JP6224533B2 - Overcharge detection device for lithium ion battery - Google Patents

Description

  The present invention relates to an overcharge detection device for a lithium ion battery.

  Lithium ion batteries have characteristics such as high voltage and energy density and low memory effect, and are used in various fields such as automobiles and portable devices. As its use progresses, further improvements in voltage and energy density are required for lithium ion batteries, and further improvements in safety are also desired.

  In order to improve safety, when an abnormality occurs in the lithium ion battery, it is necessary to detect the abnormality with high accuracy. For example, when an overcharge occurs in a lithium ion battery, it is necessary to detect the overcharge with high accuracy. As a method for detecting overcharge, a method using a battery voltage, which is a battery voltage, is known. For example, the overcharge detection device described in Patent Literature 1 detects battery overcharge based on a comparison between a voltage corresponding to the battery voltage and a reference voltage.

JP 2010-203790 A

  It has been proposed to detect overcharge of a lithium ion battery based on an increase in battery voltage as in Patent Document 1. However, the battery voltage is affected by various parameters such as the external circuit connected to the battery, the internal resistance of the battery, the temperature around and inside the battery. In particular, the internal resistance increases depending on the battery usage period and the number of times of charging / discharging, and increases or decreases depending on the battery temperature. Therefore, it is difficult to accurately grasp the state of the battery that changes every moment from the battery voltage, and therefore it is difficult to accurately grasp the overcharge of the battery from the battery voltage.

  Thus, when battery voltage is used, battery overcharge may not be detected with high accuracy. Therefore, a technique capable of improving the accuracy of overcharge detection of a lithium ion battery is desired.

  According to the present invention, there is provided an overcharge detection device for a lithium ion battery including a positive electrode, a negative electrode, and an electrolyte, wherein the light detection unit detects light emitted from at least one of the positive electrode and the negative electrode, and the light detection unit. An overcharge detection device for a lithium ion battery, comprising: an overcharge determination unit that determines that an overcharge has occurred in a lithium ion battery when the detected light intensity is greater than a preset threshold intensity. The

  According to the present invention, the accuracy of overcharge detection of a lithium ion battery can be improved.

It is a block diagram which shows the structure of a lithium ion battery system. It is a front view which shows typically an example of a structure of a lithium ion battery. It is a side view which shows typically an example of a structure of a lithium ion battery. It is a side view which shows typically an example of a structure of the front-end | tip part of an optical waveguide. It is a graph which shows the relationship between the charge curve of a lithium ion battery, and the intensity | strength of light. It is a graph which shows the relationship between the charge curve of a lithium ion battery, and the intensity | strength of light.

  According to the present invention, there is provided an overcharge detection device for a lithium ion battery including a positive electrode, a negative electrode, and an electrolyte, wherein the light detection unit detects light emitted from at least one of the positive electrode and the negative electrode, and the light detection unit. An overcharge detection device for a lithium ion battery is provided that includes an overcharge determination unit that determines that an overcharge has occurred in a lithium ion battery when the detected light intensity is greater than or equal to a preset threshold intensity. .

  The inventors have found a phenomenon that light is emitted from the positive electrode and the negative electrode when overcharge occurs in a lithium ion battery. This is considered to be a phenomenon in which radicals, peroxides, and the like are generated in at least one of the positive electrode, the negative electrode, and the electrolyte due to overcharge, and these emit light at the positive electrode and the negative electrode. The newly discovered findings include the fact that the light intensity on the positive electrode side is stronger than the light intensity on the negative electrode side, and that the light intensity becomes stronger when an electrolyte containing an overcharge inhibitor is used. The reason why the light intensity on the positive electrode side is stronger than the light intensity on the negative electrode side is considered to be because the positive electrode during overcharging is in a strong oxidizing atmosphere and the electrolytic solution is oxidized and decomposed to generate active species. The reason why the intensity of light becomes stronger when an electrolyte containing an overcharge inhibitor is used is considered to be that active species generated from the overcharge inhibitor contribute to light emission. Based on these findings, it is possible to easily determine the occurrence of overcharge of the lithium ion battery by detecting light from the positive electrode and the negative electrode, and to safely stop the battery. This light emission phenomenon is less susceptible to disturbances, occurs from an early stage of overcharge, and is easy to measure, so that overcharge can be detected early and accurately, and the accuracy of overcharge detection can be improved.

  Hereinafter, an overcharge detection device according to an embodiment of the present invention and a lithium ion battery using the same will be described with reference to the drawings.

  FIG. 1 shows an example of the configuration of a lithium ion battery system using an overcharge detection device. The lithium ion battery system A includes a lithium ion battery 1 and a protection device 2. The lithium ion battery 1 is a chargeable / dischargeable cell using lithium ions, and has a positive electrode, a negative electrode, and an electrolyte interposed between at least the positive electrode and the negative electrode. The positive electrode is connected to the positive electrode terminal 3, and the negative electrode is connected to the negative electrode terminal 4. The protection device 2 is a safety mechanism that stops the operation of the lithium ion battery 1 when the lithium ion battery 1 is overcharged, and includes an overcharge detection device 10 and an operation stop device 14. The overcharge detection device 10 detects that an overcharge has occurred in the lithium ion battery 1. The operation stop device 14 stops the operation of the lithium ion battery system A, that is, the charging operation when the overcharge detection device 10 detects overcharge.

  The overcharge detection device 10 includes an optical waveguide 11, a photodetector 12, and an overcharge determination unit 13. The optical waveguide 11 has one end inserted into the lithium ion battery 1 and the other end connected to the photodetector 12 outside the lithium ion battery 1 to receive the light emitted from the lithium ion battery 1. Lead to twelve. An example of the optical waveguide 11 is an optical fiber. The photodetector 12 detects the light output from the optical waveguide 11 and outputs a detection signal corresponding to the detected light intensity to the overcharge determination unit 13. Examples of the photodetector 12 include a CCD (Charge Coupled Device), a semiconductor detector such as a photodiode and a phototransistor, a photomultiplier tube, and a phototube. The optical waveguide 11 and the photodetector 12 can be regarded as a light detection unit that receives and detects light emitted in the lithium ion battery 1. The overcharge determination unit 13 determines that overcharge has occurred in the lithium ion battery 1 when the intensity of light detected by the photodetector 12 is greater than a preset threshold intensity. As the threshold intensity, light intensity (background) detected by the photodetector 12 in a state where no light is emitted in the lithium ion battery 1 (the lithium ion battery 1 is not overcharged), or erroneous detection due to noise or the like Considering this possibility, the intensity obtained by adding a predetermined value to the background is exemplified. Further, from the viewpoint of preventing erroneous determination, the overcharge determination unit 13 may calculate the average intensity by measuring the light intensity a plurality of times, and compare the average intensity with the threshold intensity. When the overcharge determination unit 13 determines that overcharge has occurred, the overcharge signal indicating that overcharge has occurred in the lithium ion battery 1 or a control signal for stopping the operation of the lithium ion battery system A is stopped. Output to the device 14. As the overcharge determination unit 13, an electronic circuit that performs the above determination based on the comparison result between the voltage of the detection signal corresponding to the detected light intensity and the reference voltage corresponding to the threshold intensity, or based on the detection signal It is exemplified by a measuring instrument or a computer that performs the above comparison / determination process. In addition, although the overcharge detection apparatus 10 is included in the lithium ion battery system A in the example of FIG. 1, this Embodiment is not limited to the example, and the overcharge detection apparatus 10 is a lithium ion battery system. It may be provided separately from A. Alternatively, a part of the overcharge detection device 10 may be included in the lithium ion battery 1 and integrated with the rest of the overcharge detection device 10 when in use. Further, in the example of FIG. 1, light is received using the optical waveguide 11, but this embodiment is not limited to this example, and the photodetector 12 is introduced into the lithium ion battery 1. The optical waveguide 11 may be omitted.

  The operation stopping device 14 stops charging the lithium ion battery 1 in response to the overcharge signal or the control signal from the overcharge determination unit 13. The operation stop device 14 is exemplified by a switch element such as a transistor provided on a wiring through which a charging current flows, and cuts off the charging current by turning off the switch in response to an overcharge signal or a control signal. Stop charging. In the example of FIG. 1, it is provided on the wiring connecting the negative electrode of the lithium ion battery 1 and the negative electrode terminal 4.

  2 and 3 show an example of the configuration of a lithium ion battery. The lithium ion battery 1 includes a positive electrode 21, a negative electrode 22, and at least an electrolyte layer 25 interposed between the positive electrode 21 and the negative electrode 22. The electrolyte layer 25 includes an electrolyte and may further include a separator. A positive electrode current collecting tab 23 is formed on the positive electrode 21, and a negative electrode current collecting tab 24 is formed on the negative electrode 22. The positive current collecting tab 23 and the negative current collecting tab 24 are electrically connected to the positive terminal 3 and the negative terminal 4, respectively, as shown in FIG. The positive electrode 21, the negative electrode 22, and the electrolyte layer 25 may be further laminated. 2 and 3, the lithium ion battery 1 is a stacked type, but the present embodiment is not limited to this example, and the lithium ion battery 1 may be a wound type. .

The positive electrode 21 includes a positive electrode current collector and a positive electrode active material layer including a positive electrode active material disposed on at least one surface of the positive electrode current collector. Examples of the material for the positive electrode current collector include metal materials such as aluminum, nickel, and stainless steel. As the positive electrode active material, a lithium-containing composite compound, specifically, lithium cobaltate (LiCoO ₂ ), lithium manganate (LiMnO ₂ ), lithium nickelate (LiNiO ₂ ), lithium nickel cobaltate (LiNi ₁ ) having a layered structure. _-X Co _x O ₂ ), lithium nickel manganate (LiNi _1-x Mn _x O ₂ , for example, LiNi _0.5 Mn _0.5 O ₂ ), nickel cobalt lithium manganate (LiNi _1-xy Co _x Mn _y O _2, for example, _{LiNi 1/3 Co 1/3 Mn 1/3 O 2} ), lithium manganate (LiMn ₂ of spinel structure O _4), lithium cobalt manganese oxide (LiCoMnO _4), lithium nickel manganese oxide (LiNi _{0 .5} Mn _1.5 O ₄ ), olivine-structured lithium iron phosphate (LiFePO ₄ ) and lithium iron phosphate (Li ₂ FePO ₄ F) are exemplified.

  The negative electrode 22 has a negative electrode current collector and a negative electrode active material layer containing a negative electrode active material disposed on at least one surface of the negative electrode current collector. Examples of the material for the negative electrode current collector include copper and metal materials such as alloys containing copper. As the negative electrode active substance, a particulate carbon material containing at least a graphite structure (layered structure), specifically, natural or artificial graphite (graphite), graphitizable carbon (soft carbon), non-graphitizable Examples include carbon (hard carbon), low-temperature calcined carbon, or a material combining some of these.

  Moreover, each of the positive electrode 21 and the negative electrode 22 may contain a binder. The material for the binder is not particularly limited, and polytetrafluoroethylene, polybutadiene rubber, hydrogenated butylene rubber, styrene butadiene rubber, polysulfide rubber, polyvinyl fluoride, and polyvinylidene fluoride can be used. Moreover, the positive electrode 21 and the negative electrode 22 may contain a conductive support material as desired. The conductive aid is not particularly limited, and graphite, carbon black and the like can be used.

Examples of the electrolyte of the electrolyte layer 25 include an electrolytic solution, a gel-like or solid electrolyte, and the electrolytic solution is preferably used. The electrolytic solution contains a lithium salt and a solvent. Examples of the lithium salt include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluorophosphate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), and trifluoromethanesulfone. Examples include lithium acid (LiCF ₃ SO ₃ ) and bis (trifluoromethanesulfonyl) imide lithium (Li (CF ₃ SO ₂ ) ₂ N). Solvents include carbonic acid esters, cyclic esters (ethylene carbonate (EC), propylene carbonate (PC), etc.), chain esters (dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc.) Aliphatic carboxylic acid esters (such as methyl formate (MF)), γ-lactones (such as γ-butyrolactone (BL)), chain ethers (such as 1,2-dimethoxyethane (DME)), or these Solvents combining some of these are exemplified. The solvent may be an ionic liquid. Examples of the anion of the ionic ^{_{liquid, (CF 3 SO 2) 2}} N - (TFSI), (C 2 F 5 SO 2) 2 N - (BETI), (FSO 2) 2 N - (FSI), (CF 3 SO ^{_{2) 3 C - (TFSM)}} , BF 4 -, PF 6 -, CF 3 SO 3 - (TfO), CF 3 BF 3 -, C 2 F 5 BF 3 - material or a combination of these some, Is exemplified. Examples of the cation of the ionic liquid include lithium, imidazolium such as 1-ethyl-3-methylimidazolium (EMI), ammonium such as tetraethylammonium (TEA), pyridinium such as 1-butyl-3-methylpyridinium, Pyrrolidinium, such as 1-methyl-1-propyl-pyrrolidinium (MPPy), 1-butyl-1-methylpyrrolidinium (BMP) or N-methyl-N-propylpyrrolidinium (P13), N-methyl-N Examples include piperidinium such as propylpiperidinium (PP13), phosphonium such as triethylmethoxyethylphosphonium (TEMEP), sulfonium such as triethylsulfonium (TES), or a combination of these. Moreover, as a gel electrolyte, the polymer gel electrolyte containing the said electrolyte solution is illustrated. An example of the polymer gel electrolyte matrix is a poly (vinylidene fluoride-hexafuropropylene) copolymer (PVDF-HFP).

  The electrolyte layer 25 preferably contains an overcharge inhibitor. The overcharge inhibitor preferably contains an aromatic compound, and examples thereof include biphenyl (BP) and cyclohexylbenzene (phenylcyclohexane). The overcharge preventing agent not only prevents overcharge, but also has a function of increasing the intensity of light emitted from the positive electrode 21 and the negative electrode 22. By including an overcharge inhibitor in the electrolyte layer 25, the intensity of emitted light can be increased, the overcharge detection accuracy can be improved, and the battery can be stopped more safely.

  The separator of the electrolyte layer 25 is not particularly limited as long as it is a porous film having an insulating property, but a single layer or a plurality of layers of a microporous film of polyolefin such as polypropylene (PP) or polyethylene (PE), or those And a laminated film of an inorganic porous film.

  The front end portion of the optical waveguide 11, that is, the light receiving portion that receives light, is disposed at a position where light emitted from at least one of the positive electrode 21 and the negative electrode 22 can be received. Specifically, the tip portion of the optical waveguide 11 is disposed in the vicinity of at least one of the positive electrode 21 and the negative electrode 22, for example, at a position within 1 mm from the surface or end of the electrodes. You may arrange | position so that those electrodes may be touched. The optical waveguide 11 is preferably disposed on the positive electrode 21 side. This is because the intensity of light emitted on the positive electrode 21 side is stronger than the intensity of light emitted on the negative electrode 22 side. By arranging the optical waveguide 11 on the positive electrode 21 side, the intensity of received light can be increased, the overcharge detection accuracy can be improved, and the battery can be stopped more safely. In the example of FIG. 2, the optical waveguide 11 is disposed at a position within 1 mm from the end of the positive electrode 21 so as to be supported by the separator 26. Or you may arrange | position so that it may be supported by the positive electrode 21 in the position which touches the surface of the positive electrode 21, like the optical waveguide 11c.

  The optical waveguide 11 includes a core serving as an optical path and a clad covering the periphery of the core. The optical waveguide 11 is formed such that the refractive index of the core is higher than the refractive index of the clad, and is exemplified by an optical fiber. FIG. 4 shows an example of the configuration of the tip portion of the optical waveguide. In the optical waveguide 11, it is preferable that the tip portions of the core 11 a and the clad 11 b are ground in a wedge shape, and the ground surface S is directed toward the surface of the positive electrode 21 or the surface of the negative electrode 22. This is because the amount of light taken in from the tip portion increases. Alternatively, in the optical waveguide 11, a condensing prism (not shown) or a lens (not shown) is installed at the tip so that light from the surface of the positive electrode 21 or the surface of the negative electrode 22 is collected. May be.

  The refractive index of the core of the optical waveguide 11 is preferably higher than the refractive index of the electrolyte of the electrolyte layer 25. This is to increase the incident angle of light, which is an incident condition to the core at the tip portion of the optical waveguide 11. Further, as the optical waveguide 11, an optical fiber made of quartz glass can be mentioned. In that case, the chemical stability of the optical waveguide 11 with respect to the electrolyte solution of the electrolyte layer 25 can be improved. Alternatively, as the optical waveguide 11, a polymer optical fiber in which a fluorescent dye is contained in a clad can be cited. In this case, the clad fluorescent dye emits light by light from the surface of the positive electrode 21, so that light can be detected not only from the tip of the optical waveguide 11 but also from the side surface, and the detection efficiency can be increased. Utilizing the light emission of the fluorescent dye in this manner has a role of improving the light collection efficiency of the optical waveguide 11 although the conversion efficiency to fluorescence is low. For example, in addition to the cladding, for example, a container near the optical waveguide 11 Arranging the fluorescent substance on the side surface is also a preferable configuration.

Next, an example of the operation of the overcharge detection device according to the embodiment of the present invention will be described.
In the lithium ion battery system A using the overcharge detection device 10 of FIG. 1, when the lithium ion battery 1 is overcharged, at least one of the positive electrode 21 and the negative electrode 22 emits light. The optical waveguide 11 receives light at the tip portion and guides it to the photodetector 12. The photodetector 12 detects the light output from the optical waveguide 11 and outputs a detection signal corresponding to the detected light intensity to the overcharge determination unit 13. The overcharge determination unit 13 compares the detected light intensity with a preset threshold intensity based on the detection signal. However, the threshold intensity is, for example, an intensity obtained by adding a predetermined value to the intensity (background) of light detected by the photodetector 12 in the state where the lithium ion battery 1 does not emit light. The overcharge determination unit 13 determines that light emission has occurred when the intensity of light detected by the photodetector 12 is greater than the threshold intensity, and determines that overcharge has occurred in the lithium ion battery 1. When the overcharge determining unit 13 determines that overcharge has occurred, the overcharge signal indicating that overcharge has occurred in the lithium ion battery 1 or a control signal for stopping the operation of the lithium ion battery system A is provided. Output to. The operation stopping device 14 stops charging the lithium ion battery 1 in response to the overcharge signal or the control signal from the overcharge determination unit 13.

  In the present embodiment, since the overcharge due to overcharge in the lithium ion battery can be detected reliably in real time by observing the light emission, the accuracy of the overcharge detection of the lithium ion battery can be improved. Thereby, even when overcharge occurs, the lithium ion battery can be stopped more safely. In addition, even in situations where internal resistance changes greatly, such as when the battery deteriorates, and it becomes difficult to detect overcharge at the battery voltage, it is possible to reliably detect overcharge, making lithium ion batteries safer and more secure. You can stop.

  In addition, if a circuit for detecting an abnormality with the battery voltage is attached to the lithium ion battery 1 and used in combination with the above-described overcharge detection device 10, the accuracy of the overcharge detection of the lithium ion battery can be further improved. The overcharge detection device 10 can reliably detect overcharge even when the circuit for detecting an abnormality is malfunctioning. That is, the overcharge detection device 10 can improve the redundancy of the overcharge detection of the lithium ion battery 1.

Examples of the present invention will be described below. The following examples are for illustrative purposes only and are not intended to limit the invention.
In each of the following examples, the battery voltage during charging was measured with the following charging / discharging device.
Battery voltage measuring device during charging: TOSCAT-3200 manufactured by Toyo System

(A) Confirmation of light emission (Example A1) When no overcharge inhibitor is present (a) Lithium ion battery A model battery in which the surface of the positive electrode in the lithium ion battery can be observed was produced. Specifically, LiNi _1/3 Co _1/3 Mn _1/3 O _{2 as} the positive electrode active material, acetylene black as the conductive auxiliary agent for the positive electrode, polyvinylidene fluoride as the binder for the positive electrode, natural graphite as the negative electrode active material, Polyvinylidene fluoride as the binder, LiPF ₆ (1 mol / l) + EC / DMC (3/7) as the electrolyte, polyethylene (PE) microporous film as the separator, and quartz glass optical fiber as the optical waveguide as the positive electrode A lithium ion battery introduced at the end position was prepared. As a photodetector, an H7155-01 photomultiplier tube manufactured by Hamamatsu Photonics was used.
(B) Overcharge and battery behavior The lithium ion battery produced in (a) above was overcharged at a current of 0.1 C until the battery voltage reached 4.7V. Thereafter, the battery voltage was maintained at 4.7V for 1 hour. Subsequently, the battery voltage was set to 5.0 V and held for 1 hour. However, in this specification, overcharging is performed when the battery voltage is 4.2 V or higher, and a region where the battery voltage is 4.2 V or higher is also referred to as an overcharge region. Further, as the battery behavior, the intensity of light emitted from the positive electrode surface was measured. The result is shown in FIG.

  As shown in FIG. 5, light emission was observed on the positive electrode from around 4.2 V, which is the overcharge region, and the light intensity increased with an increase in battery voltage. This is presumably because active species such as radicals are generated in the positive electrode due to overcharge, and they emit light.

(Example A2) When there is an overcharge inhibitor (a) Biphenyl as an overcharge inhibitor with respect to 100% by weight of an electrolyte solution of a lithium ion battery LiPF ₆ (1 mol / l) + EC / DMC (3/7) A lithium ion battery was prepared in the same manner as in Example A1 except that 1% by weight and 1% by weight of cyclohexylbenzene were added.
(B) Overcharge and battery behavior Overcharge was performed by applying current and voltage to the lithium ion battery with the same profile as in Example A1, and the battery behavior was examined. The result is shown in FIG.

  As shown in FIG. 6, light emission was observed at the positive electrode from around 4.2 V, which is the overcharge region, and the light intensity increased with an increase in battery voltage. In addition, the light intensity was about three times that of Example A1. It is known that the overcharge inhibitors biphenyl and cyclohexylbenzene are anodized at about 4.3 to 4.7 V, partly forming a conductive film of poniphenylene on the positive electrode, and partly becoming a cation radical. ing. Therefore, it is considered that the light intensity is increased in addition to the light emission in the case of Example A1, in addition to these poniphenylenes and cation radicals.

(B) Confirmation of overcharge protection function by light emission The battery temperature at the time of detecting the overvoltage was measured by the following temperature measuring device.
Battery temperature measuring device when overvoltage is detected: GL220 (data logger) made by Graphtec and thermocouple

(Example B1) When there is no overcharge inhibitor (i) Lithium ion battery A 1500 mAh 18650 type (cylindrical type with a diameter of 18 mm and a length (height) of 65 mm) equipped with a safety valve with a current interruption function was produced. . Specifically, LiNi _1/3 Co _1/3 Mn _1/3 O _{2 as} the positive electrode active material, acetylene black as the conductive auxiliary agent for the positive electrode, polyvinylidene fluoride as the binder for the positive electrode, natural graphite as the negative electrode active material, Polyvinylidene fluoride as the binder, LiPF ₆ (1 mol / l) + EC / DMC (3/7) as the electrolyte, polyethylene (PE) microporous film as the separator, and quartz glass optical fiber as the optical waveguide as the positive electrode A lithium ion battery introduced so as to be supported by the separator at a position of 1 mm from the end of the surface was produced. As a photodetector, an H7155-01 photomultiplier tube manufactured by Hamamatsu Photonics was used. The charge / discharge device described above was used as the overcharge determination unit and the operation stop device.
(Ii) Overcharge and battery behavior For lithium-ion batteries, overcharge is performed by supplying a current of 1C from an SOC (State of Charge) of 100%, and overcharge protection based on light emission from the positive electrode is performed. The battery temperature at the time of detecting was measured. The threshold intensity used for the determination of light emission eliminates false detection due to noise or the like in the light intensity (background) 250 cps detected by the photodetector 12 in the state without light emission before overcharging in the lithium ion battery 1. Therefore, 250 cps was added to obtain 500 cps. As the battery temperature, the temperature at the position of the length (height) 30 mm of the side surface of the container of the lithium ion battery 1 was measured. The results are shown in Table 1.

(Example B2) When there is an overcharge inhibitor (i) Biphenyl as an overcharge inhibitor with respect to 100% by weight of an electrolyte solution of lithium ion battery LiPF ₆ (1 mol / l) + EC / DMC (3/7) A lithium ion battery was prepared in the same manner as in Example B1 except that 1% by weight and 1% by weight of cyclohexylbenzene were added.
(2) Overcharge and battery behavior Overcharge was performed in the same manner as in Example B1, overcharge protection based on light emission from the positive electrode was performed, and the battery temperature at that time was measured. The results are shown in Table 1.

(Comparative Example B1)
(1) Lithium-ion battery A lithium-ion battery similar to that in Example B1 was prepared except that the optical waveguide was not introduced into the lithium-ion battery, and therefore, no detection of light emission was performed.
(2) Overcharge and battery behavior Overcharge similar to that in Example B1 above is performed, and when the safety valve with a current cutoff function is activated, at that time, when the safety valve is not activated, the battery temperature after a predetermined time has elapsed. Was measured. The results are shown in Table 1.

(Comparative Example B2)
(1) Lithium-ion battery A lithium-ion battery similar to that in Example B2 above was prepared except that the optical waveguide was not introduced into the lithium-ion battery, and therefore the detection of light emission was not performed.
(2) Overcharge and battery behavior Overcharge similar to Example B2 above is performed, and when the safety valve with a current cutoff function is activated, the battery after a predetermined time has elapsed when the safety valve is not activated. The temperature was measured. The results are shown in Table 1.

  In Example B1, as shown in Table 1, the battery temperature when luminescence was observed was about 50 ° C., and the temperature when overcharge was detected was low. By determining overcharge based on this light emission, charging could be safely stopped.

  In Example B2, as shown in Table 1, the battery temperature when luminescence was observed was about 30 ° C., and the temperature when overcharge was detected was even lower. By determining overcharge based on this light emission, the charge could be stopped more safely.

  Further, in Comparative Example B1, as shown in Table 1, light emission could not be detected, and the safety valve with a current interrupt function did not operate, so thermal runaway occurred, and the battery temperature reached a high temperature of 200 ° C. or higher after a predetermined time. It was. The reason why the safety valve with the current cutoff function did not work is that the battery was overcharged during charging, but the gas inside the battery was less generated, so the inside of the battery did not become high pressure. .

  Further, in Comparative Example B2, as shown in Table 1, since it was not possible to detect light emission, the safety valve with a current interruption function was actuated by the overcharge preventing agent to suppress the rise in battery temperature, but the battery temperature was about 80 ° C. It became. The safety valve with the current cutoff function was activated because the battery became overcharged during charging, and a large amount of gas was generated due to the decomposition of the overcharge inhibitor inside the battery, resulting in a high pressure inside the battery. Conceivable.

  As shown in Examples B1 and B2 and Comparative Examples B1 and B2, overcharge in the battery can be detected in real time by observing light emission, so that the battery could be safely stopped.

  In addition, it is thought that the battery material or its product is light-emitting by the method of detecting said overcharge by the energy of overcharge. Therefore, as a method of detecting overcharge other than the above, conversely, light is irradiated into the battery using an optical waveguide, energy is applied to the battery material or its product, and the phosphorescence is detected. It is considered possible to observe the overcharged state and the deteriorated state of the battery material.

DESCRIPTION OF SYMBOLS 1 Lithium ion battery 2 Protection apparatus 3 Positive electrode terminal 4 Negative electrode terminal 10 Overcharge detection apparatus 11 Optical waveguide 11a Core 11b Clad 11c Optical waveguide 12 Photodetector 13 Overcharge determination part 14 Operation stop apparatus 21 Positive electrode 22 Negative electrode 23 Positive electrode current collection tab 24 Negative electrode current collecting tab 25 Electrolyte layer A Lithium ion battery system S Grinding surface

Claims (1)

An overcharge detection device for a lithium ion battery including a positive electrode, a negative electrode, and an electrolyte,
A light detection unit for detecting light emitted from at least one of the positive electrode and the negative electrode;
An overcharge determination unit that determines that an overcharge has occurred in the lithium ion battery when the intensity of light detected by the light detection unit is greater than a preset threshold intensity;
Comprising
Overcharge detection device for lithium ion batteries.

Images