Fluorine-based lubricant, electrode, and secondary battery

Abstract

The present disclosure solves the problem by providing a fluorine-based lubricant which is used in an active material layer containing an active material and a sulfide solid electrolyte, and which is solid at 25°C.

Description

Fluorine-based lubricant, electrode and secondary battery

[0001] The present disclosure relates to a fluorine-based lubricant, an electrode, and a secondary battery.

[0002] Batteries such as lithium ion secondary batteries include electrodes having a current collector and an active material layer. For example, Patent Document 1 discloses a negative electrode composite layer for an all-solid-state lithium ion secondary battery that contains porous silicon particles as the negative electrode active material and a sulfide-based solid electrolyte. Patent Document 2 discloses that the active material layer contains an electrolyte (electrolytic solution) that contains an alkali metal salt dissolved in a nonaqueous solvent containing a perfluoroether. Patent Document 3 discloses an electrode that contains a perfluoropolyether group-containing compound on its surface.

[0003] JP 2020-170605 A JP 2018-200866 A JP 2018-147887 A

[0004] In an active material layer containing an active material and a sulfide solid electrolyte, the active material contained in the active material layer expands and contracts during charge and discharge. If the volume change in the active material layer is large, the active material particle interfaces may peel off, potentially causing electrode peeling. If electrode peeling occurs, the battery resistance may increase and battery performance may deteriorate. In particular, active materials containing Si (Si-based active materials) are effective in increasing the energy density of batteries, but they undergo large volume changes during charge and discharge, making them prone to the aforementioned deterioration in battery performance.

[0005] The present disclosure has been made in view of the above circumstances, and has as its main object to provide a fluorine-based lubricant that can suppress electrode peeling.

[0006] [1] A fluorine-based lubricant that is used in an active material layer containing an active material and a sulfide solid electrolyte and is solid at 25°C.

[0007] [2] The fluorine-based lubricant according to [1], having a melting point of 120°C or less.

[0008] [3] The fluorine-based lubricant according to [1] or [2], having a fluoropolyether structure.

[0009] [4] An electrode having an active material layer and a current collector, wherein the active material layer contains a Si-based active material, a sulfide solid electrolyte, and a fluorine-based lubricant, and the fluorine-based lubricant is the fluorine-based lubricant according to any one of [1] to [3].

[0010] [5] The electrode according to [4], wherein the Si-based active material and the solid fluorine-based lubricant are combined.

[0011] [6] The electrode according to [4] or [5], wherein the ratio of the fluorine-based lubricant to the Si-based active material is 4% by weight or more and 12% by weight or less.

[0012] [7] A secondary battery comprising the electrode according to any one of [4] to [6].

[0013] The present disclosure has an effect of providing a fluorine-based lubricant that can suppress peeling of electrodes.

[0014] 1 is a schematic cross-sectional view illustrating a secondary battery according to the present disclosure.

[0015] The fluorine-based lubricant, electrode, and secondary battery according to the present disclosure will be described in detail below. Here, in the present disclosure, the term "fluorine-based lubricant" refers to a lubricant containing fluorine (F).

[0016] A. Fluorine-Based Lubricant The fluorine-based lubricant in the present disclosure is used in an active material layer containing an active material and a sulfide solid electrolyte, and is solid at 25° C. The active material, the sulfide solid electrolyte, and the active material layer will be described later.

[0017] As described above, active materials expand and contract during charge and discharge, and the volume change is particularly large in Si-based active materials. Therefore, there is a risk of peeling occurring in electrodes using active materials. However, it is presumed that the fluorine-based lubricant in the present disclosure penetrates into gaps formed by peeling between the interfaces of the active materials, thereby suppressing (repairing) the peeling of the electrode.

[0018] The melting point of the fluorine-based lubricant is, for example, 38°C or higher, or may be 50°C or higher, 65°C or higher, or 80°C or higher. On the other hand, the melting point of the fluorine-based lubricant is, for example, 200°C or lower, or may be 150°C or lower, or may be 100°C or lower. When the fluorine-based lubricant has the above melting point, even if the interface between the active materials peels off due to the expansion and contraction of the active materials, the fluorine-based lubricant undergoes a phase transition to a liquid due to the heat generated by charging and discharging the battery or by heating the battery, and functions as a lubricant between the active materials to repair the peeling, thereby suppressing an increase in battery resistance. In particular, the melting point of the fluorine-based lubricant is preferably in the range of 60°C or higher and 120°C or lower. Here, the melting point of the fluorine-based lubricant can be determined using a differential scanning calorimetry (DSC) device as the temperature corresponding to the maximum value in the heat of fusion curve when the temperature is increased at a rate of 5°C / min.

[0019] Fluorine-based lubricants typically contain at least one of a fluoroalkyl group and a fluoroalkylene group. The fluoroalkyl group may be a functional group in which all of the hydrogen atoms in an alkyl group have been substituted with fluorine (perfluoroalkyl group), or a functional group in which some of the hydrogen atoms in an alkyl group have been substituted with fluorine. The number of carbon atoms in the fluoroalkyl group may be, for example, 1 to 10, or 1 to 5. The number of carbon atoms in the fluoroalkylene group may be, for example, 1 to 20, or 1 to 15. The fluoroalkyl lubricant may have a linear or branched chain structure. The fluoroalkyl lubricant may or may not have an ether bond in the main chain. The terminal functional group located at the end of the fluorolubricant is not particularly limited. Examples of terminal functional groups include a fluorine group, a hydrogen group, a hydroxyl group, an aldehyde group, a carboxylic acid group, a C1-10 alkyl ester group, an amide group which may have one or more substituents, and an amino group which may have one or more substituents.

[0020] An example of a fluorine-based lubricant is a carboxylic acid compound containing at least one of a fluoroalkyl group and a fluoroalkylene group. The number of carbon atoms in the fluoroalkyl group and the fluoroalkylene group is as described above. The carboxylic acid compound may have one carboxy group, two carboxy groups, or three or more carboxy groups. Examples of the carboxylic acid compound include the following compounds: HOOC-(CF ２ ) ２ -COOH HOOC- (CF ２ ) ３ -COOH HOOC- (CF ２ ) ４ -COOH HOOC-CF ２ O (CF ２ ) ２ OCF ２ -COOH CF ３ (CF ２ ) １０ -COOH CF ３ (CF ２ ) １２ -COOH

[0021] Other examples of fluorine-based lubricants include alcohol compounds containing at least one of a fluoroalkyl group and a fluoroalkylene group. The number of carbon atoms in the fluoroalkyl group and the fluoroalkylene group is as described above. The alcohol compounds may have one hydroxyl group, two hydroxyl groups, or three or more hydroxyl groups. Examples of alcohol compounds include the following compounds: HO-CH ２ (CF ２ ) ２ CH ２ -OH HO-CH ２ (CF ２ ) ３ CH ２ -OH HO-CH ２ (CF ２ ) ４ CH ２ -OH HO-CH ２ CF ２ O (CF ２ )２ OCF ２ CH ２ -OH CF ３ (CF ２ ) １３ -OH

[0022] Other examples of fluorine-based lubricants include fluoroalkanes. The number of carbon atoms in the fluoroalkanes is, for example, 10 or more and 20 or less. Examples of the fluoroalkanes include the following compounds: CF ３ (CF ２ ) １１ CF ３ CF ３ (CF ２ ) １４ CF ３ CF ３ (CF ２ ) １８ CF ３

[0023] Other examples of fluorine-based lubricants include ester compounds containing at least one of a fluoroalkyl group and a fluoroalkylene group. The carbon numbers of the fluoroalkyl group and the fluoroalkylene group are as described above. Among them, the carbon number of the fluoroalkylene group is preferably 8 or more and 15 or less. The ester compound may have one ester group, two ester groups, or three or more ester groups. Examples of the ester compound include the following compounds. CH ３ OOC-(CF ２ ) １０ -COOCH ３ CF ３ (CF ２ ) １２ -COOCH ３

[0024] Further, examples of fluorine-based lubricants include compounds having a fluoropolyether structure (FPE structure). Compounds having a fluoropolyether structure (FPE structure) have a structure represented by the following formula (1): E1-Rf1-RF-O-Rf2-E2 (1) [In formula (1), Rf1 and Rf2 each independently represent a C1-16 divalent alkylene group which may be substituted with one or more fluorine atoms, E1 and E2 each independently represent a monovalent group selected from the group consisting of a fluorine group, a hydrogen group, a hydroxyl group, an aldehyde group, a carboxylic acid group, a C1-10 alkyl ester group, an amide group which may have one or more substituents, and an amino group which may have one or more substituents, and RF represents -(AO) ｎ - (A contains a carbon chain as the main chain and has at least one fluorine atom bonded to the carbon chain).] The number of carbon atoms in the carbon chain of A is preferably, for example, 1, 2, 3, or 4. A may or may not contain a hydrogen atom. In addition, A may contain, as a side chain, -CF ３－ｘ H ｘ (0≦x≦3). From the viewpoint of being a solid at 25° C., RF may be -(CH ２ CF ２ CF ２ O) ｎ - is preferred, and n is a number of 1 or more.

[0025] Among the above-mentioned compounds, compounds having a fluoropolyether structure are preferred because of their electrochemical stability and low volatility at high temperatures.

[0026] B. Electrode The electrode according to the present disclosure is an electrode having an active material layer and a current collector, the active material layer containing an active material and a fluorine-based lubricant, and the fluorine-based lubricant is the fluorine-based lubricant described above.

[0027] According to the present disclosure, the active material layer in the electrode contains the above-mentioned fluorine-based lubricant, and therefore the electrode is prevented from peeling off.

[0028] 1. Active Material Layer The electrode according to the present disclosure includes an active material layer and a current collector. The active material layer contains an active material, a sulfide solid electrolyte, and a fluorine-based lubricant.

[0029] (1) Active Material Examples of active materials include carbon-based active materials, oxide active materials, and metal active materials. Examples of carbon-based active materials include graphite. Examples of oxide active materials include lithium titanate. Examples of metal active materials include Si-based active materials. Among these, Si-based active materials are preferred. Si-based active materials contain at least elemental Si. Examples of Si-based active materials include simple Si, Si alloys, and Si oxides. Preferably, Si alloys contain elemental Si as a primary component. The proportion of elemental Si in the Si alloy is, for example, 50 at% or more, or may be 70 at% or more, or even 90 at% or more. Examples of Si alloys include Si-Li-based alloys, Si-Al-based alloys, Si-Sn-based alloys, Si-In-based alloys, Si-Ag-based alloys, Si-Pb-based alloys, Si-Sb-based alloys, Si-Bi-based alloys, Si-Mg-based alloys, Si-Ca-based alloys, Si-Ge-based alloys, and Si-Pb-based alloys. The Si alloy may be a binary alloy or a multi-component alloy (three or more components). The Si alloy may be a Si-Li alloy. Examples of Si oxides include SiO.

[0030] The active material may be in the form of particles, for example. ５０ ) is, for example, 10 nm or more and 50 μm or less. ５０ ) refers to the cumulative 50% particle size in the volume-based particle size distribution measured by a laser diffraction particle size distribution analyzer.

[0031] The proportion of the active material in the active material layer is, for example, 50% by weight or more and 99% by weight or less.

[0032] (2) Sulfide Solid Electrolyte A sulfide solid electrolyte is typically an electrolyte containing sulfur (S) as a main anion element. The sulfide solid electrolyte preferably contains, for example, Li, X (wherein X is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S. The sulfide solid electrolyte may further contain at least one of O and a halogen element.

[0033] Examples of sulfide solid electrolytes include Li ２ S-P ２ S ５ , Li ２ S-P ２ S ５ - LiI, Li ２ S-P ２ S ５ -GeS ２ , Li ２ S-P ２ S ５ -Li ２ O, Li ２ S-P ２ S ５ -Li ２ O-LiI, Li ２ S-P ２ S ５ -LiI-LiBr, Li ２ S-SiS ２ , Li ２ S-SiS ２ - LiI, Li ２ S-SiS ２ - LiBr, Li ２ S-SiS ２ -LiCl, Li ２ S-SiS ２ -B ２ S ３ - LiI, Li ２ S-SiS ２ -P ２ S ５ - LiI, Li ２ S-B ２ S ３ , Li ２ S-P ２ S ５ -Z ｍ S ｎ(where m and n are positive numbers. Z is Ge, Zn, or Ga.), Li ２ S-GeS ２ , Li ２ S-SiS ２ -Li ３ P.O. ４ , Li ２ S-SiS ２ -Li ｘ MO ｙ (where x and y are positive numbers, and M is any of P, Si, Ge, B, Al, Ga, and In.)

[0034] The sulfide solid electrolyte may be glass (amorphous) or glass ceramic. ５０ ) is, for example, 0.01 μm or more and 10 μm or less.

[0035] The proportion (wt %) of the sulfide solid electrolyte in the active material layer is, for example, 10 wt % or more and 50 wt % or less.

[0036] (3) Fluorine-Based Lubricants The melting points and types of fluorine-based lubricants are the same as those described in "A. Fluorine-Based Lubricants," and therefore will not be described here.

[0037] In the active material layer, the ratio of the fluorine-based lubricant to the active material is, for example, 4% by weight or more, or may be 6% by weight or more, or may be 8% by weight or more, while the ratio may be, for example, 12% by weight or less, or may be 10% by weight or less.

[0038] In addition, in the active material layer, it is preferable that the active material and the solid fluorine-based lubricant are composited.For example, the active material and the solid fluorine-based lubricant that have been physically mixed by mechanical milling or the like are used as the active material material.Whether the active material and the solid fluorine-based lubricant are composited or not can be confirmed by microscopic observation such as SEM (scanning electron microscope) and TEM (transmission electron microscope).By composited the active material and the solid fluorine-based lubricant, the interface between the active materials is more favorably formed, and it is thought that the resistance in the initial charge / discharge cycle is particularly suppressed.

[0039] (4) Active Material Layer The active material layer may contain at least one of a conductive aid and a binder in addition to the above-mentioned active material, sulfide solid electrolyte, and fluorine-based lubricant.

[0040] Examples of the conductive additive include carbon materials, such as particulate carbon materials such as acetylene black (AB) and ketjen black (KB), and fibrous carbon materials such as carbon fiber, carbon nanotubes (CNT), and carbon nanofibers (CNF).

[0041] Examples of binders include rubber-based binders such as butadiene rubber (BR), acrylate butadiene rubber (ABR), and styrene butadiene rubber (SBR), as well as fluorine-containing binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

[0042] The thickness of the active material layer is not particularly limited, but is, for example, 0.1 μm or more and 1000 μm or less. The active material layer may be a positive electrode active material layer or a negative electrode active material layer. In other words, the electrode in the present disclosure may be a positive electrode or a negative electrode.

[0043] 2. Current Collector The current collector is a member that has the function of collecting electrons from the active material layer described above. The current collector may be a positive electrode current collector or a negative electrode current collector. Examples of materials for the current collector include metals such as aluminum, copper, SUS, and nickel. Examples of the shape of the current collector include foil and mesh.

[0044] 3. Electrodes The electrodes in the present disclosure are typically used in secondary batteries, which will be described later.

[0045] B. Secondary Battery FIG. 1 is a schematic cross-sectional view illustrating a secondary battery according to the present disclosure. The secondary battery 100 shown in FIG. 1 includes a positive electrode 10A having a positive electrode current collector 1a and a positive electrode active material layer 2a, a negative electrode 10B having a negative electrode current collector 1b and a negative electrode active material layer 2b, and an electrolyte layer 11 disposed between the positive electrode 10A and the negative electrode 10B. The secondary battery 100 includes the electrodes described above. Specifically, at least one of the positive electrode 10A and the negative electrode 10B in the secondary battery 100 corresponds to the electrode described in "A. Electrode" above.

[0046] According to the present disclosure, since the secondary battery includes the above-described electrode (electrode in which peeling is suppressed), the secondary battery is one in which an increase in resistance due to peeling of the electrode is suppressed.

[0047] 1. Positive Electrode A secondary battery typically has a positive electrode. The positive electrode typically has a positive electrode current collector and a positive electrode active material layer disposed on the electrolyte layer side of the positive electrode current collector. The positive electrode in a secondary battery preferably corresponds to the above-described electrode. On the other hand, when the positive electrode in the present disclosure does not correspond to the above-described electrode, the negative electrode in the present disclosure typically corresponds to the above-described electrode. In this case, any conventional positive electrode can be used as the positive electrode.

[0048] 2. Negative Electrode A secondary battery typically has a negative electrode. The negative electrode typically has a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector facing the electrolyte layer. The negative electrode in a secondary battery preferably corresponds to the above-described electrode. On the other hand, when the negative electrode in the present disclosure does not correspond to the above-described electrode, the positive electrode in the present disclosure typically corresponds to the above-described electrode. In this case, any conventional negative electrode can be used as the negative electrode.

[0049] 3. Electrolyte Layer A secondary battery typically has an electrolyte layer disposed between the positive electrode and the negative electrode. More specifically, the electrolyte layer typically is disposed between the positive electrode active material layer and the negative electrode active material layer. The electrolyte layer preferably contains the sulfide solid electrolyte described above as an electrolyte. In other words, the electrolyte layer is preferably a solid electrolyte layer.

[0050] 4. Secondary Battery The secondary battery in the present disclosure is typically a lithium-ion secondary battery. Preferably, the secondary battery is an all-solid-state battery containing a sulfide solid electrolyte as the solid electrolyte. Examples of uses for the secondary battery 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 secondary battery is preferably used as a driving power source for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or electric vehicles (BEVs). The secondary battery may also be used as a power source for mobile objects other than vehicles (e.g., railways, 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.

[0052] Synthesis Example 1 (Synthesis of Compound 1-1) 15.4 g of cesium fluoride, 290 mL of diglyme, and 107.0 g of methyl 2,2,3-trifluoro-3-oxopropanoate were added to a nitrogen-purged reaction vessel and stirred for 10 minutes at 5°C in an ice bath. Subsequently, 526.0 g of 2,2,3,3-tetrafluorooxetane was added dropwise to the reaction vessel from the dropping funnel over 20 minutes at 5°C in an ice bath, and the mixture was stirred for 2 hours. The ice bath was then removed, and the mixture was stirred for 50 hours to obtain a reaction solution. 60 mL of methanol was added dropwise to the obtained reaction solution over 20 minutes, and the mixture was stirred for 24 hours. Volatiles were then distilled off from the reaction solution under reduced pressure. Subsequently, 80 g of m-xylene hexafluoride and 40 g of water were added, followed by separation and washing. 5 g of magnesium sulfate was added to the extracted organic layer, and the mixture was dried to obtain a treated solution. Volatile matter was removed from the resulting treated solution by distillation to obtain Compound 1-1 (a compound having an FPE structure) represented by the following chemical formula.

[0053]

[0054] Comparative Example 1 A conductive additive, a binder, a sulfide solid electrolyte, and a positive electrode active material (LiNi ０．８ Co ０．１５ Mn ０．０５ O ２ ) was added and kneaded using an ultrasonic homogenizer. This resulted in a positive electrode slurry. The positive electrode slurry was applied to a positive electrode current collector (Al foil) and dried to produce a positive electrode having a positive electrode current collector and a positive electrode active material layer. Note that butyl butyrate was used as the organic solvent, VGCF was used as the conductive additive, PVDF was used as the binder, and 10LiI-15LiBr-75Li was used as the sulfide solid electrolyte. ３ P.S. ４ The same materials were used in the procedures described below.

[0055] Next, a conductive additive, a binder, a sulfide solid electrolyte, and a negative electrode active material (Si particles) were added to an organic solvent and kneaded using an ultrasonic homogenizer. This resulted in a negative electrode slurry. The negative electrode slurry was applied to a negative electrode current collector (Cu foil) and dried to produce a negative electrode having a negative electrode current collector and a negative electrode active material layer.

[0056] Next, a binder and a sulfide solid electrolyte were added to the organic solvent and kneaded using an ultrasonic homogenizer. This resulted in a solid electrolyte layer slurry. The resulting solid electrolyte slurry was applied to a transfer foil (Al foil) and dried to produce a transfer member having a solid electrolyte layer and a transfer foil.

[0057] The positive electrode, negative electrode, and transfer member were molded into a strip shape. Then, the positive electrode and transfer member were stacked so that the solid electrolyte layer and the positive electrode active material layer faced each other, and roll-pressed at 165°C and a pressure of 50 kN / cm. Then, the transfer foil of the transfer member was peeled off to prepare a positive electrode-side structure. The transfer member and negative electrode were stacked so that the solid electrolyte layer and the negative electrode active material layer faced each other, and roll-pressed at 25°C and a pressure of 50 kN / cm. Then, the transfer foil of the transfer member was peeled off to prepare a negative electrode-side structure.

[0058] The negative electrode side structure and the positive electrode side structure were punched into circles with diameters of 13.00 mm and 11.28 mm, respectively. A sulfide solid electrolyte was added to the solid electrolyte layer of the negative electrode side structure and pressed using a uniaxial press. The positive electrode side structure and the negative electrode side structure were then stacked so that the solid electrolyte layers faced each other to obtain a laminate. A current extraction tab was attached to the laminate, and the laminate was sealed in an aluminum laminate using a vacuum sealer. This produced an evaluation battery (all-solid-state battery).

[0059] [Examples 1 to 3] Evaluation batteries were prepared in the same manner as in Comparative Example 1, except that a fluorine-based lubricant (compound 1-1 having an FPE structure) was added to the organic solvent in the preparation of the negative electrode slurry. The fluorine-based lubricant was added in an amount such that the ratio (wt%) of the fluorine-based lubricant to the negative electrode active material (Si particles) was the value shown in Table 1. The melting point of the fluorine-based lubricant used was 66°C.

[0060] [Example 4] Si particles and a solid fluorine-based lubricant were weighed in the proportions shown in Table 1 and mixed in a mortar to prepare a composite. A battery for evaluation was prepared in the same manner as in Comparative Example 1, except that the composite was used in preparing the negative electrode slurry.

[0061] [Evaluation] (Peel Strength Test) The peel strength was measured using a micro auto fluff. First, the negative electrode structures of Comparative Example 1 and Examples 1 to 4, which had been pressed with a linear pressure of 2.5 kN / cm in a roll press, were punched out with a diameter of 14.5 mm. Next, double-sided tape was attached to the sample stage of the micro autograph, and the punched negative electrode structure was attached with the collector foil side facing downward on top of the layer, with the coated surface facing upward. In addition, double-sided tape with a diameter of 11.28 mm was attached to the terminal side of the micro autograph. Then, the terminal was moved downward to the negative electrode structure, and the pressure at the time of contact was 50 N / cm. ２ Thereafter, the negative pressure was measured when the adhesive was moved upward, and the maximum value was taken as the peel strength.

[0062] (Battery Performance Test) The resistance change rate of the evaluation batteries fabricated in Comparative Example 1 and Examples 1 to 3 was measured as follows. First, 100 charge / discharge cycles (cycle test) were performed under conditions of 25°C, 2C, and SOC 93%-10%, and then the resistance value (resistance value before heating) was measured. Then, after the cycle test, each evaluation battery was heated at 100°C for 6 hours, returned to room temperature, and the resistance value (resistance value after heating) was measured. The resistance change rate was calculated from the resistance value before heating and the resistance value after heating. The results are shown in Table 1. Note that a negative value for the resistance change rate means that the resistance increased after heating, and a positive value for the resistance change rate means that the resistance decreased after heating.

[0063] The evaluation batteries of Examples 2 and 4 were initially charged to 3.7 V and then initially discharged at a rate of 5 C. The initial resistance values ​​were calculated from the voltage drop 5 seconds after the initial discharge and compared. The results are shown in Table 1.

[0064]

[0065] As shown in Table 1, the peel strength of all of Examples 1 to 4 was higher than that of Comparative Example 1, confirming that peeling was suppressed in the electrodes of the present disclosure. Furthermore, from this, it is inferred that an increase in battery resistance is suppressed in batteries using electrodes of the present disclosure. Furthermore, compared to Comparative Example 1, Examples 1 to 3 showed a decrease in resistance value (increase in the rate of resistance change) when heated after the cycle test. It is believed that the decrease in resistance value was due to the fluorine-based lubricant that became liquid upon heating filling the spaces between the particles, maintaining and restoring a good electron conduction path. Furthermore, Example 4 had a better initial resistance than Example 2. It is inferred that a good electron conduction path was formed by the composite of the Si-based active material and the fluorine-based lubricant.

[0066] DESCRIPTION OF SYMBOLS 1 current collector 2 active material layer 10 electrode 11 electrolyte layer 100 secondary battery

Claims

1. A fluorine-based lubricant that is used in an active material layer containing an active material and a sulfide solid electrolyte and that is solid at 25°C.

2. The fluorine-based lubricant according to claim 1, having a melting point of 120°C or lower.

3. The fluorine-based lubricant according to claim 1, having a fluoropolyether structure.

4. An electrode having an active material layer and a current collector, wherein the active material layer contains an active material, a sulfide solid electrolyte and a fluorine-based lubricant, and the fluorine-based lubricant is a fluorine-based lubricant as defined in any one of claims 1 to 3.

5. The electrode according to claim 4, wherein the active material and the solid fluorine-based lubricant are composited.

6. The electrode according to claim 4, wherein the ratio of said fluorine-based lubricant to said active material is 4% by weight or more and 12% by weight or less.

7. A secondary battery comprising the electrode according to claim 4.

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