Multi-block copolymer, method for producing same, composition for electrolytes, composition for binders, composition for buffers, and lithium ion battery

Abstract

[Problem] To provide a novel polymer (multi-block copolymer) which has an ability equivalent to the conductivity of a liquid electrolyte and achieves excellent adhesion between an inorganic electrolyte and an electrode, while being safe and excellently stable. [Solution] Provided is a multi-block copolymer in which two or more unit structures, in each of which a soft segment that is composed of a polyglycidol (PGLYD) and a hard segment that is composed of a polyethylene glycol (PEG) are bonded with each other, are connected.

Description

Multiblock copolymer and its manufacturing method, electrolyte composition, binder composition, buffer composition, and lithium ion battery

[0001] The present invention relates to a multiblock copolymer, a method for producing the same, an electrolyte composition, a binder composition, a buffer composition, and a lithium ion battery.

[0002] Lithium-ion batteries are widely used in mobile phones, small home appliances, and other devices because they are lightweight, compact, have high energy density, and are capable of rapid charging and discharging.

[0003] When lithium-ion batteries are used in portable devices, physical damage during transport can cause moisture to enter the liquid electrolyte, such as ethylene carbonate. This can lead to problems, such as fires and explosions caused by the reaction of metallic lithium precipitated during charging and discharging. Current lithium-ion batteries cannot be used in extremely low temperatures or at temperatures exceeding the boiling point of organic electrolytes. Therefore, solid electrolytes, which are less flammable and less affected by operating temperatures, are attracting attention as an alternative to liquid electrolytes.

[0004] As solid electrolytes, inorganic or organic electrolytes are used. Specifically, sulfides and oxides are used as inorganic electrolytes. Also, as organic electrolytes, polyethylene glycol (PEG) and polyethylene carbonate (PEC) are used, which have ether bonds that allow lithium ions to easily conduct. Inorganic electrolytes are manufactured by baking at high temperatures, but cracks may occur in the usage environment, causing a decrease in conductivity. On the other hand, PEG, which is used as an organic electrolyte, is attracting attention as it has characteristics not found in inorganic electrolytes. However, PEG is a crystalline polymer, and when it crystallizes, it blocks the lithium conduction path, resulting in a lithium ion conductivity of 10 －８ Furthermore, PEC is an amorphous polymer and has a higher lithium ion transport number than PEG, but has poor film-forming ability and is difficult to handle.

[0005] In addition, since the melting point of PEG is 55°C, the lithium ion conductivity is 10 －４ However, in order for the solid electrolyte to be usable at room temperature, it is necessary that the polymer does not crystallize.

[0006] To suppress PEG crystallization, methods using branched PEG (Non-Patent Document 1), hydrogel (Patent Document 1), and inorganic additives such as montmorillonite and silica gel have been developed. However, the branched PEG method is complicated, and hydrogel polymers have too low mechanical strength to be practical. Furthermore, the materials used in these methods lack adhesive properties and cannot fill the gap between the inorganic electrolyte and the electrode.

[0007] On the other hand, it has been proposed to use polyglycidol (PGLYD) as a lithium ion electrolyte instead of PEG (Patent Document 2). PGLYD has a high amorphous nature, which allows it to achieve high lithium ion conductivity.

[0008] The compound obtained by removing one molecule of water from glycerin is known as glycidol. Glycidol is a hydroxymethyl epoxide and, like ethylene oxide, can undergo ring-opening polymerization. PEG can be produced from ethylene oxide, while polyglycidol (PGLYD) can be produced from glycidol. PGLYD has the same polyethylene oxide chain as PEG, but is randomly branched due to the presence of hydroxymethyl groups. Therefore, although the carbon-to-oxygen ratio is the same in both PEG and PGLYD, PGLYD has the problem of being unable to crystallize. For this reason, PGLYD cannot be used as a solid electrolyte.

[0009] Naoya Ogata, Journal of the Society of Fiber Science and Technology, pp. 52-57, 1990 H. Frey et al., J. Am. Chem. Soc. 2009, 131, 23, 7954-7955

[0010] Japanese Patent Application Laid-Open No. 5-25353 International Publication No. WO 00 / 35991

[0011] In comparison with the conventional technology, the conductivity of the liquid electrolyte (10－３ There is a need for the development of safe and stable solid electrolytes with conductivity comparable to that of liquid electrolytes, excellent adhesion between inorganic electrolytes and electrodes, and particularly for solid electrolytes capable of bonding inorganic electrolytes and electrodes. Conventional technologies require strong pressure to clamp the two materials together, necessitating the use of a heavy container around the battery. The use of adhesive electrolytes eliminates the need for such large containers. Furthermore, even if cracks develop in the inorganic electrolyte during use, the adhesive electrolyte can penetrate the gap and prevent battery degradation. The present invention has been made in light of the above circumstances, and aims to provide a novel polymer (multiblock copolymer) that has conductivity comparable to that of liquid electrolytes, excellent adhesion between inorganic electrolytes and electrodes, and is safe and stable, as well as a method for producing the same. Another aim is to provide electrolyte compositions, binder compositions, and buffer compositions containing the polymer. A further aim is to provide lithium-ion batteries containing these compositions.

[0012] To solve the above problems, the following multiblock copolymers, their production method, electrolyte compositions, binder compositions, and buffer compositions are provided. [1] A multiblock copolymer having two or more linked unit structures, each unit structure having a soft segment made of polyglycidol (PGLYD) and a hard segment made of polyethylene glycol (PEG). [2] The multiblock copolymer of [1] above, having a weight-average molecular weight of 10,000 or more. [3] The multiblock copolymer of [1] or [2] above, having a lithium ion conductive path group. [4] A composition for an electrolyte of a lithium ion battery, comprising the multiblock copolymer of any one of [1] to [3] above. [5] A composition for a binder of a lithium ion battery, comprising the multiblock copolymer of any one of [1] to [3] above. [6] A composition for a buffer of a lithium ion battery, comprising the multiblock copolymer of any one of [1] to [3] above. [7] A lithium ion battery comprising at least one of the electrolyte composition of [4], the binder composition of [5], and the buffer composition of [6]. [8] A method for producing the multiblock copolymer of [1], comprising the steps of: reacting PEG having isocyanate groups at both ends with polyEEGE (PEEGE) to produce a multiblock copolymer of the following chemical formula (1): (wherein l is a natural number of 2 or more); and reacting the compound with an acid to synthesize a compound represented by the following chemical formula (2): (wherein l is a natural number of 2 or more). [9] A method for producing a multiblock copolymer according to the above [1], comprising the step of reacting PEG having hydroxy groups at both ends, polyEEGE (PEEGE), and a diisocyanate compound to produce a multiblock copolymer represented by the following chemical formula (1): (wherein l is a natural number of 2 or more); and reacting the compound with an acid to synthesize a compound represented by the following chemical formula (2): (wherein l is a natural number of 2 or more).

[0013] The multiblock copolymer of the present invention has conductivity comparable to that of a liquid electrolyte, excellent adhesion between the inorganic electrolyte and the electrodes, and is safe and stable. Therefore, this multiblock copolymer can be suitably used in electrolyte compositions, binder compositions, and buffer compositions for lithium ion batteries. The lithium ion battery of the present invention contains at least one of the electrolyte composition, binder composition, and buffer composition, and has conductivity comparable to that of a liquid electrolyte, excellent adhesion between the inorganic electrolyte and the electrodes, and is safe and stable. Furthermore, the method for producing the multiblock copolymer of the present invention allows the above multiblock copolymer to be produced simply and stably.

[0014] 1 is a cross-sectional schematic diagram illustrating one embodiment of a lithium-ion battery of the present invention. 1 1H NMR spectrum (400 MHz, CDCl3). 1B shows the FT-IR spectrum of PEEGE. (a) shows the FT-IR spectrum of the polymer solution. 1 (b) shows the H NMR spectrum of the obtained polymer. 1 1H NMR spectrum of PEG-PEEGE. 1H NMR spectrum of PEG-PEEGE. 1H NMR spectrum of PEG-PEEGE. 1 1H NMR spectrum of PEG-PGLYD and PEG-PEEGE. 1H NMR spectrum of PEG-PGLYD and PEG-PEEGE. 112 is a diagram showing a H NMR spectrum. FIG. 13 is a schematic diagram illustrating one embodiment of a method for producing a multiblock copolymer of the present invention. FIG. 14 is a diagram showing the results of observing the solubility of 1.5 g of a synthesized multiblock copolymer added to 3 mL of NMP and stirred at room temperature for 24 hours. FIG. 15 is a diagram showing the tackiness of an NMP solution of a multiblock copolymer that has been applied and dried. FIG. 16 is a diagram showing a cathode material obtained by mixing an NMP solution of a multiblock copolymer with iron phosphate containing a conductive material, applying it to aluminum foil, drying, and pressing. FIG. 17 is a diagram showing the results of examining the initial charge / discharge characteristics of a battery fabricated by punching out the cathode material (FIG. 12) to the size of a coin battery. FIG. 18 is a diagram showing the results of a cycle test of a battery fabricated by punching out the cathode material (FIG. 12) to the size of a coin battery.

[0015] An embodiment of the multiblock copolymer of the present invention and a method for producing the same will be described below. In the following description, the terms "PEEGE-PEG" and "PEG-PEEGE" are synonymous, and the terms "PGLYD-PEG" and "PEG-PGLYD" are synonymous.

[0016] The multiblock copolymer of the present invention was designed with attention to the amorphous nature of polyglycidol (PGLYD) and the crystalline nature of polyethylene glycol (PEG). The multiblock copolymer of the present invention is a multiblock copolymer containing PGLYD and PEG, in which PGLYD functions as a soft segment that is flowable over the entire temperature range, and PEG functions as a hard segment that crystallizes at 60°C or below. That is, the multiblock copolymer of the present invention has two or more unit structures (PGLYD-PEG) in which a soft segment made of polyglycidol (PGLYD) is bonded to a hard segment made of polyethylene glycol (PEG). In other words, the multiblock copolymer of the present invention has four or more segments (soft segments and hard segments).

[0017] The number of unit structures (PGLYD-PEG) in the multiblock copolymer of the present invention is not particularly limited, but from the viewpoint of electrolyte conductivity and adhesiveness (tackiness), for example, the range of 4 to 100 can be exemplified.

[0018] While PGLYD-PEG triblock copolymers are known and were published by Frey et al. in 2009 (Non-Patent Document 2), PGLYD-PEG multiblock copolymers with four or more segments (number of blocks) have not been known. Furthermore, the method for producing the multiblock copolymer of the present invention makes it easier to increase the molecular weight compared to conventional methods for producing triblock copolymers, thereby facilitating the development of materials. Furthermore, a major feature of the multiblock copolymer of the present invention is that the PEG hard segment and the PGLYD soft segment can be stably phase-separated, resulting in the multiblock copolymer serving as a good elastomer and adhesive material.

[0019] Both the PGLYD and PEG segments constituting the multiblock copolymer of the present invention preferably have lithium ion conductive path groups. Furthermore, the multiblock copolymer of the present invention behaves as an elastomer due to the presence of the soft and hard segments at temperatures below 60°C (e.g., the temperature range used for manufacturing batteries), and functions as an adhesive.

[0020] The first embodiment of the production of the multiblock copolymer of the present invention can be roughly exemplified by the following procedure. (1) Regarding PEG: PEG having a weight-average molecular weight in the range of 10,000 to 20,000 can be synthesized by a known method. The hydroxyl groups at both ends of the PEG are converted to isocyanate groups by reacting the PEG with a compound such as hexamethylene diisocyanate, to form an A2-type macromonomer. In other words, PEG having isocyanate groups at both ends is synthesized.

[0021] (2) Regarding PGLYD: The hydroxymethyl group of glycidol (GLYD) is protected with, for example, ethyl vinyl ether (EEGE synthesis). Next, this EEGE is polymerized in the presence of a polymerization initiator such as a HO-R-OH diol, for example, tetraethylene glycol or pentaerythritol. This converts it into a PGLYD precursor, which is then converted into a macromonomer such as B2 or B4 type. This precursor has a terminal hydroxy group.

[0022] (3) Regarding multiblock copolymers (PGLYD / PEG block copolymers): The PEG having isocyanate groups at both ends (1) and the precursor (2) are heated in the presence of a tin-based catalyst to cause multiblock copolymerization, and the protection is removed using, for example, hydrogen chloride gas, hydrochloric acid, or a hydrochloric acid-methanol solution. This allows for the production of a multiblock copolymer containing PGLYD and PEG. The multiblock copolymer has two or more unit structures (PGLYD-PEG) in which a soft segment made of polyglycidol (PGLYD) is bonded to a hard segment made of polyethylene glycol (PEG). The multiblock copolymer is a polymer having four or more segments (polymer blocks), preferably a polymer having approximately 4 to 20 segments (polymer blocks).

[0023] That is, the multiblock copolymer of the present invention has two or more unit structures (PGLYD-PEG) each consisting of PGLYD and PEG linked together, and is represented by the following chemical formula (2).

[0024] In the formula, l is a natural number of 2 or more, and typically, l ranges from 4 to 100.

[0025] Of course, the method is not limited to the above, and various forms may be selected in consideration of known knowledge and means.

[0026] The weight-average molecular weight (Mw) of the multiblock copolymer of the present invention is not particularly limited and may be, for example, 2,000 or more. Furthermore, considering desirable conductivity and adhesive properties in lithium-ion batteries, the weight-average molecular weight of the polymer compound of the present invention is preferably in the range of 10,000 to 1,000,000. If the weight-average molecular weight of the multiblock copolymer is less than 10,000, it may be impossible to form a self-supporting film. If the weight-average molecular weight of the multiblock copolymer exceeds 1,000,000, the viscosity may be high and processability may be reduced. Furthermore, if the weight-average molecular weight of the multiblock copolymer exceeds 50,000, toughness can be imparted to a film containing the multiblock copolymer, and if the molecular weight is 50,000 to 1,000,000, the durability of the film can be increased.

[0027] The range of the number average molecular weight (Mn) of the multiblock copolymer of the present invention can be appropriately adjusted by selecting the molecular weights of each of PEG and PGLYD (precursor) and the reaction conditions for block copolymerization. Specifically, the number average molecular weight of the multiblock copolymer of the present invention may be 1,000 or more, and a preferred example is a range of 5,000 to 500,000.

[0028] The multiblock copolymer of the present invention can have a lithium ion conduction path group. The lithium ion conduction path group in this case can be various, including a terminal hydroxy group, but examples include a nitrile group and an ammonium group. For example, as seen in Patent Document 2, lithium conductivity can be improved by converting some of the hydroxy groups of PGLYD to nitrile groups and increasing the polarity of the polymer. Furthermore, high lithium ion conductivity can be imparted by converting the remaining hydroxy groups to an imidazolium salt having a bis(trifluorosulfo)imide anion and doping with lithium perchlorate.

[0029] PGLYD and PEG, which constitute the structural units of the multiblock copolymer of the present invention, may have various substituents, etc. Examples of the substituents include a hydroxy group, a nitrile group, an ammonium group, a carboxy group, and a sulfo group.

[0030] Next, one embodiment of the lithium ion battery and its materials (electrolyte, binder, buffer, etc.) of the present invention will be described with reference to Figure 1. This is a cross-sectional schematic diagram illustrating one embodiment of the lithium ion battery of the present invention.

[0031] The electrolyte composition of the present invention is a composition for use in lithium ion batteries, and comprises the multiblock copolymer of the present invention described above. The binder composition of the present invention is a composition for use in binders in lithium ion batteries, and comprises the multiblock copolymer of the present invention described above. The buffer composition of the present invention is a composition for use in buffers in lithium ion batteries, and comprises the multiblock copolymer of the present invention described above. The electrolyte composition, binder composition, and buffer composition may contain known components that can be used for their respective applications. The lithium ion battery of the present invention comprises at least one of the electrolyte composition, binder composition, and buffer composition described above. The electrolyte composition, binder composition, and buffer composition of the present invention comprise the multiblock copolymer of the present invention. Therefore, these compositions can be used in lithium ion batteries. For example, the electrolyte composition, binder composition, and buffer composition of the present invention have excellent adhesion, safety, and stability. Furthermore, for example, a lithium ion battery using the electrolyte composition of the present invention as a solid electrolyte has performance comparable to the conductivity of a liquid electrolyte and is safe and stable.

[0032] <One Aspect of Lithium-Ion Battery> In one aspect of the lithium-ion battery (lithium-ion secondary battery) of the present invention, the solid electrolyte may include an electrolyte composition containing the multiblock copolymer of the present invention. The lithium-ion battery 100 includes a solid electrolyte layer 11, a positive electrode active material layer 12, a negative electrode active material layer 13, a positive electrode current collector 14, and a negative electrode current collector 15. The lithium-ion battery 100 may include at least one of the electrolyte composition, binder composition, and buffer composition of the present invention in at least one of the solid electrolyte layer 11, the positive electrode active material layer 12, and the positive electrode active material layer 13. The lithium-ion battery of the present invention has conductivity comparable to that of a liquid electrolyte, excellent adhesion between the inorganic electrolyte and the electrodes, and excellent safety and stability.

[0033] (Solid Electrolyte Layer) The solid electrolyte layer 11 is a layer formed between the positive electrode active material layer 12 and the negative electrode active material layer 13. The solid electrolyte layer 11 can contain an electrolyte composition containing the multiblock copolymer of the present invention as a solid electrolyte component. The solid electrolyte can also contain a solid electrolyte other than the multiblock copolymer of the present invention. Specific examples of other solid electrolytes include lithium aluminum titanium phosphate (LATP), lithium aluminum germanium phosphate (LAGP), and lithium lanthanum zirconium oxide (LLZ). These solid electrolytes can be used alone or in combination with the multiblock copolymer of the present invention.

[0034] The solid electrolyte layer 11 may further contain a binder. The binder may be composed of a binder composition containing the multiblock copolymer of the present invention. Furthermore, a thermoplastic resin, a thermosetting resin, or the like may also be used as the binder composition. Specifically, for example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE resin), polychlorotrifluoroethylene, Examples of binders include polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer, polyacrylic acid, sodium polyacrylate, lithium polyacrylate, polymethacrylic acid, sodium polymethacrylate, lithium polymethacrylate, etc. These binders may be used alone or in combination of two or more.

[0035] (Positive Electrode Active Material Layer) The positive electrode active material layer 12 is formed on the positive electrode current collector 14. The positive electrode active material layer 12 contains a solid electrolyte, an electrode active material, and a conductive material. The positive electrode active material layer 12 may further contain various binders such as the binder composition of the present invention. The positive electrode active material layer 12 will be described below.

[0036] (Solid Electrolyte) The electrolyte composition of the present invention can be used as the solid electrolyte contained in the positive electrode active material layer 12. That is, the solid electrolyte may contain the multiblock copolymer of the present invention, or may contain a solid electrolyte other than the multiblock copolymer of the present invention. Examples of solid electrolytes other than the multiblock copolymer of the present invention include lithium aluminum titanium phosphate (LATP), lithium aluminum germanium phosphate (LAGP), and lithium lanthanum zirconium oxide (LLZ). The above-mentioned solid electrolytes other than the polymer for polymer electrolyte of the present invention may be used alone or in combination of two or more, or may be combined with the multiblock copolymer of the present invention.

[0037] (Positive electrode active material) The electrode active material (positive electrode active material) used in the positive electrode is not particularly limited as long as it can reversibly release and absorb lithium ions and transport electrons. Examples of the positive electrode active material include lithium transition metal oxides such as lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, and lithium iron phosphate, and sulfur-based active materials such as lithium sulfide and lithium polysulfide, which are discharge products of sulfur. The positive electrode active material may be composed of one of the above materials alone, or two or more of them.

[0038] (Positive Electrode Conductive Material) The positive electrode conductive material may be a conductive additive that is generally usable in lithium ion secondary batteries and all-solid-state lithium ion secondary batteries. Examples of the positive electrode conductive material include carbon black such as acetylene black and Ketjen black; carbon fiber; vapor-grown carbon fiber; graphite powder; carbon nanotubes, activated carbon, and other carbon materials. The conductive material may be composed of one of the above materials alone, or two or more of them.

[0039] (Negative Electrode Active Material Layer) The negative electrode active material layer 13 is formed on the negative electrode current collector 15. The negative electrode active material layer 13 contains a solid electrolyte, a negative electrode active material, and a negative electrode conductive material. The negative electrode active material layer 13 may further contain various binders such as the binder composition of the present invention. The negative electrode active material layer 13 will be described below.

[0040] (Solid Electrolyte) The solid electrolyte contained in the negative electrode active material layer 13 can be the electrolyte composition of the present invention. That is, the solid electrolyte may contain the multiblock copolymer of the present invention, or may contain a solid electrolyte other than the multiblock copolymer (electrolyte composition) of the present invention. Examples of solid electrolytes other than the polymer for polymer electrolyte of the present invention include lithium aluminum titanium phosphate (LATP), lithium aluminum germanium phosphate (LAGP), and lithium lanthanum zirconium oxide (LLZ). The above-mentioned solid electrolytes other than the multiblock copolymer (electrolyte composition) of the present invention may be used alone or in combination of two or more, or may be combined with the multiblock copolymer of the present invention.

[0041] (Negative electrode active material) The negative electrode active material is not particularly limited as long as it can reversibly release and absorb lithium ions and transport electrons. Examples of the negative electrode active material include carbonaceous materials such as natural graphite, artificial graphite, resin carbon, carbon fiber, activated carbon, hard carbon, and soft carbon; alloy materials mainly composed of tin, tin alloys, silicon, silicon alloys, gallium, gallium alloys, indium, indium alloys, aluminum, and aluminum alloys; conductive polymers such as polyacene, polyacetylene, and polypyrrole; metallic lithium; and lithium titanium composite oxides. The negative electrode active material may be composed of one of the above materials alone, or two or more of them.

[0042] (Negative electrode conductive material) The negative electrode conductive material can be a conductive additive that can generally be used in lithium ion secondary batteries and all-solid-state lithium ion secondary batteries. Examples of the negative electrode conductive material include carbon black such as acetylene black and Ketjen black; carbon fiber; vapor-grown carbon fiber; graphite powder; and carbon materials such as carbon nanotubes and activated carbon. The conductive material may be composed of one of the above materials alone, or two or more of them.

[0043] (Positive electrode current collector) The positive electrode current collector 14 is provided so as to be in contact with the positive electrode active material layer 12. The presence of the positive electrode current collector 14 makes it easier to extract electricity from the positive electrode active material layer 12. As the positive electrode current collector 14, a known positive electrode current collector can be used, for example, Al, SUS, etc. The thickness and shape of the positive electrode current collector 14 can be selected appropriately.

[0044] (Negative electrode current collector) The negative electrode current collector 15 is provided so as to be in contact with the negative electrode active material layer 13. The presence of the negative electrode current collector 15 makes it easier to extract electricity from the negative electrode active material layer 13. As the negative electrode current collector 15, a known negative electrode current collector can be used, for example, Cu. Note that if the negative electrode active material layer 13 has high electronic conductivity, the negative electrode current collector 15 does not need to be provided. Furthermore, the thickness and shape of the negative electrode current collector 15 can be selected as appropriate.

[0045] The lithium ion battery 100 can be manufactured by a known method.

[0046] In addition, the components in the above-described embodiments may be replaced with known components as appropriate, and the above-described modifications may be combined as appropriate, without departing from the spirit of the present invention. Specifically, for example, the lithium-ion battery may include a buffer layer. The buffer composition of the present invention can be used for the buffer layer. While the above-described embodiments include a positive electrode current collector 14, if the positive electrode active material layer 12 has high electronic conductivity, the positive electrode current collector 14 may not be provided. Furthermore, while the above-described embodiments include a negative electrode current collector 15, if the negative electrode active material layer 13 has high electronic conductivity, the negative electrode current collector 15 may not be provided.

[0047] Next, one embodiment of the method for producing the multiblock copolymer of the present invention will be described.

[0048] In a first embodiment of the method for producing a multiblock copolymer of the present invention, the method comprises the steps of: reacting PEG having isocyanate groups at both ends with polyEEGE (PEEGE) to produce a compound represented by the following chemical formula (1): (wherein 1 is a natural number of 2 or more), and reacting the compound (PEEGE-PEG) with an acid to synthesize a compound represented by the following chemical formula (2): (wherein 1 is a natural number of 2 or more)

[0049] For example, PEEGE can be synthesized from a difunctional alcohol, and a commercially available compound with hydroxy groups at both ends of PEG can be used. PEG can be reacted with a diisocyanate compound and then linked to PEEGE to synthesize a compound (PEEGE-PEG) represented by chemical formula (1). Examples of diisocyanate compounds include diphenylmethane diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, and isophorone diisocyanate.

[0050] This compound (PEEGE-PEG) is reacted with an acid to deprotect the hydroxymethyl groups, thereby synthesizing the multiblock copolymer (PGLYD-PEG) represented by the above chemical formula (2). The acid is not particularly limited, but examples include hydrogen chloride gas, hydrochloric acid, and a solution of hydrochloric acid in methanol.

[0051] In addition, the production method of the present invention can improve lithium ion conductivity by converting some of the hydroxy groups of PGLYD to nitrile groups to increase the polarity of the polymer. Also, high lithium ion conductivity can be imparted by converting the remaining hydroxy groups to imidazolium salts having bis(trifluorosulfo)imide anions and doping with lithium perchlorate.

[0052] In addition, in a second aspect of the method for producing a multiblock copolymer of the present invention, the method includes the following steps: reacting PEG having hydroxy groups at both ends, polyEEGE (PEEGE), and a diisocyanate compound, (wherein 1 is a natural number of 2 or more), and reacting the compound (PEEGE-PEG) with an acid to synthesize a compound represented by the following chemical formula (2): (wherein 1 is a natural number of 2 or more)

[0053] Specifically, in the second embodiment, poly(EEGE) (PEEGE) having hydroxy groups at both ends, synthesized from a bifunctional alcohol, is mixed with PEG having hydroxy groups at both ends, and then linked in a single step using a diisocyanate compound. Therefore, the second embodiment, which uses PEG having hydroxy groups at both ends, is a more direct and simple method than the first embodiment. For example, a compound (PEEGE-PEG) can be synthesized by reacting a solution of PEEGE and PEG having hydroxy groups at both ends with a diisocyanate compound such as 1,3-bis(isocyanatomethyl)cyclohexane.

[0054] The diisocyanate compound may be, for example, one or more compounds selected from the group consisting of aliphatic diisocyanates, alicyclic diisocyanates, and aromatic diisocyanates.

[0055] Examples of aliphatic diisocyanates include butane diisocyanate, pentane diisocyanate, hexamethylene diisocyanate (HDI), trimethylhexamethylene diisocyanate, and lysine diisocyanate.

[0056] Examples of the alicyclic diisocyanate include isophorone diisocyanate (IPDI), hydrogenated xylylene diisocyanate, hydrogenated diphenylmethane diisocyanate, and 1,4-cyclohexane diisocyanate.

[0057] Examples of aromatic diisocyanates include xylylene diisocyanate (XDI), diphenylmethane diisocyanate (MDI), and tolylene diisocyanate (TDI).

[0058] In addition to the above steps, the method for producing the multiblock copolymer of the present invention may include a step of synthesizing EEGE (protecting the hydroxymethyl group of glycidol), a step of synthesizing PEEGE, a step of substituting the terminal functional group of PEG, and the like.

[0059] Furthermore, the method for producing the multiblock copolymer of the present invention may also include a step of substituting a portion of the functional groups.

[0060] The multiblock copolymer of the present invention, its production method, and lithium ion battery will be described in more detail below with reference to examples. However, the present invention is not limited to these examples, and various embodiments are contemplated.

[0061] <1> Method for producing a multiblock copolymer (first embodiment) 1) Synthesis of a PEG polymer having isocyanate groups at both ends

[0062] PEG having hydroxyl groups at both ends (weight average molecular weight 16,000, 10 g, 2.5 mmol of OH groups) and dibutyltin dilaurate (molecular weight 631.57, 7.89 mg, 0.0125 mmol) were dissolved in 20 mL of toluene, and hexamethylene diisocyanate (molecular weight 168.2, 0.421 g, 2.5 mmol) was added and reacted at room temperature overnight. The resulting solution was poured into cold ether, and the precipitated white solid was filtered off. This was dried under reduced pressure at 50°C overnight to obtain the target product (yield 85%).

[0063] 2) Protection of the hydroxymethyl group of glycidol (synthesis of EEGE)

[0064] Ethyl vinyl ether (147 g, 2.04 mol) and glycidol (50 g, 0.675 mol) were placed in a three-neck flask equipped with a stirrer and stirred while cooling in a methanol bath. The solution was cooled sufficiently, and 1.25 g (7.26 mmol) of paratoluenesulfonic acid was added in small portions and stirred for 3 hours. 1 L of saturated NaHCO ３ The aqueous solution was prepared and placed in a 170 mL three-neck flask and stirred. The organic layer was then separated using a separatory funnel, and saturated NaHCO ３ This was washed with an aqueous solution of MgSO ４ The mixture was stirred overnight and dried. After drying, MgSO ４ The residue was removed by filtration, concentrated using an evaporator, and then purified by distillation under reduced pressure to obtain a product.

[0065] 3) Synthesis of polyEEGE

[0066] Tetraethylene glycol (molecular weight 194.23, 1.94 mg, 0.001 mmol), cesium hydroxide (molecular weight 149.912, 0.12 mg, 0.01 mmol), and toluene (30 mL) were placed in a two-neck flask and dehydrated using a Dean-Stark reflux condenser to prepare the cesium salt. This solution was heated to 90°C, and EEGE (0.146 g, 1 mmol) was added dropwise to allow polymerization. The polymer was precipitated by pouring the polymerization solution into hexane. The precipitate was dried overnight at 50°C to obtain the target compound (polyEEGE: PEEGE) (yield 68%).

[0067] 4) Synthesis of PGLYD-PEG multiblock copolymer (wherein l is a natural number of 2 or more)

[0068] The resulting PEG having isocyanate groups at both ends (weight average molecular weight 8000, 1 g, isocyanate group 0.25 mmol) and PEEGE (weight average molecular weight 14600, 1.825 g, hydroxy group 0.25 mmol) were added to a flask and stirred with 5 mL of N-methylpyrrolidone (NMP). The catalyst dibutyltin dilaurate (molecular weight 631.57, 7.89 mg, 0.0125 mmol) was added thereto and stirred at 60°C overnight. The resulting polymerization solution was poured into cold ether, and the precipitate was collected and dried overnight at 50°C to obtain a multiblock copolymer (PEEGE-PEG).

[0069] The resulting multi-block copolymer (PEEGE-PEG) was dissolved in THF, and hydrogen chloride gas was bubbled into the solution for 10 minutes. Nitrogen was then bubbled in, and the solution was poured into hexane, and the precipitated polymer (multi-block copolymer (PGLYD-PEG)) was collected. 5) Nitrilation of OH groups of the polymer, etc.

[0070] The PGLYD-PEG multiblock copolymer obtained above was dissolved in NMP, and sodium hydride was added. Then, bromopropionitrile equivalent to 80% of the hydroxyl groups was added, and the mixture was dried overnight at 60°C. The solution was poured into acetone, and the precipitate was collected.

[0071] An excess of p-toluenesulfonyl chloride was added to the nitrated PGLYD-PEG multiblock copolymer to activate the hydroxyl groups, and ethylimidazole was added to convert the hydroxyl groups to imidazolium salts. Lithium bis(trifluorosulfo)amide was then added to replace the chloride ions with bis(trifluorosulfo)imide.

[0072] 6) The PGLYD-PEG multiblock copolymer obtained above exhibited sufficient adhesion (tackiness) to aluminum foil. The multiblock copolymer also exhibited good solubility in NMP and water. The lithium ion conductivity was 10 at room temperature. －５ S / m, which was a good value for an adhesive.

[0073] <2> Production Method of Multiblock Copolymer (Second Aspect) and Properties (1) Instrumental Analysis NMR Spectroscopy: 1H-NMR, 13C-NMR, DEPT-135, and two-dimensional NMR spectroscopy were performed using a JNM-ECA500 (JEOL). Tetramethylsilane (TMS) was used as the internal standard, and CDCl3 and DMSO-d6 were used as deuterium solvents. IR Spectroscopy: FT-IR4200 Type A (JASCO) was used to measure KBr as the reference substance, and measurements were performed by the light transmission method after adding a trace amount of compound to KBr. The prepared gels or films were measured by the attenuated total reflectance (ATR) method. Molecular Weight Measurement: 15 mg of sample was dissolved in 5 mL of THF or NMP, and the weight-average molecular weight (Mw), number-average molecular weight (Mn), and polydispersity (Mw / Mn) were measured using a high-speed GPC system HLC-8420 (Tosoh Corporation) based on the elution curve in terms of polystyrene. Solubility test: 10 mg of sample was added to 5 mL of various solvents and stirred for 24 hours, after which the solubility was confirmed. For samples that did not dissolve, the temperature was raised to near the boiling point, and after stirring for a further 24 hours, the sample was left to stand at room temperature to check for the presence of precipitation. The solvents were purchased without any purification and were used as is. The solvents used are as follows: Chloroform (CHCl3), N-methylpyrrolidone (NMP), Tetrahydrofuran (THF), Methanol (MeOH), Toluene, Hexane, Acetone, Water (H2O)

[0074] (2) Synthesis of EEGE (2,3-Epoxypropyl-1-ethoxy ethyl ether) (Procedure) Ethyl vinyl ether (196 ml, 2.04 mol) and glycidol (44.6 ml, 0.675 mol) were placed in a 300 ml single-neck flask equipped with a stirrer bar and stirred in a nitrogen atmosphere while cooling in a cryostat set to -25°C. After the solution was cooled sufficiently, TsOH·H2O (1.38 g, 7.26 mmol) was added in small portions and stirred for 3 hours. (Treatment) The mixture was transferred to a separatory funnel and washed with 1 L of previously prepared saturated NaHCO3 aqueous solution. The pH was checked to be 7, confirming the removal of TsOH. MgSO4 was added, and the mixture was stirred overnight and dehydrated. (Purification) After dehydration, the MgSO4 was removed by filtration, and the mixture was concentrated using an evaporator. The product was then purified by vacuum distillation (diaphragm, 110°C) to obtain the product. (Results) Properties: Colorless, transparent liquid. Yield: 47.0 g. Yield: 47.6%.

[0075]

[0076] Figure 2 shows the product 1 1 H NMR spectrum (400 MHz, CDCl3). As shown in FIG. 2, it was confirmed that EEGE was synthesized as a product.

[0077] (3) Synthesis of PEEGE (Procedure) Tetraethylene glycol (0.074 g, 0.38 mmol) and cesium hydroxide monohydrate (0.13 g, 0.70 mmol) were placed in a 50 ml single-neck flask equipped with a stirrer, Dean-Stark trap, thermometer, condenser, and three-way stopcock. The mixture was then reacted overnight in toluene (20 ml) at 130°C under a nitrogen atmosphere. After the reaction, the Dean-Stark trap was removed, and the toluene was removed by vacuum distillation (40°C). Further vacuum distillation was performed at 100°C for 1 hour to completely remove the toluene. After that, a condenser was attached, and EEGE (4.4 g, 30 mmol) was added under a nitrogen atmosphere and reacted at 65°C for 2 days. (Treatment) The polymerization was terminated using methanol / acetic acid (1:1). (Purification) The product was dissolved in tetrahydrofuran, poured into water, and dried under reduced pressure at 100°C. The structure of the obtained product was analyzed by IR, 1H NMR, and GPC. (Results) Properties: Viscous liquid Yield: 4.49 g Yield: 94.5% GPC Data Mn = 3900, Mw = 4800, Mw / Mn = 1.24

[0078]

[0079] Figure 3 shows the FT-IR spectrum of the product. Figure 4(a) shows the FT-IR spectrum of the product solution. 1 4(b) shows the H NMR spectrum of the obtained product. 1 3 and 4 show the 1 H NMR spectrum. As shown in Fig. 3 and Fig. 4, it was confirmed that PEEGE was synthesized as the product.

[0080] (4) Synthesis of multiblock copolymer (PEG-PEEGE) (Procedure) Using the same procedure as for the synthesis of PEEGE, tetraethylene glycol (0.074 g, 0.38 mmol) and cesium hydroxide monohydrate (0.13 g, 0.70 mmol) were added to a 50 ml single-neck flask equipped with a stirrer, Dean-Stark apparatus, thermometer, condenser, and three-way stopcock, and the mixture was reacted overnight in toluene (20 ml) at 130 °C under a nitrogen atmosphere. After the reaction, the Dean-Stark apparatus was removed, and the toluene was removed by vacuum distillation (40 °C). This was followed by further vacuum distillation at 100 °C for 1 hour to completely remove the toluene. After that, a condenser was attached and EEGE (4.4 g, 30 mmol) was added under a nitrogen atmosphere. The mixture was reacted at 65 °C for 2 days to obtain the PEEGE Cs salt. The mixture was then returned to room temperature and PEG3k (2.0 g, 0.55 mmol) and hexamethylene diisocyanate (0.16 g, 0.98 mmol) dissolved in NMP solvent (1 mL) were added. Dibutyltin diuranate (0.019 g, 0.03 mmol) was added and the mixture was reacted overnight at 60 °C. (Processing) The mixture was poured into a silicone mold while still heated. (Purification) The silicone mold was placed in a vacuum oven set to 50 °C without cooling and dried under reduced pressure at 140 °C. The resulting product's structure was analyzed by IR, 1H NMR, and GPC. (Results) Form: Viscous liquid Yield: 2.84 g Yield: 42.4% Mn = 6500, Mw = 14000, Mw / Mn = 2.2

[0081]

[0082] Figure 5 shows the FT-IR spectrum of PEG-PEEGE. Figure 6 shows the FT-IR spectrum of PEG, PEEGE, and PEG-PEEGE. 1 5 and 6 show the 1 H NMR spectrum. As shown in Fig. 5 and Fig. 6, it was confirmed that a PEG-PEEGE multiblock copolymer was synthesized as the product.

[0083] (5) Synthesis of Multiblock Copolymer (PEG-PGLYD) (Deprotection) (Procedure) PEG-PEEGE (1.36 g, 0.21 mmol) and chloroform (40 mL) were placed in a 100 mL two-neck flask equipped with a stirrer and stirred at room temperature until dissolved. Concentrated sulfuric acid (10 mL, 0.184 mol) was placed in a dropping funnel with a side tube, and an excess amount of NaCl (15 g, 0.26 mol) was placed in a 200 mL two-neck flask equipped with a stirrer and connected to the dropping funnel. A three-way stopcock was attached to the other neck of the flask containing NaCl, and the equipment was assembled in the following order: an Erlenmeyer flask with a backflow prevention valve, a reaction vessel equipped with a Pasteur valve, and a bottle containing aqueous NaOH solution. Concentrated sulfuric acid was then slowly added dropwise to generate HCl gas in the reaction solution. (Processing) Nitrogen was blown into the reaction solution to remove the HCl from the reaction solution. (Purification) After removing the chloroform with an evaporator, the structure of the obtained product was analyzed by IR and 1H NMR. (Results) Properties: Viscous liquid Yield: 1.161g Yield: 85.92%

[0084] Figure 7 shows the IR spectra of PEG-PGLYD and PEG-PEEGE. Figure 8 shows the IR spectra of PEG-PEEGE and PEG-PGLYD. 1 7 and 8 show the H NMR spectrum. It was confirmed that PEEGE was converted to PGLYD by the acid, and a PEG-PGLYD multiblock copolymer was synthesized.

[0085] FIG. 9 is a schematic diagram illustrating one embodiment of the method for producing a multiblock copolymer of the present invention (the above-mentioned Production Method 2). In this production method (the above-mentioned Production Method 2), PEG having OH groups at both ends and a diisocyanate compound are added to a salt of PEEGE. Because there are fewer reaction steps compared to Production Method 1, a PEG-PGLYD multiblock copolymer can be synthesized simply and at low cost. Note that FIG. 9 also shows an example of an electrolyte application in which lithium bis(trifluorosulfo)amide is added to a multiblock copolymer, and bis(trifluorosulfo)imide is attached to the terminals.

[0086] <3> Solubility of multiblock copolymer (PEG-PGLYD) 1.5 g of the multiblock copolymer synthesized by the above method was added to 3 mL of NMP and stirred at room temperature for 24 hours. As shown in Figure 10, it was confirmed that the multiblock copolymer dissolved and became a homogeneous solution. This multiblock copolymer demonstrated high solubility.

[0087] <4> Tackiness of multiblock copolymer (PEG-PGLYD) (application to binder) Using a film forming device, an NMP solution of the multiblock copolymer synthesized by the above method was applied to a SUS substrate to a thickness of 25 microns and dried at 120°C for 10 minutes (Figure 11). The coating was sticky when touched with a finger, confirming that it had sufficient tackiness.

[0088] <5> Cathode material for lithium-ion batteries using multiblock copolymer (PEG-PGLYD) The NMP solution of the multiblock copolymer synthesized by the above method was mixed with iron phosphate containing a conductive material, and the mixture was coated onto aluminum foil to form a slurry. The mixture was then dried at 110°C for 10 minutes and pressed to form a cathode material (Figure 12). As shown in Figure 12, the cathode material showed no peeling of the coating.

[0089] <6> Charge-discharge test of lithium-ion battery using multiblock copolymer (PEG-PGLYD) The cathode material obtained in Figure 12 was punched to the size of a coin battery, and the initial charge-discharge characteristics of the fabricated battery were examined. As shown in Figure 13, there was no sudden decrease in capacity, confirming that it can be used as an electrode binder.

[0090] <7> Cycle test of lithium-ion battery using multiblock copolymer (PEG-PGLYD) The cathode material obtained in Figure 12 was punched out to the size of a coin battery, and a cycle test of the fabricated battery was carried out. As shown in Figure 14, no sudden deterioration in performance was observed in the cycle test up to 10 times, and it was confirmed that the secondary battery could operate without any problems.

[0091] REFERENCE SIGNS LIST 100 Lithium ion battery 11 Solid electrolyte layer 12 Positive electrode active material layer 13 Negative electrode active material layer 14 Positive electrode current collector 15 Negative electrode current collector

Claims

1. A multiblock copolymer in which two or more unit structures each consisting of a soft segment made of polyglycidol (PGLYD) and a hard segment made of polyethylene glycol (PEG) are linked together.

2. The multiblock copolymer according to claim 1, having a weight average molecular weight of 10,000 or more.

3. The multiblock copolymer of claim 1, having a lithium ion conductive path group.

4. An electrolyte composition for a lithium ion battery, comprising the multiblock copolymer of claim 1.

5. A binder composition for a lithium ion battery, comprising the multiblock copolymer of claim 1.

6. A buffer composition for a lithium ion battery, comprising the multiblock copolymer of claim 1.

7. A lithium ion battery comprising at least one of the electrolyte composition of claim 4, the binder composition of claim 5, and the buffer composition of claim 6.

8. A method for producing the multiblock copolymer of claim 1, comprising the steps of: reacting PEG having isocyanate groups at both ends with polyEEGE (PEEGE) to obtain a compound represented by the following chemical formula (1): (wherein l is a natural number of 2 or more); and reacting the compound with an acid to obtain a compound represented by the following chemical formula (2): (wherein l is a natural number of 2 or more), 9. A method for producing the multiblock copolymer of claim 1, comprising reacting PEG having hydroxy groups at both ends, polyEEGE (PEEGE), and a diisocyanate compound to produce a copolymer represented by the following chemical formula (1): (wherein l is a natural number of 2 or more); and reacting the compound with an acid to obtain a compound represented by the following chemical formula (2): (wherein l is a natural number of 2 or more),

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