JPH04141954A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a non-aqueous electrolyte secondary battery using lithium or a lithium compound as a negative electrode, and a method for producing a positive electrode active material made of a lithium compound. Non-aqueous electrolyte secondary batteries with negative electrodes are expected to have the potential to realize high-voltage, high-energy-density batteries.
Although Se has been well studied, Tackley et al. recently reported that LiMn 04 can be used as a positive electrode active material (
Material Research Bulletin (Material
Research Bulletin) 1983 1
Vol. 8, pp. 461-472) 6 LiMn*Qa has a cubic crystal structure with a spinel structure, and when used as a positive electrode active material in a battery, the battery discharge voltage shows a high voltage of about 4 volts. However, the report by Otsuki et al. (Proceedings of the 29th Battery Symposium 135)
According to the literature, the composition of the positive electrode active material is LixMn.
Charging and discharging occur as a result of changes in the value of X. The relationship between the amount of Li in the LiMn*Oa positive electrode active material, X, and the open circuit potential of the battery is shown in FIG. As can be seen from the figure, it shows a two-stage potential curve with flat parts near 4 volts and near 2.8 volts.

In a conventional lithium secondary battery, by focusing on the second stage of the potential curve near 2°8 volts in Table 6, and performing a charge/discharge cycle in which the charging voltage is limited to about 4 volts and the discharge is to about 2 volts, the cycle can be reduced. Even if efforts are made to obtain a battery with a long life, in this case, if we consider the overvoltage of the positive electrode during charging and discharging, even though it corresponds to charging and discharging where LijlX changes from about 1 to 1.85, for example, JP-A-2-65061 In the official bulletin (Yo) Lithium salts, manganese oxides, and metal oxides (MO, Nb5W,
An active material has been proposed in which a mixture of oxides selected from Ru, Co, Ti, B1, Cu, and Cr is heat-treated at 350 to 430°C.
61 Publication ζ L+M synthesized at a high temperature of 850℃
nzQ4 derivative Llx (Mn+-z・Bz)*
・It is a compound of Qa, and 1. 1≧X≧0.9, 0.
2≧Z≧0.0, B is V, Cr, Fe, CoS
Even though an active material that is an element selected from Ni has been proposed, both are charged to 4-3°8V and discharged to 2.7-2V, making use of the lower flat part of the LiMngO4 potential curve. However, the problem that the invention aims to solve is that it is difficult to realize a battery with a high energy density using such a conventional configuration. Charging and discharging cycle At that utilizes the higher flat part of the potential curve to discharge to volts, that is, charge until X becomes less than 1, preferably less than 0.7, until LX becomes 1, or until 1,85 However, it is more advantageous to discharge until LX becomes 0.7 or less.The charging/discharging cycle characteristics in the higher flat area were poor, and the discharge capacity decreased by half after about 50 cycles.This deterioration The degree of X was extremely large compared to the charge/discharge cycle using the lower flat potential curve shown in the above publication.Furthermore, if X exceeded 0.7, charging would fail. The condition is sufficient, and it is difficult to obtain sufficient discharge capacity (~
Furthermore, when the charging voltage exceeds 4V, there is a problem that the battery self-discharges after charging.The present invention solves this problem.
The purpose of this project is to improve the positive electrode active material of a non-aqueous electrolyte secondary battery using O4 as the positive electrode active material, extend the charge/discharge cycle life, and provide a non-aqueous electrolyte secondary battery with less self-discharge. In a nonaqueous electrolyte secondary battery in which lithium or a lithium compound is used as a negative electrode and a nonaqueous electrolyte containing a lithium salt is used as an electrolyte, the positive electrode is , Ni, Ta or Zn, and 0.85≦X≦1.15
When using a positive electrode active material with 0.02≦Y≦0.30, lithium is extracted from the positive electrode active material by L% charging.
It was designed to be charged until ≦0.7. Li salt, Mn compound, Co, and Cr.

The cathode active material is synthesized by mixing N1, Ta, or Zn salts and heat-treating at a temperature of 550°C or higher.The positive electrode active material LrMntQa has a cubic crystal structure with a spinel structure; In the battery used, Li was extracted from the crystal by charging, and Li was re-crystallized by discharging.When LIMn*QJ was examined by X-ray diffraction after repeated charging and discharging cycles, the crystallinity decreased. Furthermore, when we chemically synthesized active materials with different values of X as LixMntOa and examined the battery characteristics, we found that the discharge capacity and cycle characteristics changed depending on the value of X.9
This fact (1) indicates that the crystal stability of the active material itself affects the charge-discharge cycle characteristics, but the report by Kotsuki et al. During charging and discharging, the cathode active material undergoes a crystalline change between cubic and tetragonal, whereas in the higher flat part of the potential curve, the cubic crystal is sampled and its lattice constant changes. This is because the charging/discharging mechanism is completely different in the higher flat area. It is thought that by decreasing the crystal lattice constant of the positive electrode active material, the stability of the crystal increases and a positive electrode with good cycle characteristics can be obtained. Therefore, LiXMn=O= Some of the Mn inside is replaced with Co, Cr, Fe, Ni,
Cu, V, W, Nb, Mo, Ru
We investigated positive electrode active materials substituted with , Ti, Bi, Ta, or Zn, including Co, Cr, Fe, Ni, Cu, Ta.
, or the lattice constant of the active material substituted with Zn is 1. The force (■, W, N
b, The lattice constant of the active material substituted with Mo, Ru, Ti, or Bi remains unchanged＼ Or if it forms the positive electrode of a larger battery Will it improve the charge-discharge cycle characteristics?
, tCo, Cr, Fe, Ni, Cu,
The effect was seen in the case of Ta and Zn.9 V, W, Nb, M
No improvement effect was observed in the case of O, Ru, Ti, and Bi.Although the above publication states that it is effective for all metals except Ta and Zn, this difference is due to the charge/discharge cycle power of the above publication. (Charge/discharge cycle at the lower flat part of the potential curve of the positive electrode active material) L/, that is, Lix M n t Oa
This is a cycle of discharging until X becomes 1.8 and charging until L becomes 1. However, in the present invention, the cycle of charging and discharging at the higher flat part is included until X becomes 0.7 or less. Although the charging and discharging mechanisms, including changes in the crystal system, are completely different as described above, by reducing the crystal lattice constant of the active material, good charge-discharge cycle characteristics and a high discharge capacity after charge-discharge cycles can be achieved. After discovering that positive electrode active materials for secondary batteries with large ions can be obtained, we investigated the self-discharge after charging of batteries using these active materials as positive electrodes.As a result, we found that the original LixMn*o
A part of Mn in a is replaced with C01Ni, Cr, WNb, Ti
In the case of active materials substituted with , Ta, or Zn, the self-discharge was small (VSMo, Ru.

Self-discharge is large in active materials substituted with Bi, Fe, or Cu. When 7'-o Li x M n t Oa is charged until Even if the charging voltage exceeds 4 V, it is thought that the constituent elements of the positive electrode active material are more likely to dissolve, causing a difference in the degree of self-discharge. This is because the self-discharge was small and good, and there was almost no difference between the active materials mentioned above.Although the self-discharge behavior is quite different between the low and high plateau parts of the potential curve, from the above, the charge-discharge Mn in LixMn*04 is used as a positive electrode active material with good cycle characteristics and low self-discharge.
Active materials in which a part of CoS is replaced with Cr, Ni, Ta, or Zn are preferred.
A part of Mn in mMn*Oa is converted into co, Cr, ', Ni,
Have you considered synthesis methods for active materials substituted with Ta or Zn? = Co, Cr, Ni, Ta replacing a part of Mn
, active materials synthesized using metal salts such as nitrates, carbonates, and hydroxides had better self-discharge characteristics than using oxides of these metals as starting materials for Zn.Using metal salts This is thought to be due to the uniform distribution of metal elements within the active material particles. Heating temperature L during synthesis is preferably 550°C or higher from the self-discharge characteristics.
This effect is also thought to be due to the uniformity of the distribution of metal elements within the active material particles.Example 1 Below, examples of the present invention will be explained with reference to the drawings (Example 1) L i M n * 10% of Mn in Q- is Co, Cr,
Fe, Ni%Cu, V, W%Nb, M
o, Ru.

The charge-discharge cycle characteristics of positive electrode active materials substituted with Ti, Bi, Ta, or Zn were investigated. is an element, X:=1, Y=0.
2 is a plate of LiMntO4 (D production method) in which Mn5O4 is well mixed at a ratio of 4 moles to 3 moles of Li*CO5. The mixture is heated at 900 °C in the air for 10 hours to synthesize % LiMntQa and produce 9 LiMn5.
10% of Mn in O4 is Co, Cr as M in formula (I)
, FeS Ni, Cu, V N N b1Mo%R
Manufacturing method of active material substituted with u, Ti, Bi, Ta, or Zn LigCOs and Mn*04 and Co, Cr, Fe
, Ni, Cu, V, w, Nb, M
o, Ru5Ti, Bi, Ta or Zn nitrate, with respect to the number of Li atoms in formula (I) being 1, Mn
A method for manufacturing a battery in which the active material was synthesized by weighing and mixing so that the number of atoms was 1.8 and the number of M atoms was 0.2, and heating it in the air at 900°C for 10 hours.Conductivity for 7 parts by weight of positive electrode active material 2 parts by weight of acetylene black as an agent and 1 part by weight of poly(4-fluoro-modified tyrene resin) as a binder were mixed to form a positive electrode mixture.9 Positive electrode mixture 0.
1 gram is 1 ton/cm' in the form of a disk with a diameter of 17.5 mm.
Figure 1 shows a cross-sectional view of a battery manufactured by press-molding the positive electrode at a pressure of approximately 100 ml. Place the molded positive electrode 1 in a case 2, and place a porous polypropylene film as a separator 3 on top of the positive electrode 1 to form a negative electrode with a diameter of 17°5 m.
A lithium plate 4 with a thickness of 013 mm is crimped onto a sealing plate 5 equipped with a polypropylene gasket 6, and a propylene carbonate solution containing 1 mo I/l of lithium perchlorate is used as a non-aqueous electrolyte. Then, a sealing plate 5 with a lithium plate 4 crimped onto it in addition to the negative electrode was inserted into a case 2 equipped with a positive electrode 1 and a separator 3, and then the battery was sealed, and a cycle test of 9 batteries was conducted. 4.5 at a constant current of
Charging up to 3 volts, discharging up to 3 volts, and then repeating charging and discharging under these conditions. At the 41M1 cycle, as shown in Figure 2, the composition of Li in the positive electrode active material of formula (I) is Charging LX is 1.0° until it reaches 0°3, which is the left end of the flat part with higher potential. As an index representing the cycle characteristics of the positive electrode active material after discharging to 0, the 10th
Subtract the discharge capacity at the 50th cycle from the discharge capacity at the 10th cycle and use the value obtained by dividing it by the discharge capacity at the 10th cycle. The smaller the value, the better the charge-discharge cycle life characteristics. Table 1 shows the deterioration rates when using active materials with different M in formula (1) (see the margins below) Table 1 As shown in Table 1; 10% of Mn is made of co, Cr, Fe.
, Ni, CuS It can be seen that the charge/discharge cycle characteristics are improved when replaced with Ta or Zn. Also, V,
W, Nb, Mo5Ru, Ti or B
No effect was observed when iJ was substituted. An effect was observed. A battery using an active material in which 10% of Mn in formula (1) was replaced with Co is designated as (A). In addition, CrS N
Batteries using active materials substituted with either TaS, Zn, Fe or Cu were (B), (C),
(D), (E), (F), (G) As a conventional example, a battery using LiMn*Qi that has not been replaced with metal is (H). Figure 5 shows the relationship between the number of charging and discharging cycles and the discharge capacity of the batteries of (A) and (H) as representative examples. The horizontal axis also shows the LitX in the active material of formula (I) determined from the amount of current applied as well as the charging and discharging time.
As you can see from the figure, it is necessary to charge at least L4V to obtain a sufficient discharge amount, and it is necessary to charge until the value of X becomes 0.7 or less. (H) No. 5
A charge/discharge curve at the 0th cycle is shown.

Next, charge and discharge under the same conditions by changing only the amount of charged electricity. By changing the amount of charged electricity, when charging is completed (I)
Although the amount of X in the equation changes, we will investigate the relationship between the amount of charged energy and the amount of discharged electricity by converting it into the value of X at the end of charging and the amount of discharge per 1 g of active material. LiCo@ which is an embodiment of the present invention.

The relationship between the amount of electricity charged and the amount of electricity discharged in the first cycle of the battery using Ling Mrz, 04 was plotted according to the above. It can be seen that a sufficient discharge capacity can be obtained when the value is 0.7 or less.The composition of the positive electrode active material in this charged state is x,tto.

7 or less, the discharge capacity is sufficient.The results are the same, including the conventional example.
When the active material substituted with , Ta, and Zn is examined by X-ray diffraction,
The diffraction pattern is the same as LiMn2O4, but
The position of the diffraction line has shifted to the higher angle side compared to the original LiMntO4, and the lattice constant has become smaller.9 For example,
In the case of co, the lattice constant determined from each diffraction line (Tomomoto's Li
Compared to 8.24A of Mrz○4, it is smaller at 8.21A.9 It is thought that the crystal becomes more stable and the cycle characteristics are improved due to the smaller lattice constant. The results shown are the results of charging to 4°5 volts where the Charge LX until it becomes 7 or less
It is also effective when discharging until X becomes 1 or more and 1.8. This is because charging and discharging when X is between 1 and 1.8 is effective even with the conventional composition as disclosed in the previous publication. This is because the positive electrode active material of the present invention also showed good charge/discharge cycle life characteristics (Example 2) Next, the positive electrode active material formula (1), Li
(Cathode active material was synthesized by changing X and Y of e-t+04, and the charge/discharge cycle life characteristics of the cathode active material were investigated.
Production method of MnzO4 Production method of LiXMneQ4 conducted in the same manner as in Example 1
A plate in which Lt and Mn atoms are well mixed at a ratio of 2 moles.
The mixture was synthesized by heating at 900° C. for 10 hours in the air, and in nine Examples, X=1.20, 1.15, 1.10, 1.
05, 1.025, 1.01, 1. olo, 95.0.
Manufacturing method of Li XM IIM n +1-1110 a synthesized with cathode active material of
, Cr, Fe, Ni, Cu, Ta or Zn,
By changing the composition as shown below, t-X=1.20, 1
．． 15, 1. lOl 1.05, 1°025, 1.01
, y=o for 1.0, 0.95, 0.90°0.85.0.80, respectively.

1, 0.02, 0.05, 0.1, 0.2.0°3, 0
．． Example 1 shows the synthesis method for making 4 and using it as a positive electrode active material.
The same as , Li-elephant COs, Mns Oa, and nitrates of various metals are used to create a plate mixture in which Li atoms are X moles, M atoms are Y moles, and Mn atoms are 2-Y moles. Manufacture and charge/discharge test of a synthesized battery by heating it at 900°C for 10 hours in the atmosphere. The charge/discharge cycle characteristics were taken as in Example 1, and the capacity deterioration rate was taken as in Example 1. As a representative example, Table 2 shows the deterioration rate of the active material corresponding to each of It was found that both LLi and CO were effective, but it was also found that the effect disappears if too much LLi and CO are used (see the margin below). It is also worth noting that if the same amount of Mn is replaced with CO, the best charge-discharge cycle life characteristics can be obtained by increasing the amount of Li slightly larger than 1. -v
+04 X and Y are 0. 85≦X:i;1. 15,
By using a material satisfying 0.02≦Y≦0.3 as the positive electrode active material, L
The charge-discharge cycle life characteristics of non-aqueous electrolyte secondary batteries can be improved using materials other than Co such as Cr, Fe, Nis Cu,
Ta.

Similar results were obtained for Zn, FL, o, s.
5:ii;)≦1.15.0.02≦Y≦0.3Te Good charge-discharge cycle life characteristics were obtained (Example 3) Force studied using nitrates (carbonate hydroxide instead of nitrate)
A similar experiment was carried out using A battery was constructed in the same manner as in Example 1 using the same active material as in Example 1. After 10 cycles of charging and discharging under the same charging and discharging conditions, the battery after the 1st cycle charging was completed. 60℃
The self-discharge rate is defined as the ratio of the amount of electricity discharged in the 11th cycle to the amount of electricity discharged in the 10th cycle. As elements that partially replace the original LiMntQa and Mn, CO, Cr, NiS, ZnS, Ta, w
.

Batteries with active material positive electrodes using Nb or Ti have good self-discharge characteristics b<, Fe, Cu, V,
Batteries using active materials substituted with Mo, Ru, or Bi suffer from large self-discharges. From the results of Examples 1 to 4, LixMvMn (
As M of e−v+Q a, COl CrS Ni
, To the case using Zn or Ta Cycle poetry
It turns out that it becomes an active material with good self-discharge characteristics (Example 5) In Example 4, l! Force t studied using nitrate as the salt of M in formula (1) C01Cr, Ni instead of nitrate
Table 4 shows the results of the self-discharge rate of active materials using nitrate, carbonate, hydroxide, and oxide as the starting materials for M in which a similar test was conducted using carbonate, hydroxide, and oxides of Zn and Ta. Shown below.

(Left below) Charcoal lol! Similar results were obtained when metal salts such as salt hydroxides were used.9 From this, it is clear that metal salts such as nitrates, carbonates, and hydroxides are effective.
As Co, Cr, Ni, Ta.

In a battery using an active material synthesized using an oxide of Zn, self-discharge was greater than in a case using a metal salt.This is thought to be due to the uneven distribution of the metal element M in the active material. Also (Example 6) L i IIM vM n t*-r) Q What were the conditions for synthesizing a? -oLi Elephant C○ and Mn5
Using O4 and Ni nitrate, the Li atom content is
The pine mixture was well mixed at a ratio of 0.2 moles of atoms and 1.8 moles of Mn atoms.The mixture was heated in the air at different temperatures.
Synthesized by heating for 0 hours Using the active material synthesized in this way, self-discharge characteristics were examined in the same manner as in Example 4.1. FIG. 8 shows the relationship between the heating temperature of an active material and the self-discharge rate of a battery using that active material. As shown in Figure 's8); it is desirable that the heating temperature is 550℃ or higher.
In addition to Ni nitrates, carbonates, hydroxides, and CO1 nitrates of Cr, Ta, and Zn as M, carbonates, and hydroxides, the self-discharge will be smaller if fired at 550°C or higher. L Although it is thought that this is due to the uneven distribution of the metal element M in the active material, if a lithium salt such as lithium carbonate is used, lithium hydroxide or lithium nitrate is used, instead of kMn-rich 04, M n t Q In the above examples, good results were obtained even when Mn compounds such as manganese nitrate were used.Table 6 When a propylene carbonate solution in which 1 mol/1 lithium perchlorate was dissolved was used as the electrolyte. (other than this as the electrolyte ζζ
Electrolytes using lithium perchlorate, lithium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium fluoroborate as solutes, carbonates such as propylene carbonate and ethylene carbonate, and esters such as gamma-butyrolactone and methyl acetate as solvents are suitable. However, when ethers such as dimethoxyethane and tetrahydrofuran are used, the self-discharge characteristics are poor, and the self-discharge rate is about twice as high as when using propylene carbonate as shown in the example. In the example, the positive electrode has a voltage of 4 V or more. This is not thought to be because the ethers are oxidized. When a lithium solid electrolyte is used as the non-aqueous electrolyte in addition to the above-mentioned electrolyte, the positive electrode of the present invention has a good Effect of the invention showing self-discharge characteristics As is clear from the description of the above embodiments, a non-aqueous electrolyte secondary battery uses lithium or a lithium compound as an electrode and a non-aqueous electrolyte containing a lithium salt. positive polarity expression
t'tM expressed as Li×MyMnt*-y+Qa is any one of co, Cr, Ni% Ta or 2n, and 0.85≦X≦1, 15, and 0.0
2≦Y≦0. When using a positive electrode active material, which is No. 3, will lithium be extracted from the positive electrode active material by charging? By charging until X≦0.7, the discharge voltage of the nonaqueous electrolyte secondary battery becomes higher, the energy density becomes higher, and the charge/discharge cycle life characteristics and self-discharge characteristics improve.

[Brief explanation of the drawing]

Figure 1 is a cross-section of a battery according to an embodiment of the present invention; Figure 2 is a diagram showing the relationship between the amount of Li in the LiMnO4 cathode active material and the open circuit potential; Figure 3 is the charge-discharge cycle characteristic of the battery. Figure 5 shows the charging and discharging characteristics of the same battery in the first cycle. Figure 6 shows the discharge characteristics of the same battery in the 50th cycle. Figure 7 shows the charging and discharging characteristics of the same battery in the 50th cycle. Figure 8 shows the relationship between the composition of the active material and the discharge capacity. Figure 8 is a diagram showing the synthesis temperature and self-discharge rate of the active material. Lithium Kaede 5... Sealing plate 6... Gaskerato. Name of agent: Patent attorney Akira Okaji et al.28 No. 28 No. of case failure is reported. , tt Qa ノ入a 漣目 叉吋閏(-A) 图显彎纬了当的Ljx Coy2Mn1e04的X 语图Uff 1F! Gentleness (”c)

Claims (2)

[Claims] (1) a negative electrode made of lithium or a lithium compound;
A non-aqueous electrolyte containing a lithium salt and the formula Li_XM_YMn
It is represented by _(_2_-_Y)O_4, and M is Co, Cr,
Either Ni, Ta or Zn, and 0.85
≦X≦1.15 and a positive electrode active material that satisfies 0.02≦Y≦0.30, and after charging until lithium is removed from the positive electrode active material and X≦0.7. A non-aqueous electrolyte secondary battery that discharges. (2) Li salt, Mn compound, Co, Cr, Ni, T
A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which comprises heat-treating a metal salt of either a or Zn at a temperature of 550° C. or higher.