WO2016120917A1

WO2016120917A1 - Discharge control device and method for non-aqueous electrolyte secondary battery

Info

Publication number: WO2016120917A1
Application number: PCT/JP2015/004516
Authority: WO
Inventors: 夏彦向井
Original assignee: 三洋電機株式会社
Priority date: 2015-01-29
Filing date: 2015-09-07
Publication date: 2016-08-04
Also published as: JP2018041529A

Abstract

Within a predetermined time interval during discharging of a non-aqueous electrolyte secondary battery (10) containing graphite and silicon or a silicon compound in a negative electrode, this control device uses voltage variation dV and capacity variation dQ to detect dV/dQ and positions the inflection point of dV/dQ in the initial state of the non-aqueous electrolyte secondary battery to fall outside of a predetermined range of SOC use. Thereafter, as the charge-discharge cycles progress, the control device (12) sequentially detects the dV/dQ inflection point for the non-aqueous electrolyte secondary battery (10), sequentially detects the SOC corresponding to the inflection point, compares the detected SOC with the usage range, and when the SOC has shifted to be within the usage range, stops the discharging at this SOC. In the initial stage of the charge-discharge cycle, discharge control is carried out with a graphite utilization rate of 80% or greater and under 100%, and without using silicon or silicon compound.

Description

Nonaqueous electrolyte secondary battery discharge control apparatus and method

The present invention relates to a discharge control apparatus and method for a non-aqueous electrolyte secondary battery, and more particularly to discharge control for a non-aqueous electrolyte secondary battery for in-vehicle use.

In recent years, with the increasing importance of hybrid vehicles (HEV) and plug-in hybrid vehicles (PHEV), the need for higher input / output as well as higher capacity of in-vehicle secondary batteries is increasing.

As a non-aqueous electrolyte secondary battery for in-vehicle use, a lithium ion secondary battery (LIB) is generally used. In LIB, it is known that the input / output required for in-vehicle use is controlled by the thickness of the negative electrode plate, that is, the diffusion of lithium ions in the thickness direction, and thinning the negative electrode plate is effective for high input / output. Therefore, in order to achieve high capacity and high input / output at the same time, a negative electrode in which the electrode plate area is increased by mixing silicon or a silicon compound as a high capacity material with graphite has been proposed. .

Patent Document 1 describes a negative electrode material for a lithium secondary battery comprising a silicon particle nucleus and a carbon layer covering the surface of the silicon particle nucleus.

In addition, in Patent Document 2, when manufacturing a non-aqueous secondary battery in which a negative electrode active material is silicon, a silicon compound, or a composite material composed of silicon and a conductive material, the assembled battery has a negative electrode potential with respect to metallic lithium. Charging to terminate at a potential higher than 100 mV.

JP 2000-215887 A JP 2003-7342 A

Thus, a negative electrode in which carbon and silicon or a silicon compound are mixed is effective for increasing the capacity and increasing the input / output for in-vehicle use, but if too much of the end-of-discharge region is used, the silicon fine particles are charged. There is a problem in that deterioration of the battery characteristics is accelerated because the negative electrode expands and contracts due to the discharge, and the negative electrode expands and an unnecessary reaction with the electrolytic solution occurs.

That is, in a negative electrode in which carbon and silicon or a silicon compound are mixed, lithium ions are first released from carbon during discharge, and then lithium ions are released from silicon or silicon compound. Alternatively, the contribution of the release of lithium ions from the silicon compound increases, and the battery characteristics deteriorate.

Of course, it is theoretically possible to end the discharge before lithium ions are released from silicon or a silicon compound. However, it is difficult to determine an appropriate timing to end the discharge, and an unnecessary early timing is required. If the discharge is terminated at this point, the result is contrary to the demand for higher capacity and higher input / output.

The present invention has been made in view of the above-described conventional problems, and its purpose is to detect a discharge at a high speed, simply and reliably so as not to use an end-of-discharge area where the deterioration is accelerated. An object of the present invention is to provide a discharge control device and method for a nonaqueous electrolyte secondary battery that can be stopped to suppress deterioration while increasing capacity and increasing input / output.

The present invention is a discharge control device for controlling the discharge of a non-aqueous electrolyte secondary battery containing graphite and silicon or a silicon compound in a negative electrode, wherein the utilization rate of the graphite is 80% or more and less than 100% at the beginning of a charge / discharge cycle. And a control means for controlling the discharge stop of the non-aqueous electrolyte secondary battery without substantially using the silicon or silicon compound (utilization rate is 5% or less).

In one embodiment of the present invention, a voltage detection unit that detects a voltage V of the nonaqueous electrolyte secondary battery, a current detection unit that detects a current I of the nonaqueous electrolyte secondary battery, and the current detection unit A capacity change dQ at a predetermined time obtained based on the detection value; and a calculation means for calculating dV / dQ from the capacity change dV at the predetermined time obtained based on the detection value of the voltage detection means, The control means controls discharge stop based on dV / dQ calculated by the calculation means.

In another embodiment of the present invention, the control means controls discharge stop based on the inflection point of dV / dQ.

In yet another embodiment of the present invention, the control means stops discharging when the inflection point is calculated when the voltage of the non-aqueous electrolyte secondary battery is equal to or lower than a predetermined value.

In yet another embodiment of the present invention, the control means stops discharge when an inflection point is calculated in which the absolute value of the difference between dV / dQ in a control cycle exceeds a predetermined value.

In still another embodiment of the present invention, in the initial state of the non-aqueous electrolyte secondary battery, the inflection point exists outside a predetermined SOC usage range, and the control means detects the inflection detected. When the point exists within the use range, the discharge stop is controlled using the SOC corresponding to the inflection point.

In still another embodiment of the present invention, the predetermined time is not less than 1 ms and not more than 1 minute.

In still another embodiment of the present invention, the content ratio of the silicon or the silicon compound is greater than 0 and equal to or less than 10% (% by weight).

The present invention also relates to a discharge control method for controlling discharge of a non-aqueous electrolyte secondary battery containing graphite and silicon or a silicon compound in a negative electrode, wherein the utilization rate of the graphite is 80% or more and 100 at the initial stage of a charge / discharge cycle. The discharge stop of the nonaqueous electrolyte secondary battery is controlled so that the utilization rate of the silicon or silicon compound is 5% or less.

Further, the present invention detects dV / dQ using a voltage change dV and a capacity change dQ at a predetermined time during discharge of a nonaqueous electrolyte secondary battery containing graphite and silicon or a silicon compound as a negative electrode, The inflection point of dV / dQ in the initial state of the nonaqueous electrolyte secondary battery is positioned outside a predetermined use range of the SOC, and the dV / dQ of the nonaqueous electrolyte secondary battery is sequentially calculated, and the dV / The discharge is stopped when the inflection point of dQ is calculated.

According to the present invention, it is possible to suppress deterioration and increase the charge / discharge cycle life while increasing the capacity and input / output of the nonaqueous electrolyte secondary battery. The present invention can be suitably applied to a high-input / output non-aqueous electrolyte secondary battery in which an inflection point of dV / dQ is remarkably manifested, for example, a vehicle-mounted non-aqueous electrolyte secondary battery.

It is a block diagram of the configuration of the discharge control device of the nonaqueous electrolyte secondary battery of the embodiment. It is a graph which shows the voltage with respect to SOC of embodiment, and the change of dV / dQ. It is a processing flowchart of an embodiment.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings, taking a lithium ion secondary battery (LIB) as an example of a non-aqueous electrolyte secondary battery.

<Basic principle>
First, the basic principle of this embodiment will be described.

LIBs containing carbon such as graphite and silicon (Si) or silicon compounds (SiO) are proposed as negative electrodes because non-aqueous electrolyte secondary batteries for vehicles require high capacity and high input / output. Has been.

Silicon or a silicon compound is effective for making the negative electrode thin and large, but if lithium ions are released from silicon during discharge, the deterioration of the negative electrode is accelerated, so that the charge / discharge cycle life is ensured. As long as the discharge amount of lithium ions from silicon is as low as 10% or less, the discharge should be stopped. That is, at the initial stage of the charge / discharge cycle, the graphite utilization rate may be 80% or more and less than 100%, and the discharge may be stopped so that silicon or a silicon compound is hardly utilized (utilization rate is 5% or less). Even when the charge / discharge cycle progresses and the deterioration of graphite progresses and silicon or a silicon compound has to be used, the utilization rate may be limited as much as possible (for example, limited to about 10%). A technique for charging and discharging while limiting the utilization rate of graphite in the negative electrode to a certain level is known, but in this embodiment, silicon or a silicon compound is included in the graphite to increase the capacity, but silicon or a silicon compound is used. It should be noted that the discharge is controlled so as not to intentionally use as much as possible.

On the other hand, since carbon such as graphite and silicon or silicon compounds have different electrical characteristics, the discharge curve, specifically, the ratio dV / dQ between the voltage change dV and the capacity change dQ over a predetermined time, When lithium ions are sometimes released from silicon or silicon compounds, dV / dQ changes significantly, and becomes manifest as an inflection point.

Therefore, at the beginning of the charge / discharge cycle, the graphite utilization rate is set to 80% or more and less than 100%, and the discharge is stopped so as not to use silicon or a silicon compound, and thereafter, the inflection point of LIB dV / dQ. The discharge is stopped so as not to continue the discharge at the timing when this inflection point appears, and the deterioration of the negative electrode due to the release of lithium ions from silicon or silicon compounds is suppressed.

<Configuration>
Next, the configuration of the present embodiment will be described.

FIG. 1 is a configuration block diagram of a discharge control device for a nonaqueous electrolyte secondary battery in the present embodiment.

The nonaqueous electrolyte secondary battery 10 is LIB, and has a structure in which, for example, NCA (Li (Ni—Co—Al) O ₂ ) is used as a positive electrode, and graphite and silicon compound SiO (Si fine particles are dispersed in SiO ₂ as a negative electrode. C / SiO mixed). In addition, this invention is not limited to these structures, It can apply to LIB of the arbitrary structures containing graphite and silicon or a silicon compound as a negative electrode.

For example, as a positive electrode, a positive electrode active material containing a lithium transition metal composite oxide, a conductive agent, and a binder are each set to a predetermined weight ratio, mixed with a dispersion medium to prepare a positive electrode mixture slurry, and an aluminum foil Examples of lithium transition metal composite oxides that can be applied on both sides include lithium cobaltate, lithium manganate, lithium nickelate, lithium nickel manganese composite oxide, lithium nickel cobalt composite oxide, etc. Al, Ti, Zr, Nb, B, W, Mg can be used for these lithium transition metal composite oxides. Mo or the like may be added. As the conductive agent, carbon powders such as carbon black, acetylene black, ketjen black, and graphite may be used alone or in combination of two or more. Examples of the binder include a fluorine-based polymer and a rubber-based polymer. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), or modified products thereof as fluorine-based polymers, ethylene-propylene-isoprene copolymer, ethylene-propylene-butadiene copolymer as rubber-based polymers These may be combined, and these may be used alone or in combination of two or more. As the negative electrode, a negative electrode active material containing graphite and silicon or a silicon compound, a thickener, and a binder are set to a predetermined weight ratio, and dispersed in water to prepare a negative electrode mixture slurry. As the binder, PTFE or the like can be used as in the case of the positive electrode, but a styrene-butadiene copolymer (SBR) or a modified product thereof can also be used. Good. As the thickener, carboxymethyl cellulose (CMC) or the like can be used.

As the nonaqueous solvent (organic solvent) of the nonaqueous electrolyte, carbonates, lactones, ethers, ketones, esters and the like can be used, and two or more of these solvents can be mixed and used. . For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate, and chain carbonates such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate can be used. A mixed solvent of cyclic carbonate and chain carbonate may be used.

As the electrolyte salt of the non-aqueous electrolyte, LiPF ₆ , LiBF ₄ , LICF ₃ SO _{3 and the} like and mixtures thereof can be used. The amount of electrolyte salt dissolved in the non-aqueous solvent can be, for example, 0.5 to 2.0 mol / L.

As the separator, a polyolefin-based porous separator such as polypropylene or polyethylene can be used. A multilayer structure of polypropylene and polyethylene may be used, and a polymer electrolyte may be used as a separator.

The control device 12 includes a processor and a memory, and includes a current detection unit 120, a voltage detection unit 121, a dV / dQ calculation unit 122, and a discharge control unit 123 as functional blocks.

The current detector 120 and the voltage detector 121 detect the LIB discharge current and the terminal voltage, respectively.

The dV / dQ calculation unit 122 calculates dV / dQ during LIB discharge, in other words, a differential value of the discharge curve. Specifically, the dV / dQ calculation unit 122 is configured such that the voltage change dV at a predetermined time t from the detection voltage value of the voltage detection unit 121 and the capacity change at the predetermined time t from the discharge current value detected by the current detection unit 120. Minute dQ is detected, and dV / dQ is calculated using these.

The discharge controller 123 controls the charging / discharging of the LIB, and in this embodiment, controls the discharge stop timing based on dV / dQ. Specifically, when the inflection point of the dV / dQ value calculated by the dV / dQ calculation unit 122 is detected, the discharge control unit 123 stops the discharge at the detected SOC. If an inflection point is not detected and a preset discharge end voltage is reached, the discharge is stopped at that point.

The processor of the control device 12 executes a process for calculating dV / dQ, a process for detecting an inflection point of dV / dQ, and a process for setting a discharge stop timing according to a processing program stored in the program memory. To do.

<Inflection point shift with durability>
FIG. 2 shows changes in battery voltage and dV / dQ with respect to SOC of LIB in the present embodiment. In FIG. 2, the horizontal axis represents SOC (%), and indicates the charged state as a percentage when the fully charged state is 100. The left vertical axis is the voltage (V), and the right vertical axis is the change amount dV / dQ of the voltage V and the capacity Q every predetermined time t.

The initial SOC is high SOC, but the SOC value decreases at the end of discharge (that is, the end of discharge becomes closer to the right side in FIG. 2).

In FIG. 2, the graphs indicated by symbols a to d are dV / dQ. For example, paying attention to graph a, there is an inflection point where dV / dQ changes sharply when SOC is 10% to 20% at the end of discharge. To do. In the figure, there are a maximum point and a minimum point as inflection points from the larger SOC to the smaller SOC.

As described above, in a negative electrode in which graphite and SiO are mixed, lithium ions are first released from graphite during discharge, and then lithium ions are released from SiO. Since graphite and SiO have different electrical resistances, and (graphite) <(SiO), lithium ions are released from graphite for high-rate currents such as hybrid vehicles (HEV) and plug-in hybrid vehicles (PHEV). There is a significant change in dV / dQ due to the difference in electrical resistance between the time when lithium ions are released from SiO, and as a result, an inflection point appears in dV / dQ at the end of discharge.

In FIG. 2, the graph a → graph b → graph c → graph d changes as the charge / discharge cycle progresses or the storage time becomes longer. That is, as the charge / discharge cycle progresses or the storage time becomes longer, the inflection point of dV / dQ at the end of discharge, that is, the inflection point of dV / dQ inherent to SiO due to SiO shifts to the higher SOC side. I will do it.

Therefore, paying attention to the inflection point of dV / dQ inherent to SiO and monitoring the shift amount of the inflection point toward the high SOC side, quantitative evaluation of how much the LIB negative electrode has deteriorated Can do.

Specifically, for example, the dV / dQ inflection point dV / dQ inherent to SiO is designed to be located outside the SOC usage range (for example, a range of 20% to 80%) during LIB manufacturing. After that, the inflection point of dV / dQ inherent to SiO is detected, and the SOC corresponding to the detected inflection point is shifted to the use range where it should be outside the use range. In such a case, the discharge is stopped at the SOC so as to suppress acceleration degradation.

Here, at the initial stage of the charge / discharge cycle, the discharge is stopped when the utilization rate of graphite is 80% or more and less than 100%, for example, about 80%, and then the charge / discharge cycle proceeds to a predetermined number of times as described above. It is preferable to detect an inflection point of dV / dQ inherent to SiO and stop the discharge in accordance with the detected inflection point.

Further, in this embodiment, the inflection point of dV / dQ inherent to SiO is detected, but in order to distinguish it from other inflection points, the battery voltage is not more than a predetermined value, for example, the battery voltage is An inflection point at 3.5 V or less may be detected as a target inflection point. In FIG. 2, it should be noted that all the inflection points occur when the LIB voltage is 3.5 V or less.

The dV / dQ when detecting the inflection point is calculated from the voltage change dV and the capacitance change dQ within a predetermined time, and the predetermined time is 1 msec to 1 min, for example, 0.1 sec to 1 sec. Can do.

In this embodiment, the inflection point of dV / dQ inherent to SiO is detected. Specifically, dV / dQ (t1) at a certain time and dV / dQ (at the next detection time) It can be detected as an inflection point when the difference in t2) is larger than a predetermined value, that is, | dV / dQ (t1) −dV / dQ (t2) |> predetermined value (for example, 0.001V / Ah). .

Further, in the present embodiment, the content of silicon or silicon compound is not particularly limited, but may be greater than 0 and not more than 10%, for example, 3% to 5% by weight% with respect to graphite.

<Discharge control flow>
FIG. 3 is a flowchart of the discharge control process in the present embodiment.

First, at the time of manufacturing LIB, dV / dQ at the time of discharging is measured, an inflection point of dV / dQ inherent to silicon or a silicon compound is detected, and an SOC corresponding to the inflection point is a predetermined SOC of LIB. It sets so that it may become out of use range (S101). For example, when the SOC usage range of LIB is set to 20% to 80%, the content of silicon or a silicon compound is adjusted so that the SOC corresponding to the inflection point is located at about 10%.

Next, known charging / discharging is performed in the in-vehicle LIB (S102). That is, discharging is performed to supply power from the LIB to the drive motor in accordance with the traveling state of the automobile, and charging is performed by supplying power to the LIB by engine power or regenerative braking. The charging / discharging of LIB is performed within the SOC usage range (for example, 20% to 80%). That is, when the SOC of the LIB reaches 20%, the discharge is stopped. Further, at the initial stage of the charge / discharge cycle, the discharge is stopped so that the utilization rate of graphite is 80% or more and less than 100%, and SiO is not used.

Next, dV / dQ is calculated during discharge in a predetermined control cycle (S103). That is, the voltage change dV and the capacitance change dQ within a predetermined time are detected, and dV / dQ is calculated. The capacity change dQ is calculated from the discharge current within a predetermined time.

After calculating dV / dQ, an inflection point of dV / dQ is detected (S104). Specifically, an inflection point is detected when the absolute value of the difference between dV / dQ in a certain control cycle and dV / dQ in the next control cycle is greater than a predetermined value, for example, 0.001 V / Ah. At this time, it is confirmed that the LIB voltage is not more than a predetermined value, for example, 3.5 V or less, and only when it is not more than the predetermined value, it may be detected as an inflection point of dV / dQ inherent to silicon or silicon compound.

When the inflection point is detected (Y in S104), the discharge control unit 123 stops the discharge of the nonaqueous electrolyte secondary battery (S105). When the inflection point is not detected (N in S104) and the preset discharge end voltage is reached, the discharge is stopped at the preset discharge end voltage (Y in S106 and S105). If the preset discharge end voltage is not reached, the discharge is continued in S102 (N in S106). As shown in FIG. 2, as the charge / discharge cycle progresses or the storage time elapses, the inflection point of dV / dQ inherent to silicon or a silicon compound gradually shifts to the high SOC side. Therefore, even if the SOC corresponding to the inflection point is located outside the use range in the initial state, the SOC corresponding to the inflection point can be shifted to the use range over time. The inflection point of dV / dQ inherent to silicon or silicon compound means that lithium ions are released from the silicon or silicon compound. When charging and discharging in this region are repeated, the silicon particles become fine powder, and the negative electrode Deterioration proceeds at an accelerated rate due to the expansion of the liquid and the occurrence of an unnecessary reaction with the electrolyte.

Thus, by stopping the discharge at the SOC corresponding to the inflection point of dV / dQ inherent to silicon or silicon compound, the silicon particles become fine powder, which is caused by expansion of the negative electrode and generation of unnecessary reaction with the electrolytic solution. The acceleration of deterioration can be effectively suppressed.

In this embodiment, the discharge is controlled by paying attention to the inflection point of dV / dQ. Therefore, particularly in a hybrid vehicle, a plug-in hybrid vehicle, etc., relatively high input / output is required and the inflection is remarkable. This is particularly effective for applications where dots appear. Of course, the non-aqueous electrolyte secondary battery of this embodiment can also be applied to a drive power source of a mobile information terminal such as a mobile phone, a notebook computer, a smartphone, a tablet terminal, etc., particularly for applications that require high energy density. .

The present invention can be used for a non-aqueous electrolyte secondary battery.

DESCRIPTION OF SYMBOLS 10 Nonaqueous electrolyte secondary battery 12 Control apparatus 120 Current detection part 121 Voltage detection part 122 dV / dQ calculation part 123 Discharge control part

Claims

A discharge control device for controlling discharge of a nonaqueous electrolyte secondary battery containing graphite and silicon or a silicon compound in a negative electrode,
In the initial charge / discharge cycle, the utilization rate of the graphite is 80% or more and less than 100%;
A discharge control device for a non-aqueous electrolyte secondary battery, comprising: a control unit that controls discharge stop of the non-aqueous electrolyte secondary battery, wherein a utilization rate of the silicon or the silicon compound is 5% or less.
Voltage detecting means for detecting the voltage V of the non-aqueous electrolyte secondary battery;
Current detection means for detecting a current I of the non-aqueous electrolyte secondary battery;
A capacity change dQ in a predetermined time determined based on a detection value of the current detection means;
Calculating means for calculating dV / dQ from a capacity change dV in a predetermined time obtained based on a detection value of the voltage detecting means;
Further comprising
The discharge control device for a non-aqueous electrolyte secondary battery according to claim 1, wherein the control means controls discharge stop based on dV / dQ calculated by the calculating means.
3. The discharge control device for a non-aqueous electrolyte secondary battery according to claim 2, wherein the control means controls discharge stop based on the inflection point of dV / dQ.
4. The non-aqueous electrolyte secondary battery according to claim 3, wherein the control means stops the discharge when the inflection point is calculated when the voltage of the non-aqueous electrolyte secondary battery is a predetermined value or less. Discharge control device.
The non-aqueous electrolyte according to claim 3, wherein the control unit stops the discharge when an inflection point at which an absolute value of the difference between dV / dQ in a control period exceeds a predetermined value is calculated. Secondary battery discharge control device.
In the initial state of the non-aqueous electrolyte secondary battery, the inflection point exists outside a predetermined use range of the SOC,
The non-aqueous electrolyte according to claim 3, wherein the control unit controls the discharge stop using the SOC corresponding to the inflection point when the detected inflection point exists within the use range. Secondary battery discharge control device.
The discharge control device for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 6, wherein the predetermined time is not less than 1 ms and not more than 1 minute.
The discharge control device for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 7, wherein a content ratio of the silicon or the silicon compound is greater than 0 and 10% (wt%) or less.
A discharge control method for controlling the discharge of a nonaqueous electrolyte secondary battery containing graphite and silicon or a silicon compound in a negative electrode,
The discharge stop of the non-aqueous electrolyte secondary battery is controlled so that the utilization rate of the graphite is 80% or more and less than 100% in the initial charge / discharge cycle, and the utilization rate of the silicon or silicon compound is 5% or less. A discharge control method for a non-aqueous electrolyte secondary battery.
DV / dQ is detected using a voltage change dV and a capacity change dQ at a predetermined time during discharge of a non-aqueous electrolyte secondary battery containing graphite and silicon or a silicon compound as a negative electrode, and the non-aqueous electrolyte secondary battery The inflection point of dV / dQ in the initial state of is positioned outside the predetermined use range of the SOC,
Sequentially calculating the dV / dQ of the non-aqueous electrolyte secondary battery,
A discharge control method for a non-aqueous electrolyte secondary battery, wherein the discharge is stopped when the inflection point of dV / dQ is calculated.