JP5070768B2 - Battery with waste liquid storage chamber - Google Patents

Description

  The present invention relates to a battery that uses lithium iron phosphate as an active material and can ensure a high level of safety during overcharge.

  In recent years, non-aqueous electrolyte batteries typified by lithium secondary batteries with high energy density and low self-discharge and good cycle characteristics have attracted attention as power sources for mobile devices such as mobile phones and laptop computers, and electric vehicles. Has been.

The current mainstream of lithium secondary batteries is for consumer use, mainly for mobile phones of 2 Ah or less. Currently, LiCoO ₂ is mainly used as a positive electrode active material for lithium secondary batteries.

  However, safety is very important when considering the development of non-aqueous electrolyte batteries for future medium- and large-sized, especially industrial applications where large demand is expected. That is, since it is necessary to assume that the battery is used in a high-temperature environment that is not used in a small consumer use in industrial applications, the current specification for a small battery is not necessarily sufficient.

  In Patent Document 1, by using a filling gas that is easily dissolved in the electrolytic solution, when the battery temperature rises by pressurizing and filling the electrolytic solution, the gas dissolved in the electrolytic solution is vaporized, and the internal pressure of the battery is reduced. There is a description of a battery that not only raises and quickly activates the safety valve, but also allows the electrolyte in the micropores of the positive electrode or negative electrode to be efficiently discharged outside the battery.

  However, in this method, it is necessary to fill the electrolyte with non-combustible gas at a pressure of 500 to 1500 kPa in advance, so it is adopted for the design that detects the initial stage of battery internal pressure rise in a normal battery and opens the safety valve I couldn't.

  Patent Document 2 discloses a battery provided with an electrolytic solution extraction means that opens into a battery container and extracts the electrolytic solution to the outside by reducing the pressure in the battery container when it is determined that the battery is abnormal. There is a description.

  However, this method requires a device for detecting battery abnormality, a signal generation and signal transmission circuit, a suction pump for decompressing the inside of the battery container, etc. Even if the inside of the container is depressurized, the electrolyte retained in the power generation element composed of the positive electrode, the negative electrode, and the separator cannot be sufficiently extracted, and is insufficient to prevent thermal runaway of the battery.

  Patent Document 3 describes a configuration in which, when a battery is abnormal, the cleavage groove is cleaved after the cleavage groove is cleaved and the non-aqueous electrolyte is discharged.

However, even if the cleavage groove is cleaved, only the excess electrolyte in the battery container is substantially discharged, and the electrolyte retained in the power generation element composed of the positive electrode, the negative electrode, and the separator is sufficient. Could not discharge.
JP-A-6-150975 JP 2003-123736 A JP 2006-99977 A

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a battery that can ensure a high level of safety during overcharging.

  A power generation element storage chamber for storing a power generation element including a positive electrode containing lithium iron phosphate; and a waste liquid storage chamber capable of storing an electrolyte solution, wherein the waste liquid storage chamber is provided at a lower portion of the power generation element storage chamber The power generation element storage chamber is provided with a discharge valve through which the electrolyte can flow from the power generation element storage chamber toward the waste liquid storage chamber, and the discharge valve suppresses the outflow of the electrolyte during normal use. A battery that allows the electrolyte to flow out when the internal pressure of the power generation element housing increases.

One of the features of the present invention is that lithium iron phosphate is used as the positive electrode active material. With this feature, when the battery is abnormal, it is possible to sufficiently discharge the electrolytic solution held in the power generation element including the positive electrode, the negative electrode, and the separator. That is, LiCoO ₂ conventionally used as a positive electrode active material of a battery is a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure. When such a material is used as a positive electrode active material, When the charging current continues to flow due to a failure of the charging control circuit or the like, the potential of the positive electrode gradually rises and the Li extraction reaction continues, while gas generation is small. When the gas generation from the power generation element is small, the electrolytic solution retained in the power generation element is not substantially pushed out of the system of the power generation element. On the other hand, when lithium iron phosphate is used as the positive electrode active material, if the charging current continues to flow due to a failure of the charging control circuit or the like, when the potential reaches about 4 V, the Li extraction reaction does not continue thereafter. It has characteristics. For this reason, the charging current that continues to flow contributes exclusively to the gas generation reaction that accompanies the decomposition of the electrolyte. In reality, after the positive electrode potential reaches the potential of about 4.6 V, gas generation starts at once. Become.

  The characteristic that gas generation starts at once after the positive electrode potential reaches about 4 V, particularly after 4.6 V, makes the discharge valve highly sensitive to detecting an increase in internal pressure of the power generation element accommodating portion in the battery of the present invention. At the same time, the design of the discharge valve is facilitated.

Furthermore, when a lithium transition metal composite oxide such as LiCoO ₂ is used as the positive electrode active material, if the charging current continues to flow, the temperature of the power generation element continues to increase with the Li extraction reaction, and the temperature is 150 ° C. However, if lithium iron phosphate is used as the positive electrode active material, the charging current continues to flow, there is a risk of inducing thermal runaway due to oxygen release reaction from Li _1-x CoO ₂ or the like. Since the lithium extraction reaction terminates at a base potential lower than the decomposition potential of the electrolyte, it is switched to a gas generation reaction at an early stage during overcharge. In the gas generation reaction process, the cause of the temperature increase of the power generation element is Except for Joule heat. In addition, even when lithium iron phosphate is exposed to a high temperature in a charged state, an oxygen releasing reaction that causes oxidation of the electrolytic solution does not occur, and thus the electrolytic solution can be discharged safely.

  In order to make the flow of the electrolyte extruded from the power generation element smooth, it is preferable to arrange the waste liquid storage chamber in a direction perpendicular to the laminated cross section of the power generation element. That is, when the power generation element is a wound electrode, the waste liquid storage chamber is preferably arranged along the winding axis direction.

  The waste liquid storage chamber may be provided with a mechanism for reducing the pressure in accordance with the operation of the discharge valve, but by providing the waste liquid storage chamber in the lower part of the power generation element storage chamber, the electrolyte pushed out from the power generation element is It is led to the waste liquid storage chamber by gravity and the internal pressure increase of the power generation element storage chamber. The waste liquid storage chamber may be provided with a vent valve that can discharge gas to the outside as the internal pressure of the waste liquid storage chamber increases.

  Since the battery of the present invention includes the waste liquid storage chamber, it is possible to prevent the discharged electrolyte from leaking out of the battery. Accordingly, it is possible to prevent the surrounding contamination, the circuit damage, and the combustion due to the ignition of the leaked electrolyte.

  ADVANTAGE OF THE INVENTION According to this invention, the battery which can ensure high safety | security at the time of overcharge can be provided.

  Hereinafter, the present invention will be described with reference to an example. HYPERLINK "https://www.patent.ne.jp/patent/cache/" \ l "fig1" FIG. 1 is a structural longitudinal sectional view showing a battery of the present invention. In the figure, a power generation element 3 including a positive electrode 9, a negative electrode 10, and a separator 11 is accommodated in a power generation element accommodation chamber 1.

  In the positive electrode 9, a positive electrode mixture containing lithium iron phosphate as a positive electrode active material is held on both surfaces of a positive electrode current collector made of a strip-shaped aluminum foil by coating and pressing. In the negative electrode 10, a negative electrode mixture containing lithium titanate as a negative electrode active material is held on both surfaces of a negative electrode current collector made of a strip-shaped copper foil by coating and pressing. The separator 11 is made of a microporous thin film having a shutdown function made of polyethylene. The positive electrode 9 and the negative electrode 10 are spirally wound in a state of being opposed to each other with the separator 11 interposed therebetween, and impregnated with a nonaqueous electrolyte to constitute the power generation element 3. Here, the separator 11 is wound slightly wider than the positive electrode 9 and the negative electrode 10, and several turns at the winding core and the end of the winding are wound by the separator 11 alone. 10 and the outer can 7 are electrically insulated.

  The power generation element accommodation chamber 1 is sealed with an outer can 7 and a metal lid 8, and a discharge valve 4 having a function of detecting and opening an increase in the internal pressure of the power generation element accommodation chamber 1 at a part of the bottom 6 of the outer can 7. Is provided. A waste liquid storage chamber 2 is provided below the bottom of the can 6, and a vent valve 5 is provided that can discharge gas to the outside as the internal pressure of the waste liquid storage chamber 2 increases.

  The metal lid 8 is inserted and sealed from the opening end of the outer can 7, and the metal lid 8 and the outer can 7 are sealed by laser welding. The metal lid 21 has a positive terminal and a negative terminal via an insulator. The metal lid 8 is provided with a positive terminal 12, a negative terminal 13, and a resettable safety valve 14 through an insulating material.

Next, a method for manufacturing and assembling a secondary battery according to the present invention will be described. The outer can 7 is made of a bottomed pressure can by impact molding or deep drawing, and the end surface is cut by determining the dimension from the can bottom 6 part to the opening tip. Further, the weak point is marked on the bottom 6 part of the can by pressing to make the discharge valve 4.
The metal lid 8 has a positive terminal 12, a negative terminal 13, a return-type safety valve 14, and an injection pipe 15 that pass therethrough and is hermetically fixed. The positive electrode terminal 12 and the negative electrode terminal 13 maintain the hermeticity with the metal lid 8 and are installed on the metal lid via an insulator.
In assembling the battery, the positive electrode lead and the negative electrode lead are attached to the current collector of each electrode by spot welding or ultrasonic welding while winding the belt-like positive electrode 9 and negative electrode 10 in a spiral shape through the separator 11, and the battery is wound up. The wound electrode group is fixed at the outer periphery with a tape or the like, and the positive electrode lead and the negative electrode lead are bundled in one row and connected to the positive electrode terminal 13 and the negative electrode terminal 14 fixed to the metal lid 7 by welding or the like.
Next, an electrode group is inserted into the case, and the metal lid 8 is press-fitted until it is parallel to the opening end of the outer can 7, and the metal lid 8 and the outer can 7 are hermetically fixed by laser sealing.
Finally, an electrolytic solution is injected from the injection tube 15, and the end of the injection tube is crushed and closed by pressing, and then the tip of the injection tube is welded and sealed.

  As mentioned above, although one Example was shown, when constituting the battery of the present invention, the separator portion is made of a glass mat or paper excellent in heat resistance, a thermosetting resin (engineering plastic) or the like, or a separator having a shutdown function. It is preferable to use in combination. The polyethylene film used in the small battery has a shutdown function that closes the micropores due to the shrinkage of the polyethylene film when the temperature rises due to external short circuit or overcharge. The shutdown start temperature of the polyethylene film is about 130 ° C., and the shutdown start temperature of the polypropylene film is about 150 ° C. However, when the temperature rises above this temperature, the separator melts, which may cause an internal short circuit. On the other hand, in the case of a glass mat or paper excellent in heat resistance, a thermosetting resin (engineering plastic), etc., it is possible to avoid an internal short circuit due to a temperature rise. As the battery temperature rises, the internal pressure of the power generation element accommodating chamber 1 rises, and the discharge valve 4 operates to discharge the electrolyte, thereby increasing the internal resistance of the power generation element 3 and stopping the battery reaction. It becomes.

Examples of the non-aqueous electrolyte include organic solvents (propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, dimethoxyethane and the like alone or in a mixture thereof) LiPF ₆ , LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ , An electrolytic solution in which an electrolyte salt such as LiSO ₃ CF ₃ or LiB (C ₂ O ₄ ) ₂ is dissolved can be used.

As the outer can 7, a pressure-resistant metal case made of a metal such as stainless steel, nickel-plated iron, nickel-plated copper or aluminum can be used. The discharge valve 4 may be configured by providing a weak point such as a cut groove in the can bottom 6. Here, the discharge valve 4 is designed to open when the pressure in the power generation element accommodation chamber 1 rises above the pressure resistance of the resettable safety valve 14 provided in the metal lid 8 and discharge the electrolyte. The That is, the operating pressure of the discharge valve 4 includes the temperature in the power generation element storage chamber 1 and the power generation element storage chamber 1 (in the above embodiment, the power generation element storage chamber 1 is composed of the outer can 7 and the metal lid 8). It is determined from the withstand pressure strength. For example, the resetting safety valve 14 may be designed to open at less than 10 kg / cm ² and the discharge valve 4 to be opened at 10 kg / cm ² or more. The outside of the discharge valve 4 is a waste liquid storage chamber 2, and the discharged electrolyte is collected in the waste liquid storage chamber 2. The volume of the waste liquid storage chamber 2 needs to be greater than or equal to the amount of electrolyte retained by the battery. The waste liquid storage chamber 2 does not necessarily need to be sealed with respect to the outside of the battery, but can be sealed and set to a negative pressure rather than the external pressure of the battery. Further, the waste liquid storage chamber 2 may be pre-arranged with a compound that can be brought into contact with the electrolyte solution and impart flame retardancy to the electrolyte solution, thereby making the discharged electrolyte solution flame retardant. And secondary ignition to the electrolyte can be prevented.

  As the insulating material used for the metal lid 8, rubber materials such as ethylene / propylene / diene rubber (EPDM) and fluorine rubber which are resistant to electrolyte and have a large elastic range are suitable.

  As described above, according to the present invention, the electrolyte discharge valve operates at a pressure where the internal pressure of the battery due to overcharge or external short circuit exceeds the limit pressure of the resettable safety valve, and the electrolyte inside the battery is discharged and electrolyzed. Move to the liquid receiver. Therefore, the battery reaction is stopped, and a dangerous state such as rupture or ignition can be avoided. This mechanism is not a control by a circuit or the like, but a safety mechanism of the battery itself. Therefore, safety is drastically improved without impairing the battery performance of the lithium secondary battery. The present invention is preferably applied to a stationary battery.

It is structural sectional drawing which shows one Example of this invention battery.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Power generation element storage chamber 2 Waste liquid storage chamber 3 Power generation element 4 Discharge valve 5 Vent valve 6 Can bottom 7 Exterior can 8 Metal lid 9 Positive electrode 10 Negative electrode 11 Separator 12 Positive electrode terminal 13 Negative electrode terminal 14 Resettable safety valve 15 Injection pipe

Claims (1)

A power generation element storage chamber for storing a power generation element including a positive electrode containing lithium iron phosphate, and a waste liquid storage chamber capable of storing an electrolyte solution,
The waste liquid storage chamber is provided in a lower portion of the power generation element storage chamber,
The power generation element storage chamber includes a discharge valve through which an electrolyte can flow from the power generation element storage chamber toward the waste liquid storage chamber.
The discharge valve suppresses the outflow of the electrolyte during normal use, and allows the outflow of the electrolyte when the internal pressure of the power generation element accommodating portion increases.
battery.

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