JP2015201382A - Control method of secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charging/discharging control method capable of maintaining battery characteristics for a long time while preventing Lifrom moving to a non-opposite part in an all-solid type secondary battery.SOLUTION: A secondary battery includes: a positive electrode plate 210 including a cathode active material layer 212; a negative electrode layer 220 including an anode active material layer 222; and a solid layer 230 positioned between the positive electrode plate 210 and the negative electrode plate 220. The solid layer 230 is positioned in contact between the cathode active material layer 212 and the anode active material layer 222. An ECU 300 makes a charging/discharging device 400 charge the secondary battery to be a rate equal to or higher than 0.6 C without using a rate lower than 0.6 C, prevents Lifrom flowing out to non-opposite parts S2 and S3 and performs control to decrease the capacitance of the secondary battery or not to change the battery characteristics.

Description

  The present invention relates to a control method for an all-solid-state secondary battery, and more particularly to a charge / discharge control method for a secondary battery that maintains the characteristics of the secondary battery for a long period of time.

  2. Description of the Related Art In recent years, electric vehicles such as hybrid vehicles and electric vehicles that store electric energy used for traveling of a vehicle in a lithium ion secondary battery and rotate a motor generator using electric power stored during traveling are known.

Patent Document 1 (Japanese Patent Application Laid-Open No. 2011-238568) discloses that a liquid-type lithium ion secondary battery including an electrolytic solution is charged at a high rate, for example, charged for 5 seconds at a current value of 30 C, and discharged at a low rate, for example, 3 C. By combining the discharge for 50 seconds with the current value as one cycle and repeating 1000 cycles, the negative electrode active material moved from the facing portion facing the positive electrode active material to the non-facing portion located around the facing portion. A technique is disclosed in which lithium ions (hereinafter also referred to as Li ⁺ ) are returned to the opposing portion of the negative electrode active material layer to recover the battery capacity.

JP 2011-238568 A JP 2012-28024 A

Generally, the negative electrode active material layer of a lithium ion secondary battery has a facing part that faces the positive electrode active material layer, and a non-facing part that does not face the positive electrode active material layer at the periphery of the facing part. At the time of charging, Li ⁺ is not directly supplied to the non-opposing portion. However, since the Li ⁺ concentration gradient occurs between the facing portion and the non-facing portion in the negative electrode active material layer after charging, Li ⁺ diffuses from the facing portion to the non-facing portion when left in a charged state. There is a case. Li ^{+ that} has moved to the non-opposing portion is unlikely to be discharged because there is no opposing positive electrode active material layer. Therefore, when Li ⁺ moves from the facing portion to the non-facing portion, battery capacity is lost.

Patent Document 1 discloses a method of pulling back Li ⁺ diffused to a non-opposing part to a counter part in a liquid lithium ion secondary battery including an electrolytic solution. As a result, a reduction in capacity is suppressed to extend the life of the battery. However, this method is premised on a liquid secondary battery, and in an all-solid-state secondary battery in which a solid electrolyte is an ion transfer medium, there are portions where the Li ⁺ transfer characteristics are different from the liquid system, The charge / discharge control method for a liquid lithium ion secondary battery is not always applicable to an all-solid-state secondary battery.

For example, in an all solid state secondary battery, the diffusion of Li ⁺ as described above hardly occurs even when left in a charged state. In addition, the reaction may not occur if the current value is too low or too high (since Li ⁺ does not move), and once Li ⁺ moves to the non-opposing part, it is pulled back to the opposing part. It is not easy. When Li ⁺ is accumulated in the non-opposing section, Li ^+, which can contribute to the normal charging and discharging reactions is decreased, thereby changing the use region of the active material or a solid electrolyte, when it is not possible to exhibit stable cell properties may occur .

The present invention has been made in view of the above problems, and its object is to maintain the battery characteristics over a long period of time by suppressing the movement of Li ⁺ to the non-opposing portion in an all-solid-state secondary battery. It is in providing the charge / discharge control method which can be performed.

  The present invention is applied to a control method for a secondary battery including a positive electrode plate including a positive electrode active material layer, a negative electrode plate including a negative electrode active material layer, and a solid layer positioned between the positive electrode plate and the negative electrode plate. The negative electrode plate has, among the negative electrode active material layers, a negative electrode plate facing portion that faces the positive electrode active material layer, and a non-facing portion that does not face the positive electrode active material layer around the negative electrode plate facing portion. When charging the secondary battery, the secondary battery is charged without using a rate of less than 0.6C.

  In the following description, the unit “C” of the current value indicates a current value for charging or discharging the rated capacity of the battery in one hour. “CC (Constant Current)” indicates a constant current, and “CV (Constant voltage)” indicates a constant voltage.

The inventor has investigated in detail the relationship between the charge / discharge rate and the Li amount (charge amount) of the non-facing portion. When the charge rate is 0.6 C or higher, the charging reaction proceeds normally in the facing portion. Regardless, the present inventors have obtained a new finding that the diffusion (inflow) of Li ⁺ into the non-opposing portion is extremely small.

In the charge / discharge control method of the present invention, charging is performed without using a rate of less than 0.6C. As a result, it is possible to prevent the diffusion of Li ⁺ into the non-opposing portion during charging, and to suppress the capacity decrease and the characteristic change due to the diffusion of Li ⁺ into the non-facing portion.

It is a figure for demonstrating the secondary battery system with which the control method of the secondary battery of embodiment is applied. It is a figure explaining the relationship between the rate of charging / discharging in a general all-solid-state secondary battery, and the Li ^<+> amount of a non-facing part when it charges by the said rate for 30 minutes. It is a figure for demonstrating the outline | summary of the charge control of this Embodiment. 4 is a flowchart for explaining charging control processing performed by a control unit in the control system for a secondary battery according to the embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

[Overall configuration of secondary battery system]
FIG. 1 is a diagram for explaining a secondary battery system to which the secondary battery control method of the present embodiment is applied. Referring to FIG. 1, the secondary battery system includes a secondary battery 100, a charging / discharging device 400 that supplies power charged in the secondary battery 100, and a charging / discharging device 400 that supplies power to the secondary battery 100. ECU300 which performs charging / discharging is provided.

[Unit battery configuration]
FIG. 1 schematically shows a cross-sectional view of the unit battery 200. The secondary battery 100 generally includes a plurality of unit batteries 200. In FIG. 1, only one unit battery 200 is shown for simplicity. The unit battery 200 constituting the secondary battery 100 includes a positive electrode plate 210 including a positive electrode active material layer, a negative electrode plate 220 including a negative electrode active material layer, and a solid electrolyte layer (hereinafter referred to as a positive electrode plate 210 and a negative electrode plate 220). , Also referred to as a solid layer) 230.

  Among these, the positive electrode plate 210 includes a positive electrode current collector 211 and a positive electrode active material layer 212 that contacts the positive electrode current collector 211 and holds the positive electrode active material.

  The negative electrode plate 220 includes a negative electrode current collector 221 and a negative electrode active material layer 222 that contacts the negative electrode current collector 221 and holds the negative electrode material. The positive electrode current collector 211 and the negative electrode current collector 221 are each made of a metal such as aluminum or copper, and are electrically connected to the charging / discharging device 400, respectively.

  The solid layer 230 is provided at a position in contact with each of the positive electrode active material layer 212 and the negative electrode active material layer 222.

  The negative electrode plate 220 is provided around the facing portion S1 of the negative electrode plate 220 facing the positive electrode active material layer 212 and the facing portion S1 of the negative electrode plate 220 in the negative electrode active material layer 222, and faces the positive electrode active material layer 212. It has flange-shaped non-opposing portions S2, S3.

  An assembled battery can be configured by stacking a plurality of unit cells 200 in the same direction as the stacking direction of the positive electrode plate 210, the solid layer 230, and the negative electrode plate 220.

[Component materials of secondary batteries]
The positive electrode active material layer 212 includes a positive electrode active material, a conductive additive disposed adjacent to the positive electrode active material, and a solid electrolyte surrounding the positive electrode active material and the conductive additive. The solid electrolyte may be glass ceramics or sulfide glass around the positive electrode active material and the conductive additive. This glass ceramic is obtained by firing sulfide glass and has higher lithium ion conductivity than sulfide glass.

For example, the glass for glass sulfide was mixed with SiS ₂ , phosphorus pentasulfide (P ₂ S ₅ ), P ₂ S ₃ , and the like, and glass modifier lithium sulfide (Li ⁺ ₂ S). Later, it is obtained by quenching. Moreover, the lithium sulfide (Li ⁺ ₂ S) constituting the sulfide glass described above may be manufactured by any manufacturing method, and is used without particular limitation as long as it is industrially produced and sold. Can do.

  Further, the particle size of lithium sulfide is not particularly limited. Alternatively, the sulfide glass may be manufactured by mechanically milling a mixture of lithium sulfide and phosphorus pentasulfide as a starting material, or a mixture of simple phosphorus and simple sulfur instead of phosphorus pentasulfide. .

Furthermore, as the positive electrode active material, for example, lithium cobaltate (Li ⁺ CoO ₂ ) can be used. Moreover, as a conductive support material, carbon can be used, for example.

  The solid layer 230 formed between the positive electrode active material layer 212 and the negative electrode active material layer 222 is mainly composed of glass ceramics as a solid electrolyte. Note that sulfide glass may remain in the positive electrode active material.

  The negative electrode active material layer 222 includes a negative electrode active material and glass ceramics surrounding the negative electrode active material. Note that sulfide glass may remain around the negative electrode active material. The negative electrode active material may be graphite, Si, Sn, or the like.

  Although the conductive support material is provided in the positive electrode active material layer 212, the conductive support material is not necessarily provided. Further, although the conductive support material is not provided in the negative electrode active material layer 222, the conductive support material may be provided in the negative electrode active material layer 222.

The so-called all solid state secondary battery including the solid layer 230 between the positive electrode plate 210 and the negative electrode plate 220 has a solid electrolyte in a portion corresponding to the separator. The movement of the active material such as Li ⁺ is slow during charging / discharging. For example, the density difference due to the movement of the active material is unlikely to occur only by resting.

[Explanation of charge control]
FIG. 2 is a diagram for explaining the relationship between the charge / discharge rate in a general all solid state secondary battery and the amount of Li ^{+ in} the non-opposing portion when charged at that rate for 30 minutes.

In general, a negative electrode active material layer of a lithium ion secondary battery has a facing portion that faces the positive electrode active material layer and a non-facing portion that does not face the positive electrode active material layer extending to the periphery of the facing portion. At the time of charging, Li ⁺ is not directly supplied to the non-opposing portion. However, in the negative electrode active material layer after charging, a concentration gradient of Li ⁺ occurs between the facing portion and the non-facing portion. Therefore, if the liquid lithium ion secondary battery is left in a charged state, Li ⁺ May diffuse from the facing part to the non-facing part. Li ^{+ that} has moved to the non-opposing portion is unlikely to be discharged because there is no opposing positive electrode active material layer. Therefore, when Li ⁺ moves from the facing portion to the non-facing portion, battery capacity is lost.

According to the general knowledge in FIG. 2, Li ⁺ diffuses from the facing part to the non-facing part by setting the charging rate to a certain value (0.6 C) or more and the upper limit rate of reaction to 1.0 C or less. It turns out that it can charge so

Therefore, in the present embodiment, the all solid state secondary battery is charged using a rate of 0.6 C or higher without using a rate of less than 0.6 C (region D in FIG. 2). . Thus, charging can be performed while suppressing diffusion to the non-facing portions S2 and S3.
[Outline of charge control in this embodiment]
Next, the charge control method of the all solid state secondary battery of the present embodiment will be described with reference to FIGS.

  ECU 300 includes a CPU (Central Processing Unit), a storage device, and an input / output buffer (not shown). The ECU 300 inputs a signal from each sensor and outputs a control signal to each device, as well as a charge / discharge device 400 and the like. Control each device. Note that these controls are not limited to processing by software, and can be processed by dedicated hardware (electronic circuit).

  FIG. 3 is a diagram for explaining the outline of the charging control according to the present embodiment, in which the vertical axis indicates the current value rate (C) and the terminal voltage (V), and the horizontal axis indicates time (T). Indicated.

  Specifically, charge / discharge control of the secondary battery is performed using a constant current constant voltage control (CCCV charge control) method. Charging / discharging device 400 adjusts the power supplied to both electrodes of unit battery 200 in accordance with a control signal from ECU 300.

  First, in a region where the SOC is low, charging is performed using constant current control while maintaining the current rate at a constant value of 1.0 C, for example. In the constant current charging control CC that charges a large amount of current in a short time, charging is performed with a relatively large current in order to shorten the charging time as much as possible. In the constant current charge control CC, as shown in FIG. 3, the battery voltage increases as the charging progresses and the SOC increases (see curve F in FIG. 3).

  To shorten the charging time, a current as large as possible is preferable. However, if a large current is used with the margin for the upper limit approaching that it is close to full charge, if there is a sensor error, etc. There is a risk of charging. Overcharge promotes deterioration of the secondary battery 100.

  Therefore, when the voltage reaches a predetermined SOC that is close to full charge (time T1), ECU 300 prevents constant overcharge and maintains the storage performance of the secondary battery. Switch to control CV.

  In the constant voltage charge control CV, the current rate is gradually decreased from 1.0 C with the passage of time while maintaining the voltage value at a constant value.

  As described above, the constant current charge control CC is performed until the SOC is almost fully charged in the middle of the charge, and then the overcharge is performed by the constant current constant voltage control (CCCV charge control) method for switching to the constant voltage charge control CV. While preventing, the charging time can be shortened.

  In the present embodiment, as described with reference to FIG. 2, charging is performed at 0.6 C or more in order to suppress diffusion to the non-facing portions S2 and S3. Therefore, charging is stopped at the time T2 when the current rate is reduced to 0.6 C (cut current) by the constant voltage charging control CV.

  FIG. 4 is a flowchart illustrating a charging method according to the present embodiment. In the flowchart shown in FIG. 4, the processing is realized by executing a program stored in advance in ECU 300 at a predetermined cycle. Alternatively, for some steps, it is also possible to construct dedicated hardware (electronic circuit) and realize processing.

  Referring to FIG. 4, at S10, ECU 300 uses charge / discharge device 400 to determine whether or not the secondary battery needs to be charged. When charging is required (YES in S10), ECU 300 performs charge control using charging / discharging device 400 for the secondary battery. If charging is not required (NO in S10), the process is returned.

  In S20, ECU 300 determines whether constant current charge control CC or constant voltage charge control CV is to be performed based on the state of charge of the secondary battery. If SOC is less than predetermined value α (YES in S20), ECU 300 determines that constant current charging control CC is to be performed, and advances the process to S30.

  In S30, ECU 300 sets a predetermined current I rate of 0.6C or more. For example, in the initial state, a rate of 1.0 C may be set. In S40, ECU 300 starts charging by constant current charging control CC using the rate set in S30.

  On the other hand, when SOC reaches predetermined value α (NO in S20), ECU 300 advances the process to S50, and switches the charging method from constant current charging control CC to constant voltage charging control CV. In the constant voltage charge control CV, the rate of the current I is gradually decreased from 1.0 C with the passage of time while maintaining the voltage value at a constant value.

In S60, ECU 300 determines whether or not the rate of current I is less than 0.6C. When the rate of current I is 0.6 C or higher (NO in S60), ECU 300 returns the process to S50 and continues charging. When the rate of current I is less than 0.6 C (YES in S60), ECU 300 proceeds to S70 in order to prevent the diffusion of Li ⁺ into non-opposing portions S2, S3. Stop charging operation.

As described above, according to the secondary battery control method of the present embodiment, the charging operation is performed at a rate of 0.6 C or higher, and therefore, the non-battery electrode disposed around the facing portion S1 of the negative electrode plate 220 is not. It is possible to charge while suppressing diffusion of Li ⁺ into the facing portions S2 and S3.

Thereby, a decrease in the amount of Li ^{+ that} can contribute to a normal charge / discharge reaction is suppressed, a decrease in the capacity of the secondary battery can be suppressed, and the battery characteristics can be maintained over a long period of time.

  While the vehicle is running, for example, in order to secure the regenerative braking force, there may occur a state where power generation by regenerative control cannot be stopped even if the current I rate is less than 0.6C. In such a case, the generated current may be consumed and discarded as heat by a resistance circuit or an auxiliary circuit connected to the charging system while stopping the charging operation. Alternatively, after temporarily charging other power storage elements such as a capacitor and an auxiliary battery that can store the generated current, the main battery may be charged with a current I rate of 0.6 C or more.

Finally, the secondary battery control method according to the embodiment of the present invention will be summarized. Referring to FIG. 1, the secondary battery control method according to the embodiment includes a positive electrode plate 210 including a positive electrode active material layer 212, a negative electrode plate 220 including a negative electrode active material layer 222, and a positive electrode plate 210 and a negative electrode plate 220. And a solid layer 230 positioned therebetween. The solid layer 230 is positioned so as to be in contact with each other between the positive electrode active material layer 212 and the negative electrode active material layer 222. The ECU 300 charges the charging / discharging device 400 at a rate of 0.6C or higher without using a rate of less than 0.6C, thereby preventing Li ⁺ from flowing out to the non-facing portions S2 and S3. Thus, charging control is performed so as not to reduce the capacity of the secondary battery. ECU 300 also performs charge control so as not to change the battery characteristics of the secondary battery.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  100 assembled battery, 200 unit battery, 210 positive electrode plate, 211 positive electrode current collector, 212 positive electrode active material layer, 220 negative electrode plate, 221 negative electrode current collector, 222 negative electrode active material layer, 230 solid layer, 300 ECU, 400 charge / discharge apparatus.

Claims (1)

A control method of a secondary battery comprising a positive electrode plate including a positive electrode active material layer, a negative electrode plate including a negative electrode active material layer, and a solid layer positioned between the positive electrode plate and the negative electrode plate,
The negative electrode plate has, among the negative electrode active material layers, a negative electrode plate facing portion that faces the positive electrode active material layer, and a non-facing portion that does not face the positive electrode active material layer around the negative electrode plate facing portion. ,
The control method includes a step of charging the secondary battery without using a rate of less than 0.6 C when charging the secondary battery.

Images