Background technology
Lithium is very big because of the electric charge that it has extremely low current potential, per unit weight, so be suitable as the material of the rechargeable battery of high voltage, high power capacity.On the other hand, lithium is the unsettled material that is rich in responding property, so fire etc. is dangerous big, and, because in that can to make the energy of putting aside in the high-capacity battery big, so lithium bigger material of danger when to be electrochemical reaction out of control.As the battery of portable machine or used for electric vehicle, in order to use the lithium battery (lithium secondary battery) that can discharge and recharge, fail safe is important problem, just actively carries out the research and development to it.
Therefore, developed a kind of lithium ion battery that discharges and recharges, with absorbing the carbon-based material that discharges lithium ion etc. as negative electrode active material; With the transition metal oxide that contains lithium as positive active material; With the non-water solvent that has dissolved lithium salts as electrolyte.But this battery produces superfluous lithium and separates out, inserts when overcharged state in the electrode, its result causes the organic solvent electrolyte to decompose, and final battery abnormal heating causes the generation of problems such as battery is on fire, blast.
For guaranteeing to discharge and recharge the fail safe of lithium battery; its developmental research is just actively carried out; proposed to implement the countermeasure that easing valve, current blocking valve, protective circuit etc. overcharge; but, seek to implement reliably and do not influence simply dual, the triple safe countermeasure of battery behavior in order to guarantee its fail safe more.An example as such countermeasure, for example special opening discloses the electrolyte that contains the also passable terphenyl compounds such as o-terphenyl of useful alkyl replacement by use in the 2000-58116 communique, even having the non-aqueous secondary batteries of this electrolyte is in the state that overcharges and also can guarantees its fail safe, simultaneously, also few to the harmful effect that influences battery behaviors such as low-temperature characteristics or preservation characteristics.Like this, find that the terphenyl compound has the protection of overcharging effect than the additive of motion before really, and reduced harmful effect low-temperature characteristics and preservation characteristics.In addition, in above-mentioned communique, also mentioned following prior art.
In the motion of Te Kaiping 7-302614 communique, No. 5709968 communiques of US patent; the methyl phenyl ethers anisole derivative is disclosed to the protective effect that overcharged; but cyclophysis or preservation characteristics etc. there is harmful effect; in addition; produce gas and form polymer by methyl phenyl ethers anisole derivative oxidation Decomposition under the voltage about 4.5V, consumed and overcharge and then protected battery, but then; form according to electrolyte, its polymer dissolution is also arranged and the situation generation of the charging that can not overrun.As a result, having the aromatic compounds such as methyl phenyl ethers anisole derivative of pi-electron track to differ suppresses to overcharge surely.In the motion of No. 5879834 communiques of US patent, use the additive of biphenyl, but because biphenyl polarity is low, and dissolubility is low in electrolyte,, causes battery behavior to reduce so additive is partly separated out during low-temperature working as electrolyte.In addition, 3-chloro-thiophene has excitant, and stink seriously is difficult to handle, and further also has the problem of easy oxidation Decomposition.The also easy oxidation Decomposition of furans, all compounds all have pair battery behavior to produce dysgenic problem.
In addition, the spy opens and has proposed in the 10-74537 communique wherein to contain aromatic compound or partial hydrogenation aromatic compound for the improvement charge-discharge characteristic adds multiple compound.
In addition, in recent years,, require to increase maximum working voltage along with requiring to improve the stability of electrolyte under high voltage etc.If increase maximum working voltage, can more effectively utilize the capacitance that itself has as the battery system of the aggregate of each material, from improving the charge/discharge capacity of battery in fact.
But if increase maximal workload voltage like this, when using aforesaid terphenyl as electrolysis additive, finding has significant deterioration to battery behavior, the particularly capacitance in repeated charge.This may be that because under high pressure bad reactions such as terphenyl generation eremacausis decomposition or polymerization cause.
Summary of the invention
The objective of the invention is, a kind of electrolysis additive of using in the lithium battery that can discharge and recharge is provided, it has equal or it is above preventing the effect that overcharges with in the past electrolysis additive, and compares with electrolysis additive in the past, and is more stable under high voltage.
The inventor furthers investigate for addressing these problems, and found that the partial hydrogenation aromatic compound of 3 specific rings has excellent performance, has finished the present invention.
That is, the present invention relates to a kind of non-aqueous electrolyte, it is characterized by, in the non-aqueous electrolyte that the lithium salts electrolyte dissolution constitutes, contain the part nuclear hydride of the aromatic compounds of 3 rings shown in the following general formula (1) of 0.1~20 weight % in organic solvent.
Ar
1-R-Ar
2????(1)
(in the formula, Ar
1Be phenyl or the phenyl that replaces by the alkyl of carbon number 1~4; Ar
2The non-condensed aromatic series bases that condense aromatic series base or 2 rings of 2 rings that are the non-condensed aromatic series bases of 2 rings that condense between aromatic series base, the aromatic rings directly or connect by a carbon atom of 2 rings, replace by the alkyl of carbon number 1~4; R is singly-bound, methylene or the methylene that replaces with the alkyl of carbon number 1~4.)
Part nuclear hydride as 3 aromatic compounds that encircle, be preferably selected from terphenyl class, benzylbiphenyl class, the part nuclear hydride that has on the carbon that can replace hydrogen the aromatic compound more than a kind or 2 kinds in the aromatic compound that the alkyl by carbon number 1~4 replaces of dibenzyl benzene class, phenylnaphthalene class, benzyl naphthalene class and these aromatic compound classes, the more preferably part of terphenyl or phenyl biphenyl nuclear hydride.In addition, the nuclear hydrogenation ratio preferred 10~65% of above-mentioned part nuclear hydride.
Further, the present invention relates to use the lithium secondary battery of the non-aqueous electrolyte described in the above-mentioned arbitrary examples.
In the above-mentioned general formula (1), Ar
1For phenyl or by 1 in carbon number 1~4 alkyl (below, be called low alkyl group) or the substituted-phenyl that replaces more than 2.R is a singly-bound, or with-C (R
3R
4The methylene of)-expression or 1 or 2 methylene that low alkyl group replaces.Ar
2Be to condense the aromatic series base with what low alkyl group replaced 2 also passable rings, or with-Ar
3-R
2-Ar
4(Ar
3And Ar
4Independent, be the aromatic series base that replaces also passable monocycle with low alkyl group, R
2Be singly-bound, or with-C (R
3R
4The methylene of)-expression or, the methylene that replace of 1 or 2 low alkyl groups) the aromatic series bases of 2 rings of expression.Here, R
3And R
4Represent hydrogen or low alkyl group independently.As low alkyl group, preferable methyl; As R and R
2, preferred singly-bound, methylene or ethylidene; 2 rings condense the aromatic series base, preferred naphthyl or methyl naphthyl; As using Ar
1, Ar
4The aromatic series base of expression, preferred phenyl or aminomethyl phenyl; As using Ar
3The aromatic series base of expression, preferred phenylene or methylphenylene; As usefulness-Ar
3-R-Ar
4The aromatic series base of 2 rings of expression, preferred R
2Xenyl or methyl biphenyl and R for singly-bound
2Aromatic series base for methylene or ethylidene; Example as the latter has, phenyl methyl phenyl, tolyl aminomethyl phenyl, 1,1-tolyl ethylphenyl, 1,1-tolyl ethyltoluene base.In addition, for Ar
1And Ar
2In the number of substituted alkyl, Ar
1Preferred below 2, Ar
2Preferred below 6, and be preferably methyl or ethyl.In addition, when R was singly-bound, aromatic was Ar
1-Ar
2When R was methylene, aromatic was Ar
1-CH
2-Ar
2When R was the alkyl substituted methylene, aromatic was Ar
1-C (R
3R
4)-Ar
2Here, as R
3, R
4, be preferably H, methyl or ethyl (R
3, R
4In one of be not H).
If the aromatic compound of 3 rings of the preferred general formula of example (1) expression has the compound group as shown in the formula 2 expressions.
The aromatic compound of 3 rings, (" class " is meant " isomers " for preference such as terphenyl class, down with), the aromatic compound that contains 3 rings that replace by low alkyl group on the carbon that can replace hydrogen of benzylbiphenyl class, dibenzyl benzene class, phenylnaphthalene class, benzyl naphthalene class or these aromatics, more preferably terphenyl class or benzylbiphenyl classes.The part that the part nuclear hydride of the aromatic compound of 3 rings can be enumerated the aromatic rings of above-mentioned aromatic is the part nuclear hydride of nuclear hydrogenation structure.This part nuclear hydride can be the compound that the aromatic compound hydrogenations to 3 rings obtain, and also can be to have the two compound of aromatic rings such as the ring of nuclear hydrogenation such as cyclohexane ring and phenyl ring at first, but the former buys easily.
What the aromatic compounds of 3 rings examined partly that material that hydrogenation obtains obtains usually is the different mixture of nuclear degree of hydrogenation, the part nuclear hydride that the present invention uses can be the different mixture of nuclear degree of hydrogenation, also can be the identical compound of nuclear degree of hydrogenation that obtains by separation such as distillations.In addition, hydride is not waited by distillation with perfect kernel hydride separate more than the preferred 70wt% of content of the partial hydrogenation thing that obtains.The partial hydrogenation thing that obtains like this is that the aromatic rings more than 1 of the aromatic of aforementioned formula (1) expression is cyclohexane ring, cyclohexene ring etc.In addition, also there is the few situations of unsaturated fat ring such as wishing cyclohexene ring, at this moment, controls its hydrogenation conditions etc.
These partial hydrogenation things are even use the isolated a kind of effect that also can take into account the battery protection effect when overcharging and improve the battery behavior when improving maximum working voltage of method as described above separately.But by using the mixture of partial hydrogenation thing, further reduce the viscosity of additive, and only compare as additive with a kind of partial hydrogenation thing, the viscosity of electrolyte is difficult for raising, so battery behavior keeps good when discharging and recharging under the big electric current, preferably.
Here, do at 100% o'clock with perfect kernel hydrogenation note, the nuclear hydrogenation ratio of aromatic partly being examined hydrogenation is 10~50%, and preferred hydrogenation ratio is 15~40%.50% is difficult to guarantee its fail safe when above, and 10% guarantees fail safe simultaneously and keeps the usefulness of capacitance low when following.
If the preferred part of example is examined the compound of hydride, can enumerate as shown in the formula the compound group shown in (3).
With compound title example above-claimed cpd, can enumerate: the 2-cyclohexyl biphenyl, (2 '-phenyl)-cyclohexyl benzene, 2-phenyl bicyclohexane, 1,2-dicyclohexyl benzene, the 3-cyclohexyl biphenyl, (3 '-phenyl)-cyclohexyl benzene, 3-phenyl bicyclohexane, 1,3-dicyclohexyl benzene, 2-(cyclohexyl methyl) biphenyl, (2 '-benzyl)-cyclohexyl benzene, 2-benzyl rings hexyl benzene, (2 '-cyclohexyl methyl)-cyclohexyl benzene, 2-benzyl bicyclohexane, 1-cyclohexyl methyl-2-cyclohexyl benzene, 4-(cyclohexyl methyl) biphenyl, (4 '-benzyl)-cyclohexyl benzene, 4-benzyl rings hexyl benzene, (4 '-cyclohexyl methyl)-cyclohexyl benzene, 4-benzyl bicyclohexane, 1-cyclohexyl methyl-4-cyclohexyl benzene etc.These compounds can use separately, and the compound that also can mix more than 2 kinds uses.
Embodiment
The following describes the execution mode of rechargeable lithium battery of the present invention.
Oxidation reaction takes place at the initial stage that overcharges in the compound that contains in the non-aqueous electrolyte of the present invention, by overcharging of this effect protection battery, increases its fail safe.In addition, have, play the effect that can keep overcharging of high-capacitance to prevent agent improving operating voltage, charging battery behavior is not had dysgenic characteristics yet repeatedly.Though the concrete mechanism to this it be unclear that, but according to adding the result who measures oxidizing electrode in the lithium battery electrolytes, think with o-terphenyl current potential much at one under begin oxidation, under than this low slightly potential range, adding in the electrolyte of o-terphenyl has the electric current that shows small oxidation to produce, and this phenomenon takes place and add in the electrolyte of compound of the present invention fully not.
In addition, the amount of the partial hydrogenation thing of the above-mentioned aromatic that contains in the non-aqueous electrolyte is (when the compound more than two kinds is used, its total amount), the relative amount of the organic solvent that uses as electrolyte solvent, be 0.1~20 weight %, preferred 1~10 weight % more preferably accounts for 2~5 weight %.
In addition, the partial hydrogenation thing of above-mentioned aromatic among the present invention, as long as can share with known the having additive that prevents effect that overcharges in the scope that does not hinder effect of the present invention, but the partial hydrogenation thing of aforementioned aromatic must have the content of above-mentioned scope.
The parts of the secondary cell that the electrolyte that formation uses compound of the present invention to modulate is made do not have specific restriction, can use the various component parts that in the past used, and for example use the structure described in the above-mentioned communique, parts.
For example, as positive electrode, can use normally used any material in the discharged and recharged lithium battery that contains lithium.LiMn is for example arranged
2O
4, LiCoO
2Or LiNiO
2Deng composite metal oxide and contain the intercalation compound etc. of lithium.Be applied on the aluminium foil by the slurries that this lithium compound powder, electroconductive powder and adhesive are mixed, after the drying, suitably process, can be made into cathode foil.
As negative material, can use to absorb normally used any material in the chargeable discharge lithium battery that discharges lithium, can enumerate the carbonaceous system that interlayer at the traverse net of carbon atom inserts lithium and insert compound.Carbonaceous system inserts compound and can prepare by inserting the electrochemistry electrolyte lithium after the assembled battery in material with carbon element, also can begin carbon dust and the incompatible preparation of electrolyte premix.Can be by after this carbonaceous system being inserted slurries that compound or carbon mixes with adhesive and being applied on the Copper Foil, drying is carried out suitable processing, makes anode foil.
As dividing plate, can use normally used any material in the lithium battery that can discharge and recharge, capillary polypropylene, polyethylene film etc. are for example arranged.
Non-aqueous electrolyte uses by appropriate combination organic solvent and solute, can use normally used any non-aqueous electrolyte in the lithium battery that can discharge and recharge.As organic solvent, can lift and contain ethylene carbonate, dimethyl carbonate, diethyl carbonate, propene carbonate, Methylethyl carbonic ester equal solvent, as the liquid electrolyte solute, can lift lithium hexafluoro phosphate (LiPF
6), LiBF4 (LiBF
4), trifluoromethayl sulfonic acid lithium (LiCF
3SO
3) etc.
With above-mentioned constituent material stacked be anodal (aluminium foil)/dividing plate (impregnation non-aqueous electrolyte)/negative pole (Copper Foil)/dividing plate (impregnation non-aqueous electrolyte), constitute battery.But to various combinations of materials, for example, because propene carbonate is not suitable for etc. electrolyte when using the material with carbon element of graphite system, so must select aptly.As the shape of battery, can be the Any shape that the lithium battery that can discharge and recharge is made usually, prismatic batteries and small-sized Coin-shape cell etc. are for example arranged.
The compound that contains in the electrolyte of the present invention has to have concurrently simultaneously and prevents to overcharge effect and the effect of the uniqueness of stability under high voltage.In addition, even the viscosity of electrolyte also is difficult for increasing after adding compound of the present invention, so think that to discharge and recharge battery behavior under heavy current also good.
Below, enumerate embodiment and comparative example, specify the present invention, but the present invention is not limited to this.
The evaluation method according to the present invention is carried out the test of evaluation of measuring characteristic.In the basic electrolyte, use is dissolved as electrolytical lithium hexafluoro phosphate (LiPF in the organic solvent of 1: 1 formation of volume ratio of ethylene carbonate and diethyl carbonate
6) 1mol/L.
Embodiment 1
In the above-mentioned basic electrolyte of 100g, add 2.0g partial hydrogenation aromatic 2-cyclohexyl biphenyl, make electrolyte A.
In addition, with above-mentioned same method, in the basic electrolyte of 100g, add by about 1.0g 2 '-benzyl ring hexyl benzene, about 0.6g 2-cyclohexyl biphenyl, about 0.3g 2-phenyl bicyclohexane, about 0.1g 1 as the partial hydrogenation aromatic, the mixture 2.0g that 2-dicyclohexyl benzene is formed makes electrolyte B.
And, with above-mentioned same method, in the basic electrolyte of 100g, add by about 0.9g 2 '-benzyl ring hexyl benzene, about 0.5g 2-cyclohexyl biphenyl, about 0.2g 2-phenyl bicyclohexane, about 0.1g 1 as the partial hydrogenation aromatic, the mixture 1.7g that 2-dicyclohexyl benzene is formed, with 0.3g o-terphenyl, make electrolyte C.
With above-mentioned same method, in the basic electrolyte of 100g, add by about 0.5g 3 '-benzyl ring hexyl benzene, about 0.4g 3-cyclohexyl biphenyl, about 0.6g 3-phenyl bicyclohexane, about 0.5g 1 as the partial hydrogenation aromatic, the mixture 2.0g that 3-dicyclohexyl benzene is formed, system electrolyte D.
In addition, use same quadrat method, in the basic electrolyte of 100g, add the mixture 1.7g that forms by about 0.1g 2-(cyclohexyl methyl) biphenyl, about 0.1g 2 '-(cyclohexyl methyl) cyclohexyl benzene, about 0.2g 2-benzyl rings hexyl benzene, about 1.1g 2 '-benzyl rings hexyl benzene as the partial hydrogenation aromatic, with 0.3g o-benzylbiphenyl, make electrolyte E.
For relatively, with above-mentioned same method, in basic electrolyte 100g, add 2.0g o-terphenyl, make electrolyte F.
Embodiment 2
Mixing pulverizes native graphite for the crushed material 80 weight % of average grain diameter 0.8 μ m, with LiPF
6Pulverizing is the crushed material 10 weight % of average grain diameter 5 μ m, adhesive polyvinyl fluoride 10 weight %, makes pasty state with the N-N-methyl-2-2-pyrrolidone N-, is applied to then on the Copper Foil, after the drying, uses the roll squeezer compression forming, makes negative pole.
Mix LiCoO
2Powder 85 weight %, Kynoar 7 weight %, acetylene carbon black 8 weight % make pasty state with the N-N-methyl-2-2-pyrrolidone N-, are applied to then on the Copper Foil, after the drying, use the roll squeezer compression forming, make positive pole.
Between positive pole that is processed into specific size and negative pole, inject the electrolyte A that makes with said method, the clamping impregnation porous matter polypropylene of identical electrolyte A, make diameter 20mm, the coin battery of thick 5mm.
Embodiment 3~6
As electrolyte, electrolyte B, the C, D or the E that use said method to make, the method for pressing embodiment 2 is made coin battery.
Comparative example 1
Except as electrolyte, use outside the electrolyte F, make coin battery similarly to Example 2.
Comparative example 2
Except the aforementioned basic electrolyte of direct use, make coin battery similarly to Example 2.
For the periodic performance of the battery of more above-mentioned making, under the 4.1V upper voltage limit, with the constant current charge of 1C, then, charging reached the state that is full of electricity in 3 hours under 4.1V voltage.Then, under the 3.0V lower voltage limit,, so discharge and recharge 20 cycles repeatedly with the 1C discharge.
Measure the discharge capacity in the 1st cycle and the 20th cycle, investigate the influence of the interpolation of the part nuclear hydride that adds aromatic hydrocarbon capacitance.Carry out 3 tests respectively, the mean value of the ratio of the discharge capacity of (first cycle) and test back (the 20th cycle) is as shown in table 1 before the test.
Then, under upper voltage limit 4.2V, carry out the same evaluation that discharges and recharges, as hereinbefore, measure the discharge capacity in the 1st cycle and the 20th cycle, equally, carry out 3 tests respectively, the mean value of the ratio of the discharge capacity of (the 1st cycle) and test back (the 20th cycle) is as shown in table 1 before the test.
Table 1
| Electrolyte | After the discharge capacity ratio test/test preceding (%) |
????3.0~4.1V | ???3.0~4.2V |
Embodiment 2 | ????A | ????93 | ???92 |
Embodiment 3 | ????B | ????92 | ???91 |
Embodiment 4 | ????C | ????93 | ???91 |
Embodiment 5 | ????D | ????94 | ???93 |
Embodiment 6 | ????E | ????94 | ???93 |
Comparative example 1 | ????F | ????93 | ???87 |
Comparative example 2 | Basic electrolyte | ????98 | ???97 |
To before testing and the ratio (3.0~4.1V) of the discharge capacity after the test, use electrolyte A, B, C, D, E that adds The compounds of this invention and the battery that has added the electrolyte F of o-terphenyl, compare with the battery of the electrolyte that uses no additive, discharge capacity slightly descends, but does not all have significance difference.
In addition, to before testing and the ratio (3.0~4.2V) of the discharge capacity after the test, the battery that has mixed the electrolyte A, the B that add compound of the present invention, C, D, E maintains the level more than 90%, drops to 87% and mixed the battery that adds the electrolyte F of o-terphenyl.
This thinks as follows, and operating voltage o-terphenyl between 4.1V and 4.2V slightly reacts, and when maximum working voltage raises as a result, battery behavior is exerted an influence, and there is not this reaction in additive of the present invention, and the result is to not influence of battery behavior.Infer in order to replenish this, investigated the degree of the oxidation reaction of current potential and additive.
Embodiment 7
The effect utmost point uses SUS304 (diameter 16.0mm, thick 6.0mm), and the utmost point is used lithium (diameter 20mm, thick 0.55mm), uses polypropylene system dividing plate, adds the electrolyte 0.5ml of each embodiment, comparative example, makes the battery of estimating usefulness.
To the speed of this battery, apply voltage from 3.0V to 5.0V (to Li/Li with per second 5mV
+), measure electrical current around here, measure current density value simultaneously.Maximum electrical current density (the μ A/cm that measures
2) as shown in table 2.
Table 2
| Electrolyte | Maximum electrical current density (μ A/cm
2)
|
????4.0~4.2V | ????4.5~4.7V |
Embodiment | ????A | ????4 | ????70 |
????B | ????5 | ????60 |
????C | ????4 | ????80 |
????D | ????4 | ????20 |
????E | ????5 | ????15 |
Comparative example | ????F | ????20 | ????150 |
Basic electrolyte | ????2 | ????10 |
Can judge from this result, oxidation reaction has all taken place in all compounds in the higher voltage range of the ratio of 4.5~4.7V, the electrolyte A, the B that have mixed compound of the present invention, C, D, E's is big but the oxidation current value of using the electrolyte F mixed the o-terphenyl in the lower voltage range of 4.0~4.2V is than using.
Embodiment 8
Further, for the fail safe of the battery made relatively like this, to discharge and recharge the battery of estimating 20 all after dates with 4.2V voltage reach once more be full of electric state after, under the 1C, continue charging, it is overcharged, whether affirmation brings into play the ability of overcharging that prevents in cell fracture or before catching fire.The result is as shown in table 3.As can be seen, use the battery of the electrolyte A~E of compound of the present invention all to have the ability of overcharging that prevents, have the effect that improves battery security.
Table 3
Use electrolyte | The battery that breaks or catch fire/test number |
????A | ????0/10 |
????B | ????0/10 |
????C | ????0/10 |
????D | ????0/10 |
????E | ????0/10 |
????F | ????0/10 |
Basic electrolyte | ????3/10 |