JP2021026957A - Negative electrode for secondary battery and secondary battery using the same - Google Patents

Abstract

To improve an output input characteristic and quick charging property and also to improve shape freedom of a secondary battery.SOLUTION: A negative electrode 10 for a secondary battery is provided with a fiber bundle 14 bundled with a carbon fiber 12 and a metal wire 16 inserted into the fiber bundle 14 along a longitudinal direction of the fiber bundle 14.SELECTED DRAWING: Figure 1

Description

The invention disclosed in the present specification relates to a negative electrode for a secondary battery and a secondary battery using the same.

Conventionally, as a secondary battery having a high energy density, a plurality of columnar negative electrodes, a separation membrane provided so as to surround each columnar negative electrode, and a positive electrode provided so as to fill the space between adjacent separation films. Is known (Patent Document 1). This secondary battery has a structure in which a columnar negative electrode surrounded by a separation membrane is arranged in the positive electrode. The positive electrode of this secondary battery is obtained by spatially filling a columnar positive electrode made of a regular hexagonal prism, and a columnar negative electrode surrounded by a separation membrane is arranged in a central hole of the columnar positive electrode. An example of the columnar negative electrode is a columnar body made of a carbonaceous material capable of storing and releasing lithium ions, in which a collecting wire having a circular cross section is embedded.

JP-A-2018-152229

However, it cannot be said that the secondary battery of Patent Document 1 has sufficiently high input / output characteristics and quick chargeability, and it is difficult to lengthen the columnar negative electrode because the resistance in the longitudinal direction of the columnar negative electrode is relatively high. It was.

The present disclosure has been made in view of such a problem, and its main purpose is to improve the input / output characteristics and quick chargeability, and also to improve the degree of freedom in the shape of the secondary battery.

In order to achieve the above-mentioned object, the present inventors can improve the input / output characteristics and the quick chargeability by devising the negative electrode for the secondary battery, and also improve the degree of freedom in the shape of the secondary battery. We have found and completed the invention disclosed herein.

That is, the negative electrode for a secondary battery disclosed in the present specification includes a fiber bundle in which carbon fibers are bundled and a metal wire inserted into the fiber bundle along the longitudinal direction of the fiber bundle. ..

Further, the secondary battery disclosed in the present specification includes the above-mentioned negative electrode for a secondary battery, a separation membrane provided so as to surround the negative electrode for a secondary battery, and a positive electrode active material, and the separation membrane. It is provided with a positive electrode provided around the.

In the negative electrode for a secondary battery disclosed in the present specification, the carbon fibers constituting the fiber bundle function as a negative electrode active material and at the same time as a current collector. Further, by inserting the metal wire through the fiber bundle, the current collecting resistance is reduced. Therefore, according to the secondary battery using the negative electrode for the secondary battery, the input / output characteristics and the quick chargeability are improved. Further, since the resistance in the longitudinal direction of the negative electrode is small, the length of the negative electrode can be made relatively long, and the degree of freedom in the shape of the secondary battery is improved.

A perspective view showing a schematic configuration of the negative electrode 10. The perspective view which shows the schematic structure of the pin type secondary battery 30. The perspective view which shows the schematic structure of the square secondary battery 40.

Next, the negative electrode 10, the pin-type secondary battery 30, and the square secondary battery 40 disclosed in the present embodiment will be described with reference to the drawings. FIG. 1 is a perspective view showing a schematic configuration of a negative electrode 10, FIG. 2 is a perspective view showing a schematic configuration of a secondary battery 30, and FIG. 3 is a perspective view showing a schematic configuration of a square secondary battery 40. Here, for convenience of explanation, a lithium ion secondary battery having a lithium ion carrier as the secondary battery will be described as an example.

As shown in FIG. 1, the negative electrode 10 is a cylindrical negative electrode for a lithium ion secondary battery, and is formed into a fiber bundle 14 in which carbon fibers 12 are bundled and a fiber bundle 14 along the longitudinal direction of the fiber bundle 14. It is provided with an inserted metal wire 16.

The fiber bundle 14 is a bundle of a large number of straight carbon fibers 12. The diameter of the carbon fiber 12 is preferably 1 μm or more and 200 μm or less. When this diameter is 1 μm or more, the strength of the fiber bundle 14 can be ensured and stable charging / discharging can be performed. Further, when this diameter is 200 μm or less, the moving distance of the ion as a carrier does not become too long, and high output performance can be obtained. Further, if this diameter is in this range, the energy density per unit volume can be further increased. Alternatively, within this range, the moving distance of the carrier ions can be shortened, and charging / discharging can be performed with a larger current. The diameter of the carbon fiber 12 is more preferably 5 μm or more and 20 μm or less. The length of the carbon fiber 12 in the longitudinal direction is preferably 20 mm or more and 200 mm or less. When the length of the carbon fiber 12 is 20 mm or more, the battery capacity can be further increased, and when it is 200 mm or less (particularly 150 mm or less), the electric resistance of the negative electrode 10 can be further reduced, which is preferable.

Since the fiber bundle 14 is a bundle of conductive carbon fibers 12, it is not necessary to separately include a conductive material, but a binder may be included if necessary. The binder plays a role of connecting the carbon fibers 12 to each other and maintaining a predetermined shape. For example, a fluororesin such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, or polypropylene is used. , Polyethylene resin such as polyethylene, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, natural butyl rubber (NBR) and the like can be used alone or as a mixture of two or more kinds. Further, an aqueous dispersion of cellulose-based binder or styrene-butadiene rubber (SBR), which is an aqueous binder, can also be used.

The metal wire 16 inserts the center of the fiber bundle 14 along the longitudinal direction of the carbon fiber 12. The metal wire 16 preferably has a volume resistivity of 10 μΩcm or less at room temperature, and for example, Cu or Ni is preferable. The metal wire 16 may be a single metal wire or an aggregate of a plurality of metal wires. The length of the metal wire 16 is preferably the same as the length of the carbon fiber 12. The diameter of the metal wire 16 is preferably 10 μm or more and 100 μm or less. When this diameter is 10 μm or more, the electrical resistance of the negative electrode 10 is sufficiently small, which is preferable. When this diameter is 100 μm or less, the capacity can be relatively increased, which is preferable. The diameter of the metal wire 16 is more preferably 20 μm or more and 50 μm or less. The ratio of the weight of the metal wire 16 to the total weight of the fiber bundle 14 and the metal wire 16 is preferably 7% by weight or more and 30% by weight or less. When this ratio is 7% by weight or more, the rateability related to the input / output characteristics and the quick chargeability becomes good, which is preferable. When this ratio is 30% by weight or less (particularly 16% by weight or less), the negative electrode capacity (unit: mAh / g) standardized by the total weight of the fiber bundle 14 and the metal wire 16 becomes a relatively high value. Therefore, it is preferable.

Next, a pin-type secondary battery 30 using the negative electrode 10 will be described with reference to FIG.

As shown in FIG. 2, the pin-type secondary battery 30 includes a negative electrode 10, a separation film (also referred to as a partition wall) 18, and a columnar positive electrode 20.

The negative electrode 10 is as described above.

The separation film 18 is provided so as to surround the outer peripheral surface (excluding the upper portion) and the lower end surface of the columnar negative electrode 10. The separation film 18 is not provided on the upper end surface of the negative electrode 10. The separation membrane 18 has conductivity of ions as carriers and insulates the negative electrode 10 and the columnar positive electrode 20. As the separation membrane 18, a polymer having ionic conductivity and insulating property is suitable. Examples of the separation film 18 include a copolymer of polyvinylidene fluoride (PVdF) and hexafluoropropylene (HFP), polymethyl methacrylate (PMMA), and a copolymer of PMMA and an acrylic polymer. .. For example, in a copolymer of PVdF and HFP, a part of the electrolytic solution swells and gels this membrane to become an ionic conduction membrane. The thickness of the separation membrane 18 is preferably 0.5 μm or more, more preferably 2 μm or more, and may be 5 μm or more, for example, in consideration of ensuring insulating properties. Further, the thickness of the separation membrane 18 is preferably 20 μm or less, and more preferably 10 μm or less in consideration of suppressing a decrease in ionic conductivity. Therefore, the thickness of the separation membrane 18 is preferably in the range of 0.5 to 20 μm in order to achieve both ionic conductivity and insulating property. The separation membrane 18 may be formed, for example, by immersing the negative electrode 10 in a solution containing a raw material and coating the surface thereof.

In the present embodiment, the electrolytic solution is a non-aqueous solvent in which a supporting salt containing lithium ions is dissolved (non-aqueous electrolytic solution). Examples of the non-aqueous solvent include carbonates, esters, ethers, nitriles, furans, sulfolanes, dioxolanes and the like, and these can be used alone or in combination. Specifically, as carbonates, cyclic carbonates such as ethylene carbonate (EC), propylene carbonate, vinylene carbonate, butylene carbonate, and chloroethylene carbonate, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate, and ethyl. Chain carbonates such as -n-butyl carbonate, methyl-t-butyl carbonate, di-i-propyl carbonate, t-butyl-i-propyl carbonate, cyclic esters such as γ-butyl lactone and γ-valerolactone, Chain esters such as methyl formate, methyl acetate, ethyl acetate, methyl butyrate, ethers such as dimethoxyethane, ethoxymethoxyethane, diethoxyethane, nitriles such as acetonitrile and benzonitrile, furan such as tetrahydrofuran and methyl tetrahydrofuran, etc. Classes, sulfolanes such as sulfolane and tetramethylsulfolane, and dioxolanes such as 1,3-dioxolane and methyldioxolane. Examples of the supporting salt include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiSbF ₆ , LiSiF _{6 , LiAlF 4} , LiSCN, and the like. Examples thereof include LiClO ₄ , LiCl, LiF, LiBr, LiI, and LiAlCl _4. Of these, 1 is selected from the group consisting _{of inorganic salts such as LiPF 6} , LiBF ₄ , and LiClO ₄ , and organic salts such as LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , and LiC (CF ₃ SO ₂ ) _3. It is preferable to use a seed or a combination of two or more kinds of salts from the viewpoint of electrical characteristics. The concentration of this supporting salt in the electrolytic solution is preferably 0.1 mol / L or more and 5 mol / L or less, and more preferably 0.5 mol / L or more and 2 mol / L or less.

The columnar positive electrode 20 is formed in a cylindrical shape having a central hole 20a. In the central hole 20a of the columnar positive electrode 20, a negative electrode 10 whose outer peripheral surface and lower end surface are surrounded by a separation film 18 is arranged. The central hole 20a is a bottomed tubular hole provided along the central axis of the columnar positive electrode 20 from the upper end surface to the lower end surface of the columnar positive electrode 20. Therefore, the outer peripheral surface and the lower end surface of the negative electrode 10 and the inner wall and the bottom surface of the central hole 20a of the columnar positive electrode 20 are insulated by the separation film 18.

The columnar positive electrode 20 contains a positive electrode active material, but when the positive electrode active material does not have conductivity, it may be formed by mixing a conductive material having conductivity. The columnar positive electrode 20 may be formed by mixing, for example, a positive electrode active material, a conductive material, and a binder, if necessary. Examples of the positive electrode active material include a material capable of occluding and releasing lithium as a carrier. Examples of the positive electrode active material include compounds having lithium and a transition metal. Examples of such a compound include an oxide containing lithium and a transition metal element, a phosphoric acid compound containing lithium and a transition metal element, and the like. Specifically, a lithium manganese composite oxide having a basic composition formula of Li _(1-x) MnO ₂ (0 ≦ x ≦ 1, etc., the same applies hereinafter) or Li _(1-x) Mn ₂ O _{4, etc., basic composition} Lithium cobalt composite oxide whose formula is Li _(1-x) CoO _2, etc., Lithium nickel composite oxide whose basic composition formula is Li _(1-x) NiO _2, etc., basic composition formula is Li _(1-x) Co _a Ni _b Mn _c O ₂ (a> 0, b> 0, c> 0, a + b + c = 1), Li _(1-x) Co _a Ni _b Mn _c O ₄ (0 <a <1, 0 <b) <1, 1 ≦ c <2, a + b + c = 2), etc. Lithium cobalt nickel manganese composite oxide, basic composition formula is LiV ₂ O _3, etc. Lithium vanadium composite oxide, basic composition formula is V ₂ O _5, etc. A transition metal oxide or the like can be used. Further, a lithium iron phosphate compound having a basic composition formula of LiFePO ₄ or the like can be used as the positive electrode active material. Of these, lithium cobalt nickel-manganese composite oxides such as LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ and LiNi _0.4 Co _0.3 Mn _0.3 O ₂ are preferable. The "basic composition formula" is intended to include other elements such as components such as Al and Mg.

When the columnar positive electrode 20 contains a conductive material, the conductive material is not particularly limited as long as it is an electron conductive material that does not adversely affect the battery performance. For example, natural graphite (scaly graphite, scaly graphite) or artificial graphite is used. Use one or a mixture of two or more types of graphite, acetylene black, carbon black, Ketjen black, carbon whisker, needle coke, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.). be able to. When the columnar positive electrode 20 contains a binder, the binder is not particularly limited as long as it plays a role of holding the active material particles and the conductive material particles together to maintain a predetermined shape. For example, polytetra. Fluororesin such as fluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, or thermoplastic resin such as polypropylene, polyethylene, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, natural butyl rubber (NBR) Etc. can be used alone or as a mixture of two or more kinds. Further, an aqueous dispersion of cellulose-based binder or styrene-butadiene rubber (SBR), which is an aqueous binder, can also be used.

According to the pin-type secondary battery 30 described in detail above, the input / output characteristics and the quick chargeability are improved, and the degree of freedom in the shape of the pin-type secondary battery 30 is also improved. The reason why such an effect can be obtained is considered as follows. That is, in the negative electrode 10 of the pin-type secondary battery 30, the carbon fibers 12 constituting the fiber bundle 14 function as both a negative electrode active material and a current collector at the same time. Further, by inserting the metal wire 16 through the fiber bundle 14, the current collecting resistance is reduced. Therefore, according to the pin-type secondary battery 30 using the negative electrode 10, the input / output characteristics and the quick chargeability are improved. Further, since the resistance of the negative electrode 10 in the longitudinal direction is small, the length of the negative electrode 10 can be made relatively long, and the degree of freedom in the shape of the pin-type secondary battery 30 is improved.

Next, the square secondary battery 40 using the negative electrode 10 will be described with reference to FIG.

As shown in FIG. 3, the square secondary battery 40 includes a battery body 42, a negative electrode current collector 44, and a positive electrode current collector 46.

The battery body 42 contains m pin-type secondary batteries 30 in the left-right direction (m is an integer of 2 or more) and n in the front-rear direction (n is an integer of 2 or more) so that the upper end surface of the negative electrode 10 faces upward. ) Side by side, compressed left and right and back and forth so that the overall shape is a square. Therefore, the columnar positive electrode 20 of the pin-type secondary battery 30 constituting the battery body 42 is a rectangular parallelepiped having a central hole 20a. The lengths of each side of the battery body 42 are the length X in the left-right direction, the length Y in the up-down direction, and the length Z in the front-rear direction when arranged in order from the shortest one (X <Y <Z).

The negative electrode current collector 44 is a plate-shaped member made of a conductive material, and is arranged on the upper surface of the battery body 42. The upper end surfaces of all the negative electrodes 10 are connected in parallel to the negative electrode current collector 44. Examples of the conductive material forming the negative electrode current collector 44 include carbon paper, aluminum, copper, titanium, stainless steel, nickel, iron, platinum, calcined carbon, conductive polymer, conductive glass, and the like, as well as adhesive. For the purpose of improving the property, conductivity and oxidation resistance (reducing property), those having the surface of aluminum, copper or the like treated with carbon, nickel, titanium, silver, platinum, gold or the like can also be used.

The positive electrode current collector 46 is a plate-shaped member made of a conductive material, and is arranged on the left side surface of the battery body 42. The positive electrode current collector 46 is electrically insulated from the negative electrode 10 and the negative electrode current collector 44. Examples of the conductive material for forming the positive electrode current collector 46 include those exemplified as the conductive material for forming the negative electrode current collector 44.

Since the square secondary battery 40 described in detail above also uses the negative electrode 10, the input / output characteristics and quick chargeability are improved, and the length of the negative electrode 10 can be made relatively long. The degree of freedom in shape is improved.

It goes without saying that the present disclosure is not limited to the above-described embodiment, and can be implemented in various embodiments as long as it belongs to the technical scope of the present disclosure.

For example, in the above-described embodiment, the carrier of the secondary battery is lithium ion, but the carrier is not particularly limited to this, and as an alkali metal ion such as sodium ion or potassium ion, or a group 2 element ion such as calcium ion or magnesium ion. May be good. The positive electrode active material may be any material that can occlude and release carrier ions. Further, although the electrolytic solution is a non-aqueous electrolytic solution, it may be an aqueous electrolytic solution.

In the above-described embodiment, a battery that uses an electrolytic solution as the secondary battery has been exemplified, but an all-solid-state battery that does not use an electrolytic solution may be used.

In the above-described embodiment, the fiber bundle 14 constituting the negative electrode 10 is formed by bundling a large number of straight-shaped carbon fibers 12, but the present invention is not particularly limited to this, and for example, a large number of carbon fibers 12 are twisted. It may be the one.

In the above-described embodiment, the columnar positive electrode 20 of the pin-type secondary battery 30 has a cylindrical shape, but the present invention is not particularly limited to this, and for example, a space-fillable regular polygonal prism (for example, a regular hexagonal prism, a regular triangular prism, and a regular prism) It may be a prism (such as a prism). In addition, "space filling" means filling the space with three-dimensional objects without gaps.

In the above-described embodiment, the negative electrode current collector 44 and the positive electrode current collector 46 of the square secondary battery 40 are plate-shaped, but are not particularly limited to plate-shaped, and are, for example, foil-shaped, film-shaped, and sheet. The shape, net shape, punching sheet, glass body, porous body, foam, fiber group forming body and the like may be used. Further, the negative electrode and the positive electrode current collectors 44 and 46 may have the same shape or may have different shapes.

In the above-described embodiment, the battery body 42 of the square secondary battery 40 has been described as an assembly of pin-type secondary batteries 30 having a columnar positive electrode 20, but the present invention is not particularly limited to this, for example. The negative electrode 10 having the separation film 18 may be independently erected in the positive electrode having a rectangular shape having substantially the same size as the battery body 42 without being in contact with each other.

In the above-described embodiment, the positive electrode current collector 46 is provided on the left side surface of the square secondary battery 40, but the present invention is not particularly limited thereto, and may be provided on the right side surface, or may be provided on the front surface or the rear surface. It may be provided on the lower surface. However, since the length X in the left-right direction of the square secondary battery 40 is shorter than the length Y in the vertical direction and the length Z in the front-rear direction, the positive electrode current collector 46 is on the left side surface or the right side surface of the square secondary battery 40. It is preferable to provide. This is because the electrical resistance of the positive electrode is reduced by doing so.

[Example 1]
A Cu wire (metal wire) having a length of 100 mm and a diameter of 20 μm is inserted into a fiber bundle in which 1000 carbon fibers having a length of 100 mm and a diameter of 10 μm are bundled, and a binder, polyvinylidene fluoride (PVdF), is used. A negative electrode having a diameter of 250 μm and a length of 100 mm was prepared by immersing it in a dissolved N-methylpyrrolidone (NMP) solution and drying it. At this time, the number of Cu wires was adjusted so that the ratio of the weight of the Cu wires to the total weight of the fiber bundle and the Cu wires was 3%. A 12 μm-thick PVdF-HFP separation membrane was formed on the outer peripheral surface and the lower surface of the negative electrode by a dip coating method using an NMP solution in which polyvinylidene fluoride-co-hexafluoropropylene (PVdF-HFP) was dissolved. Subsequently, a positive electrode mixture layer was formed on the partition wall surface by dip-coating the negative electrode provided with the separation film with the aqueous positive electrode paste. As the positive electrode paste, Li (NiComn) O ₂ , carbon black, and PVdF binder dispersed in water were used. An electrolytic solution (1M LiPF ₆ , EC / DMC / EMC = 3/4/3 (volume ratio)) is injected into this integral body, sealed, and an aluminum foil is wrapped around the outer peripheral surface to collect a positive electrode current collector. , A pin-type lithium ion secondary battery was manufactured.

The rate and negative electrode capacity of the obtained pin-type lithium ion secondary battery were measured. For the rate property, the discharge capacity when the charge / discharge test was performed at 25 ° C., 4C rate, and 2V to 4.1V was determined, and the discharge capacity was defined as the ratio (percentage) of the discharge capacity to the discharge capacity of Example 4 (described later). .. The negative electrode capacity was evaluated by preparing a cell in which the above-mentioned negative electrode provided with the separation membrane was opposed to the Li metal counter electrode and injected. The charge / discharge conditions were 25 ° C., 0.1 C rate, 0.005 V to 2 V, and the discharge capacity was a value standardized by the total weight of the fiber bundle and the Cu wire. The results are shown in Table 1.

[Comparative Example 1, Examples 2-4]
The rateability and the negative electrode capacity were determined in the same manner as in Example 1 except that the weight ratio of the Cu wire was changed. The results are shown in Table 1.

[Examples 5 and 6]
The rate and the negative electrode capacity were determined in the same manner as in Example 2 except that the length of the negative electrode (the length of the carbon fiber and the length of the Cu wire) was changed. The results are shown in Table 1.

[Example 7]
The rate and the negative electrode capacity were determined in the same manner as in Example 2 except that the diameter of the Cu wire was changed to 50 μm. The results are shown in Table 1.

[Example 8]
The rate and the negative electrode capacity were determined in the same manner as in Example 2 except that the Ni wire was used instead of the Cu wire. The results are shown in Table 1.

[Example 9]
The rate and the negative electrode capacity were determined in the same manner as in Example 7 except that the Ni wire was used instead of the Cu wire. The results are shown in Table 1.

In Examples 1 to 9 in which a negative electrode in which a metal wire was inserted into a fiber bundle in which carbon fibers were bundled was used, the rateability was improved as compared with Comparative Example 1 in which a negative electrode in which a metal wire was not inserted was used. The higher the rate, the better the input / output characteristics and quick chargeability. Further, from the results of Examples 1 to 4, it was found that the rateability improved as the weight ratio of the metal wire increased, and from the results of Examples 2, 5 and 7, the rateability improved as the negative electrode length became shorter. I found out that It is considered that the reason why the rateability was improved in this way was that the electrical resistance of the negative electrode was reduced. Furthermore, from the results of Examples 2 and 8 and Examples 7 and 9, it was found that almost the same results can be obtained regardless of whether the metal wire is Cu or Ni. Regarding the negative electrode capacity, in Examples 1 to 9, the value was relatively high, although it was slightly lower than that in Comparative Example 1. Considering the rate property, the weight ratio of the metal wire is preferably 7% by weight or more and 30% by weight or less, and considering both the rate property and the negative electrode capacity, the weight ratio of the metal wire is 7% by weight or more and 16% by weight or less. Can be said to be preferable.

10 Negative electrode, 12 carbon fiber, 14 fiber bundle, 16 metal wire, 18 separation film, 20 columnar positive electrode, 20a center hole, 30-pin secondary battery, 40-square secondary battery, 42 battery body, 44 negative electrode current collector, 46 Positive electrode current collector.

Claims (4)

A fiber bundle that bundles carbon fibers and
A metal wire inserted into the fiber bundle along the longitudinal direction of the fiber bundle,
Negative electrode for secondary batteries equipped with. The length of the carbon fiber is the same as the length of the metal wire.
The negative electrode for a secondary battery according to claim 1. The ratio of the weight of the metal wire to the total weight of the fiber bundle and the metal wire is 7% by weight or more and 30% by weight or less.
The negative electrode for a secondary battery according to claim 1 or 2. The negative electrode for a secondary battery according to any one of claims 1 to 3,
A separation membrane provided so as to surround the negative electrode for the secondary battery, and
A positive electrode containing a positive electrode active material and provided around the separation membrane,
Rechargeable battery with.

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