TW201533948A - Lithium ion battery - Google Patents

Abstract

The purpose of the present invention is to provide a lithium ion battery that can suppress internal short failure without impacting battery performance, and that can improve reliability. The present invention provides a lithium ion battery that is characterized by including the following: a positive electrode and a negative electrode; a separator for insulating the positive electrode and the negative electrode from each other; and an electrolytic solution in which a charging and discharging reaction is carried out between the positive electrode and the negative electrode; and 0.0001-0.01wt% of an internal short inhibitor for suppressing internal short failure in the electrolytic solution.

Description

Lithium battery and method of manufacturing same

This invention relates to a lithium ion battery.

Japanese Patent Laid-Open No. 2007-59201 (Patent Document 1) and Japanese Patent Laid-Open No. 2001-273927 (Patent Document 2). Patent Document 1 discloses an example of a nonaqueous electrolyte secondary battery which is mixed with a metal impurity by using an electrolytic solution to which a guanamine compound having a specific structure is added. Battery performance will not be reduced.

Further, Patent Document 2 discloses an example of a lithium secondary battery which is added as an organic system by at least one of a positive electrode plate, a negative electrode plate, a separator, and a non-aqueous electrolyte. / or an inorganic Cu corrosion inhibitor, or an inhibitor of an organic and/or inorganic Cu capture agent, suppressing corrosion of a copper foil used as a negative electrode current collector, suppressing inhibition of a battery reaction, and self-discharge characteristics and circulation Excellent characteristics.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2007-59201

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2001-273927

The lithium ion battery includes, for example, an electrode wound body in which a positive electrode plate coated with a positive electrode active material, a negative electrode plate coated with a negative electrode active material, and a positive electrode plate and a negative electrode plate are wound. The partition of the contact. Further, the electrode wound body is inserted into a packaging can, and an electrolytic solution is injected into the packaging can.

Such a lithium ion battery has an internal short circuit. In the production, if metal ions such as nickel, manganese, cobalt, iron, or chromium, which are mixed with metal impurities or battery materials themselves, are eluted into the electrolyte, metal ions are deposited on the negative electrode. When the metal grown from the negative electrode reaches the positive electrode through the pore of the separator, the positive electrode and the negative electrode are internally short-circuited via the precipitated metal. If the positive electrode and the negative electrode are internally short-circuited, the function as a lithium ion battery disappears.

Patent Document 1 describes a method of using an electrolytic solution in which a guanamine compound having a specific structure is added in a range of 0.01% by weight to 2% by weight, as a method of initial charge and discharge in which metal impurities are mixed. However, in the method of Patent Document 1, the guanamine compound having a specific structure causes a side reaction due to a redox reaction of the positive electrode or the negative electrode, and the battery performance is deteriorated.

Further, as a method of suppressing corrosion of a copper foil used as a negative electrode current collector, Patent Document 2 discloses that 0.01% by weight to 10% by weight of an organic-based and/or inorganic-based Cu corrosion inhibitor or an organic system is added. And/or a method of inhibiting an inorganic Cu capture agent. However, in the case where the inorganic corrosion inhibitor is used, the method of adding the patent document 2 has a small solubility in the nonaqueous electrolytic solution, so that the undissolved fine powder is suspended and dispersed in the nonaqueous electrolytic solution to block the positive electrode-separator. And the separator hole at the interface of the negative electrode-partition, which hinders the movement of Li ions. Therefore, there is a possibility that the internal resistance is increased.

Accordingly, an object of the present invention is to provide a lithium ion battery which can suppress internal short-circuit defects and improve reliability without affecting battery performance.

In order to solve the above problems, the present invention provides a lithium ion battery comprising: a positive electrode and a negative electrode; a separator that insulates the positive electrode from the negative electrode; and an electrolysis in which a charge-discharge reaction between the positive electrode and the negative electrode is performed a liquid; and an internal short-circuit inhibitor containing an inorganic salt which inhibits internal short-circuit defects in the above electrolyte solution 0.0001 It is not more than 0.01% by weight, preferably not more than 0.0001% by weight and not more than 0.001% by weight.

According to the present invention, it is possible to provide a lithium ion battery which can suppress internal short-circuit defects and improve reliability without affecting battery performance.

CAP‧‧‧ battery cover

CR‧‧‧ shaft core

CS‧‧‧Packaging cans

CU‧‧‧Charger

EL‧‧‧ electrolyte

LIB‧‧‧Lithium-ion battery

NAS‧‧‧Negative active material

NEL‧‧‧negative

NEP‧‧‧ negative plate

NR‧‧‧Negative ring

NT‧‧‧Negative lead plate

NTAB‧‧‧Negative current collector board

PAS‧‧‧positive active material

PEL‧‧‧ positive

PEP‧‧‧positive plate

PR‧‧‧ positive ring

PT‧‧‧positive lead plate

PTAB‧‧‧ positive current collector board

SP‧‧‧Parts

SP1‧‧‧Parts

SP2‧‧‧Parts

WRF‧‧‧electrode winding body

Fig. 1 is a view showing a schematic configuration of a lithium ion battery.

Fig. 2 is a cross-sectional view showing the internal structure of a cylindrical lithium ion battery.

Fig. 3 is a view showing constituent elements of a stage before the electrode winding body is formed.

4 is a schematic view showing a state in which a positive electrode, a separator, a negative electrode, and a separator are wound around a shaft core to form an electrode wound body.

Fig. 5 is a graph showing the current flowing in the lithium ion battery at the time of constant voltage charging in the case where no internal short circuit occurs and the case where an internal short circuit occurs.

6 is a diagram showing the current value flowing in a lithium ion battery when the internal short-circuit inhibitor is not added to the electrolytic solution and when 0.00001% by weight to 0.0099% by weight of sodium nitrite as an internal short-circuit inhibitor is added to the electrolytic solution. The graph.

7 is a graph showing the internal resistance of a lithium ion battery in the case where no internal short-circuit inhibitor is added to the electrolytic solution and when 0.001% by weight to 0.05% by weight of sodium nitrite as an internal short-circuit inhibitor is added to the electrolytic solution. Figure.

Fig. 8 is a graph showing the battery capacitance when the internal short-circuit inhibitor is not added to the electrolytic solution and when the sodium nitrite as the internal short-circuit inhibitor is added to the electrolytic solution to less than 0.01% by weight.

In the following embodiments, for convenience, it is divided into a plurality of parts or embodiments as necessary, but unless otherwise specified, the ones are not related to each other, and one is the other. Some or all of the changes, details, supplements Explain the relationship.

In addition, in the following embodiments, when the number of elements and the like (including the number, the numerical value, the quantity, the range, and the like) are specifically limited to a specific number, the case is clearly defined, and the principle is clearly defined. It is not limited to the specific number, and may be more than a certain amount or less.

Further, in the following embodiments, the constituent elements (including the element steps, and the like) are of course not necessary unless otherwise specified and the case where it is considered to be essential in principle.

Similarly, in the following embodiments, the shape, the positional relationship, and the like of the constituent elements and the like are substantially similar to the shape or the like, except for the case where it is specifically indicated and the case where it is considered that the principle is not so obvious. Similar. This case is also the same for the above numerical values and ranges.

In the drawings, the same components are denoted by the same reference numerals, and the description thereof will not be repeated. Furthermore, in order to make the drawing easy to understand, there is a case where a hatching is attached even in a plan view.

[Examples] (embodiment)

<Mode composition of lithium ion battery>

Hereinafter, the mode configuration of the lithium ion battery will be described with reference to the drawings. Fig. 1 is a view showing a schematic configuration of a lithium ion battery. In FIG. 1, the lithium ion battery has a packaging can CS mainly made of iron (Fe) or stainless steel, and the inside of the packaging can CS is filled with an electrolytic solution EL. A separator SP is disposed between the positive electrode plate PEP and the negative electrode plate NEP which are disposed opposite to each other in the packaging tank CS filled with the electrolytic solution EL.

Further, a positive electrode active material is applied to the positive electrode plate PEP, and a negative electrode active material is applied to the negative electrode plate NEP. For example, the positive active material is composed of lithium containing lithium ions that can be inserted and removed. Formation of metal oxides. As a positive electrode active material, a lithium-containing transition metal oxide is mentioned. For example, lithium cobaltate, lithium nickelate, lithium manganate, etc. are mentioned as a representative positive electrode active material, but it is not limited to these. Specifically, the positive electrode active material may be a lithium-containing transition metal oxide in which a lithium material can be inserted or removed, and a sufficient amount of lithium is inserted in advance, and the transition metal may be manganese (Mn). A material such as nickel (Ni), cobalt (Co), or iron (Fe), or a material containing two or more transition metals as a main component. Further, the crystal structure such as the spinel crystal structure or the layered crystal structure is not particularly limited as long as it is the above-mentioned space and space. Further, a transition metal or a part of lithium in the crystal may be substituted with a material such as Fe, Co, Ni, Cr, Al, Mg or the like, or may be doped with Fe, Co, Ni, Cr, Al in the crystal. A material such as Mg or the like is used as a positive electrode active material. Fig. 1 schematically shows the case where the positive electrode plate PEP is coated with the lithium-containing transition metal oxide. That is, a schematic crystal structure in which oxygen, a metal atom, and lithium are disposed as a lithium-containing transition metal oxide coated on the positive electrode plate PEP is shown in FIG. The positive electrode plate PEP and the positive electrode active material constitute a positive electrode.

On the other hand, for example, the negative electrode active material is formed of a carbon material into which lithium ions can be inserted and removed. As the negative electrode active material, a crystalline carbon material or an amorphous carbon material can be used. However, the negative electrode active material is not limited to these materials, and for example, natural graphite, various artificial graphite agents, carbon materials such as coke, or the like may be used. Further, as the particle shape, various particle shapes such as a scaly shape, a spherical shape, a fibrous shape, and a block shape may be used.

Fig. 1 schematically shows a case where the carbon material is applied to a negative electrode plate NEP. That is, a pattern crystal structure in which carbon is disposed is shown in FIG. 1 as a carbon material applied to the negative electrode plate NEP. The negative electrode plate NEP and the negative electrode active material constitute a negative electrode.

The separator SP has a function as a separator that insulates between the positive electrode and the negative electrode to prevent electrical contact and allows lithium ions to pass therethrough. In recent years, as the separator SP, a high-strength and thin microporous film has been used. The microporous membrane also has a function of preventing an abnormal current caused by a short circuit of the battery, an increase in the internal pressure or temperature of the impatience, and a fire. Ie, the current separation In addition to the function of preventing the electrical contact between the positive electrode and the negative electrode and allowing lithium ions to pass, the device SP also functions as a thermal fuse for preventing short circuit and excessive charging. The safety of the lithium ion battery can be maintained by the breaking function of the microporous membrane. For example, when a lithium ion battery causes an external short circuit for some reason, a large current flows instantaneously, and there is a risk that the temperature rises abnormally due to Joule heat. At this time, when the microporous membrane is used as the separator SP, the microporous membrane is closed in the vicinity of the melting point of the membrane material (microporous), so that lithium ions between the positive electrode and the negative electrode can be prevented from permeating. In other words, by using the microporous membrane as the separator SP, the current can be blocked when the external short circuit occurs, and the temperature rise inside the lithium ion battery is stopped. As the separator SP composed of the microporous membrane, for example, polyethylene (PE), polypropylene (PP), or a combination of these materials is used as a prior art.

The electrolyte EL used to carry out the charge-discharge reaction between the positive electrode and the negative electrode is a non-aqueous electrolyte. A lithium ion battery is a battery that is charged and discharged by insertion or removal of lithium ions in an active material, and lithium ions move in the electrolyte EL. A strong lithium-based reducing agent that reacts violently with water to produce hydrogen. Therefore, a lithium ion battery in which lithium ions move in the electrolyte EL cannot use an aqueous solution for the electrolyte EL as in the prior battery. Therefore, in the lithium ion battery, a nonaqueous electrolyte solution is used as the electrolyte EL. Specifically, as the electrolyte of the nonaqueous electrolyte, LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiB(C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li or the like can be used or the like. a mixture. Further, as the organic solvent, ethylene carbonate, dimethyl carbonate, propylene carbonate, diethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, or the like can be used. Γ-butyrolactone, tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, cyclobutyl hydrazine, methylcyclobutyl hydrazine, acetonitrile, A propiononitrile or the like, or a mixture thereof.

<charge and discharge mechanism>

The lithium ion battery is configured as described above, and the charging and discharging mechanism will be described below. First, the charging mechanism will be described. As shown in FIG. 1, when charging a lithium ion battery, a charger CU is connected between the positive electrode and the negative electrode. In this case, lithium ion battery The lithium ions inserted into the positive electrode active material are removed and released into the electrolyte EL. At this time, lithium ions are removed from the positive electrode active material, and electrons flow from the positive electrode to the charger. Further, the lithium ions released into the electrolytic solution EL move in the electrolytic solution EL, and reach the negative electrode through the separator SP composed of the microporous film. The lithium ion reaching the negative electrode is inserted into the negative electrode active material constituting the negative electrode. At this time, electrons flow into the negative electrode due to the insertion of lithium ions into the negative electrode active material. In this manner, electrons move from the positive electrode to the negative electrode via the charger CU, thereby completing charging.

Next, the discharge mechanism will be described. As shown in Fig. 1, an external load is connected between the positive electrode and the negative electrode. Then, the lithium ions inserted into the negative electrode active material are removed and released into the electrolytic solution EL. At this time, electrons are released from the negative electrode. Further, lithium ions released into the electrolytic solution EL move in the electrolytic solution EL, and reach the positive electrode through the separator SP composed of the microporous film. The lithium ion reaching the positive electrode is inserted into the positive electrode active material constituting the positive electrode. At this time, electrons flow into the positive electrode by the insertion of lithium ions into the positive electrode active material. In this manner, the discharge is performed by the electron moving from the negative electrode to the positive electrode. In other words, the load can be driven by flowing a current from the positive electrode to the negative electrode. As described above, the lithium ion battery can be charged and discharged by inserting and removing lithium ions between the positive electrode active material and the negative electrode active material.

<Composition of lithium ion battery>

Next, a configuration example of an actual lithium ion battery LIB will be described. Fig. 2 is a cross-sectional view showing the internal structure of a cylindrical lithium ion battery LIB. As shown in FIG. 2, an electrode wound body WRF including a positive electrode PEL, separators SP1, SP2, and a negative electrode NEL is formed inside a cylindrical packaging can CS having a bottom. Specifically, the electrode wound body WRF is laminated so as to sandwich the separator SP1 (SP2) between the positive electrode PEL and the negative electrode NEL, and is wound around the axial core CR located at the center of the packaging can CS. Further, the negative electrode NEL is electrically connected to the negative electrode lead plate NT provided at the bottom of the packaging can CS, and the positive electrode PEL is electrically connected to the positive electrode lead plate PT provided on the upper portion of the packaging can CS. An electrolyte solution is injected into the inside of the electrode wound body formed inside the packaging can CS. Moreover, the packaging can CS is covered by a battery cover CAP It was closed.

The positive electrode PEL is formed by applying a coating liquid containing a positive electrode active material PAS and a binder to a positive electrode plate (positive electrode current collector) PEP, drying it, and then applying pressure. A plurality of rectangular positive electrode collector plates PTAB are formed at an upper end portion of the positive electrode PEL, and the plurality of positive electrode current collector plates PTAB are connected to the positive electrode collector ring PR. Moreover, the positive electrode collector ring PR is electrically connected to the positive electrode lead plate PT. Therefore, the positive electrode PEL is electrically connected to the positive electrode lead plate PT via the positive electrode current collector plate PTAB and the positive electrode current collecting ring PR. A plurality of positive electrode current collector plates PTAB are provided for low resistance of the positive electrode PEL and rapid extraction of current.

As the positive electrode active material PAS constituting the positive electrode PEL, for example, the above-mentioned materials typified by lithium cobaltate, lithium nickelate, lithium manganate or the like can be used. Further, as the binder, for example, polyvinyl fluoride, polyvinylidene fluoride, polytetrafluoroethylene or the like can be used. Further, as the positive electrode plate, for example, a metal foil or a metal mesh containing a conductive metal such as aluminum is used.

The negative electrode NEL is formed by applying a coating liquid containing a negative electrode active material NAS and a binder to a negative electrode plate (negative electrode current collector) NEP, drying it, and then applying pressure. A plurality of rectangular negative electrode collector plates NTAB are formed at the lower end of the negative electrode NEL, and the plurality of negative electrode current collector plates NTAB are connected to the negative electrode current collecting ring NR. Further, the negative electrode current collecting ring NR is electrically connected to the negative electrode lead plate NT. Therefore, the negative electrode NEL is electrically connected to the negative electrode lead plate NT via the negative electrode current collecting plate NTAB and the negative electrode current collecting ring NR.

As the negative electrode active material NAS constituting the negative electrode NEL, for example, the above-mentioned materials typified by a carbon material or the like can be used. Further, as the binder, for example, polyvinylidene fluoride, polytetrafluoroethylene or the like can be used. Further, as the negative electrode plate, for example, a metal foil or a metal mesh containing a conductive metal such as copper is used.

<Composition of electrode winding body>

Next, the detailed configuration of the electrode wound body will be described. Fig. 3 is a view showing constituent elements of a stage before the electrode winding body is formed. In FIG. 3, the constituent elements constituting the electrode wound body are a positive electrode PEL, a separator SP1, a negative electrode NEL, and a separator SP2. At this point, the positive The PEL has a structure in which the positive electrode active material PAS is coated on both surfaces of the positive electrode plate PEP, and the negative electrode NEL has a structure in which the negative electrode active material NAS is coated on both surfaces of the negative electrode plate NEP. Further, a plurality of rectangular positive electrode current collector plates PTAB are formed on the upper side of the positive electrode PEL. Similarly, a plurality of rectangular negative electrode current collectors NTAB are formed on the side below the negative electrode NEL.

Specifically, the configuration of the electrode wound body WRF of the present embodiment will be described. 4 is a schematic view showing a state in which the positive electrode PEL, the separator SP1, the negative electrode NEL, and the separator SP2 are wound around the axial core CR to form the electrode wound body WRF. As shown in FIG. 4, a separator SP1 is interposed between the positive electrode PEL and the negative electrode NEL, and the positive electrode PEL, the separator SP1, the negative electrode NEL, and the separator are wound so that the separator SP1 and the separator SP2 sandwich the negative electrode NEL. SP2. At this time, the positive electrode current collector plate PTAB formed on the positive electrode PEL is disposed on the upper side of the electrode wound body WRF, and the negative electrode current collector plate (not shown) formed on the negative electrode NEL is disposed under the electrode wound body WRF. side. The electrode wound body WRF is configured as described above.

<Features of Embodiment>

In the lithium ion battery configured as described above, the present embodiment is characterized in that an internal short-circuit suppressor containing an inorganic salt for preventing internal short-circuiting is added to the electrolytic solution EL. As a result, according to the lithium ion battery of the present embodiment, even if metal impurities are mixed, an internal short circuit can be prevented. Further, even when metal ions are eluted from the battery material into the electrolytic solution, internal short circuits can be prevented. Therefore, according to the present embodiment, the reliability of the lithium ion battery can be further improved in terms of the possibility of no internal short circuit.

Further, in the internal short-circuit inhibitor of the present embodiment, for example, an electrolyte EL (non-aqueous electrolyte solution) such as nitrite, nitrate, phosphate or chromate is used, and the solubility is less than 0.01% by weight (100 ppm), and The metal ions eluted from the metal impurities or the battery material are coordinately bonded to form an inorganic salt of the complex. The addition concentration of the internal short circuit inhibitor containing the inorganic salt to prevent internal short circuit is 0.0001% by weight (1 ppm) or more and less than 0.01% by weight (100 ppm), preferably 0.0001% by weight (1 ppm) or more and 0.001% by weight (10 ppm). the following.

Here, for example, an internal short-circuit inhibitor containing an inorganic salt that prevents internal short-circuiting The reason why the lower limit of the added concentration is 0.0001% by weight or more is that when the concentration of the internal short-circuit inhibitor is less than 0.0001% by weight, the function of preventing internal short-circuit cannot be sufficiently exhibited. That is, the reason for preventing the internal short circuit is that the metal ions eluted from the metal impurities or the battery material are trapped by the internal short-circuit inhibitor added to the electrolytic solution EL.

Therefore, qualitatively, it is considered that if the concentration of the internal short-circuit inhibitor is extremely low, the effect of the internal short-circuit inhibitor becomes weak, and the metal ions eluted from the metal impurities or the battery material cannot be captured. Therefore, in order to sufficiently prevent the internal short circuit, the concentration of the internal short-circuit inhibitor containing the inorganic salt to prevent internal short-circuiting has a lower limit. For example, according to the experiment of the present inventors, it is confirmed that the internal short-circuit prevention is included. When the concentration of the internal short-circuit inhibitor of the inorganic salt is 0.0001% by weight or more, an internal short circuit can be prevented.

On the other hand, the reason why the upper limit of the addition concentration of the internal short-circuit inhibitor containing the inorganic salt which prevents the internal short circuit is less than 0.01% by weight is that if the internal short-circuit inhibitor is added at a concentration of 0.01% by weight or more, The internal resistance of the lithium ion battery increases. Qualitatively, since the internal short-circuit inhibitor containing an inorganic salt which prevents an internal short circuit has a small solubility in the electrolyte EL, undissolved fine particles (fine powder) are suspended and dispersed in the electrolytic solution EL, and the clogging is set in the separation. The gap between the fine holes of the SP1 or the separator SP2. When the undissolved fine particles (fine powder) block a certain number of fine pores, the movement of lithium ions between the positive electrode and the negative electrode is inhibited, whereby the internal resistance of the lithium ion battery is increased, resulting in a decrease in performance. For example, according to the experiment of the present inventors, it was confirmed that the internal resistance increased when the concentration of the internal short-circuit inhibitor containing the inorganic salt to prevent internal short-circuiting was 0.01% by weight or more. Therefore, the addition concentration of the internal short-circuit inhibitor containing an inorganic salt added to the electrolytic solution EL to prevent internal short-circuiting is set to be less than 0.01% by weight.

Further, the upper limit of the concentration of the internal short-circuit inhibitor containing the inorganic salt which prevents the internal short circuit is preferably 0.001% by weight or less (and further preferably an internal short-circuit inhibitor). The reason why the solubility of the electrolytic solution is below (the electrolyte) is that the concentration is a concentration at which solid particles constituting the internal short-circuiting inhibitor are not suspended and dispersed in the electrolytic solution EL. In this case, there is no clogging of the micropores provided in the separator SP1 or the separator SP2.

Therefore, in the present embodiment, the concentration of the internal short-circuit inhibitor containing the inorganic salt added to the electrolytic solution EL to prevent internal short-circuiting is 0.0001% by weight or more and less than 0.01% by weight, preferably 0.0001% by weight or more. And 0.001% by weight or less.

Further, in the present embodiment, the type of metal impurities which can prevent internal short-circuiting by preventing the internal short-circuiting inhibitor including the inorganic salt from being short-circuited is a transition metal such as iron or nickel, and an alloy containing a transition metal as a main component such as stainless steel. Further, even when transition metal ions such as nickel, manganese, cobalt, iron, or chromium, which are components contained in the battery material, are eluted into the electrolytic solution EL, internal short-circuiting can be prevented.

<Experimental results of the embodiment>

An example of the experimental results of the embodiment will be described.

In this experiment, an active material (lithium transition metal composite oxide: LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ), a conductive auxiliary agent (acetylene black), and a binder (polyvinylidene fluoride) are used. a positive electrode, a negative electrode comprising a carbon powder, a conductive additive (graphite), a binder (polyvinylidene fluoride), a separator containing a porous polypropylene having a thickness of 20 μm, and an organic solvent (ethyl carbonate, dimethyl carbonate) A lithium ion battery is produced by using an electrolyte of an ester, ethyl methyl carbonate, and an electrolytic salt (lithium hexafluorophosphate).

(1) Add concentration lower limit

First, a method of judging the occurrence of an internal short circuit will be described. Specifically, after charging a lithium ion battery to a specific voltage at a constant current (1 C), constant voltage charging is performed, and a current flowing in the lithium ion battery during constant voltage charging is measured. (1 C is the current value of discharging the battery capacitor in 1 hour, expressed as the reciprocal of the discharge time. For example, the case of discharge for 1 hour is 1 C, and the case of discharge for 0.5 hour is 2 C.) In the case of a short circuit, the current at the time of constant voltage charging is attenuated, eventually becoming a current of only a few μA/cm ² of flow. On the other hand, in the case where an internal short circuit occurs, a short-circuit current flows because a conduction path is formed between the positive electrode and the negative electrode. Therefore, if an internal short circuit occurs in comparison with the current when no internal short circuit occurs, the current at the time of constant voltage charging increases. That is, the generation of the internal short circuit can be judged based on the value of the current flowing in the lithium ion battery at the time of constant voltage charging.

Further, a method of determining the internal short circuit generation will be specifically described using FIG. 5. Fig. 5 is a graph showing the current at the time of constant voltage charging in the case where an internal short circuit is not generated and in the case where an internal short circuit occurs. In Fig. 5, the graph 1 shows the experimental results when no internal short circuit occurs. It can be seen from the graph 1 that the current is attenuated and focused on a certain fixed value. For example, the average current of the charging time of 501 minutes to 600 minutes is 7.4 μA/cm ² . On the other hand, in Fig. 5, a graph 2 shows an experimental result when an iron particle having a diameter of 100 μm is disposed as a metal impurity between the positive electrode and the separator to cause an internal short circuit. In the graph 2, for example, the average value of the current of the charging time of 501 minutes to 600 minutes is 311.2 μA/cm ² . It is a short circuit current and shows an internal short circuit.

Thus, the internal short circuit can be determined according to the value of the current flowing in the lithium ion battery during constant voltage charging. In this experiment, the average value of the current at the charging time of 501 minutes to 600 minutes is 7.4 μA/cm ² or more. In the case, it is determined that an internal short circuit has occurred.

Next, the experimental results in the case where the internal short-circuit inhibitor is not added to the electrolytic solution and the case where 0.00001% by weight to 0.0099% by weight of sodium nitrite as the internal short-circuit inhibitor is added will be described.

In this experiment, an active material (lithium transition metal composite oxide: LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ), a conductive auxiliary agent (acetylene black), and a binder (polyvinylidene fluoride) are used. a positive electrode, a negative electrode comprising a carbon powder, a conductive additive (graphite), a binder (polyvinylidene fluoride), a separator containing a porous polypropylene having a thickness of 20 μm, and an organic solvent (ethyl carbonate, dimethyl carbonate) A lithium ion battery is produced by using an electrolyte of an ester, ethyl methyl carbonate, and an electrolytic salt (lithium hexafluorophosphate). At this time, iron particles having a diameter of 100 μm were disposed as a metal impurity between the positive electrode and the separator. The case where the internal short-circuit inhibitor is not added to the electrolytic solution and the case where the sodium nitrite as the internal short-circuit inhibitor is added is 0.00001% by weight to 0.0099% by weight.

After the fabricated lithium ion battery is charged to a specific voltage at a constant current (1 C), constant voltage charging is performed, and an internal short circuit is generated based on the value of the current flowing in the lithium ion battery during the charging of the constant voltage.

Fig. 6 is a graph showing the results of an experiment when no internal short-circuit inhibitor is added to the electrolytic solution and 0.00001% by weight to 0.0099% by weight of sodium nitrite as an internal short-circuit suppressing agent.

In Fig. 6, the graph 1 is an experimental result in the case where an internal short-circuit inhibitor is not added to the electrolytic solution, and the current value is 311.2 μA/cm ² . It represents a flow short-circuit current, that is, an internal short circuit. From this, it is understood that when an inorganic salt for preventing internal short-circuiting is not added to the electrolytic solution, an internal short circuit occurs due to iron particles disposed between the positive electrode and the separator.

In Fig. 6, the graph 2 is an experimental result when 0.00001% by weight of sodium nitrite is added to the electrolytic solution, and the current value is 22.3 μA/cm ² . It represents a flow short-circuit current, that is, an internal short circuit. From this, it was found that when 0.00001% by weight of sodium nitrite was added to the electrolytic solution, the occurrence of an internal short circuit could not be prevented.

In FIG. 6, the graph 3 is the case where 0.0001% by weight of sodium nitrite is added to the electrolytic solution, the graph 4 is added with 0.001% by weight, and the graph 5 is added with 0.0099% by weight. The current values were all less than 7.4 μA/cm ² . It indicates a situation in which a short-circuit current is not flowing, that is, an internal short-circuit is prevented. Further, after the experiment, the lithium ion battery used for the experiment was disintegrated, and it was confirmed that all of the iron particles having a diameter of 100 μm disposed as a metal impurity between the positive electrode and the separator were dissolved. Since all of the metal impurities causing the internal short circuit are dissolved, it is shown that an internal short circuit does not occur even after a lapse of time.

According to the above experimental results, it is known that it is added as an internal short circuit in the electrolyte. When the sodium nitrite of the preparation is 0.0001% by weight or more and less than 0.01% by weight, the effect of preventing internal short circuit can be obtained.

Therefore, the lower limit of the concentration of the internal short-circuit inhibitor containing the inorganic salt which prevents the internal short circuit is made 0.0001% by weight or more.

In addition, in this experiment, an example in which sodium nitrite is used as an internal short-circuit inhibitor has been described, but as an internal short-circuit inhibitor, even in the case of containing nitrite, nitrate, phosphate, chromate In the case of any of the above, it is also possible to prevent an internal short circuit.

(2) Add concentration upper limit

The internal resistance of the lithium ion battery in the case where the internal short circuit inhibitor is not added to the electrolytic solution and the case where the sodium nitrite as the internal short circuit inhibitor is added is 0.001% by weight to 0.05% by weight, and the evaluation result is performed. Description. In the present experiment, the case where the internal short-circuit inhibitor was not added to the electrolytic solution and the case where sodium nitrite was added in an amount of 0.001% by weight to 0.05% by weight were prepared.

After the fabricated lithium ion battery was fully charged to SOC 100%, constant current discharge was performed at 0.2 C to 5.0 C, and the battery voltage after 10 seconds from the start of discharge of each discharge current was measured. At this time, the discharge current has a linear relationship with the battery voltage 10 seconds after the start of discharge, and the slope at this time is the internal resistance (DCR).

Fig. 7 is a graph showing the internal resistance of a lithium ion battery in the case where no internal short-circuit inhibitor is added to the electrolytic solution and when nitrite is added in an amount of 0.001% by weight to 0.05% by weight. Further, in FIG. 7, the average value of the internal resistance when the internal short-circuit inhibitor was not added to the electrolytic solution was set to 1, and the internal resistance was represented by the relative value.

In Fig. 7, the graph 1 is the experimental result when no internal short-circuit inhibitor is added to the electrolyte, and the internal resistance is in the range of 0.9 to 1.1.

In Fig. 7, the graph 2 is an experimental result when 0.001% by weight of sodium nitrite is added to the electrolytic solution, and the internal resistance is 1. Also, the graph 3 is added with 0.0099 weight. In the case of %, the internal resistance was 1.08. From this, it is understood that the internal resistance when the sodium nitrite is added to the electrolyte is less than 0.01% by weight is equal to the internal resistance when the internal short-circuit inhibitor is not added to the electrolyte.

In Fig. 7, the graph 4 is an experimental result when 0.05% by weight of sodium nitrite was added to the electrolytic solution, and the internal resistance was 1.2. From this, it was found that the addition of sodium nitrite to the electrolyte solution was 0.05% by weight, and the internal resistance was increased as compared with the case where the internal short-circuit inhibitor was not added to the electrolyte.

According to the above experimental results, the upper limit of the concentration of the internal short-circuit inhibitor containing the inorganic salt which prevents the internal short circuit is set to be less than 0.01% by weight. Further, since the internal short-circuit inhibitor containing the inorganic salt which prevents the internal short circuit is a concentration which can be dispersed and dispersed in the electrolytic solution, the upper limit of the added concentration is preferably 0.001% by weight or less.

(3) Confirmation of battery capacitance

Then, the battery capacitance when the internal short-circuit inhibitor was not added to the electrolytic solution and the case where the sodium nitrite as the internal short-circuit inhibitor was added was less than 0.01% by weight, and the results were described.

In this experiment, an active material (lithium transition metal composite oxide: LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ), a conductive auxiliary agent (acetylene black), and a binder (polyvinylidene fluoride) are used. a positive electrode, a negative electrode comprising a carbon powder, a conductive additive (graphite), a binder (polyvinylidene fluoride), a separator containing a porous polypropylene having a thickness of 20 μm, and an organic solvent (ethyl carbonate, dimethyl carbonate) A lithium ion battery is produced by using an electrolyte of an ester, ethyl methyl carbonate, and an electrolytic salt (lithium hexafluorophosphate). The case where the internal short-circuit inhibitor is not added to the electrolytic solution and the case where the sodium nitrite as the internal short-circuit inhibitor is added is less than 0.01% by weight.

Fig. 8 is a graph showing the discharge characteristics of the battery capacity when the internal short-circuit inhibitor is not added to the electrolytic solution and the case where the sodium nitrite as the internal short-circuit inhibitor is less than 0.01% by weight. Further, in FIG. 8, the capacitance at the time of 0.2 C discharge when the internal short-circuit inhibitor is not added to the electrolytic solution is set to 1, and the discharge value is expressed by the relative value. Rong.

In Fig. 8, a graph 1 shows the results of an experiment in the case where an internal short-circuit inhibitor is not added to the electrolytic solution. Further, in Fig. 8, a graph 2 shows the results of an experiment when sodium nitrite as an internal short-circuit inhibitor was added to the electrolytic solution in an amount of less than 0.01% by weight. When the graph 1 is compared with the graph 2, it is confirmed that the discharge capacity is 0.2 C to 5.0 C, and the discharge capacity and the electrolyte are added when the sodium nitrite as the internal short-circuit inhibitor is less than 0.01% by weight. The discharge capacitance is equal when no internal short-circuit inhibitor is added.

According to the above results, even when the sodium nitrite as the internal short-circuit inhibitor is added to the electrolytic solution to less than 0.01% by weight, the battery capacity is not as compared with the case where the internal short-circuit inhibitor is not added to the electrolytic solution. Deterioration.

As described above, according to the results of (1) to (3) shown in the experimental results of the present embodiment, it is understood that sodium nitrite as an internal short-circuit inhibitor is added to the electrolytic solution in an amount of 0.0001% by weight or more and less than 0.01% by weight. Deteriorating battery performance to prevent internal short circuits.

In addition, in the experimental results of the present embodiment, sodium nitrite was used as an internal short-circuit inhibitor containing an inorganic salt to prevent internal short-circuiting, and iron particles were used as metal impurities. However, as an internal short circuit prevention, The internal short-circuit inhibitor containing an inorganic salt has the same nitrite, nitrate, phosphate, and chromate, and is also the same as a metal impurity, a transition metal such as iron or nickel, and an alloy containing a transition metal as a main component such as stainless steel. Further, even when a transition metal ion such as nickel, manganese, cobalt, iron, or chromium which is a component contained in the battery material is dissolved in the electrolytic solution EL, internal short-circuiting can be prevented in the same manner.

The invention made by the inventors of the present invention has been described in detail with reference to the embodiments thereof. However, the present invention is not limited to the embodiments described above, and various modifications may be made without departing from the spirit and scope of the invention.

In the above embodiment, the technical idea of the present invention has been described by taking a lithium ion battery as an example. However, the technical idea of the present invention is not limited to a lithium ion battery, and can be widely applied to a positive electrode, a negative electrode, and a positive electrode. Storage of separators for electrically separating the negative electrode Device (such as a battery or capacitor, etc.).

The present invention can be widely applied to, for example, manufacturing of a battery represented by a lithium ion battery.

CS‧‧‧Packaging cans

CU‧‧‧Charger

EL‧‧‧ electrolyte

NEP‧‧‧ negative plate

PEP‧‧‧positive plate

SP‧‧‧Parts

Claims (5)

A lithium ion battery comprising: a positive electrode and a negative electrode; a separator that insulates the positive electrode from the negative electrode; and an electrolyte that causes a charge and discharge reaction between the positive electrode and the negative electrode; and An internal short-circuit inhibitor containing an inorganic salt which prevents internal short-circuiting is added in a range of 0.0001% by weight or more and less than 0.01% by weight. A lithium ion battery comprising: a positive electrode and a negative electrode; a separator that insulates the positive electrode from the negative electrode; and an electrolyte that causes a charge and discharge reaction between the positive electrode and the negative electrode; and An internal short-circuit inhibitor containing an inorganic salt that prevents internal short-circuiting is added in a range of 0.0001% by weight or more and 0.001% by weight or less. The lithium ion battery according to claim 1 or 2, wherein the internal short-circuit inhibitor has a solubility of less than 0.01% by weight with respect to the above electrolyte, and forms a complex with the metal ion. The lithium ion battery according to claim 1 or 2, wherein the internal short circuit inhibitor is added in a range below the solubility of the electrolyte. The lithium ion battery according to claim 1 or 2, wherein the internal short circuit inhibitor contains at least one of nitrite, nitrate, phosphate, and chromate.