Ferritic stainless steel sheet, current collector, and nonaqueous electrolyte secondary battery

Abstract

To provide a ferritic stainless steel sheet that enables production of a current collector having superior resistance (corrosion resistance) against various types of corrosion such as sulfidation corrosion and low contact resistance with an active material layer.SOLUTION: A ferritic stainless steel sheet is used for a current collector of a nonaqueous electrolyte secondary battery. The ferritic stainless steel sheet has a composition comprising, on a mass basis: C: 0.001-0.050%, Si: 0.01-2.00%, Mn: 0.01-1.00%, P: 0.050% or less, S: 0.010% or less, Ni: 0.01-4.00%, Cr: 10.0-32.0%, Mo: 0.01-2.50%, Cu: 0.01-0.80%, Al: 0.001-0.150%, N: 0.05% or less; and Ti and / or Nb: 0.010 to 1.000%, with the balance consisting of Fe and impurities. The ferritic stainless steel sheet has a surface in which an area ratio of Ti and / or Nb carbonitrides having a circle-equivalent diameter of 0.5 μm or more is 0.0010% or greater.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a ferrite-based stainless steel sheet, a current collector, and a non-aqueous electrolyte secondary battery.

Background Art

[0002] Non-aqueous electrolyte batteries are widely used as power sources for relatively small electronic devices such as portable electronic devices. Also, against the backdrop of the growing environmental protection movement, in order to promote the introduction of electric vehicles (EVs), hybrid vehicles (HEVs), and fuel cell vehicles (FCVs), development has been carried out for power sources for driving these motors and auxiliary power sources for hybrids, etc., and non-aqueous electrolyte secondary batteries are also used for these applications. As non-aqueous electrolyte secondary batteries, lithium-ion secondary batteries (LIBs) are generally known. An LIB includes a positive electrode having a positive electrode active material layer formed on a current collector, a negative electrode having a negative electrode active material layer formed on the current collector, and an electrolyte provided between the positive electrode and the negative electrode and capable of mediating the conduction of lithium ions.

[0003] Non-aqueous electrolyte secondary batteries such as LIBs use a flammable organic-based electrolyte as the electrolyte, so there is a risk of ignition, and in some applications, characteristics such as operating temperature and energy density are not sufficient. Therefore, in recent years, research and development of all-solid-state batteries in which the electrolyte of non-aqueous electrolyte secondary batteries is made solid has been underway. All-solid-state batteries have various advantages such as less risk of ignition, a wide operating temperature range, and high energy density compared to non-aqueous electrolyte batteries using an organic-based electrolyte as the electrolyte. As electrolytes used in all-solid-state batteries, sulfide-based solid electrolytes and oxide-based solid electrolytes are known.

[0004] For the current collector of a non-aqueous electrolyte secondary battery, it is known to use an Al plate for the positive electrode and a Cu plate for the negative electrode, etc., but the use of chromium-containing steel sheets or stainless steel sheets has been considered from the viewpoint of improving durability and corrosion resistance. For example, Patent Documents 1 and 2 disclose chromium-containing steel sheets for current collectors of non-aqueous electrolyte secondary batteries. Further, Patent Documents 3 and 4 propose ferrite-based stainless steel sheets for current collectors of sulfide solid-state batteries. Also, Patent Document 5 proposes a stainless steel foil current collector for a secondary battery positive electrode.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0006] The sulfide-based solid electrolyte used in all-solid-state batteries is highly corrosive, so there is a risk that the current collector will undergo sulfidation corrosion. If the current collector corrodes, the performance of the all-solid-state battery will deteriorate. Also, generally, a passive film is formed on the surface of a stainless steel sheet, which tends to increase the electrical resistance due to its influence. In particular, when the electrolyte is solid, it becomes difficult to lower the contact resistance between the current collector and the active material layer formed thereon.

[0007] Since the chromium-containing steel sheets described in Patent Documents 1 and 2 are used for current collectors of non-aqueous electrolyte secondary batteries using an organic-based electrolyte solution as the electrolyte, they cannot suppress sulfidation corrosion when a sulfide-based solid electrolyte is used as the electrolyte. In addition, although the ferrite stainless steel sheets described in Patent Documents 3 and 4 can form a current collector having resistance to sulfidation corrosion (sulfidation resistance), they cannot reduce the contact resistance between the current collector and the active material layer formed thereon. Furthermore, since the stainless steel foil current collector for a secondary battery positive electrode described in Patent Document 5 is used for a non-aqueous electrolyte secondary battery using an organic electrolyte as the electrolyte, it cannot suppress sulfidation corrosion when a sulfide solid electrolyte is used as the electrolyte, and the contact resistance between the current collector and the active material layer formed thereon cannot be reduced either.

[0008] The present invention has been made to solve the above problems, and an object thereof is to provide a ferrite stainless steel sheet capable of manufacturing a current collector excellent in resistance (corrosion resistance) to various corrosions such as sulfidation corrosion and having a low contact resistance with an active material layer. Another object of the present invention is to provide a current collector excellent in resistance (corrosion resistance) to various corrosions such as sulfidation corrosion and having a low contact resistance with an active material layer, and a non-aqueous electrolyte secondary battery including such a current collector.

Means for Solving the Problems

[0009] As a result of intensive research on ferrite stainless steel sheets, the present inventors have found that, in addition to the composition, by controlling the area ratio of predetermined titanium and / or niobium carbonitrides on the surface within a predetermined range, the above problems can be solved, and the present invention has been completed.

[0010] That is, the present invention is a ferrite stainless steel sheet used for a current collector of a non-aqueous electrolyte secondary battery, in terms of mass basis, containing C: 0.001 to 0.050%, Si: 0.01 to 2.00%, Mn: 0.01 to 1.00%, P: 0.050% or less, S: 0.010% or less, Ni: 0.01 to 4.00%, Cr: 10.0 to 32.0%, Mo: 0.01 to 2.50%, Cu: 0.01 to 0.80%, Al: 0.001 to 0.150%, N: 0.05% or less, Ti and / or Nb: 0.010 to 1.000%, and the balance being composed of Fe and impurities, A ferritic stainless steel sheet having an area ratio of titanium and / or niobium carbonitride with a circle equivalent diameter of 0.5 μm or more on the surface of 0.0010% or more.

[0011] The present invention also relates to a current collector comprising the ferritic stainless steel sheet. Furthermore, the present invention relates to a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte provided between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode has the current collector, which is a non-aqueous electrolyte secondary battery.

Advantages of the Invention

[0012] According to the present invention, it is possible to provide a ferritic stainless steel sheet capable of manufacturing a current collector excellent in resistance (corrosion resistance) to various corrosions such as sulfur corrosion and having a low contact resistance with the active material layer. Moreover, according to the present invention, it is possible to provide a current collector excellent in resistance (corrosion resistance) to various corrosions such as sulfur corrosion and having a low contact resistance with the active material layer, and a non-aqueous electrolyte secondary battery comprising such a current collector.

Brief Description of the Drawings

[0013]

Figure 1

Modes for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be specifically described. The present invention is not limited to the following embodiments, and it should be understood that modifications and improvements may be appropriately added to the following embodiments based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention, and such modified and improved embodiments are also within the scope of the present invention. In this specification, the “%” indication regarding components means “mass %” unless otherwise specified.

[0015] <Ferritic stainless steel sheet> The ferritic stainless steel sheet according to an embodiment of the present invention is used as a current collector of a non-aqueous electrolyte secondary battery. Here, in this specification, the "non-aqueous electrolyte secondary battery" means a secondary battery using a non-aqueous electrolyte as an electrolyte, and a secondary battery using a solid electrolyte as an electrolyte is also included in the non-aqueous electrolyte secondary battery. The type of the non-aqueous electrolyte secondary battery is not particularly limited, but is typically a lithium ion secondary battery. In addition, in this specification, the "current collector" is a conductor that collects generated electricity and is a component of an electrode (positive electrode or negative electrode). The current collector can be used as an electrode by forming an active material layer (positive electrode active material layer or negative electrode active material layer) on its surface.

[0016] The ferritic stainless steel sheet according to an embodiment of the present invention contains C: 0.001 to 0.050%, Si: 0.01 to 2.00%, Mn: 0.01 to 1.00%, P: 0.050% or less, S: 0.010% or less, Ni: 0.01 to 4.00%, Cr: 10.0 to 32.0%, Mo: 0.01 to 2.50%, Cu: 0.01 to 0.80%, Al: 0.001 to 0.150%, N: 0.05% or less, Ti and / or Nb: 0.010 to 1.000%, and the balance consists of Fe and impurities.

[0017] Here, in this specification, the "stainless steel sheet" means a plate material formed from stainless steel. The stainless steel sheet includes a stainless steel strip and a stainless steel foil. In addition, in this specification, the "ferritic type" means that the metal structure is mainly a ferrite phase at normal temperature. Therefore, the "ferritic type" includes those that slightly contain phases other than the ferrite phase (for example, austenite phase, martensite phase, etc.). However, the "ferritic type" does not include a duplex structure of a ferrite phase and an austenite phase, a duplex structure of a ferrite phase and a martensite phase, and a duplex structure of a ferrite phase, an austenite phase, and a martensite phase.

[0018] Furthermore, in this specification, "impurities" refer to components that are mixed in during the industrial production of ferritic stainless steel sheets due to raw materials such as ores and scrap, and various factors in the manufacturing process, and are those that are allowed within a range that does not adversely affect the present invention. For example, impurities include inevitable impurities. Examples of impurities include O, etc. Regarding the content of each element, the phrase "including xx% or less" means that it is xx% or less, but includes an amount exceeding 0% (especially exceeding the impurity level).

[0019] The ferritic stainless steel sheet according to an embodiment of the present invention can further contain one or more selected from Sn: 0.001 to 0.300%, B: 0.001 to 0.010%, Mg: 0.001 to 0.100%, Ca: 0.001 to 0.100%, REM: 0.001 to 0.100%, V: 0.001 to 1.000%, Zr: 0.001 to 1.000%, W: 0.001 to 1.000%, Co: 0.001 to 1.000%, Hf: 0.001 to 1.000%, Ta: 0.001 to 1.000% as needed. Hereinafter, each component will be described in detail.

[0020] (C: 0.001 to 0.050%) C is an element that affects the properties such as the corrosion resistance (sensitization suppression effect) and workability of ferritic stainless steel sheets (hereinafter sometimes abbreviated as "stainless steel sheets"). If the C content is too high, the corrosion resistance and workability of the stainless steel sheet will decrease. Therefore, the upper limit value of the C content is 0.050%, preferably 0.048%, more preferably 0.045%. On the other hand, reducing the C content excessively leads to an increase in refining costs, so the lower limit value of the C content is 0.001%, preferably 0.002%, more preferably 0.003%.

[0021] (Si: 0.01 to 2.00%) Si is an element that affects deoxidation and the workability of stainless steel sheets. If the Si content is too high, the workability of the stainless steel sheet will decrease. Therefore, the upper limit of the Si content is 2.00%, preferably 1.80%, more preferably 1.60%. On the other hand, if the Si content is too low, deoxidation will be insufficient. Therefore, the lower limit of the Si content is 0.01%, preferably 0.03%, more preferably 0.05%.

[0022] (Mn: 0.01~1.00%) Mn is an element that affects the fixation of S (desulfurization) and corrosion resistance. If the Mn content is too high, it is easy to generate MnS which becomes a corrosion initiation point and the corrosion resistance of the stainless steel sheet will decrease. Therefore, the upper limit of the Mn content is 1.00%, preferably 0.95%, more preferably 0.90%. On the other hand, if the Mn content is too low, desulfurization will be insufficient. Therefore, the lower limit of the Mn content is 0.01%, preferably 0.03%, more preferably 0.05%.

[0023] (P: 0.050% or less) P is an element that affects the manufacturability of stainless steel sheets. If the P content is too high, the manufacturability of the stainless steel material will decrease. Therefore, the upper limit of the P content is 0.050%, preferably 0.048%, more preferably 0.045%. On the other hand, the lower limit of the P content is not particularly limited, but preferably 0.001%, more preferably 0.003%, still more preferably 0.005%.

[0024] (S: 0.010% or less) S is an element that affects the manufacturability of stainless steel sheets. If the S content is too high, the manufacturability of the stainless steel material will decrease. Therefore, the upper limit of the S content is 0.010%, preferably 0.008%, more preferably 0.005%. On the other hand, the lower limit of the S content is not particularly limited, but preferably 0.001%.

[0025] (Ni: 0.01~4.00%) Ni is an element that affects the corrosion resistance of stainless steel sheets. Since Ni is expensive, if the content is too high, it will lead to an increase in manufacturing costs. Therefore, the upper limit of the Ni content is 4.00%, preferably 3.50%, more preferably 3.00%. On the other hand, if the Ni content is too low, the corrosion resistance of the stainless steel sheet will decrease. Therefore, the lower limit of the Ni content is 0.01%, preferably 0.03%, more preferably 0.05%.

[0026] (Cr: 10.0 - 32.0%) Cr is an element that affects the corrosion resistance and workability of stainless steel sheets. If the Cr content is too high, the formation of intermetallic compounds will be promoted, resulting in a decrease in the workability of the stainless steel sheet and an increase in manufacturing costs. Therefore, the upper limit of the Cr content is 32.0%, preferably 31.0%, more preferably 30.0%. On the other hand, if the Cr content is too low, the corrosion resistance of the stainless steel sheet will decrease. Therefore, the lower limit of the Cr content is 10.0%. Also, from the perspective of further enhancing the conductivity by particularly reducing the volume resistivity of the stainless steel sheet, the Cr content is preferably 10.0% or more and less than 20.0%, more preferably 10.0% or more and less than 18.0%. On the other hand, from the perspective of further enhancing the corrosion resistance of the stainless steel sheet, the Cr content is preferably 18.0 - 32.0%, more preferably 20.0 - 32.0%.

[0027] (Mo: 0.01 - 2.50%) Mo is an element that affects the high-temperature strength, corrosion resistance, and oxidation resistance of stainless steel sheets. If the Mo content is too high, it will lead to an increase in manufacturing costs. Therefore, the upper limit of the Mo content is 2.50%, preferably 2.40%, more preferably 2.30%. On the other hand, if the Mo content is too low, the high-temperature strength, corrosion resistance, and oxidation resistance of the stainless steel sheet will decrease. Therefore, the lower limit of the Mo content is 0.01%, preferably 0.03%, more preferably 0.05%.

[0028] (Cu: 0.01 - 0.80%) Cu is an element that affects the workability and corrosion resistance of stainless steel sheets. If the Cu content is too high, the corrosion resistance of the stainless steel sheet will decrease. Therefore, the upper limit value of the Cu content is 0.80%, preferably 0.70%, more preferably 0.60%. On the other hand, if the Cu content is too low, the workability of the stainless steel sheet will decrease. Therefore, the lower limit value of the Cu content is 0.01%, preferably 0.02%, more preferably 0.03%.

[0029] (Al: 0.001~0.150%) Al is an element that affects the quality and manufacturability of stainless steel sheets. If the Al content is too high, the amount of inclusions generated will increase and the quality of the stainless steel sheet will decrease. Therefore, the upper limit value of the Al content is 0.150%, preferably 0.140%, more preferably 0.130%. On the other hand, if the Al content is too low, the manufacturability of the stainless steel sheet will decrease. Therefore, the lower limit value of the Al content is 0.001%, preferably 0.003%, more preferably 0.005%.

[0030] (N: 0.05% or less) N is an element that affects the corrosion resistance and workability of stainless steel sheets. If the N content is too high, the workability of the stainless steel sheet will decrease. Therefore, the upper limit value of the N content is 0.05%, preferably 0.04%, more preferably 0.03%. On the other hand, the lower limit value of the N content is not particularly limited, but it is 0.01% from the viewpoint of improving corrosion resistance.

[0031] (Ti and / or Nb: 0.010~1.000%) Ti and Nb are elements that affect the intergranular corrosion resistance (sensitization suppression effect), electrical conductivity, and workability of the stainless steel sheet. If the total content of Ti and Nb is too high, the workability of the stainless steel sheet will decrease and the manufacturing cost will also increase. Therefore, the upper limit value of the total content of Ti and Nb is 1.000%, preferably 0.900%, more preferably 0.800%. On the other hand, if the total content of Ti and Nb is too low, the intergranular corrosion resistance and electrical conductivity will decrease. Therefore, the lower limit value of the total content of Ti and Nb is 0.010%, preferably 0.015%, more preferably 0.020%. Here, either Ti or Nb may be included, or both may be included. When either Ti or Nb is included, the total content of Ti and Nb means the Ti content or the Nb content.

[0032] (Sn: 0.001~0.300%) Sn is an element that affects the corrosion resistance and manufacturability of the stainless steel sheet. If the Sn content is too high, Sn will segregate and the manufacturability of the stainless steel sheet will decrease. Therefore, the upper limit value of the Sn content is 0.300%, preferably 0.250%, more preferably 0.200%. On the other hand, if the Sn content is too low, the effect of improving the corrosion resistance cannot be sufficiently obtained. Therefore, the lower limit value of the Sn content is 0.001%, preferably 0.005%, more preferably 0.010%.

[0033] (B: 0.001~0.010%) B is an element that affects the manufacturability (hot workability) and corrosion resistance of the stainless steel sheet. If the B content is too high, the corrosion resistance of the stainless steel sheet will decrease. Therefore, the upper limit value of the B content is 0.010%, preferably 0.009%, more preferably 0.008%. On the other hand, if the B content is too low, the effect of improving the manufacturability of the stainless steel sheet cannot be sufficiently obtained. Therefore, the lower limit value of the B content is 0.001%, preferably 0.002%.

[0034] (Mg: 0.001 to 0.100%, Ca: 0.001 to 0.100%) Mg and Ca are elements that affect the manufacturability (hot workability) and quality of the stainless steel sheet. If the contents of Mg and Ca are too high, the amount of inclusions generated will increase, deteriorating the quality of the stainless steel sheet. Therefore, the upper limit values of the contents of Mg and Ca are each 0.100%, preferably 0.090%, more preferably 0.080%. On the other hand, if the contents of Mg and Ca are too low, the effect of improving the manufacturability of the stainless steel sheet cannot be sufficiently obtained. Therefore, the lower limit values of the contents of Mg and Ca are each 0.001%, preferably 0.002%.

[0035] (REM: 0.001 to 0.100%) REM is an element that affects the manufacturability (hot workability) of the stainless steel sheet. Since REM is an expensive element, if the REM content is too high, it will lead to an increase in manufacturing cost. Therefore, the upper limit value of the REM content is 0.100%, preferably 0.090%, more preferably 0.080%. On the other hand, if the REM content is too low, the effect of improving the manufacturability of the stainless steel sheet cannot be sufficiently obtained. Therefore, the lower limit value of the REM content is 0.001%, preferably 0.003%, more preferably 0.005%. Note that REM is a general term for a total of 17 elements including Sc, Y, and lanthanoids, and means rare earth elements. Specifically, La, Ce, Nd, etc. are included, and one of these can be contained alone, or two or more can be combined. When two or more rare earth elements are contained, the above REM content means the total content of these rare earth elements.

[0036] (V: 0.001 to 1.000%, Zr: 0.001 to 1.000%, W: 0.001 to 1.000%, Co: 0.001 to 1.000%, Hf: 0.001 to 1.000%, Ta: 0.001 to 1.000%) V, Zr, W, Co, Hf, and Ta are elements that affect the corrosion resistance, workability, and toughness of stainless steel sheets. If the content of these elements is too high, the workability and toughness of the stainless steel sheet will decrease, and it will lead to an increase in manufacturing cost. Therefore, the upper limit of the content of these elements is 1.000% respectively, preferably 0.900%, more preferably 0.800%. On the other hand, if the content of these elements is too low, the corrosion resistance of the stainless steel sheet will decrease. Therefore, the lower limit of the content of these elements is 0.001% respectively, preferably 0.003%, more preferably 0.005%.

[0037] The ferritic stainless steel sheet according to an embodiment of the present invention has titanium and / or niobium carbonitrides (such as TiN, NbN, TiC, NbC, etc.) on the surface. Such carbonitrides contribute to the improvement of the conductivity of the ferritic stainless steel sheet. In particular, when the ferritic stainless steel sheet is used as a current collector, the contact resistance with the active material layer can be reduced. In order to ensure such an effect, the area ratio of titanium and / or niobium carbonitrides having an equivalent circle diameter of 0.5 μm or more on the surface of the ferritic stainless steel sheet should be 0.0010% or more, preferably 0.0012% or more, more preferably 0.0015% or more. Moreover, the upper limit of the area ratio of the carbonitrides is not particularly limited, but preferably 0.0200%, more preferably 0.0150%, still more preferably 0.0100%. By controlling the area ratio of the carbonitrides to such an upper limit, a decrease in the workability of the ferritic stainless steel sheet can be suppressed. The area ratio of titanium and / or niobium carbonitrides having an equivalent circle diameter of 0.5 μm or more on the surface of the ferritic stainless steel sheet can be measured by SEM observation. Specifically, it can be measured by the method of the examples described later. Also, the equivalent circle diameter means the diameter of a perfect circle corresponding to the area of the titanium and / or niobium carbonitride (particle).

[0038] The ferritic stainless steel sheet according to an embodiment of the present invention has a contact resistance of 20.0 mΩ·cm 2It is preferably the following, 19.5 mΩ·cm 2 More preferably, it is the following, 19.0 mΩ·cm 2 Even more preferably, it is the following. If the contact resistance is within such a range, it can be said that the conductivity is excellent, and thus the contact resistance between the current collector formed of the ferrite stainless steel sheet and the active material layer formed thereon can be reduced. Note that the lower limit value of the contact resistance is not particularly limited because the lower it is, the more excellent the conductivity is, but typically it is 1.0 mΩ·cm 2 is. Here, the contact resistance of the ferrite stainless steel sheet can be measured by the method of the examples described later.

[0039] The ferrite stainless steel sheet according to the embodiment of the present invention preferably has a corrosion loss of 0.100 mg / mm 2 or less, more preferably 0.070 mg / mm 2 or less, and even more preferably 0.010 mg / mm 2 or less. If the corrosion loss is such, it can be said that the corrosion resistance (especially, sulfidation resistance) is good, and thus it can also be applied to the current collector of a non-aqueous electrolyte battery using a sulfide-based solid electrolyte as the electrolyte. Note that the lower limit value of the corrosion loss is not particularly limited because the lower it is, the higher the corrosion resistance is. Here, the corrosion loss of the ferrite stainless steel sheet can be measured by the method of the examples described later.

[0040] The ferrite stainless steel sheet according to the embodiment of the present invention preferably has a volume resistivity of 63.0 μΩ·m or less, more preferably a volume resistivity of 61.0 μΩ·m or less, and even more preferably a volume resistivity of 60.0 μΩ·m or less. If the volume resistivity is within such a range, it can be said that the conductivity is good, and thus the voltage drop across the entire electrode is suppressed, and the battery characteristics can be improved. Note that the lower limit value of the volume resistivity is not particularly limited because the lower it is, the more excellent the conductivity is, but typically it is 30 μΩ·m. Here, the volume resistivity of the ferritic stainless steel sheet can be measured by the four-terminal method at 20°C.

[0041] The ferritic stainless steel sheet according to an embodiment of the present invention is not particularly limited, but is preferably a cold-rolled sheet. The thickness of the cold-rolled sheet is typically 3.0 mm or less, preferably 1.0 mm or less, more preferably 0.1 mm (100 μm) or less, and particularly preferably 0.01 to 0.03 mm (10 to 30 μm).

[0042] The manufacturing method of the ferritic stainless steel sheet according to an embodiment of the present invention is not particularly limited as long as it can manufacture the ferritic stainless steel sheet having the above characteristics. Hereinafter, an example of a suitable manufacturing method of the ferritic stainless steel sheet according to an embodiment of the present invention will be described. The manufacturing method of the ferritic stainless steel material according to an embodiment of the present invention can be manufactured by hot-rolling and annealing a slab having the above composition, and then cold-rolling and annealing. After each annealing, known treatments such as pickling may be performed.

[0043] Hot rolling is performed after soaking the slab at 1100 to 1230°C for 30 minutes or more. If the soaking temperature is less than 1100°C and the soaking time is less than 30 minutes, Ti and / or Nb in the stainless steel will not dissolve sufficiently, making it difficult to precipitate Ti and / or Nb carbonitrides on the surface of the ferritic stainless steel material. Also, if the soaking temperature exceeds 1230°C, the slab will be easily deformed by its own weight, resulting in a decrease in productivity. The conditions for hot rolling, annealing after hot rolling, and cold rolling are not particularly limited, and known conditions can be applied.

[0044] Annealing after cold rolling (finish annealing) is carried out by setting the maximum temperature reached to 900 to 1100 °C and holding it in the temperature range of 600 to 1000 °C for 20 seconds or more. If the maximum temperature reached is less than 900 °C or the holding time in the temperature range of 600 to 1000 °C is less than 20 seconds, the carbonitrides of Ti and / or Nb do not grow sufficiently, and the size of the carbonitrides of Ti and / or Nb present on the surface of the ferritic stainless steel material becomes small. Further, if the maximum temperature reached exceeds 1100 °C, Ti and / or Nb dissolve, making it difficult to have a predetermined carbonitride present on the surface of the ferritic stainless steel material at a predetermined area ratio.

[0045] The ferritic stainless steel sheet according to an embodiment of the present invention is excellent in corrosion resistance (particularly, sulfidation resistance) and conductivity. Therefore, it is excellent in resistance to various corrosions such as sulfide corrosion, and a current collector with low contact resistance with the active material layer can be manufactured.

[0046] <Current collector> The current collector according to an embodiment of the present invention includes the above ferritic stainless steel sheet. The shape of the ferritic stainless steel sheet may be appropriately set according to the type and structure of the non-aqueous electrolyte secondary battery and is not particularly limited. That is, the ferritic stainless steel sheet can be processed into a desired shape according to the required shape of the current collector. Further, the surface may be processed as long as it does not affect the area ratio of the predetermined carbonitrides of Ti and / or Nb on the surface of the ferritic stainless steel sheet. The processing method is not particularly limited, and known processing methods may be used.

[0047] Since the current collector according to an embodiment of the present invention includes the above ferritic stainless steel sheet, it is excellent in resistance (corrosion resistance) to various corrosions such as sulfide corrosion, and can suppress the reaction with various non-aqueous electrolytes used in non-aqueous electrolyte secondary batteries, particularly sulfide-based solid electrolytes. Further, since this current collector has low contact resistance with the active material layer, the performance of the non-aqueous electrolyte secondary battery can be improved.

[0048] <Non-aqueous electrolyte secondary battery> The non-aqueous electrolyte secondary battery according to an embodiment of the present invention includes a positive electrode, a negative electrode, and a non-aqueous electrolyte provided between the positive electrode and the negative electrode. And at least one of the positive electrode and the negative electrode has the above current collector. The non-aqueous electrolyte secondary battery having such a configuration is excellent in resistance (corrosion resistance) to various corrosions such as sulfide corrosion and has a current collector with low contact resistance with the active material layer, so that the performance as a secondary battery can be improved.

[0049] Here, a schematic cross-sectional view of the non-aqueous electrolyte secondary battery according to an embodiment of the present invention is shown in FIG. 1. As shown in FIG. 1, the non-aqueous electrolyte secondary battery includes a positive electrode 10, a negative electrode 20, and a non-aqueous electrolyte 30 provided between the positive electrode 10 and the negative electrode 20. The positive electrode 10 has a current collector 11 and a positive electrode active material layer 12 formed on one surface of the current collector 11. The negative electrode 20 has a current collector 21 and a negative electrode active material layer 22 formed on one surface of the current collector 21. At least one of the current collectors 11 and 21, preferably both, is formed of the above ferrite-based stainless steel sheet. When only one of the current collectors 11 and 21 is formed of the above ferrite-based stainless steel sheet, a known one can be used as the other current collector 11 and 21.

[0050] The positive electrode active material used for the positive electrode active material layer 12 is not particularly limited, and known ones can be used. Examples of the positive electrode active material include LMO (lithium manganate, LiMn2O4), NMC (lithium nickel manganese cobalt oxide, LiNi x Mn y Co z O2 (x + y + z = 1)), LCO (lithium cobalt oxide, LiCoO2), LFP (lithium iron phosphate, LiFePO4), sulfur-based positive electrode active material, 5V-class spinel-type positive electrode active material, and the like. These can be used alone or in combination of two or more.

[0051] The negative electrode active material used in the negative electrode active material layer 22 is not particularly limited, and known materials can be used. Examples of the negative electrode active material include metallic lithium, graphite, LTO (lithium titanate, Li4Ti5O 12 ), silicon (Si), SiO, etc. These can be used alone or in combination of two or more.

[0052] The non-aqueous electrolyte 30 is not particularly limited, and liquid, gel, solid, etc. can be used. When a liquid electrolyte is used as the non-aqueous electrolyte 30, a separator (not shown) is provided from the viewpoint of avoiding physical contact between the positive electrode 10 and the negative electrode 20. Similarly, a separator may be arranged when a gel electrolyte is used. As the separator, porous films such as polyethylene (PE), polypropylene (PP), cellulose, polyvinylidene fluoride (PVdF), and non-woven fabrics made of synthetic resin can be used.

[0053] The liquid electrolyte is prepared by dissolving an electrolyte salt as a solute in an organic solvent. The concentration of the electrolyte salt is preferably 0.5 mol / L or more and 2.5 mol / L or less. Examples of the electrolyte salt include lithium salts such as lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), and lithium bis(trifluoromethylsulfonyl)imide (LiN(CF3SO2)2). These can be used alone or in combination of two or more.

[0054] Examples of organic solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC); chain carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC); cyclic ethers such as tetrahydrofuran (THF), 2-methyltetrahydrofuran (2MeTHF), and dioxolane (DOX); chain ethers such as dimethoxyethane (DME) and diethoxyethane (DEE); γ-butyrolactone (GBL), acetonitrile (AN), sulfolane (SL), and the like. These can be used alone or in combination of two or more.

[0055] The gel electrolyte is prepared by compounding a liquid electrolyte and a polymer material. Examples of polymer materials include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), and the like. These can be used alone or in combination of two or more.

[0056] The solid electrolyte may be inorganic or organic. Examples of inorganic solid electrolytes include oxide-based solid electrolytes and sulfide-based solid electrolytes. Examples of oxide-based solid electrolytes include lithium phosphate (Li3PO4), Li3PO4N X , LiBO2N X , LiNbO3, LiTaO3, Li2SiO3, Li4SiO4-Li3PO4, Li4SiO4-Li3VO4, Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3-ZnO, Li 1+X Al X Ti 2-X (PO4)3 (0 ≦ X ≦ 1), Li 1+X Al X Ge 2-X (PO4)3 (0 ≦ X ≦ 1), LiTi2(PO4)3, Li 3X La 2 / 3-X TiO3 (0 ≦ X ≦ 2 / 3), Li5La3Ta2O 12 , Li7La3Zr2O12 , Li6BaLa2Ta2O 12 , Li 3.6 Si 0.6 P 0.4 O4, etc. These can be used alone or in combination of two or more.

[0057] Examples of sulfide-based solid electrolytes include Li2S-P2S5, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2S-B2S3, Li3PO4-Li2S-Si2S, Li3PO4-Li2S-SiS2, LiPO4-Li2S-SiS, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, LGPS (Li 10 GeP2S 12 ), LSiPSCl, LSiSnPS, Li6PS5Cl, etc. These can be used alone or in combination of two or more.

[0058] Among the above non-aqueous electrolytes 30, sulfide-based solid electrolytes are likely to cause sulfidation corrosion of the current collectors 11, 21. However, by forming the current collectors 11, 21 using the above ferritic stainless steel plate, sulfidation corrosion of the current collectors 11, 21 can be suppressed. Therefore, the non-aqueous electrolyte secondary battery according to the embodiment of the present invention has a current collector excellent in resistance (corrosion resistance) to various corrosions such as sulfidation corrosion and having a low contact resistance with the active material layer, so that its performance can be improved.

[0059] The non-aqueous electrolyte secondary battery according to the embodiment of the present invention can be manufactured according to a known manufacturing method except that the current collectors 11, 21 formed from the above ferritic stainless steel plate are used.

Examples

[0060] Hereinafter, the content of the present invention will be described in detail with examples, but the present invention is not construed as being limited thereto.

[0061] A stainless steel having the composition shown in Table 1 (the balance being Fe and impurities) was vacuum melted to produce a 30-kg slab. Next, the slab was soaked under the conditions shown in Table 2, then hot-rolled to a thickness of 4 mm, and annealed by holding at 1050 °C for 3 minutes to obtain a hot-rolled annealed sheet. Next, the hot-rolled annealed sheet was cold-rolled to a thickness of 0.3 mm to obtain a cold-rolled sheet, and then annealed by holding at the maximum temperature shown in Table 2 for the time shown in Table 2 in the temperature range of 600 to 1000 °C to obtain a cold-rolled annealed sheet (ferritic stainless steel sheet). The cold-rolled annealed sheet was washed with water and pickled after annealing.

[0062]

Table 1

[0063]

Table 2

[0064] The following evaluations were performed on the cold-rolled annealed sheet obtained above.

[0065] <Area ratio of Ti and / or Nb carbonitrides with an equivalent circle diameter of 0.5 μm or more> A 30 mm × 30 mm test piece was cut out from the central part in the width direction of the cold-rolled annealed sheet, and the surface of the cold-rolled annealed sheet was mirror-polished. Next, using an FE-SEM (field emission scanning electron microscope: SU-5000 manufactured by Hitachi High-Tech Corporation), the surface after mirror polishing was observed at a magnification of 200 times in 12 fields of view (total observation area: approximately 3.4 mm 2 ) and the total area occupied by Ti and / or Nb carbonitrides (particles) with an equivalent circle diameter of 0.5 μm or more was measured. At this time, whether the particles were Ti and / or Nb carbonitrides was specified by performing point analysis on the particles with an EDX (energy dispersive X-ray analysis) device. The area ratio (%) of Ti and / or Nb carbonitrides with an equivalent circle diameter of 0.5 μm or more was calculated by dividing the total area of Ti and / or Nb carbonitrides with an equivalent circle diameter of 0.5 μm or more thus obtained by the observation area.

[0066] <Contact resistance> Two 15-mm-φ disc test pieces were cut out from the central part in the width direction of the cold-rolled annealed plate, and the surface of the cold-rolled annealed plate was mirror-polished to obtain current collectors. Next, a negative electrode active material layer was formed on the surface of one of the two current collectors (disc test pieces), and a positive electrode active material layer was formed on the surface of the other. The negative electrode active material layer was formed by mixing 90% by mass of graphite powder, 5% by mass of acetylene black as a conductive assistant, and 5% by mass of polyvinylidene fluoride as a binder, dispersing this in N-methyl-2-pyrrolidone to form a slurry, applying the slurry to one side of the disc test piece, and drying. Also, the positive electrode active material layer was formed by mixing 90% by mass of lithium manganate powder, 5% by mass of acetylene black as a conductive assistant, and 5% by mass of polyvinylidene fluoride as a binder, dispersing this in N-methyl-2-pyrrolidone to form a slurry, applying the slurry to one side of the disc test piece, and drying. Next, the two current collectors on which the respective active material layers were formed were overlapped so that the surfaces of the respective active material layers were in contact with each other. Next, a load was applied from the surface on the current collector side using a gold-plated copper jig, the surface pressure of the two current collectors was adjusted to 0.5 MPa, and the voltage between the current collectors when a direct current of 1 A / cm 2 was passed was measured with a digital multimeter. By dividing the voltage thus obtained by the current density, the contact resistance (mΩ·cm 2 ) was calculated. In the evaluation of the contact resistance, if the contact resistance is 20.0 mΩ·cm 2 or less, it can be judged that the conductivity is excellent.

[0067] <Volume resistivity> Regarding the cold-rolled annealed plate, the volume resistivity was measured at 20 °C by the four-terminal method. In the evaluation of the volume resistivity, the judgment was made as follows. A: 61.0 μΩ·m or less (excellent conductivity due to a sufficiently low volume resistivity) B: More than 61.0 μΩ·m and 63.0 μΩ·m or less (good conductivity due to a low volume resistivity) C: More than 63.0 μΩ·m (insufficient conductivity due to a high volume resistivity) Note that in the samples fabricated this time, there were no samples for Evaluation C.

[0068] <Corrosion weight loss> Two 10 mmφ disc test pieces were cut out from the central part in the width direction of the cold-rolled annealed sheet, and the surface of the cold-rolled annealed sheet was mirror-polished to obtain current collectors. Next, metallic lithium and a solid electrolyte (Li6PS5Cl) were sandwiched between two current collectors (i.e., laminated in the order of current collector, metallic lithium, solid electrolyte, and current collector), and constrained with a tightening torque of 2 N·m. Next, a holding test was conducted at 4.2 V as a positive electrode assumption test and 0.0 V as a negative electrode assumption test. Note that all potentials are the potential V (vs. Li / Li+) with respect to Li metal. Also, in the holding test, the test temperature was 60°C and the period was 2 weeks. The mass of the current collector on the solid electrolyte side after the holding test was measured, and the mass difference (mg) of the current collector before and after the holding test on the solid electrolyte side was obtained, and this mass difference was divided by the contact area (mm 2 ) of the current collector with the solid electrolyte to calculate the corrosion weight loss (mg / mm 2 ). Note that the evaluation of the corrosion weight loss can be judged as follows. A: The corrosion weight loss is 0.010 mg / mm 2 or less (excellent corrosion resistance) B: The corrosion weight loss exceeds 0.010 mg / mm 2 and is 0.070 mg / mm 2 or less (good corrosion resistance) C: The corrosion weight loss exceeds 0.070 mg / mm 2 and is 0.100 mg / mm 2 or less (fair corrosion resistance) D: The corrosion weight loss exceeds 0.100 mg / mm 2 (insufficient corrosion resistance)

[0069] The above evaluation results are shown in Table 3. Note that in Table 3, the area ratio of Ti and / or Nb carbonitrides with a circle equivalent diameter of 0.5 μm or more is abbreviated as "area ratio".

[0070]

Table 3

[0071] As shown in Table 3, the cold-rolled and annealed sheets of Samples No. 1-1 to 1-13 (Examples) had appropriate ranges of the area ratio of Ti and / or Nb carbonitrides with a circle equivalent diameter of 0.5 μm or more in terms of composition. Therefore, the contact resistance and volume resistivity were low (good conductivity), and the corrosion weight loss was also small (good corrosion resistance). On the other hand, the cold-rolled and annealed sheet of Sample No. 2-1 (Comparative Example) did not contain Ti and / or Nb, so the area ratio of Ti and / or Nb carbonitrides with a circle equivalent diameter of 0.5 μm or more was out of the range. For this reason, the contact resistance was high and the conductivity was insufficient. The cold-rolled steel sheets of Samples No. 2-2 to 2-4 (Comparative Examples) did not have appropriate manufacturing conditions, so the carbonitrides of Ti and / or Nb did not grow sufficiently, and the area ratio of Ti and / or Nb carbonitrides with a circle equivalent diameter of 0.5 μm or more was out of the range. For this reason, the contact resistance was high and the conductivity was insufficient. The cold-rolled steel sheet of Sample No. 2-5 (Comparative Example) had too little Cr content, so the corrosion weight loss was large and the corrosion resistance was insufficient.

[0072] As can be seen from the above results, according to the present invention, it is possible to provide a ferritic stainless steel sheet capable of manufacturing a current collector excellent in resistance (corrosion resistance) to various corrosions such as sulfide corrosion and having a low contact resistance with the active material layer. Further, according to the present invention, it is possible to provide a current collector excellent in resistance (corrosion resistance) to various corrosions such as sulfide corrosion and having a low contact resistance with the active material layer, and a non-aqueous electrolyte secondary battery including such a current collector.

Explanation of Reference Numerals

[0073] 10 Positive electrode 11 Current collector 12 Positive electrode active material layer 20 Negative electrode 21 Current collector 22 Negative electrode active material layer 30 Non-aqueous electrolyte

Claims

1. A ferritic stainless steel sheet used for a current collector of a non-aqueous electrolyte secondary battery, having a composition by mass of C: 0.001 to 0.050%, Si: 0.01 to 2.00%, Mn: 0.01 to 1.00%, P: 0.050% or less, S: 0.010% or less, Ni: 0.01 to 4.00%, Cr: 10.0 to 32.0%, Mo: 0.01 to 2.50%, Cu: 0.01 to 0.80%, Al: 0.001 to 0.150%, N: 0.05% or less, Ti and / or Nb: 0.010 to 1.000%, with the balance being Fe and impurities, and having an area ratio of titanium and / or niobium carbonitrides with an equivalent circle diameter of 0.5 μm or more on the surface of 0.0010% or more. A ferritic stainless steel sheet.

2. The ferritic stainless steel sheet according to claim 1, further comprising at least one selected from Sn: 0.001 to 0.300%, B: 0.001 to 0.010%, Mg: 0.001 to 0.100%, Ca: 0.001 to 0.100%, REM: 0.001 to 0.100%, V: 0.001 to 1.000%, Zr: 0.001 to 1.000%, W: 0.001 to 1.000%, Co: 0.001 to 1.000%, Hf: 0.001 to 1.000%, Ta: 0.001 to 1.000% by mass.

3. The contact resistance is 20.0 mΩ·cm 2 The ferritic stainless steel sheet according to claim 1 or 2, wherein the contact resistance is 20.0 mΩ·cm or less.

4. The corrosion loss is 0.100 mg / mm 2 The ferritic stainless steel sheet according to claim 1 or 2, wherein the corrosion loss is as follows.

5. The ferritic stainless steel sheet according to claim 1 or 2, having a volume resistivity of 63.0 μΩ·m or less.

6. The ferritic stainless steel sheet according to claim 1 or 2, wherein the non-aqueous electrolyte is a solid electrolyte.

7. The ferritic stainless steel sheet according to claim 6, wherein the solid electrolyte is a sulfide-based solid electrolyte.

8. A current collector comprising the ferritic stainless steel sheet according to claim 1 or 2.

9. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte provided between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode has the current collector according to claim 8. A non-aqueous electrolyte secondary battery.

10. The non-aqueous electrolyte secondary battery according to claim 9, wherein the non-aqueous electrolyte is a solid electrolyte.

11. The non-aqueous electrolyte secondary battery according to claim 10, wherein the solid electrolyte is a sulfide-based solid electrolyte.

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