KR100715666B1 - Lithium ion secondary battery system - Google Patents

Abstract

The present invention relates to a lithium ion secondary battery system, and more specifically, a) a positive electrode having a positive electrode active material layer formed on the positive electrode current collector, b) a negative electrode having a negative electrode active material layer formed on the negative electrode current collector, c) the positive electrode and the negative electrode A reference electrode providing a relative voltage value for each, d) an electrolyte, e) a separator to isolate the anode, the cathode and the reference electrode, and f) a voltage between the anode and the reference electrode and between the cathode and the reference electrode. A lithium ion secondary battery system comprising a control circuit for controlling charging and discharging based on voltage information. The lithium ion secondary battery system according to the present invention independently controls the electrochemical reaction at the negative electrode and the electrochemical reaction at the positive electrode. The lithium ion secondary battery according to the present invention prevents an internal short circuit due to the lithium electrodeposition reaction generated at the negative electrode during overcharging, minimizes gas generation due to electrolyte decomposition occurring at the positive electrode, and exhibits excellent stability.

Description

Lithium ion secondary battery system {LITHIUM ION SECONDARY BATTERY SYSTEM}

1 is a schematic diagram of a lithium ion secondary battery system according to the present invention.

2 is a schematic view showing a driving principle of the lithium ion secondary battery system according to the present invention.

Figure 3 is a block diagram showing a preferred embodiment of the control circuit employed in the lithium ion secondary battery system of the present invention.

<Description of the reference numerals for the main parts of the drawings>

100: anode 101: positive electrode current collector 102: positive electrode active material layer

200: negative electrode 201: negative electrode current collector 202: negative electrode active material layer

300: reference electrode 400: separator / electrolyte 500: control circuit

501: first voltage sensing circuit 502: second voltage sensing circuit

503: input and output control circuit

The present invention relates to a lithium ion secondary battery system with increased safety.

A battery is a device that converts chemical energy into electrical energy by an electrochemical reaction, and these are largely classified into a primary battery and a secondary battery. Secondary batteries may be charged and discharged, and may include lithium ion batteries, nickel-cadmium batteries, and nickel-hydrogen batteries. Among them, the lithium ion secondary battery has a high driving voltage, unit volume and high energy density per weight of about 4V. For this reason, the lithium ion secondary battery is more advantageous than other batteries for slimming and weight reduction of portable electronic devices.

However, despite these advantages, lithium ion secondary batteries have a serious disadvantage in safety due to the inherent risk of explosion during charging due to the use of highly reactive lithium ions. The causes are summarized as internal short circuit due to lithium electrodeposition reaction occurring at the negative electrode and gas generation due to electrolyte decomposition occurring at the positive electrode.

In order to solve this problem, the introduction of a polymer separator using a solid electrolyte and the use of a protection circuit for controlling the charging voltage are used. Among these, the polymer separator is a method of minimizing the lithium electrode ionization reaction occurring at the negative electrode and electrolyte decomposition occurring at the positive electrode by lowering the reactivity of lithium ions, and in the case of the protection circuit, lithium is formed by setting an appropriate charge / discharge voltage and current during charging / discharging. A method of controlling an ion secondary battery. However, these methods are based on the optimization of the capacity ratio of the positive electrode and the negative electrode, and if the optimization is not provided, there is a limitation in securing safety by minimizing gas generation due to electrolyte decomposition occurring at the positive electrode and lithium electrodeposition reaction occurring at the negative electrode. Has

An object of the present invention is to provide a lithium ion secondary battery system with improved safety. In order to increase stability, the lithium ion secondary battery system according to the present invention independently controls the electrochemical reaction at the negative electrode and the electrochemical reaction at the positive electrode.

According to a preferred embodiment of the present invention, a) a positive electrode having a positive electrode active material layer formed on the positive electrode current collector, b) a negative electrode having a negative electrode active material layer formed on the negative electrode current collector, c) a relative voltage value for each of the positive electrode and the negative electrode A reference electrode provided, d) an electrolyte, e) a separator to isolate the anode, the cathode and the reference electrode, and f) the charge and discharge based on voltage information between the anode and the reference electrode and voltage information between the cathode and the reference electrode. Provided is a lithium ion secondary battery system comprising a control circuit for controlling a.

Hereinafter, the present invention will be described in more detail.

As described above, a problem of the conventional lithium ion secondary battery is that explosion risk is inherent due to internal short circuit caused by lithium electrodeposition reaction occurring at the negative electrode and gas generation due to electrolyte decomposition reaction generated at the positive electrode.

The present inventors employ a reference electrode in addition to the positive electrode and the negative electrode in a conventional lithium ion secondary battery, and by controlling the potential information between the positive electrode and the reference electrode and the potential information between the negative electrode and the reference electrode through a control circuit, respectively, The electrochemical reaction of and the electrochemical reaction at the anode are controlled independently. This provides both minimization of gas generation due to overcharging at the anode and prevention of internal short circuit due to lithium electrodeposition reaction at the cathode. Therefore, in order to solve the problems of the conventional lithium ion secondary battery, the present invention inserts a reference electrode in the lithium ion secondary battery, and controls the potential information between the positive electrode and the reference electrode, and between the negative electrode and the reference electrode through a control circuit, respectively Characterized in that.

In the lithium ion secondary battery system according to the present invention, a) a positive electrode having a positive electrode active material layer formed on a positive electrode current collector, b) a negative electrode having a negative electrode active material layer formed on a negative electrode current collector, c) a relative voltage value for each of the positive electrode and the negative electrode A reference electrode providing a reference electrode, d) an electrolyte, e) a separator to isolate the anode, the cathode and the reference electrode, and f) the voltage between the anode and the reference electrode and the voltage information between the cathode and the reference electrode. And a control circuit for controlling the discharge.

Hereinafter, with reference to the accompanying drawings will be described the present invention in more detail.

1 is a schematic view showing an example of a lithium ion secondary battery system according to the present invention. As shown in FIG. 1, the system includes an anode 100, a cathode 200, a reference electrode 300, a separator / electrolyte 400, and a control circuit 500.

The positive electrode 100 includes a positive electrode current collector 102 and a positive electrode active material layer 101 formed on the positive electrode current collector 102. Lithium metal oxide is used as a positive electrode active material. For example, lithium manganese oxide, lithium nickel oxide, lithium cobalt oxide, lithium cobalt oxide, lithium manganese nickel oxide, lithium cobalt manganese oxide and the like can be mentioned. The negative electrode 200 includes a negative electrode current collector 202 and a negative electrode active material layer 201 formed on the negative electrode current collector 202. As the negative electrode active material, a carbon-based material is used. For example, artificial graphite, natural graphite, coke and mixtures thereof can be mentioned. In general, the positive electrode active material and the negative electrode active material (commonly referred to as "electrode active material") are coated on the current collector together with a conductive material for improving conductivity and / or a binder for adhering the electrode active material to the current collector. The selection of the conductive material and the binder may be appropriately selected depending on the type of electrode active material used, and these matters are well known to those skilled in the art of battery. If desired, additives (eg antioxidants, flame retardants, etc.) may be added.

The material that can be used as the reference electrode 300 is not particularly limited as long as it is a reference electrode that can be used in an organic electrolyte such as silver, gold, platinum, aluminum, or lithium metal. Preferably lithium metal. Lithium metal provides more direct information about the formation of dendrite that can occur at the cathode.

Lithium salt is used as said electrolyte. Examples of lithium salts that can be used include LiPF ₆ , LiBF ₄ , LiClO ₄ , Li (CF ₃ SO ₂ ) ₂ , LiCF ₃ SO ₃ , LiSbF ₆ or LiAsF ₆ or mixtures thereof.

The organic solvent in the electrolyte is not particularly limited as long as it is an organic liquid solvent commonly used in batteries and capacitors. For example, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, acetone, acetonitrile, n-methyl-2-pi Rollidone (NMP) or mixtures thereof.

The concentration of the lithium salt in the non-aqueous organic solvent used in the present invention is preferably 0.4M to 1.5M because the ion conductivity of the lithium salt is the highest in the above range.

The separator 400 electrically insulates the cathode and the reference electrode, and the anode and the reference electrode from each other, and provides a passage for moving ions. Examples of the separator 400 include polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyester nonwoven fabric, polyacrylonitrile porous separator, poly (vinylidene fluoride) hexafluoropropane copolymer porous separator, cellulose porous separator, kraft paper or rayon. Fiber, and the like.

The control circuit 500 includes a first voltage sensing circuit 501 for sensing a voltage between the anode 100 and the reference electrode 300, and a second sensing voltage between the cathode 200 and the reference electrode 300. And a voltage sensing circuit 502 and an input / output control circuit 503 for controlling input and output based on voltage information transmitted from the first voltage sensing circuit 501 and the second voltage sensing circuit 502.

2 is a schematic view showing a driving principle of the lithium ion secondary battery system according to the present invention. During charging and discharging, a normal cell voltage ΔVcell is formed by the anode 100 and the cathode 200, and at the same time, the anode voltage ΔV + and the cathode by the anode 100 and the reference electrode 300. The cathode voltage ΔV− is formed by the reference numeral 200 and the reference electrode 300. The positive voltage ΔV + is detected by the first voltage sensing circuit 501, and the negative voltage ΔV− is detected by the second voltage sensing circuit 502. The input / output control circuit 503 controls charging and discharging through a voltage limit condition set based on voltage information transmitted from the first voltage sensing circuit 501 and the second voltage sensing circuit 502. For example, the voltage limiting condition set in the input / output control circuit 503 is described. Under the condition of using lithium metal as a reference electrode, the minimum charge voltage of the negative electrode is defined to be 0 V or more relative to the reference electrode, and the positive electrode (lithium manganese oxide) is used. ) The maximum charging voltage is specified within the range of 4.3V or less reference electrode. In this case, the lithium ion secondary battery system can minimize the lithium electrodeposition reaction because the charge voltage can be adjusted above the potential (0 V relative to the lithium reduction potential) at which the lithium electrodeposition reaction occurs in the anode, and also the electrolyte decomposition reaction of the anode Gas generation can be minimized because the voltage can be controlled below the generated potential (4.3 V or more compared with the lithium reduction potential). As a result, the lithium ion secondary battery system can individually control the electrochemical reactions generated from the positive electrode and the negative electrode through the reference electrode 300 and the control circuit 500, thereby providing a lithium ion secondary battery with improved safety. do. For example, when the voltage information obtained from the first voltage sensing circuit 501 is suddenly changed, this means that the electrolyte decomposition reaction is being performed at the anode 100. In addition, when the voltage information obtained from the second voltage sensing circuit 502 is changed, this means that the lithium electrodeposition reaction occurs in the cathode 200. When an error occurs in any one or both of the voltage information obtained from the first voltage sensing circuit 501 and the voltage information obtained from the second voltage sensing circuit 502, the input / output control circuit 503 charges. The discharge will stop.

3 is a block diagram showing a preferred embodiment of the control circuit. As shown in FIG. 3, the first voltage sensing circuit 501 includes a first voltage detector 5011, a first reference voltage unit 5012, a first comparator 5013, and a first amplifier unit ( 5014). The first voltage detector 5011 detects a voltage between the anode 100 and the reference electrode 300. The first reference voltage unit 5012 generates a predetermined constant voltage (hereinafter, "constant voltage"). The voltage detected by the first voltage detector 5011 and the constant voltage generated by the first reference voltage unit 5012 are transferred to the first comparator 5013, where the voltage difference is calculated. Thereafter, the calculated voltage difference is amplified by the first amplifier 5014 and transferred to the control CPU 5035 of the input / output control circuit 503.

The second voltage sensing circuit 502 includes a second voltage detector 5021, a second reference voltage 5022, a second comparator 5023, and a second amplifier 5024. The second voltage detector 5021 detects a voltage between the cathode 200 and the reference electrode 300. The second reference voltage portion 5022 generates a predetermined constant voltage (hereinafter, "constant voltage"). The voltage detected by the second voltage detection unit 5021 and the constant voltage generated by the second reference voltage unit 5022 are transferred to the second comparison unit 5023, where the voltage difference is calculated. Thereafter, the calculated voltage difference is amplified by the second amplifier 5024 and transferred to the control CPU 5035 of the input / output control circuit 503. On the other hand, when lithium metal is used as the reference electrode 300, the second reference voltage unit 5022 and the second comparison unit 5023 may be omitted. This is because the ideal voltage difference between the reference electrode 300 and the cathode 200 is almost " 0 ".

The input / output control circuit 503 includes a third voltage detector 5031, a third reference voltage unit 5032, a third comparator 5033, a third amplifier 5034, and a control CPU 5035. And an input / output switch 5036. The third voltage detector 5031 detects an external electromotive force (cell voltage during discharge) during charging. The third reference voltage unit 5032 generates a predetermined constant voltage (hereinafter, "constant voltage"). The voltage detected by the third voltage detection unit 5031 and the constant voltage generated by the third reference voltage unit 5032 are transmitted to the third comparison unit 5033, where the voltage difference is calculated. Thereafter, the calculated voltage difference is amplified by the third amplifier 5034 and transferred to the control CPU 5035. The control CPU 5035 includes voltage information ΔV + of the first voltage sensing circuit 501, voltage information ΔV− of the second voltage sensing circuit 502, and a voltage from the third amplifier 5034. The input / output switch 5036 is controlled based on the information {ΔV _{charge / cell} (cell voltage at _charge ), simply a cell voltage (ΔV _cell )).

Hereinafter, the present invention will be described in more detail by way of example, but the scope of the present invention is not limited by these examples.

Preparation Example: Manufacturing a Lithium Ion Secondary Battery Including a Reference Electrode

A lithium metal oxide positive electrode according to the present invention was prepared as follows. Lithium manganese oxide and acetylene black as a conductive agent were dried for at least 48 hours in a vacuum atmosphere at 80 ° C. to remove moisture contained in the compound as much as possible. 95% by weight of the lithium manganese oxide and 5% by weight of the conductive agent were sufficiently mixed in a high speed mixer for 30 minutes. 6.6 parts by weight of the vinylidene fluoride-hexafluoro propylene copolymer as a binder was added to the N-methylpyrrolidone solution, 85 parts by weight of the mixed powder was added to 12% by weight of the obtained mixed solution, and the resultant was a slurry having a predetermined viscosity. Stir for about 2 hours intermittently until. The slurry was cast using a doctor blade on a 15 μm thick aluminum current collector to vary the blade gap to 50 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, and then in an oven at 100 ° C. Drying for hours completely removed N-methylpyrrolidone to prepare a positive electrode with various electrode capacities.

Graphite-based carbon negative electrode according to the present invention was prepared as follows. Artificial graphite and acetylene black, which is a conductive agent, were dried for at least 48 hours in a vacuum atmosphere at 80 ° C. to remove moisture contained in the compound as much as possible. 95% by weight of the artificial graphite and 5% by weight of the conductive agent were sufficiently powder mixed in a high speed mixer for 30 minutes. When 6.6 parts by weight of vinylitene fluoride-hexafluoropropylene copolymer as a binder was added to 12% by weight of the mixed solution added to the N-methylpyrrolidone solution, 85 parts by weight of the mixed powder was added, and the resultant was a slurry having a predetermined viscosity. Stir for about 2 hours intermittently. The slurry was cast on a copper current collector having a thickness of 15 μm using a doctor blade with a blade gap of 50 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm and then dried in an oven at 100 ° C. for 12 hours. N-methylpyrrolidone was completely removed to prepare electrodes having various capacities.

The positive and negative electrodes prepared above were laminated in order as shown in FIG. 1 with various thickness combinations, and then a lithium metal plate having a copper metal terminal was inserted as a reference electrode. This was impregnated under vacuum with an organic electrolyte in which 1M LiBF ₄ was dissolved in a solvent in which ethylene carbonate and dimethyl carbonate were mixed in a 1: 1 ratio, and packaged using an aluminum pouch.

Example 1 Configuration of a Lithium Ion Secondary Battery System

The lithium ion secondary battery combines the electrode capacity ratios of the positive electrode: the negative electrode to about 1.5: 1, 2: 1, 1: 2, and assembled after the assembly in the manner shown in the preparation example, as shown in Figure 1 Connected to the control circuit. In the input / output control circuit of FIG. 1, the positive electrode maximum charging voltage is set to 4.3 V relative to the reference electrode, and the negative electrode minimum charging voltage is set to 0.1 V relative to the reference electrode.

Comparative Example 1

A lithium ion secondary battery including a reference electrode was constructed in the same manner as in Example 1 except that no control circuit was applied.

Experimental Example 1

The batteries configured in Example 1 and Comparative Example 1 were charged at a current density of 0.1 mA / cm ² at a constant current by setting the charging voltage to 4.3 V, and the voltages between the respective reference electrodes and the electrodes were measured using a voltmeter. The results are shown in Table 1.

Anode / Cathode Electrode Capacity Ratio Reference electrode / anode voltage (ΔV +) Reference electrode / cathode voltage (ΔV-) Cell voltage (ΔVcell) Example 1 1.5: 1 4.2V 0.1 V 4.1V 2: 1 4.0V 0.1 V 3.9 V 1: 2 4.3 V 0.1 V 4.2V Comparative Example 1 1.5: 1 4.3 V 0.0V 4.3 V 2: 1 4.3 V 0.0V 4.3 V 1: 2 4.4 V 0.1 V 4.3 V

As shown in Table 1, Example 1 including the reference electrode and the control circuit limits the positive charge voltage to 4.3 V or less to minimize electrolyte decomposition regardless of the positive electrode / cathode electrode capacity ratio. It can be seen that 0.1V is maintained at 0.0V or more in which lithium electrodeposition reaction occurs. On the other hand, in Comparative Example 1, which does not include a control circuit, the maximum charge voltage of the positive electrode is charged to 4.4 V or more, which is expected to cause electrolyte decomposition, according to the electrode / capacity ratio of the positive electrode and the negative electrode, and the negative electrode reaches 0.0 V where lithium electrodeposition reaction occurs. It can be seen that.

According to the present invention, by inserting a reference electrode, and independently control the voltage information of the positive electrode and the negative electrode, to prevent the internal short circuit caused by the lithium electrodeposition reaction, and also to minimize the decomposition of the electrolyte due to overcharge, it has a high safety A lithium ion secondary battery is provided.

Claims (9)

a) a positive electrode having a positive electrode active material layer formed on a positive electrode current collector, b) a negative electrode having a negative electrode active material layer formed on a negative electrode current collector, c) a reference electrode providing a relative voltage value for each of the positive electrode and the negative electrode, d) an electrolyte, e) a separator for isolating the anode, the cathode and the reference electrode, and f) a control circuit for controlling charging and discharging based on voltage information between the anode and the reference electrode and voltage information between the cathode and the reference electrode. Lithium ion secondary battery system. 2. The apparatus of claim 1, wherein the control circuit comprises: a first voltage sensing circuit for sensing a voltage between an anode and a reference electrode, a second voltage sensing circuit for sensing a voltage between a cathode and a reference electrode, and the first voltage sensing circuit; And an input / output control circuit for controlling the input / output based on the voltage information transmitted from the second voltage sensing circuit. The lithium ion secondary battery system of claim 1, wherein the reference electrode is formed of a material selected from the group consisting of silver, gold, platinum, aluminum, and lithium metal. The lithium ion secondary battery system of claim 1, wherein the reference electrode is formed of lithium metal. The lithium ion secondary battery system of claim 1, wherein the cathode active material used in the cathode active material layer is lithium metal oxide, and the anode active material used in the anode active material layer is graphite carbon. 3. The voltage detecting circuit of claim 2, wherein the first voltage sensing circuit detects a voltage between an anode and a reference electrode, a first reference voltage section generating a constant voltage, and a voltage detected by the first voltage detecting section. And a first comparator for comparing the constant voltage generated by the first reference voltage part, and a first amplification part for amplifying a signal from the first comparator. 3. The voltage detecting circuit of claim 2, wherein the second voltage sensing circuit detects a voltage between the cathode and the reference electrode, a second reference voltage section generating a constant voltage, and a voltage detected by the second voltage detecting section. And a second comparator for comparing the constant voltage generated by the second reference voltage part, and a second amplification part for amplifying a signal from the second comparator. 3. The display device of claim 2, wherein the input / output control circuit comprises: a third voltage detector configured to detect external electromotive force or cell voltage, a third reference voltage generator configured to generate a constant voltage, a voltage detected by the third voltage detector, and the third voltage detector; A third comparison section for comparing the constant voltage generated by the reference voltage section, a third amplifier section for amplifying a signal from the third comparison section, voltage information of the first voltage sensing circuit, and a second voltage sensing circuit. And a control CPU for generating a control signal based on the voltage information, the voltage information from the third amplifier, and an input / output switch for turning on / off charge / discharge in response to the control signal of the control CPU. Secondary Battery System. 3. The method of claim 2, wherein the reference electrode is a lithium metal plate, and the second voltage sensing circuit is configured to amplify a voltage detected by the second voltage detector and a second voltage detector for detecting a voltage between the cathode and the reference electrode. Lithium ion secondary battery system, characterized in that consisting of two amplification unit.

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