Precursors for lithium transition metal oxide cathode materials for rechargeable batteries

Abstract

A particulate precursor compound for manufacturing a lithium transition metal (M)-oxide powder for use as an active positive electrode material in lithium-ion batteries, wherein (M) is Ni.sub.xMn.sub.yCo.sub.zA.sub.v, A being a dopant, wherein 0.33x0.60, 0.20y0.33, and 0.20z0.33, v0.05, and x+y+z+v=1, the precursor comprising Ni, Mn and Co in a molar ratio x:y:z and having a specific surface area BET in m.sup.2/g and a sulfur content S expressed in wt %, wherein formula (I).

Claims

1. A particulate precursor compound for manufacturing a lithium transition metal (M)-oxide powder for use as an active positive electrode material in lithium-ion batteries, wherein (M) is Ni.sub.xMn.sub.yCo.sub.zA.sub.v, A being a dopant, and wherein 0.33x0.50, 0.20y0.33, and 0.20z0.33, v0.05, and x+y+z+v=1, and the precursor comprises Ni, Mn and Co in a molar ratio x:y:z and has a specific surface area BET in m.sup.2/g and a sulfur content S expressed in wt %, and ${\left(\frac{\mathrm{BET}-25}{18-6x}\right)}^2+{\left(\frac{S-0.15}{0.25-0.05x}\right)}^{2}0.75.$

2. The particulate precursor compound of claim 1, wherein the precursor comprises a hydroxide M-OH or an oxyhydroxide M-OOH compound.

3. A method for preparing a lithium transition metal (M)-oxide powder for use as an active positive electrode material in lithium-ion batteries, comprising: providing the M-precursor according to claim 1, providing a Li precursor compound, mixing the M-precursor and the Li precursor, and firing the mixture at a temperature between 600 and 1100 C. for at least 1 hr.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 3: particle size distribution curve of cathode material in EX30 with and without being pressed by uniaxial stress.

(2) FIG. 1: the correlation between the initial charge capacity of NMC532 and the sulfur content of the corresponding precursor, where the dotted line is a linear interpretation.

(3) FIG. 2: the correlation between the initial charge capacity of NMC622 and the sulfur content of the corresponding precursor, where the dotted line is a linear interpretation.

(4) FIG. 4: Direct current resistance (DCR) measured by hybrid pulse power characterization at 25 C. at different state of charge (SOC) for NMC433 cathode materials (Ex. 1, 2, 3 and 6)

(5) FIG. 5: Direct current resistance (DCR) measured by hybrid pulse power characterization at 10 C. at different state of charge (SOC) for NMC433 cathode materials (Ex. 1, 2, 3 and 6)

(6) FIG. 6: Direct current resistance (DCR) measured by hybrid pulse power characterization at 25 C. at different state of charge (SOC) for NMC532 cathode materials (Ex. 7, 8 and 13)

(7) FIG. 7: Direct current resistance (DCR) measured by hybrid pulse power characterization at 10 C. at different state of charge (SOC) for NMC532 cathode materials (Ex. 7, 8 and 13)

(8) FIG. 8: Direct current resistance (DCR) measured by hybrid pulse power characterization at 25 C. at different state of charge (SOC) for NMC622 cathode materials (Ex. 24 and 28)

(9) FIG. 9: Direct current resistance (DCR) measured by hybrid pulse power characterization at 10 C. at different state of charge (SOC) for NMC622 cathode materials (Ex. 24 and 28)

DETAILED DESCRIPTION

(10) The precursors according to the invention are typically mixed hydroxides or carbonates prepared by precipitation reactions. Precipitation of mixed hydroxides (for example, the precipitation of a flow of NaOH with a flow of M-SO.sub.4 under controlled pH) or mixed carbonates (for example, the precipitation of a flow of Na.sub.2CO.sub.3 with a flow of M-SO.sub.4) allows precursors of suitable morphology to be achieved. The precipitation reaction can take place in a continuous flow or loop reactor (also referred to as CFR reactor) as illustrated in U.S. Pat. No. 8,609,068. In the reactor the following actions take place:

(11) a) continuously feeding an M-SO.sub.4 flow and a flow of a base like NaOH or Na.sub.2CO.sub.3 into distinct portions of a loop reaction zone comprising a stream of liquid medium, with the optional addition of ammonia (as chelating agent) to achieve a desired morphology; wherein at least a portion of the M-SO.sub.4 and the NaOH or Na.sub.2CO.sub.3 react to form the precursor in the liquid medium of the loop reaction zone;
b) continuously recirculating the liquid medium through the loop reaction zone (typically by the energy delivered by an impeller);
c) continuously discharging from the loop reaction zone a portion of the liquid medium comprising the precipitated precursor;
d) filtering and washing the precipitated precursor until a conductivity of less than 50 S is reached in the washing water; and
e) drying the precipitate at a temperature of between 70-150 C. for 12 to 30 hours.

(12) Such a reactor allows to carefully control the physical properties of the precursori.e. the BET and sulfur contentby modifying the temperature, the energy input in the loop reactor, and the addition rate of the liquid carrying the reactants (being equal to the discharge rate of the liquid carrying the reagents) which defines the number of passes of the liquid medium through the continuous loop reactor, and which corresponding to the residence time. By residence time is understood the average residence time in the reactor volume calculated from the volume of the reactor divided by the addition rate e.g.

(13) $\frac{1L}{\frac{3L}{\mathrm{hour}}}.$
Practically, when operated by a skilled person the particle size and other product characteristics can be changed by selecting certain values for the pH, the residence time and the energy input to the liquid medium. In such a loop setup a high power input per kg of treated material can be applied, and all material passes the impeller frequently. When the residence time is lowered a higher BET value is obtained. The pH is influenced by the ammonia content and the (molar) ratio of NaOH used per metal M in the precipitation, and has an effect on the sulfur content and BET. When the pH is lowered, a higher sulfur content and a higher BET is reached.

(14) In this invention, precursor compound material needs to have both a value for BET and S % falling in a specific range, to ensure that the resulting cathode material has low Q.sub.irr and low DCR. For a particulate precursor compound at a given D50 with Gaussian particle size distribution, a low BET means dense spherical precursor particles which normally lead to a dense cathode material after reaction with a lithium precursor. A high BET means that the precursor contains a certain amount of porosity, which results in porous cathode materials after lithiation. A certain amount of porosity could allow sufficient contact between cathode particles and electrolyte, which shortens the diffusion path of Li ion diffusion, hence a lower DCR at especially low state of charge where Li ion diffusion becomes more difficult. However, a too high BET precursor could lead to too many pores in the cathode material after lithiation. On the one hand, this will reduce the cathode density. On the other hand, too many particle cracking and breaking will occur during electrode calendaring, requiring more electrolyte for cathode wetting, leading to more SEI formation and probably creating a problem of low Li ion diffusion.

(15) When using metal sulfate as source material for the metal hydroxide precursor precipitation, a certain amount of sulfate normally remains as an impurityalthough it could be very low, or even zero. This sulfate will transform into lithium sulfate after reaction with the lithium source, and stay on the particle surface of the cathode material. Too much lithium sulfate will of course cause a loss of charge capacity, which is not preferred. However, a certain amount of lithium sulfate covering the particle surface could prevent the particle grain boundaries from cracking during lithium extraction and insertion, which is especially beneficial for high Ni NMC cathode material. For a precursor compound with a certain BET, a little lithium sulfate could also help to reduce the Q.sub.irr of the resultant cathode material. A dissolution of lithium sulfate could reduce the impedance between the electrolyte and cathode particle, hence resulting in a lower DCR.

(16) Precursors with small particle size (such as 4-6 m) will result in cathode powders with small particle size and are used for high rate applications, such as in hybrid electric vehicles. For these it is important to have a low Q.sub.irr, such as less than 9%. Precursor with larger particle size (such as 10-12 m) will result in cathode powders with larger particle size and are used for high capacity applications, such as in pure electric vehicles. For these a somewhat higher Q.sub.irr, such as less than 10%, is acceptable.

(17) A DCR test of the final lithiated cathode materials does not yield a single value, but its value is a function of the battery's state of charge (SOC). For LNMCO cathodes, the DCR increases at low state of charge whereas it is flat or shows a minimum value at a high state of charge. A high state of charge refers to a charged battery, a low state of charge is discharged. The DCR strongly depends on temperature. Especially at low temperature the cathode contribution to the DCR of the cell becomes dominant, hence low T measurements are quite selective to observe improvements of DCR that are directly attributable to the behaviour of the cathode materials. In the examples, DCR results of cathodes of real full cells using materials according to the invention are reported. Typically the SOC is varied from 20 to 90%, and the tests are performed at representative temperatures of 25 C. and 10 C.

GENERAL DESCRIPTION OF EXPERIMENTAL DATA

(18) a) PBET Precursor Specific Surface Area

(19) The specific surface area is measured with the Brunauer-Emmett-Teller (BET) method using a Micromeritics Tristar 3000. 2 g of precursor powder sample is first dried in an oven at 120 C. for 2 hr, followed by N.sub.2 purging. Then the precursor is degassed in vacuum at 120 C. for 1 hr prior to the measurement, in order to remove adsorbed species. A higher drying temperature is not recommended in precursor BET measurements, since a precursor may oxidize at relatively high temperature, which could result in cracks or nano-sized holes, leading to an unrealistically high BET.

(20) b) S Content of the Precursor after Washing and Drying

(21) The S content is measured with the Inductively Coupled Plasma (ICP) method by using an Agillent ICP 720-ES. 2 g of precursor powder sample is dissolved into 10 mL high purity hydrochloric acid in an Erlenmeyer flask. The flask may be covered by glass and heated on a hot plate for complete dissolution of the precursor. After being cooled to the room temperature, the solution is moved to a 100 mL volumetric flask and the flask is rinsed 34 times using distilled (DI) water. Afterwards, the volumetric flask is filled with DI water up to the 100 mL mark, followed by complete homogenization. 5 mL solution is taken out by a 5 mL pipette and transferred into a 50 mL volumetric flask for a 2.sup.nd dilution, where the volumetric flask is filled with 10% hydrochloric acid up to the 50 mL mark and then homogenized. Finally, this 50 mL solution is used for ICP measurement.

(22) c) Cathode Material Preparation

(23) In this invention, in order to evaluate the electrochemical behaviour in a coin cell, cathode materials have been prepared from the precursor compounds according to the invention, by using conventional high temperature sintering, as is described in e.g. US2014/0175329. Li.sub.2CO.sub.3 (Chemetall) or LiOH (SQM) is dry mixed with the precursor compound in a certain Li:M molar ratio using a Henschel Mixer for 30 mins. The mixture is reacted at a high temperature for 10 hr under air, using pilot-scale equipment. The Li:M molar blending ratio and sintering temperature are standard, but they differ for precursors with different Ni content, which will be specified in each individual example. After firing, the sintered cake is crushed, classified and sieved so as to obtain a non-agglomerated powder with a mean particle size D50 similar to that of the precursor.

(24) d) Evaluation of Electrochemical Properties in Coin Cells

(25) Electrodes are prepared as follows: about 27.27 wt. % of active cathode material, 1.52 wt. % polyvinylidene fluoride polymer (KF polymer L #9305, Kureha America Inc.), 1.52 wt. % conductive carbon black (Super P, Erachem Comilog Inc.) and 69.70 wt. % N-methyl-2-pyrrolidone (NMP) (from Sigma-Aldrich) are intimately mixed by means of high speed homogenizers. The slurry is then spread in a thin layer (typically 100 micrometer thick) on an aluminum foil by a tape-casting method. After evaporating the NMP solvent at 120 C. for 3 hr, the cast film is processed through two constantly spinning rolls with a 40 micrometer gap. Electrodes are punched from the film using a circular die cutter measuring 14 mm in diameter. The electrodes are then dried overnight at 90 C. The electrodes are subsequently weighed to determine the active material loading. Typically, the electrodes contain 90 wt. % active materials with an active materials loading weight of about 17 mg (11 mg/cm.sup.2). The electrodes are then put in an argon-filled glove box and assembled within a 2325-type coin cell body. The anode is a lithium foil having a thickness of 500 micrometers (origin: Hosen); the separator is a Tonen 20MMS microporous polyethylene film. The coin cell is filled with a 1M solution of LiPF.sub.6 dissolved in a mixture of ethylene carbonate and dimethyl carbonate in a 1:2 volume ratio (origin: Techno Semichem Co.).

(26) Each cell is cycled at 25 C. using Toscat-3100 computer-controlled galvanostatic cycling stations (from Toyo) at different rates in the 4.33.0V/Li metal window range. The initial charge capacity CQ1 and discharge capacity DQ1 are measured in constant current mode (CC). The irreversible capacity Q.sub.irr is expressed in % as:

(27) $Q_{\mathrm{Irr}.}=\frac{\left(\mathrm{CQ}1-\mathrm{DQ}1\right)}{\mathrm{CQ}1}100\left(\%\right)$
e) Slurry Making, Electrode Coating and Fullcell Assembly

(28) A slurry is prepared by mixing 700 g of the doped and coated NMC 433 with NMP, 47.19 g of super P (conductive carbon black of Timcal) and 393.26 g of 10 wt. % PVDF based binder in NMP solution. The mixture is mixed for 2.5 hr in a planetary mixer. During mixing additional NMP is added. The mixture is transferred to a Disper mixer and mixed for 1.5 hr under further NMP addition. A typical total amount of NMP used is 423.57 g. The final solid content in the slurry is about 65 wt. %. The slurry is transferred to a coating line. Double coated electrodes are prepared. The electrode surface is smooth. The electrode loading is 9.6 mg/cm.sup.2. The electrodes are compacted by a roll press to achieve an electrode density of about 2.7 g/cm.sup.3. To prepare pouch cell type full cells, these positive electrodes (cathode) are assembled with a negative electrode (anode) which is typically a graphite type carbon, and a porous electrically insulating membrane (separator). The full cell is prepared by the following major steps: (1) electrode slitting, (2) tap attaching (3) electrode drying, (4) jellyroll winding, and (5) packaging.

(29) (1) electrode slitting: after NMP coating the electrode active material might be slit by a slitting machine. The width and length of the electrode are determined according to the battery application.

(30) (2) tap attaching: there are two kinds of taps. Aluminum taps are attached to the positive electrode (cathode), and copper taps are attached to the negative electrode (anode).

(31) (3) electrode drying: the prepared positive electrode (cathode) and negative electrode (anode) are dried at 85 C. to 120 C. for 8 hr in a vacuum oven.

(32) (4) jellyroll winding: after drying the electrode a jellyroll is made using a winding machine. A jellyroll consists of at least a negative electrode (anode) a porous electrically insulating membrane (separator) and a positive electrode (cathode).

(33) (5) packaging: the prepared jellyroll is incorporated in a 360 mAh cell with an aluminum laminate film package, resulting in a pouch cell. Further, the jellyroll is impregnated with the electrolyte. The quantity of electrolyte is calculated in accordance with the porosity and dimensions of the positive electrode and negative electrode, and the porous separator. Finally, the packaged full cell is sealed by a sealing machine.
f) DCR (Direct Current Resistance) Evaluation

(34) The DCR resistance is obtained from the voltage response to current pulses, the procedure used is according to the USABC standard mentioned before. The DCR resistance is very relevant for practical application because data can be used to extrapolate fade rates into the future to prognoses battery life, moreover DCR resistance is very sensitive to detect damage to the electrodes, because reaction products of the reaction between electrolyte and anode or cathode precipitate as low conductive surface layers.

(35) The procedure is as follows: the cells are tested by hybrid pulse power characterization (HPPC) to determine the dynamic power capability over the device's useable voltage range, using a test profile that incorporates 10 sec charge and 10 sec discharge pulses at each 10% stage of charge (SOC) step. In the current invention, the HPPC tests are conducted at both 25 C. and 10 C. The testing procedure of 25 C. HPPC is as follows: a cell is first charged-discharged-charged between 2.74.2V under CC/CV (constant current/constant voltage) mode at 1 C rate (corresponding to the current which discharges a charged cell within 1 hr). Afterwards, the cell is discharged under CC mode at 1 C rate to 90% SOC, where 10 second discharge at 6 C rate (corresponding to the current which discharges a charged cell within hr) is applied followed by 10 second charge at 4 C rate. The differences in voltage during pulse discharge and pulse charge are used to calculate the discharge and charge direct current resistance (DCR) at 90% SOC. The cell is then discharged at 1 C rate to different SOC's (80%20%) step by step and at each SOC, 10 s HPPC tests are repeated as described above. The HPPC tests at 10 C. uses basically the same protocol as testing at 25 C., except that the 10 s discharge pulse is performed at 2 C rate and the 10 s charge pulse is performed at 1 C rate. To avoid the influence of self-heating of the cell on the cell temperature during charge and discharge, a fixed relaxation time is applied after each charge and discharge step. The HPPC tests are conducted on two cells of each cathode material at each temperature and the DCR results are averaged for the two cells and plotted against the SOC. Basically, a lower DCR corresponds to a higher power performance.

(36) The invention is further illustrated in the following examples:

Preparation of Examples: Influence of Parameters

(37) An NMC precursor is typically prepared by combining a metal salt solution and a base in a stirred reactor. The pH is influenced by the ratio of the base used per metal ion (OH/Me) during the precipitation. The stoichiometric ratio of sodium hydroxide to metal(II) is 2. If the ratio is lower than 2 the pH decreases. Sometimes ammonia is added and this will also affect the pH. As said before, during the operation the particle size can be adapted by eg. selecting a certain value for the pH, the residence time and the energy input in the reactor (=the powertime). The number of rotations per minute (rpm) of the impeller and the impeller size are responsible for the power delivered to the liquid medium. The power can be calculated or measured from the power delivered by the engine frequency drive (of the impeller motor).

(38) When during the precipitation the pH is lowered, a higher sulfur content and a higher BET is reached. A low residence time avoids the precipitation of dense crystals and can also lead to a less dense arrangement of crystals inside the particles. Some of the sulfur is present inside the crystals that make up the particles, and some of the sulfur is absorbed on the particles' surface. The sulfur present in the crystals is difficult to remove by washing. The sulfur absorbed on the surface can be washed away depending on the accessibility of the sulfur by the washing media. This accessibility is determined by both the arrangement of the crystals and the BET. Therefore it is required to make a compromise between pH, residence time and power to reach the desired BET and sulfur content. There are multiple combinations possible to prepare the desired product. For some of the Examples and Counter Examples of the invention (that are discussed further below), the precipitation parameters in a CFR reactor volume of 7 L are given below. In the process sodium hydroxide but no ammonia was used.

(39) TABLE-US-00001 TABLE 1 influence of residence time Residence Temperature Power rpm time (min) OH/Me ( C.) (W/kg) BET S EX9 Example 1200 34 1.96 150 15.0 20.8 0.150 EX20 Counter- 1200 20 1.96 150 15.0 20.3 0.520 Example

(40) In the case of EX20 versus EX9 the lower residence time at the same power (expressed by the rpm) and pH (expressed by the ratio OH/Me) gives a similar BET. Note that the third digit in the determination of the BET is not significant. The longer residence time in EX9 does not have a too big impact on the BET but due to the longer residence time S is not incorporated in the crystals. The crystals have more time to arrange the atoms into their structure and expel the sulfur, that is washed away consecutively.

(41) TABLE-US-00002 TABLE 2 influence of pH Residence Temperature Power rpm time (min) OH/Me ( C.) (W/kg) BET S EX10 Example 1200 20 1.97 149 15.0 23.2 0.300 EX22 Counter- 1200 19 1.92 149 15.0 35.6 0.470 Example

(42) The OH/Me should be carefully tuned because small variations can have a big impact on the pH and eventually the particle size and other particle characteristics such as BET. The pH has also an impact on the sulfur content. In Example 10 a compromise was made to have a high enough BET but a lower sulfur content.

(43) TABLE-US-00003 TABLE 3 influence of power input Ex- Residence Temperature Power Counter rpm time (min) OH/Me ( C.) (W/kg) BET S EX11 Example 600 20 1.96 150 1.9 27.1 0.250 EX20 Counter- 1200 20 1.96 150 15.0 20.3 0.520 Example

(44) Both Examples 11 and 20 were made at low residence times, but since the reactor can mix very fast even at low residence times, it can exercise an adequate power/kg of material. This is accomplished by using a loop setup where all material passes the pump impeller frequently. If too much power is applied the crystal arrangement inside the particles is more dense as loosely fit crystals or softer crystals are removed from the particle. The recorded BET is also lower. As both the BET is lower and the arrangement is denser the accessibility by the washing medium is lower and it is more difficult to remove the sulfur.

(45) For a reactor volume of 7 L the power by the impeller needs to be typically higher than 1 W/kg, and can go up to even higher than 10 W/kg of producta value that can be reached easily in a large scale CFR compared to a production scale CSTR. A mean residence time to make high BET particles is between 5-90 minutes.

(46) Other examples can show the influence of the temperature in the reactor: at temperatures below 45 C. the morphology of the precipitated precursor is no longer spherical. Increasing the temperature above 200 C. will increase the pressure inside the reactor and make the operation too costly.

ANALYSIS OF VARIOUS EXAMPLES AND COUNTER EXAMPLES

Example 16

(47) Examples 16 are made from 6 m NMC433 precursor compounds with different BET and different sulfur content as shown in Table 4. Each precursor compound is blended with Li.sub.2CO.sub.3 in a Li:M molar ratio of 1.08 and fired at 930 C. for 10 hr in air. The sintered cake is then crushed and classified so as to obtain a non-agglomerated powder with a mean particle size D50 similar with that of the precursor. The precursor compounds in Examples 15 have

(48) ${\left(\frac{\mathrm{BET}-25}{18-6x}\right)}^2+{\left(\frac{S-0.15}{0.25-0.05x}\right)}^2$
smaller than unity (x=0.38) and the cathode materials made from these precursor compounds show a Q.sub.irr lower than 9%, which is preferred. On the contrary, the precursor compound in Example 6 has a value for

(49) ${\left(\frac{\mathrm{BET}-25}{18-6x}\right)}^2+{\left(\frac{S-0.15}{0.25-0.05x}\right)}^2$
that is larger than unity and the cathode material made from this precursor has a Q.sub.irr higher than 9%, which is not good. Conclusion: NMC433 precursor compounds with

(50) ${\left(\frac{\mathrm{BET}-25}{18-6x}\right)}^2+{\left(\frac{S-0.15}{0.25-0.05x}\right)}^{2}1$
are desired.

Example 723

(51) Examples 723 are about 6 m NMC532 precursor compounds with different BET and different sulfur content as shown in Table 5. Each precursor compound is blended with Li.sub.2CO.sub.3 in a Li:M molar ratio of 1.02 and fired at 920 C. for 10 hr in air. The sintered cake is then crushed and classified so as to obtain a non-agglomerated powder with a mean particle size D50 similar with that of the precursor. The precursor compounds in Examples 712 have

(52) ${\left(\frac{\mathrm{BET}-25}{18-6x}\right)}^2+{\left(\frac{S-0.15}{0.25-0.05x}\right)}^2$
smaller than unity (x=0.50) and the cathode materials made from these precursor compounds show a Q.sub.irr lower than 9%, which is preferred. On the contrary, precursor compounds in Examples 1323 have

(53) 0${\left(\frac{\mathrm{BET}-25}{18-6x}\right)}^2+{\left(\frac{S-0.15}{0.25-0.05x}\right)}^2$
larger than unity and the cathode materials made from these precursors have a Q.sub.irr higher than 9%, which is not good. In addition, it is found that the initial charge capacity decreases as the precursor sulfur content increases, as shown in FIG. 1. This is another reason that too high sulfur content is not desired. Conclusion: NMC532 precursor compounds satisfying

(54) ${\left(\frac{\mathrm{BET}-25}{18-6x}\right)}^2+{\left(\frac{S-0.15}{0.25-0.05x}\right)}^{2}1$
are preferred.

Example 2430

(55) Examples 2430 are about 4 m NMC622 precursor compounds with different BET and different sulfur content as shown in Table 6. Each precursor compound is blended with LiOH in a Li:M molar ratio of 1.02 and fired at 860 C. for 10 hr in air. The sintered cake is then crushed and classified so as to obtain a non-agglomerated powder with a mean particle size D50 similar with that of the precursor. The precursor compounds in Examples 2427 have

(56) ${\left(\frac{\mathrm{BET}-25}{18-6x}\right)}^2+{\left(\frac{S-0.15}{0.25-0.05x}\right)}^2$
smaller than unity (x=0.60) and the cathode materials made from these precursor compounds show a Q.sub.irr lower than 9%, which is preferred. On the contrary, precursor compounds in Examples 2829 have

(57) ${\left(\frac{\mathrm{BET}-25}{18-6x}\right)}^2+{\left(\frac{S-0.15}{0.25-0.05x}\right)}^2$
larger than unity and the cathode materials made from these precursors have a Q.sub.irr higher than 9%, which is not good. Furthermore, it is confirmed again that CQ1 decreases with increasing precursor sulfur content, as shown in FIG. 2. In Ex30, the precursor compound has a BET higher than 50 m.sup.2/g, which gives a very brittle cathode material at the end. The cathode materialafter milling and classifyingcontains already a big amount of fine particles as shown in FIG. 3. Being pressed in a stainless-steel die under a pressure of 200 MPa, which is similar to the pressure applied during cathode electrode rolling, the particles break severely, creating much more fine particles, and most probably a lot of cracks in particles as well. So a precursor with very high BET should be avoided. Conclusion: NMC532 precursor compounds satisfying

(58) ${\left(\frac{\mathrm{BET}-25}{18-6x}\right)}^2+{\left(\frac{S-0.15}{0.25-0.05x}\right)}^{2}1$
are preferred.

Example 3135

(59) Different from all previous examples, which are about 46 m precursors, Example 3135 describe 1012 m NMC532 precursor compounds with different BET and sulfur content (see Table 7). Each precursor compound is blended with Li.sub.2CO.sub.3 in a Li:M molar ratio of 1.02 and fired at 920 C. for 10 hr in air. The sintered cake is then crushed and classified so as to obtain a non-agglomerated powder with a mean particle size D50 similar with that of the precursor. The precursor compounds in Examples 3132 have

(60) ${\left(\frac{\mathrm{BET}-25}{18-6x}\right)}^2+{\left(\frac{S-0.15}{0.25-0.05x}\right)}^2$
smaller than unity (x=0.50) and the cathode materials made from these precursor compounds show a Q.sub.irr lower than 10%, which is preferred for 1012 m big NMC532 cathode materials. On the contrary, precursor compounds in Examples 3335 have

(61) ${\left(\frac{\mathrm{BET}-25}{18-6x}\right)}^2+{\left(\frac{S-0.15}{0.25-0.05x}\right)}^2$
larger than unity and the cathode materials made from these precursors have a Q.sub.irr higher than 11%, which is worse than those of example 3132. Therefore, for big size precursor compounds, those satisfying

(62) ${\left(\frac{\mathrm{BET}-25}{18-6x}\right)}^2+{\left(\frac{S-0.15}{0.25-0.05x}\right)}^{2}1$
are preferred.

(63) The overview of all of the Examples learns that it is preferable to have a precursor that has a specific surface area with 12<BET<50 m.sup.2/g to obtain the desired low values for Q.sub.irr. It further learns that setting the criterion

(64) ${\left(\frac{\mathrm{BET}-25}{18-6x}\right)}^2+{\left(\frac{S-0.15}{0.25-0.05x}\right)}^{2}0.9$
will result in even lower values for Q.sub.irr. Furthermore, Examples 1 to 23 have shown that the criterion for the values of BET and S can be set at a more severe value to obtain the desired low Q.sub.irr. Particularly, for these compositions with x0.50,

(65) ${\left(\frac{\mathrm{BET}-25}{18-6x}\right)}^2+{\left(\frac{S-0.15}{0.25-0.05x}\right)}^{2}0.75$
is a preferred criterion.

(66) Within each NMC composition, some pouch type fullcells are prepared for DCR evaluation by using selected cathode materials (i) Ex. 1, 2, 3 and 6 from NMC433, (ii) Ex. 7, 8 and 13 from NMC532 and (iii) Ex. 24 and 28 from NMC622. The DCR tests are performed at representative temperatures of 25 C. and 10 C. within SOC range from 20 to 90%. FIGS. 4, 6 and 8 illustrate the 25 C. DCR performance of these selected NMC433, NMC532 and NMC622 cathode materials, respectively. FIGS. 5, 7 and 9 show the 10 C. DCR performance of NMC433, NMC532 and NMC622 cathode materials, respectively. All figures demonstrate that cathode materials from precursor compounds which satisfy

(67) 0${\left(\frac{\mathrm{BET}-25}{18-6x}\right)}^2+{\left(\frac{S-0.15}{0.25-0.05x}\right)}^{2}1,$
have relatively lower DCR than cathode materials from precursor compounds not satisfying the inequality, hence better power performance. This holds true for different NMC compositions, tested at different temperatures and at different SOC'S. Therefore, precursor compound with

(68) ${\left(\frac{\mathrm{BET}-25}{18-6x}\right)}^2+{\left(\frac{S-0.15}{0.25-0.05x}\right)}^{2}1$
is desired for power application.

(69) TABLE-US-00004 TABLE 4 6 m NMC433 precursor compounds property, firing conditions and coin cell properties Examples Precursor Ni/Mn/Co BET (m.sup.2/g) S (wt %) Lithium source Blend ratio Firing T/ C. ${\left(\frac{\mathrm{BET}-25}{18-6*x}\right)}^2+{\left(\frac{S-0.15}{0.25-0.05*x}\right)}^2$ Q.sub.irr EX1 38/29/33 15.5 0.000 Li.sub.2CO.sub.3 1.08 930 <1 7.9 EX2 38/29/33 22.0 0.310 Li.sub.2CO.sub.3 1.08 930 <1 6.6 EX3 38/29/33 23.8 0.292 Li.sub.2CO.sub.3 1.08 930 <1 6.7 EX4 38/29/33 19.8 0.299 Li.sub.2CO.sub.3 1.08 930 <1 7.1 EX5 38/29/33 22.1 0.277 Li.sub.2CO.sub.3 1.08 930 <1 6.7 EX6 38/29/33 8.3 0.072 Li.sub.2CO.sub.3 1.08 930 >1 9.6
Example 6 is a counterexample of the invention

(70) TABLE-US-00005 TABLE 5 6 m NMC532 precursor compounds property, firing conditions and coin cell irreversible capacity Examples Precursor Ni/Mn/Co BET (m.sup.2/g) S (wt %) Lithium source Blend ratio Firing T/ C. ${\left(\frac{\mathrm{BET}-25}{18-6*x}\right)}^2+{\left(\frac{S-0.15}{0.25-0.05*x}\right)}^2$ CQ1 Q.sub.irr EX7 50/30/20 13.8 0.063 Li.sub.2CO.sub.3 1.02 920 <1 191.5 8.8 EX8 50/30/20 16.0 0.065 Li.sub.2CO.sub.3 1.02 920 <1 191.5 8.6 EX9 50/30/20 20.8 0.150 Li.sub.2CO.sub.3 1.02 920 <1 190.0 7.6 EX10 50/30/20 23.2 0.300 Li.sub.2CO.sub.3 1.02 920 <1 189.3 7.8 EX11 50/30/20 27.1 0.250 Li.sub.2CO.sub.3 1.02 920 <1 189.9 7.9 EX12 50/30/20 27.5 0.176 Li.sub.2CO.sub.3 1.02 920 <1 189.8 7.6 EX13 50/30/20 10.2 0.112 Li.sub.2CO.sub.3 1.02 920 >1 191.4 10.7 EX14 50/30/20 3.7 0.057 Li.sub.2CO.sub.3 1.02 920 >1 189.9 12.3 EX15 50/30/20 5.5 0.077 Li.sub.2CO.sub.3 1.02 920 >1 190.5 10.1 EX16 50/30/20 7.6 0.201 Li.sub.2CO.sub.3 1.02 920 >1 189.3 9.6 EX17 50/30/20 9.8 0.048 Li.sub.2CO.sub.3 1.02 920 >1 190.0 13.1 EX18 50/30/20 11.1 0.065 Li.sub.2CO.sub.3 1.02 920 >1 190.9 10.6 EX19 50/30/20 19.0 0.450 Li.sub.2CO.sub.3 1.02 920 >1 188.8 9.1 EX20 50/30/20 20.3 0.520 Li.sub.2CO.sub.3 1.02 920 >1 188.6 11.2 EX21 50/30/20 22.1 0.650 Li.sub.2CO.sub.3 1.02 920 >1 187.2 13.7 EX22 50/30/20 35.6 0.470 Li.sub.2CO.sub.3 1.02 920 >1 188.6 12.4 EX23 50/30/20 50.5 0.460 Li.sub.2CO.sub.3 1.02 920 >1 188.7 11.9
Examples 13-23 are counterexamples of the invention

(71) TABLE-US-00006 TABLE 6 4 m NMC622 precursor compounds property, firing conditions and coin cell irreversible capacity Examples Precursor Ni/Mn/Co BET (m.sup.2/g) S (wt %) Lithium source Blend ratio Firing T/ C. ${\left(\frac{\mathrm{BET}-25}{18-6*x}\right)}^2+{\left(\frac{S-0.15}{0.25-0.05*x}\right)}^2$ CQ1 Q.sub.irr EX24 60/20/20 37.0 0.190 LiOH 1.02 860 <1 198.4 7.1 EX25 60/20/20 18.1 0.328 LiOH 1.02 860 <1 196.2 7.9 EX26 60/20/20 18.9 0.037 LiOH 1.02 860 <1 199.7 6.9 Ex27 60/20/20 21.2 0.271 LiOH 1.02 860 <1 197.2 7.4 EX28 60/20/20 7.4 0.058 LiOH 1.02 860 >1 199.0 9.5 EX29 60/20/20 4.8 0.004 LiOH 1.02 860 >1 199.1 10.6 EX30 60/20/20 50.7 0.116 LiOH 1.02 860 >1 / /
Examples 28-30 are counterexamples of the invention

(72) TABLE-US-00007 TABLE 7 10~12 m NMC532 precursor compounds property, firing conditions and coin cell irreversible capacity Examples Precursor Ni/Mn/Co BET (m.sup.2/g) S (wt %) Lithium source Blend ratio Firing T/ C. ${\left(\frac{\mathrm{BET}-25}{18-6*x}\right)}^2+{\left(\frac{S-0.15}{0.25-0.05*x}\right)}^2$ Q.sub.irr Ex31 50/30/20 13.5 0.064 Li.sub.2CO.sub.3 1.02 920 <1 9.7 EX32 50/30/20 26.1 0.194 Li.sub.2CO.sub.3 1.02 920 <1 9.6 EX33 50/30/20 4.1 0.113 Li.sub.2CO.sub.3 1.02 920 >1 11.9 EX34 50/30/20 4.4 0.146 Li.sub.2CO.sub.3 1.02 920 >1 12.1 EX35 50/30/20 4.5 0.119 Li.sub.2CO.sub.3 1.02 920 >1 11.6
Examples 33-35 are counterexamples of the invention