JP3992007B2 - Lithium secondary battery - Google Patents

Description

  The present invention relates to an active material for a lithium secondary battery and a lithium ion secondary battery using a non-aqueous electrolyte.

  With the development of the information society, the spread of personal computers and mobile phones is expected to increase in the future, but along with this, the increase in energy density and capacity of batteries, which are power sources for portable devices, will increase. It is requested. A lithium secondary battery using a non-aqueous electrolyte has a high battery voltage and a high energy density, and therefore has been actively developed, and some batteries have been put into practical use. However, the Mn spinel material currently used as the positive electrode material has several problems in practical use.

  The first is deterioration of cycle life. The spinel type oxide has trivalent manganese ions having Yarn-Teller instability, so that the capacity is remarkably deteriorated when charging and discharging are repeated. The second problem is elution, in which Mn starts to dissolve in the electrolytic solution, resulting in performance degradation. Third, there is a safety problem in that the positive electrode generates heat or fires in the event of a short circuit or collapse.

  These are problems that can be solved by increasing the structural stability of the positive electrode active material. Although it has been difficult to solve these problems with conventional positive electrode materials, several attempts have already been reported.

According to Japanese Patent Laid-Open No. 6-187933 by Technology Finance, spinel oxide Li _{1 + x} Mn _2−x O ₄ (0 ≦ x <1.33) in which the composition ratio of Li and Mn is changed is used as an active material. By using it, cycle life is improved and elution is prevented. Also, the same attempt is made by substituting with Co instead of Mn. However, such a method has a problem that the initial capacity itself is reduced.

Moreover, if by Mori Energy Corporation published patent (No. flat 9-147867), in spinel type oxides increases the composition ratio to Mn of Li, Li ₁ was replaced with a transition metal element such as more Co and Cr and Mn _{+ x M z Mn 2-xz} O 4 (0 ≦ x <0.33, M:. Co, transition metal elements such as Cr), and by using as the positive electrode active material, thereby improving the cycle life characteristics However, the life of 1000 cycles or more required for practical use has not been obtained.

  As described above, attempts have been made to stabilize the crystal structure of the positive electrode material by various methods so as to extend the battery life, prevent elution, and improve safety. However, if the battery life is extended, the battery capacity decreases, and conversely, if the battery capacity is increased, a problem arises in safety, and heat is generated or ignition occurs when an internal short circuit occurs. was there. The present invention provides a spinel oxide positive electrode active material and a method for producing the same for supplying a long-life and safe high-capacity battery.

In order to achieve the object of the present invention, an oxide having a spinel structure defined by a chemical formula of Li _{1 + x} Mn _2−x O ₄ (0 <x <1.33) is used in addition to Li, Mn, and oxygen. A positive electrode material to which at least one kind of element is added is used. The composition ratio of Li and Mn is Li /
If referred to as the Mn ratio, increasing the Li / Mn ratio acts to reduce the lattice constant, thereby stabilizing the crystal structure.

  This acts to improve cycle characteristics and prevent elution, and brings about an effect of improving battery life characteristics. However, increasing the Li / Mn ratio results in a decrease in the theoretical capacity, and the actual initial capacity cannot be reduced. In an actual battery, the capacity of the battery is defined by the capacity of the positive electrode material, and a decrease in the capacity of the positive electrode material is not preferable.

In the present invention, the spinel type Mn oxide positive electrode material defined by the above composition formula Li _{1 + x} Mn _2−x O ₄ (0 <x <1.33) is added to at least one kind other than Li, Mn and oxygen. A material to which an element is added is used. As elements to be added, B, P, Mg, As, Sb, Zr,
It is desirable to add at least one element of Na, Be, Y, Si, Al, C, F, Bi, Pb, Ge, and Sn, and the addition amount is based on the total amount of Mn contained in the positive electrode material. The molar ratio is preferably from 0.01% to 10%, but there is no problem even if it is added more or less than this.

In particular, the addition of B, P, and Sb can increase the capacity without changing the crystal structure, that is, maintaining the stability and without impairing the life characteristics. Moreover, substitution of Al, Si, Ga, and Mg is effective from the viewpoint of improving safety. The composition ratio of the material to be added is most suitably 0.02 <x <0.14 in the composition formula Li _{1 + x} Mn _2−x O ₄ .

In addition, the positive electrode material according to the present invention is manufactured as follows. First, a Mn-based spinel oxide that is a base material is manufactured. For this purpose, Li ₂ CO ₃ , LiOH, LiNO ₃ , LiCOOH, Li ₂ O or the like is used as the lithium source, and MnO ₂ (electrolytic manganese dioxide (EMD)) is used as the manganese source. Manganese dioxide (CMD) may also be used.), Mn ₃ O ₄ , Mn ₂ O ₃ , MnO, MnCO ₃ , MnCOOH, MnOOH and the like are used.

  These are mixed at a predetermined composition ratio or mixed in a solution and then precipitated and used as a raw material. The raw material is fired in air or in an oxygen stream for 40 hours. The firing temperature at this time is preferably in the range of about 600 ° C. to 900 ° C., although it depends on the composition ratio. A predetermined amount is added to the additive, and the obtained base material is later heat-treated. The temperature of the heat treatment is desirably 400 ° C. to 900 ° C. Of course, there is an effect of addition without heat treatment, but heat treatment is more desirable.

Moreover, in order to solve this subject, the following positive electrode materials are used. The active _{material, Li 1 + x M y Mn} 2-xy O 4 (0 <x <1.33,0 <y <2, M: differ by at least one or more transition metals and Mn) defined by comprising the formula It is obtained by adding at least one element other than Li, Mn, oxygen and transition metal element M to the oxide having a spinel structure. The element to be added is preferably at least one of B, P, Mg, As, Sb, Zr, Na, Be, Y, Si, Al, C, F, Bi, Pb, Ge, and Sn.

In order to solve the _{problem, Li 1 + x M y Mn} 2-xyz B z O 4 (0 <x <1.33,0 <y + z <2, M: different at least one or more of the Mn An oxide having a spinel structure defined by the chemical formula of (transition metal), wherein element B replacing Mn is at least one element different from Li, Mn, oxygen and transition metal M An active material for a secondary battery and a lithium secondary battery using the same. B is preferably a transition metal element different from the transition metal element M, for example, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, or Zn. Typical elements Al, Ga, In, Sn, Pb Etc. Further, alkaline earth metals such as Mg, Sr, and Ca may be used.

  In the present invention, in order to solve the problem, at least one element other than Li, Mn, oxygen, transition metal element M, and substitution element B is further added using the positive electrode material as a base material. . The element to be added is preferably at least one of B, P, Mg, As, Sb, Zr, Na, Be, Y, Si, Al, C, F, Bi, Pb, Ge, and Sn. In order to use as a positive electrode material, it is desirable to heat-process at the temperature between 400 degreeC and 900 degreeC after adding.

In order to solve this _{problem, (Li, A) 1 +} x M y Mn 2-xyz B z O 4 (0 <x <1.33,0 <y + z <2, M: at least one different from the Mn The above transition metal, at least one element different from A: Li.) Is used using a positive electrode active material having a spinel structure defined by a chemical formula. Here, (Li, A) represents that both Li and element A are included. The element B substituting Mn is at least one element different from Li, Mn, and the transition metal M, and the substituting element A is preferably Mg, Zn, Fe, Cu, or Ni. In addition, other elements can be added to the active material to form a positive electrode material.

  In order to solve the problem, the lattice constant of these spinel oxides is set to be larger than 8.10 angstroms and smaller than 8.25 angstroms. Thus, cycle characteristics can be improved by selecting a material having a small lattice constant as the positive electrode material. This can be achieved by selecting an element having a small ionic radius as a substitution element or by reducing the cooling rate after firing as much as possible. The cooling rate is desirably 3 ° C./min or less. In addition, firing in an oxygen stream has the same effect.

  A secondary battery positive electrode is formed using the positive electrode active material according to the present invention by the following method. First, a positive electrode active material is kneaded with carbon as a conductive material. Next, a resin binder is added as a binder to this, and after further kneading, it is applied onto the electrode substrate and press dried. As the negative electrode, an amorphous carbon material, a graphite carbon material, or the like is suitable.

For these negative electrode materials, electrode active materials other than those described above do not affect the object of the invention. For example, tin oxide can be used. As the electrode quality, for example, an organic electrolysis in which a lithium salt selected from, for example, LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiPF _6, etc., is dissolved in a nonaqueous solvent such as propylene carbonate, propylene carbonate derivative, ethylene carbonate, or the like. An electrolyte such as a liquid electrolyte or a lithium electrolyte conductive solid electrolyte or a gel electrolyte can be used.

  Moreover, even if a microporous separator is used according to the structural requirements of the battery, the effect of the present invention is not impaired at all. The produced positive electrode, negative electrode, and separator are wound around a center pin and inserted into a cylindrical or rectangular container, and then sealed by injecting an electrolyte.

  The use of the battery of the present invention is not particularly limited. The use described in claim 11 is a typical one. Besides, for example, a notebook personal computer, a pen input personal computer, a pocket personal computer, a notebook type word processor, a pocket word processor, an electronic book player, a mobile phone, a cordless phone. , Pager, handy terminal, portable copy, electronic notebook, calculator, LCD TV, electric shaver, electric tool, electronic translator, car phone, transceiver, voice input device, memory card, backup power supply, tape recorder, radio, headphone stereo, Power supplies for portable printers, handy cleaners, portable CDs, video movies, navigation systems, refrigerators, air conditioners, TVs, stereos, water heaters, microwave ovens, dishwashers, washing machines, dryers, game machines, lighting Equipment, toy , It can be used for load conditioner, medical equipment, electric vehicles, golf cart, as a power source for electric carts. Besides these consumer products, it can also be used for large power storage systems, military applications, and space applications.

  That is, it acts as a positive electrode active material.

  According to the present invention, a high-capacity, long-life active material for a secondary battery can be obtained, which makes it possible to provide a high-capacity, high-safety, long-life battery and assembled battery that can be applied to portable devices or electric vehicles.

  The following examples illustrate the invention. In addition, this invention is not limited to the Example described below.

Example 1
First, Li _{1 + x} Mn _2-x O ₄ as a base material was produced. The manufacturing method is as follows. First, lithium carbonate and electrolytic manganese dioxide (EMD) are mixed at a predetermined molar ratio. Thereafter, firing is performed at a temperature between 650 and 900 ° C. for about 10 to 40 hours. The atmosphere does this in an air or oxygen stream. An additive element was added to the obtained base material (in this example, x = 0.08). As raw materials for adding the additive element, boric acid, phosphate, and other oxides are used. The ratio of addition was set to 0.25% with respect to the number of moles of Mn in the active material.

The mixed base material and additive material were heat-treated in air at a temperature of 300 ° C. to 600 ° C. for 10 hours. In this example, the particles were classified with a sieve having a mesh diameter of 45 microns, kneaded together with a binder and a conductive material, applied onto an aluminum foil, and dried after pressing to obtain a positive electrode. A charge / discharge test was conducted using a non-aqueous electrolyte containing LiPF ₆ . Table 1 shows the initial capacity, the capacity retention after 100 cycles, and the effect of the additive elements.

  These additive elements act to stabilize the crystal structure, and it can be seen that this has the effect of improving cycle characteristics, suppressing elution, and improving safety to prevent exothermic ignition.

(Example 2)
Another embodiment of the present invention is shown below. As a base material,
Li _{1 + x} Co _y Mn _2−xyz Mg _z O ₄ (x = 0.10, y = 0.10, z = 0.15) was produced. In addition, B, P, Bi, and Pb were added. The addition ratio was set to 0.25% with respect to the number of moles of Mn in the active material similar to that in Example 1. The heat treatment temperature after addition is
Heat treatment was performed at 400 ° C. for 10 hours. FIG. 1 shows the cycle characteristics. In any of these cases, the capacity is improved. In addition, the deterioration of the cycle characteristics is not observed as compared with the additive-free material.

(Example 3)
Furthermore, the result of investigating the rate dependency of the discharge characteristics using the positive electrode material according to the present invention as an active material is shown in FIG. As a comparative example, a case where an additive-free positive electrode material is used is shown. The composition formula of the additive-free material is Li _{1 + x} Mn _2−x O ₄ (x = 0.08). In the additive-free spinel-type positive electrode material, the capacity increases as the discharge rate (1C means charging in 1 hour. 2C means 0.5 hour until full charge). Although it is observed that the material deteriorates, it can be seen that the material to which Sn and In are added has little capacity deterioration. The addition ratio was set to 0.25% with respect to the number of moles of Mn in the active material, as in Example 1. The action of these additives is to increase the electron conductivity of the positive electrode active material, thereby preventing the active material particles from being charged up for high-speed charge / discharge.

The cycle characteristic figure of the secondary battery by this invention. The characteristic view which shows the relationship between the discharge capacity and discharge rate of the secondary battery by this invention.

Explanation of symbols

1 Cycle characteristics when boron is added to active Li _{1 + x} Co _y Mn _2-xyz Mg _z O ₄ (x = 0.10, y = 0.10, z = 0.15), 2 Li _{1 + x} Co _y Mn _2-xyz Mg _z O ₄ (x =
Cycle characteristics when phosphorus is added to 0.10, y = 0.10, z = 0.15), 3.
Cycle characteristics when bismuth is added to Li _{1 + x} Co _y Mn _2-xyz Mg _z O ₄ (x = 0.10, y = 0.10, z = 0.15), 4 ... Li _{1 + x} Co _{y Mn 2-xyz Mg z O} 4 (x = 0.10, y = 0.10, z = 0.15) cycle characteristics when added _{lead, 5 ... Li 1 + x Mn} 2-x O 4 Rate characteristics when tin is added to (x = 0.08, y = 0.10, z = 0.15), 6 ... Li _{1 + x} Mn _2−x O ₄ (x = 0.08, y = 0.10, z = 0.15), rate characteristics when indium is added, 7 ... rate characteristics of active Li _{1 + x} Mn _2−x O ₄ (x = 0.08) without addition of additives.

Claims (5)

A rechargeable lithium secondary battery using a non-aqueous electrolyte, wherein the active material of the positive electrode material of the lithium secondary battery is Li _{1 + x} Mn _2-x O ₄ (0 <x <1.33). A lithium secondary battery comprising an oxide to which at least one element consisting of B and P is added. 2. The lithium secondary battery according to claim 1, comprising an oxide in which at least one element composed of B and P is added in an amount of 0.01% to 10% in terms of molar ratio to Mn. A featured lithium secondary battery. Portable information communication device, characterized in that a lithium secondary battery according to claim 1 or 2 as a power source. Electric vehicle, characterized in that a lithium secondary battery according to claim 1 or 2 as a power source. Power storage system using the lithium secondary battery according to claim 1 or 2.

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