JP2007242411A - Battery and electrolyte composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery capable of suppressing decomposition of a solvent and deformation of the battery while improving maintenance of a battery characteristic and long-term storage reliability. <P>SOLUTION: An electrolyte interlaid between positive and negative electrodes is formed into a structure having an electrolytic solution containing a nonaqueous solvent, an electrolyte salt containing lithium (Li), and a diisocyanate compound having an aliphatic carbon chain. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a battery including a positive electrode, a negative electrode, and an electrolyte, and an electrolytic solution composition constituting at least a part of the electrolyte.

With the increase in functionality of electronic devices, portable (mobile) electronic devices have been developed and widely used.
Examples of such a mobile electronic device include a mobile phone, an imaging device, and a personal computer (PC). The battery constituting the power source of these devices includes a high-performance electronic device. In accordance with the trend toward improvement, improvements in various characteristics such as thinness and lightness, capacity, and cycle characteristics that facilitate carrying are always required.

  In particular, battery deformation (for example, expansion of an exterior member or distortion of an electrode) caused by decomposition and vaporization of a solvent constituting an electrolyte (electrolytic solution) interposed between positive and negative electrodes due to repeated charge and discharge is caused by battery rupture. There is a need for a battery configuration that can reliably avoid deformation, as it may lead to a decrease in capacity and cycle characteristics, or it may cause a failure of predetermined installation in electronic equipment. Yes. In particular, when graphite is used for the negative electrode, a very strong reducing power is exhibited on the surface of the negative electrode, so that the decomposition of the electrolyte solvent becomes significant.

For example, regarding a so-called lithium ion secondary battery in which a negative electrode is formed of a carbonaceous material capable of absorbing and desorbing lithium (Li) ions, as exemplified by an intercalation reaction between graphite layers, As a solvent constituting the electrolyte, there is known a technique for suppressing deterioration of battery characteristics due to high-temperature storage by using gamma-butyrolactone (γ-butyrolactone) having a relatively high boiling point and high dielectric constant (for example, Patent Document 1). reference).
However, when gamma-butyrolactone is used, a reductive decomposition reaction occurs at the negative electrode, so that not only the characteristics deteriorate as the battery is used, but it is also pointed out that the battery may be deformed by decomposition and vaporization of the solvent. ing.

In contrast, the SEI (Solid Electrolyte Interface) is formed on the negative electrode during charge and discharge in the initial use of the battery.
A method for suppressing reductive decomposition of the solvent on the negative electrode and deformation of the battery has been proposed by using an electrolyte structure in which a compound that forms a film called a solid electrolyte membrane) is previously added to the solvent (for example, Patent Documents) 2).
However, in the case of the electrolyte configuration described in Patent Document 2, it is not possible to suppress deterioration of characteristics due to use, and gas generation and battery deformation occur during high-temperature storage.

特開平09-92329号公報 特開2003-151623号公報 特開2002-8719号公報 In addition, a nonaqueous electrolyte and a battery including an aromatic compound having an isocyanate group having a structure represented by [Chemical Formula 3] have been proposed (see, for example, Patent Document 3). In [Chemical Formula 3], Ar represents an aryl group (aromatic carbon chain).
However, although the electrolyte composition containing such an additive improves the high-temperature storage characteristics, further suppression of the solvent and further improvement of the cycle characteristics and capacity are required.

JP 09-92329 A JP 2003-151623 A JP 2002-8719 A

  The present invention has been made in view of such problems, and its object is to provide a battery in which decomposition of the solvent and deformation of the battery are suppressed while maintaining and improving battery characteristics and long-term storage reliability. An object of the present invention is to provide an electrolytic solution composition constituting at least a part of the electrolyte.

この電池においては、電解質が、非水溶媒及び含リチウム電解質塩とともに、脂肪族炭素鎖を主鎖とするジイソシアネート化合物を含んだ構成とされることから、使用初期の充放電によって負極上に安定なＳＥＩが形成される。 A battery according to the present invention includes a positive electrode, a negative electrode, and an electrolyte, and the electrolyte has a structure represented by the following [Chemical Formula 4], an electrolyte salt containing a non-aqueous solvent, lithium (Li), and the like. It has the electrolyte solution containing a diisocyanate compound, It is characterized by the above-mentioned. In [Chemical Formula 4], R represents an aliphatic carbon chain (such as an alkyl group).

In this battery, since the electrolyte includes a diisocyanate compound having an aliphatic carbon chain as a main chain together with a nonaqueous solvent and a lithium-containing electrolyte salt, the electrolyte is stable on the negative electrode by charge and discharge in the initial stage of use. SEI is formed.

本発明に係る電解液組成物は、ジイソシアネート化合物が、上記脂肪族炭素鎖の互いに異なる２つの炭素に、イソシアネート基がそれぞれ結合された構造を有し、各イソシアネート基の間に位置する炭素の数が、４以上１２以下であるものが好ましい。
また、上記ジイソシアネート化合物量が、０．５重量％以上５重量％以下含有されているものが好ましい。
更に、上記ジイソシアネート化合物を構成する上記脂肪族炭素鎖が、直鎖状であるものとすることが好ましい。
上記ジイソシアネート化合物を構成する脂肪族炭素鎖の一部が、ヒドロキシル基、カルボキシル基、アミノ基以外の官能基のみで置換されているものとすることが好ましい。
上記電解質を構成する主たる成分に含まれる官能基が、ヒドロキシル基、カルボキシル基、アミノ基以外の官能基のみであるものとすることが好ましい。 The electrolytic solution composition according to the present invention can be used as an electrolytic solution contained in an electrolyte in a battery, and has a structure represented by the following [Chemical Formula 5], a nonaqueous solvent, an electrolyte salt containing lithium (Li). It has the structure containing a diisocyanate compound, It is characterized by the above-mentioned.

In the electrolyte composition according to the present invention, the diisocyanate compound has a structure in which an isocyanate group is bonded to two different carbons of the aliphatic carbon chain, and the number of carbons positioned between the isocyanate groups. Is preferably 4 or more and 12 or less.
Moreover, what contains 0.5 to 5 weight% of said diisocyanate compound amount is preferable.
Furthermore, it is preferable that the aliphatic carbon chain constituting the diisocyanate compound is linear.
It is preferable that a part of the aliphatic carbon chain constituting the diisocyanate compound is substituted only with a functional group other than a hydroxyl group, a carboxyl group, and an amino group.
It is preferable that the functional group contained in the main component constituting the electrolyte is only a functional group other than a hydroxyl group, a carboxyl group, and an amino group.

According to the battery of the present invention, the electrolyte interposed between the positive and negative electrodes is an electrolysis containing a nonaqueous solvent, an electrolyte salt containing lithium (Li), and a diisocyanate compound having a structure represented by the above [Chemical Formula 4]. Since the liquid is included, it is possible to suppress the decomposition of the solvent and the deformation of the battery by the SEI formed at the initial stage of use, while maintaining and improving the battery characteristics and long-term storage reliability.
Moreover, according to the electrolytic solution composition according to the present invention, since the diisocyanate compound having the structure represented by the above [Chemical Formula 5] is included, an excellent electrolytic solution suitable for constituting a battery as described above is obtained. Can be obtained.

  Embodiments of the present invention will be described below with reference to the drawings.

<First Embodiment>
A first embodiment of a battery according to the present invention will be described.
In the present embodiment, a wound battery having a laminate film as an exterior member as illustrated in FIG. 1A in a perspective view in which each member is separated and further partially cut will be described as an example.

In the battery 1 according to the present embodiment, a wound body 3 is accommodated in an airtight structure formed by the exterior member 2 and the exterior member 4, and only the leads 5 and 6 to be described later are provided from the wound body 3. However, it is derived | led-out in the same direction, for example toward the exterior of an airtight structure.
As shown schematically in FIG. 1B, the wound body 3 in the present embodiment includes a strip-like (elongated thin plate-like) positive electrode 9 and negative electrode 10 with separators 7 and 8 including electrolytes interposed therebetween. Are arranged opposite to each other and have a configuration in which they are wound. Moreover, although not shown in figure, the outermost periphery part of this wound body 3 is protected by the protective tape.
In FIG. 1B, the wound body 3 is schematically illustrated by being wound so that the cross section thereof is substantially rectangular. However, the wound body 3 is formed by the exterior member 2 and the exterior member 4. It can also be set as the shape which has a curve part (non-bending curved part) so that a cross section may become a substantially ellipse shape inside an airtight structure.
The leads 5 and 6 are respectively provided so as to be electrically connected to a positive electrode 9 and a negative electrode 10 which will be described later. For example, the leads 5 and 6 are thin plates made of a metal material such as aluminum (Al), copper (Cu), nickel (Ni) or stainless steel It is formed in a shape or a mesh shape.

In the present embodiment, the exterior member 2 and the exterior member 4 are each composed of, for example, a rectangular aluminum laminate film in which a nylon film, an aluminum foil, and a polyethylene film are bonded together in this order, and the polyethylene film side and the wound body 3 are arranged so as to face each other, and the outer edge portions are in close contact with each other by fusion bonding or an adhesive. An adhesive film (not shown) for preventing the entry of outside air is inserted between the exterior member 2 and the exterior member 4 and the leads 5 and 6 as necessary.
The exterior member 2 and the exterior member 4 may be made of a laminate film having another structure, a polymer film such as polypropylene, or a metal film instead of the above-described aluminum laminate film.

In the present embodiment, the positive electrode 9 has, for example, a first positive electrode active material layer 12 and a second positive electrode active material layer 13 supported and formed on both main surfaces of a belt-like (thin plate-like) positive electrode current collector 11. It has a configuration.
The positive electrode current collector 11 can be made of, for example, aluminum, nickel, stainless steel, or the like.

The 1st positive electrode active material layer 12 and the 2nd positive electrode active material layer 13 contain any 1 type, or 2 or more types of the positive electrode material which can occlude and discharge | release lithium as a positive electrode active material, for example. Depending on the case, a conductive material such as a carbon material and a binding material such as polyvinylidene fluoride may be included. As a positive electrode material capable of inserting and extracting lithium, for example, a lithium transition metal composite oxide containing lithium and a transition metal is preferable. This is because a high voltage can be generated and a high energy density can be obtained. Examples of the lithium transition metal composite oxide include those represented by the general formula Li _x MO ₂ . In this general formula, M contains one or more transition metal elements, and for example, preferably contains at least one of cobalt and nickel. x varies depending on the charge / discharge state of the battery and is usually a value in the range of 0.05 ≦ x ≦ 1.10. Specific examples of such a lithium transition metal composite oxide include LiCoO ₂ , LiMnO _{2, and} LiNiO ₂ .

  When a particulate lithium transition metal composite oxide is used as the positive electrode active material, the powder may be used as it is. However, at least part of the particulate lithium transition metal composite oxide contains this lithium transition metal. A surface layer containing at least one member selected from the group consisting of oxides, halides, phosphates, and sulfates having a composition different from that of the metal composite oxide may be provided. This is because stability can be improved and a decrease in capacity can be further suppressed. In particular, it is preferable to use lithium fluoride as the metal halide. In this case, the constituent element of the surface layer and the constituent element of the lithium transition metal composite oxide may be diffused with each other.

The 1st positive electrode active material layer 12 and the 2nd positive electrode active material layer 13 contain at least 1 sort (s) of the group which consists of the simple substance of 2 group element, 3 group element, or 4 group element and a compound in a long period type periodic table. It is preferable. This is because stability can be improved and a decrease in capacity can be further suppressed. Examples of the Group 2 element include magnesium (Mg), calcium (Ca), and strontium (Sr), among which magnesium is preferable. Examples of the Group 3 element include scandium (Sc) and yttrium (Y). Among them, yttrium is preferable. Examples of the Group 4 element include titanium (Ti) and zirconium (Zr), and among them, zirconium is preferable. These elements may be dissolved in the positive electrode active material, or may exist as a simple substance or a compound at the grain boundary of the positive electrode active material.
Note that both the first positive electrode active material layer 12 and the second positive electrode active material layer 13 do not necessarily have to be provided, and are preferably provided according to the intended battery configuration and characteristics.

  On the other hand, as a material constituting the first negative electrode active material layer 15 and the second negative electrode active material layer 16 constituting the negative electrode 10, a carbonaceous material capable of absorbing and desorbing lithium, or a metal capable of forming an alloy with lithium, or The alloy compound containing the metal is mentioned.

  Examples of carbonaceous materials include non-graphitizable carbon, graphites such as artificial graphite and natural graphite, pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke, etc.), glassy carbons, organic high carbon At least one kind of carbonaceous material such as a molecular compound fired body (phenol resin, furan resin, etc., fired at an appropriate temperature and carbonized), activated carbon, fibrous carbon, or the like can be used. Moreover, you may include the material which does not contribute to charging / discharging.

Examples of the alloy compound include those containing at least one metal that can be alloyed with lithium. Specifically, when the metal element capable of forming an alloy with lithium is M, the chemical formula M _x M ′ _y Li _z (M ′ is one or more metal elements other than Li element and M element, x> 0, y As a compound having a composition of ≧ 0, z ≧ 0). Note that in this specification, elements such as B, Si, and As, which are semiconductor elements, are also included in the metal elements.
Examples of such metals and metal compounds include Mg, B, Al, Ga, In, Si, Ge, Sn, Pb, Sb, Bi, Cd, Ag, Zn, Hf, Zr, and Y, and those. Alloy compounds of Li, Al-Li, Li-Al-M (M: 2A, 3B, 4B, consisting of one or more of transition metal elements), AlSb, CuMgSb, and the like.

In particular, it is preferable to use a group 4B typical element as an element capable of forming an alloy with lithium, and more preferably Si or Sn. For example, M _x Si, M _x Sn (M excludes Si or Sn, respectively) And compounds represented by one or more metal elements). Specifically, SiB ₄ , SiB ₆ , Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , CaSi ₂ , CrSi ₂ , Cu ₅ Si, FeSi ₂ , MnSi ₂ NbSi ₂ , TaSi ₂ , VSi ₂ , WSi ₂ , ZnSi _{2 and the} like.
Further, in the battery according to the present embodiment, the first negative electrode active material layer 15 and the second negative electrode active material layer 16 can also be configured by a 4B group compound other than carbon containing one or more nonmetallic elements. . Specifically, for example, SiC, Si ₃ N ₄ , Si ₂ N ₂ O, Ge ₂ N ₂ O, SiO _x (0 <x ≦ 2), SnO _x (0 <x ≦ 2), LiSiO, LiSnO, etc. Can be.

Examples of the method for producing the negative electrode active material layer using these materials include a mechanical alloying method, a method in which raw material compounds are mixed and heat-treated in an inert atmosphere, a melt spinning method, a gas atomizing method, a water atomizing method, and the like. Although it is mentioned, it is not limited to this. In addition, each material may or may not be pulverized, or two or more of the above materials may be mixed.
The negative electrode active material layer may be doped with lithium in the battery after the battery is manufactured, or supplied from a positive electrode or a lithium source other than the positive electrode after the battery is manufactured or before the battery is manufactured. It may be electrochemically doped, synthesized as a lithium-containing material during material synthesis, and contained in the negative electrode during battery fabrication.

On the other hand, the separators 7 and 8 separate the positive electrode 9 and the negative electrode 10 and allow lithium ions to pass while preventing a short circuit of current due to contact between both electrodes, and are made of, for example, polyethylene or polypropylene.
The separators 7 and 8 are impregnated with an electrolytic solution (not shown) serving as an electrolyte interposed between the positive electrode 9 and the negative electrode 10. This electrolytic solution is the first embodiment of the electrolyte composition of the present invention.

In the battery according to the present embodiment, the electrolytic solution has a configuration in which the diisocyanate compound having the structure represented by [Chemical Formula 4] described above is dissolved in a nonaqueous solvent (organic solvent).
This diisocyanate compound has a structure having an aliphatic carbon chain (alkyl group) R as a main chain as shown in [Chemical Formula 4], and two carbons having different aliphatic carbon chains as described later. In particular, the number of carbons located between each isocyanate group is selected to be 4 or more and 12 or less, thereby improving the battery characteristics and long-term storage reliability. However, the decomposition of the solvent and the deformation of the battery can be particularly suppressed.

Moreover, it is preferable that the aliphatic carbon chain which comprises the principal chain is a linear form as for the diisocyanate compound which comprises the electrolyte solution of the battery which concerns on this embodiment. This is because, in a single molecule diisocyanate compound, when the surface area occupied by other than the isocyanate group increases, the reactivity of the isocyanate group relatively decreases, and even when the structure of the diisocyanate compound has side chains. It is preferable that the predetermined reaction of the isocyanate group including SEI formation is not inhibited. That is, as long as the structure of the diisocyanate compound is within a range not impairing the reactivity of the isocyanate group, it is preferable to appropriately select the number of carbons of the main chain of the aliphatic carbon chain and the constitution of the side chain. A structure having such a branch (branch having a side chain) may be used.
In addition, the aliphatic carbon chain that is the main chain constituting the diisocyanate compound is directly or indirectly substituted with a hydroxyl group (—OH), a carboxyl group (—COOH), an amino group (—NH ₂ ), or the like. Since the diisocyanate compound cannot be stably present and is changed by a reaction within or between the molecules and cannot contribute to a desired purpose such as SEI formation, a functional group including a side chain includes a hydroxyl group, It is preferably substituted only with a functional group other than a carboxyl group and an amino group. Similarly, in order to suppress the loss of the isocyanate group due to the intermolecular reaction, not only the main components constituting the electrolytic solution (not only the diisocyanate compound but also a solvent and a lithium electrolyte salt described later, for example, 0.1% with respect to the electrolytic solution). It is considered that it is particularly preferable for the functional group to have only a functional group other than a hydroxyl group, a carboxyl group, and an amino group as a functional group with respect to a component contained in a proportion of not less than% by weight.

According to the electrolyte configuration including such a diisocyanate compound, it is possible to select a solvent that has been conventionally difficult to handle, such as a solvent that has a high boiling point but is easily decomposed, and the degree of freedom in selecting a non-aqueous solvent is also increased. improves. In addition, by selecting the length of the carbon chain of the aliphatic carbon chain, that is, the number of carbon atoms, it becomes possible to adjust the thickness of the SEI formed on the surface of the negative electrode, so that the resistance increases due to being too thick. It is possible to obtain a moderate thickness by avoiding the occurrence of deterioration of the battery characteristics and the occurrence of damage to the electrode due to being too thin.
In addition, if the number of carbon atoms in the aliphatic carbon chain is too large, the solubility as a polymer may be reduced and it may not be suitable for a non-aqueous solvent. However, as described later, if the carbon number is within 12 and is relatively small, It is considered that sufficient solubility can be obtained even when the aliphatic carbon chain has a side chain other than the main chain (not linear). This is thought to be due to the fact that the viscosity and the reactive groups per weight decrease as the number of carbon atoms increases. In addition, it is preferable that the aliphatic carbon chain has a linear structure suitable for the reactivity of the isocyanate group in order to ensure solubility even when the number of carbon atoms in the main chain is larger.
Such a problem of deformation or expansion of the battery exterior member is useful not only in the configuration of the exterior member made of the laminate film but also in the configuration of the exterior member made of the metal can in order to cope with the recent thinning of the container. it is conceivable that.

As will be described later, the amount of the diisocyanate compound added in the electrolyte (electrolytic solution in the present embodiment) is preferably 0.5% by weight or more and 5% by weight or less with respect to the electrolytic solution. These values are particularly effective in the state before the initial charge, and a part of the diisocyanate compound is consumed for the formation of SEI on the negative electrode during charging (mainly during initial charging). It is considered that after the initial charging in which the amount and concentration of the diisocyanate compound are changed, the values are somewhat different.
In addition, by including the diisocyanate compound described above at a concentration corresponding to this numerical range, necessary and sufficient SEI is formed through charge / discharge at the time of use. As a particularly preferable example, this concentration is set before the first charge. By doing so, it is considered that substantially all of the necessary and sufficient SEI is formed by the initial charge. Note that SEI may be further formed during the second and subsequent charging.

  In the present embodiment, the solvent constituting the electrolytic solution is mixed with a cyclic carbonate having an unsaturated bond such as 1,3-dioxol-2-one or 4-vinyl-1,3-dioxolan-2-one. And preferably used. This is because a decrease in capacity can be further suppressed. In particular, it is preferable to use 1,3-dioxol-2-one and 4-vinyl-1,3-dioxolan-2-one together because higher effects can be obtained.

Furthermore, in addition to vinylene carbonate and vinyl ethylene carbonate, a carbonate ester derivative having a halogen atom such as fluoroethylene carbonate may be mixed and used as the solvent. This is because a decrease in capacity can be suppressed. In this case, it is more preferable to use a mixture with a cyclic carbonate having an unsaturated bond. This is because a higher effect can be obtained.
The carbonic acid ester derivative having a halogen atom may be either a cyclic compound or a chain compound, but the cyclic compound is preferable because a higher effect can be obtained. Such cyclic compounds include 4-fluoro-1,3-dioxolane-2-one, 4-chloro-1,3-dioxolane-2-one, 4-bromo-1,3-dioxolane-2-one Or 4,5-difluoro-1,3-dioxolane-2-one, among which 4-fluoro-1,3-dioxolan-2-one is preferred. This is because a higher effect can be obtained.

In the present embodiment, examples of the lithium-containing electrolyte salt added to the organic solvent together with the diisocyanate compound described above include lithium salts such as LiPF ₆ , LiCF ₃ SO _{3, and} LiClO ₄ . Any one electrolyte salt may be used alone, or two or more electrolyte salts may be mixed and used.
Examples of other substances constituting the solvent include carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. For example, a high-boiling solvent such as ethylene carbonate or propylene carbonate; It is preferable to use a mixture with a low boiling point solvent such as dimethyl, diethyl carbonate or ethyl methyl carbonate because high ionic conductivity can be obtained.

  In addition, although electrolyte solution may be used as it is, it is good also as what is made to hold | maintain to a high molecular compound and comprises what is called a gel-like electrolyte. In that case, the electrolyte may be impregnated in the separator 15, or may exist in a layer form between the separator 15 and the negative electrode 13 or the positive electrode 14. As the polymer material, for example, a polymer containing vinylidene fluoride is preferable. This is because the redox stability is high. Moreover, as a high molecular compound, what was formed by superposing | polymerizing a polymeric compound is also preferable. Examples of the polymerizable compound include monofunctional acrylates such as acrylic acid esters, monofunctional methacrylates such as methacrylic acid esters, polyfunctional acrylates such as diacrylic acid esters and triacrylic acid esters, dimethacrylic acid esters and trimethacrylic acid esters. There are polyfunctional methacrylates such as acrylonitrile, methacrylonitrile, and the like. Among them, esters having an acrylate group or a methacrylate group are preferable. This is because the polymerization proceeds easily and the reaction rate of the polymerizable compound is high.

<Second Embodiment>
A second embodiment of the battery according to the present invention will be described.

  In the present embodiment, a so-called element-wound cylindrical battery as shown in a perspective view with a part cut in FIG. 2A will be described as an example.

In the battery 21 according to the present embodiment, a winding body 23 (described later) is wound around a center pin (not shown) inside a cylindrical battery can 22a having an open upper surface. It has a sealed configuration.
The battery can 22a is made of, for example, aluminum (Al). The battery lid 22b is similarly made of, for example, aluminum, and a safety valve mechanism 25 is provided together with a thermal resistance element 24 (Positive Temperature Coefficient; PTC element) inside. The battery lid 22b is caulked to the battery can 22a via a gasket 26. It is attached. That is, the battery 21 has a configuration in which the wound body 23 is hermetically sealed inside by the battery can 22a and the battery lid 22b.
The safety valve mechanism 25 is electrically connected to the battery lid 22b via the heat sensitive resistance element 24. When the internal pressure of the battery exceeds a certain level due to internal short circuit or external heating, for example, The built-in disk plate is reversed and the electrical connection between the battery lid 22b and the wound body 23 is cut. Here, the heat-sensitive resistance element 24 limits the current by increasing the resistance value when the temperature rises, and prevents abnormal heat generation due to a large current.

In the present embodiment, in the wound body 23, the first positive electrode active material layer 32 and the second positive electrode active material layer 33 are formed on both main surfaces of a belt-like (elongated thin plate-like) positive electrode current collector 31 made of, for example, aluminum. A positive electrode 29 and a negative electrode 30 in which a first negative electrode active material layer 35 and a second negative electrode active material layer 36 are formed on both main surfaces of a strip-shaped negative electrode current collector 34 made of copper, for example, are a pair of separators 27 containing an electrolyte. And 28 are arranged opposite to each other, and these are wound in the longitudinal direction of the electrodes 29 and 30.
A positive electrode lead 37 made of aluminum and a negative electrode lead (not shown) made of nickel, for example, are connected to the positive electrode 29 and the negative electrode 30 of the wound body 23, respectively. The positive electrode lead 37 is welded to the safety valve mechanism 25 and is connected to the battery. The lead 22b is electrically connected to the lid 22b, and the negative electrode lead is directly welded and electrically connected to the battery can 22a at a position separated from the wound body 23 via the insulating plate 38.

The first positive electrode active material layer 32 and the second positive electrode active material layer 33 include a positive electrode active material, and may include a conductive agent such as a carbonaceous material and a binder such as polyvinylidene fluoride as necessary. . As the positive electrode active material, for example, a lithium-containing metal composite oxide containing a sufficient amount of lithium (Li), for example, lithium represented by the general formula LixMO2 and a transition metal is preferable. This is because the lithium-containing metal composite oxide can generate a high voltage and has a high density, so that it is possible to further increase the capacity of the secondary battery. In this general formula, M is one or more transition metals, and for example, at least one of the group consisting of cobalt, nickel, and manganese is preferable. x varies depending on the charge / discharge state of the battery and is usually a value in the range of 0.05 ≦ x ≦ 1.10. Specific examples of such a lithium-containing metal composite oxide include LiCoO ₂ , LiMnO _{2, and} LiNiO ₂ . In addition, any 1 type may be used for a positive electrode active material, and 2 or more types may be mixed and used for it.

  On the other hand, as a material constituting the first negative electrode active material layer 35 and the second negative electrode active material layer 36 constituting the negative electrode 30, a carbonaceous material capable of absorbing and desorbing lithium, or a metal capable of forming an alloy with lithium, or The alloy compound containing the metal is mentioned.

  Examples of carbonaceous materials include non-graphitizable carbon, graphites such as artificial graphite and natural graphite, pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke, etc.), glassy carbons, organic high carbon At least one kind of carbonaceous material such as a molecular compound fired body (phenol resin, furan resin, etc., fired at an appropriate temperature and carbonized), activated carbon, fibrous carbon, or the like can be used. Moreover, you may include the material which does not contribute to charging / discharging.

Examples of the alloy compound include those containing at least one metal that can be alloyed with lithium. Specifically, when the metal element capable of forming an alloy with lithium is M, the chemical formula M _x M ′ _y Li _z (M ′ is one or more metal elements other than Li element and M element, x> 0, y As a compound having a composition of ≧ 0, z ≧ 0). Note that in this specification, elements such as B, Si, and As, which are semiconductor elements, are also included in the metal elements.
Examples of such metals and metal compounds include Mg, B, Al, Ga, In, Si, Ge, Sn, Pb, Sb, Bi, Cd, Ag, Zn, Hf, Zr, and Y, and those. Alloy compounds of Li, Al-Li, Li-Al-M (M: 2A, 3B, 4B, consisting of one or more of transition metal elements), AlSb, CuMgSb, and the like.

In particular, it is preferable to use a group 4B typical element as an element capable of forming an alloy with lithium, and more preferably Si or Sn. For example, M _x Si, M _x Sn (M excludes Si or Sn, respectively) And compounds represented by one or more metal elements). Specifically, SiB ₄ , SiB ₆ , Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , CaSi ₂ , CrSi ₂ , Cu ₅ Si, FeSi ₂ , MnSi ₂ NbSi ₂ , TaSi ₂ , VSi ₂ , WSi ₂ , ZnSi _{2 and the} like.
Further, in the battery according to the present embodiment, the first negative electrode active material layer 35 and the second negative electrode active material layer 36 can be formed of a 4B group compound other than carbon containing one or more nonmetallic elements. . Specifically, for example, SiC, Si ₃ N ₄ , Si ₂ N ₂ O, Ge ₂ N ₂ O, SiO _x (0 <x ≦ 2), SnO _x (0 <x ≦ 2), LiSiO, LiSnO, etc. Can be.

Examples of the method for producing the negative electrode active material layer using these materials include a mechanical alloying method, a method in which raw material compounds are mixed and heat-treated in an inert atmosphere, a melt spinning method, a gas atomizing method, a water atomizing method, and the like. Although it is mentioned, it is not limited to this. In addition, each material may or may not be pulverized, or two or more materials may be mixed.
The negative electrode active material layer may be doped with lithium in the battery after the battery is manufactured, or supplied from a positive electrode or a lithium source other than the positive electrode after the battery is manufactured or before the battery is manufactured. It may be electrochemically doped, synthesized as a lithium-containing material during material synthesis, and contained in the negative electrode during battery fabrication.

The separators 27 and 28 constituting the battery according to the present embodiment are for preventing a short circuit due to physical contact between the positive electrode 29 and the negative electrode 30 while allowing lithium ions to pass through. For example, a polyethylene film or a polypropylene film It is comprised by the microporous polyolefin film etc., such as. In order to ensure safety, the separators 27 and 28 preferably have a function of closing a hole by heat melting at a predetermined temperature (for example, 120 ° C.) or higher to increase resistance and interrupting current.
Also in this embodiment, the separators 27 and 28 are impregnated with an electrolytic solution (not shown) that becomes a liquid electrolyte. This electrolytic solution is the second embodiment of the electrolyte composition of the present invention.

Also in the battery according to this embodiment, as in the first embodiment, the electrolytic solution has a configuration in which the diisocyanate compound having the structure represented by the above [Chemical Formula 4] is dissolved in a non-aqueous solvent (organic solvent). is doing.
This diisocyanate compound has a structure having an aliphatic carbon chain (alkyl group) R as a main chain as shown in [Chemical Formula 4], and two carbons having different aliphatic carbon chains as described later. In particular, the number of carbons located between each isocyanate group is selected to be 4 or more and 12 or less, thereby improving the battery characteristics and long-term storage reliability. However, the decomposition of the solvent and the deformation of the battery can be particularly suppressed.

Moreover, it is preferable that the aliphatic carbon chain which comprises the principal chain is a linear form as for the diisocyanate compound which comprises the electrolyte solution of the battery which concerns on this embodiment. This is because in one molecule of the diisocyanate compound, the reactivity of the isocyanate group is relatively lowered when the surface area occupied by other than the isocyanate group is increased, and even when the structure of the diisocyanate compound has a side chain, It is preferable that the predetermined reaction of isocyanate groups including the formation of SEI is not inhibited. That is, as long as the structure of the diisocyanate compound is within a range not impairing the reactivity of the isocyanate group, it is preferable to appropriately select the number of carbons of the main chain of the aliphatic carbon chain and the constitution of the side chain. A structure having such a branch (branch having a side chain) may be used.
In addition, if the aliphatic carbon chain that is the main chain constituting the diisocyanate compound is directly or indirectly substituted with a hydroxyl group, a carboxyl group, an amino group, or the like, the diisocyanate compound cannot exist stably, and the molecule The functional group including the side chain is substituted only with a functional group other than a hydroxyl group, a carboxyl group, and an amino group, because it changes due to a reaction inside or between molecules and cannot contribute to a desired purpose such as SEI formation. It is preferable. Therefore, in order to suppress the loss of the isocyanate group due to the intermolecular reaction, the main component constituting the electrolytic solution (not only the diisocyanate compound but also 0.1 wt. % Of components) are also free of functional groups that react with isocyanate groups such as hydroxyl groups, carboxyl groups, and amino groups, and have only functional groups other than functional groups that react with isocyanate groups. A configuration is particularly preferable.

According to the electrolyte configuration including such a diisocyanate compound, it is possible to select a solvent that has been conventionally difficult to handle, such as a solvent that has a high boiling point but is easily decomposed, and the degree of freedom in selecting a non-aqueous solvent is also increased. improves. In addition, by selecting the length of the carbon chain of the aliphatic carbon chain, that is, the number of carbon atoms, it becomes possible to adjust the thickness of the SEI formed on the surface of the negative electrode, so that the resistance increases due to being too thick. It is possible to obtain a moderate thickness by avoiding the occurrence of deterioration of the battery characteristics and the occurrence of damage to the electrode due to being too thin.
In addition, if the number of carbon atoms in the aliphatic carbon chain is too large, the solubility as a polymer may be reduced and it may not be suitable for a non-aqueous solvent. However, as described later, if the carbon number is within 12 and is relatively small, It is considered that sufficient solubility can be obtained even when the aliphatic carbon chain has a side chain other than the main chain (not linear). This is thought to be due to the fact that the viscosity and the reactive groups per weight decrease as the number of carbon atoms increases. In addition, in order to ensure solubility even when the number of carbon atoms in the main chain is larger, it is preferable that the aliphatic carbon chain has a linear structure suitable for isocyanate group reactivity.
Such a problem of deformation or expansion of the battery exterior member is useful not only in the configuration of the exterior member made of the laminate film but also in the configuration of the exterior member made of the metal can in order to cope with the recent thinning of the container. it is conceivable that.

As will be described later, the amount of the diisocyanate compound added in the electrolyte (electrolytic solution in the present embodiment) is preferably 0.5% by weight or more and 5% by weight or less with respect to the electrolytic solution. These values are particularly effective in the state before the initial charge, and a part of the diisocyanate compound is consumed for the formation of SEI on the negative electrode during charging (mainly during initial charging). It is considered that after the initial charging in which the amount and concentration of the diisocyanate compound are changed, the values are somewhat different.
In addition, by including the diisocyanate compound described above at a concentration corresponding to this numerical range, necessary and sufficient SEI is formed through charge / discharge at the time of use. As a particularly preferable example, this concentration is set before the first charge. By doing so, it is considered that substantially all of the necessary and sufficient SEI is formed by the initial charge. Note that SEI may be further formed during the second and subsequent charging.

  Examples of the organic solvent include propylene carbonate, ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3- Examples include dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, propyl nitrile, anisole, acetic acid ester or propionic acid ester.

In addition, any 1 type of these may be used for a solvent, and 2 or more types may be mixed and used for it.
When mixing and using, the structure which added asymmetrical chain carbonates, such as methyl ethyl carbonate and methyl propyl carbonate, as a 2nd component especially using ethylene carbonate as a main solvent is suitable. Furthermore, a mixed solvent of methyl ethyl carbonate and dimethyl carbonate can be used. In this case, the volume ratio to be mixed is preferably in the range of ethylene carbonate: second component solvent = 7: 3 to 3: 7. Moreover, when using the above-mentioned mixed solvent as a 2nd component solvent, it is preferable to make a volume ratio into the range of methyl ethyl carbonate: dimethyl carbonate = 2: 8-9: 1.
Addition of the second component suppresses decomposition of the main solvent, improves conductivity and improves current characteristics, reduces freezing point of electrolyte and improves low temperature characteristics, reaction with lithium metal The effect that safety | security falls and safety is improved is acquired.

LiPF ₆ is suitable as the lithium-containing electrolyte to be added to the organic solvent together with the diisocyanate compound described above, but any of those used in this type of battery can be used. For example, as a lithium salt, LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (C ₄ F ₉ SO ₂ ) ( CF ₃ SO ₂ ), LiCl or LiBr. Among these, LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ or LiN (C ₄ F ₉ SO ₂ ) (CF ₃ SO ₂ ) is preferable, and LiPF ₆ or LiBF ₄ is particularly preferable. Any one of the lithium salts may be used, or a mixture of two or more may be used.

<Example>
Hereinafter, as specific examples of the present invention, characteristics measurement results in the battery having the configuration described in the first embodiment and the second embodiment will be described in detail.
In each of the following examples, the evaluation of the initial characteristics was performed with a charging condition of 0.1 C constant current to 4.2 V constant voltage, 12 h cut-off, and a discharge condition of 0.2 C constant current, 3 V cut-off. The measurement was performed by measuring the capacity when discharged under the discharge conditions as the initial capacity. In addition, the storage characteristics are evaluated by charging conditions as 1C constant current to 4.2V constant voltage, 2.5h cutoff, discharging conditions as 1C constant current, 3V cutoff, and storage conditions as 60 ° C for 30 days ( (Battery thickness after storage−battery thickness before storage) was measured as battery swelling. In addition, the evaluation of the cycle characteristics was performed with a charging condition of 1C constant current to 4.2V constant voltage and 2.5h cut-off, and a discharging condition of 1C constant current to 3V cut-off. The capacity retention rate was calculated as (the capacity at the 300th cycle / the capacity at the first cycle) as the capacity retention rate after 300 cycles.

<First embodiment>
In this example, as the battery having the battery configuration of the first embodiment described above, a positive electrode in which a positive electrode active material layer made of lithium cobaltate was formed on the surface of a 50 mm × 350 mm band current collector, and a 52 mm × 370 mm band current collector. Lithium ion 2 in which a wound body formed by winding a separator between a negative electrode having a negative electrode active material layer made of artificial graphite formed on the surface of the body is hermetically sealed in an exterior member made of an aluminum laminate film A secondary battery was prepared and used for measurement.
The electrolyte was a nonaqueous solvent of EC: PC = 6: 4 (volume ratio), LiPF _{6 at} a ratio of 0.7 mol / kg, and VdF (vinylidene fluoride) of 6.9% copolymerization of HFP (hexafluoropropylene). ) And a gel electrolyte dissolved therein.
With respect to the battery having this configuration, initial characteristics, storage characteristics, and cycle characteristics were evaluated by changing the carbon number of the aliphatic carbon chain (R) of the diisocyanate compound added to the electrolyte.
The results are shown in [Table 1].

From this result, it was confirmed that battery swelling was suppressed by the electrolyte configuration containing a diisocyanate compound having an aliphatic carbon chain as the main chain. In addition, it was confirmed that swelling can be suppressed particularly when the carbon number of the aliphatic carbon chain (R) is 4 or more and 12 or less.
Moreover, in order to compare with the thing which has a structure by an aromatic ring instead of an aliphatic carbon chain in a diisocyanate compound, in Comparative Example 1-2, measurement was performed by adding 1,3-diisocyanato-4-methylbenzene. Although it was conducted, it was confirmed that the swelling could not be sufficiently suppressed and the capacity retention rate was lowered as compared with the case of the configuration of the present invention.

<Second embodiment>
In this example, for a battery having the same configuration as in the first example, the amount of swelling and capacity retention rate were measured by changing the amount of diisocyanate compound having an aliphatic carbon chain as the main chain.
The results are shown in [Table 2] to [Table 5]. In addition, [Table 2] is the measurement result in the configuration in which the carbon number of the aliphatic carbon chain of the diisocyanate compound is 4, and [Table 3] is the measurement result in the configuration in which the carbon number of the aliphatic carbon chain of the diisocyanate compound is 6. [Table 4] is the measurement result in the configuration in which the carbon number of the aliphatic carbon chain of the diisocyanate compound is 8, and [Table 5] is the measurement result in the configuration in which the carbon number of the aliphatic carbon chain of the diisocyanate compound is 12. Are shown respectively.

From this result, it was confirmed that swelling was particularly suppressed when the addition amount was 0.5% by weight or more, regardless of the number of carbon atoms constituting the main chain of the diisocyanate compound added to the electrolyte.
Further, when the amount added was too large, the capacity retention rate tended to decrease. This is considered to be due to an increase in surface resistance due to excessive generation of SEI in the negative electrode. Therefore, in order to avoid deterioration of cycle characteristics, it is considered that the addition amount of the diisocyanate compound is particularly preferably 5% by weight or less.

<Third embodiment>
In this example, for a battery having the same configuration as in the first example, the composition of the solvent constituting the electrolyte with a different electrolyte composition was 0.7 mol / wt in a non-aqueous solvent of PC: DMC = 7: 3 (volume ratio). A system in which LiPF ₆ was dissolved at a rate of kg was examined.
The results are shown in [Table 6]. In addition, in the present Example, it measured by changing the addition amount of this diisocyanate compound about the structure which made the carbon number of the aliphatic carbon chain of a diisocyanate compound 6.

  From this result, even when the composition of the non-aqueous solvent constituting the electrolyte is different, the configuration of the present invention suppresses the swelling of the battery and the decrease in the capacity maintenance rate, as in the first and second embodiments described above. I was able to confirm that it was possible.

<Fourth embodiment>
In this example, as a battery having the battery configuration of the second embodiment described above, a positive electrode in which a positive electrode active material layer made of lithium cobaltate was formed on the surface of a 50 mm × 350 mm band current collector, and a 52 mm × 370 mm band current collector. Cylindrical lithium in which a wound body formed by sandwiching a separator between a negative electrode having a negative electrode active material layer made of artificial graphite formed on the body surface is hermetically sealed in an outer member made of an aluminum can An ion secondary battery was produced and used for measurement.
The electrolyte was configured as a non-gel electrolyte solution in which LiPF ₆ was dissolved at a rate of 1.2 mol / kg in a non-aqueous solvent of EC: PC: DMC = 1: 2: 7 (volume ratio).
The results are shown in [Table 7]. In addition, in the present Example, it measured by changing the addition amount of this diisocyanate compound about the structure which made the carbon number of the aliphatic carbon chain of a diisocyanate compound 4.

  From this result, not only in the case of the laminate film exterior member but also in the case of the metal can exterior member, according to the battery according to the present invention, the deformation of the battery can be suppressed by avoiding the swelling and the capacity retention rate decrease. Was confirmed.

As described in the above embodiments and examples, according to the battery and the electrolytic solution composition of the present invention, the electrolyte composition includes a diisocyanate compound having an alkyl chain as a solvent additive serving as an SEI forming agent. As a result, the battery characteristics and deformation suppression can be maintained or improved.
In particular, it is possible to sufficiently suppress the deterioration of battery characteristics accompanying long-term storage or long-term use and deformation inside and outside the battery. That is, according to the battery according to the present invention, the swelling of the battery can be suppressed while maintaining high cycle characteristics.
In addition, as described above, the configuration of the battery according to the present invention may exhibit excellent characteristics as compared with a configuration in which the electrolyte includes a diisocyanate compound having an aromatic carbon chain (phenyl group or aryl group) as a main chain. It was confirmed that the diisocyanate compound with an aliphatic carbon chain as the main chain has the aliphatic carbon chain as the main chain in terms of viscosity, number of reactive groups per weight, and reduced reactivity due to steric hindrance. This is considered to be because the configuration of the present invention is more advantageous.

  Note that the numerical conditions such as the materials used, the amount thereof, the processing time, and the dimensions mentioned in the description of the above embodiments are only preferable examples, and the dimensional shape and the arrangement relationship in each drawing used for the description are also schematic. Is. That is, the present invention is not limited to this embodiment.

For example, as the material for the positive electrode current collector, nickel, stainless steel, or the like can be used in addition to aluminum.
Further, for example, the shape of the positive electrode and the negative electrode is not limited to the winding type, and for example, it can be a foldable configuration, and the shape of the exterior member is not limited to the above-described one. And modifications can be made.

2A and 2B are a schematic perspective view and a schematic cross-sectional view, respectively, partially cut away showing a configuration of an example of a battery according to the present invention. It is a schematic perspective view partly cut open which shows the structure of the other example of the battery which concerns on this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Battery, 2 ... Exterior member, 3 ... Winding body, 4 ... Exterior member, 5, 6 ... Lead, 7, 8 ... Separator, 9 ... Positive electrode, DESCRIPTION OF SYMBOLS 10 ... Negative electrode, 11 ... Positive electrode collector, 12 ... 1st positive electrode active material layer, 13 ... 2nd positive electrode active material layer, 14 ... Negative electrode collector, 15 ... 1st negative electrode active material layer, 16 ... 2nd negative electrode active material layer, 21 ... battery, 22 ... exterior member, 22a ... battery can, 22b ... battery lid, 23 ... winding Rotating body, 24 ... Heat-resistive resistance element, 25 ... Safety valve mechanism, 26 ... Gasket, 27, 28 ... Separator, 29 ... Positive electrode, 30 ... Negative electrode, 31 ... Positive electrode Current collector, 32 ... first positive electrode active material layer, 33 ... second positive electrode active material layer, 34 ... negative electrode current collector, 35 ... first negative electrode active material layer, 36 ... Second negative electrode active Quality layer

Claims (9)

A battery comprising a positive electrode, a negative electrode, and an electrolyte,
The battery has an electrolyte solution containing a nonaqueous solvent, an electrolyte salt containing lithium (Li), and a diisocyanate compound having a structure represented by the following [Chemical Formula 1].

(In the formula, R represents an aliphatic carbon chain which may have a substituent.) The diisocyanate compound has a structure in which an isocyanate group is bonded to two different carbons of the aliphatic carbon chain,
The number of carbons located between each isocyanate group is 4 or more and 12 or less. The battery according to claim 1. 2. The battery according to claim 1, wherein the amount of the diisocyanate compound added is 0.5% by weight or more and 5% by weight or less with respect to the electrolytic solution constituting the electrolyte. The battery according to claim 1, wherein the aliphatic carbon chain constituting the diisocyanate compound is linear. 2. The battery according to claim 1, wherein a part of the aliphatic carbon chain constituting the diisocyanate compound is substituted only with a functional group other than a hydroxyl group, a carboxyl group, and an amino group. The battery according to claim 1, wherein the functional group contained in the main component constituting the electrolyte is only a functional group other than a hydroxyl group, a carboxyl group, and an amino group. The battery according to claim 1, wherein the negative electrode includes a carbon material that absorbs and desorbs the lithium constituting the electrolyte. The battery according to claim 1, wherein the positive electrode, the negative electrode, and the electrolyte are arranged inside an exterior member made of a laminate film. An electrolyte solution composition comprising: a non-aqueous solvent; an electrolyte salt containing lithium (Li); and a diisocyanate compound having a structure represented by the following [Chemical Formula 2].

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