US007749641B2
`
`a2) United States Patent
`US 7,749,641 B2
`(10) Patent No.:
`
` Renet al. (45) Date of Patent: Jul. 6, 2010
`
`
`(54) SECONDARY LITHIUM ION CELL OR
`BATTERY, AND PROTECTING CIRCUIT,
`ELECTRONIC DEVICE, AND CHARGING
`DEVICE OF THE SAME
`
`5,487,960 A *
`5,604,418 A
`6,558,848 B1*
`2003/0113613 Al*
`
`1/1996 Tanaka oe eee 429/332
`2/1997 Andrieuet al.
`.......... 429/241
`5/2003 Kobayashi et al.
`6/2003 Takeuchi etal. 0.0.00... 429/60
`
`(76)
`
`Inventors: Xiaoping Ren, 17A No. 4 Building,
`Shijijiayuan, 45 Xiaoguanbeili, Anwai,
`Being, 100029 (CN); Jie Sun, 17A, No.
`4 Building, Shijijiayuan, 45
`Xiaoguanbeili, Anwai, Beijing, 100029
`(CN)
`
`(*) Notice:
`
`Subject to any disclaimer, the term ofthis
`patent is extended or adjusted under 35
`US.C. 154(b) by 1561 days.
`
`(21) Appl. No.:
`
`10/491,134
`
`(22) PCT Filed:
`
`Sep. 28, 2002
`
`(86) PCT No.:
`
`PCT/CN02/00696
`
`§ 371 (©),
`(2), (4) Date: May 6, 2004
`
`(87) PCT Pub. No.: WO03/030293
`
`PCT Pub. Date: Apr. 10, 2003
`
`(65)
`
`(30)
`
`Prior Publication Data
`
`US 2004/0209156 Al
`
`Oct. 21, 2004
`
`Foreign Application Priority Data
`
`Sep. 28,2001
`
`(CN)
`
`veeeeteeeteeeneees 01 1 41615
`
`(51)
`
`Int. Cl.
`(2006.01)
`HOIM 10/44
`(2006.01)
`HOIM 10/42
`(2010.01)
`HOIM 4/58
`(2006.01)
`HO25 7/00
`(52) US. Ch cece 429/50; 429/49; 429/231.6;
`320/137
`
`(58) Field of Classification Search ................... 429/60,
`429/231.95, 49, 50; 320/137
`See application file for complete search history.
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`FOREIGN PATENT DOCUMENTS
`
`CN
`CN
`JP
`
`1135103 A
`1185860 A
`2000-270491 A
`
`11/1996
`6/1998
`9/2000
`
`OTHER PUBLICATIONS
`
`K. Mizushimaet al., “Li,Co, (0<x<1): A New Cathode Material for
`Batteries of High Energy Density”, Mat. Res. Bull., vol. 15, pp.
`783-789 1980.
`G.Pistoia et al., Synthesis of Mn spinels from different polymorphs
`of MnO,Journal of Power Sources, 56 (1995) 37-43.
`Lei Yongquan,“Materials for New Energy”, 2000, p. 136.
`Office Action dated Jun. 9, 2009, in corresponding Japanese Appli-
`cation No. 2003-533374, English Translation 3 pages.
`Patent Abstracts of Japan Publication No. 2001-176559 dated Jun.
`29, 2001, *Abstract*.
`Patent Abstracts of Japan Publication No. 09-259928 dated Oct. 3,
`1977, *Abstract*.
`International Search Report, Dated: May 6, 2003.
`
`* cited by examiner
`
`Primary Examiner—Patrick Ryan
`Assistant Examiner—Muhammad Siddiquee
`(74) Attorney, Agent, or Firm—Stephen A. Bent; Foley &
`Lardner LLP
`
`(57)
`
`ABSTRACT
`
`The present invention provides a new method for improving
`capacity, average operating voltage and specific energy of a
`secondary lithium ioncell or battery. This method is achieved
`by means of properly adjusting the ratio between a positive
`material and negative material, which is calculated by theo-
`retical specific energy, and properly increasing charge cut-off
`voltage. The present method can greatly increasing specific
`energy and average operating voltage of a secondary lithium
`ion cell without influence on recycle property of the cell. The
`present invention also provides a secondary lithium ion cell or
`battery practicing the method,a protecting circuit adapted for
`the secondary lithium ion cell or battery, a electronic device
`using said protecting circuit and said secondary lithium ion
`cell or battery, and a charging device for the secondary
`lithium ion cell or battery.
`
`5,260,148 A * 11/1993 Idota veces 429/307
`
`18 Claims, No Drawings
`
`1
`
`APPLE-1001
`
`APPLE-1001
`
`1
`
`

`

`US 7,749,641 B2
`
`1
`SECONDARY LITHIUM ION CELL OR
`BATTERY, AND PROTECTING CIRCUIT,
`ELECTRONIC DEVICE, AND CHARGING
`DEVICE OF THE SAME
`
` TECHNICAL FIELD
`
`The present invention relates to a new method for improv-
`ing capacity, average operating voltage and specific energy of
`a secondary lithium ion cell or battery, and to a secondary
`lithium ion cell or battery prepared by using the method, a
`protecting circuit adapted for the secondary lithium ion cell or
`battery, a electronic device using the secondary lithium ion
`cell or battery, and a charging device for the secondary
`lithtum ion cell or battery.
`
`BACKGROUND ART
`
`The industry of lithium ion cell develops quickly since
`SONY corporation of Japan invented and commercialized a
`secondary lithium ion cell. Up to 2000, the manufactures of
`lithium ion battery around the world compete allsidedly for
`improving the competitive power of their products mainly
`around the key issue, the capacity of lithium ion battery. At
`present, the improvementof capacity of commercialized sec-
`ondary lithium ion battery generally dependsonthe increase
`of loading quantities of active substances (positive electrode
`materials and negative electrode materials). However, the
`limitation of the volumeof lithium ion battery greatly restricts
`the increase of the battery capacity. For notably raising the
`capacity, the researches for the developmentof active sub-
`stances (positive electrode materials and negative electrode
`materials) having higher specific energy are been conducting
`around the world, but so far, there is no notable breakthrough
`in this aspect for various technical difficulties.
`In fact, the positive electrode materials and negative elec-
`trode materials used in the current secondary lithium ion
`battery have relatively higher theoretical capacity, and the
`problem merely lies in the loweractual utilization rate of said
`capacity. For example, lithium cobalt oxides as a positive
`electrode material of secondary lithium ion cell has a theo-
`retical capacity of 248 mAh/g,while the actually used capac-
`ity of it is merely about 140 mAh/g,i.e., about half of said
`theoretic capacity is not utilized. This is mainly caused by the
`limitation of charge cut-offvoltage commonlyused in the art.
`At present, the charge cut-off voltage of single secondary
`lithium ion cell is limited to no more than 4.2 V, and this is
`well accepted as a technical requirement in the industry of
`manufacture of secondary lithium ion battery. Further, all
`lithium ion batteries in the markets around the world are
`manufactured underthis technical requirement For example,
`the charge cut-off voltage is limited to below 4.2 V and the
`overcharge release voltage of its protection circuit is con-
`trolled below 4.15 V during the formation of single lithium
`ion cell. The reasons that the charge cut-off voltage being
`limited to below 4.2 Vlie in the following opinionsin the prior
`research results and documents: although the capacity and
`average operating voltage are improved by increasing the
`charge cut-off voltage, the positive electrode materials and
`the negative electrode materials will undergo structure
`change,the electrolyte may decompose, andthe recycle prop-
`erty of the cell will be adversely affected when the charge
`cut-off voltage is greater than 4.2 V.
`For instance, as to lithium cobalt oxides that is used as
`positive electrode material in the most commercial lithium
`ion batteries, the charge cut-offvoltageis limited to below 4.2
`V andthe actual capacity is 120-140 mAh/g,i.e., about 50%
`
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`2
`of the theoretical capacity, although many documents indi-
`cate that the charge cut-off voltage can be over 4.2 V for a test
`cell using metallic lithium as counter electrode. In fact,
`according to MIZUSHIMAKet al., “A new cathode material
`for batteries ofhigh energy density”, Mater. Res. Bull., 1980,
`15:783, the quantity ofdedopedlithium ionincreases with the
`increase of charge voltage, and the electrochemical capacity
`of lithium cobalt oxides increases accordingly. However, the
`study deems that the reversible charge-discharge voltage is
`about 4.3 V when metallic lithium is used as counter elec-
`trode, and whensaid voltageis higher than 4.3 V, the structure
`of lithium cobalt oxides changes andthe lattice parameter C
`decreases from 4.4 nm to 4.0 nm,andthusthe recycle life of
`cell is affected.
`
`G. PISTOIA et al., J. Power Source, 56(1995), 37-43,
`deems that the structure the lithium cobalt oxides changes
`with the charge voltage, and the coexistence of monoclinic
`phase and hexagonalphasewill appear whenthe chargevolt-
`age is over a certain value, which will spoil the recycle prop-
`erty of cell. The results of experiments showedthatas to a test
`button cell having metallic lithium as negative electrode, the
`capacity of lithium cobalt oxides reaches 159 mAh/g when
`the charge cut-offvoltage is 4.35 V, but it drops to 135 mAh/g
`after several cycles; and the capacity attenuates quickly when
`the charge cut-off voltage is 4.25 V. This documenttakes the
`opinion thatlithium cobalt oxides maintains excellent recycle
`property and a capacity about 130 mAh/g only whenthe
`charge cut-off voltage is 4.15 V, and the corresponding volt-
`ages of monoclinic phase and hexagonalphase separately is
`4.05 V and 4.17 V, i.e., both of them are below 4.2 V.
`In addition, Lei Yongquan, “Materials for New Energy” (in
`Chinese), 2000, p136, discloses that the decomposition volt-
`age of electrolyte solution using LiPF, as electrolyte and
`EC/DMCas mixture solventis 4.2 V, and thus deemsthat the
`electrolyte solution will be decomposed andthe recycle life
`will be affected when the charge cut-off voltage is above 4.2
`V.
`
`In 1990, Sony Corporation issued the lithium ion cell using
`coke as negative electrode, which has a charge cut-offvoltage
`of not more than 4.20 V, and it is accepted as a common
`technical requirementof lithium ion cells thereafter.
`Theprior art deems:
`1. The increase of charge cut-off voltage will change the
`structure of positive electrode material, which mainly
`exhibits at the following two aspects: one aspect is that
`the phase change, i.e., the coexistence of monodinic
`phase and hexagonal phase and the conversion between
`them mayseriously affect the recyclelife of lithium ion
`cell; and another aspect is that the change of lattice
`parameter may narrow the channel for passing lithium
`ions, squeeze the space occupied bylithium ions, jam
`the channel of lithium ions, and decrease the recycle
`property of lithium ioncell.
`2. The elevated charge cut-off voltage may decomposethe
`electrolyte solution, and the loss of electrolyte solution
`renders the transportation of lithium ion moredifficult,
`and thus the recycle life of cell is seriously affected.
`Therefore, it can be seen that the limitation of charge volt-
`age restricts the actual utilization of active electrode materi-
`als. Underthis condition, even ifnew positive electrode mate-
`rial and negative electrode material having higher specific
`energy are developed, the lithium ion cell cannot exhibit the
`best performance. Hence,it is urgently needed to provide a
`method that can improvethe efficacy of active substances of
`lithium ion cell, consequently increase the capacity and aver-
`age operating voltage, and maintain the better cell perfor-
`mance simultaneously.
`
`2
`
`

`

`3
`SUMMARYOF INVENTION
`
`US 7,749,641 B2
`
`4
`cell, or a single lithium ion cell comprising a protecting
`circuit, or a battery comprising a numberofsingle lithium ion
`cells, or a battery comprising a numberofsingle lithium ion
`cell and protecting circuits. For briefness, sometimes it may
`also be termedas “lithium ion cell”. In addition, “theoretical
`capacities of positive electrode and negative electrode”
`meansthe capacities ofthe positive electrode andthe negative
`electrode calculated with an charge cut-off voltage set at 4.2
`V.
`
`As to the commonopinion in the art that increasing the
`charge cut-off voltage above 4.2 V maygreatly shorten the
`recyclelife, the inventor of the present invention conducted a
`large numberof experiments and studies to elevate the charge
`cut-off voltage andthe capacity ofcell. Contrary to this opin-
`ion, the inventor unexpectedly foundthatthe efficacy of elec-
`trode active materials is greatly increased by increasing the
`charge cut-off voltage and property adjusting the ratio of
`positive electrode material to negative electrode material of
`single lithtum ion cell. Consequently, the specific energy,
`capacity and average operating voltage of secondary lithtum
`ion cell or battery are improved, while the performanceofcell
`is substantially not changed. The present inventionis fulfilled
`based on the aforesaid discovery.
`Tt is one object of the present invention to provide a new
`method for improving capacity, average operating voltage
`and energy density of a secondary lithium ioncell or battery,
`wherein the charge cut-off voltage of the singe cell is greater
`than 4.2 V, and less than 5.8 V, and the ratio of positive
`electrode material to negative electrode material of the single
`cellis from 1:1.0 to 1:2.5, preferably from 1:1.16 to 1:2.5, as
`calculated by the specific capacity with the charge voltage
`limited to 4.2 V.
`Another object of the present invention is to provide a
`secondary lithium ion cell or battery, wherein the single sec-
`ondary lithtum ion cell has an charge cut-off voltage of
`greater than 4.2 V but less than 5.8 V, andthe ratio of positive
`electrode material to negative electrode material of the single
`cellis from 1:1.0 to 1:2.5, preferably from 1:1.15 to 1:2.5, as
`calculated by the specific capacity with the charge voltage
`limited to 4.2 V.
`
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`inventor studied the relation between the
`The present
`charge cut-off voltage and the cell properties of secondary
`lithium ion cell by gradually elevating the charge cut-off
`voltage. For example,in the formationtest for the commercial
`secondary single lithium ion cells and the self made single
`secondary lithium ion cells, the inventor elevated the charge
`cut-offvoltage from 4.2 V to 4.30 V, 4.35 V, 4.40 V, 4.45 V and
`4.6 V, and the results showed that when the charge cut-off
`voltageis, 4.3 V, 4.35 V and 4.40V, the specific energy of cell
`increases by 6-20% than that underthe charge cut-off voltage
`of4.2 V, and the cells still maintain excellent recycle property,
`e.g., the capacity maintains more than 95% after 50 cycles,
`and more than 80% after 300 cycles. However, when the
`charge cut-off voltage is 4.45 V or high, the specific energy
`increases by about 30%,butthe cell exhibits inferior recycle
`property, e.g., the capacity maintains merely 83.9% after 6
`cycles.
`For investigating the reasons ofpoor recycle property when
`the charge cut-off voltage is 4.45 V or high, the inventor
`adjusted the ratio of positive electrode material to negative
`electrode material, i.e., said ratio was adjusted within the
`range from 1:1.3 to 1:2.5 calculated according to the theoreti-
`cal capacity underthe charge cut-offvoltage of4.2 V, and then
`the single lithium ion cell having the adjusted ratios were
`tested by charging at an charge cut-off voltage of 4.45 V, 4.6
`Yet another object of the present invention is to provide a
`V, 4.8 V, 5.0 V, 5.2 V, 5.4 V, 5.6 V and 5.8 V, preferably said
`protecting circuit adaptedfor the secondary lithiumion cell or
`charging tests were conducted during the formation andtest
`battery, said protecting circuit having a first overcharging
`of the cells. Experimental results show that the specific
`protection voltage of greater than 4.35 V, and an overcharge
`energy wasgreatly increased underthe charge cut-offvoltage
`release voltage of greater than 4.15 V.
`of 4.45 V or higher, and the corresponding recycle property
`Yet another object of the present invention is to provide an
`wasessentially not affected, when appropriate ratios of posi-
`electronic device using the secondary lithtum ion cell or
`battery as power supply, said electronic device comprising a
`tive electrode material to negative electrode material were
`
`protecting circuit havingafirst overcharging protection volt- adopted.
`age of greater than 4.35 V, and an overchargerelease voltage
`In the present method, the elevating of the charge cut-off
`of greater than 4.15 V.
`voltage is advantageously carried out during the formation
`Yet another object of the present invention is to provide a
`and examinationofthe cell. The use of charge cut-off voltage
`charging device for the secondary lithium ion cell or battery,
`of4.20V or high could increase the specific energy ofcell, the
`said charging device controlling an charge cut-off voltage for
`capacity of pasitive electrode active material and the average
`the single lithium ion cell within the range of greater than 4.3
`operating voltage, and activate the cell so thatthe cell reaches
`V butless than 5.8 V, preferably within the range from 4.3 V
`its optimal working state with simultaneously achieving the
`to 5.2 V, and morepreferably from 4.3 V to 4.8 V.
`effect of the formation, substantial improvementof the spe-
`cific energy of commercial lithium ion cells, and imparting
`the competitiveness of lithium ion cells without altering the
`original process.
`The mechanism of the above experimental results needs
`more researches. Without limited by any theory, the presumed
`reasonsare as follows.
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`1. After the elevation of charge cut-off voltage, the amount
`of lithium ion dedoped from the positive electrode greatly
`increases, which renders an unmatchedstate to the original
`negative electrode material, and deposition of excessive
`lithium ions on the surface of negative electrode as metallic
`lithium, which jam part of the channel for passing lithium
`ions and result in the reduction of capacity and the deteriora-
`tion of recycle property. The increase of the amountof nega-
`tive electrode material meets the requirement of doping the
`relatively excessive lithium ions, and avoids the deposition of
`lithium ions on the surface of negative electrode as metallic
`
`EMBODIMENTS FOR CARRYING OUT THE
`PRESENT INVENTION
`
`
`
`Being contrary to the commonopinion in the art that the
`charge cut-off voltage shall be controlled below 4.2 V, the
`present inventor unexpectedly found that the capacity, spe-
`cific energy and average operating voltage of the secondary
`lithium ion cell or battery were notably improved withlittle
`cost and with the other properties substantially unchanged,
`when investigating the effect of the elevated charge cut-off
`voltage on the cell performances with a large number of
`experiments of gradually elevating the charge cut-off voltage
`and appropriately adjusting the ratio of the positive electrode
`to the negative electrode of the single lithium ion cell. In the
`present invention, “lithium ion cell or battery” meansthat the
`present invention can be appliedto eithera single lithium ion
`
`3
`
`

`

`US 7,749,641 B2
`
`5
`lithium, and thus the maintaining properties (self-discharge
`properties) and recycle property are not affected. The suitable
`ratio ofpositive electrode materialto negative electrode mate-
`rial will avoid the deposition ofmetallic lithium on the surface
`ofnegative electrode and the obstruction of channelfor pass-
`ing lithium ions, and consequently avoid the attenuation of
`capacity of cell. In particular, when the charge cut-offvoltage
`of lithium ion cell is greater than 4.45 V, the negative elec-
`trode material of the ordinary commercial lithium ioncell is
`still more deficient, and the excessive lithium ions will
`deposit on the surface ofnegative electrode and form metallic
`lithium, which jams the channel for passing lithium ions and
`attenuates the capacity ofcell. The great increase ofcontent of
`negative electrode could reducethe attenuation of capacity of
`lithtum ion cell caused by the increase of recycle times.
`According to this viewpoint, the inventor performed a lot of
`experiments, and the results prove the aforesaid assumption
`(see the Examples).
`2. Within a certain range of charge cut-off voltage, the
`decompositionoflittle electrolyte solution brings about neg-
`ligible effect on the recycle property of cell. The electrolyte
`having a high decomposition potential or an additive increas-
`ing the decomposition potential of electrolyte solution may
`bring about better performance. The decomposition of elec-
`trolyte solution mainly occurs on the positive electrode.
`Although prior documents disclosed that the decomposition
`voltage ofthe electrolyte solution comprising LiPF, as elec-
`trolyte and the mixture of EC/DMCassolventon the surface
`of aluminum foil is 4.2 V, according to the results of experi-
`ments, this factor essentially does not affect the recycle life of
`the currently commercialized lithium ion cell. Namely, even
`though the electrolyte solution decomposes under a voltage
`higher than 4.2 V, the electric energy is mainly converted into
`chemical energy and the electric energy involved in the
`decomposition of electrolyte is very little, thus, this decom-
`position of electrolyte can hardly affect the recycle life of the
`lithium ion cell. As to the voltages above the decomposition
`voltage, such as above 5.0 V, the substance A can be added
`into the electrolyte solution, or the electrolyte solution B
`having a higher decomposition voltage can be used. The
`decomposition potentials of the components of electrolyte
`solution commonlyused in the art are depicted in Table 1. It
`can be seen that the lowest decomposition voltage of solvent
`is above 4.5 V.
`
`TABLE1
`
`Decomposition potentials of various mixture electrolyte solutions
`Solute
`
`Mixture
`solvent
`PC:DME
`PC:DEC
`PC:EC
`PC:EC:DME
`PC:DEC:2MLF
`EC:DEC
`EC:DMC
`B
`
`Liclo,
`Decomposition
`potentials (V)
`4.51
`4.5
`
`4.5
`
`LiAsF,
`Decomposition
`potentials (V)
`4.72
`45
`45
`4.62
`4.52
`49
`
`LiPF,
`Decomposition
`potentials (V)
`
`48
`49
`5.9
`
`3. As to the reasonthatthe lithium ion cell does not appear
`attenuation of capacity caused by the changeofstructure as
`mentioned in the prior documents when the charge cut-off
`voltage is above 4.2 V, it may be due tothat: after the ithium
`ionsfirst intercalaton into anode, there is about 10% lithium
`ions which form a SEI film, so that the actual space of the
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`lithium ions is more than the space that should be occupied by
`the lithium ions, i.e., the space available to the lithium ions
`exceeds about 10% of the space needed by the activated
`lithium ions, thus, although the elevation of the charge volt-
`age changesthe structure of positive electrode material, i.e.,
`reduces the lattice parameter, the recycle life is not affected
`because the space occupied by the actually deintercalation
`and intercalation lithium ions is less than the space actually
`possessed by the positive electrode material, and thus the
`change of structure in a certain extent will not obstruct the
`dedoping and doping oflithium ions and will not affect the
`recycle life of cell. Using positive material more stable in
`structure with respect to the change of charge voltage exhibit
`better performance. Althoughthepositive electrode generates
`inert substance poor in conductivity when overcharged,
`according to the results of experiments, it occurs only when
`the lithium ions completely dedoped. For example, as to
`lithium cobalt oxides,
`lithium nickel oxides, and doped
`lithium cobalt oxides and lithtum nickel oxides, when they
`are charged with 3C5A current, the experimental data show
`that only when the voltage is about 6.20 V the lithium ions
`completely dedoped, with releasing a lot of oxygen, and
`forming an insulator. As to lithium manganese oxides and
`dopedlithium manganeseoxides, the lithium ions completely
`dedoped under the same charge current whenthecell poten-
`tial is about 6.50 V. Generally, the specific energy of positive
`electrode active substance actually used in the present com-
`mercialized lithium ion cell is far less than the theoretical
`
`capacity thereof, and even if the charge cut-off voltage is
`elevated up to 5.8 V,
`the theoretical capacity cannot be
`achieved underthe proviso that suitable formulation is used,
`thus,
`the cell
`is not overcharged. Therefore,
`the present
`methodstill enjoys satisfactory safety.
`4. Besides the aforementioned factors, the self-discharge
`of cell, the selection of current collector, and the formation of
`passivefilm all affect the recycle life oflithium ion cell, while
`these factors mainly dependon the preparation of lithium ion
`cell. It is believable that if the optimal processesare used, the
`capacity, average operating voltage and specific energy can
`be greatly improved, while the recycle life and other proper-
`ties of the cell are not affected.
`
`Hence, the present invention is to provide a novel method
`for effectively improving the specific energy and average
`operating voltage of secondary lithium ion cell or battery.
`Contrary to the prior art, the present method elevates the
`charge cut-offvaltage to greater than 4.2 V but less than 5.8 V,
`and control theratio ofpositive electrode material to negative
`electrode material of single lithtum ion cell at 1:1.0 to 1:2.5
`calculated by theoretical specific energy, so as to increase the
`efficacy of electrode active materials, to improve the capacity,
`energy density and output voltage of cell, and to maintain the
`performance of cell. For achieving the better effect, the
`charge cutoff voltage used in the present invention is prefer-
`ably 4.3-5.2 V, and more preferably 4.2-4.8 V. In addition,the
`ratio ofpositive electrode material to negative electrode mate-
`rial of cell is 1:1.0 to 1:2.5 calculated by the theoretical
`capacity underthe chargecut-offvoltage of 4.2 V. The experi-
`ments showed that when the process parameters go beyond
`the aforesaid ranges, the properties of cell are deteriorated
`and unsuitable for use. When the ratio of positive electrode
`material to negative electrode material is less than 1.0 calcu-
`lated by theoretical capacity, the recyclelife of cell is exces-
`sively reduced, while when saidratio is greater than 2.5, the
`volumeefficiency of cell is notably reduced. Further, when
`the charge cut-off voltage is greater than 5.8 V, the cell has
`inferior properties and is unsuitable foruse.
`
`4
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`

`

`US 7,749,641 B2
`
`7
`It can be seenthat the capacity, specific energy and average
`operating voltage of secondary lithium ion cell can be greatly
`improved by elevating the charge cut-off voltage and by
`appropriately adjustingthe ratio ofpositive electrode material
`to negative electrode material calculated by the theoretical
`capacity, while the recycle property of cell is not affected,
`which rendersthe lithium ion cell possess more commercial
`value and broader application range. Hence, it can also be
`seen that the present method further optimizes the utilization
`of positive electrode material, and thus is an economical
`method. The inventors believe that the method canstill be
`
`used to positive and negative electrode materials having
`higher specific energy developed in future, and achieves the
`optimal effect.
`In addition, it is worthy to be noted that the used in the
`present method is not such that the cell works in extreme
`conditions. After repetitive experiments, the inventor never
`found that the present method increased the probability of
`damage of cell. Hence, the present method is also a safe
`method.
`
`15
`
`Further, the present invention further provides a novel sec-
`ondary cell or battery having improved specific energy and
`average operating voltage. Contrary to the prior art,
`the
`charge cut-offvoltage ofthe single cell of said secondary cell
`or battery is greater than 4.2 V butless than 5.8 V, andtheratio
`of positive electrode material to negative electrode material
`calculated by the theoretical capacity under the charge cut-off
`voltage of 4.2 V is 1:1.0 to 1:2.5. As comparedto the prior
`secondary lithium ioncell or battery cell, the capacity, energy
`density and output voltage of the present secondary lithium
`ion cell or battery are greatly improved, while its recycle life
`is equivalentto that of the prior art cell. For achieving better
`effect, the aforesaid charge cut-offvoltage usedin the present
`invention is preferably in the range from 4.3 V to 5.2 V, more
`preferably in the range from 4.3 V to 4.8 V. In addition, the
`ratio ofpositive electrode materialto negative electrode mate-
`rial of said singe lithium ion cell, which is calculated by the
`theoretical capacity underthe charge cut-off voltage of 4.2 V,
`is 1:1.5 to 1:2.5. Experiments showed that when the process
`parameters go beyondthe aforesaid ranges, the properties of
`cell are deteriorated and unsuitable for use. Whenthe ratio of
`
`40
`
`8
`electrode material to negative electrode material is calculated
`by theoretical capacity underthe charge cut-off voltage of 4.2
`Vv.
`
`Positive Electrode
`
`Thepositive electrodeis prepared e.g., by dispersing posi-
`tive electrode active material, conducting agent and binderin
`a suitable solvent to form a suspension, coating said suspen-
`sion ona current collector, such as aluminum foil, then drying
`and pressing the coated current collector by rollers.
`Thepositive electrode active substance usedin the present
`invention is lithitum-containing compound. Although the
`examples use lithium cobalt oxides (lithium cobalt composite
`oxides), lithium manganese oxides andlithium nickel oxides
`as positive electrode material, it is understood that the prac-
`tice of the present invention is not limited to the specific
`properties of said lithitum-containing composite oxides,
`rather a wide rangeofpositive electrode active substance can
`be used in the present invention. The commonfeature ofthese
`oxidesis that their specific energy increases with the increase
`of voltage, and the experiments (see the examples) prove that
`the capacity of cell is greatly elevated when the charge cut-off
`voltage is above 4.20 V, while the other properties of cell are
`not affected. The present invention can also be usedto lithium
`ion cells having dopedlithtum-containing compoundasposi-
`tive electrode active material, such as various positive elec-
`trode active materials containing various oxides andsulfides,
`such as lithium cobalt composite oxides, lithtum manganese
`composite oxides, lithium nickel composite oxides, lithium
`nickel cobalt composite oxides, lithtum manganese cobalt
`composite oxides, and vanadium oxides. Amongthese posi-
`tive electrode materials,
`lithium cobalt composite oxides
`(such as LiCoO,),
`lithtum manganese composite oxides
`(such as LiMn,O,,), lithium nickel composite oxides (such as
`TaNiO,), lithium nickel cobalt composite oxides (such as
`LiNi,_,Co,O.,), and lithium manganese cobalt composite
`oxides (such as LiMn,Co,_,O.), which have highercell volt-
`age, are preferably used. In addition, the present invention can
`use conventional conducting agent and binder, and the mix-
`ture ratio for each componentsin the positive electrode active
`material can be those well knownin the art.
`
`Separator
`The separator used in the present invention is a separator
`well known in the art. For example, it can be a non-woven
`fabric made of synthetic resin, polyethylene porous mem-
`brane or polypropylene porous membrane, and a material
`formed by like materials.
`
`positive electrode material to negative electrode materialis
`less than 1.0 calculated by theoretical capacity, the recycle
`life of cell is excessively reduced, while whensaid ratio is
`greater than 2.5, the volume efficiency of cell is notably
`reduced. Further, when the charge cut-off voltage is greater
`than 5.8 V, the cell has inferior properties and is unsuitable for
`use.
`
`50
`
`Negative Electrode
`The negative electrode is prepared e.g., by dispersing nega-
`Moreover,it is importantthat the present method not only
`tive electrode active material, conducting agent and binderin
`can be usedto the secondary lithium ion cell or battery of the
`a suitable solvent to form a suspension, coating said suspen-
`present invention, but also can be used to the secondary
`sion on a current collector, such as copperfoil, nickel foil or
`lithium ioncell or battery prepared according to the method of
`stainless steelfoil, then drying andpressing the coated current
`the prior art, such as the present commercialized secondary
`collector by rollers.
`lithtum ion cell or battery.
`The negative electrode active material used in the present
`invention is a carbonaceous or non-carbonaceous substance
`Withoutlimitation,the following contents more concretely
`capable of doping and dedoping lithium ion, including, such
`introduce the secondary lithium ion cell used in the present
`as, lithium alloy (such as Li,Ti;O,,), metal oxide (such as
`method. Generally, a secondary lithium ion cell comprises a
`amorphous tin oxide, WO, and MoO,), TiS, and carbon-
`positive electrode, a negative electrode, a non-aqueouselec-
`aceous substance capable of absorbing and desorbinglithium
`trolyte, andaseparatorthe positive electrode andthe negative
`ions, and especially,
`the carbonaceous substance is the
`electrode. The non-aqueouselectrolyte can be obtained by
`desired negative electrode active material.
`dissolving lithium-containing metal salt, such as LiPF,, as
`electrolyte into a non-aqueous solvent, such as ethylene car-
`The carbonaceous substance used in the present invention
`bonate or dimethyl carbonate. The separator can be insoluble
`includes: graphite, non-oriented graphite, coke, carbon fiber,
`in said non-aqueoussolvent,