low filling rate. Therefore, such high-concentration electrolyte solutions can be preferably used.

[0041] The electrolyte layer may have a separator. The separator may be made of either an organic or inorganic material. Specific examples include porous membranes made of polyethylene (PE), polypropylene (PP), cellulose, polyvinylidene fluoride, polyamide, polyimide, or the like; nonwoven fabrics such as resin nonwoven fabrics and glass fiber nonwoven fabrics; and ceramic porous membranes. The separator may have a single-layer structure or a laminated structure.

[0042] 3. Positive electrode layer (1) Positive electrode active material layer The positive electrode active material layer contains at least a positive electrode active material, and may further contain at least one of an electrolyte, a conductive material, and a binder.

[0043] Examples of the positive electrode active material include oxide active materials, such as LiCoO2, LiMnO2, LiNiO2, LiVO2, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc., rock salt layered active materials, LiMn2O4, Li4Ti5O 12 , Li(Ni 0.5 Mn 1.5)O4, and olivine type active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4.

[0044] The positive electrode active material may be in the form of particles, for example. 50 ) is not particularly limited, but may be, for example, 10 nm or more, or may be 100 nm or more. On the other hand, the average particle diameter (D 50 ) is, for example, 50 μm or less, and may be 20 μm or less.

[0045] The conductive material used in the positive electrode active material layer is the same as that described in "1. Negative electrode layer" above, and therefore will not be described here. Examples of the electrolyte used in the positive electrode active material layer include the electrolytic solution described in "2. Electrolyte layer." Examples of the binder used in the positive electrode active material layer include the binders described in "1. Negative electrode." The thickness of the positive electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less.

[0046] (2) Positive electrode current collector The positive electrode current collector is a layer that collects current from the positive electrode active material layer. Examples of materials for the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon.

[0047] 4.Battery The battery in the present disclosure is typically a battery in which metal ions are conducted between the positive electrode layer and the negative electrode layer. Examples of such batteries include lithium ion batteries. The battery in the present disclosure is also a liquid battery in which the electrolyte layer contains an electrolytic solution. Alternatively, the battery may be a nonaqueous electrolyte battery that uses an electrolytic solution in which a supporting salt (Li salt) is dissolved in a solvent (ionic liquid) as the electrolyte.

[0048] Furthermore, the battery in this disclosure may be a primary battery or a secondary battery, but a secondary battery is preferable because it can be repeatedly charged and discharged and is useful, for example, as an in-vehicle battery. Secondary batteries also include secondary batteries used as primary batteries (use for the purpose of only the initial charge).

[0049] The battery in the present disclosure may be a single cell or a stacked battery. The stacked battery may be a monopolar stacked battery (a parallel-connected stacked battery) or a bipolar stacked battery (a series-connected stacked battery). The battery may also include a battery case that houses the negative electrode layer, the positive electrode layer, the electrolyte layer, and the like. Specific examples of the shape of the battery case include a coin type, a flat type, a cylindrical type, and a laminate type.

[0050] Applications of the battery in the present disclosure are not particularly limited, but examples include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered vehicles, and diesel-powered vehicles. In particular, the battery may be used as a driving power source for hybrid electric vehicles, plug-in hybrid electric vehicles, or electric vehicles. The battery in the present disclosure may also be used as a power source for mobile objects other than vehicles (e.g., trains, ships, and aircraft), or as a power source for electrical appliances such as information processing devices.

[0051] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Example]

[0052] (Comparative Example 1) A half cell was prepared comprising the following negative electrode, counter electrode, and electrolyte solution. The negative electrode active material layer was formed by coating a negative electrode current collector (Cu foil) with a slurry containing np-Si (nanoporous Si) particles as the negative electrode active material, polyimide resin as the binder, Ketjen Black (KB) as the conductive material, and vapor-grown carbon fiber (VGCF) in a ratio of 82:12:5:1 (wt%), in that order, and further containing a solvent. The slurry was then dried to form a negative electrode active material layer. This produced a negative electrode having a negative electrode current collector and a negative electrode active material layer. The np-Si particles had an average particle size (D 50 ) is 0.5 μm, and the specific surface area is 50 m 2 / g of porous Si particles. Li metal was used as the counter electrode. The electrolyte used was a mixture of LiFSI as the Li salt and ethylmethylimidazolium bis(fluorosulfonyl)imide (EMIm-FSI) and methylpropylpyrrolidinium bis(fluorosulfonyl)imide (P13-FSI) as the ionic liquid, with the Li salt dissolved in the ionic liquid at a molar ratio of Li salt / ionic liquid of 2 / 3.

[0053] (Comparative Example 2) A half cell similar to that of Comparative Example 1 was fabricated, except that pc-Si (porous clathrate Si) particles were used as the negative electrode active material. The pc-Si particles had an average particle size (D 50 ) is 0.6 μm, and the specific surface area is 33 m 2 / g of porous clathrate particles.

[0054] (Reference example) A half cell similar to that of Comparative Example 1 was fabricated, except that crystalline Si particles without pores were used as the negative electrode active material. The crystalline Si particles had an average particle size (D 50 ) is 2.6 μm, and the specific surface area is 1 m 2 / g.

[0055] Example 1 The np-Si particles used in Comparative Example 1 and granulation binder 1 were dispersed and dissolved in dimethyl carbonate at a ratio (wt%) of np-Si particles:granulation binder 1 = 100:14 to obtain a slurry. This slurry was sprayed into a spray dryer in a nitrogen gas atmosphere at a temperature of 140°C and dried. Granulation particles 1 were thus produced. A random copolymer containing VdF:HFP (molar ratio) = 89:11 and having a molecular weight of 650,000 was used as granulation binder 1. An SEM image of the obtained granulation particles 1 is shown in Figure 2(a). The average particle size (D 50 ) was 7.2 μm. A half cell similar to that of Comparative Example 1 was produced except that granulated particles 1 were used as the negative electrode active material.

[0056] Example 2 The pc-Si particles used in Comparative Example 2 and granulation binder 2 were dispersed and dissolved in dimethyl carbonate at a ratio (wt%) of pc-Si particles:granulation binder 2 = 100:8 to obtain a slurry. This slurry was sprayed into a spray dryer in a nitrogen gas atmosphere at a temperature of 140°C and dried. Granulation particles 2 were thus produced. A block copolymer with a molecular weight of 700,000 containing VdF:HFP (molar ratio) = 90:10 was used as granulation binder 2. An SEM image of the obtained granulation particles 2 is shown in Figure 2(b). The average particle size (D 50 ) was 5.5 μm. A half cell similar to that of Comparative Example 1 was prepared except that granulated particles 2 were used as the negative electrode active material.

[0057] [Calculation of average coulombic efficiency for 50 cycles using half-cell] In each of Comparative Examples 1 and 2, Reference Example, and Examples 1 and 2, 50 charge-discharge cycles were performed on each half-cell at 25°C and 0.1C, with a charge capacity of 1200 mAh / g. The cutoff voltage (discharge) was set to 10 mV. Charge-discharge curves for Comparative Example 1, Comparative Example 2, Reference Example, Example 1, and Example 2 are shown in Figures 3(a), 3(b), 3(c), 4(a), and 5(a), respectively. Comparative Example 1 reached the cutoff voltage at the 7th cycle, and Comparative Example 2 at the 10th cycle. This is presumably due to an increase in resistance caused by peeling of the current collecting foil, as described below.

[0058] The coulombic efficiency per cycle was calculated for each half-cell of Example 1 and Example 2. The results are shown in Figure 4(b) and Figure 5(b). Coulomb efficiency (%) = (discharge capacity / charge capacity) x 100

[0059] For each half-cell of Comparative Examples 1 and 2, Examples 1 and 2, and Reference Example, the results of the coulombic efficiency immediately before reaching cutoff (Comparative Examples 1 and 2) or after 50 cycles (Examples 1, 2, and Reference Example) are shown in Table 1. Table 1 confirms that the coulombic efficiency after cycling is improved compared to before granulation (Comparative Examples 1 and 2).

[0060] [Table 1]

[0061] Figure 6(a) shows cross-sectional SEM images of the Reference Example at the time of the first discharge and after cycling. Figure 6(b) shows cross-sectional SEM images of the Comparative Example at the time of the first discharge and after cycling. As shown in Figure 6(a), in the Reference Example, the current collector foil and the negative electrode active material layer remained bonded even after cycling. On the other hand, as shown in Figure 6(b), in the Comparative Example 1, peeled portions occurred where the negative electrode active material layer and the negative electrode current collector had peeled off during the first discharge, and it was confirmed that the current collector foil had completely peeled off after cycling.

[0062] Impedance measurements were performed on the initial and post-cycle batteries (SOC=100%) of Examples 1 and 2. The impedance measurement results (Nyquist plots) are shown in Figures 4(c) and 5(c). The horizontal axis represents the real component (resistance component) of the complex impedance. The vertical axis represents the imaginary component (capacitance component) of the complex impedance. Since there was no increase in the DC component (DC resistance), it was confirmed that no peeling of the current collecting foil had occurred. [Explanation of symbols]

[0063] 1 … Negative electrode current collector 2 … Negative electrode active material layer 3 … Electrolyte layer 4... Positive electrode active material layer 5 … Positive electrode current collector 10…Battery

Claims

1. A battery having a positive electrode layer, an electrolyte layer containing an electrolytic solution, and a negative electrode layer in this order, the negative electrode layer includes, from the electrolyte layer side, a negative electrode active material layer and a negative electrode current collector, the negative electrode active material layer contains granulated particles containing Si particles having pores, The average particle size of the granulated particles (D ５０ ) is 5.5 μm or more and 7.2 μm or less, The battery, wherein the electrolyte comprises an ionic liquid.

2. The electrolyte solution further contains lithium bis(fluorosulfonyl)imide (LiFSI) as a Li salt, the ionic liquid contains a bis(fluorosulfonyl)imide anion (FSI) as an anion moiety, 2. The battery according to claim 1, wherein a molar ratio of the Li salt to the ionic liquid (molar number of the Li salt / molar number of the ionic liquid) is 2 / 3 or more.

3. The average particle size (D ５０ 3. The battery according to claim 1, wherein the thickness of the first electrode is 0.5 μm or more and 0.6 μm or less.

4. 3. The battery according to claim 1, wherein the granulated particles contain polyvinylidene fluoride-hexafluoropropylene copolymer.

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