JP2013027243A - Battery pack and discharge control method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery pack including plural secondary battery cells capable of preventing deterioration of cycle characteristics due to movement of electrolyte.SOLUTION: A battery pack 1 includes: a battery pack 10 connected to an external load 2 in which plural battery blocks 11, which has one secondary battery cell 12 or plural secondary battery cells 12 connected to each other in series, and which are connected to each other in parallel; and a discharge control section 13 that individually turns ON/OFF the connection with each of the battery blocks 11 and the external load 2 respectively. When discharging the power from the battery pack 10 to the external load 2, the discharge control section 13 controls to turn OFF the connection between at least one of the battery blocks 11 and the external load 2 for a predetermined period of time and to turn ON the connection between the other battery blocks 11 and the external load 2.

Description

  The present invention relates to a battery pack and a discharge control method thereof. More specifically, the present invention relates to an improvement in a discharge method in a battery pack including an assembled battery in which a plurality of battery blocks each including one or a plurality of secondary battery cells are connected in parallel.

  The secondary battery has a drawback that the cycle characteristics deteriorate as the number of charge / discharge cycles increases. In particular, in a secondary battery using a negative electrode active material that causes volume expansion by occlusion of ions, the cycle characteristics may be significantly deteriorated. Known negative electrode active materials having a large volume expansion include, for example, alloy-based active materials and carbon materials used as negative electrode active materials for lithium ion secondary batteries. In particular, the alloy-based active material undergoes significant internal stress due to the significant expansion of its particles due to the occlusion of lithium ions, resulting in a decrease in cycle characteristics due to the alloy-based active material falling off the current collector or deformation of the negative electrode. Is likely to occur.

  In order to reduce internal stress generated when the alloy-based active material expands, a negative electrode made of an alloy-based active material and having a plurality of micron-sized columnar bodies formed on the surface of the negative electrode current collector is known (patent) Reference 1). In such a negative electrode, a gap is formed between a pair of adjacent columnar bodies. Such voids alleviate the generation of internal stress when the alloy-based active material expands. That is, even if the alloy-based active material expands significantly during charging, the generation of stress is suppressed by the voids formed between adjacent columnar bodies. As a result, the alloy active material is prevented from dropping from the negative electrode current collector, or the negative electrode is deformed.

  On the other hand, Patent Document 2 discloses a charge / discharge method in which a lithium ion secondary battery containing lithium manganese composite oxide as a positive electrode active material is charged / discharged in a voltage range of an upper limit voltage of 4.1 V or less and a lower limit voltage of 1.5 V. Disclose. As a result, changes in the crystal structure of the active material and side reactions between the active material and the non-aqueous electrolyte are suppressed, and attempts are made to suppress a decrease in battery capacity associated with charge / discharge.

  Patent Document 3 discloses that in an assembled battery including a plurality of secondary battery cells connected in series, in order to maintain the remaining capacity of each secondary battery cell within a predetermined range, the remaining capacity of each secondary battery cell is individually set. Disclosed is a charge control method to be adjusted. Specifically, the adjustment of the remaining capacity of the secondary battery cell is performed by measuring the remaining capacity of the secondary battery cell, and discharging the secondary battery cell when the obtained measurement result exceeds the above range. When the measured result is less than the above range, the measurement is performed by charging the secondary battery.

International Publication WO2008 / 026595 JP-A-1-294375 JP 11-299122 A

  As described above, in the secondary battery, as the number of times of charging / discharging increases, the cycle characteristics easily deteriorate. As a result of repeated studies on this cause, the present inventors have obtained the following knowledge. That is, when the secondary battery is charged / discharged, the electrolytic solution moves from the positive electrode to the negative electrode or vice versa, and thus the distribution of the electrolytic solution in the positive electrode and the negative electrode may vary. As a result, a part where the battery reaction proceeds sufficiently in the battery and a part where the battery reaction proceeds insufficiently may occur.

  In particular, in a lithium ion secondary battery, since the negative electrode absorbs lithium ions and expands greatly during charging, the electrolyte impregnated in the negative electrode is pushed out from the negative electrode. At the time of discharging, it is necessary to return the electrolytic solution in order to release and contract lithium ions. However, when the mobility of the electrolytic solution is insufficient, the distribution of the electrolytic solution in the negative electrode varies greatly. When the discharge proceeds in this state, lithium ions are released only in the portion where the electrolyte solution of the negative electrode exists, thereby causing variations in the structure of the negative electrode active material layer and promoting the deterioration of the negative electrode active material layer. The inventors have clarified that the cycle characteristics of the lithium ion secondary battery are deteriorated due to such a cause.

In particular, in a lithium ion secondary battery using a negative electrode active material that causes large volume expansion such as an alloy-based active material, the structure of the negative electrode active material layer tends to vary. Therefore, even if it is patent document 1 which ensures the space where an alloy type active material expand | swells by forming a columnar body of micron size on the surface of an electrical power collector, the fall of cycling characteristics may become remarkable.
In addition, none of Patent Documents 2 and 3 does not suppress the deterioration of the cycle characteristics accompanying the movement of the electrolytic solution.

  One of the objects of the present invention is to suppress deterioration of cycle characteristics associated with movement of an electrolyte in a battery pack including a plurality of secondary battery cells.

  The battery pack of the present invention includes an assembled battery in which a plurality of battery blocks including one secondary battery cell or a plurality of secondary battery cells connected in series are connected in parallel and connected to an external load, and each battery. A discharge control unit that individually turns ON or OFF the connection between the block and the external load, and the discharge control unit connects between at least one of the battery blocks and the external load when discharging from the assembled battery to the external load. Are sequentially turned off for a predetermined period to be paused, and the connection between at least one other battery block and an external load is turned on during the predetermined period.

Further, the discharge control method of the present invention is a discharge control method for a battery pack connected to an external load, and the battery pack includes one secondary battery cell or a plurality of secondary battery cells connected in series. Including a battery pack including a plurality of battery blocks connected in parallel, and at the time of discharging from the battery pack to an external load, the connection between at least one of the battery blocks and the external load is sequentially turned off for a predetermined period and stopped. During the predetermined period, the connection between at least one other battery block and an external load is turned on.
That is, the number of connections between the plurality of battery blocks and the external load is plural, and each connection is sequentially turned off for a predetermined period, and the remaining connections are turned on. At this time, a plurality of connections may be simultaneously turned OFF. For example, two or more connections may be simultaneously turned off for a predetermined period. In addition, the period of OFF of each connection may partially overlap so that one or more other connections are switched from ON to OFF while one or more connections are OFF.

  According to the present invention, a battery pack including a plurality of secondary battery cells and having excellent cycle characteristics is provided.

It is a basic diagram which shows typically the structure of one Embodiment of the battery pack of this invention. It is a flowchart for demonstrating each step in one Embodiment of the discharge control method of this invention. It is a side view which shows typically the internal structure of an electron beam type vacuum evaporation system. 2 is a longitudinal sectional view schematically showing a configuration of a negative electrode produced in Example 1. FIG.

The battery pack of the present invention is used by being connected to an external load, and a plurality of battery blocks including one secondary battery cell or a plurality of secondary battery cells connected in series are connected in parallel. And an assembled battery that discharges to the external load, and a discharge control unit that individually turns on or off the connection between each battery block and the external load.
When discharging from the assembled battery to the external load, the discharge controller turns off the connection between at least one of the battery blocks and the external load sequentially for a predetermined period and pauses at least the other of the battery block during the predetermined period. Discharge control is performed to turn on the connection between one and an external load. In this discharge control, at least one battery block whose connection to the external load is OFF (disconnected) is sequentially changed during the discharge period. Accordingly, at least one battery block whose connection with the external load is ON (connected) is also sequentially changed during the discharging period.

The discharge control unit, for example, turns on the connection with the external load of the battery block whose suspension has been terminated for each predetermined period, and connects the external load with at least one of the battery blocks other than the battery block whose suspension has been terminated. Set to OFF.
The discharge controller preferably performs the process of turning off all the battery blocks and the external load once each for a predetermined period of time only once, intermittently twice or more, or continuously twice or more. When the above process is intermittently performed twice or more, for example, after performing the process of turning off all the battery blocks and the external load once each for a predetermined period one or more times, all for a while Discharge the battery block. Thereafter, a step of turning off all the battery blocks and the external load once each for a predetermined period is further performed.
The discharge control unit preferably sets the number of battery blocks for turning off the connection with the external load to one for each predetermined period. It is preferable that the discharge control unit includes a timer that detects a predetermined period for suspending each battery block.

  By performing the discharge control as described above, it is possible to suppress the deterioration of the cycle characteristics of the secondary battery cells constituting the battery block for each battery block. Therefore, it is possible to efficiently suppress the deterioration of the cycle characteristics of all the secondary battery cells in the battery pack.

  In addition, in the secondary battery cell in the battery block in which the discharge to the external load has been suspended for a predetermined period by the discharge control as described above, for example, the electrolyte pushed out from the negative electrode during charging returns to the negative electrode again, Dispersion of electrolyte is eliminated. Thereby, a battery reaction advances uniformly in the whole area of a negative electrode active material layer. As a result, variations in the structure of the negative electrode active material layer are less likely to occur, deterioration of the negative electrode active material layer is suppressed, and deterioration in cycle characteristics of the secondary battery cell is suppressed.

  The secondary battery cell is a lithium ion secondary battery including a negative electrode including a negative electrode active material that causes volume expansion by occlusion of lithium ions, and the predetermined period is preferably in the range of 10 seconds to 5 hours. The negative electrode active material that causes volume expansion by occlusion of lithium ions is preferably at least one selected from a carbon material and an alloy-based active material. By using a lithium ion secondary battery as the secondary battery cell, the effect of performing the discharge control is increased.

  The battery pack of the present invention further includes a voltage detection unit that detects an open circuit voltage and a closed circuit voltage of the assembled battery, and the discharge control unit detects a closed circuit from the open circuit voltage in a predetermined charging state detected by the voltage detection unit. It is preferable to correct the discharge end voltage based on the change to the voltage. By changing the discharge end voltage according to the open circuit voltage and the closed circuit voltage of the assembled battery together with the discharge control, deterioration of the positive electrode and the negative electrode in the secondary battery cell is further suppressed.

  Next, an embodiment of a battery pack and a discharge control method of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram schematically showing the configuration of one embodiment of the battery pack of the present invention. FIG. 2 is a flowchart for explaining each step in the embodiment of the discharge control method of the present invention.

  The battery pack 1 of this embodiment shown in FIG. 1 is electrically connected to an external load 2 and an external power source 3, and includes an assembled battery 10, switches SWa, SWb, SWc, a discharge control unit 13, and a switching circuit 14. The voltage measuring unit 15 and the exterior body 16 are provided. The assembled battery 10 has three battery blocks 11a, 11b, 11c connected in parallel (these may be collectively referred to as “battery block 11”), discharges to the external load 2, and external power 3 is charged. The switches SWa, SWb, and SWc turn on or off the connection between the battery blocks 11a, 11b, and 11c in the assembled battery 10 and the external load 2 or the external power source 3 independently. The discharge control unit 13 performs control so that the connection by the switches SWa, SWb, and SWc is individually turned on or off. The switching circuit 14 switches the electrical connection between the assembled battery 10 and the external load 2 or the external power source 3. The voltage measuring unit 15 measures the open circuit voltage (OCV) and the closed circuit voltage (CCV) of the assembled battery 10.

  Note that turning on the switches SWa, SWb, and SWc means that the battery blocks 11a, 11b, and 11c are connected to the external load 2 or the external power source 3 so as to be energized. To turn off the switches SWa, SWb, and SWc is to release the energized connection between the battery blocks 11a, 11b, and 11c and the external load 2 or the external power source 3, respectively.

  The external load 2 is connected to the assembled battery 10 via the discharge control unit 13 and the switching circuit 14. The connection between the external load 2 and the assembled battery 10 is turned ON or OFF by the switching circuit 14. By turning on the connection with the assembled battery 10, the assembled battery 10 is discharged to the external load 2. The external load 2 may be connected to an electric circuit in the battery pack 1 by a connector connection, or may be connected by another connection method such as an outlet connection.

  Examples of the external load 2 include an electronic device, an electric device, a transport device, a work device, and a power storage device that use the battery pack 1 as a main power source or an auxiliary power source. Examples of the electronic device include a personal computer, a mobile phone, a mobile device, a portable information terminal, a portable game device, and the like. Examples of the electric device include a vacuum cleaner and a video camera. Examples of the machine tool include a power tool and a robot. Examples of the transportation device include an electric vehicle, a hybrid electric vehicle, a plug-in HEV, and a fuel cell vehicle. Examples of the power storage device include an uninterruptible power supply.

  The external power supply 3 is connected to the assembled battery 10 via the discharge control unit 13 and the switching circuit 14. By turning on the connection with the assembled battery 10, the assembled battery 10 is charged by the external power source 3. The external power supply 3 may be connected to an electric circuit in the battery pack 1 by a connector connection, or may be connected by another connection method such as an outlet connection.

  In the battery pack 1, when the switch SW1 of the switching circuit 14 is connected to one terminal (terminal A), the assembled battery 10 is connected to the external load 2 via the discharge control unit 13 to form a discharge circuit. At this time, discharge from the assembled battery 10 to the external load 2 is performed. When the switch SW1 of the switching circuit 14 is connected to the other terminal (terminal B), the assembled battery 10 is connected to the external power source 3 via the discharge control unit 13 to form a charging circuit. At this time, the battery pack 10 is charged by the external power source 3. Connection of the switch SW1 to the terminal A or the terminal B is controlled by the discharge control unit 13. That is, the discharge control unit 13 of the battery pack 1 controls both the discharge circuit and the charging circuit.

  In the battery block 11, three secondary battery cells 12 are connected in series. However, the number of secondary battery cells 12 in the battery block 11 is not particularly limited, and may be one or more. When there are a plurality of secondary battery cells 12, these secondary battery cells 12 are connected in series.

  Although the secondary battery cell 12 is not particularly limited, a secondary battery in which a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolytic solution are accommodated in a battery case can be used. Among these, the discharge control method of the present invention is suitable for a secondary battery using a negative electrode active material that expands and contracts due to insertion and extraction of ions. As such a secondary battery, for example, a positive electrode including a lithium-containing composite oxide as a positive electrode active material, a negative electrode including a negative electrode active material that expands and contracts due to insertion and extraction of lithium ions, a polyolefin porous separator, And a lithium ion secondary battery including a non-aqueous electrolyte. In the lithium ion secondary battery, examples of the negative electrode active material that repeatedly expands and contracts include carbon materials and alloy-based active materials.

  Examples of the carbon material include graphites such as natural graphite and artificial graphite. The alloy-based active material is a substance that occludes lithium by alloying with lithium and repeats occlusion and release of lithium under the negative electrode potential of the lithium ion secondary battery. Specific examples thereof include silicon-based active materials such as silicon, silicon oxide, silicon nitride, and silicon alloy, and tin-based active materials such as tin, tin oxide, tin alloy, and tin compounds. Among the negative electrode active materials described above, the effect of improving the cycle characteristics of the assembled battery 10 provided in the battery pack 1 becomes even more remarkable by using the secondary battery cell 12 containing an alloy-based active material having a large volume change. .

  The form of the secondary battery cell 12 is not particularly limited, and a battery in which the wound electrode group is accommodated in a cylindrical battery case or a rectangular battery case, and an electrode group in which the wound electrode group is formed into a flat shape is a rectangular battery case. Examples include a battery that is housed, a battery in which a stacked electrode group is housed in a coin-type battery case, a rectangular battery case, or a battery case made of a laminate film.

  The discharge controller 13 controls the switches SWa, SWb, and SWc to individually turn on or off the connection between the battery block 11 and the external load 2. The discharge controller 13 is configured as a processing circuit including a microcomputer having a central processing unit (CPU) and a microprocessor (MPU), an interface, a timer, and the like.

  Further, the discharge control unit 13 includes a storage unit (not shown). The storage unit is preliminarily input with a program for charging / discharging, a reference numerical value for executing the program, and the like. The program includes a program for executing the discharge control method of the present embodiment. Various memories can be used as the storage unit, and examples include a read only memory (ROM), a random access memory (RAM), and a nonvolatile flash memory. The discharge control unit 13 performs a calculation based on the program and the reference value input to the storage unit, and controls charging / discharging timing and conditions based on the calculation result.

  The discharge control method of the present embodiment by the discharge control unit 13 will be described with reference to FIG. In the case of FIG. 2, although the process of S0-S11 is implemented once, the process of S2-S10 may be intermittently performed twice or more, and the process of S2-10 may be performed twice or more continuously. Good.

  In step S0, the discharge control method of this embodiment starts, and at the same time, the voltage measurement unit 15 detects the open circuit voltage (OCV) of the assembled battery 10, and outputs the detection result to the storage unit of the discharge control unit 13 as needed. To do. For example, a voltmeter can be used as the voltage measuring unit 15. The detection of the open circuit voltage of the assembled battery 10 in step S0 is performed in a state where the switch SW1 is disposed at a neutral position where the switch SW1 is not connected to both the terminal A and the terminal B and the switches SWa, SWb and SWc are turned on. ON / OFF of each switch is controlled by the discharge control unit 13. Simultaneously with the detection of the open circuit voltage of the assembled battery 10 by the voltage measurement unit 15, the process proceeds to step S1.

  In step S <b> 1, the discharge control unit 13 receives the detection result of the open circuit voltage of the assembled battery 10 from the voltage measurement unit 15, and connects the switch SW <b> 1 on the terminal A side in the switching circuit 14. Thereby, discharge from the assembled battery 10 of the battery pack 1 to the external load 2 is started.

  In step S1, the voltage measurement unit 15 detects the closed circuit voltage of the assembled battery 10 after a lapse of a minute time (Δt) after the switch SW1 is connected to the terminal A side, and the detection result is stored in the discharge control unit 13. Output to the part at any time. The discharge control unit 13 receives an input of the detection result to the storage unit, and is set in advance if necessary based on the detection result and the detection result of the open circuit voltage of the assembled battery 10 obtained in step S0. Correct the discharge end voltage. The detection of the closed circuit voltage of the assembled battery 10 is performed in a state where all the switches SWa, SWb, and SWc are turned on.

  Specifically, the end-of-discharge voltage correction by the discharge control unit 13 is performed as follows. The discharge control unit 13 subtracts the detection result of the open circuit voltage of the assembled battery 10 from the detection result of the closed circuit voltage of the assembled battery 10 input to the storage unit to obtain a change ΔV between the closed circuit voltage and the open circuit voltage. When ΔV is large, it is assumed that the polarization resistance increases and the capacity of the assembled battery 10 is reduced. In this state, if discharge is performed up to a preset discharge end voltage, overdischarge is likely to occur. By performing the control for correcting the discharge end voltage based on the change ΔV, the deterioration of the positive electrode and the negative electrode is suppressed, and the deterioration of the cycle characteristics of the assembled battery 10 is further suppressed.

  When such control is performed, the relationship between the change ΔV of the assembled battery 10 and the capacity of the assembled battery 10 in a predetermined charging state is obtained through experiments, and the obtained experimental results are converted into a data table and stored in the discharge control unit 13. Enter in the department. The discharge control unit 13 uses such a data table to perform correction to increase the discharge end voltage according to the change ΔV value. Such correction may be performed every time the discharge control method of the present embodiment is performed, but may be performed, for example, when the assembled battery 10 is charged by the external power source 3 and becomes fully charged.

  In step S1, the discharge time to the external power source 2 by the assembled battery 10 in a state where all the switches SWa, SWb, and SWc are turned on is not particularly limited, but partial ions are present in the negative electrode of the secondary battery cell 12. It is preferable to select from the range of 1 second to 10 hours in consideration of the time when the space where the electrolyte solution is not impregnated between the active material particles is generated due to the contraction of the active material particles due to the release. The discharge in step S1 can be referred to as a preliminary discharge process. Next, the process proceeds to step S2.

  In step S2, the discharge controller 13 turns off the switch SWa and turns on the switch SWb and the switch SWc. As a result, the battery block 11a and the external load 2 are disconnected from each other. However, since the battery blocks 11b and 11c and the external load 2 are connected, power is supplied from the assembled battery 10 to the external load 2. In such a state, the process proceeds to step S3.

  In step S3, the discharge pause time of the battery block 11a is detected. The detection of the discharge pause time is performed by a timer provided in the discharge control unit 13. That is, with the start of step S3, the discharge control unit 13 starts detecting the discharge pause time of the battery block 11a by the timer. The detection interval of time by the timer is appropriately set according to a predetermined period (reference time) set in advance for the discharge stop. The detection result by the timer is output to the discharge controller 13, and the process proceeds to step S4.

  In step S4, the discharge control unit 13 compares the detection result input from the timer with the reference time input in advance in the storage unit, and determines whether or not the discharge pause time of the battery block 11a has reached the reference time. Determine. When the discharge control unit 13 determines that the reference time has been reached (Yes), the process proceeds to step S5. When the discharge control unit 13 determines that the reference time has not been reached (No), the process returns to step S3, and detection by the timer is continued.

  When the secondary battery cell 12 is, for example, a lithium ion secondary battery, the secondary battery cell 12 in a charged state has its electrolyte solution pushed out from the negative electrode due to the negative electrode active material absorbing and expanding lithium ions. . When the discharge is started, the electrolytic solution pushed out from the negative electrode needs to return to the inside of the negative electrode. However, when the mobility of the electrolytic solution is insufficient or when the discharge current value is large, the dispersion of the distribution of the electrolytic solution in the negative electrode may increase. When discharging is continued for a long time in such a state, the release of lithium ions from the negative electrode to the positive electrode does not occur as a whole, but occurs only partially. As a result, when the structure of the negative electrode active material layer is partially changed, the negative electrode active material layer is further deteriorated, and the cycle characteristics of the secondary battery cell 12 are easily lowered.

  On the other hand, by providing a predetermined discharge quiescent time for each battery block 11, the secondary battery is discharged in the battery block 11 where the discharge is stopped without stopping the power supply from the assembled battery 10 to the external load 2. The re-impregnation (returning) of the electrolytic solution to the negative electrode of the battery cell 12 can proceed. By appropriately changing the discharge pause time and stopping each battery block 11 at least once, it is possible to suppress a change in the structure of the negative electrode active material layer.

  There is no particular limitation on the reference time for each pause in which the discharge of the battery block 11a is paused, but it is preferably selected from the range of 10 seconds to 5 hours, more preferably 10 seconds to 2 hours. By selecting the reference time from the above range, a sufficient amount of the electrolytic solution returns to the negative electrode in the secondary battery cell 12, the dispersion of the distribution of the electrolytic solution in the negative electrode is eliminated, and the negative electrode active material layer is deteriorated. It is suppressed.

  In step S5, the discharge controller 13 turns off the switch SWb and turns on the switch SWa and the switch SWc. As a result, the battery block 11b stops discharging, and the battery blocks 11a and 11c supply power to the external load 2. In this state, the process proceeds to step S6.

  In step S6, the discharge pause time of the battery block 11b is detected by a timer, and the process proceeds to step 7. The detection of the discharge pause time in step S6 is performed in the same manner as in step S3.

  In step S7, the discharge control unit 13 determines whether or not the discharge pause time of the battery block 11b has reached the reference time in the same manner as in step S4. When the discharge control unit 13 determines that the reference time has been reached (Yes), the process proceeds to step S8. When the discharge control unit 13 determines that the reference time has not been reached (No), the process returns to step S6, and detection by the timer is continued. The reference time of the battery block 11b may be the same as the reference time of the battery block 11a, and may be shorter or longer. However, it is preferable that the reference time be the same so that the discharge amount does not vary among the battery blocks 11.

In step S8, the discharge controller 13 turns off the switch SWc and turns on the switch SWa and the switch SWb. Thereby, the battery block 11c stops discharging, and the battery blocks 11a and 11b supply power to the external load 2. In this state, the process proceeds to step S9.
In step S9, the discharge pause time of the battery block 11c is detected by a timer. This detection is performed in the same manner as in steps S3 and S6. Then, the process proceeds to step S10.

  In step S10, the discharge controller 13 determines whether or not the discharge pause time of the battery block 11c has reached the reference time in the same manner as in steps S4 and S7. When the discharge control unit 13 determines that the reference time has been reached (Yes), the process proceeds to end S11, and the discharge control method of the present embodiment ends. If the discharge control unit 13 determines that the reference time has not been reached (No), the process returns to step S9, and the detection of the discharge pause time of the battery block 11c by the timer is continued.

  As described above, the steps S2 to S10 may be performed only once. However, while discharging from the assembled battery 10 to the external load 2, the steps S2 to S10 are intermittently performed twice or more or 2 times. You may carry out continuously more than once. Two or more intermittent implementations are, for example, alternately performing the processes of S2 to S10 and the discharge by the assembled battery 10 in a state where all the battery blocks 11 are turned on, each twice or more alternately. .

The voltage measuring unit 15 is connected to the electric circuit at a predetermined position in the battery pack 1, but may be disposed outside the battery pack 1.
The exterior body 16 accommodates the assembled battery 10, the switches SWa, SWb, SWc, the discharge control unit 13, the switching circuit 14, and the voltage measurement unit 15 therein. The material of the outer package 16 is not particularly limited, and a resin material, a rubber material, a metal material, a laminate film, or the like can be used.

Hereinafter, a description will be given of an experiment conducted in order to evaluate the importance of pause during discharge in a battery using an alloy-based active material as a negative electrode.
(Experimental example 1)
(1) Production of positive electrode N-methyl-2-pyrrolidone solution containing 96 parts by mass of positive electrode active material (LiNi _0.80 Co _0.15 Al _0.05 O ₂ ), ₂ parts by mass of natural graphite powder and 2 parts by mass of vinylidene fluoride was mixed, A positive electrode mixture slurry was prepared. The obtained positive electrode mixture slurry was applied to both surfaces of an aluminum foil (positive electrode current collector) having a thickness of 15 μm, and the obtained coating film was dried and rolled to produce a positive electrode having a thickness of 130 μm. The obtained positive electrode was cut into a width that can be inserted into a battery case of a 18650 cylindrical battery (diameter: about 18 mm, height: about 65 mm).

(2) Production of Negative Electrode Plate FIG. 3 is a side perspective view schematically showing the configuration of an electron beam vacuum deposition apparatus 20 (hereinafter referred to as “deposition apparatus 20”). FIG. 4 is a longitudinal sectional view schematically showing the configuration of the negative electrode 30 obtained in this example. In FIG. 4, only one surface of the negative electrode 30 is shown, but a plurality of columnar protrusions 32 are formed on the other surface, and one columnar body 34 is formed on the surface of each columnar protrusion 32. Has been. The columnar protrusion 32 is a protrusion whose inside is not hollow. The columnar body 34 is made of silicon oxide which is one type of alloy-based active material. A negative electrode active material layer 33 composed of a negative electrode current collector 31 and a plurality of columnar bodies 34 was produced as follows.

(2-1) Production of negative electrode current collector 31 Two forged steel rollers having a plurality of recesses (opening shape: rhombus) arranged in a staggered pattern on the surface are pressed so that the respective axes are substantially parallel. A nip portion was formed. A negative electrode current collector in which a plurality of columnar convex portions 32 are formed on both surfaces by passing an alloy copper foil HCL-02Z (manufactured by Hitachi Cable Ltd.) having a thickness of 26 μm through this nip portion at a linear pressure of 1000 N / cm. A body 31 was produced. Further, the columnar convex portions were roughened using a plating method on the current collector.

  The plurality of columnar protrusions 32 had an average height of 8 μm and were arranged in a staggered pattern at predetermined intervals.

(2-2) Formation of Negative Electrode Active Material Layer 33 The vapor deposition apparatus 20 includes a feed roller 22 around which the negative electrode current collector 31 is wound in advance, and transport rollers 23a, 23b, 23c, 23d that guide the negative electrode current collector 31. 23e and 23f, cans 24a and 24b having a cooling device (not shown) inside, and depositing an alloy-based active material on the surface of the columnar convex portion 32 of the negative electrode current collector 31 running on the surface, and the negative electrode current collector A take-up roller 25 that winds 31, vapor deposition sources 26 a and 26 b that store the raw material of the alloy-based active material, and a pair of shielding plates 27 that regulate the supply region of the alloy-based active material vapor to the surface of the negative electrode current collector 31. , 28, an oxygen nozzle (not shown) for supplying oxygen, a chamber 21 for accommodating these, a vacuum pump 29 for reducing the pressure inside the chamber 21, and an alloy-based active material accommodated in the vapor deposition sources 26a and 26b of An electron beam irradiation device (not shown) that irradiates the raw material with an electron beam to generate a vapor of the raw material of the alloy-based active material. The shielding plate 27 includes shielding pieces 27a, 27b, and 27c. The shielding plate 28 includes shielding pieces 28a, 28b, and 28c.

  In the vapor deposition apparatus 20, in the conveyance direction of the negative electrode current collector 31, a first vapor deposition region is formed between the shielding pieces 27a and 27b, a second vapor deposition region is formed between the shielding pieces 27b and 27c, and the shielding pieces 28c and 28b. A third vapor deposition region is formed therebetween, and a fourth vapor deposition region is formed between the shielding pieces 28b and 28a.

As an alloy-based active material raw material, scrap silicon (purity 99.9999%, manufactured by Shin-Etsu Chemical Co., Ltd.) was used and accommodated in evaporation sources 26a and 26b. After evacuating the chamber 21 to 5 × 10 ⁻³ Pa with the vacuum pump 29, oxygen was supplied from the oxygen nozzle into the chamber 21 to create an oxygen atmosphere with a pressure of 3.5 Pa. Next, the scrap silicon accommodated in the evaporation sources 26a and 26b was irradiated with an electron beam to generate silicon vapor. In the middle of the rise of silicon vapor, it mixed with oxygen to generate a mixed gas of silicon vapor and oxygen.

  On the other hand, the negative electrode current collector 31 is fed from the feed roller 22, and a mixture of silicon vapor and oxygen is vapor-deposited on the surface of the columnar convex portion 32 of the negative electrode current collector 31 running in the first vapor deposition region. 34a was formed. Next, a lump 34b was formed on the remaining surface of the columnar protrusion 32 of the negative electrode current collector 31 running in the second vapor deposition region and the surface of the lump 34a. Further, in the third and fourth vapor deposition regions, the masses 34a and 34b were formed on the surface of the columnar convex portion 32 on the surface opposite to the surface where the masses 34a and 34b were formed in the first and second vapor deposition regions.

  Next, the direction of conveyance of the negative electrode current collector 31 is reversed by reversing the rotation directions of the feed roller 22 and the take-up roller 25, and the lump 34 c is formed on the surfaces of the lumps 34 a and 34 b on both sides of the negative electrode current collector 31. , 34d were laminated. Thereafter, one round reciprocal vapor deposition is performed in the same manner, and a columnar body that is a laminated body of lumps 34a, 34b, 34c, 34d, 34e, 34f, 34g, and 34h on the surface of both columnar convex portions 32 of the negative electrode current collector 31. 34 was formed.

The columnar body 34 was supported by the surface of the columnar convex portion 32 and grew to extend outward from the negative electrode current collector 31. The columnar body 34 had a substantially cylindrical solid shape. The columnar body 34 had an average height of 20 μm and an average width of 40 μm. Further, when the amount of oxygen contained in the columnar body 34 was quantified by a combustion method, the composition of the columnar body 34 was SiO _0.25 . In this embodiment, the columnar body 34 has a columnar shape, but is not limited thereto, and may have a spindle shape, a prismatic shape, or the like. The three-dimensional shape of the columnar body 34 can be adjusted by selecting the incident angle of vapor to the negative electrode current collector 31, the thickness of the lump, the number of lump stacks, and the like.

  Prior to assembling the battery, the negative electrode active material layer 33 of the negative electrode 30 obtained above was filled with lithium for an irreversible capacity by vapor deposition. The negative electrode 30 after lithium deposition was cut into a width that could be inserted into a battery case of a 18650 cylindrical battery to produce a negative electrode plate.

(3) Preparation of non-aqueous electrolyte LiPF ₆ was dissolved at a concentration of 1.0 mol / L in a mixed solvent of ethylene carbonate and dimethyl carbonate in a volume ratio of 2: 8, and further, fluoroethylene carbonate was 10% by weight. This was added to prepare a non-aqueous electrolyte.

(4) Battery assembly Between the positive electrode plate obtained above and the negative electrode plate obtained above, a separator having a thickness of 20 μm (trade name: hypopore, polyethylene porous membrane, Asahi Kasei E-materials ( Winding type electrode group was manufactured by interposing the product manufactured by the company. One end of an aluminum lead was connected to the positive electrode current collector, and one end of a copper lead was connected to the negative electrode current collector. An upper insulating plate and a lower insulating plate were respectively attached to the wound electrode group. Next, the wound electrode group is accommodated in a bottomed cylindrical iron battery case, the other end of the aluminum lead is connected to a stainless steel sealing plate, and the other end of the copper lead is connected to the inner surface of the bottom of the battery case. Connected to.

  Next, a non-aqueous electrolyte was injected into the battery case by a decompression method. The battery case was hermetically sealed by caulking the open end of the battery case toward the sealing plate. Thus, a cylindrical lithium ion secondary battery having an outer diameter of 18 mm and a height of 65 mm was produced.

(5) Cycle test First, with respect to the battery obtained above, (a) to (g) were charged and discharged (25 ° C) for 300 cycles, and the total discharge capacity at the 300th cycle relative to the total discharge capacity at the first cycle. The percentage was found to be 83%.

(A) Constant current charging: current value 0.3C, charging end voltage 4.2V.
(B) Constant voltage charge: Voltage value 4.2V, charge end current 0.05C.
(C) Pause for 20 minutes (d) Constant current discharge: Current value of 0.75 C, 40 minutes.
(E) Pause for 30 minutes (f) Constant current discharge: Current value 0.75 C, discharge end voltage 2.5 V.
(G) Pause for 20 minutes

  For the battery produced in the same manner as described above, after charging (a) to (c) above, charging / discharging (f) to (g) is performed without performing steps (d) and (e) ( 25 ° C.) was repeated 300 cycles. When the percentage of the total discharge capacity at the 300th cycle with respect to the total discharge capacity at the first cycle was determined, the capacity maintenance ratio was 80%.

  From the above, it can be understood that by implementing the discharge control method according to the present invention, the deterioration of the cycle characteristics of the battery is suppressed. By carrying out the present invention, the non-aqueous electrolyte pushed out from the negative electrode during charging can return to the negative electrode during the rest, so that the dispersion of the non-aqueous electrolyte in the negative electrode can be eliminated. Conceivable.

  The battery pack of the present invention can be used for the same application as a conventional battery pack including a secondary battery such as a lithium ion secondary battery, in particular, an electronic device, an electric device, a machine tool, a transport device, a power storage device, etc. It is useful as a main power source or an auxiliary power source. Examples of the electronic device include a personal computer, a mobile phone, a mobile device, a portable information terminal, and a portable game device. Examples of the electric device include a vacuum cleaner and a video camera. Examples of the machine tool include an electric tool and a robot. Examples of the transportation device include an electric vehicle, a hybrid electric vehicle, a plug-in HEV, and a fuel cell vehicle. An example of the power storage device is an uninterruptible power supply.

DESCRIPTION OF SYMBOLS 1 Battery pack 2 External load 3 External power supply 10 Assembly battery 11 Battery block 12 Secondary battery cell 13 Discharge control part 14 Switching circuit 15 Voltage measurement part 16 Exterior body 20 Electron-beam-type vacuum evaporation apparatus 30 Negative electrode

Claims (9)

A battery pack connected to an external load,
A battery pack including a plurality of battery blocks including one secondary battery cell or a plurality of secondary battery cells connected in series and a connection between each battery block and the external load are individually turned on. Or a discharge controller that turns off,
The discharge control unit, during discharging from the assembled battery to the external load, pauses the connection between at least one of the battery blocks and the external load by sequentially turning off each predetermined period, and during the predetermined period A battery pack for turning on the connection between at least one other battery block and the external load.   The discharge control unit turns on the connection of the battery block that has finished the suspension with the external load for each predetermined period, and at least one of the battery blocks other than the battery block that has finished the suspension. The battery pack according to claim 1, wherein connection between the external load and the external load is turned off.   The discharge controller performs the process of turning off the predetermined period of time once for all the battery blocks and the external load, only once, intermittently twice, or continuously twice or more. The battery pack according to claim 1 or 2.   The said discharge control part is a battery pack of any one of Claims 1-3 which makes the number of the said battery block which turns off the connection with the said external load one for every the said predetermined period.   The battery pack according to claim 1, wherein the discharge control unit includes a timer that detects the predetermined period.   The secondary battery cell is a lithium ion secondary battery including a negative electrode including a negative electrode active material that causes volume expansion by occlusion of lithium ions, and the predetermined period is in a range of 10 seconds to 5 hours. The battery pack according to any one of 1 to 5.   The battery pack according to claim 6, wherein the negative electrode active material includes at least one selected from a carbon material and an alloy-based active material. A voltage detection unit for detecting an open circuit voltage and a closed circuit voltage of the assembled battery;
The discharge control unit corrects a discharge end voltage based on a change from the open circuit voltage to the closed circuit voltage in a predetermined charging state detected by the voltage detection unit. The battery pack according to item. A discharge control method for a battery pack connected to an external load,
The battery pack includes an assembled battery in which a plurality of battery blocks including one secondary battery cell or a plurality of secondary battery cells connected in series are connected in parallel,
At the time of discharging from the assembled battery to the external load, the connection between at least one of the battery blocks and the external load is sequentially turned off for a predetermined period to be paused, and at least the other of the battery block during the predetermined period A discharge control method for turning on a connection between one and the external load.

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