JP2011124166A - Method for charging lithium-ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for charging a lithium-ion secondary battery that realizes reduction in charging time and improves the service life characteristics of the charging and discharging cycle, at the same time. <P>SOLUTION: In the method for charging the lithium-ion secondary battery where electrode group composed by winding a positive electrode and a negative electrode in which a lithium compound oxide with a layered crystal structure is used as a positive-electrode active material via a separator, and a non-aqueous electrolyte are housed in a battery case, a constant-current charging is performed repeatedly as constant current and voltage charging, the constant-current sequentially is diminished at each charging from initial charging and upper-limit voltage is made sequentially larger starting from the initial charging. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a charging method that realizes shortening of charging time and improvement of charge / discharge cycle life characteristics of a lithium ion secondary battery.

Conventionally, lithium ion secondary batteries having high voltage and high energy density have been widely used as power sources for electronic devices such as notebook computers, mobile phones, and AV devices. In a lithium ion secondary battery, for example, a carbon material capable of inserting and extracting lithium is used as a negative electrode active material, and a lithium-cobalt complex oxide (LiCoO ₂ ) having a layered crystal structure is used as a positive electrode active material. It has been.

  In recent years, as electronic devices have become smaller and higher in performance, there has been an increasing demand for higher capacity and longer life of lithium ion secondary batteries, and the frequency of use of electronic devices with the progress of the ubiquitous society. From the viewpoint of increasing the battery life, there is a great demand for shortening the battery charging time.

  For increasing the capacity, for example, it is conceivable to increase the utilization rate of the active material itself by setting the upper limit value of the charging voltage higher than the conventional 4.2 V.

However, when the upper limit value of the charging voltage is higher than 4.2 V, the constant current charging time becomes longer in the conventional constant current / constant voltage charging method.
As a method for improving the charge / discharge cycle life characteristics, conventionally, a method has been considered in which the charge current is reduced and the decrease in the cycle life characteristics due to the decrease in Li acceptability at the negative electrode due to the increase in density is considered. In addition, there is a method in which the upper limit value of the charging voltage is made lower than the conventional 4.2 V to suppress the cycle life characteristic deterioration associated with the decomposition reaction of the electrolytic solution. However, these methods increase the charging time, and it is very difficult to achieve both shortening the charging time and improving the cycle life characteristics.

  In addition to the above, for example, in a method of charging with a set of constant current pulses that gradually decrease, a charging method that reduces the charging current every time a predetermined cutoff voltage is reached has been proposed (for example, Patent Document 1). reference).

Japanese Patent Laid-Open No. 10-145579

  However, in Patent Document 1, the internal resistance is calculated based on the voltage change at the time of current interruption, and the voltage obtained by multiplying the internal resistance by a predetermined charging current is added to the cut-off voltage. Off voltage. For this reason, if the voltage change (internal resistance) at the time of interruption of current is large, the cut-off voltage becomes high and an overcharge state is established. As a result, cycle life characteristics may deteriorate.

By the way, a lithium ion secondary material using a lithium-containing composite oxide containing nickel and cobalt having a lower potential than lithium cobaltate or a composite oxide containing nickel, cobalt and manganese (hereinafter referred to as nickel-containing active material) as a positive electrode active material. In the battery, the constant current charging time is longer than the lithium ion secondary battery using lithium cobalt oxide as the positive electrode active material, and the ratio of the constant current charging time to the entire charging time is increased.

  Further, even in a battery system characterized by a charging voltage of 4.2 V or more for the purpose of increasing the capacity, the proportion of the constant current charging time is larger than that of a battery system having a conventional charging voltage of 4.2 V. .

  The present invention solves the above-mentioned conventional problems, and reduces the constant current charging time for a battery system having a large ratio of constant current charging in the constant current / constant voltage charging method, effectively shortening the charging time and charging / discharging. It is an object of the present invention to provide a method for charging a lithium ion secondary battery that can simultaneously improve cycle life characteristics.

  In order to achieve the above object, the present invention provides a method for charging a lithium secondary battery using a lithium composite oxide having a layered crystal structure as a positive electrode active material, and repeating constant current charging as constant current / constant voltage charging. Each charge is performed by decreasing the constant current from the first time and increasing the upper limit voltage sequentially from the first time so that the potential of the negative electrode does not reach lithium deposition during charging.

  ADVANTAGE OF THE INVENTION According to this invention, the charging method of the lithium ion secondary battery which can implement | achieve shortening charging time and charging / discharging cycle life characteristic improvement simultaneously can be provided.

Schematic longitudinal sectional view of a lithium ion secondary battery used in an embodiment of the present invention The flowchart which showed the charging method of this invention

The present invention is a charging method by constant current / constant voltage charging of a lithium ion secondary battery using a lithium-containing composite oxide having a layered crystal structure as a positive electrode active material. The constant current charging is repeatedly performed, and each charging is performed by gradually decreasing the constant current from the first time and increasing the upper limit voltage sequentially from the first time so that the potential of the negative electrode does not reach lithium deposition during charging. To do. That is, as shown in FIG. 2, a constant current charging step 1 until the voltage V ₁ is reached with the current I ₁ , and a constant current charging step until the voltage V ₂ is reached with the current I ₂ after the constant current charging step 1. 2, since the current _{I n} up to a constant current charging step n to reach the voltage _{V n, I 1> I 2} >...> I n>...> I n, and _{V 1 <V 2 <... <} V n <… <V _N (1 ≦ n ≦ N) is repeated in constant current charging in multiple steps, and after the constant current charging step N, up to a predetermined amount of electricity by constant voltage charging at the voltage V _N Charge. Also, if the battery voltage V begins to charge in the range of V _{n-1 <V} <V _n begins charging from the constant current charging step n to charge with a constant current I _n, since the current I _N The constant current charging is repeated by the above method until the constant current charging step N until the voltage V _N is reached, and after the constant current charging step N, charging is performed to a predetermined amount of electricity by constant voltage charging at the voltage V _N. .

Li-containing composite oxide containing nickel and cobalt and having a lower potential than LiCoO ₂ LiNi _x Co _y M _(1-xy) O ₂ (wherein M is Na, Mg, Sc, Y, Mn, Fe , Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B, and 0.3 ≦ x <1.0, 0 <y <0.4) The battery used in the above has a lower charging voltage profile than the battery in which the positive electrode active material is LiCoO ₂ , and the time required to reach the upper limit voltage during constant current charging is longer.

A battery system characterized by a charging voltage of 4.2 V or more has a longer charging time and a larger proportion of constant current charging time than a battery system having a conventional charging voltage of 4.2 V.

  According to the present invention, in the constant current / constant voltage charging method, the constant current charging time is reduced particularly in a battery system having a large proportion of constant current charging time, and the shortening of the charging time and improvement of the charge / discharge cycle life characteristics are realized at the same time. It is possible to provide a method of charging a lithium ion secondary battery that can be performed.

  Regarding the above charging method, in any constant current charging step n, the negative electrode Li acceptability is good when the battery voltage is 4.0 V or less, and in order to shorten the charging time in this region, 0.5 It or more. It is desirable to charge the battery so that the constant current gradually decreases from the first time and the upper limit voltage gradually increases from the first time.

  Regarding the above charging method, in any constant current charging step n, when the battery voltage is 4.0 V or higher, the negative electrode Li acceptability is reduced and Li is liable to precipitate, so that charging at 0.7 It or lower is desirable.

  By performing constant current charging in multiple steps as described above, the life characteristics can be improved and the charging time can be reduced.

  Here, the above-mentioned It represents a current and is defined as It (A) / X (h) = Rated capacity (Ah) / X (h). Here, X represents the time for charging or discharging electricity for the rated capacity in X hours. For example, 1 It means that the current value is the rated capacity (Ah) / 1 (h).

  According to the present invention, the constant current charging time can be shortened and the time required for full charging can be shortened, and excellent cycle life characteristics can be obtained in the charge / discharge cycle, thereby shortening the charge time and improving the cycle life characteristics. It can be realized at the same time.

  Examples of the present invention will be described in detail below, but the present invention is not limited to the examples.

  The cylindrical lithium ion secondary battery shown in FIG. 1 used in the charging method of the present invention was produced by the following procedure.

(Battery configuration)
The positive electrode plate 5, the negative electrode plate 6, and the separator 7 which isolate | separates both electrode plates were wound in the shape of a spiral, and the electrode group 4 was comprised. As the separator 7, a polypropylene microporous film having a thickness of 16 μm was used. This electrode group 4 was inserted into a bottomed cylindrical battery case 1 (diameter 18 mm, height 65 mm). At this time, insulating rings 8a and 8b were arranged above and below the electrode group 4, respectively. The nonaqueous electrolytic solution obtained above was injected into the battery case 1. The negative electrode lead 6 a drawn from the negative electrode plate 6 was welded to the inner bottom surface of the battery case 1, and the positive electrode lead 5 a drawn from the positive electrode plate 5 was welded to the lower surface of the battery lid 2. The opening end of the battery case 1 was caulked to the peripheral edge of the battery lid 2 via the gasket 3 to seal the opening of the battery case 1. In this way, a 18650 size cylindrical lithium ion secondary battery (diameter 18 mm, height 65 mm) was produced. Details of the production of the positive electrode plate 5, the negative electrode plate 6, and the non-aqueous electrolyte will be described below.

(1) Production of positive electrode plate The production method of the positive electrode is as follows. For example, first, 100 parts by weight of the positive electrode active material, 1.7 parts by weight of the binder polyvinylidene fluoride fluoride, and 2.5 parts by weight of the conductive agent acetylene black are mixed with the liquid components to prepare a positive electrode paste. Positive electrode paste 15μm thick
The positive electrode current collector made of the aluminum foil was coated on both surfaces and dried to form a positive electrode active material layer on both surfaces of the positive electrode current collector to obtain a plate-shaped positive electrode plate. Thereafter, this positive electrode plate was rolled and cut to obtain a strip-like positive electrode plate 5 (thickness 0.128 mm, width 57 mm, length 667 mm).

Examples of the positive electrode active material include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiCoNiO ₂ , LiCoMO ₂ , LiNiMO ₂ , LiCoNiMO ₂ (where M = Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu , Zn, Al, Cr, Pb, Sb and B), or a part of these lithium-containing compounds substituted with a different element.

A predetermined ratio of Co and Al sulfate was added to the NiSO ₄ aqueous solution to prepare a saturated aqueous solution. While stirring this saturated aqueous solution, an aqueous sodium hydroxide solution is slowly added dropwise, the saturated aqueous solution is neutralized, and a precipitate of hydroxide Ni _0.8 Co _0.15 Al _0.05 (OH) ₂ is precipitated by a coprecipitation method. Obtained. The resulting precipitate was filtered, washed with water and dried at 80 ° C. Lithium hydroxide monohydrate was added to this hydroxide so that the total number of moles of Ni, Co and Al and the number of moles of Li were equal, and heat treatment was performed in dry air at 800 ° C. for 10 hours. . In this manner, LiNi _0.8 Co _0.15 Al _0.05 O ₂ (hereinafter referred to as NCA) was obtained.

Examples of the binder include polytetrafluoroethylene (PTFE). Examples of the conductive material include carbon black, natural graphite, and artificial graphite. (2) Production of Negative Electrode Plate 100 parts by weight of graphite as a negative electrode active material and 0.6 weight of binder polyvinylidene fluoride fluoride Part, 1 part by weight of the thickener carboxymethylcellulose, and an appropriate amount of water were stirred with a double-arm kneader to obtain a negative electrode paste. This negative electrode paste was applied to both sides of a negative electrode current collector made of a copper foil having a thickness of 8 μm and dried to form a negative electrode active material layer on both surfaces of the negative electrode current collector, thereby obtaining a plate-shaped negative electrode plate. Thereafter, this negative electrode plate was rolled and cut to obtain a strip-shaped negative electrode plate 6 (thickness 0.155 mm, width 58.5 mm, length 745 mm).

(3) Preparation of non-aqueous electrolyte solution LiPF ₆ was dissolved at a concentration of 1 mol / L in a non-aqueous solvent in which ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate were mixed at a volume ratio of 1: 1: 8. Thus, a non-aqueous electrolyte was prepared.

  The following charge / discharge cycle life test was carried out using the cylindrical lithium ion secondary battery produced above. The cylindrical lithium ion secondary battery produced above was charged at a constant current of 0.5 It until the upper limit voltage reached 4.0 V, and then charged to an upper limit voltage of 4.2 V at a constant current of 0.3 It. After the constant current charge, the battery was charged at 4.2 V until the end current reached 0.02 It (constant voltage charge).

After charging in this way, it was paused for 20 minutes. Thereafter, the cylindrical lithium ion secondary battery was discharged at 1.0 It to a discharge end voltage of 2.5V.
The above charging / discharging was repeated 300 times.

  The procedure was the same as in Example 1 except that charging was performed at a constant current of 0.7 It until the upper limit voltage reached 4.0 V.

  The procedure was the same as in Example 1 except that charging was performed at a constant current of 0.7 It until the upper limit voltage reached 3.8 V, and thereafter charging was performed at a constant current of 0.5 It until reaching the upper limit voltage of 4.0 V.

Li ₂ CO ₃ , Co ₃ O ₄ , NiO and MnO ₂ are mixed so as to be Li _0.94 Ni _0.35 Mn _0.35 Co _0.35 O ₂ (hereinafter referred to as NMC) after firing, The active material obtained by firing at 900 ° C. for 10 hours is used for the positive electrode, charged at a constant current of 1 It until the upper limit voltage reaches 4.0 V, and then charged at a constant current of 0.7 It until the upper limit voltage reaches 4.2 V. Further, the same procedure as in Example 1 was performed except that the discharge end voltage was set to 3.0V.

Li ₂ CO ₃ and Co ₃ O ₄ are fired and mixed so as to be LiCoO ₂ (hereinafter referred to as Co), and the active material obtained by firing at 900 ° C. for 10 hours is used for the positive electrode, and the upper limit voltage is 4.0 V. The battery is charged with a constant current of 0.7 It until reaching the upper limit voltage, then charged with a constant current of 0.5 It until reaching the upper limit voltage of 4.3 V, and the discharge end voltage is set to 3.0 V. The procedure was carried out.

(Comparative Example 1)
The same procedure as in Example 5 was performed, except that charging was performed at a constant current of 0.7 It until the upper limit voltage of 4.2 V was reached.

(Comparative Example 2)
The same procedure as in Example 1 was performed except that charging was performed at a constant current of 0.3 It until the upper limit voltage of 4.2 V was reached.

(Comparative Example 3)
The same procedure as in Example 1 was performed except that the battery was charged with a constant current of 0.5 It until the upper limit voltage of 4.2 V was reached.

(Comparative Example 4)
The same procedure as in Example 1 was performed, except that charging was performed at a constant current of 0.7 It until the upper limit voltage of 4.2 V was reached.

(Comparative Example 5)
The same procedure as in Example 4 was performed except that charging was performed at a constant current of 0.7 It until the upper limit voltage of 4.2 V was reached.

(Comparative Example 6)
The same procedure as in Example 4 was performed except that charging was performed at a constant current of 1 It until the upper limit voltage of 4.2 V was reached.

(Comparative Example 7)
The procedure was the same as in Example 5 except that charging was performed at a constant current of 0.5 It until the upper limit voltage reached 4.3 V.

(Comparative Example 8)
The same procedure as in Example 5 was performed except that charging was performed at a constant current of 0.7 It until the upper limit voltage reached 4.3 V.

正極活物質にＣｏを用いた電池を定電流０．７Ｉｔで充電する一般的な仕様である比較例１と比べ、正極活物質にＮＣＡを用い０．３Ｉｔの定電流で充電する比較例２は、容量
維持率が大幅に向上したが、充電時間は大幅に長くなった。正極活物質にＮＣＡを用いた電池で、０．５Ｉｔの定電流で充電する比較例３は、比較例１と比べほぼ同じ充電時間であるが、容量維持率は若干低下した。さらに充電電流を大きくし０．７Ｉｔの定電流で充電する比較例４は、充電時間は短縮されているが、容量維持率が大幅に低下した。これら比較例からも分かるように、充電時間短縮するために充電電流を大きくすると、負極Ｌｉ受入れ性が低下し容量維持率の低下に繋がる。

Compared with Comparative Example 1, which is a general specification for charging a battery using Co as a positive electrode active material at a constant current of 0.7 It, Comparative Example 2 using NCA as a positive electrode active material and charging at a constant current of 0.3 It is The capacity maintenance rate has been greatly improved, but the charging time has become significantly longer. A battery using NCA as a positive electrode active material and charging in Comparative Example 3 with a constant current of 0.5 It had substantially the same charging time as Comparative Example 1, but the capacity retention rate was slightly reduced. In Comparative Example 4 in which the charging current was further increased and charging was performed at a constant current of 0.7 It, although the charging time was shortened, the capacity retention rate was significantly reduced. As can be seen from these comparative examples, when the charging current is increased in order to shorten the charging time, the negative electrode Li acceptability is lowered, leading to a decrease in the capacity retention rate.

  In Example 1, charging is performed at a constant current of 0.5 It at 4 V or less where the Li acceptability of the negative electrode is good, and charging is performed at a constant current of 0.3 It to 4.2 V at 4 V or more where the Li acceptability of the negative electrode is reduced. Thus, the charging time can be shortened with almost no decrease in capacity maintenance rate.

  However, with the aim of further shortening the charging time, in Example 2 where charging was performed at a constant current of 0.7 It at 4 V or less and charging to 4.2 V at a constant current of 0.3 It was performed at 4 V or more, a decrease in capacity maintenance rate was also observed. . Therefore, in Example 3, the battery was charged up to 3.8 V with a constant current of 0.7 It, then charged up to 4.0 V with a constant current of 0.5 It, and then charged up to 4.2 V with a constant current of 0.3 It. By sequentially decreasing the current value in this way, it is possible to further shorten the charging time without greatly reducing the capacity maintenance rate.

  When NMC is used for the positive electrode, it can be seen from the results of Comparative Examples 5 and 6 that the capacity retention rate decreases when the charging time is shortened by the conventional method. In Example 4, the charging time can be shortened compared to Comparative Example 5, and a substantially equivalent capacity retention rate is obtained.

  Even in the case where Co is used for the positive electrode and the battery is charged to a high voltage of 4.2 V or higher, the results of Comparative Examples 7 and 8 show that the capacity retention rate decreases when the charging time is shortened by the conventional method. In Example 5, the charging time can be shortened compared to Comparative Example 7, and a substantially equivalent capacity retention rate is obtained.

  As can be seen from the above results, in the battery system using the Ni-containing positive electrode that is charged with a constant current for a longer time than in the past and in the battery of the high voltage specification, the charging method of the present invention is used to shorten the charging time and cycle. Improvement of life characteristics can be realized at the same time.

  A lithium ion secondary battery employing the charging method of the present invention is suitably used as a power source for electronic devices such as portable devices and information devices.

DESCRIPTION OF SYMBOLS 1 Battery case 2 Battery cover 3 Gasket 4 Electrode group 5 Positive electrode 5a Positive electrode lead 6 Negative electrode 6a Negative electrode lead 7 Separator 8a, 8b Insulation ring

Claims (3)

  In a charging method of a lithium ion secondary battery using a lithium composite oxide having a layered crystal structure as a positive electrode active material, constant current charging is repeatedly performed as constant current and constant voltage charging, and each charging is performed from the first constant current. A charging method for a lithium ion secondary battery, wherein the charging is performed by sequentially decreasing and increasing the upper limit voltage sequentially from the first time so that the potential of the negative electrode does not reach lithium deposition during charging. As the lithium-containing complex oxide of the general formula _{LiNi x Co y M (1-} x-y) O 2 ( wherein, M represents, Na, Mg, Sc, Y , Mn, Fe, Co, Ni, Cu, Zn 2. An element represented by at least one element selected from Al, Cr, Pb, Sb and B, wherein 0.3 ≦ x <1.0 and 0 <y <0.4). To charge the lithium ion secondary battery.   The method of charging a lithium ion secondary battery according to claim 1, wherein the upper limit charging voltage is 4.2V to 4.4V.

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